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Japan Nuclear Watch, April 23: Can You Rebuild a Cooling System Inside a No-Go Zone?

8:53 am in Uncategorized by Scarecrow

Reactor Containment & Fuel Storage from UCS; (h/t commenter lobster)

The good news is that over the last two weeks or so at the Fukushima Daiichi Nuclear plant, there have been no further spectacular explosions, no new massive breaches of containment or as far as we know, massive releases of radiation, though there continue to be dangerous levels inside the reactors, in nearby water and in surrounding areas.

The bad news is the Japanese authorities have been unable to make substantial progress against the massive quantities of contaminated water still leaking from the damaged units. In the last three days, for example, they attempted to pump contaminated water out of the flooded trench outside Unit 2′s turbine building, but managed to lower the water level by only a few centimeters. In previous weeks, they would pump some out one day, but then find the water rising back the next with varying degrees of radiation, because water injected into the reactors leaked and found its way out and downhill.

Also discouraging, as they slowly and haltingly begin to take a closer look inside the reactor buildings — see TEPCO photos here — they’re discovering such massive structural damage that each day’s plans and assumptions get scrapped. They’re now on ad hoc plan #xqb and tomorrow it may be #yrz.

As lobster reported a week ago, the utility owner, TEPCO, released what it called a “roadmap” and some news media called a “blueprint” but which was neither. To me, it seems a package of optimistic goals laying out in logical sequence the problems that must be overcome, with some vague timeframes — three months, six to nine months — designed to reassure the Japanese people and themselves that there is hope things will get better over time.

I thought the most important revelation then was TEPCO’s acknowledgement that their best case recovery plan, which assumed the normal cooling systems could be restarted soon after external electrical power and controls were restored, has been abandoned. This was not suprising; it always seemed likely that critical pumps, valves, seals, meters and controls that operate those cooling systems would have been at least partially damaged by the 9.0 quake that greatly exceeded design capacity.

The only question was: how much damage had these systems sustained? And indeed, in the weeks after external power was restored to the control rooms at each unit, TEPCO admitted that various pumps and valves were too damaged to repair and would need to be replaced. It sounded like they just needed to order a few parts. That was then.

The “roadmap” documents let us know that TEPCO now realizes that if it wants something better than its current ad hoc water injections, it must completely rebuild the cooling systems, or even create an entirely new cooling system. The new system would replace the current ad hoc approach of just dumping water from above (Unit 4′s spent fuel pool) or injecting it from the outside (Units 1-3 reactors) through external hoses and pumps.

The current system is not a closed loop, and it leaks badly; they inject water one day, and it boils off or leaks out the next, requiring continuous reinjections with more and more water. And that’s just to stabilize the assumed level of fuel exposure and melting that’s already occurred in the Units 1-3 reactor vessels and Unit 4′s spent pool. The new system would presumably be a closed loop, just like the original system, so that if water boiled to steam, the steam would be captured, condensed back to water, cooled and returned to the reactor vessel for more cooling, while keeping the core covered.

That immediately raised the question, which I’ve not seen even discussed, is how do you build such a system? It would be one thing to take a never used reactor vessel outside a contaiment structure and refit it with new injection/release pipes and seals and attach those to valves, pumps, pipes, controls, etc. But how do you do that to the still hot reactor vessels inside the contaimment structure at Units 1-3 that have full radioactive cores and that have to be continuously cooled with the existing ad hoc water injection? If there’s even a conceptual design for that, I haven’t seen it mentioned.

Let’s take the problem one step further. Let’s assume that eventually they can do better than the tiny robots that have only managed to crawl a few meters into the reactor building to take photos and measure radiation. They’ll need much larger robots and heavy equipment to clear away the explosion debris and allow radioactive cleanup crews to make it possible to work inside for more than a few minutes. What next?

In the April 2 post where I summarized the AREVA presentation on the accident sequence, we explained a sequence in which the space between the outer containment structure and the reactor vessel inside that containment could gradually fill with radioactive steam and hydrogen. Some of that steam could condense and leave water inside the containment structure. As we explained elsewhere, water is also probably leaking into the containment structure from, for example, damaged seals for the piping that carries water/steam to/from the reactor vessel, making it difficult to keep the core covered, because the leak points are below the top of the fuel rods.

About the same time, the New York Times had a report describing other concerns by US experts. One of those concerns, buried at the end of the story, was that the ad hoc measures to pump outside water into the system would gradually fill up the containment structure, which was not designed to hold lots of water. Water is heavy. The weight/force of that water on the structure, coupled with continuing afterquakes, might eventually cause the containment structure to fail.

Now it seems that warning is being taken seriously. According to this report, TEPCO is now worried about how much water the containment structure at Unit 1 can safely hold if there is another significant afterquake. And if that’s a problem at Unit 1, it could become a problem at Units 2 and 3.

Is excessive water injection also a concern at Unit 4? Apparently so. This NHK World report says TEPCO is now worried that the pace of water dumping into Unit 4′s spent fuel storage pool — and remember, that exposed pool has a full core load of non-spent fuel — could make the structure supporting the storage pool, and thence its walls and steel lining, vulnerable to a serious afterquake. It’s a concern similar to that at Unit 1, except the pool is totally outside any containment structure. If the integrity of that pool, which may already be leaking, is suspect, their “roadmap” boils down to hoping Mother Nature gives them a break.

Sources:

NHK World
Kyodo News
Hi-res photos
IAEA Updates
Union of Concerned Scientists

Japan Nuclear Watch, Wed: Radiation Leak to Sea Stopped, But Other Concerns Grow

7:39 am in Uncategorized by Scarecrow

Japanese officials announced early Wednesda they have managed to stop the serious leak of water with high radiation levels that had been flowing into the Pacific Ocean from the pit and sea-water intakes near Unit 2.

That was the good news. The bad news is what’s still unsolved and may be getting worse.

[Update: David Dayen reports Congressman Markey claims NRC officials told him some portion of the core in Unit 2 has "probably" melted through the reactor vessel, into the containment floor. That would be very bad news if confirmed.]

[Update II: The NRC disputes this interpretation even though Markey received an e-mail from an NRC staffer saying some NRC experts had speculated there might have been a reactor vessel breach]

The bad news, compiled by the New York Times, listed the very serious threats still facing the Fukushima Daiichi Units 1-4, as the Japanese stuggle with what are, as lobster points out, the potential for four simultaneous INES level 7 accidents. Be sure to read lobster’s post on how the situation at any of these Units could be credibly rated in the same category as Chernobyl.

From the New York Times:

United States government engineers sent to help with the crisis in Japan are warning that the troubled nuclear plant there is facing a wide array of fresh threats that could persist indefinitely, and that in some cases are expected to increase as a result of the very measures being taken to keep the plant stable, according to a confidential assessment prepared by the Nuclear Regulatory Commission.

Among the new threats that were cited in the assessment, dated March 26, are the mounting stresses placed on the containment structures as they fill with radioactive cooling water, making them more vulnerable to rupture in one of the aftershocks rattling the site after the earthquake and tsunami of March 11. The document also cites the possibility of explosions inside the containment structures due to the release of hydrogen and oxygen from seawater pumped into the reactors, and offers new details on how semimolten fuel rods and salt buildup are impeding the flow of fresh water meant to cool the nuclear cores.

Paraphrasing the Times’ list of serious causes for concern:

– Continuing potential for exposure of the cores in Units 1-3, all of which have suffered varying degrees of “meltdown” from loss of cooling water, leaving the possibility of further fuel rod cladding breakdown and release of radioactive materials, plus hydrogen gas. Hence the need for injecting nitrogen gas to inhibit explosions and boron to prevent recriticality.

– Continuing potential for further hydrogen explosions that could damage/breach containment and/or cause further radiation releases into the environment.

– Growing concern about the non-spent fuel stored in Unit 4′s storage pool, which is outside containment and thus open to the outside environment and has already suffered fire/explosion after the pool’s cooling water was partially or fully lost for some period.

– Concern that earlier explosions, especially from Unit 4′s exposed spent fuel storage pool, could have spewed radioactive materials up to a mile away.

– Growing concerns about possible containment vulnerability at Units 1-3 from the weight of massive water injections already made into the containment structures. These structures surrounding the reactor vessel are not designed to hold that much water, increasing the potential for containment breach in the event of further quakes.

– Concerns about the ability to continue, without fail, essential fresh water injections indefinitely, with no near-term solution yet available for how to get beyond this stage.

– Growing concerns about sea-water salt deposition on fuel assemblies, restricting water flow around them and thus reducing any water’s ability to carry away heat.

Because slumping fuel and salt from seawater that had been used as a coolant is probably blocking circulation pathways, the water flow in No. 1 “is severely restricted and likely blocked.” Inside the core itself, “there is likely no water level,” the assessment says, adding that as a result, “it is difficult to determine how much cooling is getting to the fuel.” Similar problems exist in No. 2 and No. 3, although the blockage is probably less severe, the assessment says.

It’s good that TEPCO was able to stop the flow of contaminated water into the Pacific Ocean, though radiation levels remain high as of Wednesday night. It’s at least better for workers who must function outside the reactor buildings. Still, radiation levels inside the reactor buildings are so high they’re literally off the scale.

Stopping the sea leak won’t change the decision to dump other supposedly less contaminated water from storage areas directly into the ocean, to make room for pumping out somewhat worse contaminated water from each unit’s turbine buildings and outside trenches. But I wonder what stopping the leak to the sea means.

After failing to stop the leak with concrete, shredded paper and other mixtures, they apparently succeeded with liquid glass — sodium silicate.

On Tuesday, the plant operator drilled a hole into a layer of gravel around the pit, and poured a hardening agent called liquid glass, or sodium silicate, to stop the leak of highly radioactive water into the sea.

TEPCO says the flow was confirmed to have stopped on Wednesday morning, and that there has since been no change in the water level in the pit and the nearby turbine building.

But where was the water coming from? And if the flow to the sea has been stopped, where is that water going or pooling now?

Sources:

NHK World
Kyodo News
Hi-res photos
IAEA Updates
Union of Concerned Scientists

Japan Nuclear Watch, April 2: Leaks to the Sea and Comments on AREVA Presentation

10:57 am in Uncategorized by Scarecrow

Reactor Containment & Fuel Storage from UCS; (h/t commenter lobster)

It’s Saturday 3:00 pm EDT; it’s Sunday 4:00 am in Japan.

The news on Saturday was discovery of a large crack in the concrete floor of a staging area “pit” outside Fukushima Daiichi Reactor Unit 2. See story and video from NHK World. New York Times coverage is here.

Cracks in concrete floors are rarely a crisis, but since this crack was in a low spot outside Unit 2, and radioactive water from the Daiiche units was apparently leaking through the it, the crack is a pathway for leaking radioactivity into the nearby ocean, where higher readings were again recorded. They’ll try to seal the crack with concrete, but do they know where the water is coming from?

[Update: Unfortunately, per CNN, initial efforts to seal the leak have failed to stop radioactive water from leaking into the sea. ]

The Japanese utility, TEPCO, also continued efforts Saturday to pump contaminated water out of the turbine buildings basements and outside trenches and into any storage facility that still had room. Removing this water is necessary to be able to work in the area and to continue hooking up electrical equipment they hope will eventually allow a restart of cooling water pumps, values and related equipment. That’s still the main objective for stabilizing these reactors and the fuel in their storage pools.

To remove this water, they’ve filled condenser units inside the turbine buildings and are trying to make room in condenser storage tanks on site. To do that, and to make way for new fresh water brought on by US Navy barges, they’re trying to decide where to put excess contaminated water, such as on barges or an offshore floating “island” that might be able to store, temporarily, up to 10,000 tons of water. They’ll need more than that, as they keep pouring more fresh water into the reactors and spent fuel storage pools each day.

It’s important to keep in mind Unit 4′s storage pool has a full load of “non-spent” fuel that was removed from the core last December. The pool has already suffered a fire and/or explosion and may be damaged/leaking. Most important, the storage pool is outside the containment structure, and even the external building walls/roof have been destroyed. Unlike the damaged fuel in the reactor cores, which are still, we hope, inside one or more layers of containment, whatever happens to that still vulnerable fuel in the storage pool has a direct path to the environment.

Sources:

NHK World
Kyodo News
CNN
Hi-res photos
IAEA Updates
Union of Concerned Scientists

____________
The AREVA Presentation

A few days ago, a number of folks began seeing a PowerPoint presentation by Dr. Matthias Braun at the French nuclear firm, AREVA. Then on Thursday, an apparently approved version of the presentation was posted at the blogsite, EnergyFromThorium.

[Update: This is the same AREVA presentation described by the New York Times in an article posted Saturday evening. That story confirms the analysis relies on computer simulations based on observed hydrogen and types of fission products -- e.g., iodine, cesium -- and models of how the fuel reacts at various temperatures to release them. This allows analysts to understand what's probably happening in the core or pools even without other on-site measurements.]

The presentation is very helpful for its pictures, descriptions and accident time lines and sequence. So read through that link, and if possible, open that presentation in a separate tab. I’ll add a few comments here and refer to specific pages.

Slides 4, 5 and 6: The reactor design we’ve used in our posts here is on slide 4, along with a picture of an actual reactor of this type under construction at Browns Ferry. Slide 5 has a picture we haven’t used before of the reactor “service floor.” This service floor is above the reactor and containment structure and is used for loading/unloading the fuel, to/from the reactor or storage pool, using the crane.

In slide 6, we see a crane from the service floor lifting the dome cap off the containment vessel below. In the right panel of that slide the dome is sitting to the left. I believe the reactor vessel is down below, in the dark hole to the mid-upper right, and the spent fuel storage pool could be lower right, beneath the crane.

Slide 7′s schematic of the plant design identifies the key features and illustrates how fresh water is introduced to the reactor core (“main feedwater”) and how steam is drawn from the reactor (“fresh steam line”) to eventually drive the turbines.

Slide 8 begins the accident sequence, with the quake on March 11, 14:46. The term SCRAM = the automatic shutdown sequence that each reactor follows to bring the reactor to a safe cold shutdown. The figures for continuing heat generation after the SCRAM of 6%, 1% after a 1 day, and 0.5% after 5 days represent, I believe, what is supposed to happen, but didn’t. As slide 9 shows, in a normal shutdown, the reactor is sealed off from the outside systems, and even if electricity from the grid is lost, the backup generators kick in to power the cooling system.

Slide 10, the tsunami happens at 15:41, just 55 minutes after the quake. It floods the backup generators and cooling pumps/equipment in the turbine building. We have a station blackout, but an emergency, battery-operated cooling system is still available, as long as it lasts.

Slide 11 illustrates that emergency cooling system. Steam is still being produced from boiling water inside the reactor, and that steam can be used to drive a turbine which in turn drives a pump. The steam then goes into the “wetwall” structure where it condenses to water, and the somewhat cooler water is pumped back into the reactor. This works as long as the batteries continue to control this system and the pumps work, but since this is a closed system, gradual heat buildup can’t be avoided. It’s designed to be only a temporary solution until power is restored, but that didn’t happen.

In slide 12, either the batteries or the steam-driven pumps fail. At unit 1, the batteries fail within an hour after the tsunami. For some reason, in Unit 3, they fail 35 hours after the tsunami (given the short 8-hour expected life for the batteries, did this system not begin sooner?) And in Unit 2, the pump fails before the batteries give out, almost 3 days after the tsunami.

Slides 12 through 17 then follow the consequences of the emergency cooling system failures. Each successive slide shows the water level in the core falling until parts of the core containing the fuel become uncovered.

Slide 17 shows what they would predict as the core becomes exposed (I don’t believe these are actual measurements of the event). At 50% exposure, the core may still be undamaged, but at 2/3 exposure the fuel rod cladding starts to break down and release of radioactive fission products begins.

In slide 18, at 3/4 of core exposure, the zirconium cladding begins to burn, which produces hydrogen gas. Pressure pushes hydrogen out of the reactor vessel, down into the wet well (doughnut at bottom), where it escapes up into the containment structure. At this point, the hydrogen and fission products radiation are still partially “contained,” though outside the reactor vessel.

However, from slide 19, the core continues to heat up, the fuel rod cladding begins to melt and that melts adjoining steel structures. Even higher heat can destroy the fuel rods and leave molten debris on the reactor vessel bottom.

According to slide 19, the “restoration of water supply stops the accidents.” I assume this means it stopped the accident from getting even worse. The author notes that the core was “27h w.o. water” at Unit 1, which I take to mean that the core was at least partially (or totally?) uncovered for 27 hours in Unit 1. It was uncovered for 7 hours in units 2 and 3 each.

Slides 20 – 22 illustrate the progression that led to the release of radiation (“fission products”) and hydrogen from the containment structure surrounding the reactor vessel. From the melting core, it moves down into the wet wall and then up into the space contained by the dry well. Pressure inside the dry well containment rises — up to 8 atmospheres in a structure designed for 4-5 atmospheres. And the reactor core is still melting, creating more steam and pressure. So TEPCO decides to relieve this pressure within a day or two after the quake/tsunami. Slide 22 shows steam/hydrogen being released outside the containment — it goes first into the service floor area at the top of the building and gathers there. Of course, the hydrogen is flammable and can explode.

Slide 23 depicts the resulting hydrogen explosion at the tops (service floor) of Units 1 and 3. These destroy much of the outer buildings and equipment on the service floor.

But as slide 24 shows, Unit 2′s fire or explosion occurs below, down at/by the wet well/condenser, not in the upper service floor. The outer building remains mostly intact, but there is presumably some damage to the emergency cooling system. The author doesn’t know why Unit 2 was different.

Finally, slides 30-32 illustrate the problems at Unit 4′s spent fuel storage pool. Down for maintenance, it had a full non-spent fuel load recently removed from the reactor core to the storage pool. All storage pools are outside containment. So any fire or explosion associated with that fuel, if it becomes uncovered by cooling water, has an unrestricted direct path to the environment.

These are just initial comments without the benefit of actually hearing the presentation. So if folks see errors in my reading, let us know in the comments.

Japan Nuclear Watch, 3/31: Increased Radiation Detected On Land and Sea

11:23 am in Uncategorized by Scarecrow

Japanese officials on Thursday confronted significantly increased radiation readings, well above safe levels on land and sea. The increases occurred even as they continued efforts to inject fresh water in Units 1-3 reactors and spent fuel storage ponds and pumped contaminated water out of turbine building basements and nearby trenches. [NHK World reports there's some progress in removing that water.}

MSNBC's Rachel Maddow showed a graphic of the high radiation levels found by IAEA some 40 kilometers northwest of the damaged Fukushima Daiiche Nuclear Station. That's twice as far as the Japanese Government's official 20 km evacuation zone and beyond the out-to-30 km "voluntary" evacuation zone. Union of Concerned Scientists and others are citing this as a reason to expand the area of requirement evaculation.

Ocean readings later Thursday showed excessive levels increasing in the ocean near the plant. From the New York Times:

On Thursday workers prepared more tanks for transferring the water from turbine buildings at Reactors 1, 2 and 3 in a quest to keep the radioactive water from flooding into the ocean.

But readings taken in the sea near the plant showed that levels of radioactive iodine 131 had risen for another day, testing at 4,385 times the statutory limit, according to Hidehiko Nishiyama, deputy director general of the Nuclear and Industrial Safety Agency.

The rise increases the likelihood that contaminants from the plant are continuously leaking into the sea, he said. On Wednesday the water tested at 3,355 times the safety standard for the isotope, up from Sunday’s reading of 1,150 times the maximum level.

The same isotope was detected at levels 10,000 the safety limit at Reactor No. 1, Bloomberg reported, citing a report by the plant’s operator, the Tokyo Electric Power Company, or Tepco.

Kyodo News reports the 10,000 times reading near Unit 1 was from ground water. The report also indicates TEPCO is considering spraying a [synthetic chemical] resin around Unit 4 to prevent radioactive dust from being dispersed by winds.

The type of radiation found by the IAEA and mention on Rachel Maddow is particularly troublesome.

The isotope, cesium 137, was measured in one village by the International Atomic Energy Agency at a level exceeding the standard that the Soviet Union used as a gauge to recommend abandoning land surrounding the Chernobyl reactor, and at another location not precisely identified by the agency. Using a measure of radioactivity called the becquerel, the tests found as much as 3.7 million becquerels per square meter; the standard used at Chernobyl was 1.48 million.

In contrast to iodine 131, which decays rapidly, cesium 137 persists in the environment for centuries. The reported measurements would not be high enough to cause acute radiation illness but far exceed standards for the general public designed to cut the risks of cancer.

Read the rest of this entry →

Japan Nuclear Watch, 3/30: If That’s Not China, We Still Need a Tardis

6:36 am in Uncategorized by Scarecrow

Reactor Containment & Fuel Storage from UCS; (h/t commenter lobster)

It’s Wednesday, 10:30 a.m. EDT; Wednesday night, 11:30 p.m. in Japan

Japanese officials and media are now acknowledging they’re in a very long term nightmare at Fukushima Daiichi Nuclear Station. They’re out of quick solutions — like getting power to the units to restore normal cooling — that provided an earlier hope. And they’re even running out of acceptable long-run answers.

All of their choices are between bad and godawful. They face years of battling an unstable set of partially damaged reactors and spent fuel storage pools, some of which can become critical, even literally so.

The day to day problem focuses on water — how to keep enough covering the fuel rods inside the reactors, but also what to do with it once it becomes contaminated and leaks out, and what to do when they can’t keep enough of the right kind of water at the right place at the right time. And it’s become a logistics problem. Where do you put the huge and growing quantities of contaminated water?

They’ve got hundreds of tons of contaminated water preventing workers from getting close enough to pumps, valves, monitors needed to stabilize conditions. So they have to pump this water out and put it somewhere, but where? There are tanks at/near some units that can hold some of it, but not all, and external temporary storage may allow exposure to the atmosphere. Meanwhile, they must keep pumping more fresh water into the reactors and spent fuel storage pools, while more leaks out.

There are large pools of dangerously contaminated water in the turbine buildings adjacent to each reactor buidling, with more leaking in from somewhere, and few places to put it. Just outside the turbine buildings, there are long, deep trenches nearer the ocean and likely filled with water from the tsunami. But they’re now contaminated with radiation and water leaks from the turbine building.

Where can they put all this water? And given varying degrees of contamination, which water should they put where? For example, should they just pump out the least radioactive water in the trenches/pools and dump it in the ocean? That would be awful, but there’s no other safe tank, pool or storage basin large enough or available quickly enough, and they need to move it quickly. That’s this week’s dilemma, and next week, or tomorrow, there will be another.

While they worry about where to put all the contaiminated water, some of it keeps geting more contamination. Government and TEPCO (utility) officials now generally acknowledge that the fuel rods within Units 1, 2, and 3 suffered what they’re calling “melting,” meaning some portion of the fuel cladding distintegrated and the fuel inside broke down, releasing further radiation. There’s general agreement the fuel rods at Units 1-3 were early on partially or fully uncovered for at least several (10-20?) hours, leading to the explosions at each Unit early on.

Yesterday, there was a [still unconfirmed] claim by a former GE expert in the reactor design at Fukushima Daiiche that at least some of the fuel in Unit 2 had not only melted but had burned through the reactor vessel and onto the concreat reactor floor. That’s always a very bad sign, because it puts the irradiating fuel outside containment; but it’s just one nightmare scenario they face. [See comment thread from previous update for discussion of its plausibiity] If that claim were true, from there, the molten fuel on the floor could undergo further melting, be exposed to more water/steam (possible uncontained steam exlosion?) and/or continue melting through the floor on its way to . . . down and out.

But it’s not just the continuing need to keep injecting more water into the reactors. There’s also the spent fuel storage pools, especially Unit 4′s pool, which has a full inventory of relatively “unspent” fuel that was removed from Unit 4′s core before the earthquake. The storage pools are also outside containment, so it’s important to keep them cooled and avoid even the smallest likelihood of going critical.

Unit 4′s pool may have a serious leak, and the fuel rods there (and other units) likely were uncovered for some unknown period. They have to keep this fuel covered to prevent further damage and radiation releases, but the water is leaking out and/or boiling off when the rods overheat. They have to deal with this every day, from now on, until that fuel is removed . . . how? and placed somewhere safe . . . where?

In the great Dr. Who series, Tom Baker had a solution. His Tardis could not only travel through time, but once you got inside the British call box, there was infinite space inside. You could just pump all the contaminated water into one of the infinite number of rooms and levels and never worry about it again. But that’s science fiction. Without a Tardis, the Japanese have to think about pumping lots of this water directly into the ocean, or into a large super tanker that just sits along the coast for . . . years? . . . until . . . what?

So they’re stuck; they have to keep inventing ad hoc temporary fixes for months, possibly years. Wet blankets to cover the Units? Tanker ships filled with radioactive water sitting off the coast? And so far, I haven’t heard or seen a single expert, pro-industry, anti-industry, or just smart people trying to help, tell us there’s a simple answer.

But not to worry. Yesterday, a US NRC official assured a Senate Hearing that of course we’d make our nukes improve their safety features if that was warranted, but there’s no reason to hold up current licensing efforts. And today, Barack Obama will reportedly embrace President McCain’s energy policy: let’s move ahead with every dangerous energy source that has suffered catastrophic failure in the last two years.

Helpful Sources:

NYT: Japan’s Confidence Slips in Nuclear Crisis

NHK World

NHK English tv feed

Union of Concerned Scientists

Kyodo News: Japan Nuclear Crisis

Nuclear Power Plant Primer — good expert video

Unit by Unit status updates (pdf) at the IAEA site

NYT Radiation chart
Washington Post simple graphics

TEPCO press releases

fleep.com/earthquake
NHK press releases
The Breakthrough Institute (including the Twitter feeds)

Japan Nuclear Watch, 3/29: Defense in Depth Now Has Sandbags!

6:12 pm in Uncategorized by Scarecrow

Reactor Containment & Fuel Storage from UCS; (h/t commenter lobster)

It’s 10:00 pm EDT here; it’s 11:00 a.m. Tuesday in Japan.

Sandbags. That’s right, we’re literally down to sandbags to keep a trench filled with highly radiative water from spilling its content into the sea. From NHK World (and see video of drawings here):

On Monday, the power company detected radiation of more than 1,000 millisieverts per hour on the surface of puddles in the No. 2 reactor’s turbine building and in a trench outside the building.

The concrete trench stretches toward the coast but does not connect to the sea.

Puddles of water were also found in the trenches of the No.1 and No.3 reactors.

The No.1 reactor’s trench will overflow if the water rises by 10 centimeters. TEPCO has blocked the trench outlet with sandbags and concrete to prevent the water from reaching the ocean.

The water in the trenches of the No.2 and No.3 reactors is reportedly 1 meter from overflowing.

To provide context, recall from our last update that TEPCO was trying to figure out how to remove contaminated water from two to five feet deep in the lower rooms of each of the turbine buildings. There is a turbine/generator building next to the reactor building at each Unit of the Fukushima Daiichi Nuclear Station.

Apparently, the water is leaking from somewhere, still unknown, along the chain of pipes and valves coming from the reactor into the turbine building and eventually returning to the reactor. In the turbine building the pressurized steam enters and turns the turbine/generators. The expanded, now cooler steam then passes through a condenser where it becomes water. Then it’s further filtered for mineral buildup and then piped/pumped back into the reactor building and returned to the reactor.

So an initial plan was to pump the contaminated water into the condenser tanks, putting it back into the closed loop leading back to the reactor. But apparently the condensers for Units 2 and 3 are already full.

The authorities still don’t know where the water leaks are occurring along that chain. But given the levels and types of radiation, that water is presumable picking up radiation from the damaged fuel rods in the reactor, suggesting fuel rod disintegration and fuel deterioration inside (what the media are calling “melting”). Japanese officials have essentially admitted there is some degree of core damage or “melting” in Unit 2.

There may also be contaminated water in the large pressure suppression pool beneath the reactor core. They suspect this structured was damaged in the explosion more than a week ago in Unit 2.

[Update, Tuesday a.m. EDT: the "trenches" appear to be several meters deep and filled with water (h/t powwow). Recall that these lower levels nearer the ocean were flooded by the tsunami, so most of the water could be left over from that, with only part of it contributed by leaks from inside the turbine building. Since the first reports, I haven't seen updates that indicate the levels are rising, and if so, how fast. So for the moment, its yet another large pool of contaminated water they have to monitor closely and work around.]

In addition to not knowing the source/location of the water leaks within the turbine building, they can only guess at the rate at which water is leaking. That means that as they continue to inject water into the reactor to keep the core from overheating, they have to guess at how much water/pressure they can “safely” inject without exacerbating the leaks that are flooding parts of the turbine building next door. And now, it seems the leaked water accumulating inside the turbine building is following gravity on its way to the ocean, via a tunnel that leads from the turbine building towards the sea.

And each of those tunnels is close to overflow, so they’re literally piling sandbags and concrete to erect a barrier to hold it in until they can figure out how and where to pump it out.

They can’t get close enough to find the leaks, but they have to keep injecting water. The more they inject, the more they have to worry about it overflowing and eventually spilling into the ocean. Inject too little, risk further “melting” in the reactor; inject too much, risk further ruptures and worse leaks and an overflow into the sea.

And in the meantime, there’s now a clear pathway for high radiation levels from the damaged reactor to the open environment.

Nightmare.

In slightly better news, they’ve found traces of plutonium in soil samples near the plants that, they claim, are not much elevated from normal levels. Here’s a Q&A from Kyodo News on what this may mean. Detailed readings here (h/t Selise).

Helpful Sources:

NYT: Contaminated water escaping nuclear plant, Japanese officials say

NHK World

NHK English tv feed

Union of Concerned Scientists

Kyodo News: Japan Nuclear Crisis

Nuclear Power Plant Primer — good expert video

Unit by Unit status updates (pdf) at the IAEA site

NYT Radiation chart
Washington Post simple graphics

TEPCO press releases

fleep.com/earthquake
NHK press releases
The Breakthrough Institute (including the Twitter feeds)

Japan Nuclear Watch, Sunday: Pools, Puddles, Panic and Apologies

7:02 am in Uncategorized by Scarecrow

Reactor Containment & Fuel Storage from UCS; (h/t commenter lobster)

It is Sunday, 11:00 a.m. EDT here; 12:00 p.m. Sunday night in Japan.

It’s been three days since Japanese officials told us that three workers were exposed to potentially dangerous levels of irradiated water that had accummulated in the lower levels of the turbine/generator buildings connected to Reactor Unit 2 of the Fukushima Daiichi Nuclear Station.

Since then, the Japanese public has been exposed to revelations that there are similar puddles or pools of water in the turbine buildings for all four Units, that some of the “puddles” are 3-5 feet deep, and that others have highly elevated levels of radiation. How is it they’re just now discovering and reporting this? Officials still do not know the source of the water/leaks or its causes, nor what it means for the condition of each corresponding reactor or spent fuel storage pool.

And to top it off, the plant owner/operator, Tokyo Electric Power Comany (TEPCO) first reported radiation readings 10 million times normal at one unit, causing an immediate plant evacuation and risk of panic, only to announce later Sunday that these extreme measurements were in error. TEPCO officials apologized for the mistake, adding they were trying to get a more accurate measurement. The fact they didn’t immediately have a revised number, didn’t explain the mistake, and didn’t say when they’d have revised, accurate numbers was not reassuring. [Update: latest estimate says reading was 100,000 times normal levels.]

But take note, America; here is a picture of what an apology looks like.

Here’s what’s been reported in the last 24 hours or so. (See summaries at Kyodo News) from Sunday, March 27 Note: These levels were reported late Saturday; we don’t know whether the depths/readings are increasing or stable. Radiation levels from this Kyodo News report.]

Unit 1: Radioactive “puddle” in turbine room = 40 cm (about 15-16 inches)

Unit 2: Radioactive water level in lower turbine room = 1.0 meter deep; surface readings more than 1000 millisieverts/hour (the meter maxed out at 1000 milisieverts; actual measure unknown). Radioactive iodine-134 found at extremely high concentration of 2.9 billion becquerels per cubic centimeter; iodine-131 and cesium-137 also found, suggesting damage to core. According to Kyodo News:

At a radiation level of 1,000 millisieverts per hour, people could suffer a decrease in the number of lymphocytes — a type of white blood cell — in just 30 minutes, and half of the people could die within 30 days by staying in such conditions for four hours.

[Commentor lobster translates various dosage levels here. For a simplified comparison of various radiation levels and their possible effects, see this NYT chart.]

Unit 3: Radioactive water in turbine room = 1.5 meters deep; surface reading of 400 millisieverts/hour

Unit 4: The water level in turbine room = 80 centimeters (about 30 inches); radiation levels lower than other units, but recall that all of Unit 4′s fuel rod assemblies had been removed from the core to the spent fuel storage pool for inspection/maintenance prior to the earthquake.

What they don’t know: Where is the water coming from? Is some left from the tsunami? (The turbine building is on the seaward side of the reactor building, and the puddles are in lower level rooms.)

Are there leaks in pipes and/or valves coming into/going out of the turbine building from/to the reactor? In the same loop, there are also pipes/valves between the turbines and the condensor units, which turn the cooling steam back to water before returning it to the reactor. There’s another part of the loop for removing minerals from the water before returning it to the reactor, and those elements were reportedly (NYT) found in the water.

What is the source of the excessive radiation? Is it fuel/cladding deterioration within the core? A crack in the pressure suppression pool beneath the reactor (Unit 2)? Answering this requires analysis of the radioactive content of the water, but the levels of radiation are limiting their ability to conduct the analysis.

In the meantime, the dangerous radiation levels have limited other actions to regain control. Earlier hopes that connecting electrical power to each Unit would lead quickly to restoration of some normal cooling functions were dashed when they discovered pumps/valves in Unit 2 were damaged and must be replaced. We’ve had no recent word on progress there.

Off-site power is now restored to each Unit, but so far mostly for control room lighting. It remains unclear how much of the instrumentation is operable, which means they may not yet be able to get accurate readings on radiation, water pressures, temperature and levels inside each core, and they probably don’t yet know which pumps and valves are operable.

Reports a day ago said they were beginning to inject fresh water into the reactors. A later report Sunday said they hope to start injecting (which is correct?), and then they’ll try to get fresh water into the spent fuel storage ponds.

Recall that injections of sea water lead to corrosion and salt buildup around the fuel rods/assemblies in the reactor core and the spent fuel storage ponds. That buildup then limits the ability of cooling water to carry away heat, allowing the rods to continue to get hotter and become further damaged. So removing/limiting the salt buildup has become one of their all too many priorities.

Also, continuous sea water spraying and rain at the site outside have increased radioactive runoff into the sea. From Kyodo News:

Radioactive iodine-131 at a concentration 1,850.5 times the legal limit was detected in a seawater sample taken around 330 meters south of the plant, near a drainage outlet of the four troubled reactors, compared with 1,250.8 times the limit found Friday, the agency said.

So, in addition to the growing circle of civilian evacuations (now out to 30 kilometers), and bans/warnings about consumption of milk, produce, tap water, they now have to worry about ocean/sea-food contamination nearby. Officials are also warning water supply/treatment plants not to use rain water.

More as this nightmare unfolds.

Helpful Sources:

NHK live tv feed

Union of Concerned Scientists

Kyodo News: Japan Nuclear Crisis

Nuclear Power Plant Primer — good expert video

You can also find Unit by Unit status updates (pdf) at the IAEA site

NYT Radiation chart
Washington Post simple graphics

TEPCO press releases

fleep.com/earthquake
NHK press releases
The Breakthrough Institute (including the Twitter feeds)

Japan Nuclear Watch, Friday: Where Did the Water Radiation Come From at Unit 3?

5:44 am in Uncategorized by Scarecrow

Reactor Containment & Fuel Storage from UCS; (h/t commenter lobster)

It’s 9:30 a.m. EDT, which is 10:30 p.m. on Friday evening in Japan. [Updates below.]

[Update II, 11:00 a.m. EDT]: Kyodo News reports workers have begun to inject fresh water into the reactors at Units 1 and 3 (Unit 2 is next) to help flush sea water and salt buildup out of the reactor and cooling water systems. That’s a good step, because salt buildup can lock the valves and inhibit water flows within the reactor. (They’re still spraying sea water into the spent fuel storage pools.) They’re also finding more radioactive water leaks and standing water in other units. ]

Concerns on Friday focused on (1) the continuing spread of radiation in Fukushima and surrounding prefectures, with local citizens anxious to evacuate areas beyond the mandated 20 kilometer radius and (2) the inability of the government either to gain control of the crippled Fukushima Daiichi reactors or to explain the exact source and nature of the continuing radiation leaks.

The latter concern increased yesterday when authorities reported that three workers suffered radiation exposure while standing in water, trying to lay cables to connect an outside electrical power cable to Unit 3. (Power cables are already connected at Units 1 and 2; see previous updates.)

Two of those workers had to be hospitalized for possible radiation burns on their feet. [A late medical report claims that two of the three exposed workers do not appear to have skin damage but have suffered from "internal exposure."] Initial reports jumped at the claim that the workers had walked through puddled water (with no protective boots) outside the reactor building and that the exposure levels were “10,000 times normal exposure levels.”

Since normal levels are extremely small, the “10,000 times normal” figure was not the only point. Rather, the concern quickly shifted to where the exposure occurred, where the water was coming from and how it became contaminated. I originally thought the source might be runoff from the sea water spraying, but that assumed the water was outside. It was inside.

It now appears the workers were inside a part of the turbine/generator building, which is separate from but connected to the reactor building. The connections with the reactor include a series of pipes that carry pressurized steam from the reactor to the turbines, which then drives the generators to produce electricity. Other pipes then carry the cooler condensed water back to the reactor. There are various valves along the way.

[Update I]: as the NYT reports, there are pipes from the reactor carrying away corrosive materials from the reactor to a filtering system inside the turbine-generator building.

But Michael Friedlander, a former nuclear power plant operator for 13 years in the United States, said that the presence of radioactive cobalt and molybdenum in water samples taken from the basement of the turbine building of reactor No. 3 raised the possibility of a very different leak.

Both materials typically occur not because of fission but because of routine corrosion in a reactor and its associated piping over the course of many years of use, he said.

These materials are continuously removed from the reactor’s water system as it circulates through a piece of equipment called a condensate polisher, which is located outside the reactor vessel. The discovery of both materials in the basement suggests damage to that equipment or its associated piping, as opposed to a breach of the reactor vessel itself, Mr. Friedlander said.]

Did the excess irradiated water on the floor of the turbine/generator building come from leaks in these pipes or valves coming from/returning to the reactor building? That would indicate the source of the irradiated water was inside the reactor itself, not the spent fuel storage pool. And the type of irradiation would be another sign, if they needed one, of likely breakdown, possibly continuing, of fuel inside the reactor core [or corrosion in the reactor]. But as of Friday night, they apparently had not found the “leak” inside the turbine/generator building, so they’re haven’t confirmed this scenario.

Regarding the other units, a Defense Forces helicopter made an overhead video of the four reactor buildings. It’s shown periodically on the NHK TV feed and gives a better perspective on the damage to each reactor.

At Unit 1, where a hydrogn explosion a week ago destroyed the upper walls and roof of the reactor, we can now see that the roof was not blown off; it collapsed down, effectively covering the reactor components and spent fuel storage pool below. Commentators explaining the video did not know how much that complicates the ability to spray water into the storage pool from above, so it’s not clear how they’re maintaining cooling water levels in the storage pool.

At Unit 2, the earlier hydrogen explosion caused minimal damage to the exterior of the reactor building, but it is suspected of causing damage at least to the pressure suppression pool at the bottom of the reactor. In an emergency, if pressure builds up inside the reactor, it can inject steam into the suppression pools to relieve the pressure and cool the reactor down, while cooler water is, one hopes, injected back in. We so much damage from the top, we can’t see that lower structure in this video. The emergency crews punched out two holes in the building exterior, one in the upper levels on one side, another in the roof. They did this to allow venting of steam to prevent another hydrogen explosion, and you can see steam escaping from both holes.

At Units 3 and 4, explosions at each caused massive damage to the external building and likely serious damage to some components inside. For example, among the twisted steel rubble at Unit 4, you can make out a green structure that might have been the massive crane that operates above the reactor vessel and that is used for moving fuel rods in and out of the building and between the reactor vessel and the spent fuel storage pool. If that fallen structure we see is the crane, the question is, what did it damage on the way down? It’s usually above the reactor vessel, the containment structure, the spent fuel storage fuel and lots of critical coolding/steam pipes and valves, etc.

The inability of authorities to get these events under control, and continuing reports of worker exposure, unsafe tap water and produce is naturally increasing the alarm among residents. TV interviews are showing more and more folks saying they want to leave, just get out, but not getting answers they believe from the Japanese Government. Government officials are now saying it’s okay for folks within the 30 kilometer radius to leave voluntarily, but as of Friday, they hadn’t ordered that evacuation. Instead, the Times reports they are quietly encouraging folks to move away. And it’s all complicated by the fact the quakes and tsunami left tens of thousands homeless and requiring massive relief efforts on water, food, shelter medical care.

They need a break, some good news, if the gods are listening.

Helpful Sources:

NHK live tv feed

Union of Concerned Scientists

Kyodo News: Japan Nuclear Crisis

Picture of Unit 1 control room, via Kyodo News

Nuclear Power Plant Primer — good expert video

You can also find Unit by Unit status updates (pdf) at the IAEA site

Japan Nuclear Watch Thurs: Don’t Drink the Water and the Man on the Ladder

4:49 am in Uncategorized by Scarecrow

Reactor Containment & Fuel Storage from UCS; (h/t commenter lobster)

It’s Thursday morning here and Thursday evening in Japan. It’s been a frustrating day for crews trying to contain the radiation dangers at the crippled Fukushima Daiichi Nuclear Station.

Update I, 1:30 pm EDT: Watching NHK TV English feed indicates the coverage has shifted strongly from containment activities at the plant sites (it’s 2:30 a.m. Friday there) and to increasing public and official concern about the dispersion of radiation and its possible health effects. Lots of stories of citizens worried about the tap water, about their children, with many parents having already used tap water for bathing and cooking before they got the warnings.

Maps showing locations of higher readings go well outside the 30 km stay indoors radius and as far south at Tokyo, 140 miles away. Key point: increased radiation doesn’t spread uniformly out from the plant. Rather it is driven by wind direction and speed and weather. So we get increased readings south of the plant on one day, which falls the next day, but increased readings east and northeast the next day, as wind direction changes. Further, rain in one area can increase radiation readings there by bringing more of the airborne radiation to earth, even though it’s further away from the site than areas with lower readings nearer the plant. So the patterns of dispersion are highly variable and difficult to model for predictive purposes. But they’re now dealing with increased radiation in the air, on the ground and produce, in water supplies at many locations and in the ocean, while trying to prevent panic. [It appears the Tokyo tap water warnings ended on Thursday.]
_____________

Earlier hopes that restoring offsite power to the control rooms at Units 1-2 and 3-4 would allow quick reactivation of normal cooling systems were dashed with discovery, anticipated in our coverage, that critical pumps, valves and pressure sensors might be damaged and need repair or replacement. With radioactive smoke still coming from Unit 3, three more workers (laying electrical cables) at the site were exposed to dangerous levels in excess water outside, two of them hospitalized.

And as radiation continued to spread from the reactors, officials found unacceptable levels of radiation in tap water as far as Toyko and continuing unacceptable levels in produce and milk in the prefectures surrounding the Fukushima Daiichi reactors. It’s now clear that the evacuation and stay indoors areas should be expanded from the current 20 and 30 kilometer circles respectively, and they’re losing time to carry that out.

But if you want a flavor of the nightmare they’re still facing, consider yesterday’s New York Times story about the the salt buildup, stuck valves and the man on the ladder. First, a little history.

More than 30 years ago, I was a counsel at the California Energy Commission assigned the task of drafting the Commission’s first decisional document, a preliminary assessment of critical safety features at a proposed nuclear plant that was applying for a state construction license in California. Much of the assignment was just learning about and explaining how a nuke functions and how its safety features should work during normal and emergency conditions.

So I got emersed in reading reports and testimony on “defense in depth,” the nuclear industry’s talking point invented to assure the public that no matter what happened, there was always another backup safety mechanism that would avoid a catastrophe. I vaguely remember the witnesses talking about the cladding, and the boron-filled control rods (to absorb neutrons and stop/slow the reaction), and the integrity of the reactor vessel, the multiple containment structures, emergency cooling systems, back-up generation and so on. But I’m quite certain the one thing the witnesses never mentioned was the poor guy on the ladder. My report never mentioned him.

Yesterday, the New York Times described the situation inside the crippled Daiichi Units, even after they restored power to the control rooms and could start testing gauges and controls. Debris and damaged equipment from the explosion could be everywhere. And before they could even attempt to restart the cooling pumps, they had to know water levels and be certain all the valves on the water cooling system were in the correct open/closed position.

But much of the equipment could have been rendered inoperable from salt corrosion and build up, coming from 10 days of injecting sea water into the emergency cooling systems. Since some of the valves might be stuck, or the power to them inoperable, a plant worker might have to manually close or open the stuck valves. Now, it’s not unusual for plant workers to manually open/close valves. They just normally don’t do this under such dangerous conditions. From the Times: (my bold)

The emergency cooling system pump and motor for a boiling-water reactor are roughly the size and height of a compact hatchback car standing on its back bumper. The powerful system has the capacity to propel thousands of gallons of water a minute throughout a reactor pressure vessel and storage pool. But that very power can also be the system’s Achilles’ heel.

The pump and piping are designed to be kept full of water. But they tend to leak and develop alternating pockets of air and water, Mr. Friedlander said.

If the pump is turned on without venting the air and draining the water, the water from the pump would hit the alternating pockets with enough force to blow holes in the piping. Venting the air and draining the water requires a technician to reach a dozen valves, sometimes using a ladder. The water is removed through a hose to the nearest drain, usually in the floor, that leads to machinery designed to remove radiation from the water.

The process takes a full 12 hours in a reactor that is operating normally, Mr. Friedlander said. But even then, the water in the pipes tends to be radioactively contaminated because the valves that separate it from the reactor are not entirely tight.

So, some very brave soul, possibly one of the already exposed Fukushima Fifty, will have to walk around inside the reactor building, withstand the internal radiactivity, seek out the damaged valves, remove the debris, climb up a ladder and manually open or close the valves at just the right moment. Defense in depth.

That same article contains a better description of the damaging toll the use of sea water is likely having on safety equipment, possibly rendering much of it inoperable unless the salt buildup can be quickly and safely flushed from the cooling system using massive injections of purified fresh water. That pure water will come from . . . where? If they had enough of that already, they would have used it.

So if I’m ever in a position again (unlikely) to have to write a safety assessment, I need to remember to add to the list of “defense in depth” features the following items: Water flushing system, garden hoses, debris remover, extra strength hazmat suits, an undamaged ladder or two, and at least one very brave worker. Also, better boots for the guys laying the power lines outside. Oh, and millions of gallons of bottled water and relief food supplies for the neighbors in a 50 mile or so radius while they wait to see if this works. I’ll keep the list open.

We’ll add some actual details as updates come in. Thanks again to all commenters who have helped in this effort.

Ongoing sources:
NHK live tv feed

Union of Concerned Scientists

Kyodo News: Japan Nuclear Crisis

New York Times coverage has generally been very good, especially from Matt Wald, a 30-year veteran of nuclear/energy reporting, who was part of a media coverage panel I saw at Harvard’s Kennedy School yesterday. Bottom line: Mixed bag: lots of misinformation, some scaremongering and confusion (tv first showed harmless cooling towers instead of reactors); governments often don’t understand what’s happening, even if they’re honest, which they aren’t. Where have you gone, Harold Denton? The Harvard expert who’s co-principal investigator of nuclear studies isn’t sure what info the US had when they second guessed Japanese officials last week. Matt Wald’s latest is here.

Democracy Now video on radiation in food

Picture of Unit 1 control room, via Kyodo News

Nuclear Power Plant Primer — good expert video

Japan Nuclear Watch, Mon Nite (JST): Power! Unit 3 Smoking, Radiation Spreads

5:12 am in Uncategorized by Scarecrow

Reactor Containment & Fuel Storage from UCS; (h/t commenter lobster)

Update: Monday 5:30 pm (EDT): AP reports utility officials say some of the pumps in Unit 2 are damaged and must be replaced. They’re on order.

It’s Monday morning in the US; it’s Monday evening in Japan.

Quick Summary: Over the weekend, hopes of getting the reactors and spent fuel storage pools cooled rose significantly at the Fukushima Daiichi Nuclear Station, although on Monday, new smoke rose from Unit 3 (see NYT photo) forcing another evacuation there. They’re not sure whether there was another explosion (none was heard) nor do they know the source/cause of the smoke.

Rising hopes are attributed to getting power connected to some Units, though cooling systems have not yet been restated, and their improving ability to target sea water spray into the spent fuel storage pools and sustain it for several hours. This appears to be lowering temperatures at the critical hot spots.

In the meantime, they’re finding higher radation levels in surrounding communities, creating concerns about milk, local produce and tap water.

Power to the Units. Over the weekend, plant officials were able to complete laying transmission cables to transmit electric power from the grid to Units 1 and 2; they’re now completing connections to Units 3 and 4. There are reports they were able to connect to terminal/hubs providing power to a central control room between Units 1 and 2.

As of 8:30 am Monday (EDT), they have not attempted to turn on the cooling systems at Units 1 and 2. They’re still testing gauges, water temps, and other equipment to determine water levels and temperatures, and thus which pumping/cooling equipment needs to be tested for restarting. So even though they have power, the normal cooling systems are not yet functioning and we don’t yet know what equipment will work.

As we feared, the New York Times reports this morning (EDT) that workers are finding critical equipment, including a ventilation system, that must be repaired before they can restart the cooling systems at Unit 2. Recall that all four units suffered explosions, but Unit 2 suffered minimal exterior wall/roof collapse, whereas Units 1, 3, and 4 were extensively damaged.

After connecting the transmission line on Sunday, engineers found on Monday that they still did not have enough power to fully run the systems that control the temperature and pressure in the building that houses the reactor, officials from the nuclear safety agency said.

Engineers were also trying to repair the ventilation system in the control room that is used to monitor conditions in the No. 1 and No. 2 units. When that work is completed, possibly on Monday, it will allow the power company, also known as Tepco, to begin cleansing the air in the control room so that workers can eventually re-enter and begin using equipment inside to monitor conditions in the two reactor units.

At the same time, they’ve restored back-up generation at Units 5 and 6. With restored cooling functions, those two reactors and their spent fuel storage pools are out of danger, at least for the moment.

Continued spraying of sea water at Units 3 and 4. With the normal cooling functions still unavailable at units 1-4, they’ve continued spraying water from high-pressure fire hoses. They’ve brought in more crews and equipment, including a large crane that pictures show getting a hose above a reactor building and focusing spray down towards the fourth floor spent fuel pools. The ability to do this remotely (thus limited worker exposure next to the reactor) and to continue for several hours at a time has greatly increased their ability to inject water into the reactor buildings.

On Sunday, there was a report they had determined the spent pool fuel at Unit 4 was full. What accounts for this? Recall that last week, US Nuclear Regulatory Commission officials disagreed with the Japanese by insisting that Unit 4′s spent fuel pool was dry — all the water had either evaporated from the rising heat/boiling (which meant uncovering and damage to fuel and fuel cladding) or had leaked from cracks to the pool walls or floor. [One NHK TV segment interviewed a plant worker who, at the time of the quake, was near one of the pools; he and others were splashed with water as the quake sloshed the storage pool water.] The US claim led to a hypothesis by Union of Concerned Scientists that pool water could also have escaped through a breach in the “gate” that allows transfer of fuel assemblies between the reactor core and the spent fuel pool. [See my previous update].

Now, however, plant officials are claiming the Unit 4 spent fuel pool is full. If true, was it ever damaged or dry? Or is this simply the result of continuing efforts to spray sea water into the pool? Whatever, it’s a good sign that sufficient water is there and temperatures have fallen.

One issue we touched on early last week but haven’t heard much about lately is the corrosive effect of sea water on containment structures and pumping equipment. Remember that the decision to start injecting sea water was interpreted at the time as a decision to give up on any hope of saving the plant for future operation, since the sea water would over time destroy critical equipment. But it was necessary given the need to prevent a wider meltdown and public health hazard.

They have now spent over a week pumping sea water into units 1-4 (and Units 5-6?), both into the cooling systems circulating through the reactors and into the spent fuel storage pools. When does that necessary emergency action become the corrosion that causes the next system breakdown, even if they are able to restore pumps and other cooling mechanisms? And what will they do to prevent this inevitable breakdown?

Increasing concern about area radiation and public health. Dozens of plant workers have now received dangerous levels of radiation, possibly lethal for many of the “Fukushima 50″ who stayed at the plant when others were evacuated. They’ve continued to cycle in new workers, particularly those who can operate the fire trucks and other sea water pumping equipment.

Yesterday, various radiation monitoring systems near Fukushima and another plant were reporting spikes in radiation readings, but it’s unclear what caused this. Another event at Fukushima? Another plant? Rain? Commenter lobster was tracking last night.

Over the weekend, there were reports of officials finding unsafe radiation levels in milk and increased levels in local produce, first spinach and now other foods grown in Fukushima and neighboring prefectures. There is a ban on exporting produce from these areas, and they are continuing to monitor for food contamination. Also, there is warning against drinking tap water in a community about 30 miles away. That signals a spreading public health problem. As of Monday, more than 29,000 people have been evaculated from the area.

The NHK live tv feed (English) has been showing frequent updates on radiation levels at various locations, comparisons with normal exposure levels and recommended precautions.

And it’s been raining in northern Japan. So, for people still there, it’s stay indoors, don’t go out in the rain, avoid contaminated produce and wash everything.

More updates as warranted.

Sources:
NHK World TV

New York Times, New Repairs Delay Work at Crippled Nuclear Plant

New York Times, Status of Each Unit, with timelines

Breakthrough Institute, Situation Report

Union of Concerned Scientists, All Things Nuclear; and Daily Briefings

Radiation dose chart (please note disclaimers)