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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 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)

Japan Nuclear Watch: Press Conf. on Unit 2 Explosion and Unit 4 Fire

6:40 pm in Uncategorized by Scarecrow

Breaking: There are [now confirmed] reports of yet another explosion at Unit 4, presumably associated with the fire.
________

Japan’s Prime Minister gave a press conference at 11:00 a.m. (Tokyo) Tuesday and an official overseeing the nuclear emergencies answered questions about the status of the four units at Fukushima Nuclear Station.

The briefing part revealed there has been an explosion and fire at Unit 4 which, as of the presser, they were still trying to control. [Later reports say it's [now] extinguished.

Unit 4 had not been operating when the quakes hit last week and was supposedly in safe cold shutdown. However, cooling at that reactor is still required for the spent fuel pools, and its absence is a problem that can allow heat buildup from residual radioactive decay. The damage associated with this fire caused a significant radiation leak and apparently an explosion.

Officials suggested that this source, and not solely or necessarily the explosion at Unit 2, may be the source of highly elevated radiation readings at the Station. Because of increased levels, the government evacuated about 800 non-essential personnel from the Fukushima Daiichi Station, leaving only 50 workers to continue with sea water injections at all units.

The Government also directed that the public evacuation radius be set at 20 kilometers, and that between 20 and 30 km, residents remain indoors. Later reports note detecting higher levels of radiation in Tokyo and other cities.

The official emphasized the very high levels of radiation near Unit 4, with the measurement units being expressed in mili-sievert levels instead of micro-sievert levels. Whereas before we had as high as 8,217 micro-sievert/hour, the new readings were more like 300-400 mili-sieverts/hour near Unit 4. The official noted this level is clearly dangerous to humans.

The official said that as of 6:00 a.m. Tuesday, all but 50 workers involved in water injections have been evacuated. Sea water injections are still bein attempted at Units 1, 2, and 3. [earlier reports suggested they only had the fire equipment to deal with one plant at a time.]

Following is a paraphrase of the Q and A with the official overseeing nuclear issues:
Q. How are you sure the pressure vessel has not been damaged?
A. Water injection has been maintained. And pressure has been stabilized; we have to continue those efforts.
Q. How serious is fire at Unit 4?
A. I mentioned it first because it occurred earlier.
Q. Is there damage to part of the containment vessel?
A. There is a high probability that it was. [May be a mistranslation of terms here]
Q. Radiation levels a threat to the public?
A. Very little possibility of harm to public
Q. Status of fire at Unit 4?
A. Still working to extinguish the fire at Unit 4.
Q. Evacuation radius?
A. Out to 20 km = evacuate. Considering out to 30 km; but for now, just stay indoors.
Q. Radiation readings related to damage to Unit 2?
A. Explosion at #4 reactor could have caused that [after explosion?]
Q. What if fire continues?
A. We’re making every effort to put it out. The spent fuel is not going to “catch fire” in general sense, but its heat likely caused the fire. Fire is in building area; but it’s best to extinguish to keep temps down and prevent release of radiation.
Q. Further release from other units?
A. Possible some could have been released. Ask TEPCO. But current high readings are from this fire/explosion at Unit 4, not from the Unit 2.
Q. What is your advice?
A. [Repeats evac and remain indoors] Minimal amounts may spread further, but further away the level is lower, so stay calm.
In another Onadaga plant, the levels will not cause damage to health.
A. For people between 20-30 km range, there are towns that overlap/in beetween. He calls them out. [About 8-10 towns]
Q. Sec. Gen. of IAEA says you asked for experts?
A. Not aware of any Japanese request to IAEA, but after quake, we’ve asked for support from various countries.
Q. Neutron radiation?
A. That was from Unit 3, because of its nature [fuel type]
Q. How long to extinguish Unit 4 fire, given you think it’s source of radiaion?
A. Working on it.
Q. Are you ontinuing to inject water at all units?
A. Yes. Thank you for your questions.


Live Streaming by Ustream.TV

Japan Nuclear Watch: Third Explosion, Possible Cracked Containment at Unit 2

3:17 pm in Uncategorized by Scarecrow

This cutaway diagram shows the central reactor vessel and thick concrete containment in a typical boiling water reactor of the same era as Fukushima Daiichi 1 (image: www.world-nuclear-news.org)

Japanese authorities now reporting that about 6:14 a.m. (Tokyo) Tuesday, March 15, there was an explosion at the Daiichi Unit 2 of the Fukushima Nuclear Station. This explosion was heard, not seen from the outside. The explosion reportedly did not blow off the roof/walls, as the explosions did at Units 1 and 3.

The explosion reportedly occurred near the containment area. Plant officials fear there may now be a crack in the reactor containment, which would allow more serious releases of radiation. A “pressure suppression pool,” the doughnut-shaped area at the bottom of the reactor vessel may have been damaged, which officials are describing as “serious.”

They are evacuating non-essential personnel in/around the plant after initial outside readings reached 965 micro-Sievers/hour. Radiation levels spiked to 8,217 micro-SV/hour, before dropping. That’s “more than eight times the 1,000 micro sievert level to which people are usually exposed in one year.” Winds are reported from the NNW.

At the time of the explosion, about one half of the reactor core — about 2.7 meters — had become uncovered. According to one analyst, at some point, the entire core was exposed. Pressure reached 3 atmospheres, but has fallen back to 1.

These pressure and radiation readings suggest the reactor pressure vessel holding the core may have been breached.

There is also an inoperable value that would otherwise allow pressure releases. That’s preventing or limiting the ability to inject cooling water.

An official is describing the event on this live tv feed, with English translation.

In a follow up news conference by TEPCO . . . utility officials said they’re continuing to inject sea water, with only a few essential personnel. They’re apologizing to the public. Reporters keep asking for details of the incident, and the officials keep apologizing!

Reporter: “we’re not asking for your feelings! Tell us the facts.”

Response: “The blast was heard; we checked parameters; pressure readings indicated some damage to the pressure pool. That caused the evacuation of the operators. Being carried out for the first time.”

“Water level was at minus 2700 mm [?} before and after; we're trying to decide what that means."

Q. What caused the damage to the suppression pool?
A. We have only confirmed the pressure went down. The Cabinet official assumed there was damage.
[Reporters obviously frustrated]
Q. Can anyone explain this? Have Unit 1 and 3 been evacuated?
A. Only those necessary are there.

Update from 11:00 a.m. (Tokyo) presser from Cabinet Official:

As of 6:00 a.m. Tuesday, all but 50 involved in water injections have been evacuated. Injections are occurring at Units 1, 2, and 3. There was a fire earlier at Unit 4, which was in cold shutdown when the quake occurred.)

Evacuations directed around 30 km radius. Everyone else urged to remain indoors.

Cabinet meetings continuing.

[note: these are paraphrases of Q and A]
Q. How are you sure the pressure vessel not been damaged?
A. Water injection has been maintained. And pressure has been stabilized; we have to continue those efforts.
Q. How serious is fire at Unit 4?
A. I mentioned it first because it occurred earlier.
Q. Is there damage to container vessel?
A. Report there is a high probability that it was.
Q. Radiation levels?
A. Very little possiblity of harm to public
Q. Status of fire at Unit 4?
A. Still working to extinguish the fire at Unit 4.
Q. Evacuation radius?
A. Out to 20 km = evacuate. Considering out to 30 km; but for now, just stay indoors.
Q. Radiation readings related to damage to Unit 2
A. Explosion at #4 reactor could have caused that [explosion?]
Q. What if fire continues?
A. We’re making every effort to put it out. The spent fire is not going to “catch fire” in general sense. Fire is in building area; but it’s best to extinguish to keep temps down and prevent release or radiation.
Q. Release possible.
A. Possible some could have been released. Ask TEPCO. But current high readings are from this fire, not from the Unit 2.
Q. What is your advice?
A. [Repeats evac and remain indoors] Minimal amounts may spread further, but further away the level if lower, so stay calm.
In another Onadaga plant, the levels will not cause damage to health.
A. For people between 20-30 km range, there are towns that overlap/inbeetween. He calls them out. [About 8 towns]
Q. Sec. Gen of IAEA says you asked for experts?
A. Not aware of any Japanese request t IAEA, but after quake, we’ve asked for support from various countries.
Q. Neutron radiation?
A. That was from Unit 3, because of its nature [fuel type]
Q. How long to extinguish Unit 4 fire, given you think it’s source of radiation?
A. Working on it.
Q. Continue to inject water?
A. Yes. Thank you for your questions.


Live Streaming by Ustream.TV

Japan Nuclear Watch, Wed. am JST: New Fire and Explosion at Unit 4 Fuel Pond

4:56 am in Uncategorized by Scarecrow

This cutaway diagram shows the central reactor vessel and thick concrete containment in a typical boiling water reactor of the same era as Fukushima Daiichi 1 (image: www.world-nuclear-news.org)


Japanese responders continue to battle rising heat and pressure and falling water levels in the damaged reactors, Units 1 and 3, at Fukushima I (Daiichi) Nuclear Power Station.

But the big news is that Unit 2 lost cooling and the core was left uncovered, allowing a likely partial meltdown. There has not yet been an explosion at Unit 2, and they’re trying to relieve pressure to prevent that. More on that below.

And there is concern about the condition of spent fuel rods in pools located above the reactor. They too must be continuously cooled, but the cooling systems are also disabled.

The New York Times interviewed US industry and regulatory officials who had been briefed on the Japanese efforts and reports several interesting facts mentioned in FDL threads here but not previously summarized. Also note the photo at the top of the Times’ article, showing the damage to the Unit 3 reactor building from yesterday’s explosion.

– In addition to the reactors themselves, they’re worried about the condition of the spent fuel holding ponds, which are inside the reactor buildings. The spent fuel has ceased fission reactions, but residual radioactive decay continues and must be continuously cooled.

. . . there was deep concern that spent nuclear fuel that was kept in a “cooling pond” inside one of the plants had been exposed and begun letting off potentially deadly gamma radiation.

– The reason they not only lost the back-up generators when the tsunami hit, but can’t easily replace them with portable generators brought to the site is because the connection points, with the generators, were completely flooded by the tsunami.

[The tsunami] easily overcame the sea walls surrounding the Fukushima plant. It swamped the diesel generators, which were placed in a low-lying area, apparently because of misplaced confidence that the sea walls would protect them.

– The core in Daiichi Unit 1 suffered significant exposure when water levels fell:

While estimates vary, several officials and industry experts said Sunday that the top four to nine feet of the nuclear fuel in the core and control rods appear to have been exposed to the air — a condition that that can quickly lead to melting, and ultimately to full meltdown.

– Official reports of pressure readings inside the reactors are, as we’ve suspected, not necessarily reliable.

Workers inside the reactors saw that levels of coolant water were dropping. They did not know how severely. “The gauges that measure the water level don’t appear to be giving accurate readings,” one American official said.

– With all the normal/backup water cooling systems inoperable, the responders where attempting to inject sea water using fire-fighting equipment, but with limited success.

To pump in the water, the Japanese have apparently tried used firefighting equipment — hardly the usual procedure. But forcing the seawater inside the containment vessel has been difficult because the pressure in the vessel has become so great. . . . it was “not clear how much water they are getting in, or whether they are covering the cores.”

– The outer structure of the Daiichi units was reportedly designed to be blown away in an explosion, to relieve pressure but preserve the reactor vessel and containment structure inside.

The walls of the outer building blew apart, as they are designed to do, rather than allow a buildup of pressure that could damage the reactor vessel.

We’ll be updating as needed.

Update I: (h/t lobster) Last night (our time) the core at Unit 2 became uncovered when sea water cooling efforts failed for a time, so we’ve got another meltdown in the works:

Kyodo (22:15) reporting Unit 2 fuel rods were fully exposed for about 2.5 hours.

This would be Fukushima Daiichi Unit 2, where the fuel rods were completely exposed for a time when the fire equipment pumping sea water into the reactor ran out of fuel. (h/t lobster)

Fuel rods at the quake-hit Fukushima No. 1 nuclear power plant’s No. 2 reactor were fully exposed at one point after its cooling functions failed, the plant operator said Monday, indicating the critical situation of the reactor’s core beginning to melt due to overheating. . . .

The seawater injection operation started at 4:34 p.m., but water levels in the No. 2 reactor have since fallen sharply with only one out of five fire pumps working. The other four were feared to have been damaged by a blast that occurred in the morning at the nearby No. 3 reactor.

The utility firm said a hydrogen explosion at the nearby No. 3 reactor that occurred Monday morning may have caused a glitch in the cooling system of the No. 2 reactor.

. . . To prevent a possible hydrogen explosion at the No. 2 reactor, TEPCO said it will look into opening a hole in the wall of the building that houses the reactor to release hydrogen.

Apparently they only have one operable fire pump available to pump sea water at Daiichi, so they’re focused now on Unit 2, even though Units 1 and 2 also need sea water.

Update 2, 12:00 p.m. EDT: Reports now indicate that despite efforts to inject sea water into Unit 2′s reactor, the core became exposed again. Officials are now conceding that partial meltdowns of exposed fuel are likely occurring at all three units at Fukushima Daiichi.

Two [Now Five] Japanese Nuclear Units Still at Serious Risk

2:59 pm in Uncategorized by Scarecrow

Boiling Water Reactor with emergency cooling system (image: Nuclear Regulatory Commission)

In the aftermath of the devastating earthquakes and tsunami that struck Japan, we’ve been trying to piece together the status of the nuclear station at Fukushima. There are six units there, and the oldest, Units 1 and 2, brought in service in the early 1970s, appear to be at risk. [Update: There is some confusion about how many units are now at risk. There are at least 2 at one station; another report suggests another 3 units at another station with similar issues in same area.]

The New York Times has a useful summary, and we’re getting a more detailed picture from the Union of Concerned Scientists, which includes scientists and nuclear engineers with direct familiarity with the 1970s era General Electric boiling water reactor designs used at the station. The UCS are more prone to explain the risk analysis than government officials understandably concerned about public panic and safety.

Here’s what appears to be happening.

1. As soon as the earthquake began, all the Japanese nukes began their automatic shutdown sequences. That’s what they’re supposed to do. Control rods that help separate the radioactive fuel rods/elements and reduce the heat buildup were immediately inserted. As far as we know, this worked at every reactor.

2. When this happens, the cooling water system, run by electric pumps, is supposed to continue circulating water through the reactor vessel containing the fuel rods, to continue to remove their heat. However this system runs on electricity from the grid or from backup generators. The grid was damaged, so the plant was isolated.

3. With grid electricity unavailable, all plants automatically activate back-up, on-site generators, probably fueled by diesel. The diesel generators provide enough electricity to keep the control rooms functioning and to operate the electric pumps that continue to circulate water over the reactor core to continue its cooling. This normal back-up system worked at almost all plants until . . .

4. The tsunami hit the Fukushima station and apparently damaged the back-up diesel generators. At this point, Units 1 and 2 were without power from either the grid or back-up generators. It was flying blind.

5. When this happens, there is a fail-safe mechanism attached to the reactor that runs on steam that can still force cooling water across the core and continue the cooling process . . . for a while. This system is controlled by batteries with a limited life. The UCS think this is about 8 hours. That time has probably lapsed.

6. The Japanese operators are trying to bring in replacement batteries to keep the emergency fail-safe cooling system functioning. We don’t know the status of that effort at this time.

Bottom line: There may be not one but two units at risk. They’re both on last-ditch, fail-safe systems that rely on limited-life batteries to keep cooling water flowing and covering the core. The operators are in a race against time to replace them or to get electric power either from repaired or replaced back-up generators or restored access to the grid. We don’t know the status of any of these efforts.

Without continuously circulating cooling water, the still very hot reactor core will slowly (over hours) boil away the remaining cooling water, and that could eventually leave the reactor core and its radioactive fuel rods uncovered. We don’t know how far along we are in that sequence. What happens after that can lead to an uncontrolled meltdown and releases of radiation.

“Controlled” radiation releases, through filters (we don’t know their effectiveness), have already been used to relieve pressure inside the reactor. [There's a report they've lost any other ability to control pressure.] suspect most has been contained inside a massive containment structure, which is designed to withstand everything except the things they didn’t plan for, like the loss of everything. We’re there.

There have already been pressure buildups inside the reactor (or containment?) that exceed its design capacity. We don’t know what it’s real limits are, and we don’t know what damage the earthquake caused to its integrity.

Evacuations are underway, in increasingly larger areas. Stay tuned.

Related articles:
UCS: Nuclear crisis at Fukushima
NYT: Japan expands evacuation around nuclear plant
Nuclear plant under state of emergency
Design features of a boiling water reactor
Risks of nuclear catastrophe escalates . . .
Radiation 1000 times higher than normal

Update: keep in mind there are two multi-unit nuclear power stations in play. In all, five units are at risk at these two stations.

Fukushima I (Daiichi) Nuclear Power Station = six units built in the 1970s
Fukushima II (Daini) Nuclear Power Station = four units built in the 1980s

At Daiichi, Unit 1 had the explosion on Saturday; Unit 2 is also at risk.
At Daini, Units 1, 2, and 3 are also at risk.

Disclosure. I once consulted for Tokyo Electric Power Company, the plant owners, on an unrelated matter, explaining US grid coordination. I’m not a nuclear expert.