You are browsing the archive for Daiichi.

Japan Nuclear Watch, Thurs: UCS Briefing on NRC Fukushima Reactor Concerns

2:03 pm in Uncategorized by Scarecrow

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

It’s Thursday, 6:00 pm EDT: Friday, 7:00 am in Japan.

Today’s update focuses not so much on anything new happening — another quake, near loss of power at another plant, broken power lines — but on further analysis of the range of concerns the Japanese are facing at Fukushima.

The Union of Concerned Scientists held a press briefing with David Lochbaum and Edwin Lyman to help reporters understand the details of the NRC report on reactor conditions at Fukushima Daiichi Nuclear Station. The details explain how dire the conditions are at Units 1-4.

The March 26 NRC report had been the basis of a New York Times story, which we summarized on our Wednesday update, noting that nuclear plant experts had serious concerns about several conditions facing the Japanese as they try to get the three reactors cores and at least two spent fuel storage pools under control.

The entire UCS briefing is worth reading, but here I focus on two aspects: the continuing concern about the spent fuel pools, particularly at Unit 4 but also at Unit 3, and the condition of the reactors in Units 1-3 and the challenge of trying to keep cooling water covering their respective cores.

Why they can’t keep the reactor cores covered.

As explained by UCS, and based on the March 26 NRC analysis, it appears they may not yet have the ability to sustain water over more than about half of the core. And they have limited ability to circulate water over portions that are nominally covered because of salt build up (or core damage).

UCS nuclear scientist Lochbaum first explains the problem created by the salt and other obstruction inside the core. That’s restricting the flow of water into the core and around the fuel rods, leaving them at least partially uncovered.

The fuel that’s or the water that’s being injected is being injected into the reactor vessel outside a device called the core shroud that’s kind of like a can within a can, and the reactor core is within the inner-most can, the core shroud. The water that’s being injected is supposed to flow down through the annulus region between those two pieces of metal, be turned around by the lower dome, and then flow up through the reactor core to cool it. There are pretty clear signs that that’s not happening and the fuel inside the core shroud is not fully covered.

Lochbam further explains that each reactor vessel has, for this discussion, two sets of water injection points where external pumps can inject water into the reactor core to maintain cooling. The pipes are sealed at the point where they enter the reactor vessel, but those seals can break down when exposed to intense heat. If the seals fail, water can leak back out of the reactor vessel, offsetting the ability to inject cooling water in.

Two points then become critical. One injection point where the seals may have failed is about half way down the reactor vessel relative to the height of the core. That means water is leaking from a point that could leave half the core uncovered if not offset.

Moreover, if the pumps available for water injection cannot keep up with the rate water is leaking out, they can never get the core fully covered. That appears to be what’s happening at least at Unit 1 and possibly Units 2 and 3 as well. Here’s Lochbaum:

If [the seals] fail, they’re deliberately designed to limit how much water they leak out through a failed seal to about 60 gallons per minute, more or less. It’s more if the pressure inside of the reactor vessel goes up to squeeze more water through that narrow opening; it’s less if the pressure in the reactor vessel drops down.

But if you assume that both recirculation pumps on each reactor has failed seals, you could have upwards of 100 to 120 gallons per minute leaking out through those failed seals. Their elevations are about half of the reactor vessel core height. If those seals are intact, you should be able to at least flood the vessel back up to two-thirds core height. At that point, water leaks out through what are called the jet pumps. Right now, the fact that they are having trouble get the water level above one-half of core height is telling them that the reactor seals have likely failed.

To answer your question, could they get out of this situation, if they can get flow rate through the reactor core greater than the leakage rate and greater than the boil-off rate, which if that’s the only losses you have, is about 120 gallons per minute for the seals and about 50 gallons per minute for evaporation right now, and if you could get 200 gallons or more makeup and it’s not being blocked or bypassed from the core, then you should be able to refill the entire vessel. Right now, that’s not happening, so water’s going somewhere.

So, to summarize: Water injected at the top and pushed down the annulus inside the reactor may not be circulating back up through the fuel rods. And they can’t keep the fuel in the core covered more than half way because some water is boiling off and other water is leaking out half way down at a rate faster than they can inject it through whatever pumping equipment they have now.

And what about the Unit 3 and 4 spent fuel pools?

As we’ve noted many times, the fact the spent fuel storage pools are outside containment creates additional risks of nuclear materials being dispersed to the environment from any explosion. Here’s Lochbaum:

It’s difficult to determine which is worse, the spent fuel pool situation or the reactor core situation. There are signs that the explosions in the Unit 4 and perhaps also the Unit 3 spent fuel pool have caused irradiated material to leave the building. That could have been the reason for the high or the reports periodically of neutron beams. That actually could be coming from decay from fuel or fuel particles that are now no longer in the spent fuel pool and were carried away by the explosion. That was already known to cause high radiation levels. It caused challenges for the workers, including even the helicopter pilots that were dropping water onto the site a week or so ago.

There’s also a discussion of concerns about other issues, including why they need to be injecting nitrogen into the containment vessel — it was displace by hydrogen and the explosions and must be present to prevent further hydrogen explosions — and the need to expand the evacuation range. As Lyman emphasizes, the zone between 20 and 30 kilometers has been exposed for a month, and there is no sign conditions are improving. Those people (and probably others further out) should have been moved long ago.

Sources:

NHK World
Kyodo News
Hi-res photos
IAEA Updates
Union of Concerned Scientists
fleep Graphing Earthquate, radiation and water readings

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: 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.

Japan Nuclear Watch: New Explosion at Fukushima Daiichi Unit 3

6:49 pm in Uncategorized by Scarecrow

Reports from various sources and the video above indicate there has been another explosion at the Fukushima Daiichi Nuclear Station, this time at Unit 3. The video shows a dark plume rising hundreds of feet in the air, a bad sign if there is significant radiation involved.

An earlier report from Tokyo Electric indicated the water level in the reactor dropped 3 meters, exposing the core. The most ominous news, as reported by Union of Concerned Scientists (h/t commenter 4cdave):

… after multiple cooling system failures, the water level in the Unit 3 reactor vessel dropped 3 meters (nearly 10 feet), uncovering approximately 90 percent of the fuel in the reactor core. Authorities were able to inject cooling water with a fire pump after reducing the containment pressure by a controlled venting of radioactive gas. As they did with Unit 1, they began pumping sea water into Unit 3 … the water level in the Unit 3 reactor still remains more than 2 meters (6 feet) below the top of the fuel, exposing about half the fuel to air, and they believe that water may be leaking from the reactor vessel. … In September 2010, 32 fuel assemblies containing MOX fuel were loaded into this reactor. This is about 6% of the core.

The use of MOX generally increases the consequences of severe accidents in which large amounts of radioactive gas and aerosol are released compared to the same accident in a reactor using non-MOX fuel, because MOX fuel contains greater amounts of plutonium and other actinides, such as americium and curium, which have high radio-toxicities.

The utility, Tokyo Electric is reporting there are three persons injured and seven person missing. [Update: they've reportedly been found] BBC says there may be 11 persons missing.

Unit 3 is at the same Station as Unit 1 where the earlier hydrogen explosion occurred two days ago. There are also reports of smoke rising from Unit 1, but this may be from the same blast.

The earlier explosion blew the roof and upper walls off of the reactor building at Unit 1. At this point, we don’t have any indication of the damage done to Unit 3 reactor, but utility/govt officials are claiming the reactor vessel was not damaged. As for the building housing the reactor, before/after images captured by Jim White indicate this latest explosion blew the roof and walls off the reactor building. See below.

The plant operators have been struggling with the loss of the cooling system and a resulting rise in pressure in the reactor. They have been injecting sea water, using fire pumps, to sustain at least some cooling and may have attempted another controlled release to relieve the rising pressure. That procedure was also presumably involved in the first explosion at Unit 1.

We’ve captured a screen grab, below, that shows before/after. This new explosion appears to have caused substantially more external damage to the outer building than the first explosion. The NYT also reports the same thing.

We will update as we get more details and confirmation.

Japan Nuclear Watch: Struggling to Prevent and Limit Meltdowns

5:32 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)

First, thanks much to our great commentors — Masoninblue, earlofhuntingdon, Professor Foland and many others — who continue to provide updates and expert analysis on the Japanese nuclear crisis. And hat tip to commentor “lobster” for finding a better schematic that helps illustrate the conflicting stories about a “meltdown.” [Updated to reflect suggestions for clarity.]

Desperate efforts continue to contain the damage at at least six nuclear reactor units at Fukushima Stations I (Daiichi) and II (Daini), following the explosion early this a.m. (US Eastern) at Daiichi Unit 1.

There are confusing/conflicting reports of a “meltdown,” at Unit 1. CNN reported a Japanese nuclear official seeming to confirm that a “meltdown” was probably underway, but there has been no other official confirmation. As Bill Egnor’s comment thread highlights, there’s no official definition, and there are different ways the term “meltdown” is being used.

1. Using lobster’s diagram, we can see in the middle the metal core of the reactor, which contains the fuel and control rods. Let’s call it the reactor vessel. Emergency cooling systems are beneath that vessel.

2. But surrounding and containing that reactor vessel and other equipment is a fairly substantial containment structure, with various parts of the normal steam and emergency cooling water systems feeding into it to reach the reactor.

3. Then all of this structure and more is housed in a large building, which some might call a reactor building. In this vintage, it’s not a hardened structure designed to contain explosions or high pressure. The roof and outer walls of this building, we believe, are what was destroyed by the explosion.

Explained this way, we can then account for some of the apparently conflicting reports and claims.

Was the containment structure destroyed? Officials say no. Well, it’s possible it wasn’t destroyed; however, the walls and roof of the larger building were destroyed, leaving the internal structure exposed. We don’t know the extent of the damage to this internal structure.

Is the reactor core still viable? Officials say yes, but what they may mean is that there hasn’t been a major breach of the inner reactor vessel, even after the explosion. We can’t tell for sure, but other evidence suggests some damage inside.

Has their been a “meltdown,” as CNN quotes the official as confirming [and see LA Times Version]? It depends on what you call a “meltdown.” If you ask, did any of the fuel rods melt? the answer is “maybe”
or even “probably.” There are reports the fuel rods were expose somewhat, for some period, and some melting could have occurred then. That type of initial “melting” would account for the presence of hydrogen, which led to the explosion, and the release of cesium. [I'll edit this as I get confirmation/better explanation.] But . . .

It’s also possible this limited melting has not proceeded to the stage where it becomes so pervasive that it melts through the reactor vessel, and continues on through the rest of the containment structure and floor. If the reactor then became “critical” again, that might lead to a full “meltdown” — the so-called China Syndrone — but we don’t seem to have evidence that that has occurred. Hence the confusion over whether a “meltdown” has or hasn’t happened.

In the meantime, the plant emergency teams continue to pump sea water into the reactor, though there’s no evidence they’re also trying to fill the internal “containment structure.” Since the normal and emergency cooling water systems have failed, the point of the sea water is to continue carrying heat away from the reactor as it slowly cools. The hope is that the core reaches lower temperatures where further melting cannot occur.

There are also reports of sea water being injected into at least [one other?] reactor. Unit 3′s cooling water system failed earlier today, and there is a BBC report that seems to suggest the core has become partially uncovered.

Quoted by Kyodo, Tepco said the tops of the MOX fuel rods were 3m above water.

So there are still at least six units in varying stages of risk. We should note, however, that as time passes and matters don’t deteriorate further, the heating processes being driven by the core/fuel rod decay will slow and the danger lessen. For the first time, time may be on the peoples’ side. [Update: Prof Foland notes via e-mail that “on the other hand, if coolant is slowly boiling off in other units, then the cores are slowly heating up.” So they may need to take additional measures — sea water cooling? — to bring those temps down, provided they’re willing to lose those units by using sea water.

Japanese authorities are steadily increasing the number of people being evacuated in areas surrounding the two Fukushima nuclear stations. The last confirmed report I saw was 140,000 people being asked to leave, but later reports suggest the number at 180,000 (CNN) or exceeding 200,000 (BBC).

People are being given iodine treatment to help limit the effects of radiation exposure, as the number of folks possibly exposed climbs. That suggests they’re clearly worried about losing more of these plants and having more radiation releases, with associated health implications.

Again, we’ll update as events warrant. And thanks to our commentors for all their help.

John Chandley