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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.
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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.


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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.


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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.