Japan Earthquake: nuclear plants

Cire

Some good reading:

http://www.new.ans.org/pubs/journals/nt/a_14634

Summary and opinion: http://atomicinsights.com/2012/10/oa...tml#more-13073

etudiant

The paper mentioned here: http://www.new.ans.org/pubs/journals/nt/a_14634
is unfortunately behind a paywall, but the second reference from Atomic Insights does provide the meat of the paper.
The paper shows quite clearly that left entirely to itself, the Reactor 4 SPF and its contents would have reached equilibrium around 90*C, well below the boiling point, with enough water present to keep the fuel covered for at least 13 days.
So NRC Chairman Jaczko's comments to the contrary were wrong.
In Jaczko's defense, there had been a big quake and several explosions, suggesting leaks were possible, plus the Reagan had encountered a massive nuclear plume, so that SPF was a reasonable source of concern.
What is surprising is that with three reactors having had explosions, the NRC heads concern should focus on the SPF of the only reactor left unfuelled at the time of the accident.

zapperzero

I seem to remember the #4 SFP was making the most heat, as it contains the most recently-extracted fuel, but I may be wrong.

Rive

Without knowing the whole paper and the used models I cannot be sure, but if the equilibrium of the pool was around 90*C, then for me it definitely suggest that around some hot fuel bundles there was boiling.

90 -> 100*C temperature change with natural convection means a very limited cooling.

I have some serious doubts.

Hiddencamper

In the US, we assume boiling begins at 200F, or about 93C. I agree that 90C suggests localized boiling was happening as 90C was probably a bulk temperature and not localized, and as we know (and can be seen in PWRs), localized boiling can happen in various amounts as you approach boiling points.

Now I do know that it takes a few days for boiling to start in a normal SFP, additionally unit 4 had a much large water inventory to work with because the separator gate was out and the reactor was opened up. 13 days before full boiloff is possible, but some more specific data would be needed. Its likely boiling started within 4-5 days (full core decay heat load at 90 days since reactor shutdown for that mass of water).

I do know that spent fuel pools with a 1/3rd core offload (on their own) will BEGIN boiling in <72 hours, but the time to complete the boiloff takes longer than the time to start boil off (due to latent energy of water).

tsutsuji

If the mean temperature value is 90°C and if some parts are reaching 100°C, it means that other parts are lower than 90°C. Then, those colder parts would generate less steam. Are you sure that all in all the steam quantities are much different than when you use the simple model where all parts have the same temperature ?

Also, wouldn't the steam bubbles generated in the hot spot condensate before reaching the pool's surface ?

Cire

Don't forget that the pressure at the fuel bundles isn't atmospheric due to their depth. The boiling temperature is going to be a few degrees higher at that location. There will also be fairly significant thermals moving through the bundles.

jmelson

I believe this is correct, fuel from the #4 reactor had been removed and placed in the
pool a couple months (?) before the earthquake, to prepare for major work in the reactor
vessel before refueling. Also, the pool was loaded with the fresh fuel to go in after the
work was complete.

Jon

etudiant

Without having seen the actual paper, the summary suggested that the SPF water temperature would rise over a period, but that the equilibrium for heat loss from evaporation versus decay heat from the stored fuel was slightly below 90*C, 87*C by the researcher's etimates.
That overall thermal balance would of course include hot spots around the more recently used fuel, so localized boiling with subsequent quenching of the steam bubbles would be a reasonable expectation.

rmattila

While the difference between 90 and 100 Celsius probably does not have a significant effect on the fuel cooling conditions, it may have an important effect on the fuel pool liner stresses. I don't know if the Fukushima pools were rated for 100 C, but I know that there are pools in some (European) plants dimensioned to withstand with certainty only about 85 C.

Burnsys

Is this report true?

http://www.agoracosmopolitan.com/new...0/19/4621.html

Mitsuhei Murata, who served his country as Ambassador to both Senegal and Switzerland, explained in a recent interview that far from the situation at the Fukushima Daiitsu plant improving, it is actually worsening in an alarming way: the ground beneath the plant's number 4 reactor is sinking. Mr Murata implied that the whole structure is on the verge of collapse. He wrote to the Secretary General of the United Nations stating unequivocally that the fate, not only of Japan, but of the rest of the world depends on the No. 4 reactor.

tsutsuji

http://www.iaea.org/newscenter/focus...port280912.pdf Fukushima Daiichi Status Report, 28 September 2012 (A summary of the latest information provided by Tepco)

One of Tepco's replies to such fears is available at http://www.tepco.co.jp/en/nu/fukushi...2062901-e.html (29 June 2012)

See also the following:

Also, that the whole Fukushima coast sunk by some 60 cm (and moved by 2.4 m Eastwards) during the 11 March 2011 earthquake is not the same as saying that unit 4 or anything else is still sinking now.

http://en.wikipedia.org/wiki/2011_ea...ysical_effects "A 400 km (250 mi) stretch of coastline dropped vertically by 0.6 m (2.0 ft), allowing the tsunami to travel farther and faster onto land"

See also http://www.tepco.co.jp/en/nu/fukushi...20413_04-e.pdf "Water level measurement in order to confirm the soundness of the Unit 4 Reactor Building" (13 April 2012)

ronaldkr

Dear etudiant,
you are falling for a part of the never-ending witchhunt against chairman Jaczko. The problem at that time was not evaporation of the SFP at unit 4; they did not know if it lost water. Remember the helicopter overflights for refilling (a show by the Japanese SDF for sure)? The first attempt was cancelled because of high radiation dose. The second attempt was done with a lead plate under the chopper.

Now, how much water was in the pool that the government-ordered show flight was abandoned? And why did they order a large concrete pump after getting the radiation readings?

Of course, we all know that fission boilers with SFPs on the top level are totally safe -- so it cannot be, and must not be that a pool loses water. Jaczko had concerns and even dared to voice them.

etudiant

I have no problems with his statement. He could have been right in the event of SPF damage from the quake, which does not seem impossible given the quake shifted the entire region by several feet and dropped the land by a couple of feet, as Tsutsuji-san notes above.
He specifically did note a potentially catastrophic risk if the SPF 4 were low on water. He apparently believed that was the case, based on an incorrect work flow document from TEPCO that did not make clear that both RPV and SPF were filled with water to the top for the fuel removal. So he was mistaken, but understandably so.
That said, your idea that merely noting the mistake is to join in a witch hunt against Chairman Jaczko seems a little overprotective.

Hiddencamper

Just to add a little bit to the water level, for US nuclear plants the technical specifications change greatly if the RPV and SPF are filled at least 22 feet above TAF, as the total inventory of water requires many days prior to a critical situation with regards to fuel cooling. Above 22 feet less ECCS pumps and emergency power systems are required to be in effect, and alternate decay heat removal systems can be used in place of normal removal systems. Additionally secondary containment is allowed to be breached provided OPDRVs or fuel moves arent in effect (Operations with Potential for Draining the Reactor Vessel)

tsutsuji

is linking to :

http://www.nsr.go.jp/archive/nisa/en...t_handout.html Side Event by Government of Japan at 56th IAEA General Conference, Sep 17, 2012 Briefing on TEPCO's Fukushima Dai-ichi NPS accident

including:

http://www.nsr.go.jp/archive/nisa/english/files/P-4.pdf Harutaka Hoshi and Masashi Hirano, Japan Nuclear Energy Safety Organization (JNES): Severe Accident Analyses of Fukushima-Daiichi Units 1 to 3

Rive

I'm sure that seeing/assuming the boiling would made me scared in those times with so few direct information regarding the U4 pool. With only hot water, you can see how much heat is there, or at least you can give an upper limit: if it's boiling, then you can only assume.

As I see this part of the discussion has no real basis if we are about the 'who was right/wrong' track.