Japan Earthquake: nuclear plants

Rive

I've seen papers about similar strategies for PWRs too.

MadderDoc

Yes, but they were measuring temperatures in the 2-300s deg. C range at the top of the depressurised vessel. It would be physically impossible to heat anything to that kind of temperature by condensation of saturated steam inside the vessel.
Oh yes, and certainly an agency like NISA had people who could do it. Even a BOE would indicate the madness of the matter. Tepco's proposition that the pool was steaming due to failed cooling postulated the occurrence of a plain physical impossibility -- yet NISA didn't bark, just placated it down as the operator's estimate of the situation.

jim hardy

hmm i hadnt actually tried the arithmetic out. Real rough back-of-envelope::

half megawatt of decay heat (post 13115) = 500kw X 3412.7 BTU/kwh = 1.706E6 BTU/hr
for 5 days = 120 hours X 1.706E6 BTU/hr = 2.05E8 BTU
to raise water from (let's guess) 72F to 212F is about 140 BTU/lb
so 2.05E8 / 140 = 1.46E6 pounds of water could be warmed that much by the fuel
that's 731 US tons of water
or 664 metric tons of water

i think the pool holds considerably more so i figured it had leaked some.
But that was just an assumption.
This reference gives 1.5 million liters as typical BWR SFP water inventory
http://books.google.com/books?id=ltF...0water&f=false

which would be 1.5 million KG , 1500 metric tons, 2.25 X my estimate above.

So if it's 'typical' per that book it would have to have lost ~half its water.

Dont know if this is of any use at all
it's just the kind of rough sanity checks i do on myself to keep that "excess of imagination" from getting me in trouble.
please check my arithmetic.............

old jim

MadderDoc

Do check your physics, there's a thing called latent heat of evaporation which you appear to have neglected.

NUCENG

Caveat: the following applies to a US BWR. Japanese mileage may vary.

If I remember correctly instrument racks contain the pressure and level transmitters/ analog sensors and those racks are located on the first floor outside of the drywell. The inside drywell piping is routed out to these instruments so there are no wires or junctions inside the containment. No guarantee, but I think 1C55 and 1C56 were the numbers on those racks.

Temperature elements are inside containment and thermocouple and RTD cabling is routed out of the drywell and there are junction boxes in the systems inside and outside containment. The Environmental Qualification program qualifies cabling for design basis conditions of pressure, temperature, humidity, spray, submergence, seismic loads, and radiation. However, it is clear that the conditions at the Fukushima plants exceeded design basis conditions. Further the period these instruments are qualified for is not unlimited. I have previously shared the possibility that the post-accident chemistry and radiation are likely attacking the electrical wiring as well. Nuclear plant instrumentation tends to use redundancy, diversity, and independent routing to prevent local failures from being single points of failure.

I have been reluctant to weigh in on some of these discussions because they seem too speculative and I am not sure we will gain anything by trying to answer why instruments failed until they can actually retrieve them and do post mortems. I am not suggesting that this discussion isn't valid or interesting. I will try to provide answers on my experience where I can. I am reading these posts and appreciate the effort being made to understand what happened.

One of the most important things is to get good simulations of the conditions inside the drywell and torus during the accidents that match the information we actually have. This is likely to be available to develop new qualification requirements well before they can actually start retrieving failed cables or sensors.

jim hardy

i just figured the heat to raise the pool temperature to boiling, absent evaporation

steaming carries away copious heat thereafter
a half megawatt should evaporate 1760 lbs/hr, or 29 lbs/minute (latent heat 970 BTU/lb)
making 785 cubic ft/minute of steam, less than a ten foot cube

of course approach to that would be asymptotic as evaporation rate increases.

MadderDoc

Yes, you found the decay heat to be sufficient only to heat the water of the pool to about 140^oF (60^oC), not even warm enough to make instant coffee of, and with na'r a BTU left for evaporating any of it.

Right, so even assuming every BTU of decay heat in miraculous contradiction of the laws of thermodynamics could have been channelled into evaporation, the pool could have had lost only an insignificant fraction of its water by March 16th.

MadderDoc

I'd like first to see some honest curiosity to understand what happened at that plant, without which I can't see how one can conceptualise it and produce a proper model. Once there, implementing a good simulation of the model ought to be the trivial part. I couldn't care less about the fiddling with parameters and assumed events to get existing models to produce output with some semblance to actual data and that's all I've seen so far.

jim hardy

well more exactly , ... sufficient to heat HALF the water in a 'typical' pool BY 140 deg....

Boiling away 1760 lbs/hr would be around 20 tons a day, which is hardly a dent in that 1500 ton inventory.

So if the pool was not pretty low on water it got more heat from someplace.

Conversely if it got no more heat, it musta been pretty low?

i dont know which is the truth, but assumed at the time it was low on water.
Again, that was an assumption but it did fit with the 'gamma backscatter' idea as cause of high radiation readings around building, and with high radiation readings from helicopters..loss of water = loss of shielding above spent fuel.

But i wasn't there. And there's surely other possibilities.
That one could unravel.

What's your thoughts?

Rive

We know that there were leaks around the reactor cavity on the side of the EQ pool. Maybe there were leaks on the other side too?

For the first times, when the internal pressure of the reactor were high that would mean steam condensing in the pool, raising it's temperature: later on as the pressure drops water would flow in and cool the containment cap.



Slightly connected: the water in the pool were filtered for cesium and other radioactive elements, but this filtering stopped after some time. Do we have any data about the pool water contamination after the filtering stopped?

I think if there is fuel with damaged cladding in the pool then the cesium level would rise after the filtering stopped. If the fuel cladding is intact, the Cs level would be steady.

If the fuel cladding is intact then there must have been other source for that Cesium.
Maybe from steam coming from the reactor, condensed in the pool?

MadderDoc

Well. First, look at the facts: There's a 1400 m³ pool of water with 0.5 MW of decay heat from spent fuel in it and its cooling has failed. 5 days later the operator informs its safety regulatory agency that due to the failed cooling, steam plumes are being emitted from the pool. The safety agency informs the public that this is the operator's estimate of the situation.

Next, there's the impeccable assumption: The laws of physics were not suspended in the pool.

Then follows the inescapable conclusion: What passed in this case as information from the operator to the agency, and from the agency to the public, was not information, not even false information. It was nonsense. Had it only been false information, that would be understandable. But no, for a statement to be possibly false, it must be implied that it can be possibly a true description of reality. Otherwise the statement is just so much nonsense -- and as your math has shown you, what was reported by the operator and sent on to the public by the agency was postulating a physical impossibility had occurred. All such statements are alike, they express nothing, they are all nonsense.

Imagine the operator had reported some other physical impossibility, e.g 'that gravity had reversed over the plant and was emptying the pool', and the safety agency reported this on to the public, the nonsensical nature of it all would have been clear to many people. It takes more knowledge to realise that a 1400 cubic meter pool of water cannot possibly be steaming plumes due to failed cooling after having been heated with 0.5 MW for a couple of days. The unsuspecting and ill-informed public would be excused in not 'getting it'. For Tepco the operator, and for NISA the agency, there is no excuse, and only a few credible explanations, none of which are flattering, and this is not the place to express them.

The fact remains, that what we were told about the situation in the pool did not make sense.

OK, so back to your considerations. If I get it, you meant to be able to extract as a fact that the pool was boiling from the nonsense "White smoke was seen rising from the vicinity of Unit-3 <..>TEPCO estimates that failing to cool the SFP has resulted in evaporation of pool water, generating steam.", then you added the assumptions that either the pool had lost a lot of water for unknown reasons, or it had an unknown heat source, then you coupled it to the observation of high doserate measured above the building, and got a plausible case of exposed fuel in the pool. But that seems to me to have been assumption upon assumption upon nonsense, and no surprise then that it was all wrong.

MadderDoc

The pool interface is of a different construction than that of the equipment pool, it is a double layered gate, held tight by the hydraulic pressure of the pool water. From what can be discerned in published video footage, the gates are in place, and a major steam route from inside the reactor seems to have passed close by, but on the side of the reactor, not that of the pool. While of course it cannot be held that the gates must be completely tight, there is no indication of any significant leak between the pool and the space over the reactor cavity, no indication that the pool has lost water to that space, or that steam from that space has added heat to the pool water. The added assumption of such a leak would seem to me superfluous, it doesn't appear to explain anything.

Pass on the Cesium thing. IRC the plan has been, using mobile units, with first reverse osmosis, then ion exchangers, to desalinate the water in the pools in turn, starting with unit 4. I do not know where SFP3 would be in the process.

wizwom

There could very well have been localized boiling.
However, steam plumes occur in air very commonly far below the boiling temperature. The air above the surface just has to get a saturation above the prevailing dew point.
It is fairly rare in pool applications, but any fisherman can tell you about a misty lake, which is exactly the same effect, but with the lake microclimate as the cool side.

Rive

Yes, you are right. Even if the FHM wreck damaged it the effect would be different. Thanks.

MadderDoc

Yes, wizwom, but this is the steam plume from 'the vicinity of Unit 3' which Tepco is talking about on March 16th:


Edit: See also the March 16th hourly webcam images

jim hardy

you got it.
IF that steam indeed came from the pool, there had to be a cause for pool being so hot.
With the modest heat input that pool had, either its thermal capacity was less than expected for that much water
or the heat input was more than expected.


If neither of those is so then the steam came from someplace else.

why is that "nonsense" ?

EDIT
I think one of us misunderstands something the other is saying and our difference lies in semantics not thermodynamics. It is sooooo difficult to make communication precise.

old jim

MadderDoc

I apologize if I have given you the impression that seems implied by your question, I really thought I had clearly identified the target of that description to be the estimate by Tepco, that the pool was steaming plumes due to failed cooling, indeed I think you just quoted me to that effect.

What you have written there is just the sort of mental model one makes of possibilities and logical implications when one is trying to get a foothold in regards of some problem. I wouldn't call any of it nonsense. Otoh, I can't see where you are coming from with it, nor where you are going, also I think the option 'someplace else' might be specifiable both as to its whereabouts, and its logical implications. Better to chalk up the whole playing field, before deciding how to tackle the problem.

Yes surely, but I think we will get by.