I’ll just summarize the gist of my cooling idea: Combined evap and recirc as poor man’s external primary/secondary loop. At this point, this proposal is only viable if the current filtration process fails either in part or in whole.
[ UPDATE: It has failed again
“At the Fukushima plant, meanwhile, recovery efforts have been slow and perilous. A circulation system that would allow the plant’s reactors to re-use cooling water — which officials have called an important step toward resolving the crisis — was started up Monday but shut down just 1.5 hours later.
The system was designed to reduce the amount of contaminated runoff from the reactors, which are being kept cool with water. Tokyo Electric officials have said that 110,000 tons of radioactive water has already accumulated under the reactors, and there is a danger that the water will overflow.” Tokyo Electric Power Defeats Shareholders’ Efforts to Exit Nuclear Business
By HIROKO TABUCHI
Published: June 28, 2011
I do not know what caused this or the previous efforts to fail, but I know that the symptom of the first failure was excessive contamination blowing expectations of the system’s performance. I suspect that is the problem here.
THE WHOLE POINT of my proposal is to draw off lightly contaminated condensate and cool THAT for recirc. By drawing it off in the first place, you make room for it to return cool, and solve the imminent overflow problem. ]
Potential Background, Many Unknowns
All I know about the current efforts to cool the reactors is based on articles in the papers and so forth, the most recent of which I have seen is this: Tepco starts cooling reactors by recycling water, which is great news, but leaves me with questions. So I don’t know if I’m addressing problems which are important or even real. It’s just a thought. For all I know, the system is already working fine.
My concern is that they are reportedly injecting a total of nearly 20 cubic meters of water per hour into the reactors. When I compare the flow rates with the temperatures, it is consistent with this being the mass flow rate required to bring the temperature down (or more likely, hold it stable while radioactive decay takes the oomph out of the remaining reaction, thus gradually lowering temperature). Of course I have not done the thermal math, I’m just looking at the correlation between temperature and flow.
[pullquote]every other day 1,000 m³ hot contaminated water must come out of the reactor to make room for cooling water[/pullquote]
So if it currently takes 20 cubic meters of water per hour to cool the things, then every other day that’s another 1,000 cubic meters of heavily contaminated (and thermally hot) water which must come OUT of the reactor to make room for the clean and thermally cool water needed to stabilize or reduce the temperature. A few days ago, a story said there was in excess of 110,000 tons of contaminated water stored at the site. I do not know if this includes water currently working in containment or only water which has been released from containment. I know this includes water in storage tanks; I do not know if it also includes water in locations such as the turbine building. I did read that a plan was in place to remove water from the turbine buildings to a “Central Treatment Facility”, but I do not know if this has begun.
All reports seem to agree that the immediate threat is a lack of storage forcing another release of contaminated water.
The Basic Idea
[pullquote] can we condense lightly contaminated steam for a much cleaner closed cooling cycle[/pullquote]
Reduce the bulk of water. The Kurion / Areva process currently operating seems to attempt to decontaminate all of the water which flows through it. If this can treat 20 cubic meters of heavily contaminated water per hour sustained, great! If not, then would it be possible to use evaporators to draw off lightly contaminated steam and condense that for a much cleaner closed cooling cycle? If the basic process is sound (concentrating radioactive contaminants through evaporation), then it should simply be a matter of building up to enough capacity to evaporate 20 cubic meters per hour.
Critically, this is how much the bulk of the water in containment would be reduced each hour, and if this level can be reached, then we have made room for the necessary amount of cooling water to be injected. It doesn’t take a nuclear physicist to see that if we now treat the lightly contaminated water and recirculate that (after cooling), we have closed the cycle, and stopped adding to the storage problem.
It may even be that the decontamination is not necessary, if the evaporator produces clean enough condensate. We’re not pumping it into the ocean (it’s going right back into the reactor), we just want to allow cooling of a fairly clean stock of water, instead of shuffling around the most heavily contaminated water in the world. This would shorten the round trip time for the “brine loop”, and clean up the cooling process.
Drawbacks
It’s a bit more complex, and perhaps hazardous, as it operates a dynamic process (evaporation) on the heavily contaminated water, rather than simply filtering and sifting. Also, the present course requires only the actual 20 cubic meters per hour to be drawn from the reactor in order to balance cool input. Evaps only take up a percentage of the water, so the total mass flow out and right back in on the brine loop is likely to be several times higher than 20 cubic meters per hour. And it would have to be much higher, in order to keep the concentration of radioactive contamination as low as possible. It may be that this process therefore offers no real benefit, if increased risk from the proposed process itself cancels out reduced risk from the current process overflowing storage of heavily contaminated water. But it looks like overfilling is a sure thing, unless the current process gets better, fast.
Finally, if this process is new, it will take time to implement, and time is the problem–every hour that goes by, 20 cubic meters of heavily contaminated water are added to storage.
Moving On
If this process can be made to work, then as either evaporative capacity grows or the requirement dwindles, any reserve capacity can be put to use in treating the existing stored waste water. All you have to do is mix discharge from storage with the intake flow to the evaporator, and taking any excess treated water away as neither heavily nor lightly contaminated, but merely “suspect”. I wouldn’t drink it, but the Areva people might. I’m no expert.
