Idea discussion - How useful are super freezers as an additional powerless safety precaution?

I think it’a a great idea @mattbrowne! It would be costly, but doable in terms of the cost of reactors now.

Thanks. Well, state of the art insulation should minimize the running costs. But the one-offs would be significant.

That sounds like a great idea.

Have you considered sendin a letter with your suggestion to the Nuclear Regulatory Commission (or whatever it’s equivalent would be in Germany) ?

So a million cubic feet of ice (assuming no volume changes from water to ice) at minus 65 F weighs roughly 62,380,000 pounds. Multiply times 54 BTU/lb to get the ice to 32 degrees F, another 144 BTU/lb to convert to water, 180 BTU/lb to raise it to 212 F, and 970 BTU /lb to raise it to steam. 1,186 BTU for every lb of ice at -65 degrees F to become steam, or 74 billion BTUs. (I know this is an approximation.)

So how much heat is being generated by the core that needs cooling?

Apparently, according to a comment to a Scientific American article on cooling a nuclear reactor, there is a nuclear power plant design incorporating ice.

@Buttonstc – Well, I was thinking about installing this in nuclear plants in coastal areas first (prone to complete power loss including backup). Yesterday, the German government decided to shut down seven of our most vulnerable nuclear power plants, while rethinking the overall strategy. Would the freezer idea help US nuclear plants on the East Coast? There can be major earthquakes too, and there are tsunamis in the Atlantic, although they are less frequent than in the Pacific. But what about

http://en.wikipedia.org/wiki/Cumbre_Vieja#Future_threat

for example. A 150-foot wave would damage nuclear power plants on the eastern seaboard. It might damage the super freezer too, so maybe this only makes sense for tsunamis up to 30 feet.

@zenvelo – As far as I know it depends on the age of the fuel rods. The control rods shut down uranium decay, but intermediate fission products will continue to create and accumulate heat. Thanks for the link. I need to study this article in detail.

@mattbrowne

Sounds like a great idea to me, although it would be expensive! You should pursue this. : )

I had been thinking along the lines that @zenvelo mentioned.

First off, the wind and weight loading on a 100 cubic foot structure alone would be enormous, and we’re talking about a heavy structure in and of itself. Then add the roughly 32,000 tons of water to be frozen and suspended… above a nuclear power plant. If there is a “significant” seismic event, then you’ve got the Sword of Damocles hanging over the plant in the form of a 32,000 ton chunk of ice, plus the weight of the structure and equipment itself.

I’ll take my chances with the as-is scenario.

@WasCy How about siting the reactor above a huge underground chamber full of ice. The melting ice would allow a controlled fall of the reactor to the bottom of the chamber which could then be safely sealed by pouring in concrete.

I don’t want to be the one to say “no possible way”, but… you’re adding a tremendous burden to construction costs just to build the thing. Excavating the hole (not “100 cubic feet” as I said above, but 100×100 x 100 = 1,000,000 cubic feet), when the plant is already near the local water table, is an enormous undertaking – and then there needs to be a place to put all that fill.

I think we’re going to learn what went wrong in Japan to prevent adequate stoppage of the reactor, exposure of the fuel rods to air (and hence hydrogen generation), no controlled venting of the containment vessel, and failure to locate and protect the diesel generators to provide necessary backup power, and resolve those problems. Those are discrete, solvable and interrelated problems and they can be fixed at a manageable cost.

This isn’t Chernobyl. The plant hasn’t collapsed and burned, but the systems that were supposed to be “fail safe” were allowed to fail or were inadequately designed and built. We really don’t need extraordinary (and extraordinarily expensive) fixes or a complete shutdown of the industry.

In addition, I haven’t calculated the power loss to keep a million cubic feet of ice cooled, but that’s a huge and permanent parasitic load on the plant, and what do you do when that fails? You have to plan on failure, and I can’t even imagine how to plan for the failure of a one million cubic foot freezer located 100 feet under a power plant. Yikes. I’ll take my chances swimming in the tsunami.

@WasCy – I see your point. What about a somewhat smaller cube? Could it still work not depending on the availability of power?

In the pressurized water reactors that I’m familiar with, the first fail-safe device is the control rods set into the reactor head. Those are held out of the reactor by solenoids, which consume relatively small amounts of electricity. In the event of a need to scram the reactor (to shut it down instantly), then the power to the solenoids is cut, and the boron control rods drop by gravity into the reactor to shut down the fission process. (This would happen automatically in case of a total system failure: loss of primary and backup power would cause the same scenario in a sort of dead-man trigger.)

The next fail safe is the Safety Injection Tanks, which is an arrangement of large tanks of water (possibly borated water, but I’m not sure) suspended inside the containment vessel and above the reactor pool. Though I’m not familiar with the piping and valving arrangement, my presumption is that these are valved so that in the event of a total system failure the valves would “fail open”. In other words, when control of the system is lost, the operators are dead or missing and the power is off (or other triggers occur), then the valves fail to remain closed (“fail open” is the term we use) and flood the containment with water to cool and cover everything that could be critical to the reaction process. Again, it’s a gravity-driven process that doesn’t depend on having power to do anything.

The reactor pool is set near the bottom of the containment vessel, and the reactor itself sits low in the flooded pool. If the primary level of containment has been breached, the 7” thick reactor vessel itself or the equally massive coolant piping from the steam generators or the steam generator “primary side” itself (a LOCA – Loss of Coolant Accident), and if the stainless steel lined concrete walled pool of water that it normally sits in has failed somehow, then the Safety Injection Tanks will flood the entire bottom of the containment vessel to cool everything and keep the fuel rods covered with boron and water. That’s key. The boron stops the fission process, and the water cools.

I don’t know yet what kind of screwup exposed the fuel rods to air, but that’s what lets the fissioning proceed, uncooled and potentially uncontrolled. It’s still not “a bomb”, but it’s not doing anything good.

That’s the reason that I don’t think that ice will be a major assist. The main problem seems to have been a failure to keep the rods covered with water. Everything after that is secondary. (On the other hand, spent fuel has been kept in “dry casks” in the US for a number of years without incident. I’m not familiar with how that process works; it’s not my area of expertise. I’ve seen that it does work, however, and left it at that.)

So in the cases we’re seeing now the earthquake and tsunami did not break containment, but something has happened to keep the entire process from working. Maybe – I’m just speculating here – the reactor was damaged and a LOCA did occur, but someone prevented the SIT flooding (assuming the boiling water reactor has SITs – I just don’t know). I can understand, maybe, why someone might try to be a hero and save the plant without doing that, because when you flood the containment with the SITs you’re going to have a major cleanup and economic loss in any case. SIT flooding means that you’ll irreparably damage a lot of other equipment in the containment in the attempt to save the entire plant.

My first guess here is that there’s going to have to be some kind of system that takes away a “decision” about whether or not to flood the containment. No one wants to make a decision to potentially lose a two billion dollar plant, so there has to be a way to make it a non-decision event, and one which cannot even be overridden by operators. But I’m just guessing here.