Fukushima Daiichi Reactors: Exploring a Controlled Meltdown

[M. Bachmeier]

In the case of the Fukushima Daiichi reactors; would an explosion of a primary containment vessel dissipate some, most or all of the fuel?

My speculation is that it would be like a directional charge leaving much of the melted fuel intact (possibly held together in the base of the primary containment) allowing it to super heat, which would be a very bad thing.

I welcome any and all comments.

 

[mathman]

The reactor core would not be dissipated by the explosion. The main problem is loss of coolant and the resultant meltdown.

 

[M. Bachmeier]

The reactor core would not be dissipated by the explosion. The main problem is loss of coolant and the resultant meltdown.

If that's the case, then would it be possible for crews on site to dissipate the fuel before super heating? And what of the crews? Would they be able to perform such a miracle twice more?

I do not believe that an explosion in primary containment is the worst thing that may happen. I fear a super heated meltdown to the water table.

Again, any comments are welcome.

 

[Drakkith]

It depends on the cause of the explosion. If it another hydrogen explosion, it is unlikely to spread the fuel out anywhere because the gas will be on top of the reactor and force everything in the core down instead of out.

If the fuel experiences a nuclear excursion, (sort of like a mini nuke. Happened at chernobyl and was about 0.01 Kilotons) then the fuel will most likely be spread out everywhere if the explosion is powerful enough to breach the containment vessel.

 

[CAC1001]

It depends on the cause of the explosion. If it another hydrogen explosion, it is unlikely to spread the fuel out anywhere because the gas will be on top of the reactor and force everything in the core down instead of out.

If the fuel experiences a nuclear excursion, (sort of like a mini nuke. Happened at chernobyl and was about 0.01 Kilotons) then the fuel will most likely be spread out everywhere if the explosion is powerful enough to breach the containment vessel.

So a mini-nuclear explosion could occur you are saying...?

 

[Drakkith]

So a mini-nuclear explosion could occur you are saying...?

Yes, with much emphasis on the MINI. Nukes are designed to contain everything for as long as possible before the fuel is blown apart to build up the energy. Reactors are definitely not like this. A reactor would have a large release of energy and radiation that could be energetic enough to breach the containment vessel pretty severely, but it wouldn't come anywhere close to leveling a city. The most dangerous aspect of that would be the large release of radioactive materials, just like Chernobyl.

 

[Andrew Mason]

Yes, with much emphasis on the MINI. Nukes are designed to contain everything for as long as possible before the fuel is blown apart to build up the energy. Reactors are definitely not like this. A reactor would have a large release of energy and radiation that could be energetic enough to breach the containment vessel pretty severely, but it wouldn't come anywhere close to leveling a city. The most dangerous aspect of that would be the large release of radioactive materials, just like Chernobyl.

If the reactor is shut down, fission will stop (control rods fully inserted). The fuel will not spontaneously start to fission and create a mini-nuclear explosion if the reactor is shut down.

Chernobyl was caused because they did not shut the reactor down. They just slowed it down and do experiments with it while the reactor was operating. There was still fission going on. They removed the control rods completely to keep it going after the core became poisoned with neutron absorbing xenon. Then when the xenon concentration decreased, the power spiked and they could not get the control rods re-inserted. So the reactor went out of control and exploded due to build up of heat in the reactor core.

AM

 

[Drakkith]

Thats right Andrew. I don't think there much chance of an excursion happening in Japan, but was just bringing it up. I don't know what would happen if the fuel melts though.

 

[M. Bachmeier]

Thats right Andrew. I don't think there much chance of an excursion happening in Japan, but was just bringing it up. I don't know what would happen if the fuel melts though.

The reason I posed this question in the first place is because I suspected that some core reactants have melted. If reactants have melted another hydrogen explosion could occur, in primary containment, further damaging what's left of the cooling systems.

In either case use of sea water to maintain cooling must also fail at some point, because sea water contains impurities (such as calcium & salt) which will eventually cause pump and valve failure.

What remains is the question of removal of melted core reactants and diffusing that material into something like borax to transport in into some other containment.

Can melted core reactants be removed? Can they be transported into secondary containment? Will some form of excursion occur if melted remnants are exposed too air without coolant for a short time?

 

[QuantumPion]

Can melted core reactants be removed?

Yes, although it may take years to clean up. TMI-2 took 5 years to de-fuel and remove the core debris.

Can they be transported into secondary containment?

Yes, see above. TMI-2 core debris was transported to a DOE repository where other waste is stored.

Will some form of excursion occur if melted remnants are exposed too air without coolant for a short time?

No, one the core has cooled down there is no further danger as the isotopes responsible for the decay heat have decayed away.

 

[M. Bachmeier]

No, one the core has cooled down there is no further danger as the isotopes responsible for the decay heat have decayed away.

Yes, but I don't believe that there are any claims that these cores have been effectively cooled. In fact, it seems they've had repeated problems with temperature rises.

 

[Drakkith]

Yes, but I don't believe that there are any claims that these cores have been effectively cooled. In fact, it seems they've had repeated problems with temperature rises.

If they can keep the temperature under control for long enough the decay products will burn off and the fuel will no longer be producing heat. They just have to keep the temperature from reaching too high of a point while the products gradually decay.

 

[M. Bachmeier]

If they can keep the temperature under control for long enough the decay products will burn off and the fuel will no longer be producing heat. They just have to keep the temperature from reaching too high of a point while the products gradually decay.

They length of time it will take reactive products to decay is very critical because of the limited nature of the present cooling methods.

Even drinking water contains many compounds and is either harder or softer (more or less dissolved compounds like calcium carbonate etc.).

Unfiltered fresh water, let alone sea water, would contain more dissolved or suspended compounds. Calcium carbonate does not fully dissolve in water, but can be dissolved in nitric acid making calcium nitrate. Boric acid will not prevent precipitation of calcium carbonate in pumping and valve control systems. That's why I'm concerned.

Can nitric acid be added to the cooling water with the boric acid already being used to absorb neutrons? The nitric acid would help dissolve or suspend many hard compounds.

Any and all comments and or corrections to my perceived knowledge on this subject are welcome.

 

[promecheng]

They length of time it will take reactive products to decay is very critical because of the limited nature of the present cooling methods.

Even drinking water contains many compounds and is either harder or softer (more or less dissolved compounds like calcium carbonate etc.).

Unfiltered fresh water, let alone sea water, would contain more dissolved or suspended compounds. Calcium carbonate does not fully dissolve in water, but can be dissolved in nitric acid making calcium nitrate. Boric acid will not prevent precipitation of calcium carbonate in pumping and valve control systems. That's why I'm concerned.

Can nitric acid be added to the cooling water with the boric acid already being used to absorb neutrons? The nitric acid would help dissolve or suspend many hard compounds.

Any and all comments and or corrections to my perceived knowledge on this subject are welcome.

Mineral deposits in water systems take years to accumulate. The systems pumping seawater are stop-gap measures and are not intended for long term operation. I think this is the least of their worries. Also, Nitric acid is nasty stuff and would do much more harm to the pumps, valves and piping than seawater.

 

[Reno Deano]

Reactor safe guards: fuel matrix, fuel rod cladding, reactor vessel, primary reactor vessel containment, secondary containment, safety systems. Excursion are far more likely in high to highly enriched fuel (>30%) rather than <5% commerical reactor fuel. Once the fuel starts to degrade and melt it looses its favorable geometry. Normally this is also accompanied by loss of neutron moderation and the resultant mixture heads for subcritical conditions. Hopefully cooling fluids are added to carry away the decay heat of the mixture.

 

[M. Bachmeier]

Mineral deposits in water systems take years to accumulate. The systems pumping seawater are stop-gap measures and are not intended for long term operation. I think this is the least of their worries. Also, Nitric acid is nasty stuff and would do much more harm to the pumps, valves and piping than seawater.

Nitric acid is used in hydroponic irrigation systems to prevent problems, primarily calcium carbonate buildup. The amount is small and has little impact on pumps and valves.

Salt will buildup faster. Sea water can contain large amounts of suspended material like calcium carbonate that would not need to precipitate out, but only collect and bind.

Adding anything unnecessary is not what I suggest, but how long will they be depending on sea water?

I've had pumping and valve problems (hydroponic irrigation) in the space of a day from suspended (not dissolved) calcium carbonate impurities. Mine is a very low volume system. In a large high volume system buildup could occur quickly.

Sea water would be more comparable to a hydroponic nutrient solution than clean filtered water. It would have a significant E.C. level due to those impurities. The P.H. is also significant in determining the rate of deposition and precipitation of hard compounds.

P. S.

If I'm not mistaken the emergency cooling system injects water through jets, which is functionally comparable to an irrigation emitter, and could plug from impurities much quicker than you might suspect. It would not require any large particulate substance, just the buildup of suspended material.

 

[minerva]

It depends on the cause of the explosion. If it another hydrogen explosion, it is unlikely to spread the fuel out anywhere because the gas will be on top of the reactor and force everything in the core down instead of out.

If the fuel experiences a nuclear excursion, (sort of like a mini nuke. Happened at chernobyl and was about 0.01 Kilotons) then the fuel will most likely be spread out everywhere if the explosion is powerful enough to breach the containment vessel.

But that massive power transient and explosion that happened at Chernobyl is completely irrelevant to Fukushima or any other LWR power plant.

It was caused by the intrinsic physics characteristics of the graphite-moderated RBMK, and the fact that it was being operated by people who knew nothing about nuclear engineering, did not have any understanding of things like xenon-135 poisoning, and let it be put into that dangerous configuration.

 

[M. Bachmeier]

http://search.japantimes.co.jp/cgi-bin/nn20110320x1.html

Opinions about what type of radiation would be seen from venting the number 3 core directly (not through the suppression pool).

What are the dangers of (not or delaying such venting)?

 

[M. Bachmeier]

More from Michio Kaku on the subject. More specific details leading to his assumptions and conclusions.

http://bigsciencenews.blogspot.com/2011/03/cooling-down-nightmare-tepco-daiichi.html

 

[Drakkith]

But that massive power transient and explosion that happened at Chernobyl is completely irrelevant to Fukushima or any other LWR power plant.

It was caused by the intrinsic physics characteristics of the graphite-moderated RBMK, and the fact that it was being operated by people who knew nothing about nuclear engineering, did not have any understanding of things like xenon-135 poisoning, and let it be put into that dangerous configuration.

Yep. You are correct.