This is a link to a series of comments posted by Micheal Goad a retired nuclear accident management instructor in answer to some questions I had about the nature of a nuclear meltdown. I'm passing this on because his comments were similar to some comments made here to some of my recent diaries about Fukushima. I am not an expert on this subject. Though I still have questions, I feel it's important to demure to the experts, some of whom may have spoken here.
These are the relevant comments at the link above:
Very interesting post. For several years, I taught severe accident management classes for nuclear plant operators. It included discussion on corium, eutectic formation and core concrete interaction (CCI). I'm now retired, but, on occasion do contract work as an ops instructor.
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R Crosby Lyles Michael Goad • 5 days ago
This is an idea I had about stopping a meltdown. Nuclear Engineering is not my particular field though I have studied some Chemistry, Electrical Engineering and Thermodynamics. I'm not necessarily promoting the idea but I am curious about its feasibility. Any feedback is greatly appreciated.
Michael Goad R Crosby Lyles • 4 days ago
The "meltdown" is not a result of fission, but, rather, is due to the inability to remove heat produced by the decay products from an already shutdown reactor. The key is to remove the heat that is being produced. The simplest way to stop the melt process is to add borated water to the reactor vessel if the core is still in the vessel or to the building if the core has gone ex-vessel (vessel breached). The boron is to prevent any potential recriticality once the mass is covered by water. If borated water is not available, the melt process can be significantly slowed or even stopped by adding unborated water in quantities less than or equal to the amount that will be totally boiled off by the heat being generated.
R Crosby Lyles Michael Goad • 2 days ago
This is the second time I have heard that the generated heat is not do to fission but to the heat given off by the decay products. Is this a matter of semantics? If a "meltdown" occurs doesn't that imply "criticality?" What is a criticality but a runaway fissile chain reaction? Will not dispersal of a mass of decay products into a particle absorbent substrate cause this material to not generate as much heat? The heat generated is not a function of the concentration of radioactive matter?
Michael Goad R Crosby Lyles • a day ago −
Is this a matter of semantics? No.
If a "meltdown" occurs doesn't that imply "criticality?" No. A meltdown is a result of the failure to remove decay heat.
What is a criticality but a runaway fissile chain reaction? Criticality is the point during reactor operations where the nuclear chain reaction is exactly self-sustaining. Every fission causes an average of one more fission.
Will not dispersal of a mass of decay products into a particle
absorbent substrate cause this material to not generate as much heat? No -- the same amount of heat will be generated. It would just be spread out. The heat is generated by the nuclear decay of products that were produced during the period the fuel was critical and their daughter products.
The heat generated is not a function of the concentration of radioactive matter? No. The heat generated is a function of the original power history of the fuel prior to shutdown and how long it's been shutdown. "Quantitatively, at the moment of reactor shutdown, decay heat from these radioactive sources is still 6.5% of the previous core power, if the reactor has had a long and steady power history. About 1 hour after shutdown, the decay heat will be about 1.5% of the previous core power. After a day, the decay heat falls to 0.4%, and after a week it will be only 0.2%."
R Crosby Lyles Michael Goad • an hour ago
Thanks for taking the time for a point by point explanation. Seeing your qualifications, I'm sure you know what you are talking about. The discussion is a worthwhile endeavor because not many people understand what is going on(apparently myself included) at Fukushima in particular and there is a lot of misinformation out there.