NRC Description of a "Loss of Pool Coolant" Event
- March 18, 2011
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I re-read the “Spent Fuel Pool” chapter in the National Research Council 2006 study “Safety and Security of Commercial Spent Nuclear Fuel Storage: Public Report” published by the National Academies Press. It is amazing how different it was to read this now as opposed to when I read it a few months ago.
Getting right to what the NRC says is a possible consequence of what it took at the time to be an extremely unlikely event:
“A paper by Alvarez et al. (2003a; see also Thompson, 2003) took the analyses in NUREG-1738 to their logical ends… Namely, what would happen if there were a loss-of-pool-coolant event that drained the spent fuel pool?”
This panel was commissioned to assess what terrorists could do to a spent fuel pool at a nuke plant. The concern was, spent fuel pools were not designed to withstand air attack. They aren’t in containments with roofs. Terrorists are another subject. The report went into more relevant detail as it assessed the worst that could happen if things go the wrong way now at Fukushima.
“Alvarez and his co-authors concluded that such an event would lead to the rapid heat-up of spent fuel in a dense-packed pool to temperatures at which the zirconium alloy cladding would catch fire and release many of the fuel’s fission products, particularly cesium-137. They suggested that the fire could spread to the older spent fuel, resulting in long-term contamination consequences that were worse than those from the Chernobyl accident.
Citing two reports by Brookhaven National Laboratory (BNL, 1987, 1997), they estimated that between 10 and 100 percent of the cesium-137 could be mobilized in the plume from the burning spent fuel pool, which could cause tens of thousands of excess cancer deaths, loss of tens of thousands of square kilometers of land, and economic losses in the hundreds of billions of dollars. ”
Here’s proof they needed to learn something about a tsunami:
“The report concludes that the greatest risk is from a beyond-design-basis seismic event.”
So they designed the hell out of Fukushima and it did stand up to a 7 times more powerful seismic event than the design spec called for. Then the beyond-design-basis tsunami showed up.
This may explain why attention was not focused on the threat from the pools from the beginning. The plan seemed to be to make sure the reactors were under control. The voices saying a Chernobyl type radiation release is not conceivable from a reactor core in a containment might not have been correct, but if they are, the plan should have been primarily to make sure the pools had no possibility of getting to this and secondarily to keep the reactors from melting down. Maybe that was the plan and things just evolved until things got this far. Time will tell.
The literature I consulted and the senior people I contacted were calm in the face of the widespread fear of a reactor core meltdown escaping containment. I felt reassured. But this steaming pool thing after tsunami inundation of the site is a new thing for me to think about.
No wonder there is open talk of suicide squads to head this off at all costs. But this panel assessed and concluded:
“there would likely be sufficient time to bring in auxiliary water supplies to keep the water level in the pool at safe levels until the cooling system could be repaired.”
Well let’s hope so. Barry’s site has updates that are encouraging.
I like to stare right at the worst possibility, and I didn’t bring this worst possibility into my mind until I re-read this report tonight.
“…this conclusion presumes, of course, that technical means, trained workers, and a sufficient water supply were available to implement such measures. The Nuclear Regulatory Commission requires that alternative sources of water be identified and available as an element of each plant’s operating license.”
“Large scale offsite releases of the radioactive constituents would not occur, however, unless they were mobilized by a zirconium cladding fire that melted the fuel pellets and released some of their radionuclide inventory. Such fires would create thermal plumes that could potentially transport radioactive aerosols hundreds of miles downwind under appropriate atmospheric conditions.”
Some of this report is classified. It was classified because it was primarily done to assess the possibility of terrorists causing this problem and they didn’t see the need to tell the terrorists everything they knew.
“The committee provides a discussion of the Alvarez et al. (2003a) analysis in its classified report. The committee judges that some of their release estimates should not be dismissed.”
Some; so that’s a few tens of thousands of square kilometers less land that is lost, etc?
Greater experience than I possess is necessary to interpret something like this, full access to all classified material, and a lot of thought. No wonder about the open dispute about evacuation distance between Japan and the US.
And here’s something many may remember, if this situation turns for the worse. There are a lot of people in the nuclear industry who haven’t had this possibility top of mind. :
“The Nuclear Regulatory Commission considered such an accident to be so unlikely that no specific action was warranted, despite changes in reactor operations that have resulted in increased fuel burn-ups and fuel storage operations that have resulted in more densely packed spent fuel pools”