There was a “near miss” at the San Onofre nuclear power plant on August 3, 2018. The lives and economic well-being of 8.4 million people within a 50-mile radius of the plant have been put at risk. As workers were lowering a 49-ton thin-walled, 17-foot tall canister packed with high-burnup spent nuclear fuel, the canister got caught on the lip of a guiding ring, “hanging by about a quarter inch,” an OSHA inspector and whistleblower, David Fritch, told a stunned crowd at the end of a community meeting on August 9th. “It’s a bad day. That happened, and you haven’t heard about it, and that’s not right. What we have is a canister that could have fallen 18 feet.”
What would have happened if it had fallen? My colleagues at UCSD and the Samuel Lawrence Foundation have been examining the basic physics of that question. By examining the dropping of the canister in free fall, we can estimate the upper energy involved in the initial impact. For example, the falling canister could hit the concrete floor of the nuclear waste facility with the explosive energy larger than that of 2 large sticks of dynamite. The resultant damage to the canister could cause a large radiation release.
The NRC has previously done an analysis of a similar dropped nuclear waste canister with slightly thinner walls.1 This computer simulation included a 19-foot drop of the canister from the transfer cask onto a storage overpack pedestal. The canister failure rate was 28%. Similar calculations need to be performed for San Onofre to determine if the currently used system has such a catastrophically high probability of canister failure to levels that are considered acceptable in such a high population area.
The damage to the concrete and metal structure at the bottom of the hole could ruin the canister’s cooling system. The damage to the concrete would be like that of a fully loaded 18-wheeler truck with a gross weight of 80,000 pounds crashing into reinforced concrete at 23 miles per hour.
These nuclear canisters contain 37 spent fuel assemblies which generate an enormous amount of heat. They are cooled by a simple airduct system, whose pathway could be blocked by the damage caused by the canister’s fall. If this happens, large quantities of water would have to pour into the hole to cool the reaction and prevent or control a meltdown. Similarly, as at Japan’s Fukushima nuclear power facility, the enveloping water would instantly become radioactive steam and require the evacuation of millions of people. Since both the canister and the surrounding structure could be badly damaged, there may be no available way to pull the damaged canister from the hole.
The analysis that we have done alerts the Nuclear Regulatory Commission (NRC) and others that a more substantial analysis needs to be done of the damage caused by a falling 49-ton nuclear storage canister. Continuation of the loading of the fuel is clearly a very dangerous threat to the lives and livelihood of over 8.4 million people. Software and computer resources are available by which estimates can be made of the impacts of the drop on both the reinforced concrete, and the deformation of the walls on the canister.
Our preliminary calculations have already revealed that the combination of the weight and velocity of the canister exceeds the Independent Spent Fuel Storage Installation (ISFSI), “design criteria for tornado missiles,” by a factor of 4. It shall be important to also perform drop tests of the canisters with non-radioactive loads to experimentally determine what will happen to actual canisters.
Dr. Tom English is a former advisor on high-level nuclear waste disposal to President Carter’s Office of Science and Technology Policy, NASA, the Ministry of Industry of the Government of Sweden, and the California Energy Resources Conservation and Development Commission.
1 Pg.4-24 Table 12, NUREG-1864 – A Pilot Probabilistic Risk Assessment of a Dry Cask Storage System at a Nuclear Power Plant March 2007, A. Malliakos, NRC Project Manager.