Commenter Neutron Flux has also operated reactors and served as a consultant and trainer in the nuclear industry (and I’ve verified that). He’s offered to do a Q&A here. To prime the pump, here are a few questions I asked with his answers:
Q: The basic GE boiling water reactor design used at Fukushima is also used in some plants in the US. Is there something different about US plant design that makes them safer?
A: US plants all have a better containment building. They are designed for seismic events and remain functional after the Design Basis Accident (DBA). The worst DBA at the time of licensing for these plants at the time was the Loss of Cooling Accident (LOCA).
The operators at US plants are better trained and the Nuclear Regulator Commission is more intrusive than other countries. We have had operators and managers from Russian plants visit and this is what they tell us.
Q: Fukushima was an old plant, with the first unit commissioned in 1971. The US is re-licensing old plants (e.g., the plant near me, Ginna, was commissioned in ’70 and has a license to operate until 2029.) How can we be sure those plants are still safe?
A: The original license to operate the plant from the NRC was 40 years. As the plants got older the NRC instituted ap process to extend the license. The licensee had to show that it was testing certain aspects of the design and the components to manage the risk of the extension. For example with the extension there is more testing and monitoring required for the Reactor Vessel to monitor for neutron embrittlement. We do that by installing samples in the core and testing after certain periods of service.
Q: Some of the issues at Fukushima were related to spent fuel ponds losing cooling. My layman’s understanding is that if those ponds aren’t cooled, they evaporate and expose rods that will undergo various ugly changes that could release large amounts of radioactivity. Since Fukushima, has the US done anything to mitigate the danger of these ponds? Is there a realistic way to cut down the danger of these ponds?
A: This is a big issue for the industry. Several plants are actually suing the government to make good on their obligation to build a repository for spent fuel. The plant I work at now came on the line in 1985. Every fuel element that it has ever used is still in the spent fuel pool. To quantify that statement, typically a 1200 MWe plant has 192 fuel assemblies in the core. This core lasts 18 months. At that point the plant shuts down for a refueling outage, where 1/3 of the assemblies are replaced. If the plant has been operating 25 years, well you can see that there is a lot of spent fuel. Obviously,the longer the fuel has been in the spent fuel pool the safer it is from the meltdown perspective.
Older plants have moved to a dry cask storage system. In this case they take the oldest ones from the pool and store them in a rugged cask since they require very little cooling to remove decay heat. Just because the decay heat load is down, critics rightly point out there is still very dangerous radioisotopes that would be public health issue if they were to go airborne. I really can’t say much more about this because it would require a discussion of the physical security of plant and the NRC takes a dim view of that.
For me, this is the most important issue that must be solved. It is not even an issue for the industry to remain viable, it is a legacy issue that effects future generations.
Q: Fukushima lost all site power when the tsunami hit and destroyed generators in the basement. Since Fukushima, has the US industry come up with a plan to get generators to a site quickly if a site experienced this kind of a disaster? Given the generator needs of a plant, is this even feasible?
First question, yes. Here is what my old friend sent for what my particular site is doing in response to Fukushima:
“Building 2 buildings to house 2 each pumps, generators, hoses, cables, trucks, trailers, etc. to provide water to RCS, SGs, CST, ESW and power to NBs and NKs when we have a extended loss of all AC or loss of ultimate heat sink.”
(RCS is the Reactor Coolant System, SGs are Steam Generators, CST is the Condensate Storage Tank, ESW is the Essential Service Water System NB and NK are the safety related power systems. These are all the primary systems for establishing and maintaining core heat removal after a shutdown and during accident conditions)
“I addition to this modification during the last refueling outage we installed 3 additional diesel generators for the loss of all AC power scenario. All the US plants are taking similar steps to respond. The NRC and the Institute of Nuclear Power Operations (INPO) are both mandating these actions Since all plants are doing this, there is also commitments to send any plant that needs help any of this equipment that they need.”
Second question, yes. It takes about 7 MWe generation to run all the equipment we need to maintain safe shudown core cooling
Q: Looking at Fukushima as a whole, what do you think the most important lesson the US nuclear industry can learn from that disaster?
Look, who would have thought that you needed to design for design basis earthquake CONCURRENT with a 30 foot tsunami. I hope as an industry we get serious about grid stability and take a long look at scenarios where the grid is down for more that seven days. All plants in the US can self sustain for 7 days. There has been no effort that I am aware of to at least understand events and make contingencies for a sustained loss of the grid.
Neutron Flux has agreed to answer factual questions in the comments, so go ahead and ask yours. Speaking of, my follow-up would be: since the spent fuel ponds are a known risk, what’s keeping the industry from moving to cask storage faster?