Are Passive Systems in Nuclear Power Really Safe?
I just read an interesting article in the latest issue of New Humanist about how many environmentalists are now going nuclear. I understand and appreciate the points being made, but one passage really surprised me, though I have heard this argument before:
Fully passive safety systems depend on natural, physical phenomena such as pressure differentials, convection, gravity or the natural response of materials to high temperatures to slow or shut down the reaction.
However, hybrid systems also exist. For instance, some systems use pressure relief valves to manage excess pressure levels. While these valves are supposed to function without human intervention, there is a possibility, however slight, that they can fail. Parallel redundant systems may be used, but the possibility of failure still exists.
Some examples of passive systems include:
If that’s not enough, nuclear energy creates other accident possibilities including the transportation and storage of nuclear wastes. Don’t forget the accident at France’s Tricastin facility last year, caused by liquid containing unenriched uranium spilling from an overflowing reservoir. I can also point to the small plutonium leak at an Austrian IAEA facility last August.
Sure, things may be getting safer, but inherent danger from nuclear power continues to exist.
Len Green, an engineer who helped build Sizewell B nuclear power station on the Suffolk coast, explained that modern plants are engineered to meet every possible contingency, including the kind of employee negligence that lead to the explosion at Chernobyl: “The designs have to be thoroughly assessed, then every stage of construction is assessed, and when they’re operating, they’re assessed.” According to Professor Robin Grimes, a materials physicist at Imperial College London and former researcher at the US Los Alamos National Laboratory, they’re not just safe, they’re foolproof: “The new designs of power stations use passive systems, which means that they automatically behave in such a way as to shut the reactor down. The operator doesn’t even have to take any action at all.”What bugs me is the statement that new reactors using passive systems are foolproof. First of all, there are different types of passive systems.
Fully passive safety systems depend on natural, physical phenomena such as pressure differentials, convection, gravity or the natural response of materials to high temperatures to slow or shut down the reaction.
However, hybrid systems also exist. For instance, some systems use pressure relief valves to manage excess pressure levels. While these valves are supposed to function without human intervention, there is a possibility, however slight, that they can fail. Parallel redundant systems may be used, but the possibility of failure still exists.
Some examples of passive systems include:
- Increasing the probability that neutrons are captured by U-238 atoms instead of U-235, which initiates fission
- Utilizing steam voids to moderate fewer neutrons and dropping power - this is currently used in Pressurized and Boiling Water Reactors
- Using pools of liquid metal for thermal expansion that allows more neutrons to escape the core - this is currently used in some Fast Breeder Reactors
If that’s not enough, nuclear energy creates other accident possibilities including the transportation and storage of nuclear wastes. Don’t forget the accident at France’s Tricastin facility last year, caused by liquid containing unenriched uranium spilling from an overflowing reservoir. I can also point to the small plutonium leak at an Austrian IAEA facility last August.
Sure, things may be getting safer, but inherent danger from nuclear power continues to exist.
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