Every nuclear reactor, large or small, runs on neutrons. The core of the reactor is swarming with these subatomic projectiles. Each time a neutron splits a uranium atom, energy is released and radioactive waste is created.
Indeed, the broken fragments of uranium atoms are fiercely radioactive materials called
“fission products”, and they accumulate in the fuel. Used nuclear fuel is millions of times
more radioactive than unused fuel because of the fission products. This “high-level radioactive waste” must be isolated from the environment for many millennia.
But some neutrons penetrate into the structural materials of the reactor, making them
radioactive too. When a stray neutron is absorbed by a non-radioactive atom, that atom is
often “activated” –it becomes radioactive.
Neutrons can turn ordinary non-radioactive hydrogen into radioactive tritium.
Non-radioactive cobalt-59 is transformed into highly radioactive cobalt-60. Dozens of
different kinds of “activated” materials are created, some of them extremely long-lived.
A recent publication from the US National Academy of Sciences found that smaller reactors have even more decommissioning radioactivity than larger nuclear plants. There is more neutron leakage from a smaller core, and the structural materials are closer to the used fuel where neutrons come from.
When a nuclear plant is dismantled, much of the rubble is too radioactive to be reused for other purposes. Such radioactive “decommissioning waste” must be kept out of the food chain and the water for tens of thousands of years.
Current plans are to bury the radioactive remains of two small nuclear reactors right
beside the rivers where they were originally constructed. This approach, called “in-situ”
decommissioning, is condemned as unacceptable by the International Atomic Energy Agency. Canada has chosen to ignore the Agency’s wise advice.
If the same approach is used for decommissioning small modular reactors, then every community that builds such a reactor will become the site of a permanent radioactive waste dump. To be successful, hundreds or thousands of these reactors would have to be deployed across Canada. The country could then become peppered with underground dumps of radioactive poisons that will be leaking and dangerous for many thousands of years.