Which chemical is commonly used as a neutron absorber in a spent fuel pool to prevent recriticality?

Which chemical is commonly used as a neutron absorber in a spent fuel pool to prevent recriticality?

• A. Neon
• B. Argon
• C. Boron
• D. Helium

Answer: (C)

Keeping a spent fuel pool subcritical relies on absorbing enough neutrons so the chain reaction cannot sustain itself. Boron, especially its isotope boron-10, has a very high ability to capture thermal neutrons. When a neutron is absorbed by boron-10, it undergoes a reaction that removes that neutron from the pool’s neutron population, preventing additional fission events. Filling the pool water with boron (borated water) or using boron-containing materials provides this neutron poison and greatly reduces the chance of recriticality. The other gases—neon, argon, and helium—are noble gases with very low neutron absorption cross sections, so they don’t meaningfully reduce neutron availability or prevent a chain reaction. They may serve as inert atmospheres or cooling media, but they don’t help prevent recriticality like boron does.

Keeping a spent fuel pool subcritical relies on absorbing enough neutrons so the chain reaction cannot sustain itself. Boron, especially its isotope boron-10, has a very high ability to capture thermal neutrons. When a neutron is absorbed by boron-10, it undergoes a reaction that removes that neutron from the pool’s neutron population, preventing additional fission events. Filling the pool water with boron (borated water) or using boron-containing materials provides this neutron poison and greatly reduces the chance of recriticality.

The other gases—neon, argon, and helium—are noble gases with very low neutron absorption cross sections, so they don’t meaningfully reduce neutron availability or prevent a chain reaction. They may serve as inert atmospheres or cooling media, but they don’t help prevent recriticality like boron does.