When is neutron radiation mainly a concern?

• A. When the Reactor Is Powered On
• B. During Maintenance
• C. When the Reactor Is Shut Down
• D. When the System Is Sealed

Answer: (A)

Neutron radiation is driven by the rate of fission in the reactor core. When the reactor is powered and producing energy, fission events occur at a high rate, generating a large neutron flux that can penetrate shielding and expose personnel. That makes neutron radiation the main concern during operation, so safety controls, barriers, and monitoring are focused on the time when the reactor is critical.

During maintenance or when the reactor is shut down, the fission rate drops essentially to zero, so the neutron flux falls dramatically. The remaining radiation is mainly from activated materials and other non-neutron sources, not from ongoing neutron production. Sealing a system doesn’t create neutrons either; without fission, neutron production is minimal. So the period with the highest neutron radiation risk is when the reactor is powered on.