Photoneutrons and the Control of a Pool Type Reactor

In a pool type reactor installation, the fission chambers or ionization chambers controlling the reactor detect two types of neutrons, e.g., thermalized fission neutrons and photoneutrons produced around the detector in a D(γ, η) H reaction. If the photoneutrons are produced by fission product gamma rays, there will be a superimposed neutron flux that may lead to unsafe operating conditions. This effect has been analytically and experimentally studied, and it is shown here that the unsafe conditions can be suppressed either by placing the detector closer to the reactor or by limiting the rate of change of reactor flux to a safe value.