The neutron lifetime is an important parameter of the reactor kinetics. When the inserted reactivity is more than the effective fraction of delayed neutrons, the reactor kinetics becomes very rapid. The fast reactor kinetics can be slowed down by increasing the neutron lifetime. The possibility of using lead isotope 208Pb as a neutron reflector with specific properties in the lead-cooled fast reactor is considered. A point kinetics model has been chosen to assess the emerging effects. The model takes into account the effects produced by neutrons returning from 208Pb-reflector to the reactor core.
Such specific properties of 208Pb as large atomic weight, weak neutron absorption allow neutrons from the reactor core to penetrate deeply into 208Pb-reflector, slow down there and have a noticeable probability to return to the reactor core and affect the chain fission reaction. The neutrons coming back from 208Pb-reflector have a long “dead-time” which represents the sum of times when neutrons leave the reactor core entering 208Pb-reflector and then diffuse back into the reactor core. During the “dead-time” these neutrons can’t affect the chain fission reaction. The neutrons returning from deep layers of 208Pb-reflector are close to the delayed neutrons in the terms of time delay. Moreover, the number of the neutrons coming back from 208Pb-reflector considerably exceeds the number of the delayed neutrons.
As a result, the neutron lifetime formed by the prompt neutron lifetime and the “dead-time” of the neutrons from 208Pb-reflector can be substantially increased. This can lead to the longer reactor period, which mitigates the effects of prompt super-criticality. To conclude, the use of lead isotope 208Pb as a neutron reflector can improve significantly safety of the fast reactor operation.
|Country/Int. organization||Russian Federation|
|Speaker's email email@example.com|
|Affiliation/Organization||National Research Nuclear University MEPhI|