[1F01-04] Subcriticality Evaluation and Monitoring 1

[1F04] Asymptotic behavior of power in subcritical state based on one-point kinetics equation

*Yuichi Yamane¹ (1. Japan Atomic Energy Agency)

Keywords:subcritical, reactivity measurement, one-point kinetics, prompt neutron lifetime, effective delayed neutron fraction

In the condition such as erroneous transport of nuclear fuel solution in fuel reprocessing plant, criticality approach in reactor and critical assembly, the retrieval work of fuel debris in FUKUSHIMA DAI-ICHI, and so on, in which an amount of reactivity is inserted into nuclear fuel in a subcritical state, an equation is derived which relates the total reactivity to the asymptotic behavior of the power based on one-point kinetics equation.

Existing methods of reactivity measurement needs prompt neutron lifetime, the calculation of which requires the information of the composition and structure of the nuclear fuel. But the new equation doesn’t include prompt neutron lifetime. Therefore, it is clearly shown the possibility of reactivity measurement only with neutron counts without the information of inside the nuclear fuel.

The power profile calculated by using the new equation shows good agreement with that by using one-point kinetics code.