Determination of Neutron Multiplication, (II):Experiments and Analysis

概要

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The purpose of the present work is to confirm experimentally that the prompt neutron decay constant of fundamental mode, α000, satisfies the following two requirements from the concept proposed in Part (I): To be uniquely measurable free from space dependence and detector specification, and to be calculable from the Boltzmann equation. To prove this, a series of pulsed experiments was made at various subcritical states in a reflected graphite-moderated 20% enriched fuel system (SHE). The experimental results confirmed that α000 was obtained as a common and unique value at any point of both core and reflector, determined by separation of spatial harmonics, using bare and Cd-covered BF3 counters. The state of SHE was changed by attenuating the core, with or without central control rod, and by adding distributed poison to the core and/or to the reflector. Direct comparison was made between the experimental results and the calculated values from multigroup treatment using P1 and S4 approximation. Calculated values of α000 for subcritical states with attenuated core, with or without control rod, showed fairly good agreement with the measured values. In addition, the time-dependent spectral changes of the subcritical systems were also investigated in the experiments.
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