The behavior of the effective delayed neutron and effective delayed photo neutron fractions in beryllium reflected cores is investigated. An MCNPX analysis of the dependence of the effective beta fractions on the fuel depletion is performed for different fuel types. An alternative method for estimation of the delayed neutron fraction during the reactor operating, avoiding double criticality simulation on prompt neutrons only (k_p), is compared to the standard MCNP approach (1-k_p/k_p_+_d). The methodology is based on MCNP tally calculations of fission integrals and actual delayed neutron fraction, β_m"k, for each fissile isotope m("2"3"5U, "2"3"9Pu, "2"4"1Pu) in a given reactor configuration and fuel type k. The methodology is verified on a generic infinite lattice and after that applied for the MCNP whole core model of the BR2 reactor at different depletion steps during the reactor operation.
|Title of host publication||Proceedings of the International Conference on Physics of Reactors |
|Subtitle of host publication||PHYSOR 2014|
|Publisher||JAEA - Japan Atomic Energy Agency|
|Number of pages||20|
|State||Published - 28 Sep 2014|