B. Cochet

Continuous-Energy Sensitivity Coefficients in the MORET Code

Abstract A continuous-energy sensitivity coefficient calculation to nuclear data capability has been recently developed in Version 5.C.1 of the MORET Monte Carlo code developed at Institut de Radioprotection et de Sûreté nucléaire (IRSN). The method used for implementation is the differential operator method. In this method, the estimation of the fission source derivatives is replaced by an estimation of the adjoint flux. Both methodology and tallies are described in this paper. The preliminary verification is mainly performed using code-to-code comparisons with the SCALE6.1 and MCNP6.1 software packages. Configurations used for verification are the Organisation for Economic Co-operation and Development/Nuclear Energy Agency (OECD/NEA) Uncertainty Analyses for Criticality Safety Assessment (UACSA) Expert Group benchmarks, the Jezebel International Criticality Safety Benchmark Evaluation Project (ICSBEP) benchmark, and a configuration from the Matériaux en Interaction et Réflexion Toutes Epaisseurs (MIRTE) French proprietary experimental program. Results show good agreement among the different codes.

A Burnup-Dependent Isomeric Production Branching Ratio Treatment

Abstract To take the production of isomeric states into account during the irradiation of a material, a depletion code needs the proper isomeric branching ratio λs for every isomeric state s produced in a reaction. The composition of some nuclides such as, for example, 238Pu and some Cm isotopes is quite sensitive to the value of the isomeric branching ratio for the 241Am neutron capture reaction. Existing depletion codes use constant burnup-independent values for the isomeric branching ratio data, which were calculated in advance for a particular type of spectrum (e.g., pressurized water reactor, boiling water reactor, or fast reactor systems). In this paper, we propose a burnup-dependent treatment using evaluated nuclear data from ENDF files as a function of the irradiation history. This treatment has been implemented into the VESTA Monte Carlo depletion code using both the multigroup binning approach and Monte Carlo estimators. The validity and usefulness of this new treatment has been demonstrated using experimental data from the MALIBU program and has shown that it improves the prediction of 242mAm when using JEFF 3.1 data. It is also shown that more work is required on the measurement and evaluation of the cross-section data for the Am isotopes in general and the energy-dependent 241Am branching ratio in particular to improve the results of depletion calculations.