Status of fission fragment observables measured with the LOHENGRIN spectrometer

S Julien-Laferrière,T Materna,M Ramdhane,G Kessedjian,O Méplan,U Köster,O Litaize,O Serot,J Nicholson,C Sage,A Blanc,A Letourneau,L Thombansen,D Bernard,M Rapala,P Mutti,A Chebboubi,H Faust

doi:10.1051/epjconf/201921104004

Abstract

Nuclear fission yields are key parameters to evaluate reactor physics observables, such as fuel inventory, decay heat, spent fuel radiotoxicity, criticality but also for understanding the fission process. Despite a significant effort allocated to measure fission yields during the last decades, the recent evaluated libraries still need improvements in particular in the description of the uncertainties with the associated correlations. Additional kinds of measurements provide complementary information in order to test the models used in the nuclear data evaluation. Moreover, some discrepancies between these libraries must be explained. A common effort by the CEA, the LPSC and the ILL aims at tackling these issues by providing precise measurement of isotopic and isobaric fission yields with the related variance-covariance matrices. Nevertheless, the experimental program represents itself a large range of observables requested by the evaluations: isotopic yields, nuclear charge polarization, odd-even effect, isomeric ratio and their dependency with fission fragment kinetic energy as a probe of the nuclear de-excitation path in the (E*, Jπ) representation. Measurements for thermal neutron induced fission of 241Pu have been carried out at the Institut Laue Langevin using the LOHENGRIN mass spectrometer. Experimental program, observables reachable, results and comparison to model calculations are shown.

Highlights

The collaboration is involved in an experimental program using thermal neutrons to study the fission process and to answer the specific requests concerning the fission yields for the current and innovative fuel cycle studies
The program on fission yields with the LOHENGRIN spectrometer at ILL has been initiated for several years [1,2] and we developed different methodologies to obtain absolute fission yields with the description of the Probability Density Function (PDF) and the covariance matrices associated to the measurements [3]
Previous studies made by the collaboration show that under specific conditions, isomeric ratios are dependent on fission fragment kinetic energy [15]

Summary

Introduction

The collaboration is involved in an experimental program using thermal neutrons to study the fission process and to answer the specific requests concerning the fission yields for the current and innovative fuel cycle studies. The program on fission yields with the LOHENGRIN spectrometer at ILL has been initiated for several years [1,2] and we developed different methodologies to obtain absolute fission yields with the description of the Probability Density Function (PDF) and the covariance matrices associated to the measurements [3]. This information on measurements is required in order to consider statistical tests as the cornerstone of the evaluation program [4,5]

Methods

Results

Conclusion