A sensitivity analysis for the new generation of fast reactors [Salvatores (2008)] has shown the importance of improved cross section data for several actinides. Among them, the 240,242Pu(n,f) cross sections require an accuracy improvement to 1-3% and 3-5%, respectively, from the current level of 6% and 20%. At the Van de Graaff facility of the Institute for Reference Materials and Measurements (JRC-IRMM) the fission cross section of the two isotopes was measured relative to two secondary standard reactions, 237Np(n,f) and 238U(n,f), using a twin Frisch-grid ionization chamber. The secondary standard reactions were benchmarked through measurements against the primary standard reaction 235U(n,f) in the same geometry. Sample masses were determined by means of low-geometry alpha counting or/and a 2π Frisch-grid ionization chamber, with an uncertainty lower than 2%. The neutron flux and the impact of scattering from material between source and target was examined, the largest effect having been found in cross section ratio measurements between a fissile and a fertile isotope. Our 240,242Pu(n,f) cross sections are in agreement with previous experimental results and slightly lower than present evaluations. In case of the 242Pu(n,f) reaction no evidence for a resonance at En=1.1 MeV was found.

SALVADOR CASTINEIRA Paula;  BRYS Tomasz;  EYKENS Roger;  HAMBSCH Franz-Josef;  GÖÖK Alf;  OBERSTEDT Stephan;  PRETEL C.;  SIBBENS Goedele;  VANLEEUW David;  VIDALI Marzio; 

2017-01-11

ELSEVIER BV

JRC105084

1875-3892,   

http://www.sciencedirect.com/science/article/pii/S1875389215001406,    https://publications.jrc.ec.europa.eu/repository/handle/JRC105084,   

10.1016/j.phpro.2015.04.024,