Calculations of Neutron Multiplicities and Spectra for Different Actinides

The neutron balance in present day reactor systems is a crucial quantity, which needs continuous attention. Refinements in modelling of the prompt neutron multiplicities and spectra are the key to improved predictions of critically benchmark exercises. 235U and 252Cf are key isotopes, since the latter is an important prompt neutron spectrum standard and the former is the main isotope of today's fuel cycle. Hence, improved models to describe prompt neutron characteristics for the above mentioned isotopes are highly appreciated. Based on experimental fission yield and total kinetic energy data, new calculations of the prompt neutron multiplicity and spectra for 235U(n,f) in the incident neutron energy range up to 50 MeV and for 252Cf(SF) have been performed. For 235U(n,f) a new fission cross section calculation was necessary up to 50 MeV prior to being able to deduce the partial fission cross sections above the fist fission chance and the corresponding cross-section ratios, important quantities entering the multiplicity and spectrum modelling. For 252Cf(SF), the multi-modality of the fission process was taken into account. Additionally, a more realistic fission fragment residual temperature distribution as well as an anisotropy of the prompt neutron emission has been introduced leading to improved agreement with experimental results.

HAMBSCH Franz-Josef; 

2006-10-31

Joint Institute for Nuclear Research, 2006

JRC34314