Measurements of effective delayed neutron fraction in a fast neutron reactor using the perturbation method

Abstract：

A perturbation method is proposed to obtain the effective delayed neutron fraction β _effof a cylindrical highly enriched uranium reactor. Based on reactivity measurements with and without a sample at a specified position using the positive period technique, the reactor reactivity perturbation Δ ρof the sample in β _effunits is measured. Simulations of the perturbation experiments are performed using the MCNP program. The PERT card is used to provide the difference d kof effective neutron multiplication factors with and without the sample inside the reactor. Based on the relationship between the effective multiplication factor and the reactivity, the equation β _eff=d k/Δ ρis derived. In this paper, the reactivity perturbations of 13 metal samples at the designable position of the reactor are measured and calculated. The average β _effvalue of the reactor is given as 0.00645, and the standard uncertainty is 3.0%. Additionally, the perturbation experiments for β _effcan be used to evaluate the reliabilities of the delayed neutron parameters. This work shows that the delayed neutron data of ²³⁵U and ²³⁸U from G.R. Keepin's publication are more reliable than those from ENDF-B6.0, ENDF-B7.0, JENDL3.3 and CENDL2.2.