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

TL;DR

This paper introduces a perturbation method to measure the effective delayed neutron fraction (ff) in a uranium reactor, utilizing reactivity measurements and MCNP simulations, and compares data reliability from different nuclear data libraries.

Contribution

The study develops a novel perturbation technique for ff measurement in a reactor and evaluates the reliability of delayed neutron data from various sources.

Findings

Average ff value is 0.00645 with 3.0% uncertainty.

Reactor reactivity perturbations measured for 13 samples.

Delayed neutron data from G.R. Keepin are more reliable.

Abstract

The perturbation method is proposed to obtain the effective delayed neutron fraction (\b{eta}eff) of a cylindrical highly enriched uranium reactor. Based on the reactivity measurements with and without a sample at a designable position using the positive periodic technique, the reactor reactivity perturbation {\Delta}\r{ho} of the sample in \b{eta}eff units is measured. The simulation of the perturbation experiments are performed by MCNP program. The PERT card is used to provide the difference dk of 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 \b{eta}eff =dk/{\Delta}\r{ho} is derived. In this paper, the reactivity perturbations of 13 metal samples at the designable position of the reactor are measured and calculated. The average \b{eta}eff value of the reactor is given as 0.00645, and the standard uncertainty is 3.0%. Additionally, the perturbation experiments for \b{eta}eff can be used to evaluate the reliabilities of the delayed neutron parameters. This work showed 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.