Errors in the Estimated Neutron Source and Gamma Source Strengths for Reactivity Measurement and the Influence on the Measured Reactivity

Abstract

A new method has been proposed to estimate both neutron source and gamma source strengths to be taken into account for reactivity measurement using a digital reactivity meter. The method is based on a transient analysis with addition of known reactivity, p. In the analysis reactivity (p_m) is calculated using the neutron detector signal (N) including both the unknown strengths of neutron source (S) and gamma source (γ). It is used to calculate the value (p_m-p)N/l, which is equal to S-7gamma;p/l, a constant, where l is the neutron life time. With two values of known reactivity, both S and γ can be estimated in a short time.

The key parameter of the method is the known reactivity. When the values of the known reactivity have some errors, the estimated S and γ have errors, respectively. The errors influence the measured reactivity which is corrected by the estimated S and γ From this point of view we studied on the estimation errors of S and γ due to the given reactivity error. And the afterwards reactivity measurement error caused by the estimation errors is also discussed. It is shown that the measured reactivity error caused by the erroneous correction can be quite larger than the error in the correction when the neutron flux level becomes low.

KEYWORDS:

• neutron sources
• gamma sources
• inverse kinetic equation
• reactivity meters
• reactor kinetics
• measuring methods
• evaluations
• errors
• reactivity