Reactivity Measurements at GUINEVERE Facility Using the Integral kp Method

Abstract

International audienceIn the framework of the GUINEVERE (EUROTRANS-IP FP6) and FREYA (FP7) projects, a two-level procedure is developed to measurethe time variations of an ADS reactivity ρ(t). First, the time variations of the reactor power and neutron source intensity are monitored online,allowing to extract the fast fluctuations of ρ(t) around a reference value. Then, absolute measurements of ρ are periodically performed toreadjust the relative measurements. These calibration measurements require the analysis of the decay of the neutron population triggeredby programmed beam interruptions. In this paper, we describe an innovative method developed to measure the prompt multiplicationfactor, kp, of a subcritical reactor (and therefore its absolute ρ). Unlike conventional methods used for reactivity measurements, ourapproach only relies on the prompt decay of the neutron population, therefore enabling the use of shorter beam interruptions (< 50 μs) thanusual (~ 1 ms). After a review of the method’s mechanics, we apply it to measurements performed at the GUINEVERE facility, with theVENUS-F reactor, a zero power lead subcritical fast reactor. During these measurements, the neutron source was operated in pulsemode. Our results, promising, are compared with reference reactivity values provided by a MSM analysis