Reactivity measurements at guinevere facility using the integral kp method

In the framework of the GUINEVERE (EUROTRANS-IP FP6) and FREYA (FP7) pro- jects, a two-level procedure is developed to measure the time variations of an ADS reac- tivity ?(t). First, the time variations of the reactor power and neutron source intensity are monitored online, allowing to extract the fast fluctuations of ?(t) around a reference value. Then, absolute measurements of ? are periodically performed to readjust the relative measurements. These calibration measurements require the analysis of the decay of the neutron population triggered by programmed beam interruptions. In this paper, we de- scribe an innovative method developed to measure the prompt multiplication factor, kp, of a subcritical reactor (and therefore its absolute ?). Unlike conventional methods used for reactivity measurements, our approach only relies on the prompt decay of the neutron population, therefore enabling the use of shorter beam interruptions (< 50 ?s) than usual (∼ 1 ms). After a review of the method's mechanics, we apply it to measurements per- formed at the GUINEVERE facility, with the VENUS-F reactor, a zero power lead sub- critical fast reactor. During these measurements, the neutron source was operated in pulse mode. Our results, promising, are compared with reference reactivity values provided by a MSM analysis.