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Building up on the former activities accomplished in the previous FPs, namely MUSE in FP5 and EUROTRANS in FP6, it is proposed in the FREYA project to extend the investigations of the subcritical configurations for validation of the methodology for on-line reactivity monitoring of ADS systems.

One of the main MUSE conclusions was that the most appropriate on-line subcritical reactivity monitoring technique would be the current to flux method, but it was not applied in the MUSE project since the GENEPI accelerator could only work in pulsed mode and not in continuous mode. In the MUSE conclusions, it was also mentioned that this method needs checking of the source importance and detector efficiency during operation on a regular base (thus verifying the proportionality constant) by independent measurement techniques such as PNS fitting techniques and/or the ADS source jerk. Also the need of calibration of the above mentioned techniques via additional independent and robust measurement techniques as PNS Area Method was concluded.

In the part of the FREYA project that deals with the ADS tasks we refer to the investigations of these MUSE conclusions. The MUSE conclusions also explicitly mentioned that the experiments performed with the central lead buffer region within the sodium core were not sufficient to allow a validation of the measurement techniques in representative experimental conditions for a heavy liquid metal based ADS such as MYRRHA.

The MUSE conclusions were used as the starting basis for the EUROTRANS FP6 project GUINEVERE, where the GENEPI accelerator is operated in continuous and pulsed mode and were a full lead core was designed and constructed. However, in the EUROTRANS FP6 proposal only the first part of the experimental programme for the validation of the methodology for on-line reactivity monitoring was included: one critical and one subcritical core (Keff = 0.97) configuration. The remaining and largest part of the experimental programme is included in the FREYA project.