Framatome has recently developed ARITA, a statistical Non-LOCA methodology based on the external coupling of the 3D core simulator ARTEMIS and the system thermal-hydraulics code S-RELAP5. As part of the qualification of the coupled approach used in ARITA, operating plant transients were analyzed. This paper considers one of these transients; a planned Loss of External Load transient performed on a 1300 MWe plant. This transient was initiated at End-of-Cycle conditions while in coastdown. The purpose of the transient was to measure plant responses to a Loss of External Load. An ARTEMIS/S-RELAP5 model was developed to simulate the transient and provide comparison data. Deviations between calculated and measured results are well behaved and show that ARTEMIS/S-RELAP5 provide a good representation of an operating reactor during transient conditions. The observed maximum deviation in the short-term corrected power is less than 1% rated thermal power, the maximum average coolant temperature deviation is less than 1 °C, and primary pressure difference during the initial peak is within 1 bar, while the peak near the end of the transient is within 2 bar. When steam generator level stabilizes, the final measured level is slightly over-predicted by about 3%. ARTEMIS trends well with the fixed incore detectors.

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