Blind post-test analysis performed by RELAP5/MOD2 code of the LOBI-MOD2 small break test BL-44 high power counterpart to LOBI BL-34 experiment

The document deals with the description of results obtained by the Relap5 code in the ‘blind post-test’ (i.e. without any code-user modification of code-related input parameters) of the Counterpart Test (CT) BL-44 performed in the Pressurized Water Reactor (PWR) experimental simulator LOBI installed at the EURATOM JRC Research Center in Ispra, Italy. The Relap5 is the well-known computer code developed at Idaho National Laboratory in US: the code is in use at UNIPI since more than a decade. The LOBI loop is an Integral Test Facility (ITF) simulating with full height, full pressure, full linear power a German 4-loop KWU-Siemens PWR. The concerned test is the high power CT of the LOBI test BL-34 which was the CT of experiments performed in SPES, BETHSY and LSTF ITF. Because of the maximum power limitations of BETHSY and LSTF, the test BL-34 was performed starting from a ‘low power condition’ (about 20% nominal power): thus, the initial 10-50 seconds of the experiments were ‘highly’ distorted with respect to the test scenario expected in the reference Nuclear Power Plant (NPP), the prototype. Therefore a new test was performed (in the same way in SPES ITF, CT SP-SB-03 and SP-SB-04, low and high power test were performed) and called BL-44.. The present document discusses the comparison between code prediction and measured data in test BL-44.