OECD PKL3 Project - Final Report on the ROCOM Tests

In the frame of the OECD PKL 3 Project three groups of experiments have been conducted at the HZDR coolant mixing test facility ROCOM.
The first series concerned the influence of the coolant mixing in the reactor pressure vessel on the Natural Circulation Interruption (NCI). For that purpose boundary conditions (mass flow rates and temperatures in the individual loops at the inlet of the RPV) have been derived for subsequent tests in the ROCOM test facility on coolant mixing inside the pressure vessel. The ROCOM tests were designed to address the fluid/fluid mixing of hot and cold water in the RPV downcomer and in the lower plenum and the temperature distribution at the core inlet. A series of three quasi-stationary experiments was carried out. Boundary conditions were taken from the PKLIII test H4.1 (Schoen, 2014).
The second test series was dedicated to the investigation of the mixing of unborated coolant which is injected into the reactor pressure vessel in the late phase of an accident. It is assumed that the standard sources of the emergency core cooling water are not available. Unborated water is injected to ensure the core cooling. Due to the injection of unborated water, an occurrence of re-criticality in the shut-down reactor is threatening. This possible re-criticality depends in a dominant manner on the mixing of the injected water with the high-borated coolant in the reactor pressure vessel. The ROCOM experiments provided an insight into the mixing and therefore allow drawing corresponding conclusions.
The last series (consisting of one experiment) was on the investigation of the thermal-hydraulic behavior inside the RPV during the ECC-injection from ACCU into the cold leg of loop 1. It is based on the PKLIII test H3.1, which objective was to explore the effectiveness of ECC-injections from ACCU to restore operating conditions of RHRS during the core heat-up phase. The test H3.1 addressed the failure of RHRS under cold shut-down condition with open RCS (RPV closure head removed). Experimental results at the RPV inlet from the PKLIII test H3.1 Run 1 Phase C were used as boundary conditions for the corresponding ROCOM test.
Altogether six ROCOM tests have been conducted within the OECD PKL3 Project.
The current report describes the results of all tests.