Passive integral LOCA accident testing at Karlstein test facility

KERENA is an innovative boiling water reactor concept with passive safety systems (Generation III+) of AREVA . In order to verify the functionality and performance of the concept required for the transient and accident management, the test facility "Integral Teststand Karlstein" (INKA) was built in Karlstein (Germany). It is a mockup of the KERENA boiling water reactor containment, with integrated pressure suppression system. The complete chain of passive safety components is available. While the scaling of the passive components and the levels match the original values, the volume scaling of the containment compartments is approximately 1:24. The reactor pressure vessel (RPV) is simulated via the steam accumulator of the Karlstein Large Valve Test Facility (GAP). This vessel provides an energy storage capacity of approximately 1/6 of the KERENA RPV and is supplied by a Benson boiler with a thermal power of 22 MW. With respect to the available power supply, the containment- and system-sizing of the facility is by far the largest one of its kind worldwide. On March 21, 2013 the worldwide first large-scale, only passively managed, integral accident test of a boiling water reactor was simulated at INKA. The integral test measured the combined response of the KERENA passive safety systems to the postulated initiating event "Main Steam Line Break" (MSLB) inside the Containment with decay heat simulation. The main goals were to show the performance and the interaction of the KERENA passive safety systems, the ability to keep the core covered, to discharge the decay heat via the appropriate pathway under all circumstances and to maintain the containment within defined limits, i.e. to bring the plant to a controlled state. The performed integral test (MSLB) was being initiated via the opening of the leak at original RPV boundary conditions (75 bar reactor pressure). The leak causes a mass and energy flow from the reactor pressure vessel into the containment. The resulting drop in the RPV water level activates the Emergency Condenser, so that an additional path for energy transfer out of the RPV in parallel to the leak is opened. The pressure increase in the containment is limited via the containment pressure suppression system (short term) and the containment cooling condensers (long term). The results of the test showed that the passive safety systems alone are capable to bring the plant to stable conditions meeting all required safety targets with sufficient margins. Therefore the test verified the function of those components and the interplay between them as response to an anticipated accident scenario. The test provided evidence that the INKA is worldwide the first large scale test facility to perform integral verification tests of passive safety concepts under plant-like scaling and thermodynamic conditions.