A passive system for long-term heat removal in advanced light water reactors: Prototype test results and analysis

The simplified boiling water reactor makes use of an isolation condenser (IC) submerged in a large water pool; following a postulated accident, the pool water boils off, releasing steam to the atmosphere and ensuring passive containment cooling for at least 3 days. A further improvement is the isolation condenser pool cooling system (ICPCS), proposed by ENEL/CISE. It makes use of reflux condensing heat exchangers directly connected to the pool gas space of the IC; noncondensable gases can be vented during the earlier phase of operation by means of a water seal mechanism operating in a passive way. The expected benefits from the ICPCS are the elimination of constraints on the ''grace period'' duration and the possibility of avoiding an extended release of a visible and potentially radioactive steam plume. To verify the performance both at component and system level, an instrumented ICPCS prototype, operating with a thermal power scaling factor of similar to 1:615, has been built and tested at CISE laboratories, both in steady and dynamic conditions. The experimental results confirm the capability of the tested ICPCS module to operate in a safe and passive way.