Strategies and dismantling solutions for RPV internals of Trino NPP

The last step of nuclear power plants’ life is the decommissioning phase. Many strategies have been developed in the last decades; the main options consists in: immediate dismantling, safe storage and entombment. In Italy, due to the premature shutdown of nuclear power plants (NPP) as a consequence of the 1986 referendum following the Chernobyl accident, all the NPPs were shut down. Therefore, currently decommissioning activities are under way. In this work specifically the dismantling procedures of the “Enrico Fermi” NPP reactor pressure vessel (RPV) are dealt with. The attention is so focused on the optimization of number, position and length of the Internals cuts, optimization of volume and number of waste containers, and of the dose rates, according to the imposed site and the transport requirements. The systematic approach developed to identify the optimum dismantling solution is presented and discussed. To the intent three solutions have been identified as more advantageous. In addition, the evaluation of dose rate outside the container has been performed by means of VISIPLAN software, in order to guarantee the respect of the limits imposed by National and International regulations. The obtained results suggest that the cutting of Zircalloy elements in correspondence of the gap between two non-consecutive central stumps, with the possibility to re-arrange the element, led to a significant reduction of the number of containers, with consequent decrease of the stowed RWs volume and overall supplying costs of the activity.