Risk-Based Approach for Thermal Profiling of Sodium Vessel and Pipelines of Prototype Fast Breeder Reactor

Abstract

Monitoring of the temperature profile and accurate assessment of temperature data from the measured values in main vessel (MV), primary and secondary sodium piping and related pipe-mounted equipment, during the commissioning phase of a sodium-cooled fast reactor, is extremely important, since a fall in temperature below the plugging temperature value of sodium could result in freezing of sodium within the pipes or in various crevasses in valves, pumps, etc., or also in the MV. While it is possible to augment the heating of the piping segments for re-melting the sodium, the same will not be possible, if the large volume of sodium in the MV (of the order of 1000 tonnes) is to either freeze completely or even agglomerate and settle down in the various crevasses of in-pool equipment. This paper deals with the various failure modes of heating equipment and the necessary precautions to be taken for ensuring the required temperature by monitoring the temperature data along with the uncertainties during commissioning phase of PFBR. It is essential to ensure that the temperature profiles of the MV are well above the plugging temperature of the sodium, and for this, a detailed failure mode and effect analysis (FMEA) is carried out. Also, based on the computed reliability numbers from the mechanistic models of the nitrogen blowers and heaters and the rotor dynamic equipment of the secondary loops, viz. main sodium pumps and electromagnetic pumps, a risk-based model is proposed.