Method for the thermo-hydraulic analysis of the test facility for the PBMR reserve shutdown system

Abstract

The Pebble Bed Modular Reactor (PBMR) is a revolutionary small, compact and safe nuclear power plant. It operates on a direct closed Brayton cycle. One of the unique features of this concept is its load following capability enabled by extracting or injecting of the working fluid (in the PBMR's case Helium) from or to the system during operation. The Reserve Shutdown System (RSS) is one of the essential subsystems of the PBMR. The RSS is used as a maintenance and secondary shutdown system for the PBMR. Small Absorber Spheres (SAS) containing boron are used to perform the shutdown. When shutdown is required, the spheres flow into eight borings in the centre reflector of the reactor core. To continue the reactor operation, the spheres are removed from the borings in the centre reflector and transported back into the storage containers. As the RSS is a safety-related system, the functioning and components of the system must be tested in a non-nuclear environment, before the design can be finalized for the demonstration plant. A test set-up for the RSS was designed and forms part of the Helium Test Facility (HTF) for the PBMR. A method had to be identified and a process developed which can be used to perform a thermo-hydraulic analysis and determine the specifications of the components in the test facility that will enable the test facility to perform all the required tests at the required conditions. This method also had to predict the performance of the test facility before the building of the actual plant. The method of simulation was identified as the most suitable method to perform the thermo-hydraulic analysis on the proposed test facility. The process developed included the set-up of a thermal fluid network with the use of Flownex Nuclear, a thermal fluid software package. With the method that was used for the thermo-hydraulic analysis of the RSS test facility, it was possible to obtain the process data for the components and to predict the functioning and performance of the proposed test facility. This method and process can be used widely in the industry for the design and performance prediction of large industrial plants and testing facilities. It can also be used in the design process of plants to optimize the layout and performance of the plants and processes.