Design modification for the modular helium reactor for higher temperature operation and reliability studies for nuclear hydrogen production processes

摘要

Design options have been evaluated for the Modular Helium Reactor (MHR) forhigher temperature operation. An alternative configuration for the MHR coolant inletflow path is developed to reduce the peak vessel temperature (PVT). The coolant inletpath is shifted from the annular path between reactor core barrel and vessel wall throughthe permanent side reflector (PSR). The number and dimensions of coolant holes arevaried to optimize the pressure drop, the inlet velocity, and the percentage of graphiteremoved from the PSR to create this inlet path. With the removal of ~10% of thegraphite from PSR the PVT is reduced from 541 0C to 421 0C.A new design for the graphite block core has been evaluated and optimized toreduce the inlet coolant temperature with the aim of further reduction of PVT. Thedimensions and number of fuel rods and coolant holes, and the triangular pitch havebeen changed and optimized. Different packing fractions for the new core design havebeen used to conserve the number of fuel particles. Thermal properties for the fuelelements are calculated and incorporated into these analyses. The inlet temperature, massflow and bypass flow are optimized to limit the peak fuel temperature (PFT) within anacceptable range.Using both of these modifications together, the PVT is reduced to ~350 0C whilekeeping the outlet temperature at 950 0C and maintaining the PFT within acceptablelimits. The vessel and fuel temperatures during low pressure conduction cooldown and high pressure conduction cooldown transients are found to be well below the designlimits.The reliability and availability studies for coupled nuclear hydrogen productionprocesses based on the sulfur iodine thermochemical process and high temperatureelectrolysis process have been accomplished. The fault tree models for both theseprocesses are developed. Using information obtained on system configuration,component failure probability, component repair time and system operating modes andconditions, the system reliability and availability are assessed. Required redundanciesare made to improve system reliability and to optimize the plant design for economicperformance. The failure rates and outage factors of both processes are found to be wellbelow the maximum acceptable range.