A study of reduction in fuel requirement and enhancement of neutron flux in typical MTR type research reactors

Pakistan Research Reactor-1 (PARR-1) is a typical swimming pool type MTR utilizing low enriched uranium (19.99% in 235U) silicide dispersion fuel of density 3.28 gU/cm3. The benefits of loading available and upcoming higher density fuels in the existing PARR-1 core have been explored in this study with constraints of no change in the existing moderator/coolant channel width and existing reactor systems. The study was conducted by employing the standard reactor physics simulation codes WIMS-D/4, CITATION, and burnup analyses code FCAP along with a reactor thermal hydraulics simulation code PARET. The study reveals that by directly replacing the fuel currently in use in PARR-1 core with a similar type of fuel of density 4.8 gU/cm3, an equilibrium core slightly smaller than the existing equilibrium core of PARR-1 can be established. The new equilibrium core can provide neutron fluxes similar to those that are available in the existing equilibrium core of PARR-1 but will require about 14.4 kg less LEU fuel for its one effective full power year operation at 10 MW. Size of this new equilibrium core can be reduced to achieve about 47% higher thermal neutron fluxes at the irradiation sites without increasing the existing cost of producing neutron fluxes. In case of new cores, fuel cycle length is also six effective full power days (EFPDs) larger than that of the existing equilibrium core. Thermal hydraulic analysis results show that these suggested cores can be operated safely at 10 MW with the existing coolant flow rate of 1000 m3/h. The study was further extended by considering direct substitution of higher density fuels, being developed under the RERTR program, in the proposed core. This extended study revealed that the utilization of further higher density fuels being developed under the RERTR program is not feasible from the viewpoint of relative production cost of neutron flux.