A neutronic model of the PMR200 prismatic modular reactor using MCNP5

Abstract

The PMR200 reactor is a prismatic modular High Temperature Reactor. The High Temperature Reactor is a near term Generation IV reactor with the capability of producing electricity, and its high outlet temperature enables thermochemical hydrogen production. This makes the PMR200 one of the candidates for the Nuclear Hydrogen Development and Demonstration plant in Korea and the Next Generation Nuclear Project. The most desirable aspect of the PMR200 is its range of safety features. It is imperative to determine whether the reactor meets the required safety standards. In this work a neutronic analysis of the PMR200 core is performed. The model of the pre-conceptual design for the PMR200 is modelled using radiation transport and simulation code, MCNP5. The temperature of all the materials is set at 300 K and the pre-conceptual model is found to be supercritical. The reactor is made into a critical configuration by controlling the mass fraction of boron carbide to 4.2% so that the neutron multiplication factor, keff ≅ 1. The fuel temperature coefficients are computed for the coated particle and the fuel compact and are found to be negative. The moderator coefficient, total temperature coefficient and isothermal temperature coefficients are all found to be negative. Reactivity of the PMR core is controlled by three banks of control rods and burnable neutron poisons. Control rod worth and SCRAM reactivity are assessed for the three banks of control rods and the rods are found to have enough reactivity to change the reactor from a supercritical to a subcritical state. The effect of the neutron absorbers on the neutron economy is assessed by analysing the flux distribution in response to an insertion of absorbers. The neutron economy decreases when the control rods are fully inserted or are at the critical position. The same behaviour can be seen when the mass fraction of the boron carbide in the control rods is altered