Reactor Physics Calculations for Conversion of McMaster Nuclear Reactor from Use of HEU to LEU Fuel

Abstract

This paper presents the results of the reactor physics analysis performed to support the conversion of the McMaster Nuclear Reactor (MNR) from the use of HEU fuel to LEU fuel. The overall objective of this work was to demonstrate that the use of LEU fuel will not change the present performance or safety margins of the MNR core. The LEU silicide fuel that will be used in the MNR has been approved by the US Nuclear Regulatory Commission (USNRC) for use in non-power reactors. The new LEU assemblies have the same overall design as the current HEU assemblies with the exception of the fuel composition. The methods and codes used in this work have been qualified by AECL [l] and MNR [2] for use in this type of analysis. The reactor parameters investigated in this work were those that could change as a result of using LEU fuel in the core instead of HEU fuel. The results show that MNR facility can be operated as safely with the new LEU fuel as with the present HEU fuel. There is no significant change to the operating safety margin of the MNR as a result of using LEU fuel. It is worth noting that since 1988, the MNR core has operated with two LEU fuel assemblies at two low power core positions. The AECB approved the use of these two assemblies in 1988. They are identical in overall design and enrichment to the new LEU fuel assemblies which MNR plans to use later this year. The only difference is the new LEU assemblies have a lower 235U loading (225 grams vs. 284 grams) which is more conservative in terms of assembly power peaking factors and reactivity. The new LEU fuel assemblies have nearly the same power peaking factors as the current 18-plate HEU assemblies.