Neutronics analysis of target, moderators and reflector design for the ISIS TS-1 project

The aim of the Target Station 1 (TS-1) project at the ISIS Neutron and Muon Source is a complete refurbishment of the internals of the TS-1, including the design of the target and its cooling systems, the moderators, the reflector and all their associated services. The main reason for this refurbishment is to secure the future of the, 30 years old, ISIS Target Station 1. In this paper, the neutronics analysis of possible improvements of ISIS TS-1 is described. The goal is to deliver a new model of Target Station 1 which maintains the instruments pulse time characteristics within the limits defined by instrument scientists and provides the largest collective gain. A number of the MCNPX models of the TS-1 future TRaM assembly have been prepared and optimized by ISIS neutronics team using the CombLayer package. New models have been benchmarked against a baseline TS-1 model taking into account flux and time distribution of all existing TS-1 instruments. The best model, described in this paper, shows that significant benefits (operational improvements, additional flexibility and neutron flux increase) can be achieved without modification of existing instruments.