Supporting Design Analysis of the VTR Using MCNP and TRACE

The Versatile Test Reactor (VTR) is a sodium-cooled fast reactor designed to accelerate the design and approval of new nuclear material and reactor concepts by providing a high neutron fast flux environment on U.S. soil. To ensure that the reactor simultaneously achieves the target irradiation environment while maintaining sufficient margin to safety limits, supporting design analysis of the VTR has been performed using MCNP and TRACE. High-fidelity MCNP calculations have been performed that confirm design parameters, such as control rod worth and neutron and photon flux distributions, and provide needed reactivity coefficients for TRACE analyses. The MCNP simulations additionally provide fuel rod power profiles of interest to fuel performance designers and provide an excellent model for experimental cartridge design within the VTR core. TRACE simulations of several postulated transients, such as station blackout, loss of heat sink, and transient overpower, have been performed (results included here are limited to the transient overpower), and the obtained results confirm the robust safety behavior of the VTR. The TRACE simulations provide a valuable confirmatory transient analysis capability using a U.S. Nuclear Regulatory Commission–developed safety analysis tool incorporating inputs from the high-fidelity neutronic simulations performed with MCNP. Taken together, the confirmatory analysis capability provided by MCNP and TRACE serves to further strengthen the understanding of and confidence in the VTR’s performance.