Highly Perturbed Operational Test Configurations at the WSMR Fast Burst Reactor

Abstract

Abstract. The White Sands Missile Range (WSMR) MoLLY-G reactor has a long history of producing a well characterized environment for testing electronic systems/devices in fission environments. As an unmoderated, unreflected, bare critical assembly, it provides a slightly degraded fission spectrum with a 1/E tail. For radiation hardness testing of electronics, the neutron fluence is usually reported as the 1-MeV Equivalent Neutron Fluence for Silicon. In this paper, we examine additional neutron environments and characterizations ranging from low intensity neutron fields to more extreme modifications of our normal test environment. White Sands Missile Range MoLLY-G ReactorThe WSMR MoLLY-G reactor is an unmoderated, unreflected bare critical assembly. The reactor can be operated in either the steady state mode at the several kilowatt level or made super prompt critical, producing a pulse with a full-width half-maximum time of 45 microseconds or longer. The neutron spectrum leaking from the reactor is a slightly degraded fission spectrum. The reactor is operated in an exposure cell approximately 15 m by 15 m by 6.1 m high. The exposure cell has thick concrete walls lined with gypsum and borated gypsum wall board. The free field neutron environment at any position in the cell is a combination of the slightly degraded fission spectrum leaking from the reactor and a wall-return component which ties to the fission spectrum at a few keV in energy [1][2][3].The MoLLY-G core is a cylindrical assembly consisting of six annular fuel rings made of enriched uranium-molybdenum alloy. The safety block is a large fuel element which is inserted into the central cavity of the core. The fuel rings are bolted to a stainless steel support plate by three Inconel metal bolts. There is a stainless steel retaining plate at the top of the core. The power level of the core is adjusted by two control rods of the same fuel alloy which are inserted into voids in the body of the rings. A third control rod can be pneumatically driven into the core for burst operations. The core is covered by a cylindrical decoupling shield containing a 10 B loaded silastic. The decoupling shroud minimizes the effect of reactivity changes due to experiments and other environmental considerations external to the core. The core geometry is shown schematically in Fig. 1 with a typical MCNP [4] model of the core shown in Fig. 2. A more comprehensive model used for spectral characterization at experimental a Corresponding