Neutron energy spectrum determination and flux measurement using MAXED, GRAVEL, and MCNP for RACE experiments

Stainless steel flux wires were used to determine the neutron energy spectra and total flux during the Reactor Accelerator Coupling Experiments (RACE) at The University of Texas at Austin. A LINAC electron accelerator produced 20 MeV electrons at a power of 1.6 kW, which struck a tungsten-copper target to produce bremsstrahlung radiation and photoneutrons. The neutrons produced in the target were multiplied by the subcritical core of a Triga reactor. The purpose of the RACE experiments is to develop a sub-critical accelerator driven system that would be capable of transmuting actinides from spent fuel. Flux measurements were made with 1.58 mm diameter stainless steel wires placed throughout the core between the fuel rods and cadmium covered and uncovered gold and indium foils above the target. The MAXED and GRAVEL computer codes were used to perform the spectrum unfolding. The composition of the stainless steel wires was determined using neutron activation analysis with comparators prior to the flux measurement. The reactions measured in the stainless steel to determine the flux were ⁵⁰Cr(n,γ) ⁵¹Cr, ⁵⁸Ni(n,p)⁵⁸Co, ⁵⁴Fe(n,p) ⁵⁴Mn, and ⁵⁸Fe(n,γ)⁵⁹Fe. Flux measurements agreed well with an MCNP simulation of the experiment.