Radionuclide Inventory Calculations for the Materials Test Station

Radionuclide inventory calculations support design and accident analyses for the Materials Test Station (MTS). MTS is a spallation source facility being designed to irradiate reactor fuels and materials in a fast neutron spectrum. Calculated radionuclide inventories are used to provide decay heat input to cooling system design, decay radiation source terms for hot cell design, and material-at-risk input to accident analyses. CINDER'90 is a transmutation code that uses MCNPX-calculated spallation product yields and neutron fluxes to calculate residual nuclide concentrations based on irradiation history. The code also calculates decay heat and photon spectra for the resulting radionuclide inventories. A total activity of 2 × 10¹⁷ Bq is created during MTS operation. Decay heat is an important factor since in loss of primary cooling scenarios, this heat must be removed. The major sources at shutdown are 3000 W for the tungsten target plates and 6000 W for fuel pins being irradiated. Decay photon spectra result in unshielded dose rates that hot cell design must accommodate on the order of 1000 Sv/h. The MTS design includes lead-bismuth eutectic (LBE) coolant. For accident analysis ²¹⁰Po activity in the LBE is a significant concern. The calculated ²¹⁰Po activity following 2.5 yr of operation is 2 × 10¹⁴ Bq. Radionuclide inventory calculations are important for MTS design. The CINDER'90 code is a valuable tool for this purpose.