Monitoring for Actinide Neutron Emissions From Spent Nuclear Fuel Under Extreme Gamma Fields Using Centrifugally Tensioned Metastable Fluid Detector Sensor Technology

Abstract

This paper presents research work focused on assessments for meeting the challenge of monitoring actinide content in spent nuclear fuel (SNF) via characteristic neutron emissions [from spontaneous fission and (α,n) reactions] with CTMFDs. A challenge problem was posed to examine if a CTMFD could operate reliably over 1 hour for conducting neutron spectroscopy at a 1 m standoff from a 30-y cooled SNF, in a ~1012:1 (gamma:neutron) and a 150 Gy (15 kRad) accumulated dose. The impacts on operability were studied for the effects of gamma radiation on: (i) radiolysis in the CTMFD sensing fluid; (ii) 3 MeV gamma photoneutrons; and, (iii) CTMFD electronics. A Co-60 irradiator was used for dose effects on the CTMFD. A 14 MeV DT accelerator was used with a NaCl target to produce 3-4 MeV photons from activated 37S (via. neutron absorption in 37Cl) expected from SNF at 1-m standoff. Our examinations revealed the absence of any significant impact on CTMFD performance for meeting and exceeding the challenge problem metrics. We validated for no discernible impact of: 3-4 MeV gamma-produced photoneutrons when combined with a fission neutron source and radiolysis in the DFP sensing fluid through a 150 Gy absorbed dose. Past research results at Purdue University have validated survivability above the targeted 150 Gy level. This paper also provides extended evidence for survivability (from radiolysis) at higher gamma doses through 750 Gy with a borated DFP-sensing fluid formulation-based CTMFD.