Spent thermal reactor fuel assembly characterization with solid state tract recorders

Abstract

A scoping experiment to characterize the neutron field generated from a Light Water Reactor spent fuel assembly has been successfully completed. Solid State Track Recorder (SSTR) neutron dosimeters were exposed at the surface of a spent fuel assembly from a Pressurized Water Reactor. Acceptable track densities were obtained. From these SSTR neutron dosimetry measurements, an absolute neutron flux of about 8 x 10^ n/cnr sec was determined at the surface of the spent fuel assembly some three years after discharge from the reactor. This deduced neutron energy flux, with a mean neutron energy of about 1.3 MeV, is intimately dependent upon the actinide content of the spent fuel. Hence, the results of this preliminary experiment have demonstrated that, with suitable calibration, SSTR neutron dosimetry can be successfully applied for nondestructive spent fuel actinide assay and for characterization of the radiation environment associated with spent reactor fuel assemblies. Follcw-on studies are described.

Performance and Applications of Silicon Carbide Neutron Detectors in Harsh Nuclear Environments

“…Gamma rays will also be present primarily from the fission-product inventory present in the fuel. For example, a Pressurized Water Reactor fuel assembly with a burnup of 25,655 MWd/MTU had a total surface neutron fluence rate of 8000 cm -2 -s -1 at midplane three years after discharge [43], and typical gamma dose rates in spent-fuel environments are in the 10 2 -10 3 Gy/hr range [17][18].…”

“…A related safeguards-monitoring application is long-term monitoring of spent fuel. The axial distribution of the neutron emission rate at the surface of a spent fuel assembly will depend on the burnup history of the assembly [43]. Deviations from the expected distributions can be used as an indicator of off-normal conditions resulting from diversion of fuel rods, mechanical or corrosive deterioration of the assembly, water incursion, etc.…”