Evaluation of the in-situ performance of neutron detectors based on EJ-426 scintillator screens for spent fuel characterization

Summary, in English

The reliable detection of neutrons in a harsh gamma-ray environment is an important aspect of establishing non-destructive methods for the characterization of spent nuclear fuel. In this study, we present results from extended in-situ monitoring of detector systems consisting of commercially available components: EJ-426, a ⁶Li-enriched solid-state scintillator material sensitive to thermal neutrons, and two different types of Hamamatsu photomultiplier tubes (PMT). Over the period of eight months, these detectors were operated in close vicinity to spent nuclear fuel stored at the interim storage facility CLAB, Oskarshamn, Sweden. At the measurement position the detectors were continuously exposed to an estimated (moderated) neutron flux of approx. 280n/scm² and a gamma-ray dose rate of approximately 6Sv/h. Using offline software algorithms, neutron pulses were identified and characterized in the data. Over the entire investigated dose range of up to 35kGy, the detector systems were functioning and were delivering detectable neutron signals. Their performance as measured by the number of identified neutrons degrades down to about 30% of the initial value. Investigations of the irradiated components suggest that this degradation is a result of reduced optical transparency of the involved materials as well as a reduction of PMT gain due to the continuous high currents. Increasing the gain of the PMT through step-ups of the applied high voltage allowed to partially compensate for this loss in detection sensitivity even when the detectors were highly irradiated. The integrated neutron fluence during the measurement was experimentally verified to be in the order of 5×10⁹ncm⁻². The results were interpreted with the help of MCNP6.2 simulations of the setup and the neutron flux.

• Author: Hanno Perrey; Linus Ros; Mikael Elfman; Ulrika Bäckström; Per Kristiansson; Anders Sjöland
• Department/s: Nuclear physics
• Publishing year: 2021-12-21
• Language: English
• Publication/Series: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
• Volume: 1020
• Links: http://dx.doi.org/10.1016/j.nima.2021.165886
• Document type: Journal article
• Publisher: Elsevier
• Topic: Subatomic Physics
• Keywords: EJ-426; Mixed-field radiation environment; Neutron detector; Photo-multiplier tube; Radiation hardness; Spent nuclear fuel characterization
• Status: Published
• ISBN/ISSN/Other: ISSN: 0168-9002