A cubic CeBr3 gamma-ray spectrometer suitable for the decommissioning of the Fukushima Daiichi Nuclear Power Station

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Accelerators, spectrometers, detectors and associated equipment, 2020-08, Vol.971, p.164118, Article 164118
• Main Authors: Kaburagi, Masaaki, Shimazoe, Kenji, Otaka, Yutaka, Uenomachi, Mizuki, Kamada, Kei, Kim, Kyoung Jin, Yoshino, Masao, Shoji, Yasuhiro, Yoshikawa, Akira, Takahashi, Hiroyuki, Torii, Tatsuo
• Format: Article
• Language: English
• Subjects: Cerium bromide; Fukushima Daiichi Nuclear Power Station Accident; High dose-rate; High energy gamma-ray spectrometry; Passive gamma-ray analysis
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/j.nima.2020.164118

In the decommissioning of the Fukushima Daiichi Nuclear Power Station (FDNPS), the retrieval of the nuclear fuel debris is a critical step, and the localization of these debris speeds up the decommissioning operation and prevents criticality. Our work focused on the passive gamma-ray analysis (PGA) of the nuclear fuel debris based on measuring gamma rays with an energy greater than 1 MeV. The PGA requires gamma-ray spectrometers to be used under the high dose rates in the FDNPS, then we fabricated a small cubic CeBr3 spectrometer with dimensions of 5 mm × 5 mm × 5 mm, which was coupled to a Hamamatsu R7600U-200 photomultiplier tube (PMT). We investigated the performance at dose rates of 4.4 to 750 mSv/h in a60Co field. The energy resolution of the full width at half maximum at 1333 keV ranged from 3.79% to 4.01%, with a standard deviation of 6.9%, which met the narrow gamma decay spectral lines between154Eu (1274 keV) and60Co (1333 keV). However, the spectra shifted to a higher energy level as the exposure dose rate increased, there was a 51% increase at the dose rates of 4.4 to 750 mSv/h. The spectral shifts were caused by the increase in the PMT gain due to the large direct current flows.