Performance study of a new LiCAF:Ce detector developed for high-efficient neutron detection in intense -ray fields

冠城 雅晃; 鎌田 圭*; 石井 隼也*; 松本 哲郎*; 真鍋 征也*; 増田 明彦*; 原野 英樹*; 加藤 昌弘*; 島添 健次*

Journal of Instrumentation (Internet), 19(11), p.P11019_1 - P11019_16, 2024/11

https://doi.org/10.1088/1748-0221/19/11/P11019

A new LiCAF:Ce detector with an ultra-thick (99 m) crystal and optimized readout was developed. The LiCAF:Ce and KG2 detectors were used to detect a sealed Cf-252 neutron source (neutron emission rate of ~) using a 5 cm thick high-density polyethylene (HDPE) block located at the front of the detector. At the air kerma rates at the front surface of the HDPE block () of up to 1.07 Gy/h, the effective neutron count rate () for the LiCAF:Ce detector was the same within margins of errors, but it decreased by 5.7 0.8% at 2.97 Gy/h. In contrast, for the KG2 detector, with increased up to 1.07 Gy/h, for KG2 increased up to 20 1.0 % at 1.07 Gy/h. Then, decreased by 20 1.0% at 2.97 Gy/h. Therefore, the LiCAF:Ce detector exhibited a smaller influence on neutron count rates by -rays compared to the KG2 detector because of the faster decay time and optimization of digital pulse processing.

Structural and compositional characteristics of Fukushima release particulate material from Units 1 and 3 elucidates release mechanisms, accident chronology and future decommissioning strategy

Martin, P. G.*; Jones, C. P.*; Bartlett, S.*; Ignatyev, K.*; Megson-Smith, D.*; 佐藤 志彦; Cipiccia, S.*; Batey, D. J.*; Rau, C.*; 末木 啓介*; et al.

Scientific Reports (Internet), 10, p.22056_1 - 22056_17, 2020/12

https://doi.org/10.1038/s41598-020-79169-2

The structural form and elemental distribution of material originating from different Fukushima Daiichi Nuclear Power Plant reactors (Units 1 and 3) is hereby examined to elucidate their contrasting release dynamics and the current in-reactor conditions to influence future decommissioning challenges. Complimentary computed X-ray absorption tomography and X-ray fluorescence data show that the two suites of Si-based material sourced from the different reactor Units have contrasting internal structure and compositional distribution. The known event and condition chronology correlate with the observed internal and external structures of the particulates examined, which suggest that Unit 1 ejecta material sustained a greater degree of melting than that likely derived from reactor Unit 3. In particular, we attribute the near-spherical shape of Unit 1 ejecta and their internal voids to there being sufficient time for surface tension to round these objects before the hot (and so relatively low viscosity) silicate melt cooled to form glass. In contrast, a more complex internal form associated with the sub-mm particulates invoked to originate from Unit 3 suggest a lower peak temperature, over a longer duration. Using volcanic analogues, we consider the structural form of this material and how it relates to its environmental particulate stability and the bulk removal of residual materials from the damaged reactors. We conclude that the brittle and angular Unit 3 particulate are more susceptible to further fragmentation and particulate generation hazard than the round, higher-strength, more homogenous Unit 1 material.

定常臨界実験装置(STACY)及び過渡臨界実験装置(TRACY)の燃料調製施設の運転記録; 平成1620年度

石仙 順也; 住谷 正人; 関 真和; 小林 冬実; 石井 淳一; 梅田 幹

JAEA-Technology 2012-041, 32 Pages, 2013/02

JAEA-Technology-2012-041.pdf:1.6MB

定常臨界実験装置(STACY)及び過渡臨界実験装置(TRACY)の燃料調製施設においては、臨界実験で使用する硝酸ウラニル溶液を準備するため、実験目的に応じてウラン濃度,硝酸濃度,可溶性中性子毒物濃度等の調整を行っている。平成16年度から平成20年度にかけては、STACY及びTRACYで使用する燃料の調整のため、硝酸ウラニル溶液のU濃縮缶による濃縮及び脱硝を行った。並行して、平成17年度及び平成18年度には、核分裂生成物等の中性子吸収効果を定量するためのSTACY実験のために、可溶性中性子毒物を添加した溶液燃料の調整を行った。この実験が終了した後、平成18年度及び平成19年度にかけて可溶性中性子毒物添加燃料の一部について、ミキサセトラを用いた溶媒抽出法により、中性子毒物の除去を行った。本報告書は、これらの平成16年度から平成20年度に実施した燃料調製施設の運転データについてまとめたものである。

-ray spectroscopy study in intense -ray fields using a small LBC scintillator for an in situ nuclear fuel debris assay

冠城 雅晃; 石井 隼也*; 加藤 昌弘*

no journal, , 

A -ray spectroscopy system using a small cubic LaBrCl scintillator measuring the crystal dimensions of 5 5 5 mm was developed for an in situ nuclear fuel debris assay. In an intense Cs radiation field, this study showed that the system had good energy resolution (4%) at dose rates up to 0.407 Gy/h. The full energy peak at 662 keV can be identified at dose rates of up to 2.97 Gy/h.

Identification of -ray nuclide in an intense -ray field for nuclear decommissioning

冠城 雅晃; 石井 隼也*; 加藤 昌弘*

no journal, , 

-ray spectroscopy assay is a supporting technique for managing and disposing radioactive waste and spent nuclear fuel. A -ray-spectroscopy system for intense -ray fields without radiation shields was developed using a small LaBrCl (1 x 3) scintillator with dimensions of 5 mm 5 mm 5 mm. The scintillator has suitable properties of fast decay time ( 25 ns) and high energy resolution (2.8% - 3.5%). The scintillator was coupled to a photomultiplier tube covered with an aluminum case for shading and shielding electromagnetic noise. The anode pulse signals were digitized with 10 samplings per second and 14-bit quantum resolution. The digital values were averaged over 8 ns and applied to a 10 ns digital low-pass filter integrated for 136 ns. -ray nuclide identification of Ba (6.45 MBq) was investigated in a Cs radiation field at varying dose rates. In the measured -ray spectra, full energy peaks (peak) of Ba with primary emission ratios (emission ratio 5%) were detected at 0.0658 Gy/h. As the irradiation dose rate increases, peaks with low emission rates were not detected initially. This -ray spectroscopy system detected a low energy peak at 81 keV at 0.474 Gy/h and Ba at dose rates up to 1.07 Gy/h using the peak with the highest emission ratio (356 keV).