Field tests for performance evaluation of a new spent-fuel verification system in heavy water reactor

Abstract The optical fiber-based measurement system has been utilized for inspecting CANDU-type spent fuel at the Wolsung site in South Korea under the nuclear safeguards of the International Atomic Energy Agency (IAEA). In our previous studies, we developed a new spent-fuel verification system to address issues of the existing instrument. While our prior work primarily focused on equipment development, we had not yet conducted comprehensive field tests to assess its performance. Recently, we conducted field tests at the Wolsung Unit 4 to thoroughly evaluate the newly developed spent-fuel verification system's performance. This paper discusses the results of these field tests, with a focus on signal sensitivity, the system's capability to distinguish neighboring spent-fuel bundles, and the optical fiber background signals. Additionally, we conducted experiments to assess how different scintillation materials impact the system's performance, including p-terphenyl organic scintillator, PVT plastic scintillator, and lithium glass scintillator. The experimental results demonstrated that the new instrument equipped with the p-terphenyl organic scintillator outperformed the existing system. The p-terphenyl scintillator emerged as the superior choice among the three radiation scintillators. Signals that were previously undetectable using the Li glass scintillator were observed in the signals obtained with the p-terphenyl and PVT plastic scintillators. The remarkable performance of the new verification instrument is attributed mainly to the p-terphenyl's high light output and low decay time. The newly developed verification system is expected to streamline IAEA safeguards inspection efforts, reducing both time and the burden on nuclear operators. This report represents the first successful application of the p-terphenyl scintillator as a radiation detector in a wet spent fuel pool. The experimental findings presented in this paper are anticipated to be valuable for researchers working on radiation detectors suitable for high radiation environments in water.