Investigation of a fast partial defect detection method for safeguarding PWR spent fuel assemblies Haneol Lee, Man-Sung Yim ⇑ Department of Nuclear and Quantum Engineering, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea article info Article history: Received 23 October 2019 Received in revised form 19 March 2020 Accepted 20 March 2020 Available online 7 April 2020 Keywords: Scintillator – photodiode detector Spent fuel safeguards Partial defect detection Screening verification abstract As the number of countries with their spent fuel inventory in storage increases, spent fuel verification for nuclear safeguards becomes important. In particular, detection of partial defect, which is the result of local diversion of fuel rods, deserves special attention. This is because accumulation of small scale fuel rod diversions could lead to undesirable consequences. While the necessary detection technologies are available, the cost and detection time associated make it difficult for the partial defect detection tech- nologies to be applied to all spent fuel assemblies. This research investigated the feasibility of developing an efficient and cost-effective method for detecting partial defects of spent fuel assemblies. The approach is based on using the gamma radiation emitted from spent fuel and converting its energy to electric energy. Such approach was incorporated into a new detector concept called, ‘‘scintillator based partial defect detector (SPDD)”. SPDD detects the intensity of passive gamma by converting gamma radiation into photons using a CdWO 4 scintillator and then into electric current by using amorphous silicon pho- todiode. Along with the use of detector measurements, a parallel approach of estimating generated elec- tric current by using computation models using the declared spent fuel information is implemented. Detection of partial defects is based on comparing the differences in the electric current between mea- surements and the expected results. The proposed method was tested using the scenario of detecting 1 SQ (significant quantity) of Pu missing among spent fuel assemblies loaded for a shipment in a typical transportation cask. Results from selected test cases indicated the feasibility of as well as limitations in detecting partial defects by using the proposed method for screening purposes. The irradiation damage to the CdWO 4 scintillator of SPDD was also examined for the periods of in-reactor application. In addition, the cost associated with SPDD was estimated in comparison to that of existing partial defect technologies. Purpose of the research: To design a cost-effective partial defect detector with fast screening capability. To demonstrate the feasibility of applying the detector in high radiation environment. To setup partial defect detection criterion. To examine the feasibility of applying the developed detector to partial defect detec- tion. Approaches: Design a scintillator – photodiode based gamma detector. Develop a method for detecting partial defects. Setup detection criterion for partial defect detection. Analyze radiation damage issue and cost – effectiveness of the proposed detection method. Demonstrate the feasibility of partial defect detection base on examining test case assemblies. Ó 2020 Elsevier Ltd. All rights reserved. 1. Introduction Nuclear safeguards continues to face challenges as the number of nuclear facilities, the amount of nuclear material, and types of facilities to be safeguarded increase. Similarly, the diversion path- ways of nuclear material may become complex as the experiences in nuclear reactor operation accumulate and the capabilities of plant operating personnel increase. This may translate into increase in inspection time for nuclear material verification. Such considerations are reflected in the creation of research projects, such as the U.S. Department of Energy Next Generation Safeguards Initiative Spent Fuel (NGSI-SF), conducted specifically for estab- lishing the baseline of future nuclear safeguards and non- destructive assay (NDA) detectors. The objective of nuclear safeguards is ‘‘timely detection of diversion of significant quantities of nuclear material and deter- rence of such diversion by the risk of early detection”, according to the IAEA (IAEA, 1972). To meet the requirements, spent fuel assemblies have to be verified before they are emplaced in a https://doi.org/10.1016/j.anucene.2020.107496 0306-4549/Ó 2020 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: msyim@kaist.ac.kr (M.-S. Yim). Annals of Nuclear Energy 144 (2020) 107496 Contents lists available at ScienceDirect Annals of Nuclear Energy journal homepage: www.elsevier.com/locate/anucene