The upcoming disposal of spent nuclear fuel in Finland creates new challenges for nuclear safeguards. Part of the national safeguards concept for geological repositories, developed by STUK — Radiation and Nuclear Safety Authority, is non-destructive assay (NDA) verification of all fuel items before disposal. The proposed verification system is a combination of PGET (Passive Gamma Emission Tomography), PNAR (Passive Neutron Albedo Reactivity) and weight measuring NDA-instruments. PGET takes a pin-level image of the fission products inside of a fuel assembly and PNAR verifies the multiplication of the assembly, a quantity that correlates with the fissile content. PGET is approved by IAEA (International Atomic Energy Agency) for safeguards measurements, but the feasibility of PNAR has not yet been established. A first of its kind PNAR prototype instrument was built in a collaboration coordinated by STUK. This paper concludes the results of the first measurements of spent BWR (Boiling Water Reactor) nuclear fuel with the prototype in July 2019. Based on the measurements, the ability of the PNAR instrument to detect the presence of fissile material in a repeatable manner in a reasonable amount of time was demonstrated. Furthermore, the instrument was able to detect differences in multiplication between partially and fully spent fuel assemblies, and axial differences in multiplication within a single assembly.

芬兰即将弃置的乏核燃料处置给核保障提出了新的挑战。由STUK（辐射与核安全局）制定的国家地质处置库保障构想的一部分，是在处置之前对所有燃料进行无损检测（NDA）验证。拟议的验证系统是PGET（被动伽马发射断层扫描），PNAR（被动中子反照率反应性）和称重NDA仪器的组合。PGET对燃料组件内部的裂变产物进行销平图像处理，而PNAR验证组件的倍增，该数量与易裂变含量相关。PGET已由IAEA（国际原子能机构）批准用于保障措施的测量，但PNAR的可行性尚未确定。在STUK的协作下，制造了第一台此类PNAR原型仪器。本文总结了2019年7月用该原型进行的乏水BWR（沸水堆）核燃料的首次测量结果。基于这些测量，PNAR仪器能够以可重复的方式以可重复的方式检测裂变材料的存在的能力。证明了合理的时间量。此外，该仪器能够检测部分和完全用尽的燃料组件之间的倍增差异，以及单个组件内的轴向倍增差异。证明了PNAR仪器能够在合理的时间内以可重复的方式检测易裂变物质的存在的能力。此外，该仪器能够检测部分和完全用尽的燃料组件之间的倍增差异，以及单个组件内的轴向倍增差异。证明了PNAR仪器能够在合理的时间内以可重复的方式检测易裂变物质的存在的能力。此外，该仪器能够检测部分和完全用尽的燃料组件之间的倍增差异，以及单个组件内的轴向倍增差异。