Unattended Neutron-Based NDA Systems

The plutonium canister assay system (PCAS) determines the content of plutonium in MOX and pure oxide powders in cans contained in a specific transport container (four cans per canister) (Menlove et al. 1986). The system can be integrated into an operator s material handling system and continuous measurement cycles are performed, which are evaluated at the end of a given collection period. Thereby, continuous verification of the flow of canisters can be performed without inspectorate intervention. For inventory verification, an inspector provides an electronic list of canisters to be verified and the operator transfers the selected 

The MOX fuel assembly capsule assay system (FAAS) determines plutonium content in the final assembly contained in a storage capsule. Coupled to the automated capsule transfer system, it provides information about the movements of fuel into and out of the product storage (Menlove et al. 1993). It is designed to assay the complete active zone of the assembly with plutonium loadings up to 10 kg and can accommodate 5 m long capsules that contain the fuel assemblies. The unshielded detector body has 12 He tubes and an efficiency of 16%. In addition, the continuous mode gives a time history of movements of neutron source material in the vicinity. The FAAS is augmented with a surveillance system to meet verification requirements. 

The vitrified waste canister assay system (VCAS) is intended to determine the residual uranium and plutonium content in canisters of vitrified high-level spent-ffiel reprocessing waste prior to the termination of safeguards on this material. It consists of five neutron detectors (two fission chambers, two U chambers and a bare chamber sensitive to thermal neutrons) and one gamma detector (ionization chamber, meant to authenticate the presence of gamma radiation). In contrast to the VWCC, the VCAS uses fission chambers 

The entrance gate monitor (ENGM) is a passive neutron coincidence collar detector permanently installed at the entrance to the fresh fuel transfer route of a fast breeder reactor (Hashimoto et al. 1994 Iwamoto et al. 1997). The detector head has four groups of He with six tubes each. Fresh fuel assemblies entering the reactor facility must pass through the ENGM so that their Pu content can be verified. Therefore, the ENGM is the system that verifies the amount of fresh fissile fuel in an assembly and serves as the first detector in a sequence of detector systems that follow the movement of fuel assemblies within the reactor facility. 

The EVRM has the same detection features as the CCRM. It controls the flow of assemblies to and from the core. 

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