Design and use of an unattended measurement and surveillance station in the product store of a large reprocessing plant

摘要

Plutonium produced at a reprocessing plant in Sellafield is stored in a dedicated product store until it is moved for further use or longer term storage. The continuous production mode made it necessary to have a buffer store for produced Pu cans before their transfer, in campaigns, to a product store. These campaigns are performed with the presence of DG Energy inspectors and involve manual neutron and gamma measurements of the Pu cans before they are transferred to the main storage channels and placed under seal. The above mode of operation has resulted in a heavy manpower burden on the inspectorate, and restricted the flexibility and accessibility of the store to the operator. In order to increase efficiencies for all involved, an unattended combined measurement system (UCMS) together with associated containment and surveillance (C&S) was conceived, designed, constructed and installed. Close cooperation throughout the duration of the project between the three parties involved assured that the final product would satisfy the defined requirements. The installation was entrusted by DG Energy to Joint Research Centre, (JRC) with the support of Sellafield Ltd. The installed unattended C&S equipment monitors the passage of items at the entrance of the store with the possibility to categorize the exit/entry events (e.g. a Forklift Truck, a person or a trolley to transfer a PuO_2 can into the store) and to determine if nuclear material (NM) is involved. The UCMS is equipped with He-3 tubes, a CdZnTe gamma detector, a laser scan system, an optical camera and a balance. It performs neutron and gamma measurements, can identification and gross weight determination of PuO_2 cans upon their transfer from the production line into the store. Video surveillance of the buffer store is ensured by Power over Ethernet cameras. With the UCMS and C&S fully operational, the safeguards approach will allow the operator to transfer Pu cans without inspector presence. Inspectors will be able to identify all objects entering or leaving the store, and to correlate the observed movements with the ID, weight, and neutron and gamma data. Efficiencies could be further increased with the full use of the remote data transmission capability built into the system.