CANDU 3 - Single-Ended Refuelling

Abstract

The CANDU 3 fuel handling system is a version of the CANDU 6 and Pickering designs based on proven CANDU technology, updated with improvements resulting from on-going development and operating experience. The CANDU 3 design is based on the following requirements: Single-ended fuelling, one fuelling machine; The fuelling machine dedicated to one reactor unit; Applied proven CANDU technology; Competitive capital and operating cost and implementation. schedule One significant aspect of CANDU 3, to meet competitive cost targets is to adopt single-ended refuelling. Previous CANDU plants carry out refuelling by the coordinated operation of two fuelling machines, one accepting used fuel, the other inserting new fuel at opposite ends of a selected fuel channel. Single-ended fuelling permits refuelling with only one fuelling machine, at the downstream end of the fuel channel. This results directly in significant capital cost saving and indirectly to a smaller reactor building. With the previous CANDU 6 and Pickering systems, the upstream fuelling machine inserts new fuel bundles into the channel. In the central core high-flow channels, hydraulic drag on the fuel bundles is sufficient to move the fuel string along the channel. In the outer, low-flow channels, a flow-assist ram extension (FARE) tool, which is basically a free piston, is inserted by the upstream fuelling machine to create the required impedance to move the fuel string towards the downstream fuelling machine which accepts the used fuel. With single-ended refuelling, each upstream fuel channel end fitting is provided with a resident fuel pusher, which is basically a modified version of the FARE tool, to create the impedance required to move the fuel string. The fuel channels have balanced flow adjusted for equal enthalpy and all channels have a fuel pusher to provide the required impedance to move the fuel string downstream. The outlet end fitting is provided with a shield plug and a channel closure operable by the fuelling machine, as in the previous system, to achieve on-power refuelling. Magazine capacity is arranged to suit single-ended refuelling allowing the operation to be carried out during a single visit to a fuel channel. Adaptation of the existing Pickering fuelling machine head has been accomplished by incorporating modifications restricted mainly to the magazine rotor. This paper will describe single-ended refuelling and the equipment integral with the refuelling operation. Modifications from present CANDU reactors incorporated to expedite maintenance and operations associated with single-ended refuelling based on proven CANDU experience will also be discussed.