BR3/Vulcain Nuclear Power Station. Construction and Operational Experience

A full-scale reactor experiment was set out as the main objective of the Vulcain research and development programme agreed in May 1962 between the UKAEA and BelgoNucléaire, manager of ''Syndicat Vulcain''. Vulcain uses variable moderation as the long-term method to control reactivity: the reactor is cooled and moderated by a mixture of heavy and light water, the D2O content being stepwise reduced to permit power operation with all control rods completely out of the core. To carry out the Vulcain power experiment it was decided to modify the BR3 nuclear power plant located at Mol, Belgium, which had operated from 1962 to 1964 as a conventional PWR with outputs of 40.9 MW(th) and 11.45 MW(e). The BR3/Vulcain plant was started in December 1966 and since then is running with a load factor around 90%. It is the first time that such a reactor type has been built and operated and the experience gained by its design, construction, commissioning and operation has proven to be most valuable. D2O is being used at a pressure (2000 lb/in2 abs.) never before achieved in a heavy-water reactor and the leak rate from the HP primary systems to the atmosphere has been kept to a negligible value, around 1 to 2 grams/h. Commissioning of the primary plant had been carried out with light water first without fuel, and thereafter with fuel, at which time the water was poisoned with boric acid. The reactor vessel contains experimental devices such as 65 in-pile instrumentation detectors and four hydraulically operated Zircaloy control rods. They required the interposition of a collar between the vessel and its lid. Refuelling is performed under boronated light water, the interchange between the primary water and the H2O being carried out by means of a draining and spraying system. The reactor had been operated for two years before its modifications for Vulcain: many lessons have therefore been learned about working on irradiated systems. The BR3/Vulcain core has a power density of 41 MW(th)t U. The expected average fuel burnup and core life are 25 000 MWd/t U and 620 equivalent full-power days, respectively. These characteristics have been achieved without taking advantage of various improvements - such as the possibility of flattening the power distribution in the core by the use of two or more fuel enrichments - which are planned for more advanced Vulcain cores. The successful construction and operation of BR3/Vulcain will have demonstrated that components and techniques are available to build and operate simple, compact reactors in the small to medium power range, using long-life, high-power density cores and variable moderation. From the analyses carried out so far this concept competes well with other reactor concepts, while market surveys have indicated that there is a world market for small to medium power stations at prices within reach of those currently mentioned for the Vulcain design. (author)