JASON

the following is an account of a visit to the Royal Naval College Nuclear reactor by a party from GLIAS in 1989

On Tuesday 14th November 1989 a small party of members of the GLIAS Recording Group visited the Royal Naval College, Greenwich, SE10, to see the nuclear reactor Jason. The design of this reactor was developed by Hawker Siddeley from the American Argonaut reactor which first operated in 1957. After running for two years at Hawker Siddeley Jason was bought by the Admiralty and transported to Greenwich where it first ran on 6th November 1962. . ,
Jason is a ten kilowatt, water moderated and cooler graphite reflected, thermal reactor using eighty per cent enriched uranium-aluminium plate fuel elements separated by graphite wedges. Two rows of fuel elements mounted in a ninety degree sector of an annulus formed by two concentric aluminium core tanks make up a single slab core with 'a critical mass of about 2 kilograms of Uranium 235. There are four independent control mechanisms; safety, coarse and fine cadmium control rods and a moderator dump, fail-safe and each capable of shutting down the reactor.
Three flux measuring instrumentation channels ensure coverage by at least two channels throughout the power range. More independent power limit instrumentation is provided by two shutdown amplifiers and there are three radiation monitors which measure levels close to each of the main experimental areas. The fail safe magnetic logic of the safety and interlock circuits makes certain that the correct sequence of operations is followed during the start of operation. Automatic shut down commences should the likelihood of dangerous conditions arise. The reactor is inherently safe owing to the large negative void and temperature coefficients of reactivity. For removable experiments administrative control limits the reactivity available to half a per cent.
The reactor is uses by students taking nuclear courses and is a versatile critical facility. A high neutron and gamma flux environment enables many aspects of operation and control to be demonstrated and training in health and safety procedures is given. Research is carried out by staff and long term students and the reactor’s facilities are also used by outside organisations.
A pneumatic transfer system enables up to three 0.6 ml samples to be irradiates for a given time and recovered to a properly lined lead cell within 3 5 seconds. Supporting services include extensive and well equipped electronic and mechanical workshops, and extensive computing, and simulating facilities. There is a fully equipped radiological protection service.
During our visit safety arrangements were stressed and each member of the party was provided with appropriate protective clothing, including; white cotton shoe covers, and we were obliged to wash afterwards. . Visually one sees a pile of: concrete blocks and the interest is in the control arrangements. Jason is probably the only nuclear reactor housed in a buildin, dating fron 1699. The walls are about six feet thick. As the power output is small the fuel elements installed when Jason went to Greenwich are still viable so there are no problems of transporting nuclear waste. Only about one gramme of Uranium 235 has been consumed in twenty seven years of operation. We are particularly grateful to. Professor J. Head for permitting the visit, and Mr. C. Proust who acted as our host.
Bob Carr (GLIAS Newsletter 127)