Dounreay fast reactor

The Dounreay site was established as the site of the UK Fast Breeder Nuclear programme in 1955 and became operational in 1958. It accommodated three reactors, the Materials Test Reactor, (DMTR, 1958-1969), the Dounreay Fast Reactor (DFR, 1959-1977) and the Prototype Fast Reactor (PFR, 1974-1994). With all reactor operations now finished and the reactors already de-fuelled the site is undergoing active decommissioning which is planned to be completed by 2032. The Dounreay site has been cited by UKAEA as being the second biggest nuclear decommissioning challenge in the UK with similar liabilities to those at Sellafield but with smaller waste volumes. 

The philosophy of Dounreay fast reactor (DFR), (full power 60 MWth/15MWe, sodium-potassium coolant) was to have the experimental part of the system only inside the reactor vessel, and in the outside zone every effort was to be made to minimize the risk of breakdown of the cooling system. This explains the unusual feature of 24 coolant loops, which results in a size of pumps and heat exchanger where experience had been accumulated in previous experimental work. 

I was initially appointed as a junior engineer in the operations department, looking after final preparation of new fuel before loading to the reactor. A first impression was that all the staff seemed old. When I started work at Dounreay I was 24, and most of the rest of the staff at PFR seaned to be over 40. PFR had been operating since 1974, and its construction had begun in me late 1960s. In addition, many of the staff had been transferred to PFR when me old Dounreay Fast Reactor had closed. Hence most of me staff had been at Dounreay for a long time and mere had not been many recent new recruits. 

Plate 1.13 DFR. Dounreay Fast Reactor. The photo provided by SSEB Scotland 1988... 

As an initial experimental stage in this programme, a decision was made in 1954 to build the 60MW(th), 15MW(e) Dounreay Fast Reactor (DFR), which subsequently operated from 1959 to 1977. The information and experience gained from DFR provided the necessary confidence that a commercial-sized fast reactor could be successfully built and operated. However, because a large increase in size between DFR and a commercial plant was necessary, the need for an intermediate plant incorporating the major steps in concept and scale was identified. 

In addition a study of clad carburization was carried out on different cladding materials after the irradiation of sodium-bonded pins in the Rapsodie and Dounreay fast reactors at bum-ups ranging from 2.6 to 12.5at.% and linear powers between 80 and lOOkW/m. The following conclusion was drawn ... 

The condition of the brazed-on wear pads after irradiations in NRX and Halden has been excellent. Pig. 16. The braze metal fillet has a grey appearance and undergoes a little more corrosion than the can, but the actual penetration Is very small. The H concentration in the wear pad is up to 50 greater than in the can, presumably because of the lower temperature. Specimens having brazed wear pads attached have been irradiated In the Dounreay Fast Reactor (DFR) to total neutron doses of 2.5x10 without any noticeable effects on micro-structure. Mechanical tests on similar samples are being carried out. 

The problem becomes much more acute in a fast reactor, where there is no moderator to slow down the neutrons. This means the core is far smaller, and megawatts of heat may be generated in very small volumes. In these reactors, liquid metals are the only viable option — the Dounreay Fast Reactor used sodium-potassium alloy and the Prototype Fast Reactor used liquid sodium. 

The experimental fast breeder reactor was considered to be something of a potential hazard, and a remote site was needed in case of accident As mentioned above, the site chosen was Dounreay, on the northern coast of Caithness, in the Scottish Highlands. Two fast reactors would be built there one which would be known as the Dounreay fast reactor (DFR), and the other being the prototype fast reactor (PFR). In a sense the DFR was the prototype the second reactor was intended as a prototype for a commercial fast reactor which never materialised. 

Figure 3.8. The iconic dome of the Dounreay Fast Reactor, designed to contain any radiation in the case of an accident with the reactor. (Image courtesy of NDA and copyright NDA.)...

Figure 7.3. A cutaway view of the Dounreay fast reactor (DFR).

The liquid metal-cooled option would require a very great deal of development and would probably have been an over-ambitious choice for a British submarine reactor (the Dounreay fast reactor, which was liquid metal cooled, first went critical in November 1959). The United States Navy s second nuclear submarine, USS Seawolf, which was launched in July 1955 and commissioned in March 1957, used a liquid sodium cooled reactor. It was not regarded as a success, and was only operational for a short period before being replaced by a PWR, which would then become standard in the United States Navy. Harwell was also taking some interest in a PWR at this time, with plans to build a prototype to be named LEO. It thus made sense for the Admiralty to work in parallel with Harwell on a water-cooled reactor. 

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