The Dounreay Prototype Fast Reactor

The general layout of the reactor core and pressure vessel is shown in Fig. 11.3. Unlike the DFR, the reactor is of the pool type, the core and the primary circuit sodium pumps and heat exchangers all being submerged in liquid sodium within a stainless steel pressure vessel of diameter 12.2 m and depth 15.2 m. The pressure vessel is suspended by its periphery from the concrete roof structure. All the main components of the primary circuit are likewise suspended from the roof and all connections are routed through it. 

The layout of the coolant circuit and steam-raising plant has already been shown in Fig. 7.2. The intermediate heat exchangers are of the counterflow tube and shell type, with the primary sodium flowing through the tubes. Each pair of intermediate heat exchangers is connected to a secondary loop where the heat is transferred to one of the three 200-MW steam-raising plants, each of which includes reheater, evaporator, and superheater sections. All heat exchangers in the steam plant are vertically mounted shell and U-tube units. Steam at standard conditions of 538 C and 163 kg cm pressure is delivered to the turbine, which has a nominal output of 270 MW. 

For the initial fuel loading, the assemblies in the inner and outer regions of the core itself contained fuel having equivalent plutonium contents of 21 % 

The problems that have arisen at PFR have been almost exclusively on the conventional, or steam-raising, side of the plant. The sodium-to-water steam generators, which were deliberately chosen to be of a type that would be appropriate for a full-scale commercial reactor, developed small leaks due to stress corrosion of welds at the sodium-water interface. Techniques have been developed for locating and repairing the defective welds, and the steam generators have been redesigned so that the welds are above the cover plates, and thus removed from the sodium-water interface. As a further insurance, the tube material for a commercial plant can be changed from stainless to ferritic steel, at the cost of a reduction in the steam temperature obtainable. 

Radioactivity is induced in the liquid sodium passing through a fast reactor core as a result of neutron capture in Na. If the transit time of the coolant through 

---

Whilst 1994 had a sad start, particularly for fast reactors with the closure of the Dounreay Prototype Fast Reactor (PFR) the period since has seen many successes for the UK nuclear industry. The Utilities efforts have been rewarded with significant improvements in the operation efficiency of existing reactors and the UK s first Pressurised Water Reactor at Sizewell B achieved criticality on 31 January 1995. Good progress has also been achieved with a number of fuel cycle facilities which will make a major contribution to nuclear fuel recycle, ie ... 

Recent events in the energy field have emphasised the need for more thoughtful uses of energy and action on securing its transformation and its distribution. The fast breeder reactor has its natural, reasonable rate of development. The Dounreay prototype fast reactor has successfully ended its useful purpose in... 

---