Operating experience and design criteria of sodium valves

The development of valves for use in liquid metal systems was initiated about 18 years ago, when the UK embarked on its fast reactor programme. Initially the requirement was for a hand operated valve of about 1 in. nominal bore for rig applications and since none of the standard valves commercially available at that time were suited to this duty the development of a special valve was initiated by the UKAEA. With the initiation of construction of the Prototype Fast Reactor at Dounreay there arose a new requirement for a large number of small valves, covering the size range 1/4 in. to 6 in. nb., capable of automatic or manual operation, and manufactured to stringent quality standards appropriate to reactor duty. A special range of valves were developed for this duty by the English Electric Company. Applications have also been found for these valves in test rigs and non-nuclear process plant which involves the handling of liquid alkali metals. The only other requirements for valves of larger diameter than those mentioned above have also arisen from PFR. Large butterfly valves are fitted to the main secondary pipework in order to isolate the steam generators from the reactor plant in the event of a major sodium/water reaction. Stop and non-return valves are fitted to the discharge pipes of each of the main primary pumps. Large sleeve type valves are fitted to the primary side of the Intermediate Heat Exchangers. Satisfactory experience with the development of these valves allows future requirements for large valves to be tackled with confidence. (U.S.)