Design of the primary containment for pool and loop arrangements of LMFBRs

Abstract

LMFBR prototypes use different technical concepts for the primary system: France and the UK are constructing pool-type reactors, the US and DEBENELUX have selected loop-type reactors. Obviously, the relationship between the technical concept and the possibilities of limiting the consequences of a hypothetical whole-core accident is a widely discussed question. Three modes of loading phenomena are considered: (1) the transient pressures due to expansion of a vaporized fuel; (2) the transient pressures given by a coherent sodium-fuel interaction; and (3) the ‘equilibrium’ pressure given by transferring the excess heat in the fuel to an amount of sodium which produces the highest possible quasi steady-state pressure in the system. The structural response of the pool and loop systems are studied with respect to salient modes (2) and (3). Axial forces during the accident have to be transferred via the plug and core support to the reactor vessel support. The technical solutions depend on the primary system concept. The given structures can be supplemented by special devices to protect the cover and the vessel against excessive loads. To a first approximation, such safeguards are independent of the technical concept. Post-accident heat removal is accomplished for commercial plants preferably by in-vessel solutions. The expenditure for in-vessel solutions depends more on the singularities of a given design than on the particular design concept. The intermediate (primary/secondary sodium) heat exchanger is a critical component of the containment system. The coupling between the source of the accident and the intermediate heat exchanger is different in both systems. Pool and loop systems are both adequate in limiting the consequences of an unprevented nuclear excursion of a reasonable size. Advantages and disadvantages are well-balanced for both systems.