The Republic of Korea has recently initiated design work for an integral reactor to be used for power generation and sea water desalination. The design dates from mid 1994 and the schedule points to construction around 2005. The primary vessel is contained in an outer safeguard vessel, half-filled with water, and is designed to the same pressure as the primary. Residual heat removal in emergency is through the vessel wall to the water in the safeguard vessel and from there, by heat pipe to a cooler outside the containment. The internal pressurizer uses nitrogen gas for pressurization, with pressure driven sprays and no heaters. The heat exchanger is a once through helical one, giving 30 C super heated steam There is a steam injector to drive a containment spray system. A new control rod drive mechanism(CRDM) is under development, giving finer movement than the previous Korean magnetic jack type The fuel elements are hexagonal An extensive research and development programme is envisaged

3 6 Japan

Development work at the Japanese Atomic Energy Research Institute (JAERI) has concentrated on maintenance and cost estimates of the Marine Reactor-X (MRX). This is a compact system with forced circulation of the primary, in-vessel control rods and a water filled containment, cooled by a natural circulation system The water filled containment eliminates the need for a secondary heavy shield, giving weight advantages even over a diesel system when the weight of fossil fuel to cross the Pacific Ocean is taken into account With a fleet of 20 ships, such a nuclear powered ship was

shown to be economically better compared with a diesel powered ship. The suggested mode for maintenance and refueling (every four years) is to lift out the entire core with its containment and to replace it with another one. The estimated time for this operation is three weeks. The same principle would be used for decommissioning, in an appropriate facility.