Mitsubishi Heavy Industries, Ltd. (MHI) has received an order for pressurizer nozzle spool piece replacement work on the Ringhals 3 reactor at the Ringhals Nuclear Power Plant in Sweden.

Pressurizer is a core component of pressurized water reactor (PWR) nuclear power plants, and the replacement work will enhance operating reliability through the use of more corrosion-resistant alloys in critical weld joints. The replacement work is scheduled for completion in 2016.

Ringhals Nuclear Power Plant is located 60 kilometers south of Gothenburg (Göteborg), Sweden’s second-largest industrial city. The plant consists of four reactors, of which three (Ringhals 2, 3 and 4) are PWR. Ringhals 3, a 1,069 MWe (megawatt electrical) PWR, went on-stream in 1981.

Under the terms of the order, MHI will perform technical justification, qualification tests, equipment manufacturing, material procurements and replacement work at the Ringhals site. As part of the replacement work, MHI will replace six nozzle weld, including the safety and relief valve lines. Joints in the new spool piece will be constructed of Alloy 690 material that ensures higher corrosion resistance in high-temperature and high-pressure environments than Alloy 600 material used in the current weld joints.

As nozzle spool piece replacement entails work in a narrow, enclosed workspace subject to high radiation doses, MHI will dispatch skilled engineers with extensive experience in working under such conditions. In MHI’s nuclear business, it will be the first such on-site replacement work to be performed in Europe.

Pressurizers are key components of PWR reactor coolant systems, and serve to maintain the pressure of reactor-related systems at constant levels. In recent years, many nuclear power plant operators in Japan, the U.S., and some European countries have begun to replace steam generators, reactor vessel heads, pressurizers, and other related components to reduce the risks associated with stress-corrosion cracking (SCC) of aging materials, and thereby enhance plant reliability and operational life. The replacement work at Ringhals 3 is in line with this trend.