Mitsubishi Heavy Industries, Ltd. (MHI) said Tuesday it had completed replacement work on a pressurized water reactor (PWR) pressurizer nozzle spool piece for Unit 3 at the Ringhals Nuclear Power Plant in Sweden. The work completed involved over 100 engineers working in shifts day and night for 45 days, said MHI in a statement.
The work at the Unit-3 reactor has improved reliability by replacing the nozzle welds with an alloy of higher corrosion resistance. The project was MHI's first large-scale on-site replacement work for nuclear power generation in Europe.
MHI was also contracted to perform technical assessment, verification tests, equipment manufacture, material procurement and replacement work at the Ringhals site. Over a period of approximately two months, while Unit-3 was stopped for planned outages, MHI raised the high-temperature and pressure corrosion resistance of six nozzle welds of the pressurizer (height 12m, diameter 2.4m) through the replacement of the Alloy 600 nickel material with high chrome content Alloy 690 nickel material.
The pressurizer, which is installed in the primary PWR cooling equipment, is an important component that maintains the reactor system at a constant pressure. In order to comply with Swedish standards, and to ensure absolute safety on site, MHI conducted preliminary investigations and training over a period of around two years, including a demonstration using a full-scale mock-up. This allowed MHI to implement the complex welding work in the space-constricted, highly-radioactive environment.
"MHI has performed very complicated work in a difficult environment in the reactor building,” said Roland Gabrielsson, the Ringhals AB project manager. “The work has been completed to the highest quality, on schedule and in a safe manner. Further, co-operation with MHI representatives has been excellent throughout the delivery process," he said.
"We came up with tailored solutions, in circumstances that are different to Japan, and completed a high quality job on time, working with the customer as one team. This project gives us great confidence going ahead,” said MHI project manager Jun Takahara.
The Ringhals Nuclear Power Plant is located approximately 60 km south of Goteborg, Sweden's second largest city. Unit-3 has an output of 1,034 MW and began operations in 1981.
Ringhals AB is an affiliate of Vattenfall AB, Sweden's public energy company. MHI has previously delivered replacement reactor vessel closure heads (RRVCHs) and replacement control rod drive mechanisms (CRDM) to Ringhals. The order reflects MHI's outstanding experience in numerous replacement works of pressurizer nozzle spool piece replacement at PWRs in Japan, as well as its outstanding technological expertise and track record for quality and reliability in work performed on Ringhals projects in the past.