First Diablo Canyon vessel head completed

Tuesday, 21 July 2009

Babcock & Wilcox (B&W) has manufactured the replacement reactor vessel closure head for Unit 2 of Pacific Gas & Electric's (PG&E's) Diablo Canyon nuclear power plant in California.

 

Diablo Canyon, the best-looking nuclear power plant in the world? (Image: Jim Zimmerlin)

The closure head was produced at B&W's plant in Mount Vernon, Indiana, as part of a contract awarded to Areva NP by PG&E in August 2006. The contract included the manufacture, delivery and installation of the reactor vessel heads, control rod drive mechanisms, integrated head assemblies, and installation and disposal of used equipment for both Units 1 and 2 at Diablo Canyon. Both units are 1100 MWe, Westinghouse-designed four-Loop pressurized water reactors (PWRs). Unit 1 started up in 1985, while Unit 2 began operating in 1986.

 

Installation of the new closure head for Unit 2 is scheduled to begin during a routine maintenance outage this autumn. The manufacture of the vessel head for Unit 1 is expected to be completed during the first quarter of 2010 and it will be installed later that year.

 

The closure head is an integral part of the reactor vessel pressure boundary. The head provides access for the replacement of spent fuel and Alloy 600 penetration nozzles for control rod drive mechanisms and instrumentation. The closure head is typically made of low alloy steel and clad with stainless steel like the rest of the reactor vessel. Boric acid in the coolant water of PWRs can cause corrosion of vessel heads and recently many operators have decided to undertake replacements.

 

B&W began precise cladding, machining and welding work on the closure head after receiving the forged "blank" head from Japan Steel Works in October 2007. After adding the control rod drive housings, the entire assembly was placed in a protective cover and began its trip to Diablo Canyon. The closure heads are being provided to Areva NP to replace the existing closure heads at the plant.

 

B&W said that its Mount Vernon plant, which has obtained the American Society of Mechanical Engineers' (ASME's) N-Stamp quality accreditation, is the only plant in the USA that is certified to manufacture heavy pressure vessels for the nuclear industry.

 

Richard Reimels, president of B&W's nuclear power generation group, commented: "As anyone who is familiar with nuclear manufacturing in the US will tell you, this is an historic day for our industry domestically." He added, "For many years, the manufacturing of heavy vessels for the nuclear industry has been done outside of the United States."