Orders for MHI

(MHI) has received two separate orders from electricity companies in the

for the supply of four replacement reactor vessel closure heads (RRVCHs), a key component of a pressurised water reactor (PWR) nuclear power plant (NPP).

Of the four RRVCHs, two are being supplied under a subcontract from Westinghouse Electric Company for Unit 1 and 2 at the South Texas Project Electric Generating Station (STP) of STP Nuclear Operating Company (STPNOC).

The other two units are a direct contract with Southern California Edison (SCE) for Unit 2 and 3 at the San Onofre Nuclear Generating Station (SONGS).

All units are to be installed as replacements for existing units to allow continued operation of the plants. The delivery of RRVCH will commence in 2009 and last through to 2012, with one unit being shipped every year.

The RRVCHs on order are made of low-alloy steel, have a diameter of approximately five meters and weigh approximately 75 tons. They will be manufactured at MHI's Kobe Shipyard and Machinery Works. Fifty seven stainless-steel control rod drive mechanisms (CDRMs) will be mounted on each STP RRCVH, and the overall structure will measure approximately 10 metres in height.

CRDMs are devices that play a key role in the safe and stable operation of nuclear power plants. They enable control of thermal output from the reactor by precisely inserting the control rods into the reactor core during regular operation. In the event of a system malfunction, CRDMs promptly insert the control rods into the reactor core to achieve emergency shutdown.