UPDATE 3-FirstEnergy to restart Pa. Beaver Vly 2 reactor soon

(Updates with NRC comments)

NEW YORK Nov 24 (Reuters) - FirstEnergy Corp (FE.N) planned to start restarting the 846-megawatt Unit 2 at the Beaver Valley nuclear power station in Pennsylvania later Tuesday, a spokesman for the plant said.

The unit shut for refueling and maintenance by Oct. 12.

On Nov. 24, the company declared an unusual even, the lowest of the U.S. Nuclear Regulatory Commission's four emergency classifications, due to unidentified leakage greater than 25 gallons per minute in the reactor coolant system.

Beaver Valley has two trains of shutdown cooling used when the plant is in an outage to keep the reactor fuel covered with water.

When operators were preparing the unit for restart, a spokesman at the NRC said, a cross connect valve between the two trains opened, allowing pressure from one train to affect the other.

That caused a relief valve to open on the suction of one of the residual heat removal pumps, allowing coolant from the reactor cooling system to flow into a pressurizer relief tank.

It was open for about nine minutes, the NRC spokesman said, and about 800 gallons of water flowed into the tank before operators isolated the train and restored things to normal.

The NRC is looking into why the valve opened but does not have a problem with FirstEnergy trying to restart the unit again later Tuesday so long as they fixed and understand what cause the earlier problem, the NRC spokesman said.

The unit last shut for refueling from about April 14 to May 27, 2008. It is on an 18-month refueling cycle. (Reporting by Scott DiSavino; Editing by Lisa Shumaker) ((scott.disavino@thomsonreuters.com; +1 646 223 6072; Reuters Messaging: scott.disavino.reuters.com@reuters.net)) ((For help: Click "Contact Us" in your desk top, click here [HELP] or call 1-800-738-8377 for Reuters Products and +1-888-463-3383 for Thomson products; For client training: training.americas@thomsonreuters.com; +1 646-223-5546))