UPDATE 2-PSEG shuts N.J. Salem 2 reactor

(Updates with company, NRC comment)

NEW YORK, May 13 (Reuters) - Public Service Enterprise Group Inc (PEG.N) shut the 1,130-megawatt Unit 2 at the Salem nuclear power station in New Jersey from 80 percent on May 12 due to an instrument problem related to the steam generator flow channels, a spokesman for the company said Tuesday.

He could not say when the unit would restart noting workers were still investigating the cause of the problem.

Electricity traders guessed it would return within a week.

At the time of the May 12 shutdown, the unit was increase power following a May 9 outage.

Operators manually shut the unit on May 9 from 47 percent due to high steam generator level.

At the time of the May 9 shutdown, the unit was increasing power after exiting a refueling outage earlier in the week.

It shut for refueling by March 12.

During the refuel, workers replaced the unit's four steam generators in addition to the usual refueling activities.

The unit last shut for refueling from Oct. 11-Nov. 1, 2006. It is on an 18-month refueling cycle.

A spokesman at the U.S. Nuclear Regulatory Commission said the plant was still in hot shutdown, which means it could restart somewhat quickly. The NRC spokesman however noted the federal agency does report on the timing of future reactor restart or shutdowns.

The NRC spokesman said the May 12 outage was the second "unplanned" shutdown in a few days and noted if the plant goes down again in a short period of time the unit could go from green to white in the shutdown performance category.

The NRC uses color-coded indicators to evaluate plant performance. The colors start with "green" and then increase to "white," "yellow" or "red," commensurate with the safety significance of the issues involved.

As the colors increase, the NRC, which is already sending a specialist to evaluate the plant, would increase inspections and oversight until the company addresses the problem.

The 3,403 MW Salem/Hope Creek station is located along the Delaware River in Salem about 40 miles south of Philadelphia. There are three reactors at the station, the 1,174 MW Salem 1, Salem 2 and the 1,061 MW Hope Creek, along with the 38 MW Salem 3 oil-fired turbine.

Salem 1 and 2 entered service in 1977 and 1981, and Hope Creek in 1986.