* GE says problem could occur under limited conditions
* NRC says problem not an "immediate" safety issue
* Boiling-water design similar to GE reactors at Fukushima
By Jim Brumm
WILMINGTON, NC Sept 30 (Reuters) - GE Hitachi Nuclear Energy has warned operators of boiling water reactors (BWR) worldwide -- including 35 in the U.S. -- that the plants could fail to shut automatically during an earthquake, potentially risking the safety of the power plant.
In an event notification posted by the Nuclear Regulatory Commission this week, GE Hitachi told nuclear operators to conduct tests to determine what conditions would prevent the reactors from shutting safely during an earth quake.
GE Hitachi Nuclear Energy is a venture between General Electric Co (GE.N) and Hitachi Limited (6501.T).
GE Hitachi spokesman Michael Tetuan said most nuclear plants could fix the problem by replacing fuel channels, if needed. A typical boiling water reactor has between 400 and 800 such channels.
The affected plants are of the same GE design as Japan's Fukushima reactors which were crippled by an earthquake and tsunami in March.
GE said the probability of a reactor not shutting properly is very low. Because of the limited circumstances under which a unit might not shut automatically, NRC spokesman Scott Burnell said the issue "is not an immediate safety issue."
He said GE's notice is information the agency wants nuclear vendors to raise so that companies can respond.
Affected by the potential glitch are type 2-5 BWRs designed by General Electric and built between the late 1960s and the early 1990s.
In the U.S., 12 of those nuclear units are owned by Exelon Corp (EXC.N); five by Entergy Corp (ETR.N); and three by the Tennessee Valley Authority.
Other affected plants are owned by Constellation Energy Group CEG.N, Progress Energy (PGN.N), Southern Co (SO.N), NextEra Energy (NEE.N), DTE Energy (DTE.N), Public Service Enterprise Group (PEG.N), PPL Inc (PPL.N), Xcel Energy (XEL.N), Energy Northwest and the Nebraska Public Power District.
GE Hitachi identified the problem in July 2010 and reported to the NRC last September, months before an earthquake-spawned tsunami crippled GE reactors in Japan.
U.S. reactors included are Nine Mile Point Units 1 and 2; Fermi 2; Columbia; FitzPatrick; Pilgrim; Vermont Yankee; Grand Gulf; River Bend; Clinton; Oyster Creek; Dresden 2 and 3; LaSalle 1 and 2; Limerick 1 and 2; Peach Bottom 2 and 3; Quad Cities 1 and 2; Perry; Duane Arnold; Cooper; Monticello; Brunswick 1 and 2; Hope Creek; Hatch 1 and 2; and Browns Ferry 1, 2 and 3.
"We've proactively identified a very unique set of conditions in which a plant rarely operates where this is a concern," Tetuan said. "With the guidance provided to our customers, they will be able to monitor potentially affected fuel channels and avoid a safety concern."
Tetuan said the company also notified operators of BWRs located elsewhere.
The World Nuclear Association (WNA) website lists 53 BWRs outside the U.S., including 29 operating in Taiwan, Sweden, the Netherlands, Mexico, Japan, Italy, Germany and Finland.
The seven operating Japanese BWRs include Fukushima Daiichi 5 and 6 which were shut when the March earthquake hit.
GE Hitachi told the NRC the problem does not affect BWR/6 or ABWR - advanced boiling water reactor plants. (Additional reporting by Eileen O'Grady in Houston; Editing by Bob Burgdorfer)