GE Hitachi has discovered unexpected cracking and material distortion in some of the companies' control-rod blades, according to a report made public Wednesday by the Nuclear Regulatory Commission.

GE Hitachi reported to the NRC that the problems could present a safety hazard, and the design life of the companies' Marathon Blades may be reduced. Malfunction of control rods can limit operators' ability to control the nuclear reaction within a reactor.

"A recent inspection of near 'end-of-life' Marathon Control Rod Blades (CRB) at an international BWR/6 has revealed crack indications. The CRB assemblies in question were manufactured in 1997. GE Hitachi Nuclear Energy (GEH) continues to investigate the cause(s) of the crack indications. Once the cause of the crack indications is determined, GEH will evaluate the nuclear and mechanical lifetime limits of the Marathon Control Rod Blade design in light of the new inspection data and make revised lifetime recommendations, if necessary," read a report to NRC. In communications with the agency, GE Hitachi indicated the cracks appeared in blades with D and S lattice configurations during inspections last year.

NRC spokesman Neil Sheehan told the Associated Press that signs of blades cracking would include elevated levels of boron and tritium in water used to cool the reactor. "As long as there is no significant increase in boron or tritium observed, the recommendation would be continue operation until the end of the operating cycle," Sheehan said in an e-mail to the news agency.
In a statement issued by GE Hitachi after the NRC disclosed the problem, chief engineer Jim Klapproth  wrote "customers with affected control blades can avoid the safety concern by monitoring the water chemistry of their plants and replacing affected blades prior to the end of the revised service life."

Communication with NRC indicated the following reactors use Marathon D-lattice and S-lattice blades that may be affected:
Nine Mile Point, Unit 1 (N.Y.); Fitzpatrick (N.Y.); Millstone, Unit 1 (Conn.); Pilgrim (Mass.); Vermont Yankee (Vt.); Grand Gulf (Miss.); River Bend (La.); Clinton (Ill.); Oyster Creek (N.J.); Dresden 2 and 3 (Ill.); Peach Bottom 2 and 3 (Penn.); Quad Cities 1 and 2 (Ill.); Perry 1 (Ohio); Duane Arnold (Iowa); Cooper (Neb.); Monticello (Minn.); Brunswick 1 and 2 (N.C.); Hatch 1 and 2; Browns Ferry 1, 2 and 3 (Ala.).