Home > Electronic Reading Room > Document Collections > News Releases > 1998 > I-98-120

	NRC NEWS U. S. NUCLEAR REGULATORY COMMISSION OFFICE OF PUBLIC AFFAIRS, REGION I 475 Allendale Road, King of Prussia, Pa. 19406
	CONTACT:	Diane Screnci (610)337-5330/ e-mail: dps@nrc.gov Neil A. Sheehan (610)337-5331/e-mail: nas@nrc.gov

I-98-120

November 2, 1998

NRC STAFF AUTHORIZES POSTPONEMENT OF CORE SHROUD INSPECTION AT NINE MILE POINT 1 NUCLEAR POWER PLANT

Following a lengthy and detailed safety evaluation, the Nuclear Regulatory Commission staff has approved Niagara Mohawk Power Co.'s request to postpone an inspection of a reactor component, the core shroud, at the Nine Mile Point 1 nuclear power plant. Niagara Mohawk owns and operates the boiling-water reactor, located in Scriba, N.Y.

The core shroud is a large stainless-steel cylinder that surrounds the reactor core and controls the flow of water through it. Previous inspections of the component have revealed cracking at vertical welds. (Contributing to such cracking are operating time, coolant chemistry, carbon content, neutron flux, residual stress from welding and fabrication and operating stresses.)

Last February, Niagara Mohawk asked for permission to inspect the core shroud after 14,500 hours of hot operation (about 19 months) during the present operating cycle, rather than after 10,600 hours (about 14 months), its earlier commitment to the NRC. That extension would allow Nine Mile Point 1 to stay on-line through the end of its current operating cycle, until April 1999.

In a letter sent today to Niagara Mohawk, the NRC staff informed the utility it found the proposed extension to be acceptable, concluding there is reasonable assurance the plant can be safely operated during the extension because "the structural integrity of the vertical welds will be maintained with safety margin(s) specified by the ASME (American Society of Mechanical Engineers) Code." The agency's staff determined the crack growth rate estimated by Niagara Mohawk was appropriate, based on a review of metallurgical testing of two vertical weld samples, as well as on measurements and calculations performed by both the company and the NRC.

During its review of the request, the NRC conducted a public meeting in Oswego, N.Y., on September 24, to obtain comments on the request.

The company has agreed to provide the NRC with a proposed inspection plan for the core shroud at least three months before the next refueling outage. In addition, it has agreed to maintain the chemistry of reactor coolant so as to minimize the potential for cracking.