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Information Notice No.80-02 - 8X8R Water Rod Lower End Plug Wear
SSINS: 6870 Accession No: 7912190654 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 January 25, 1980 Information Notice No. 80-02 8X8R WATER ROD LOWER END PLUG WEAR On October 3, 1979, Vermont Yankee-Nuclear Power Corporation (VY or Licensee) reported (LER-79 25/IP) observance of lower end plug wear on the water rods of 8X8R demonstration fuel assemblies. These observations were obtained during refueling outage inspections. Subsequent to the initial LER, the Licensee issued LER 79-25/IT on October 17, 1979, which provided more detailed descriptions of the cause and corrective action associated with this event. The lower end plug wear was isolated to the water rods of the 8X8R fuel assemblies. The cause of the wear was attributed to flow excitation of the water rods by coolant cross flow within the lower tie plate flow volume. The repetitive contact of the Zircaloy lower end plug with the stainless steel lower tie plate, resulted in preferential wear of the softer Zircaloy end plug. No significant wear was observed in the lower tie plate. To provide in-reactor experience on the modification proposed to mitigate lower end plug wear, the Licensee will include four modified 8X8R fuel bundles in their upcoming cycle of operations. The primary modification consists of using two capture water rods with shorter lower end plugs to eliminate the flow-induced excitation. Two of these fuel assemblies were previously irradiated. The staff was informed that VY plans to perform surveillance on these four modified bundles at the next refueling outage. The surveillance will confirm the efficacy of the modifications and the currently estimated rate of wear. Based on evaluation of the lower end plug wear rates, and the absence of any indicated rotational movement of the water rods with worn lower end plugs, General Electric Company (GE) and the Licensee have concluded that no additional corrective action is warranted at this time. To support this conclusion, on December 11, 1979, VY and GE presented detailed status of their evaluations and analyses of this condition to the NRC staff. As a result of the information provided in the December 11, 1979 meeting, the staff agreed with the conclusion that no additional corrective action is warranted at this time. The staff requested that GE document and formally submit proprietary, and nonproprietary versions of their evaluations and analysis. In addition, the staff requested the Licensee to submit a supplement to the earlier LER's considering the potential for loose parts. . Information Notice No. 80-02 January 25, 1980 Page 2 of 2 To provide additional confirmatory evidence supporting the findings by GE and the Licensee, GE will develop a surveillance program specifically addressed at inspections for wear of the lower end plugs. When this program is developed, GE will propose the program to the NRC staff. BWR Licensees are encouraged to participate in a surveillance program on this matter. This Information Notice is provided as an early notification of a possibly significant matter that is still under review by the NRC staff. It is expected that recipients will review the information for possible applicability to their facilities. No specific action or response is requested at this time. If you have any questions regarding this matter please contact the Director of the appropriate NRC Regional Office.
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