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.