Information Notice No.80-02 - 8X8R Water Rod Lower End Plug Wear
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
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.
Page Last Reviewed/Updated Thursday, March 25, 2021