Information Notice No. 84-48: Failures of Rockwell International Globe Valves
SSINS No.: 6835 IN 84-48 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 June 18, 1984 Information Notice No. NO- 84-48: FAILURES OF ROCKWELL INTERNATIONAL GLOBE VALVES Addressees: All nuclear power reactor facilities holding an operating, license (OL) or a construction permit (CP). Purpose: The intent of this information notice is to alert licensees of a potential deficiency in the design, application, or maintenance of Rockwell International globe valves that may have safety and/or economic significance at nuclear power facilities. These deficiencies have resulted in two types of failures: (1) the stem separating from the disk and (2) the disk being backed off its disk nut (see Attachment 1). Although no specific action or response is required, recipients are expected to review the information contained in this notice for applicability to their facilities and initiate any needed diagnostic, preventive, or corrective action. Likewise, licensees finding similar or related defects at their facilities are encouraged to report their findings to the Commission, including the corrective actions taken, so that the industry may benefit from their experience. However, suggestions contained in this information notice do not constitute NRC requirements and, therefore, no specific action or written response is required. Background: The discovery of these failures is attributed to what appeared to be a completely unrelated event described in Information Notice No. 83-65, "Surveillance of Flow in RTD Bypass Loops Used in Westinghouse Plants" (dated October 7, 1983) and the sharing of information by two utilities. Information Notice 83-65 was issued because of a low-flow condition in a reactor coolant loop RTD bypass line that occurred at Salem Unit 1. The manner by which this apparently unrelated event led to the discovery of the described globe valve failures is described below. Description of Circumstances: On January 29, 1983, during routine shutdown operations, a low-flow alarm was received from a reactor coolant loop RTD bypass line at Salem Unit 1. Investigation of the event led to the assumption that corrosion products were restricting flow in the bypass line. This event was reported in Licensee Event 8406180353 . IN 84-48 June 18, 1984 Page 2 of 3 Report (LER) 83-007/31 which in turn resulted in the NRC issuing IE Information Notice 83-65. Because no previous surveillance requirements existed, the information notice recommended that the flow sensors be calibrated on a refueling outage basis and that the alarm set point be verified on a monthly basis. As a result of the above cited notice, Salem received information from Kewaunee, through the Westinghouse site representative, informing them of a similar reduced flow problem experienced at Kewaunee. The Kewaunee problem was caused by a stem-to-disk separation of a bypass line isolation valve. The valve disk had fallen, resulting in restriction of RTD bypass loop flow. Given the right conditions, the valve disk could lift and flow would be reestablished such that the failure could easily be mistaken for an obstruction caused by crud. (It should be noted that these failures can occur and be undetected during operation.) Although the January 1983 occurrence of reduced flow was the only one of its kind experienced at either of the Salem units, Salem decided to radiograph all RTD bypass line valves in all reactor coolant loops of both units during their next refueling outages. During a January 1984 outage, the Unit 2 RTD bypass line valves were radiographed. Five valves in each of the four bypass lines were radiographed indicating that 2 of the 20 valves had disks that had separated from the stems. Because of a large flow margin, these valves were not replaced; however, to assure that flow blockage has not occurred, the licensee has increased the frequency of flow surveillance. Salem attributes the separation of the stem from the disk to the force exerted on the joint when the valve is backseated. Accordingly, Salem has advised their operators to use caution while backseating these types of valves. During the April, 1984 refueling outage, the Unit 1 RTD bypass line valves were radiographed, and 11 of the 20 valves were found with their disks separated from the stems. All 20 RTD bypass line valves in Unit 1 were replaced. Because of the generic implications associated with the failures of Rockwell International globe valves, Salem undertook to examine a sample of similar valves used in critical systems. On or about May 25, 1984, similar valves used as throttle valves in the high pressure safety injection subsystem of the emergency core cooling system on Unit 1 were radiographed. The unit was in a refueling outage at the time and 1 of the 12 throttle valves was found with its disk backed off the disk nut. As a result of this discovery, Salem also radiographed the Unit 2 throttle valves while the plant was operating at 100% power. On May 30, 1984, two of these valves were found with the disks backed off the disk nut. Because proper flow through these valves could not be ensured, the valves were declared inoperable. Consequently, the plant was placed in an action statement that required the valves to be operable or to be in a hot shutdown mode within 6 hours. These throttle valves are 1-1/2 inch Rockwell International globe valves and are set during surveillance testing once per 18 months to ensure that flow from the boron injection tank is properly distributed to each of the four cold legs during safety injection. The licensee has removed, replaced and inspected the 3 throttle valves having disks that had backed off their disk nut. The inspection revealed that in each case the lock weld attaching the disk to the disk nut was missing and that a portion . IN 84-48 June 18, 1984 Page 3 of 3 of the lower disk guide was broken off in the same location relative to the lock weld holding the disk. Consequently, the licensee believes that the disk became partially unthreaded from the disk nut during those periods when the valves are closed for flow blocking purposes during shutdown and then opened. To assure proper positioning of the disks, the licensee plans to radiograph the valves after any valve movement. No action or written response to this notice is required. If you have any questions regarding this matter, please contact the Regional Administrator of the appropriate NRC regional office or this office. Edward L. Jordan Director Division of Emergency Preparedness and Engineering Response Office of Inspection and Enforcement Technical Contact: I. Villalva (301) 492-9635 R. Kiessel (301) 492-8119 Attachments: 1. Cross-section, Rockwell Globe Valve 2. List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021