Information Notice No. 82-13: Failures of General Electric Type HFA Relays
SSINS No.: 6835 IN 82-13 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 May 10, 1982 Information Notice No. 82-13: FAILURES OF GENERAL ELECTRIC TYPE HFA RELAYS Addressees: All holders of a nuclear power reactor operating license (OL) or construction permit (CP). Purpose: This inforation notice is provided as an early notification of a potentially significant problem pertaining to General Electric type HFA relays with LEXAN or NYLON coil spools in safety related systems. It is expected that addressees will review the information for applicability to their facilities. No specific action or response is required at this time. Description of Circumstances: NRC IE Inforation Notice 81-01, dated January 16, 1981, alerted licensees and holders of construction permits of LEXAN coil spool surface cracking. General Electric Service Inforation tetter (SIL) No. 44 Supplement 2 dated February 1981 directed to all boiling water reactor (BWR) owners and General Electric Service Advice PSM 152.1 dated April 28, 1976 directed to all General Electric ,(GE) customers advised them of the coil cracking problem and recommended replacing cracked LEXAN and NYLON coil spools with new Century Series "TEFZEL" coil spools or replacement of the entire relay with a HFA Century Series relay. Recently, in addition to the previously identified cracking problem, there have been several instances of melting of LEXAN and NYLON coil spool material. The licensee reports listed below are some reported instances, of melting in HFA relays: 1. Monticello - Northern States Power Company reported on November 6, 1981 that during cold shutdown, a GE type 12HFA 51A49F relay pertaining to primary containment isolation system logic circuit failed to open when deenergized. Follow-up investigation indicated that partial melting of the NYLON coil spool prevented the relay from moving to the deenergized position for several minutes after the coil was deenergized. Several switches in series with the relay coil circuit were burned-out and had to be replaced. 2. Millstone 1 - Northeast Nuclear Energy Company reported on February 24, 1982 that during a routine surveillance one GE type HFA relay associated with the containment isolation logic circuit stayed in the energized position when deenergized. As discussed below, melted LEXAN material 8202040146 . IN 82-13 May 10, 1982 Page 2 of 3 was found to be the cause. The relay deenergizes to cause main steam isolation valve closure on main steam ine high radiation. The logic requires one of two channels in each of two trip systems to deenergize and cause the isolation. The other three channels were operable, therefore, an actual high main streamline radiation level would have resulted in valve closure. 3. Brunswick 2 - Carolina Power & Light Company reported on February 4, 1982 that during the functional performance test of the primary containment isolation system main streamline high flow channel it was discovered that the main streamline high-flow channel "C" logic would not actuate. The details of this failure are somewhat different than the failures observed at Monticello and Millstone 1. In Brunswick 2, the armature apparently did move to the deenergized position. However, melted insulation from the relay coil of the actuation relay GE Model 12HFA 5lA49F had coated the relay contacts, preventing electrical contact. Like the Millstone 1 event, the remaining main streamline high flow channels "A", "B" and "D" were operable and would have initiated isolation upon an actual high flow condition. During earlier surveillance and coil replacement programs, testing did not identify a failure in the mechanism which would prevent the relay contacts from opening. Subsequent evaluation of the Millstone l relay by GE Power Systems Management Business Department in Philadelphia, led to the following analysis: A piece of the spool flange fell into the gap between the open armature and pole face. When the relay was energized the armature attempted to close but was prevented from sealing against the pole face due to the piece of spool flange in the air gap. At this point, the contacts could have been just touching. This created a fixed air gap in the magnetic circuit. The increase in the current caused by an air gap produced an excessive temperature rise in the coil. This excessive temperature rise, thru conduction and convection to the armature assembly and shading ring and eventually the piece of spool flange caused the loose piece of spool flange and remaining spool flange to soften, melt and move. As the piece of spool flange in the gap melted, the air gap closed permitting the normally open contacts to fully close. In addition, the closure of the gap reduced the current to normal. This reduction in current caused a lower temperature and melted LEXAN then hardened and created a bond between the armature and the pole face. Thus, when the coil was deenergized the return spring force was not enough to break this bond. Subsequent testing of the coil shows that the coil is in normal operating condition (no shorted turns). Although the examples cited above relate to BWRs, the. GE type HFA relays are also commonly used in the safety system logic circuits of pressurized water reactors (PWRs). The above information identifies means whereby the function of a major safety-related system can be jeopardized or compromised by relay malfunctions. GE has notified its BWR and PWR customers of its findings and has reiterated the need for periodic visual inspections. In addition, GE has also amplified its earlier recommendations. In the event that cracked spools or evidence of overheating is observed, GE recommends that either the entire . IN 82-13 May 10, 1982 Page 3 of 3 relay be replaced with a HFA Century Series relay or that the LEXAN or NYLON 1 coil spool be replaced with Century Series TEFZEL coil spools. If you have any questions regarding this matter, please contact the Regional Administrator of the appropriate NRC Regional Office, or this office. Sincerely, Edward L. Jordan, Director Division of Engineering and Quality Assurance Office of Inspection and Enforcement Technical Contact: W. Laudan 301-492-4766 Attachment: Recently Issued IE Information Notices
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021