Information Notice No. 84-47: Environmental Qualification Tests of Electrical Terminal Blocks
SSINS NO: 6835 IN 84-47 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 June 15, 1984 Information Notice No. NO 84-47: ENVIRONMENTAL QUALIFICATION TESTS OF ELECTRICAL TERMINAL BLOCKS Addressees: All nuclear power reactor facilities holding an operating license (OL) or construction permit (CP). This information notice is being issued to provide licensees and construction permit holders with information pertaining to the results of a recent NRC-sponsored environmental qualification methodology research test conducted on electrical terminal blocks. This information notice also serves as an early notification regarding the reduction of insulation resistance values sustained by certain terminal blocks used in a Conax Electrical Penetration Assembly during a design basis event simulation test. It is expected that recipients will review the information for applicability to their facilities. No specific action or response notice is required. Description of Circumstances: 1. Additional information on NRC-sponsored test on terminal blocks In 1981, the NRC sponsored a research test on-terminal blocks to investigate the insulator deterioration of the terminal blocks under accident conditions. This test was conducted at the Sandia National Laboratories (SNL) in Albuquerque, New Mexico. The test results of this earlier test program were published in Information Notice No. 82-03. The results then indicated that the performance of the terminal blocks was questionable, however, the results were inconclusive because there were several areas where test conditions deviated from the actually installed conditions. Recently, in order to quantify the performance of realistically installed and protected terminal blocks in a LOCA environment, SNL tested 24 more terminal blocks of different models from four selected manufacturers. Previous testing data on the terminal blocks indicated that neither the accelerated aging process nor the seismic testing will significantly affect terminal block performance; therefore aging and seismic simulation was not incorporated in the later SNL test. Terminal blocks were tested in the "as received" condition to simulate normal handling during installation. Additionally, no special care was taken during test preparation to prevent the deposit of fingerprints or other contaminants on the terminal block surfaces. 8406130315 . IN 84-47 June 15, 1984 Page 2 of 4 Test terminal blocks were installed inside NEMA-4 electrical enclosures with 1/4" diameter weep holes in the bottom. Cables entered the boxes from the side through "liquid tight" conduit. To simulate cables entering through conduit from a cable tray system, the conduit was terminated inside the test chamber and the conduit end was not sealed. The test was divided into two phases; each phase was tested under temperature profiles closely following the PWR temperature profile as described in Appendix A of IEEE 323-1974. Phase I consisted of an 11-day exposure to a steam-only environment, and Phase II consisted of approximately one day of simultaneous steam/chemical spray followed by a 5-day exposure to a steam environment. Saturated steam conditions were maintained throughout both test phases. Details of the test and test connections are being documented in NUREG/CR-3418 which will soon be published by the NRC. The terminal blocks were powered at voltages typical of in-plant applications: 4 V dc typical of RTD circuits, 45 V dc typical of instrumentation circuits, and 125 V dc typical of control circuits. The terminal-to-terminal leakage currents were monitored during both Phase I and Phase II tests, and the terminal-to-ground leakage currents were monitored during the Phase II tests only. The SNL test provides the following significant results: (1) the surface moisture film formed during the test reduced insulation resistance to 10-2 to 10-5 ohms from initial values of 10-8 to 10-10 ohms; the reduction in insulation resistance occurred during the steam exposure portion of the LOCA simulation, (2) at 45 V dc, leakage currents were on the order of 0.1 to 10 mA, (3) at 4 V dc, insulation resistance was at 5 x 10-3 to 7 x 10-4 ohms, and (4) one open failure was observed when leakage currents continued to increase for a 90-minute period to values which caused a 12-AWG wire to separate from the terminal point of the terminal block. The separation occurred at the terminal block - wire junction of a 125 V dc circuit. 2. Low insulation resistance resulted during qualification testing of terminal blocks used in low voltage instrumentation/control (I/C) electrical penetration assembly (EPA) In a Part 50.55(e) Potential Reportable Deficiency Report, the Arizona Public Service Company (APS) has recently reported to the NRC that during the review of a qualification test report on terminal blocks used in low-voltage (I/C) EPA supplied by CONAX Corporation, APS has observed that insulation resistance (IR) values between terminal points of the terminal blocks were substantially reduced during simulation of design basis events. APS concluded that the low-level signals (up to a maximum 48 V dc and 4-20 mA range) cannot tolerate this low IR condition. This . IN 84-47 June 15, 1984 Page 3 of 4 condition could result in erroneous response in the sensing and control functions, which in turn might jeopardize reliable plant operation during accident conditions. APS reported that the test terminal blocks were made by Kulka Electric Corporation and that during an investigative test, the terminal blocks also failed the "as-installed conditions" test in transmitter and RTD circuits. APS further indicated that Raychem splices are under consideration as replacement for the terminal blocks for transmitter and RTD circuit applications at the Palo Verde units. Discussion: This information notice highlights a potential concern that may exist when terminal blocks are exposed to a steam environment. The results of the SNL test show that a moisture film will form on the surface of the terminal block during the simulation of the LOCA/MSLB events, and will result in the reduction of insulation resistance between terminal points and ground, and thus will allow some leakage currents to flow to ground. Based on the review of the SNL test and the review of other qualification test reports on terminal blocks, the NRC staff recognizes that leakage currents do exist during LOCA/MSLB simulations and that the leakage currents may be of significance in some applications. Although no written response to this notice is required, it is suggested that licensees and construction permit holders 1) review their facilities to determine if terminal blocks are used in low-voltage applications, such as in transmitter and RTD circuits, and 2) review terminal block qualification documents to ensure that the functional requirements and associated loop accuracy of circuits utilizing terminal block will not degrade to an unacceptable level due to the flow of leakage currents that might occur during design basis events. Instances where fuses were used to monitor leakage currents, and where failure criteria were based on the failure of these fuses (1 ampere or less) do not provide information about leakage currents of magnitude that are less than the fuse rating. Data provided under these instances are not considered to be acceptable data. The NRC staff considers this review to be part of the on-going activities that the licensees are currently undertaking to resolve other environmental qualification deficiencies to meet the deadline and requirements set forth in the EQ final rule, 10 CFR 50.49. When supporting data for leakage currents are not substantiated during this review, one of the following possible corrective actions should be considered: 1) Perform a valid qualification test of the installed terminal blocks with provision for the continuous monitoring of leakage currents throughout the test, and perform analysis to demonstrate that acceptable loop accuracy and associated response time for instrument circuit utilizing terminal block are being maintained throughout various operating conditions. . IN 84-47 June 15, 1984 Page 4 of 4 2) Obtain documentation from valid qualification tests already performed with substantiated data for leakage currents, and perform appropriate analysis as stated in 1) above. 3) Replace the installed terminal blocks with qualified splices. In addition to the concern of leakage currents being addressed in this notice, licensees and construction permit holders are reminded that other information concerning on-going preventive maintenance activities that involve periodic inspection of terminations and terminal blocks for cleanliness as described in the previously published information notice No. 82-03 remains in effect. 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: R. G. LaGrange, NRR (301) 492-8208 N. B. Le, IE (301) 492-9673 Attachment: List of Recently Issued Information Notices
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021