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Information Notice No. 95-21: Unexpected Degradation of Lead Storage Batteries
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555-0001 April 20, 1995 NRC INFORMATION NOTICE 95-21: UNEXPECTED DEGRADATION OF LEAD STORAGE BATTERIES Addressees All holders of operating licenses or construction permits for nuclear power reactors. Purpose The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert addressees to possible degradation of lead storage batteries within the first two years of service. It is expected that recipients will review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems. However, suggestions contained in this information notice are not NRC requirements; therefore, no specific action or written response is required. Discription of Circumstances Palo Verde Arizona Public Service Company (APS, the licensee) installed AT&T round cell batteries at Palo Verde, after continued problems with the originally installed batteries. During a 1994 maintenance outage at Palo Verde Unit 2 the licensee tested performance on the AT&T batteries which were less than two years old. The capacities of the batteries were lower than expected; the capacities had decreased instead of increasing. Train B (Battery Banks B and D) had been declared inoperable on October 1, 1994, because the measured capacity was slightly less than 90 percent capacity. On October 7, 1994, Train A (Battery Banks A and C) was declared inoperable because a projection of the capacity test results indicated that the battery capacities would be below 90 percent. The Palo Verde Technical Specifications acceptance criterion for the AT&T battery capacity is at least 90 percent of the manufacturer's rating when subjected to a performance discharge test. Oconee Unit 2 Replacement Exide batteries of the standard lead calcium cells (rectangular) were installed less than two years ago. In testing batteries 2CA and 2CB, certain cells were found to have capacities lower than expected. 9504140211. IN 95-21 April 20, 1995 Page 2 of 3 At Oconee Unit 2, Battery 2CB was tested on January 4, 1995. The test indicated that the overall capacity of the battery was only 77 percent. Battery 2CA was tested on January 12, 1995, and its overall capacity was about 80 percent. The Oconee design commitments require that the battery capacity should exceed 80 percent. The two batteries were installed in January 1993, and the testing took place within two years of installation. Discussion IEEE Standard 450-1987, "IEEE Recommended Practice for Maintenance, Testing and Replacement of Vented Lead-Acid Batteries for Stationary Applications," recommends that a performance test of the battery capacity should be made within the first two years of service. It is typically expected that battery capacity will not decrease in that period and, in fact, it often shows a slight increase. Although the designs differ, in both cases the batteries indicated a significant decrease in capacity, and a decrease is not consistent with the normal behavior expected for either of these batteries. Both licensees are taking steps to rectify the degradation in the batteries by replacing the defective cells or entire battery banks. In addition, they are attempting to find the root cause of the abnormal degradation. At Palo Verde, the licensee determined that adequate margin existed between the projected battery capacities and worst case design loading. With respect to the AT&T batteries, APS maintains that the root cause of the drop in capacity in the Unit 2 cells likely involves contamination and an inadequate curing process because of an increase in production rate during the time the Palo Verde Unit 2 cells were manufactured. These problems apparently did not exist when the Palo Verde Unit 1 and 3 cells were manufactured. After the licensee noted the degradation of the Unit 2 batteries, spare cells in Units 1 and 3 were found to have no decrease in expected capacity. In addition, the licensee has learned that the AT&T cells used as the Class 1E dc sources in McGuire and Byron/Braidwood nuclear plants were also not manufactured in this time of very high production. Although not as significant as the capacity loss noted above, APS and AT&T have found additional cells that show some of the same tendency toward early loss of capacity. This may be due to existing variations occurring in the materials selection and manufacturing process. To minimize the effect on final battery capacity, APS and AT&T developed a specific dedication process to be used during the manufacture acceptance testing phase to identify and reject cells that show early loss of capacity. AT&T and APS also believe that some of the drop in capacity in the Palo Verde Unit 2 cells, as well as the unexpected drop seen during the dedication testing of the new cells purchased for replacement, is due to the additional testing which has involved a number of discharge and recharge cycles in a relatively short period of time. . IN 95-21 April 20, 1995 Page 3 of 3 APS has replaced the Unit 2 battery cells with new AT&T cells that have undergone factory testing for at least two discharge/recharge cycles, that still show substantially greater capacity than is needed for the design basis Palo Verde Unit 2 loading, and that meet the specific dedication criteria developed by APS and AT&T. The licensee is also studying the influence of the recharging methodology on battery performance. AT&T and APS plan an extensive test program to establish the cause of the unexpected capacity decrease in the replacement cells. Exide is still in the process of establishing the root cause for the degradation at Oconee. This information notice requires no specific action or written response. If you have any questions about the information in this notice, please contact one of the technical contacts listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager. /S/'D BY BKGRIMES Brian K. Grimes, Director Division of Project Support Office of Nuclear Reactor Regulation Technical contacts: S. N. Saba, NRR (301) 415-2781 Thomas Koshy, NRR (301) 415-1176 Attachment: List of Recently Issued NRC Information Notices.
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