Information Notice No. 83-11: Possible Seismic Vulnerability of Old Lead Storage Batteries
SSINS NO.: 6835 IN 83-11 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 March 14, 1983 Information Notice No. 83-11: POSSIBLE SEISMIC VULNERABILITY OF OLD LEAD STORAGE BATTERIES Addresses: All nuclear power plant facilities holding an operating license (OL) or construction permit (CP). Purpose: This information nctice informs you that lead-acid storage batteries approaching their end of operational life may be vulnerable to seismically induced failure. Description of Circumstances: A series of events involving spontaneous battery failure or degradation over the past few years, not related to seismic events, has caused concern in the NRC staff regarding the potential vulnerability of old batteries to a seismic event. In each of several events, spontaneoUs battery failure or degradation has been attributed to swollen positive plates and/or cracked cases. Even for those plants that have seismically qualified batteries, the batteries are rarely qualified by prototype testing of aged cells. Consequently, a pattern is developing of spontaneous failure of old batteries that suggests a seismic event could cause a common-mode failure of the plant DC systems. One such example occurred at the Haddam Neck plant on September 19, 1982. While in Mode 2 (startup) the emergency DC Battery Bank B, cell 42, was discovered to be leaking eletrolyte through a seam crack. Further inspection revealed eleven other cells with casing cracks, that did not extend through the wall. If cell 42 were jumpered out, battery bank voltage would have been 125.3 V DC, only just above the technical specification limit of 125 V DC. Consequently, the licensee decided to declare the Battery Bank B inoperable and completely replace it. The occurrence on September 19, 1982, was preceded by a similar instance on June 18, 1982, when Battery Bank B, cell 23, was discovered leaking and was jumpered out. After removing Battery Bank B, some of the failed cells were sent to the manufacturer for a determination of the failure mechanism. The original "B" train battery that failed was composed of Gould FTA-15 cells each with a rated capacity of 840 ampere-hours. The "A" train battery was 8212060378 . IN 83-11 March 14, 1983 Page 2 of 3 composed of Gould FTA-17 designed cells with a rated capacity of 960 ampere- hours. Haddam Neck obtained Gould NCX-1500 cell from Calvert Cliffs as a temporary replacement for "B" battery. Haddam Neck is purchasing Gould NCX-1200 cells as a permanent replacement for the "B" battery. The FTA design has not been manufactured by Gould for more than ten years. The FTA cells used at Haddam Neck comprised the original battery and were therefore about 15 years old at the time of their failure. (Operating license date is June 30, 1967.) Other examples of cells failing because of swollen positive plates or cracked cases have been identified. An Licensee Event Report (LER) search revealed six other instances of battery case cracking. LER# Plant Date(s) Battery Manufacturer 81-5 Diablo Canyon (10/81) C & D, Div. of ELTRA 82-16, 82-7 Indian Point 2 (4/82) and (2/82) Not described 81-42 Browns Ferry (7/81) C & D, Div. of ELTRA 77-55 FitzPatrick (9/77) Gould 74-5 Turkey Point 4 (10/74) Not described Although it is impossible to tell in every instance from the LER alone what precisely caused each failure, 5 of these LER's bear some similarity to the Haddam Neck battery failure. The battery failure at Diablo Canyon is attributed to a design flaw of the battery case and is not similar to the Haddam Neck failure. Like the Gould FTA batteries at Haddam Neck, most batteries now used in nuclear power plants are not qualified to withstand a seismic event at their end-of-life condition. Even those batteries that are qualified in accordance with Regulatory Guide 1.100 "Seismic Qualification of Electric Equipment for Nuclear Power" are not necessarily brought to their end-of-life condition prior tb seismic testing. Regulatory Guide 1.100 endorses IEEE Std. 344 "Recommended Practices for Seismic Qualification of Class IE Equipment for Nuclear Power Generating Stations." At the end-of-life condition, the battery plates are more vulnerable because they are brittle. Also material can slough off the plates, shorting out the battery, or reducing its capacity. Discussion: Surveillance tests required by technical specifications will detect a degradation in a battery's ability to deliver it's rated charge but will not detect those degradations of a battery's structure making it vulnerable to even a mild seismic event. The structure of a battery is weakened as it becomes old because the positive plates crack ahd swell or because of a wide variety of other failure mechanisms. Usually, degradation of the positive plate is the limiting factor in the life . IN 83-11 March 14, 1983 Page 3 of 3 of a properly maintained battery. As the positive plate becomes more cracked and embrittled it becomes less able to resist seismic motion and to retain its mechanical integrity. For this reason the NRC staff suspects that the useful electrical life of a large lead storage battery may be longer than its seismic-qualified life. The NRC staff does not yet know of any definitive surveillance test for identifying incipient seismic vulnerability of an old battery other than seismic testing of selected cells. Batteries not maintained at proper float voltage, stored or used at high temperatures, or subject to improper maintenance may undergo accelerated aging processes reducing the life of the battery and increasing its seismic vulnerability. The Institute of Electrical and Electronics Engineers has published IEEE Std. 535-1979, "IEEE Standard for Qualification of Class 1E Lead Storage Batteries for Nuclear Power Generating Stations." This standard requires, as part of a qualification process, bringing a prototype cell to its end-of-life condition prior to seismic testing. Battery cells qualified in accordance with IEEE Std. 535 will have a qualified life reflecting the increased seismic vulnerability of old batteries. Although no seismically induced battery failure has occurred to date, the serious consequences of such a failure are worthy of concern. Several postulated examples follow: A seismic event might accelerate cracking of the case resulting in loss of electrolyte and complete loss of the battery. A seismic event might cause accelerated cracking of embrittled plates or loss of lead-dioxide coating of plates resulting in substantial drop in battery capclcity almost instantly. A complete loss of the DC system would put the plant in a unanalyzed condition. The NRC staff is considering research that will define the seriousness of agerelated seismic vulnerability of lead storage batteries. Further regulatory guidance on the issues raised in this information notice may be forthcoming. No written response to this information notice is required. If you need other information regarding this matter, please contact the Regional Administrator of the appropriate NRC Regional Office. Edward L Jordan, Director Division of Emergency Preparedness and Engineering Response Office of Inspection and Enforcement Technical Contact: Eric Weiss, IE (301) 492-4973 Attachment: List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021