Information Notice No. 86-37: Degradation of Station Batteries

                                                           SSINS No:  6835 
                                                           IN 86-37        

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, DC 20555

                                May 16, 1986

Information Notice No. NO 86-37:   DEGRADATION OF STATION BATTERIES 

Addressees: 

All nuclear power reactor facilities holding an operating license (OL) or a 
construction permit (CP) 

Purpose: 

This notice is provided to alert recipients to a significant problem 
occurring in station batteries It is expected that recipients will review 
this information for applicability to their facilities and consideration, if
appropriate, to preclude a similar problem occurring at their facilities 
However, suggestions contained in this notice do not constitute NRC 
requirements; therefore, no specific action or written response is required

Description of Circumstances: 

While shut down, recent inspections at the Rancho Seco Nuclear Power Plant 
revealed substantial degradation of all station batteries The batteries 
exhibited flaking of the cell plates and flaking of the plate's hook area 
where the plates connect to the cell posts Although the licensee performed 
visual inspections that included examination of the electrolyte level and 
accumulation of sediment in the bottom of the cell, the severe flaking went 
unnoticed The deteriorated cells were of the Plante design and over 15 
years old The batteries were expected to last about 20 years and an 
inspection by the battery vendor l year earlier did not reveal abnormal 
degradation Subsequent NRC inspections related to the cell-to-cell spacing 
and cell-to-rack spacing also revealed that the batteries were not installed 
in accordance with the battery vendor's seismic qualification 
recommendations As a result of the flaking, the battery vendor advised the 
licensee that the batteries at Rancho Seco should be replaced and the 
licensee is now in the process of replacing the batteries 

On April 16, 1986, North Anna Unit 2 declared three out of four station 
batteries inoperable The specific gravities in the pilot cells of the 
affected batteries were found below the technical specification limit In 
two of the batteries, approximately half of the cells had specific gravities 
that were out of specification The cause was attributed to the inadequate 
float voltage These three batteries had recently been replaced with a 
different make and model that required a different float voltage The 
corrective action included readjusting the float voltage and applying an 
equalizing charge to the batteries 



                                                            IN 86-37      
                                                            May 16, 1986  
                                                            Page 2 of 2   

Discussion: 

Although the batteries at Rancho Seco passed a duty cycle discharge test, 
this has little relevance to the ability of the batteries to survive a 
seismic event which could cause mechanical failure of internal connections 
weakened by flaking The NRC has sponsored a series of tests of the seismic 
response of naturally aged nuclear station safety-related batteries One of 
these tests concluded that while case cracks were propagated and leaks were 
observed in the propagation tests at high g-levels, it appears that this 
failure mechanism is less significant than failures of the interface between
the bus-bar and post (See NUREG/CR-3923, SAND84-1737, "Test Series 1: 
Seismic-Fragility Tests of Naturally-Aged Class 1E Gould NCX-2250 Battery 
Cells") Although the type of cells in this test were different than those 
that experienced severe flaking at Rancho Seco, the test results suggest the
importance of examining the internal connection between the plates, the 
bus-bar, and post 

The event at North Anna demonstrates the need for continuing attention to 
the detailed requirements for station batteries 

Other IE information notices on problems related to batteries include: 

Number    Title                                        Date of Issuance 

85-74     Station Battery Problems                     August 29, 1985 
84-83     Various Battery Problems                     November 19, 1984
83-11     Possible Seismic Vulnerability of Old Lead   March 14, 1983 
          Storage Batteries 

No specific action or written response is required by this information 
notice If you have any questions about this matter, please contact the 
Regional Administrator of the appropriate regional office or this office 


                                   Edward L Jordan, Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  Eric W Weiss, IE 
                    (301) 492-9005 

Attachment:    List of Recently Issued IE Information Notices