United States Nuclear Regulatory Commission - Protecting People and the Environment

REGION IV  MORNING REPORT     PAGE  2                    MARCH 27, 1995

Licensee/Facility:                     Notification:

Houston Lighting & Power Co.           MR Number: 4-95-0039
South Texas 1                          Date: 03/27/95
Wadsworth,Texas                        Resident Inspector                 
Dockets: 50-498

Reportable Event Number: N/A


South Texas Project is a two-unit site, with three safety trains per     
unit.  All six SDGs are 20-cylinder Cooper Bessemer diesels.             
During scheduled inspections of the SDGs during the current Unit 1       
refueling outage, the licensee found indications of tin transfer on some 
of the pistons of Diesels 12 and 13.  The licensee inspected all 20 of   
the pistons and liners, with the following results:                      
SDG 12:  Five pistons rejected for indications of tin transfer:  two     
advanced, two intermediate, and one beginning stages.  Three cylinder    
liners were also rejected.                                               
SDG 13:  One piston and its associated liner were rejected based on      
indications of late stages of intermediate tin transfer.  Two other      
pistons were rejected for tin separation (considered a manufacturing     
defect).  One piston was rejected for indications of piston pin seizure. 
The root cause for the piston pin seizure is being evaluated.            
A lubricating oil modification is being installed on both of these       
generators, which involves removing the lower piston ring and lower oil  
ring seal.  This modification has been shown to be successful in         
preventing tin transfer.  After installation on these two diesels, this  
modification will have been installed on three of South Texas' SDGs.  The
third is Unit 2 SDG 22, which had a failed piston due to advanced tin    
transfer last year.  The licensee plans to install the modification on   
the other three EDGs on a case-by-case basis when piston removal/        
inspections are performed.                                               

Regional Action:

For information only.                                                    

Contact:  David Loveless             (512)972-2507
          Ryan Lantz                 (817)860-8104

Page Last Reviewed/Updated Monday, January 27, 2020