United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 82-45: PWR Low Temperature Overpressure Protection

                                                            SSINS NO. 6835 
                                                            IN 82-45 

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

                             November 19, 1982 

Information Notice No. 82-45: PWR LOW TEMPERATURE OVERPRESSURE PROTECTION

Addressees: 

All pressurized water reactors (PWRs) holding an operating license (OL) or 
construction permit (CP). 

Purpose: 

This notice is to provide PWR licensees and construction permit holders with
pertinent information related to operation of the low temperature 
overpressure protection system. This information updates that presented in 
Information Notice No. 82-17 (June 10, 1982) and reflects the initial 
findings of NRC staff review of operating experience, Licensee Event 
Reports, and technical specifications related to low temperature 
overpressure protection. NRC staff review of this issue is continuing. 
Recipients of this information notice should review the information herein 
for applicability to their facilities. No specific action or response is 
required at this time. 

Description of Circumstances: 

In August of 1976, the issue of low temperature overpressure protection was 
raised and licensees initiated procedures and proposed systems to mitigate 
postulated overpressure events. The main concern was with the low 
temperature modes of cooldown and heatup, during which overpressurization 
could cause brittle fracture of the reactor vessel. In most cases, licenses 
proposed a manually enabled low pressure setpoint on the existing 
pressurizer power-operated relief valves (PORVs) supplemented by procedures 
and technical specifications. 

The low temperature overpressure events at Turkey Point Unit 4, on November 
28 and 29, 1981 have been designated by the Commission as abnormal 
occurrences. These events were described in Information Notice No. 82-17.
The events were caused by failure of the backup train of the low temperature
overpressure protection system (LtopS) because of inadequate surveillance 
and valve lineup procedures. Following the Turkey Point events, 
investigation of the contributing factors led to a review of the Turkey 
Point Unit 4 LtopS surveillance procedures which showed that the 
surveillance requirement did not include a test of the complete instrument 
channel. 

Staff review of LERs indicates that no overpressure events similar to those 
at Turkey Point have occurred at operating PWRs since 1978. However, events 
have occurred in which both trains of LtopS have been inoperable 
simultaneously, 


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                                                           IN 82-45  
                                                           November 19, 1982 
                                                           Page 2 of 3 

apparently from common cause factors. The following causes have each 
resulted in both LtopS trains being inoperable at the same time. 

1.   Operation with both PORVs isolated (block valves closed) because of 
     known PORV leakage. 

     On June 12 and again on June 18, 1981 at the Salem 2 plant, the PORV 
     block valves were closed because of leaking LtopS PORVs, thus rendering
     both, trains inoperable. Also, on December 12, 1978 at the Ft. Calhoun 
     plant, during plant heatup, a technician troubleshooting the failure of
     one train of LtopS pulled fuses which caused both PORVs to open. To 
     stop the discharge, both PORV block valves were closed, disabling the 
     LtopS. The PORVs were returned to service within 15 minutes. 

2.   Operator error during maintenance. 

     On May 21, 1981 at the Surry 2 plant, one train of LtopS was inoperable
     because of a wiring error while the isolation valve for the pressure 
     transmitter for the second train of LtopS was closed. Also, on May 6, 
     1980 at the Ginna plant, during post-installation test of the reactor 
     vessel head vent, DC power switches for both trains of LtopS were found
     in the off position. 

3.   Isolation and venting of instrument air to the PORV actuators during, 
     integrated leak rate testing. (ILRT) 

     On June 18, 1980 at the Zion 2 plant, the accumulators for both PORVs 
     were vented and the instrument air source was isolated, rendering both 
     trains of LtopS inoperable. To prevent recurrence, a procedure change 
     was made to block both PORVS open during the ILRT. Also, on May 27, 
     1980 at the Surry 2 plant the LtopS was inoperable due to ILRT. 

4.   Low nitrogen pressure to both PORV actuators. 
     
     On numerous occasions at North Anna 1 and 2, leakage in the backup 
     nitrogen supply to the PORVS degraded the nitrogen supply pressure and 
     rendered the LtopS inoperable. 

The events involving low nitrogen pressure were caused by excessive leakage,
from the pneumatic system coupled with a limited supply of bottled nitrogen.
Although, these events occurred in a LtopS where the backup air supply is 
bottled nitrogen, the events could have direct applicability to those 
systems which employ air accumulators to provide opening force for the PORVS 
in, case of loss of air. Because these air-operated systems are normally 
continuously supplied from the plant air compressors, even when in shutdown, 
the lack of effectiveness of the pneumatic system and the air accumulators 
may not be discovered unless the plant experiences a loss-of-air event or 
unless the normal air supply to the accumulators is deliberately interrupted 
to perform an operability check. In these cases, periodic inspection or 
surveillance may be needed to detect excessive leakage and to ensure 
operability of the backup pneumatic supply. 
.

                                                           IN 82-45 
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                                                           Page 3 of 3 

In addition to instances in which both LtopS trains were found to be 
inoperable, some LtopS may have been in a degraded condition as a result of 
failure to update the LtopS setpoints to correspond to changes in the 
Appendix G temperature pressure limits. This condition was found at both 
Kewaunee and Turkey Point. 

If you have any questions regarding these matters, please contact the 
administrator of the appropriate Regional Office or this office. 



                              Edward L. Jordan, Director 
                              Division of Engineering and  
                                Quality Assurance 
                              Office Inspection and Enforcement 

Technical Contact:  George F. Lanik, IE 
                    (301) 492-9636 

Attachment: 
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