United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 87-40: Backseating Valves Routinely to Prevent Packing Leakage

                                                 SSINS No.:  6835
                                                   IN 87-40

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                      OFFICE OF NUCLEAR REACTOR REGULATION
                             WASHINGTON, D.C.  20555

                                 August 31, 1987


Information Notice No. 87-40:  BACKSEATING VALVES ROUTINELY TO 
                                   PREVENT PACKING LEAKAGE


Addressees:

All nuclear power reactor facilities holding an operating license or a con-
struction permit. 

Purpose:

This information notice is provided to alert recipients to potentially sig-
nificant safety problems that could be caused by backseating valves routinely 
to prevent packing leakage.  It is expected that recipients will review the 
information for applicability to their facilities and consider actions, if 
appropriate, to preclude a similar problem.  However, suggestions contained in 
this notice do not constitute NRC requirements; therefore, no specific action 
or written response is required.

Description of Circumstances:

On June 12, 1987, Virginia Electric and Power Company reported (Licensee Event 
Report [LER] 87-011-00) that on May 16, 1987, a low flow reactor trip occurred 
at its Surry Power Station, Unit 1.  The cause of the low flow was the failure 
of the stem of the A hot leg loop stop valve.  The stem failure permitted the 
disk to drop and partially block flow in the A loop.  The licensee is 
performing a detailed metallurgical examination to determine the failure mode 
and mechanism of the valve stem.  The preliminary report indicated that 
failure was due to stress or fatigue.

Before this event, the licensee had routinely backseated the loop stop valves 
as part of its Containment Checklist Procedure before startup.  In accordance 
with this procedure, the valves were manually torqued onto their backseats to 
1/16-inch deflection while the unit was in cold shutdown.  This value was 
reverified when the unit reached a hot shutdown condition.  To reduce the 
stress on the valve stem, the licensee is revising the operating procedure so 
that the valves are normally operated off the backseat.

A similar event had occurred with the B hot leg loop stop valve on December 1, 
1973.  This failure was evaluated by Westinghouse, and a failure report, 
"Surry Unit No. 1 Reactor Coolant Isolation Valve Stem Failure Report," was 
issued on March 7, 1974.  In the report, the failure mechanism was identified 
as a high 



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strain, low-cycle failure with little deformation.  The high strain was at-
tributed to the licensee's practice of routinely electrically backseating the 
valves on torque during plant startup.  In this method, the valve's motor 
operator is used to drive the valve open until the forces resulting from the 
disk pressing against the backseat are high enough to cause the open torque 
switch to open.  This practice caused the valve stem to be subjected to high 
stresses each time the valve was opened.  Depending on the gearing within the 
motor operator, these stresses may have remained until the valve was closed 
during the next plant shutdown.

The report recommended that the valves not be electrically backseated on 
torque.  It further recommended that if backseating became necessary during 
maintenance, it should be done manually by the use of the handwheel with 
minimum applied load and without exceeding the compensating spring pack 
deflection specified in the manufacturer's revised instruction manual.  This 
manual, "Instruction Manual Motor Operated Reactor Coolant 30" Loop Stop 
Valves for Reactor Coolant System Westinghouse WNES 546-CAK-70497B Darling 
Valve S.O.  E-5004," states in a caution that manual backseating is 
permissible only if the open deflector indicator reading does not exceed 
1/16-inch maximum and that manual backseating may be used only when the 
packing needs replacement.  As noted above, contrary to this recommendation, 
it had been the licensee's recent policy to routinely manually backseat these 
valves during plant startup.

Before the 1973 valve stem failure, it had been the licensee's practice to 
routinely electrically backseat the valves during plant startup.  Although 
Virginia Electric and Power Company had stopped this practice in 1974, the NRC 
staff is aware that other licensees routinely electrically backseat valves.  
The most common reason for this is to stop valve leakage from around the stem 
on valves that are not readily accessible during plant operations.

The following inspection reports reflect current practices and problems 
related to electrical backseating.  

(1)  NRC Inspection Report 50-321/85-34 provides the results of an inspection 
     at Edwin I. Hatch Nuclear Plant, Unit 1, performed between November 10 
     and December 20, 1985.  In the report, the inspectors noted observing 
     information tags that indicated that the reactor core isolation cooling 
     (RCIC) system inboard steam line isolation and the reactor water cleanup 
     (RWCU) system inboard isolation valves had been electrically backseated.  
     The operating personnel indicated that they were not aware that any 
     testing had been done to verify that the valves would close within the 
     required time limits.  A violation was issued when subsequent testing of 
     the RWCU valve demonstrated that it could not close within the required 
     time limits.  Additional testing of the RWCU valve showed that it did 
     meet the closure time limits when it was not starting from a backseated 
     condition.

     NRC Inspection Report 50-321/86-22 and 50-366/86-22 provides the results 
     of an inspection performed at Hatch Units 1 and 2 between July 28 and 
     August 1, 1986.  In the report, the inspectors noted that the licensee 
     routinely electrically backseated containment isolation valves in the 
     high pressure coolant injection, RCIC, RWCU, and recirculating pump 
     systems.  
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                                                            Page 3 of 4


     Review of maintenance records indicated that the valves had been electri-
     cally backseated as many as 18 times during the previous 2 years.  The 
     procedure used by the licensee to electrically backseat the valves con-
     sisted of bypassing the open limit switch and then driving the valve disk 
     onto the backseat until the locked motor current of the motor was ap-
     proached.

(2)  NRC Inspection Report 50-277/86-25 provides the results of an inspection 
     at Peach Bottom Atomic Power Station, Unit 2, performed between December 
     8 and 19, 1986.  In the report, the inspectors noted the licensee's 
     practice of electrically backseating valves suspected of having excessive 
     packing leakage.  The procedure used by the licensee involved an operator 
     manually closing the motor contacts at the motor control center.  The 
     contacts were held closed until the operator noticed an increase in the 
     motor current shown on a clamp-on amp meter.

Discussion:

General Electric Company's Service Information Letter (SIL) 385 issued 
November 1982 discusses potential valve damage and provides recommendations 
for motor-operated valves that are normally backseated or are subjected to 
excessive backseating torque.  This describes the types of damage that could 
be the result of backseating as valve stem failure, valve stem elongation, 
backseat damage, cracking of the stem nut, and other related component 
distress.  It also notes that most damage progresses slowly to the point where 
valve operability is uncertain or valve failure occurs, before the damage is 
apparent.  Among the recommendations were:

(1)  identification of the valves that are normally backseated or that may 
     have had excessive backseating torque applied and establishment of a 
     program for evaluation, inspection, and repair of these valves

(2)  consultation with valve and motor operator vendors to establish any 
     procedures or modifications that could minimize damage, including the use 
     of torque switches or other vendor-recommended alternatives to 
     backseating motor-operated valves.

The inspectors also indicated that the licensees for the Hatch and Peach 
Bottom plants are taking actions to prevent recurring packing leaks.  Georgia 
Power Company is instituting a program at the Hatch units to replace the 
packing on these valves at regular intervals and also plans to live load the 
packing to help prevent packing leakage.  At Peach Bottom, Philadelphia 
Electric Company is modifying the packing gland area, replacing the existing 
asbestos-based packing with graphite packing, installing carbon bushings, and 
live loading the packing.

The information herein is being provided as an early notification of a 
possibly significant matter that is still under consideration by the NRC 
staff.  If NRC evaluation so indicates, further licensee action may be 
requested.

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                                                            Page 4 of 4


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.





                              Charles E. Rossi, Director
                              Division of Operational Events Assessment
                              Office of Nuclear Reactor Regulation


Technical Contacts:  George A. Schnebli, Region II
                     (404) 331-5582

                     Larry E. Nicholson, RI, Surry Power Station
                     (804) 357-2102

                     Keith Poertner, RI, Edwin E. Hatch Nuclear Plant
                     (615) 842-8001

                     Richard J. Kiessel, NRR
                     (301) 492-9605


Attachment:  List of Recently Issued Information Notices

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