Information Notice No. 86-05: Main Steam Safety Valve Test Failures and Ring Setting Adjustments
SSINS No: 6835
IN 86-05
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, DC 20555
January 31, 1986
Information Notice No. NO 86-05: MAIN STEAM SAFETY VALVE TEST FAILURES AND
RING SETTING ADJUSTMENTS
Addressees:
All pressurized-water-reactor (PWR) facilities holding an operating license
(OL) or a construction permit (CP)
Purpose:
This notice is being provided to alert recipients of a potentially
significant problem pertaining to spring-actuated main steam safety valves
that may possess less than the full-rated flow capacity It is expected that
recipients will review the information for applicability to their facilities
and consider actions, if appropriate, to preclude a similar problem at their
facilities However, suggestions contained in this information notice do not
constitute NRC requirements; therefore, no specific action or written
response is required NRC is continuing to obtain and evaluate pertinent
information If specific actions are determined to be required by NRC, an
additional notification will be made
Description of Circumstances:
In the fall of 1984, Public Service of New Hampshire sent the main steam
safety valves (MSSVs) for its Seabrook plant to Wyle Laboratories for
full-flow testing to determine the proper vent stack size To determine full
flow, Wyle measured disc travel of the model number 6R1O valves manufactured
by the Crosby Valve and Gage Company The results of the tests indicated
that the valves could not achieve the required disc travel with the
factory-set ring setting (+155 notches) The disc travel achieved was 50% of
the full lift necessary to develop required steam flow capacity Adequate
lift was not attainable even with the largest diameter tailpipe
Additional tests were done in July 1985 to determine the appropriateness of
the ring settings Specifically, the tests were to determine if the
"as-shipped" ring settings of the valves would allow the required disc
travel with minimum tailpipe backpressure and to determine the effects on
valve disc travel for a range of backpressures between 180 and 390 psig
During these tests, the upper (guide) ring setting was adjusted from +155 to
O and then to +25 to achieve the required disc travel This is a substantial
adjustment Subsequently, the
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IN 86-05
January 31, 1986
Page 2 of 2
licensee consulted with the valve manufacturer and agreed on ring settings
of +25 for the guide ring and -25 (the original setting) for the lower
(nozzle) ring (see figure 1)
Full flow, full size tests of the sort described in this notice are not
normally performed by the licensee or valve vendor for large secondary
safety valves, nor are they required by the ASME Code, Section III Instead
the valves are certified by extrapolations on data from tests of smaller
valves
The MSSVs on most PWRs, while not necessarily the same model or manufacturer
as those at Seabrook, are generally at the upper end of the valve size
range This raises the concern that full-sized flow demonstration may never
have been performed for many MSSVs and these may have incorrect ring
settings In addition, similar problems with ring settings have been found
when full-size tests were performed for PWR primary safety valves Thus,
these MSSVs may not be capable of providing full-relief capacity in
accordance with facility design requirements
NRC is continuing to obtain and evaluate pertinent information If specific
actions are determined to be required by NRC, an additional notification
will be made
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: Mary S Wegner
(301) 492-4511
Attachments:
1 Figure 1, Typical Main Stream Safety Valve
2 List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Friday, May 22, 2015