Information Notice No. 85-84: Inadequate Inservice Testing of Main Steam Isolation Valves
SSINS No.: 6835
IN 85-84
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
October 30, 1985
Information Notice No. 85-84: INADEQUATE INSERVICE TESTING OF MAIN
STEAM ISOLATION VALVES
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP).
Purpose:
This notice is being provided to alert recipients of a potentially signifi-
cant problem concerning the possible failure of main steam isolation valves
(MSIVs) to close under low steam flow conditions and the testing of these
valves with non-safety-related motive power in place. It is expected that
recipients will review the information for applicability to their facilities
and consider actions, if appropriate, to preclude a similar problem
occurring at their facilities. However, suggestions contained in this
information not-ice do not constitute NRC requirements; therefore, no
specific action or written response is required.
Past Related Correspondence
Information Notice 85-21, "Main Steam Isolation Valve Closure Logic", March
18, 1985.
Description of Circumstances:
During inspections at Robinson Unit 2 in November 1984 and at Turkey Point
Units 3 and 4 in February 1985, NRC inspectors noted that MSIV surveillance
testing procedures did not call for securing the instrument air supply to
the MSIV control system during a test. Recognizing this as contrary to the
objec-tive of operational verification of the MSIVs, the NRC cited these
plants for violating 10 CFR 50.55a(g).
After reviewing the matter to determine the corrective action, Florida Power
& Light Co., the licensee for Turkey Point Units 3 and 4, reported to the
NRC on July 23, 1985, that a deficiency existed concerning the ability of
MSIVs to close under low steam flow conditions. The safety-related air
supply, stored in accumulators, was not adequate to close the valves in the
event of loss of the non-safety-related instrument air system. This had not
been discovered during routine testing because that testing had been
performed improperly using the non-safety-related instrument air to achieve
closure.
8510250546
.
IN 85-84
October 30, 1985
Page 2 of 3
Operating air for the MSIVs is stored in accumulators mounted on the valve
assembly; the non-safety-related plant instrument air system provides addi-
tional supply. During normal operation the MSIVs at Turkey Point are held
open against steam flow by air pressure acting on the bottom of the actuator
operating piston. When a closing signal is received, air is directed to the
top of the piston while air is vented from the bottom of the piston. Closure
of each MSIV is assisted by a spring that moves the piston part way, by
steam flow in the steam line, and by gravity. Assuming a loss of the
instrument air system, the air stored in the safety-related accumulators may
not be adequate to close the MSIV without sufficient assistance from steam
flow.
The Turkey Point MSIVs are required to close within 5 seconds to mitigate
the consequences of a large main steam line break accident. In the event of
such an accident, the high steam flow rate would assist in closing the
MSIVs. However, MSIV closure also is required for other events in which
large steam flow may not exist. Under these conditions and a loss of
instrument air pressure, the accumulator air volume may not be sufficient to
close the MSIVs.
In the regulations, 10 CFR 50.55a(g) requires that inservice testing to ver-
ify operational readiness of pumps and valves whose function is required for
safety be accomplished in accordance with Section XI of the ASME Boiler and
Pressure Vessel (BPV) Code. The ASME BPV Code, Section XI, 1980 edition
through winter 1980 addenda, Paragraph IWV-3415, requires that fail-safe
valves be tested by ob,serving the operation of the valves upon loss of
actuator power. Since the MSIVs have been identified as fail-safe valves
they should have been tested with the instrument air supply, as well as
electric power, removed. Proper testing would have revealed the inadequate
accumulators much earlier.
Discussion:
The practice of performing inservice testing of components, which are relied
on to mitigate the consequences of accidents, with sources of power not con-
sidered in the safety analyses is not in keeping with the objective of per-
iodic testing. This objective is to test equipment to verify operational
readiness under conditions that reasonably duplicate the design basis. When
such testing was performed at Turkey Point, it was shown that with low or no
steam flow, MSIV closure could only be assured with instrument air powering
the actuator.
Continued operation at Turkey Point has been justified by the availability
of two instrument air systems as backups and by procedures that require
plant shutdown if the instrument air supply is lost. In addition, design
modifications are being implemented on an expedited basis that will ensure
MSIV closure in 5 seconds without steam flow assistance or
non-safety-related instrument air power. These modifications also will
resolve the testing deficiency noted above.
.
IN 85-84
October 30, 1985
Page 3 of 3
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: Vern Hodge, IE
(301) 492-7275
Attachment: List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Tuesday, March 09, 2021