United States Nuclear Regulatory Commission - Protecting People and the Environment

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 

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                                                          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. 

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                                                          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, November 12, 2013