United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-80: Unit Startup with Degraded High Pressure Safety Injection System

                                                           SSINS No.: 6835 
                                                           IN 86-80       
                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555

                             September 12, 1986

Information Notice No. 86-80:   UNIT STARTUP WITH DEGRADED HIGH PRESSURE 
                                   SAFETY INJECTION SYSTEM 

Addressees: 

All nuclear power reactor facilities holding an operating license or a 
construction permit. 

Purpose: 

The purpose of this notice is to inform recipients of an event where unit 
startup involved improper interpretation of the terms "OPERABLE" and 
"OPERABILITY" in the technical specifications. 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 notice do not constitute NRC requirements; therefore, no 
specific action or written response is required. 

Description of Circumstances: 

At the McGuire Station on November 2, 1985, a single failure in a shared 
instrument air system caused a trip of both units from 100% power and a 
safety injection in Unit 1. A detailed sequence of events is provided for 
information in attachment 1. The isolation valves between the volume control
tank (VCT) and the charging pumps closed as designed when the SI signal 
initiated a transfer of the charging pump suction to the refueling water 
storage tank from the VCT. Later, when the SI was reset, it was discovered 
that the VCT isolation valve motor operators had burned-up due to overload. 

Although work requests were written to repair both of the valves, operations
personnel made the erroneous decision to start-up based on the determination
that these VCT isolation valves are not in the direct ECCS flow path 
required by technical specifications. They believed that the HPSI system was 
still capable of performing its design requirement. The unit entered the 
start-up mode (mode 2) at about 6:15 a.m. the following day, (November 3, 
1985), but only stayed in this mode until 12:55 p.m. when mode 3 was 
re-entered to repair a severed instrument fitting on the secondary side of a 
steam generator. 

Discussion: 

The safety significance of this event is that the VCT isolation valves would
not have automatically closed if an SI signal were received. The charging 
pumps 

8609100228 
.

                                                       IN 86-80          
                                                       September 12, 1986 
                                                       Page 2 of 2       

would then be taking suction from both the VCT and the RWST with the 
following possible consequences: (1) the VCT could be drained allowing 
hydrogen gas to be entrained in the charging pump suction, possibly leading 
to gas binding of the charging pumps and (2) the water injected into the 
reactor vessel would have a lower boron concentration than it would in the 
required line-up. 

Duke Power personnel made their decision to start-up the unit on the basis 
that neither of the two valves in question is specifically identified in 
Technical Specification 3.5.2 as being a part of the required ECCS flow 
path. The technical specification requires "an OPERABLE flow path capable of 
taking suction from the RWST on an SI signal and automatically transferring 
suction to the containment sump during the recirculation phase of 
operation." However, the standard definition of OPERABLE requires that all 
necessary attendant instrumentation, controls, normal and emergency power 
sources, cooling or seal water, lubrication or other auxiliary equipment 
that are required for the system, sub system, train, component or device to 
perform its function(s) are also capable of performing their related support
function(s). A generic letter was issued by the NRC Office of Nuclear 
Reactor Regulation on April 10, 1980 to clarify the meaning of the term 
OPERABLE and to request licensees to take specific actions to assure that 
the term is appropriately applied at their facilities. This definition of 
operability was also part of the McGuire technical specifications at the 
time of the event. 

Information Notice No. (IN) 86-38, entitled "Deficient Operator Actions 
Following Dual Function Valve Failures" also addresses operator actions with
regard to valves that serve more than one function. The valves addressed in 
IN 86-38 not only accommodate emergency core cooling flow, but also provide 
a containment isolation function. The information notice also refers to the 
generic letter dated April 10, 1980 that requests licensees to adopt the 
standard definition of OPERABLE in their technical specifications. 

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:  Joe Giitter, IE
                    (301) 492-9001

                    William T. Orders, RII
                    (704) 875-1681

Attachments:
1.   Detailed Sequence of Events
2.   List of Recently Issued IE Information Notices
.

                                                       Attachment 1      
                                                       IN 86-80          
                                                       September 12, 1986 
                                                       Page 1 of 1       

11/2/85   A fatigue-induced failure of the discharge line from one of three 
~0640     instrument air compressors, which comprise a shared instrument air
          system, resulted in the loss of instrument air pressure to all 
          loads on both units. The main feedwater flow control valves on 
          both units closed as designed as a result of the loss of 
          instrument air. 

          Due to low-low steam generator levels, both units tripped from 
          100% power. The auxiliary feedwater systems auto-started and 
          provided feedwater to the team generators. 

          A safety injection (SI) signal was received on Unit 1 when the 
          reactor coolant system pressure dropped below the SI set point of 
          1845 psig. Injection occurred for about 10 minutes. The pressure 
          decrease was caused by several factors: (1) post-trip steam loads 
          were higher than normal because the main steam drains opened on 
          loss of instrument air; (2) three steam generator power operated 
          relief valves and code safeties opened to relieve the initial 
          pressure transient; (3) pressurizer heaters failed to energize as 
          required; and (4) steam generators were overfed because flow 
          control valves in the auxiliary feedwater system went open as a 
          result of the loss of instrument air; and (5) Unit 1 was providing
          house load auxiliary steam. 

          When the SI signal was received, the high-pressure safety 
          injection (HPSI) charging pump suction transferred from the volume 
          control tank (VCT) to the refueling water storage tank (RWST) as 
          designed. 

          This requires that the valves between the RWST and the charging 
          pumps open and the two motor operated isolation valves between the
          VCT and the charging pumps closed. The isolation valves between 
          the VCT and the charging pumps closed (i.e. , the required safe 
          position). 

          SI was reset, the isolation valves could not be opened from the 
          control room. An equipment operator was dispatched to manually 
          open the valves. The valves were subsequently determined to be 
          electrically inoperable because the valve motors had burned-up due
          to overload. Work requests were written to repair both of the 
          valves. Operations personnel made the erroneous decision to 
          start-up based on the determination that these VCT isolation 
          valves are not in the direct ECCS flow path required by technical 
          specifications. They believed that the HPSI system was still 
          capable of performing its design requirement. 

11/3/85   Unit entered the start-up mode (mode 2) with the VCT isolation 
~0615     valves open and electrically inoperable. The unit did not exceed 
          2% reactor power while in mode 2. 

11/3/85   Mode 3 was re-entered to repair a severed instrument fitting on 
~1255     the secondary side of a steam generator. 
Page Last Reviewed/Updated Tuesday, November 12, 2013