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
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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.
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