Information Notice No. 86-38: Deficient Operator Actions Following Dual Function Valve Failures
SSINS No: 6835
IN 86-38
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, DC 20555
May 20, 1986
Information Notice No. NO 86-38: DEFICIENT OPERATOR ACTIONS FOLLOWING DUAL
FUNCTION VALVE FAILURES
Addressees:
All nuclear power facilities holding an operating license (OL) or a
construction permit (CP)
Purpose:
This notice is provided to alert licensees to recent events that resulted
from confusion regarding the proper actions to be taken on failure of dual
function valves (eg, those that must accommodate emergency core cooling
system flow and also provide containment isolation) It is expected that
recipients will review this information for applicability to their
facilities and consider actions, if appropriate, to preclude similar
problems at their facilities However, the suggestions contained in this
notice do not constitute NRC requirements; therefore, no specific action or
written response is required
Description of Circumstances:
The emergency core cooling systems for all light water reactors (LWRs) are
equipped with numerous valves that serve both core cooling functions and
containment isolation functions The failure of one of these valves to
function as designed results in the degradation of at least one of its
safety functions The following events illustrate instances in which one of
the functions was not promptly recognized following various types of
failures
Peach Bottom Unit 3: On January 7, 1985, a residual heat removal (RHR)
system torus spray valve malfunctioned following a reactor core isolation
cooling (RCIC) system test The valve had been opened to provide suppression
pool cooling for the test and could not be reclosed using the attached motor
operator To satisfy its containment isolation function, the valve was
closed with a wrench, deactivated, and declared inoperable However, the
licensee failed to declare the torus cooling function of the RHR train
inoperable On January 15, with the unit operating at 87 percent power and
one emergency diesel generator inoperable, causing the equipment including
the remaining RHR train to be inoperable, the NRC Resident Inspector
discovered that the previously described train of RHR was inoperable as a
result of the closed torus spray valve The licensee declared an "Unusual
Event" and began an orderly shutdown of the unit
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May 20, 1986
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The operability of the containment cooling mode of RHR requires the
operability of such equipment as the RHR pumps, the RHR heat exchangers, an
open flow path to the containment and the high pressure service water (HPSW)
system However, review of the Peach Bottom Unit 3 Technical Specifications
by the resident inspectors revealed that only the HPSW system is specified
for containment cooling system operability It is believed that the absence
of the usual open flow path requirement statement in the plant technical
specifications contributed to the failure to declare the RHR train
inoperable The licensee agreed to provide interim administrative controls
for ensuring operability of the containment cooling subsystem until the
issue is permanently addressed through a revision to the plant technical
specifications or by some other means
Brunswick Units 1 and 2: On May 23, 1984, operations personnel at Unit 2
observed that the minimum flow valve for the 2A core spray system (CSS) pump
would not stay in the closed position following receipt of a "close" signal
from the remote manual operator in the control room (These valves do not
receive a close signal on actuation of the containment isolation system)
Engineering personnel determined that the control logic for the minimum flow
valves was such that the valves would reopen after closure whenever a low
flow condition was sensed in the core spray line, including conditions in
which the CSS pumps were not running
On June 1, the normally open minimum flow valves for the CSS trains in both
units were declared inoperable, closed, and deactivated in accordance with
the technical specification requirement for inoperable primary containment
isolation valves (PCIVs) The action statement requires that the line be
isolated if the valve has not been restored to operability within 8 hours
The technical specifications did not explicitly list an open minimum flow
path as a requirement for CSS operability, and the licensee failed to
declare the CSS trains inoperable The licensee did establish procedures
intended to ensure effective operator action to minimize the potential for
pump damage in the event of a CSS pump start However, from subsequent
discussions with the pump vendor, the licensee learned that damage to the
CSS pumps could occur in as little as l minute of operation at shutoff head
without the required minimum flow The plant staff re-evaluated the
situation and concluded that the risk of pump damage with the valves closed
was unacceptable On June 12, the minimum flow valves were reopened and
actuator power was restored Administrative controls and special procedures
were implemented to ensure closure of the valves when required for
containment isolation The licensee plans to modify the logic to allow
remote isolation capability for the valves when their associated pumps are
not running so that minimum flow and containment isolation functions can
both be ensured
Dresden Unit 3: On February 8, 1983, a low pressure coolant injection
(LPCI) system suppression pool suction valve was cycled closed and failed to
reopen The valve, which provides both an emergency core cooling system
(ECCS) and a containment isolation function, was then manually opened and
electrically deactivated This ensured the LPCI function of the valve, but
negated the
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May 20, 1986
Page 3 of 4
containment isolation function Because the swing diesel generator that
supports the redundant train of LPCI was out of service, an "Unusual Event"
was declared, and unit shutdown was initiated
In reviewing the event, it was noted that, during the period when the valve
was deactivated in the open position, the licensee did not declare the valve
inoperable or enter the technical specification action statement for an
inoperable PCIV Although the LPCI suction valves are listed in the Dresden
Final Safety Analysis Report (FSAR) as containment isolation valves, they
were not listed as such in the technical specifications The licensee was
requested to submit an application for a license amendment to add to the
technical specification PCIV list all dual function valves not already
listed
Discussion:
The locations and purposes of dual function valves are diverse They are
found in the suction lines, discharge lines, and minimum flow lines of a
variety of diverse ECCS pumps Some of the suction sources are inside
containment, and some are outside Some recirculation paths penetrate
containment, and some do not
In general, limiting conditions for operation (LCOs) for inoperable PCIVs
allow reactor power operations to continue provided that at least one valve
in the line having the inoperable valve is closed However, in the case of
an inoperable dual function valve, this generally would defeat the ECCS
function of the line and would require entry into the action statement for
an inoperable ECCS train Alternatively, the decision to maintain the ECCS
function generally requires entry into the action statement for an
inoperable PCIV
The operating staff occasionally may have difficulty determining the most
appropriate valve position (open or closed) and valve technical
specification requirement status (enabled or disabled) when a dual function
valve fails This difficulty is compounded when the technical specifications
are not specifically provided in the plant license for one or the other
function of the failed valve, as illustrated by the events described
With regard to the technical specifications for operability of safety
systems, all licensees were requested by a generic letter dated April 10,
1980, to adopt the standard definition that had been developed for NRC's
Model Technical Specifications That definition requires all necessary
attendant instrumentation, controls, normal and emergency electrical power
sources, cooling or seal water, lubrication, or other auxiliary equipment
that are required for the system to perform its function(s) to be capable of
performing their support functions
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No specific action or written response is required by this information
notice If you have any questions regarding this matter, please contact the
Regional Administrator of the appropriate NRC regional office or this
office
Edward L Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contacts: S M Long, NRR
(301) 492-8413
E J Leeds, AEOD
(301) 492-4445
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