ML20059K943
| ML20059K943 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 09/18/1990 |
| From: | Joel Wiebe NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | |
| Shared Package | |
| ML20059K934 | List: |
| References | |
| 50-498-90-28, 50-499-90-28, NUDOCS 9009250267 | |
| Download: ML20059K943 (7) | |
See also: IR 05000498/1990028
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' APPENDIX B
U.S. NUCLEAR REGULATORY C0!HISSION
REGION IV
NRC Inspection Report:
50-498/90-28
Operating License: NPF-76
50-499/90-28
Dockets: 50-498
50-499
Licensee: Houston Lighting & Power Company (HL&P)
P.O. Box 1700
Houston, Texas 77251
Facility Name:
South Texas Project (STP), Units 1 and 2
Inspection'At: STP, Matagorda County, Texas
Inspection Conducted: July 30 through August 8, 1990
Inspectors: J . I. Tapia, Senior Resident Inspector, Project Section D
Division of Reactor Projects
J. E. Whittemore, Operator Licensing Examiner, Operator
Licensing Section, Division of Reactor Safety
Approved:
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(1ebe, Chd ef, Project Section D
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inspection Summary-
Inspection Conducted July 30 through August 8,1990 (Report 50-498/90-28;
50-499/90-28)
Areas Inspected:
Special, announced inspection included onsite followup of
two events.
Results: Within the area inspected, two apparent violations were identified.
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The first violation involved an-improperly aligned auxilary feedwater test
return line.. This resulted in the affected train being inoperable when needed
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following a' loss of normal feedwater. The lineup error was also not identified
by the required independent check.- The inadvertant boron dilution event
represented a lock of licensee awareness for processes which could potentially
affect reactivity. The second violation (failure to include criteria in
procedure to determine that important activities were satisfactorily
accomplished) involved the failure to ensure that a mixed bed demineralizer
contained the proper boron content. This resulted in an inadvertant boron
dilution event during full power operation on August 6,1990, which resulted
in reactor thermal power exceeding 100 percent. (paragraph 2.B).
An enforcement
. conference was held on August 29, 1990, to discuss the apparent violations and
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' the corrective actions. Based on the inspection' and infomation provided in'
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the enforcement conference..the NRC concluded that operator actions to control-
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reactor power and reactor coolant system temperature were appropriate,
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DETAILS
1.
' Persons Contacted
- W. H. Kinsey, Plant Manager
- M. R. Wisenburg, General Manager of Assessnent
- M. A. McBurnett, Nuclear Licensing Manager
- J. Loesch, Operations Manager
- K. Christian, Manager of Operations Unit 1
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- C
A. Ayala, Supervising Engineer, Licensing
- A. K. Khosla, Senior Engineer, Licensing
- Denotes those individuals attending the exit interview conducted on
August 1, 1990.
- Denotes those individuals attending the exit interview conducted on
August 8, 1990.
2.
Onsite Followup of Plant Events
A.
Auxiliary Feedwater System Valve Lineup Error
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At 7:48 p.m. on July 30, 1990, Unit I was manually tripped when
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the "A" feedwater isolation valve went fully closed during the
performance of a surveillance procedure. The surveillance was being
performed to verify that both the permanent test circuitry and the
electrohydraulic control fluid solenoid dump valves were operating
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correctly. This surveillance is accomplished by stroking the
feedwater isolation valve from fully open to 90 percent open and then
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back to fully open. While placing a jumper wire for the
surveillance, the I&C technician inadvertently made contact with the
wrong tenninal block which caused the feedwater isolation valve to go
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fully closed. Control room operators manually tripped the reactor
when Steam Generator IA level reached 40 percent. An automatic reactor trip would have occurred at a level of 33 percent.
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' Subsequent to the trip, control room operators noted that the level
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in Steam Generator 1A was continuing to decrease even with auxiliary
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feedwater (AFW) in service at a flow of 600 gpm. A reactor plant
operator was dispatched to the AFW pump to attempt to identify the
problem. Atter verifying the integrity of the piping and the pump,
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the dispatched operator discovered that the long path recirculation
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valve (AF-0040) was locked open although it should have been locked
closed. The open valve was allowing AFW to be pumped back to the
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' AFW storage tank instead of into the steam generator.
Steam.
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Generator 1A was then fed through the cross-connect valve and AFW
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Pump No. 11 was stopped. Steam Generator 1A level decreased to
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35 percent before the level stabilized and started to increase.
The
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recirculation valve was repositioned, and AFW was then established to
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Steam Generator 1A via the No. 11 AFW pump.
The valve restoration
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took about 40 minutes. All other manual recirculation valves
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associated with engineered safety feature (ESF) functions were
subsequently verified to be locked closed in both units.
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The last time that AF-0040 was known to have been operated was on
July 26, 1990, during the performance of procedure IPSP03-AF-0001,
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" Auxiliary Feedweter Pump 11 Inservice Test." Step 5.13.1
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recuires AF-0040 to be closed and locked. Steo 5.13.2 recuires an
incependent verification that AF-0040 is closrd and lockec.
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Subsequent investigation by the licensee disclosed that Steps 5.13.1
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and 5.13.2 were performed at the same time.
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Recirculation Valve AF-0040 was apparently not locked closed and the-
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independent verification requirements of Procedure 1 PSP 03-AF-0001,
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" Auxiliary Feedwater Pump 11 Inservice Test" Step 5.13.2, apparently
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did not ensure that the long path recirculation valve (AF-0040) was
satisfactorily locked closed.
Plant Procedure OPGP03-ZO-0004, " Plant
Conduct of Operations," Revision 11. Step 4.4.11, requires that
independent verifications shall be performed as prescribed by approved
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procedures or instructions in accordance with Procedure OPGP03-ZA-0010,
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" Plant Procedure Compliance, Implementation, and Review." Plant
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Procedure OPGP03-ZA-0010, Revision l's Step 3.3.2.1, states that the
act of performing the independent y'
~fication must be completely
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separate and independent of G: '
,i alignment, installation, or
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verification. The fact that Stec ' 13.1 and 5.13.2 were performed
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concurrently and not separate au, udependent represents a failure to
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follow the procedure specified for independent verification and is
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consideredanapparentviolation(50-498/9028-01).
B.
Inadvertent Dilution of Reactor Coolant System Boron Concentration
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On August 6, 1990 Unit 1 experienced a decrease in boron
concentration in the reactor coolant system (RCS). This resulted
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in an unexpected positive reactivity addition.
The reactor was
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initially in a steady state condition at 100 percent power with
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the control rods in manual. Control Rod Bank D was at 244 steps.
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All other banks were at 259 steps. The sequence of events, as
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established during this inspection, is shown in the attachment to
this report.
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At approximately 8:30 a.m. on August 6,1990, shift turnover briefings
were conducted between reactor operators and chemical analysis
technicians. At that time the chemical analysis techniciaas indicated
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that' chemical volume and control system (CVCS) mixed bed
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Demineralizer 1A needed to be placed in service in order to reduce
the sodium content in the RCS.
They also informed the>>perators that
.CYCS mixed bed Demineralizer 1A had been previously bo'ated to
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2500 ppm. At 9:10 a.m. , pursuant to procedure IP0P02-CV-0004,
" Chemical and Volume Control System Subsystem," the control room
requested chemical analysis personnel to determine th! amount of
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water needed to flush the demineralizer bed to achieve equilibrium
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conditibns with the RCS. Based on the infonnation that mixed bed
Demineraiizer IA had 2500 ppm boron, the chemical analysis technician
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calculatt'd that 2500 gallons of RCS effluent would be required for a
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preservice t!ush.
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As discussed below, it was later demonstrated that mixed bed
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Demineralizer 1A did not contain the expected amount of boron and,
as a result, the calculated amount of flush water was in error.
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Neither operations Procedure IPOP02-CV-0004, Revision 8. or any
administrative procedure contained adequate acceptance criteria to
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determine that the activities to place a mixed bed demineralizer
in service had been satisfactorily accomplished. This is an apparent
violation of 10 CFR Part 50. Appendix B, Criterion V which requires,
in part, that procedures include acceptance criteria to be used to
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determine that important activities have been satisfactorily
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accomplished (498/9028-02).
At approximately 9:58 a.m., mixed bed Demineralizer 1A was aligned
to the waste holdup tank and 2500 gallons of RCS effluent was flushed
through the bed. At 10:58 a.m., mixed bed Demineralizer IA was
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placed in serv. ice and, at 11 a.m., mixed bed Demineralizer IB.was
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removed from service.
At approximately 11 a.m., the Proteus computer was taken out of
service for a maintenance adjustment. When it was returned to
service at approximately 11:10, the reactor operator noted that a
slight increase in Tavg of 0.2 degrees had occurred.
In response
to the increasing Tavg the reactor operator added boric acid by
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.the batch method. He added one 10-gallon and three 5-gallon volumes
within the next 4 minutes. These actions served to momentarily
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inhibit the Tavg increase, but power continued a slow increase.
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During this period the unit supervisor went to the control boards to
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observe indication and operator action. The demineralizer was
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bypassed approximately 4 minutes after the event detection
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. (11:10 a.m.), according to the licensee. This action was not
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documented.
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The licensee's subsequent review shows that:the operators started
to insert control rods at 11:17 (the Proteus computer data printout
shows that the control rods had been inserted four steps before
11:15). As shown in the attachments, thermal power exceeded licensed
power from 11:15 until 11:36 and then again from 11:41 until 11:45.
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During this time the operators injected boron and inserted control
rods.in an attempt to reduce and stabilize reactor power below 100
percent.
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Two other evolutions were in progress at the start of this event.
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The:first evolution was an Analog Channel Operational Test (ACOT),
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which was being performed on RCS Loop 2 deltaT-Tavg and several
associated bistables were, therefore, tripped. This ACOT was secured
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shortly after the start of the event and, therefore, had little if any
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influence on subsequent operator action. The second evolution was
that the operating crew was attempting to maintain a steady Bank "D"
rod position so that the shift technical advisor (STA) could
determine and establish a new core delta flux (delta-I) target band.
Interviews were held with the reactor operator (RO) and the unit
supervisor (US) on duty at the time of the event. Both operators
stated that they were concerned about inserting rods too fast and
too deep which would cause a core power distribution (delta-flux)
problem. Discussions were subsequently held with the Unit 1
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operations manager who stated that he was completely satisfied with
the control room operators' pcformance during this event. He
further stated that it was necessary to use a slow, deliberate
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approach to control the transient and preclude other problems, such
as safety injection initiation or severe flux tilts. The operators
themselves expressed the same reservations about complicating the
event. The inspectors observed that following this slow, deliberate
approach to control the transient, rather than initiating emergency
boration or significantly inserting control rods, allowed-the
indicated power level to exceed 103 percent by the highest indicating
nuclear instrument channel and to exceed 100 percent of licensed
thermal power for 21 minutes and then for 3 minutes.
Subsequent to the event, an enforcement conference was conducted
in the Region IV office on August 29, 1990, to discuss the causes
of the event and.the adequacy of operator actions. The handouts
used by the. licensee at this conference are attached to this
inspection report. .At this meeting the licensee presented the
following causes for.the event:
The procedure for placing the demineralizer in service did not
require a sample or provide acceptance criteria for boron
concentration prior to demineralizer use.
The procedure for ensuring proper boron concentration in the
demineralizers was less than adequate.
The conduct of operations procedure for controlling power
excursions contained less than adequate guidance..
The licensee also presented evidence that showed that maximum reactor
thermal power attained was 101 percent and that the reactor was above
100 percent reactor themal power for about 24 minutes. This
operation was'shown to be within the bounds assumed in the design
basis analyses.
Operator actions were found to have been adequate to control the
event and assure safety, however, the licensee has implemented
program improvements to assure that control rod insertion is to be
used in the event reactor power unexpectedly exceeds 100 percent
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power. Additionally, specific guidance was also developed to reduce
reactor power prior to planned evolutions that have the potential to
cause reactivity additions.
As a result of the NRC review of this event and the information
provided during the enforcenent conference, the NRC concluded that
o>erator actions in response to the transient were adequate. Although
tierwel power was above 100 percent for approximately 24 minutes, the
operators were aware of the cause of the transient and took adequate
actions to control the power increase. The transient was within the
plant design basis. ' One violation was identified involving the lack
of appropriate acceptance criteria in procedures to ensure that the
demineralizers have an appropriate boron concentration prior to being
placed in service.
3.
Exit Interview
The inspectors met with licensee representatives (denoted in paragraph 1)
on August 1 and 8, 1990. The inspectors summarized the scope and findings
of the inspection. The licensee did not identify as proprietary any of
the information provided to, or reviewed by, the inspectors.
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