ML20151R914
| ML20151R914 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 07/27/1988 |
| From: | Harrell P, Reis T, Westerman T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | |
| Shared Package | |
| ML20151R908 | List: |
| References | |
| 50-285-88-22, NUDOCS 8808120343 | |
| Download: ML20151R914 (10) | |
See also: IR 05000285/1988022
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APPENDIX A
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U.S. NUCLEAR REGULATORY COMMISSION
REGION IV
NRC In'spection Report:
50-285/88-22
License:
Docket:
50-235
Licensee:
Omaha Public Power District (0 PPD)
1623 Harney Street
Omaha, Nebraska 68102
Facility Name:
FortCalhounStation(FCS)
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Inspection At:
Fort Calhoun Station, Blair, Nebraska
Inspection Conducted:
June 29 through July 18, 1988
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Inspectors:
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7/17/98'
P. H. Harrell, Senior Resident Redctor
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Inspector
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I. Reis, Resident Reactor Inspector
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Approved:
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T. F. Westerman,'. Chief, Project Section B
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DivisionofReactorProjects
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8808120343 880729
ADOCK 05000285
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Inspection Summary
Inspection Conducted June 29 through July 18, 1988 (Report 50-285/88-22)
Areas Inspected:
Special, unannounced inspection of the thermal margin / low
pressure reactor protection system trip setpoint and the limiting condition for
operation for excore monitoring of linear heat rate.
Results:
Two potential violations (inoperability of the thermal margin / low
pressure trip function of the reactor protection system,dentified. paragraph 3; and
reporting of inaccurate information, paragraph 7) were i
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DETAILS'
1.
Persons Contacted
- K. Morris, Division Manager, Nuclear Operations
- W. Gates, Plan'c Manager
- J. Fisicaro, Supervisor, Nuclear Regulatory and Industry Affairs
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J. Gasper, Manager, Administrative and. Training Services
- K. Holthaus, Manager, Nuclear Engineering
R. Jaworski, Section Manager, Technical Services
- J.
Kecy, Reactor Engineer
- L. Kusek, Manager, Nuclear S?.foty Review Group (Acting Plant Manager)
D. Matthews, Supervisor, Nuclear Licensing
R. DeMeu1meester, Shift Supervisor
- C. Simmons, Plant Licensing Engineer
J. Spilker, Op cations Support Engineer
- W. Weber, Supervisor, Reactor Perfonnance and Analysis
- Denotes attendance at the exit interview conducted on July 8,1988.
- Denotes attendance at the exit interview conducted on July 18, 1988.
The NRC inspectors also contacted other plant personnel including
operators, technicians, and administrative personnel.
2.
Improper Limit on Excore Monitoring of Linear Heat Rate
On June 28, 1988, licensee engineers were performing setpoint analyses and
developing reactor protection system trip setpoint.1 for the upcoming
twelfth fuel cycle. The analyses revealed that the data for the limiting
condition for operation (LCO) for excore monitoring of linear. heat
rate (LHR) was incongruous with the results obtained for the previous
eleventh fuel cycle. The plant is currently operating in the eleventh
fuel cy:le. The licensee alerted the core vendor, Combustion
Engineering (CE), of the discrepancy. Together, they investigated and
found the LC0 for excore monitoring of LHR was nonconservative for
Cycle 11.
During the current cycle, the licensee was not required to monitor the LHR
with the excore detectors. The use of excore detectors is required only
when the incore detectors are inoperable.
Had the licensee monitored this
parameter during the cycle with the excore cetectors, the current -
Technical Specification (TS) LC0 2.10.4(1)(c) would have allowed power
operation at a maximum level of 90 percent when the reanalysis
demonstrated that the maximum level should have been 86 percent to prevent
exceeding the required LHR margin.
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The limitation on LHR ensures that, in the event of a loss-of-coolant
accident, the peak temperature of the fuel cladding will-not exceed
2200"
This limitation is normally monitored by the incore detection
sys h which provides an alarn function.
In the absence 'of incore
monitoring, linear heat is evaluated by the excore detectors. However, in-
this mode, operation is limited by TS LC0 2.10.4(1)(c). This LC0 requires
operation within the bounds of TS Figure 2-6.
In developing the limits of
TS Figure 2-6, the licensee failed to incorporate the required overpower
margin (ROPM) in the calculations.
This resulted in an allowed
operational power greater (i.e., 90 percent versus 86 percent) than that
allowed had the R0PM been properly incorporated into the calculations.
The licensee contended that had the use of the excore monito-ing LC0 been
necessary during Cycle 11, the required LHR margin would not have been
exceeded since sufficient margin would have existed due to the margin
between the actual total planar-radial peaking factor and the TS limit of
1.85.
The maximum total planar radial peaking factor recorded in the
current cycle is 1.72.
3.
Nonconservative Reactor Protection System Setpoint
After the licensee confirmed the error concerning the excore monitoring 'of
the linear heat rate, the entire Cycle 11 setpoint analyses were
independently verified.
It was found that the thermal margin / low
pressure (TM/LP) trip function of the r:! actor protection system was set in
a nonconservative direction by 79 pounL per square inch (psia). This
nonconservatism rendered all four TM/LP channels inoperable.
Continuous
operation with inoperable reactor protection system channels is an
apparent violation of TS 2.15.
(285/822-01)
The TM/LP trip .s provided to prevent operation when the departure from
nucleate boiling ratio (DNBR) is less ^.t.an 1.18.
DNBR is a function of
total integrated radial peaking factor, mass flow rate, average coolant
temperature, total flow, and reactor coolant system pressure,
in calculating the TM/LP setpoint for Cycle 11, the licensee failed +o
incorporate a penalty factor involving the total integrated radial peaking
factor into the calculation. This resulted in a TM/LP setpoint lower than
would normally be allowed. The significance of this is that during a
depressurization event, the reactor would not trip until pressure
decreased by 79 psia below the desired setpoint. This reduced pressure
would cause conditions which would put the core closer to DNB.
FCS has not oxperienced any depressurization events during Cycle 11. The
licensee contends that had one occurred, the violation of-the TM/LP
limiting safety system setting would not have allowed the DNBR limit to be
exceeded because of the conservatism of the total integrated radial
peaking factor inherent in the Cycle 11 core. This conservatism is
reported by the licensee to be 180 psia.
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The total radial p(eaking factor used in the calculation of thermal margin
reactor pressure Pvar) was 1.80 as allowed by TS.
Paragraph 3.4.5 of the
Updated Safety Analysis Report states that the maximum expected total
integrated radial peaking factor for Cycle-11:is 1.69. - The actual maximum
recorded to date has been 1.68.
Using the' smaller value of the total
radial peaking factor in calculating Pvar would trend this pressure in the
conservative direction. The licensee stated that a value of 1.80 was used
because the engineers realized that the value was conservative. The
licensee stated that this cognitive action was taken to coaservatively
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establish core operating limits as the engineers routinely add as much
conservatism as possible to the calculations.
This was done to ensure.
that the plant is opented with as much conservatism as possible within
the established plant imitations.
The licensee reported
at the error resulting from the failure to
incorporate the total .ategrated radial peaking factor penalty factor into
the computations was 79 psia in the nonconservative direction. This
results in the as-found TM/LP setpoint being conservative by (180-79)
101 psia as reported by the licensee.
NRR will review the licensees calculations to verify the conservatism
asserted by the licensee.
4.
Root Cause
Prior to Cycle 11, the licensee performed its setpoint analyses manually
using an NRR-approved methodology. The results were verified internally
within the licensee's organization. Beginning with Cycle 11, the licensee
employed a computer-aided technique of performing the setpoint analyses.
Due to a misunderstanding between CE and the OPPD staff during training,
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the licensee wrongly assumed that the R0PM term and the total integrated
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radial peaking factor penalty factor had been incorporated into the
computer program algorithm, while' the CE instructor training licensee
personnel on the use of the new software assumed that the licensee would
incorporate these factors.
The NRC inspector determined that the computer program supplied by CE was
purchased under the requirements of the licensee's quality assurance (QA)
program and the computer program is maintained in accordance with QA
requirements. However, the licensee stated that no instruction manual was
supplied with the computer program to inform the user on how to properly
input data into the program.
When the licensee changed from manual calculations to computer program
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calculations, NRR was not notified via a change to the Topical Report used
to describe the method of setpoint analyses used by the licensee. The
licensee stated that a change was not required because the
.me nathod was
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being used, but in a computer program fonnat.
The licensee personnel that performed the calculations for Cycle 11 were
somewhat taxperienced in performing the calculations because they had
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only done the calculations one previous time.
This fact may have
contributed to the omission of the R0PM in the calculation. To ensure
that errors are not inadvertently made by the plant staff during the-
performance of setpoint analyses in the future, the licensee stated that
they will have CE independently review all analyses.
5.
Generic Implications
The licensee stated that for CE analog plants only FCS and Maine Yankee.
perform their 'own setpoint analyses. CE provides this service for the
remainder of the domestic units.
CE has asserted to the licensee that
Maine Yankee methodology is not applicable and that this error was not
generic to CE analog plants.
On July 11, 1988, CE issued a letter to the licensee's supervisor of
reactor performance analysis confirming that OPPD is the only utility
organization utilizing their own personnel to generate plant setpoints by
employing the CE setpoint methodology.
6.
Sequence of Events and Corrective Action
The excore monitoring of linear heat rate was found to be nonconservative
at approximately 5 p.m. on June 28, 1988.
Engineers continued working
that evening and discovered that the TM/LP setpoint had also been affected
by the transition from manual to computer-aided calculations. At this
time, neither of the errors had been quantified and it was not known
whether the TM/LP was affected conservatively or nonconservatively. The
TM/LP setpoint was found to be nonconservative and this fact reported to
the reactor engineer at approximately 7:30 a.m. on June 29, 1988. At this
time, the nonconservative error had not yet been quantified.
The NRC inspector became aware of the potential problem when reviewing the
shift supervisor's log at approximately 7:30 a.m. on June 29, 1988. The
reactor engineer had left instructions in the log to call him in the event
the linear heat rate monitoring by incore detectors became inoperable
during the night.
In addition, the reactor engineer advised the onshift operations staff via
log entry that there may be some errors in the TM/LP calculation. The
reactor enoineer informed the staff that he had detennined th1. if
cold-leg temperature was maintained below 541 F, the margin would be
acceptable.
It was further conveyed to the operaticn. staff that there
appear?d to be no reportability requirements on these items.
The NRC inspector also observed an additional log entry on June 29, 1988,
in which it was reported tht.t the reactor engineer called and stated that
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due to the TM/LP problem he did not want the operations staff to reset the
variable high power trip on a power increase from the present 90 percent
setting.
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At 10 a.m. on June 29, 1988, the plant manager, reactor engineer, and
technical assistants briefed the NRC inspector on the situation. They
explained that they had declared .the TM/LP channels inoperable and had
entered LC0 2.15(3) of the TS at 9:20'a.m. This LC0 requires that the
reactor be placed in hot shutdown within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> if the channels are not
returned to service.
Plant management stated that resetting the TM/LP
trip setpoints had begun and that the situation would be reassessed in
4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> and at that time, if it did not appear that the equipment could be
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returned to operability within a reasonable time, an orderly shutdown
would commence. A reasonable time frame was defined as leaving 4 to
6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> for a controlled shutdown.
It was further explained that administrative controls had been placed on
monitoring linear heat rate with the excore detectors. The licensee had
determined that the parameters of TS Figure 2-6 were nonconservative.
Therefore, the shift supervisor was directed to reduce power to 80 percent
in the event that incore monitoring of linear heat rate became inoperable.
Pursuant to 10 CFR Part 50.72(b)(2)(111), the licensee made a 4-hour
report on the inoperability of the TM/LP channels to NRC Headquarters.
The report was made at 12:50 p.m.
Throughcut the day, the NRC inspector observed I&C technicians reset Ing
the TM/LP setpoints of the reactor protection system with the use of
approved procedures. The reactor engineer monitored their progress and
assisted almost continuously. At 4 p.m., three of the four channels had
been reset. The NRC inspector met with the plant manager at 4:30 p.m. to
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discuss the situation. The plant manager felt at that time the situation
was under control and he would not have to commence shutdown, although he
was prepared to do so. At 5:30 p.m., on June 29, 1988, all four channels
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of TM/LP were declared operable.
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In response to the errors identified ir, tia Cycle 11 analyses, the
licensee requested that CE perfom an independent review for the analyses
that were done for Cycle 10. No problems were identified during th
review. A review of the analyses was not performed by CE for Cycles 8
and 9.
Cycle 8 was selected by the licensee as the appropriate cycle to
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perform reverification on the analyses since the analyses method was
changed by the licensee starting with Cycle 8.
The licensee submitted a
Topical Report change to NRR and the Topical Report was approved. The
licensee felt that a reverification of the Cycle 8 analyses was not
appropriate since CE independently reviewed the analyses at the time the
calculations were performed. The licensee felt that reverification of the
Cycle 9 analyses was not required since CE worked closely with licensee
personnel during performance of the calculations.
In addition to the above actions, the licensee is also mobilizing the
management investigative safety team (MIST) to provide an indepth,
independent review of this event. The MIST was established by the
licensee to identify the root causes of events and provide recommendations
for the pennanent corrective actions to be taken to prevent recurrence.
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When the MIST completes a review of these events in the near future, the
licensee will take actions to implement the MIST recommendations.
7.
Reporting
in July 1,1988, the licensee submitted a letter to the NRC sunnarizing a
telephone discussion held between the licensee, Region IV, and NRR on
'une 30,1988, regarding the nonconservative errors discovered in the
cycle 11 setpoint analyses and the corrective actions taken.
The NRC
inspector reviewed this document and found some of the information to be
inaccurate.
The letter states, in part, that on June 28, 1988, the reactor engineer
contacted th shift supervisor and discussed with him the conservative
actions to te taken until the errors could be quantified. The letter
further sta'.es that the shift supervisor placed, in his log, instructions
that if any situation arose that necessitated the use of the excore linear
heat rati LC0, the unit would be brought to 80 percent power and not the
90 percent power level identified in TS Figure 2-6.
The NRC inspector reviewed the shift supervisors log entry and found the
instructions did not state that power should be reduced to 30 percent if
the affected LCO was entered.
Instead, the instructions stated that the
shift supervisor should call the reactor engineer if the incore detectors
became inoperable. The NRC inspector interviewed the on-duty (3:30 p.m.
to 11:30 p.m.) shift supervisor who initially received the instructions
from the reactor engineer and the p.m. snift supervisor could not recall
receiving instructions that if the excore monitoring LC0 war invoked to
reduce power to 80 percent.
At that time, he only recalls discussing a
nonconservative but nonquantified error existing with TS Figure 2-6.
In addition, the p.m. shift supervisor did not recall the 80 percent limit
being presented to him until the following day.
The NRC inspector
interviewed other personnel associated with the information provided to
the on-duty p.m. shift supervisor. The reactor engineer stated that he
diriussed the 80 percent limit with the on-duty p.m. shift supervisor on
two occasions. The reactor engineer also stated thct he discussed the
80 percent limit with the night (11:30 p.m. to 7:30 a.m.) shif t supervisor
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and the plant manager.
During an interview with the night shift
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supervisor, the NRC inspector determined that the night shift supervisor
also could not recall the reactor engineer discussing the 80 percent power
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limit. However, the night shift supervisor stated that the on-duty p.m.
shift supervisor notified him af the 80 percent power limit during siifft
turnover.
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During an interview with the plant manager, the plant manager stated to
the NRC inspector that he had called the on-duty p.m. shif t superviser and
had stated that, should problems with the incore detecters occur, power
should be reduced to 80 percent
Therefore, it appears, eeen though the
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on-duty p.m. shift supervisor could not recall being provided with' the
information, approximately 10 days after -the event, that the information
had been provided..to him.
However, the information submitted by the licensee in the letter dated
July 1,1988, provided inaccurate information. .This is an apparent -
violation of 10 CFR Part 50.9.
(285/8822-02)
8.
Exit Interview
The NRC inspectors met with Mr. L. T. Kusek-(Acting Plant Manager) and
other members of the licensee staff on July 8,1988. At this meeting, the
NRC inspectors sumarized the scope of the inspection and the findings.
On July 18, 1988, the NRC inspector met with Mr. W. G. Gates (Plant.
Manager) to discuss additional information related to this inspection that
was discovered after the initial exit interview had been given.
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APPENDIX'B
. PROPOSED. ENFORCEMENT CONFERENCE AGENDA
'0MAHA PUBLIC-POWER DISTRICT-
4
August'1988 ~~
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I.
Introduction and Purpose of Meeting
L.-J. Callan
II. Licensee Presentation
.OPPD Staff
III. NRC Contents
L. J. Callan
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~IV.
Licensee Response
OPPD Staff
V.
Closing Coments
L. J. Callan
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