ML15261A359
| ML15261A359 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 06/03/1998 |
| From: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | |
| Shared Package | |
| ML15261A358 | List: |
| References | |
| 50-269-98-12, 50-270-98-12, 50-287-98-12, NUDOCS 9806160200 | |
| Download: ML15261A359 (9) | |
See also: IR 05000269/1998012
Text
U.S. NUCLEAR REGULATORY COMMISSION
REGION II
Docket Nos:
50-269, 50-270, 50-287, 72-04
License Nos:
DPR-38, DPR-47, DPR-55, SNM-2503
Report No:
50-269/98-12, 50-270/98-12, 50-287/98-12
.Licensee:
Duke Energy Corporation
Facility:
Oconee Nuclear Station, Units 1, 2, and 3
Location:
P. 0. Box 1439
Seneca, SC 29679
Dates:
April 22 - May 20, 1998
Inspectors:
M. Scott, Senior Resident Inspector
D. Billings, Resident Inspector
R. Carroll, Project Engineer
Approved by:
C. Ogle, Chief. Projects Branch 1
Division of Reactor Projects
Enclosure
9806160200 980603
ADOCK 05000269
EXECUTIVE SUMMARY
Oconee Nuclear Station, Units 1, 2. and 3
NRC Special Inspection Report 50-269/98-12.
50-270/98-12, and 50-287/98-12
The purpose of this special inspection was to review and assess the effects of
deficiencies identified with the Oconee Nuclear Station borated water storage
tank level instrumentation and emergency operating procedures. [Applicable
template codes and the assessment for items inspected are provided.]
Engineering
An apparent violation of Technical Specifications and 10 CFR 50.46 was
identified in all three Oconee units for inoperable borated water
storage tank level instruments due to uncompensation for instrument tap
height differences. This not only had the potential to render emergency
core cooling system pumps inoperable and interrupt long-term core
cooling, but could have precluded meeting the required 46 feet (350,000
gallons) of borated water available in the borated water storage tank
for emergency core cooling. (Section E.8.1; [4A-Poor])
An apparent violation of 10 .CFR 50 Appendix B. Criterion III was
identified in all three Oconee units for failures to appropriately
account for the as-built height configuration of the borated water
storage tank level instrument taps (in
system design drawings and
calibration procedures) and the reactor building emergency sump level
instrument uncertainties (in
emergency operating procedures). This not
only had the potential to render emergency core cooling system pumps
inoperable and interrupt long-term core cooling, but could have
precluded meeting the required 46 feet (350,000 gallons) of borated
water available in the borated water storage tank for emergency core
cooling.
(Section E.8.1; [4A-Poor])
Considered noteworthy, was the questioning attitude on the part of Self
Initiated Technical Audit team which initially identified the borated
water storage tank level instrumentation height discrepancy and the
potential emergency operating procedure sump swapover initiation
conflict brought on by reactor building .emergency sump level instrument
uncertainties.
(Section E.8.1; [5A-Good])
Appropriate root cause analysis and short-term corrective actions were
taken by the licensee upon identification of the borated water storage
tank level instrumentation height discrepancy and the potential
emergency operating procedure sump swapover initiation conflict brought
on by reactor building emergency sump level instrument uncertainties.
(Section E.8.1; [5B-Good])
Report Details
Summary of Plant Status
Unit 1 began and ended the period at 100 percent power.
Unit 2 began the period in a scheduled refueling outage. The unit ended the
period in hot shutdown with startup activities in progress.
Unit 3 began and ended the period at 100 percent power.
Review of Updated Final Safety Analysis Report (UFSAR) Commitments
While performing inspections discussed in this r
eport, the inspectors reviewed
the applicable portions of the UFSAR that related to the areas inspected. The
inspectors verified that the UFSAR wording was consistent with the.observed
plant practices, procedures, and parameters.
III. Engineering
E8
Miscellaneous Engineering Issues (92903)
E8.1
Borated Water Storage Tank Level Set Point Error and Emergency Operating
Procedure Discrepancy
a. Inspection Scope (37551. 92903)
Between November 10, 1997 and December 11, 1997, a licensee Self
Initiated Technical Audit (SITA) of the high pressure injection (HPI)
and low pressure injection (LPI) systems identified items requiring
engineering followup. Followup to the SITA findings by the licensee.
identified two concerns involving the borated water storage tank (BWST)
level instrumentation and an EOP conflict concerning manual emergency
core cooling system (ECCS) swapover from the BWST to the reactor
building emergency sump (RBES).
It was the scope of the special
inspection to review and assess the overall effects of these two
concerns.
b. Observations and Findings
Concern number (1):
BWST Level Instrumentation
On February 12. 1998, engineering conducted evaluation and followup of
the lack of a zero reference on the BWST design drawing. Engineering
identified an error on the drawing that affected all of the level
transmitters on each unit's BWST. The drawing revealed the BWST level
indicator taps to be approximately 1 foot (worst case 1.5 feet) below
the value used in the EOP calculations. Since this was not compensated
for in instrument scaling, this introduced an error between indicated
and actual BWST level.
To prevent air entrainment into the suction of
the ECCS pumps, the EOPs require the swapover from the BWST to the RBES
to be completed (i.e., RBES valves open and BWST valves closed) when
BWST level is
< 6 feet and > 2 feet. The condition of the as-found
2
instrumentation (i..e.. worst case indicating 1.5 feet above actual BWST
level) coupled with the EOP guidance, could have led to vortexing in the
BWST and ECCS pump air entrainment prior to completion of the swapover.
Accordingly, operations declared the BWST level instrumentation
inoperable on all three units, entered Technical Specification (TS) 3.0
for all three units, and initiated a one hour non-emergency notification
to the NRC. Maintenance personnel commenced calibrations of the level
transmitters simultaneously on all three units.
Each unit exited TS 3.0
and entered TS 3.3.4 for instrumentation when the calibration of the
first train of level instrumentation was completed. On February 13,
1998, maintenance completed the calibration of the second train of BWST
level instrumentation for each unit and exited TS 3.3.4 at 2:30 a.m. for
Unit 1, 3:09 a.m. for Unit 2. and 3:05 a.m. for Unit 3.
Licensee investigation identified that the BWST level instruments did
not have a height difference calculation included in the instrument
calibration from initial design. The 1986 safety analysis error
calculations, which became the "Emergency Procedure Guidelines Set
Point" document in 1988 (and revised in July 1989). did not identify the
height differences. The licensee replaced the level transmitters in
1989 to conform to Reg Guide 1.97 criteria, but did not identify the
height difference during that modification either. Another missed
opportunity to discover and correct the problem was during the
licensee's evaluation of Information Notice 91-75, Static Head
Corrections Mistakenly Not Included in Pressure Transmitter Calibration
Procedure.
Concern number (2): .EOP Conflict
During outages from December 1984 - December 1986. the current reactor
building (RB) level instruments were installed. On February 19. 1998,
during a review of the aforementioned SITA findings, engineering
identified that the RB wide range level instruments have large
uncertainties (+8.8 inches/-18.1 inches). These uncertainties could
create a conflict with EOP guidance for mitigation of Loss of Coolant
Accidents (LOCAs).
-The guidance in the EOPs from June 1995 - February 1998 required
initiation of the swapover of the suction for the Building Spray (BS)
and the LPI pumps from the BWST to the RBES when BWST level > 6 feet and
RB level > 4 feet. [Note: Implemented in 1985 to assure adequate RBES
inventory for beyond design basis accidents, the required EOP RB level
was changed from > 2 feet to > 3.5 feet in April 1988;-and then again to
> 4 feet at the end of May 1994. (The required EOP BWST level from 1985
to June 1995 was < 6 feet.)] The licensee determined that actual RB
water level at the time of swapover initiation would be 4.5 feet (worst
case 3.07 feet from April 1986 - November 1997 if trapped water issue
initially identified in Licensee Event Report 50-269/97-10 is
considered); thus, indicated sump levels could range from - 3 feet to
5 feet (worst case - 1.5 to - 3.8 feet). Considering the uncertainties
3
in .the RB level instrumentation, the EOP required BWST and RB level
conditions may not have indicated simultaneously (if
at all).
This
could have caused a delay in swapover initiation, resulting in possible
air binding of the pumps as described in concern number (1)
above.
Following licensee review, operations management provided interim
guidance to the operators to address the procedural deficiency and
completed a revision to the EOPs in late February 1998, which requires
swapover initiation when BWST level > 6 feet and RB level is increasing.
(Also a NOTE was added indicating that wide.range RB water level should
be 3 feet and increasing at the time of swapover.) Additionally,
engineering initiated a Failure Investigation Process (FIP) team to
assess the root cause, corrective actions; and past operability of the
systems. The licensee made a 10 CFR 50.72 notification to the NRC. The
licensee issued a preliminary report in Licensee Event Report (LER) 269/98-04, dated March 14, 1998, which was revised on April 7. 1998.
As indicated above, the licensee installed the current RB level
instruments from December 1984 - December 1986. Revised RB level
instrument uncertainty calculations in February 1988 (+8.8 inches/-21
inches) did not identify an EOP conflict since the RB level for a design
basis LOCA was 5.3 feet at the time. Similarly, an EOP conflict was not
identified in April 1988 when the RB level set point was changed to >
3.5 feet. However, in July 1989 (when the "Emergency Procedure
Guidelines Set Point" document was revised) and in May 1994 (when the RB
level set point was changed to 4 feet) the EOP conflict existed, but was
not recognized. Another opportunity to.identify the EOP conflict was
missed in November 1997 when the trapped water issue (i.e., potentiaT
blocking of installed reactor cavity flange drain and fuel transfer
canal drain strainers traps -
100,000 gallons of water) resulted in an
actual RB water level determination of 3.07 feet (to which the 1996
revised RB level uncertainties of +8.8 inches/-18.1 inches should have
been applied).
Due to previously unaccounted for water allowances
(i.e.. reactor coolant system shrinkage, pressurizer refill, BS piping
refill, and vapor content maintaining RB pressure), actual calculated RB
water level only increased to 4.5 feet after the trapped water issue was
resolved.
Evaluation of Safety Significance
10 CFR 50.46 requires that the ECCS must be designed to be capable of
long-term cooling of the reactor core. In conjunction with this: TS 3.3.4 requires that the BWST have operable two level instrument channels
and contain a minimum level of 46 feet of borated water: TS 3.3.1
requires two independent HPI trains capable of taking suction from the
BWST and LPI system to be operable TS 3.3.2 requires two independent
LPI trains capable of taking suction from the BWST and RBES to be
operable; and TS 3.3.6 requires both BS trains capable of taking suction
from the LPI system to be operable.
The time to exhaust the BWST inventory and manually swapover the ECCS
4
pumps to the RBES varies, depending on the size and location of the
break and the operating times of the pairs of ECCS suction valves from
the BWST and RBES. To prevent air entrainment into the suction of the
ECCS pumps, the EOPs require swapover to be completed (i.e., RBES valves
open and BWST valves closed) when BWST level is < 6 feet and > 2 feet.
Original EOP guidance indicated that swapover to the RBES should occur
upon receipt of a low-low level-alarm that was set at a BWST level of 3
feet (for which actual level would have been 1.5 feet if worst case
instrument tap height of 1.5 feet were applied): there was no
conditional RB level. Subsequently, EOP swapover guidance was changed
to:
BWST level < 6 feet AND RB level > 2 feet (1985); BWST level < 6
feet AND RB level > 3.5 feet (April 1988); BWST level < 6 feet AND > 4
feet (May 1994); and BWST level > 6 feet AND RB level > 4 feet (June
1995 - February 1998).
For all LOCA scenarios where indicated RB level would have been less
than that specified in the EOP at the time for swapover initiation, the
licensee determined that long-term cooling would be achieved. As
discussed in associated LER 50-269/98-04 (revision 1), this conclusion
was predicated on: personnel (operators, Shift Technical Advisor,
Technical Support Center) diligence; LPI and BS pump durability;
availability of the spare C LPI pump: and EOP recovery guidance. The
incremental core damage potential was estimated by the licensee to be
9.2E-7 for this event, compared to the nominal core damage probability
of 8.9E-5 per reactor.
Regardless, a conflict would have existed and the EOP could not have
been performed as written in all LOCA scenarios where RB level
instrument uncertainties would have resulted in indicated RB level being
less than that specified in the EOP at the time for swapover initiation.
Consequently, a resultant delay (coupled with an actual BWST water level
lower than indicated) could have led to vortexing the BWST in a time
limited LOCA scenario thereby, causing possible ECCS (LPI, HPI and BS)
pump inoperability and interruption of long-term core cooling due to air
entrainment prior to completion of the swapover from the BWST to the
RBES.
The inspectors determined that from initial construction until
correction in February 1998, the BWST level instrumentation in all three
Oconee Units did not have a height difference calculation included in
their instrument calibration: thereby making them inoperable due to
indicating as much as 1.5 feet higher than actual BWST level. This not
only had the potential to render ECCS-pumps inoperable and interrupt
long-term core cooling as discussed above, but could have precluded
meeting the required 46 feet (350.000 gallons) of borated water
available in the BWST for emergency core cooling. Accordingly, this is
being identified as apparent violation (EEI) 50-269.270.287/98-12-01:
Failure.to Meet TS and 10 CFR 50.46 for Long-Term Cooling Requirements.
The inspectors also determined that the failures to appropriately
account for the as-built height configuration of the BWST level
5
instrument taps (in
system design drawings and calibration procedures
from initial construction until February 1998) and the RBES level
instrument uncertainties (in
EOPs since instrument installation in
December 1986 until February 1998) did not meet the design control
requirements of 10 CFR 50 Appendix B. Criterion III.
This not only had
the potential to render ECCS pumps inoperable and interrupt long-term
core cooling as discussed above,-but could have precluded meeting the
required 46 feet (350,000 gallons) of borated water available in the
BWST for emergency core cooling. Accordingly, this is being identified
as EEI 50-269,270,287/98-12-02: Failure to .Meet Design Control
Requirements of 10 CFR 50 Appendix B. Criterion III.
Root Cause Analysis and Corrective Actions
The licensee's root cause investigation team concluded that the root
cause of the BWST level instrumentation problem was deficient
documentation (deficient written procedure). The root cause of the RBES
wide range water level EOP Set Point conflict was attributed to design
deficiency (inadequate design analysis). These failures to account for
the as-built height configuration of the BWST level instrument taps and
the RBES level instrument uncertainties could have led to the ECCS being
'seriously degraded or inoperable.
As indicated in LER 50-269/98-04 (revision 1). the licensee's corrective
actions included: revising the BWST drawing and level instrument
calibration procedure to add a zero reference for calibration:
recalibrating BWST level indicators: changing EOPs to resolve the
conflict; reviewing installed instruments used in surveillances and
periodic tests which might require head corrections (none impacted):
surveying Unit 2 reactor coolant system narrow and wide range pressure
instruments and revising calibration procedures to include head
correction (bounding evaluation performed for Units 1 and 3. revealing
no impact): plans to review all EOP.set points for accuracy, minimum,
and maximum values; plans to obtain precise elevations for Units 1 and 3
reactor coolant system narrow and wide range pressure instruments and
revise calibration procedures: plans to ensure directives/procedures
used to perform SITAs assure relevant operating experience is
appropriately addressed; plans to perform risk-informed review of
operating experience: and plans to develop a process to identify,
control and maintain Oconee-specific calculation inputs.
c.
Conclusions
Licensee-identified failures to appropriately account for the as-built
height configuration of the borated water storage tank level instrument
taps (in
system design drawings and calibration procedures) and the
reactor building emergency sump level instrument uncertainties (in
emergency operating procedures)could have potentially rendered emergency
core cooling system pumps inoperable and interrupted long-term core
cooling during a loss of coolant accident in any of the three Oconee
Units. Accordingly, two apparent violations were identified .for failure
6
to meet design control requirements of 10 CFR 50 Appendix B, Criterion
III and failure to meet the requirements of Technical Specifications and
10 CFR 50.46 for long-term core cooling.
Noteworthy was the questioning attitude on the part of Self-Initiated
Technical Audit team which initially identified the borated water
storage tank level instrumentat-ion height discrepancy and the potential
emergency operating procedure sump swapover initiation conflict brought
on by reactor building emergency sump level instrument uncertainties.
The root cause analysis and short-term corrective actions taken by the
licensee upon identification of the issue were considered appropriate.
E8.2 (Closed) Unresolved Item (URI) 50-269,270,287/98-02-10: Inaccurate BWST
and RBES Instrumentation
Following initial inspection of identified deficiencies with the borated
water storage tank level instrumentation and emergency operating
procedures for all three Units of the Oconee Nuclear Station, this URI
was opened pending an in-depth review of associated LER 50-269/98-04
(revision 1).
Based on such a review and the resultant apparent
violations identified in Section E8.1. this URI is considered closed.
V. Management Meetings and Other Areas
X1
Exit Meeting Summary
The inspectors presented the inspection results to members of licensee
management at the conclusion of the inspection on May 21. 1998. The licensee
acknowledged the findings presented. The inspectors asked the licensee
whether any materials examined during the inspection should be considered
proprietary. No proprietary information was identified.
PARTIAL LIST OF PERSONS CONTACTED
E. Burchfield, Regulatory Compliance Manager
T. Curtis, Operations Superintendent
T. Saville, Primary Systems Supervisor
W. Foster, Safety Assurance Manager
C. Little, Electrical Systems/Equipment Engineering Manager
W. McCollum, Vice President, Oconee Site
M. Nazar, Manager of Engineering
J. Forbes, Station Manager
J. Smith, Regulatory Compliance
Other licensee employees contacted included operations, engineering, and
maintenance personnel.
7
INSPECTION PROCEDURES USED
IP 37551:
Onsite Engineering
IP 92903:
Followup - Engineering
ITEMS OPENED, CLOSED, AND DISCUSSED
oened
50-269,270,287/98-12-01
Failure to Meet TS and 10 CFR 50.46 for
Long-Term Cooling Requirements (Section
E8.1)
50-269,270,287/98-12-02
Failure to Meet Design Control
Requirements of 10CFR 50 Appendix B,
Criterion III (Section E8.1)
Closed
50-269,270,287/98-02-10
Inaccurate BWST and RBES Instrumentation
(Section E8.2)
Discussed
50-269/98-04 (rev 0 & 1)
LER
ECCS -Outside Design Basis Due To
Instrument Errors/Deficient Procedures
(Section E8.1)
LIST OF-ACRONYMS USED
BS
Building Spray
BWST
Borated Water Storage Tank
CFR
Code of Federal Regulations
Enforcement Action
Apparent Violation
Emergency Operating Procedures
Engineered Safeguards
High Pressure Injection
LER
Licensee Event Report
Low Pressure Injection
Loss of Coolant Accident
Reactor Building
RBES
Reactor Building Emergency Sump
SITA
Self-Initiated Technical Audit
TS
Technical Specification(s)
Updated Final Safety Analysis Report
.
Unresolved Item
United States Nuclear Regulatory Commission