ML24135A177
| ML24135A177 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 05/15/2024 |
| From: | Richard Skokowski NRC/RGN-III/DORS/RPB3 |
| To: | Conboy T Northern States Power Company, Minnesota |
| References | |
| IR 2024001 | |
| Download: ML24135A177 (1) | |
See also: IR 05000282/2024001
Text
Thomas A. Conboy
Site Vice President
Prairie Island Nuclear Generating Plant
Northern States Power Company, Minnesota
1717 Wakonade Drive East
Welch, MN 55089-9642
SUBJECT:
PRAIRIE ISLAND NUCLEAR GENERATING PLANT - INTEGRATED
INSPECTION REPORT 05000282/2024001 AND 05000306/2024001
Dear Thomas Conboy:
On March 31, 2024, the U.S. Nuclear Regulatory Commission (NRC) completed an inspection
at Prairie Island Nuclear Generating Plant. On April 9, 2024, the NRC inspectors discussed the
results of this inspection with you and other members of your staff. The results of this inspection
are documented in the enclosed report.
Two findings of very low safety significance (Green) are documented in this report. One of these
findings involved a violation of NRC requirements. We are treating this violation as a non-cited
violation (NCV) consistent with Section 2.3.2 of the Enforcement Policy.
If you contest the violation or the significance or severity of the violation documented in this
inspection report, you should provide a response within 30 days of the date of this inspection
report, with the basis for your denial, to the U.S. Nuclear Regulatory Commission,
ATTN: Document Control Desk, Washington, DC 20555-0001; with copies to the Regional
Administrator, Region III; the Director, Office of Enforcement; and the NRC Resident Inspector
at Prairie Island Nuclear Generating Plant.
If you disagree with a cross-cutting aspect assignment or a finding not associated with a
regulatory requirement in this report, you should provide a response within 30 days of the date
of this inspection report, with the basis for your disagreement, to the U.S. Nuclear Regulatory
Commission, ATTN: Document Control Desk, Washington, DC 20555-0001; with copies to the
Regional Administrator, Region III; and the NRC Resident Inspector at Prairie Island Nuclear
Generating Plant.
May 15, 2024
T. Conboy
2
This letter, its enclosure, and your response (if any) will be made available for public inspection
and copying at http://www.nrc.gov/reading-rm/adams.html and at the NRC Public Document
Room in accordance with Title 10 of the Code of Federal Regulations 2.390, Public
Inspections, Exemptions, Requests for Withholding.
Sincerely,
Richard A. Skokowski, Chief
Reactor Projects Branch 3
Division of Operating Reactor Safety
Docket Nos. 05000282 and 05000306
License Nos. DPR-42 and DPR-60
Enclosure:
As stated
cc w/ encl: Distribution via LISTSERV
Signed by Skokowski, Richard
on 05/15/24
SUNSI Review
Non-Sensitive
Sensitive
Publicly Available
Non-Publicly Available
OFFICE
RIII
EICS
RIII
NAME
RElliott:gmp
DBetancourt-Roldan
via email
RSkokowski
DATE
05/14/2024
05/15/2024
05/15/2024
Enclosure
U.S. NUCLEAR REGULATORY COMMISSION
Inspection Report
Docket Numbers:
05000282 and 05000306
License Numbers:
Report Numbers:
05000282/2024001 and 05000306/2024001
Enterprise Identifier:
I-2024-001-0078
Licensee:
Northern States Power Company
Facility:
Prairie Island Nuclear Generating Plant
Location:
Welch, MN
Inspection Dates:
January 01, 2024 to April 10, 2024
Inspectors:
M. Abuhamdan, Reactor Inspector
T. Ospino, Resident Inspector
K. Pusateri, Resident Inspector
D. Tesar, Senior Resident Inspector
Approved By:
Richard A. Skokowski, Chief
Reactor Projects Branch 3
Division of Operating Reactor Safety
2
SUMMARY
The U.S. Nuclear Regulatory Commission (NRC) continued monitoring the licensees
performance by conducting an integrated inspection at Prairie Island Nuclear Generating Plant,
in accordance with the Reactor Oversight Process. The Reactor Oversight Process is the NRCs
program for overseeing the safe operation of commercial nuclear power reactors. Refer to
https://www.nrc.gov/reactors/operating/oversight.html for more information.
List of Findings and Violations
Failure to Adequately Implement the Requirements of 10 CFR 50, Appendix B, Criterion XVI
Cornerstone
Significance
Cross-Cutting
Aspect
Report
Section
Mitigating
Systems
Green
NCV 05000282,05000306/2024001-02
Open/Closed
[P.3] -
Resolution
The inspectors identified a Green finding and associated non-cited violation of Title 10 of the
Code of Federal Regulations (10 CFR), Part 50, Appendix B, Criterion XVI, Corrective
Action, associated with the licensees failure to correct conditions adverse to quality (CAQ).
Specifically, the inspectors identified that the licensee failed to take adequate corrective
actions to correct a CAQ. Consequently, this failure would have allowed a CAQ associated
with safety related structures, systems, and components (SSC's) to remain uncorrected
absent inspector intervention.
Failure to Provide Adequate Oversight to Supplementary Personnel Resulting in a Reactor
Trip
Cornerstone
Significance
Cross-Cutting
Aspect
Report
Section
Green
FIN 05000282,05000306/2024001-03
Open/Closed
[H.2] - Field
Presence
The inspectors identified a Green finding when the licensee failed to meet the standards of
procedure FP-MA-COM-02, "Oversight and Control of Supplementary Personnel."
Specifically, the licensee failed to provide supplemental workers with an appropriate level of
oversight and engagement to ensure performance was commensurate with station standards
and expectations, resulting in a loss of all non-safeguards busses and a Unit 1 turbine and
Additional Tracking Items
Type
Issue Number
Title
Report Section
Status
Unresolved Item Associated
with Modifications to
Motor-Operated Valve Limit
Switch
Open
LER
05000282,05000306/20
23-001-01
LER 2023-001-01 for Prairie
Island Nuclear Generating
Plant, Units 1 and 2, Reactor
Trip, Auxiliary Feedwater
Closed
3
and Emergency Service
Water System Actuation due
Control Power Cables
LER
05000282,05000306/20
23-001-00
LER 2023-001-00 for Prairie
Island Nuclear Generating
Plant, Units 1 and 2, Reactor
Trip, Auxiliary Feedwater
and Emergency Service
Water System Actuation due
Control Power Cables
Closed
4
PLANT STATUS
Unit 1 entered the inspection period shut down in Mode 3 (hot standby). Unit 1 went critical on
January 24, 2024, entered Mode 1 (power operation) on January 27, 2024, and reached
full-rated thermal power on January 29, 2024. Unit 1 was then shut down to Mode 3 to facilitate
repairs on a main feed pump discharge line on February 8, 2024. Unit 1 returned to critical on
February 11, 2024, entered Mode 1 on February 12, 2024, and reached full-rated thermal power
on February 14, 2024. Unit 1 maintained at or near full-rated thermal power for the remainder of
the inspection period.
Unit 2 entered the inspection period shut down for refueling outage 2R33. Unit 2 went critical on
February 29, 2024, reached Mode 1 on March 1, 2024, and reached 50 percent power on
March 2, 2024. Unit 2 subsequently tripped from 50 percent power and entered Mode 3 on
March 3, 2024. Unit 2 returned to critical on March 7, 2024, Mode 1 on March 8, 2024, and
reached full-rated thermal power on March 18, 2024. Unit 2 remained at or near full-rated
thermal power for the remainder of the inspection period.
INSPECTION SCOPES
Inspections were conducted using the appropriate portions of the inspection procedures (IPs) in
effect at the beginning of the inspection unless otherwise noted. Currently approved IPs with
their attached revision histories are located on the public website at http://www.nrc.gov/reading-
rm/doc-collections/insp-manual/inspection-procedure/index.html. Samples were declared
complete when the IP requirements most appropriate to the inspection activity were met
consistent with Inspection Manual Chapter (IMC) 2515, Light-Water Reactor Inspection
Program - Operations Phase. The inspectors performed activities described in IMC 2515,
Appendix D, Plant Status, observed risk significant activities, and completed on-site portions of
IPs. The inspectors reviewed selected procedures and records, observed activities, and
interviewed personnel to assess licensee performance and compliance with Commission rules
and regulations, license conditions, site procedures, and standards.
REACTOR SAFETY
71111.01 - Adverse Weather Protection
Seasonal Extreme Weather Sample (IP Section 03.01) (1 Sample)
(1)
The inspectors evaluated readiness for seasonal extreme weather conditions prior to
the onset of a winter storm for the following systems:
AB-2 entry for winter storm warning on January 11, 2024
71111.04 - Equipment Alignment
Partial Walkdown Sample (IP Section 03.01) (4 Samples)
The inspectors evaluated system configurations during partial walkdowns of the following
systems/trains:
(1)
D6 emergency diesel generator on January 3, 2024
(2)
C1.1.38 common fuel system status on January 4, 2024
5
(3)
D1/D2 diesel generators on March 11, 2024
(4)
Unit 2 auxiliary feedwater system on March 13, 2024
71111.05 - Fire Protection
Fire Area Walkdown and Inspection Sample (IP Section 03.01) (5 Samples)
The inspectors evaluated the implementation of the fire protection program by conducting a
walkdown and performing a review to verify program compliance, equipment functionality,
material condition, and operational readiness of the following fire areas:
(1)
door 43 fire impairment and fire areas 8 and 32 on February 20, 2024
(2)
fire zone 82, D1 diesel room on March 11, 2024
(3)
fire zone 35, battery rooms 21 and 22 on March 13, 2024
(4)
fire zone 2, auxiliary feed pump room, elevation 695' on March 13, 2024
(5)
fire zone 1, battery rooms 11 and 12 on March 13, 2024
Fire Brigade Drill Performance Sample (IP Section 03.02) (1 Sample)
(1)
The inspectors evaluated the onsite fire brigade training and performance during an
unannounced fire drill for crew 5 on March 19, 2024.
71111.06 - Flood Protection Measures
Flooding Sample (IP Section 03.01) (1 Sample)
(1)
The inspectors evaluated internal flooding mitigation protections following failure of
door 43 to close on February 28, 2024.
71111.11Q - Licensed Operator Requalification Program and Licensed Operator Performance
Licensed Operator Performance in the Actual Plant/Main Control Room (IP Section 03.01)
(7 Samples)
(1)
The inspectors observed and evaluated licensed operator performance in the control
room during Unit 1 reactor startup on January 24, 2024.
(2)
The inspectors observed and evaluated licensed operator performance in the control
room during Unit 1 reactor shutdown for a steam leak on February 8, 2024.
(3)
The inspectors observed and evaluated licensed operator performance in the control
room during Unit 1 reactor startup from a forced outage on February 11, 2024.
(4)
The inspectors observed and evaluated licensed operator performance in the control
room during Unit 2 reactor startup from a refueling outage with source range NI failure
on February 20, 2024.
(5)
The inspectors observed and evaluated licensed operator performance in the control
room during Unit 2 reactor startup from a refueling outage on February 29, 2024.
(6)
The inspectors observed and evaluated licensed operator performance in the control
room during Unit 2 trip response on March 3, 2024.
(7)
The inspectors observed and evaluated licensed operator performance in the control
room during Unit 2 reactor startup from a forced outage on March 7, 2024.
6
Licensed Operator Requalification Training/Examinations (IP Section 03.02) (1 Sample)
(1)
The inspectors observed and evaluated licensed operator requalification training
as-found testing on March 18, 2024.
71111.12 - Maintenance Effectiveness
Maintenance Effectiveness (IP Section 03.01) (6 Samples)
The inspectors evaluated the effectiveness of maintenance to ensure the following
structures, systems, and components (SSCs) remain capable of performing their intended
function:
(1)
21 cooling water pump replacement on January 17, 2024
(2)
multiple trips CB401 breaker on 28 inverter on January 17, 2024
(3)
Corrective Action Plan (CAP) 501000079768, "ISI [inservice inspection] Indication
Evaluation for SP2168.13," on January 17, 2024
(4)
MV-32019 21 turbine driven auxiliary feedwater (TDAFW) pump steam inlet isolation
valve on January 18, 2024
(5)
Work Order (WO) 700087060, "22 TDAFW Pump Maintenance," on
February 22, 2024
(6)
condensate demineralizer review following Unit 2 reactor trip on March 4, 2024
71111.13 - Maintenance Risk Assessments and Emergent Work Control
Risk Assessment and Management Sample (IP Section 03.01) (6 Samples)
The inspectors evaluated the accuracy and completeness of risk assessments for the
following planned and emergent work activities to ensure configuration changes and
appropriate work controls were addressed:
(1)
operational decision-making instruction (ODMI) for Unit 1 startup on January 8, 2024
(2)
risk evaluation for transition from shutdown risk to online risk on January 15, 2024
(3)
risk associated with emergent issues on Unit 1 circulating water and impact on Unit 1
startup on January 18, 2024
(4)
extended operation in lowered inventory risk evaluation on February 6, 2024
(5)
ODMI & adverse condition monitoring plan for Unit 2 startup with 22 reactor coolant
pump (RCP) second seal degraded on February 29, 2024
(6)
risk management following Unit 2 trip and subsequent startup on March 4, 2024
71111.15 - Operability Determinations and Functionality Assessments
Operability Determination or Functionality Assessment (IP Section 03.01) (8 Samples)
The inspectors evaluated the licensee's justifications and actions associated with the
following operability determinations and functionality assessments:
(1)
reactor coolant system evaluation for Technical Specification 3.4.3 on
October 25, 2023
(2)
source range nuclear instrument seismic qualification on December 5, 2023
(3)
CAP 501000080389, "D6 Fuel Oil Leak Getting Worse," on January 3, 2024
7
(4)
past operability review MV-32019 21 TDAWF pump on January 11, 2024
(5)
application of Technical Specification Limiting Condition for Operation (LCO) 3.0.4.b
for mode change on January 25, 2024
(6)
bus 25/26 and bus 27 circuit breaker sequencing on February 6, 2024
(7)
prompt operability determination for D1/D2 HELP question on February 29, 2024
(8)
CAP 501000082220, "POD 50000327699 Unit 1 HELB," on March 6, 2024
71111.20 - Refueling and Other Outage Activities
Refueling/Other Outage Sample (IP Section 03.01) (1 Sample)
(1)
The inspectors evaluated refueling outage activities from January 1, 2024, to
March 1, 2024.
71111.24 - Testing and Maintenance of Equipment Important to Risk
The inspectors evaluated the following testing and maintenance activities to verify system
operability and/or functionality:
Post-Maintenance Testing (PMT) (IP Section 03.01) (8 Samples)
(1)
WO 700133040, "CV-31321 Diaphragm Leaking (PMT/LLRT [local leak rate test]),"
on January 11, 2024
(2)
22 reactor coolant pump seal replacement PMT on January 17, 2024
(3)
22 turbine driven auxiliary feedwater pump PMT on January 31, 2024
(4)
WO 700087060, "22 Turbine Driven AFW [auxiliary feedwater] Pump Quarterly
Test - PMT," on February 18, 2024
(5)
WO 700127367, "MV-32016," on March 13, 2024
(6)
WO 700135613, "SP 2406 MSIV [main steam isolation valve] In Service Test," on
March 21, 2024
(7)
SP 1073B, "Monthly Train B Shield Building Ventilation System Test," on
March 25, 2024
(8)
WO 700133173, "SP 1106B 22 DDCL [diesel-driven cooling water] Pump
Comprehensive Test," on March 25, 2024
Surveillance Testing (IP Section 03.01) (4 Samples)
(1)
WO 700044983, "SP 1070 Rx Coolant Sys Integrity Test," on January 11, 2024
(2)
SP 2750, "Containment Close-out," on January 29, 2024
(3)
SP 2750, "Containment Close-out," on February 16, 2024
(4)
WO 700125323, "SP 1155B 12 Component Cooling Water Quarterly Surveillance,"
on March 20, 2024
Inservice Testing (IST) (IP Section 03.01) (1 Sample)
(1)
WO 700125737, "SP 1106C 121 Cooling Water Pump Quarterly Test," on
February 22, 2024
8
Reactor Coolant System Leakage Detection Testing (IP Section 03.01) (2 Samples)
(1)
LLRT total leak rate for Unit 2 2R33 refueling outage on October 6, 2023
(2)
SP 2070, "RCS Integrity Test Unit 2," on January 1, 2024
OTHER ACTIVITIES - BASELINE
71151 - Performance Indicator Verification
The inspectors verified licensee performance indicators submittals listed below:
IE01: Unplanned Scrams per 7000 Critical Hours Sample (IP Section 02.01) (2 Samples)
(1)
Unit 1 (January 1, 2023, through December 31, 2023)
(2)
Unit 2 (January 1, 2023, through December 31, 2023)
IE03: Unplanned Power Changes per 7000 Critical Hours Sample (IP Section 02.02)
(2 Samples)
(1)
Unit 1 (January 1, 2023, through December 31, 2023)
(2)
Unit 2 (January 1, 2023, through December 31, 2023)
IE04: Unplanned Scrams with Complications (USwC) Sample (IP Section 02.03) (2 Samples)
(1)
Unit 1 (January 1, 2023, through December 31, 2023)
(2)
Unit 2 (January 1, 2023, through December 31, 2023)
71153 - Follow Up of Events and Notices of Enforcement Discretion
Event Follow up (IP Section 03.01) (1 Sample)
(1)
The inspectors evaluated site response to the Unit 1 trip on January 25, 2024.
Event Report (IP Section 03.02) (2 Samples)
The inspectors evaluated the following licensee event reports (LERs):
(1)
LER 05000282, 05000306/2023-001-00 for Prairie Island Nuclear Generating Plant,
Units 1 and 2, "Reactor Trip, Auxiliary Feedwater and Emergency Service Water
System Actuation due to Electrical Transient in DC Control Power Cables"
(ADAMS Accession No. ML23338A277). The inspection conclusions associated with
this LER are documented in this report under Inspection Results Section 71153. This
LER is closed.
(2)
LER 05000282, 05000306/2023-001-01 for Prairie Island Nuclear Generating Plant,
Units 1 and 2, "Reactor Trip, Auxiliary Feedwater and Emergency Service Water
System Actuation due to Electrical Transient in DC Control Power Cables"
(ADAMS Accession No. ML24081A153). The inspectors reviewed the updated LER
submittal. The previous LER submittal was also reviewed in this inspection report
under Inspection Results Section 71153. This LER is closed.
9
INSPECTION RESULTS
Unresolved Item
(Open)
Unresolved Item Associated with Modifications to
Motor-Operated Valve Limit Switch
Description:
During the 2R33 refueling outage, modifications were made to the safety related limit switch
installed on motor-operated valve, MV-32019, 21 steam generator main steam supply to the
22 turbine driven auxiliary feedwater pump. Specifically, the gears inside the replacement
switch were stainless steel rather than bronze (not like for like), the intermittent shaft had an
additional hole drilled through it perpendicular to the manufacturer provided hole, and the
orientation of the rotor was changed from that provided by the vendor.
Planned Closure Actions: Review licensee evaluation of the changes in material and the
modifications made to the limit switch, their impact on seismic qualification, and the potential
impact to operability.
Licensee Actions: Evaluate the impact of the differences in material and the impact of the
modifications made as well as the resultant impact on seismic qualification and potential
operability impacts.
Corrective Action References: 501000079553, "Bkr 211J-13 Tripped During PMT/RTS"
501000079667, "Manually Operated MV-32019 per COO-17"
501000081027, "MOV Limit Switch Grease Related Failures"
501000081105, "MV-32019 Thermals Tripped D"
501000083170, "LEGACY: MV-32019 Limit Switch Material"
501000083626, "MV-32019 Limit Switch"
Failure to Adequately Implement the Requirements of 10 CFR 50, Appendix B, Criterion XVI
Cornerstone
Significance
Cross-Cutting
Aspect
Report
Section
Mitigating
Systems
Green
NCV 05000282,05000306/2024001-02
Open/Closed
[P.3] -
Resolution
The inspectors identified a Green finding and associated non-cited violation of Title 10 of the
Code of Federal Regulations (10 CFR), Part 50, Appendix B, Criterion XVI, Corrective
Action, associated with the licensees failure to correct conditions adverse to quality (CAQ).
Specifically, the inspectors identified that the licensee failed to take adequate corrective
actions to correct a CAQ. Consequently, this failure would have allowed a CAQ associated
with safety related structures, systems, and components )SSC's) to remain uncorrected
absent inspector intervention.
Description:
During the Prairie Island Unit 2 refueling outage, inspectors identified an example where the
licensee failed to take corrective actions adequate to resolve the condition adverse to quality
absent inspector intervention:
Preventive maintenance (PM) procedure, "PM 3132-1-22: 22 TDAFWP [Turbine Driven
Auxiliary Feedwater Pump] Minor Insp [Inspection]" step 7.10.2 specifies to Measure and
10
Document "As-Found" data in the corresponding table. The step is followed by the following
note: "RCE 01132098 indicates that proper coupling alignment is critical in preventing turbine
bearing failure. Deviations from the values listed in the Reference table must be evaluated by
the system engineer. The most critical dimension is the vertical offset value due to predicted
thermal expansion which would occur during turbine operation." The "As-Found" data
recorded in the table was outside of the values listed in the Reference table in both the
horizontal and vertical directions. Despite the note indicating that the values must be
evaluated by the system engineer, no CAP was written, and the PM was documented as
having been completed satisfactorily. Inspectors determined that this was a condition adverse
to quality, and the requisite corrective action to perform an engineering evaluation was not
performed, as required by procedure PM 3132-1-22.
Corrective Actions: The licensee has entered the item into the corrective action program and
completed the required actions to address the condition adverse to quality.
Corrective Action References: 501000082185
Performance Assessment:
Performance Deficiency: The licensee's failure to identify and correct a condition adverse to
quality, such as nonconformances and deficiencies, in accordance with 10 CFR 50,
Appendix B, Criterion XVI was a performance deficiency. Specifically, the inspectors
identified that during preventive maintenance procedure PM 3132-1-22: 22 "TDAFWP Minor
Insp," maintenance personnel recorded data which did not meet acceptance criteria, a
condition adverse to quality, and the requisite corrective action to perform an engineering
evaluation was not performed. Inspectors determined that the failure of the licensee to
identify and correct this CAQ was within the ability of the licensee to foresee and correct and
was therefore a performance deficiency.
Screening: The inspectors determined the performance deficiency was more than minor
because it was associated with the Equipment Performance attribute of the Mitigating
Systems cornerstone and adversely affected the cornerstone objective to ensure the
availability, reliability, and capability of systems that respond to initiating events to prevent
undesirable consequences. Inspectors determined that the licensee's failure to identify and
correct a condition adverse to quality could have result in the failure of a safety related SSCs
to perform its intended safety function. Specifically, the deviation from acceptance criteria
associated with the TDAFWP had the potential to cause premature bearing failure as
specified in PM 3132-1-22 and Root Cause Evaluation (RCE) 1132098.
Significance: The inspectors assessed the significance of the finding using IMC 0609
Appendix A, The Significance Determination Process (SDP) for Findings At-Power. The
inspectors determined that the issue was of very low safety significance and screened to
Green by answering "No" to all of the questions in Exhibit 2 - Mitigating Systems Screening
Questions.
Cross-Cutting Aspect: P.3 - Resolution: The organization takes effective corrective actions to
address issues in a timely manner commensurate with their safety significance. The licensee
failed to ensure appropriate corrective actions for a condition adverse to quality were taken in
a manner commensurate with its safety significance.
11
Enforcement:
Violation: The requirements of 10 CFR 50, Appendix B, Criterion XVI, "Corrective Action,"
specifies in part that, "Measures shall be established to assure that conditions adverse to
quality, such as failures, malfunctions, deficiencies, deviations, defective material and
equipment, and nonconformances are promptly identified and corrected."
Contrary to the above, from December 5, 2023 thru January 28, 2024, the licensee failed to
establish measures to assure that conditions adverse to quality are promptly identified and
corrected. Specifically, the licensee failed to identify and correct deviations associated with
the as-found acceptance criteria requirements for the Turbine Driven Auxiliary Feedwater
Pump (TDAFWP). The as-found turbine bearing coupling alignment data were outside the
acceptance criteria values.
Enforcement Action: This violation is being treated as a non-cited violation, consistent with
Section 2.3.2 of the Enforcement Policy.
Failure to Provide Adequate Oversight to Supplementary Personnel Resulting in a Reactor
Trip
Cornerstone
Significance
Cross-Cutting
Aspect
Report
Section
Green
FIN 05000282,05000306/2024001-03
Open/Closed
[H.2] - Field
Presence
The inspectors identified a Green finding when the licensee failed to meet the standards of
procedure FP-MA-COM-02, "Oversight and Control of Supplementary Personnel."
Specifically, the licensee failed to provide supplemental workers with an appropriate level of
oversight and engagement to ensure performance was commensurate with station standards
and expectations, resulting in a loss of all non-safeguards busses and a Unit 1 turbine and
Description:
On October 19, 2023, horizontal directional drilling (HDD) activities were being performed at
the Prairie Island Nuclear Generating Plant (PINGP) in support of degraded cable
replacement as part of the Unit 2 refueling outage. The HDD was from the plant switchyard to
just inside the protected area fence and was being conducted by the Xcel Energy
Transmission & Distribution (T&D) group. At 11:10 a.m. on October 19, 2023, with Unit 1
operating at 100 percent power, multiple substation breakers unexpectedly opened and,
simultaneously, multiple grounds were detected on direct current (DC) control power cabling
from the plant to the substation control house. This resulted in a loss of all non-safety related
busses simultaneously with a Unit 1 turbine trip and reactor trip, and the actuation of auxiliary
feedwater and emergency service water. Operators responded to the event in accordance
with approved plant procedures and safely placed the plant in Mode 3, hot shutdown. NRC
inspectors responded to the site to provide oversight of licensee response. Unit 1 was
subsequently cooled down to Mode 5, cold shutdown.
The site determined that the HDD in progress at the site damaged DC control cables resulting
in the identified plant response. The licensee root cause evaluation determined the root
causes were weakness in the excavation permit approval process as well as inadequate
oversight of the personnel performing the work. The T&D workers were Xcel Energy
12
employees with authorized access to the respective areas, and little oversight was provided
based upon this. However, this was not in compliance with licensee procedure
FP-MA-COM-02 "Oversight and Control of Supplementary Personnel," which specifies that
oversight be provided to supplemental personnel "anytime work is to be accomplished at
NSPM nuclear facilities by personnel other than permanent nuclear business unit
employees." The procedure further specifies that it is the responsibility of the department
manager/functional area manager or designee to "provide in-field oversight, observations,
and coaching to supplemental workers."
This finding is NRC-identified because the inspectors had identified a previous weakness in
the licensee's oversight of work from the same workgroup (Transmission and
Distribution - T&D), both in the quality of work and the oversight of the supplemental workers.
This issue was reviewed using Inspection Procedure 71153, "Follow up of Events and
Notices of Enforcement Discretion," and was reported in Licensee Event Reports (LERs)
05000282, 05000306/2023-001-00 and 05000282, 05000306/2023-001-01 for Prairie Island
Nuclear Generating Plant, Units 1 and 2, "Reactor Trip, Auxiliary Feedwater and Emergency
Service Water System Actuation due to Electrical Transient in DC Control Power Cables"
(ADAMS Accession Nos. ML23338A277 and ML24081A153).
Corrective Actions: The licensee replaced and tested all damaged cables. In addition, they
implemented procedure changes to strengthen the requirements for excavation onsite as well
as incorporating duties and responsibilities of individuals responsible for oversight of
supplemental personnel.
Corrective Action References: CAP 501000077958
Performance Assessment:
Performance Deficiency: Licensee procedure FP-MA-COM-02 "Oversight and Control of
Supplemental Personnel," requires that oversight be provided to supplemental personnel
"anytime work is to be accomplished at NSPM nuclear facilities by personnel other than
permanent nuclear business unit employees." The procedure further specifies that it is the
responsibility of the department manager/functional area manager or designee to "provide
in-field oversight, observations, and coaching to supplemental workers."
Contrary to the above, at 11:10 a.m. on October 19, 2023, the licensee failed to provide
adequate oversight to the T&D group performing HDD onsite at the Prairie Island Nuclear
Generating Plant, resulting in the drill head damaging DC control power cables, tripping the
turbine generator output breakers, the turbine, and the reactor.
Inspectors determined that the licensee's failure to provide adequate oversight to
supplementary workers was within the ability of the licensee to foresee and correct and was
therefore a performance deficiency.
Screening: The inspectors determined the performance deficiency was more than minor
because it was associated with the Human Performance attribute of the Initiating Events
cornerstone and adversely affected the cornerstone objective to limit the likelihood of events
that upset plant stability and challenge critical safety functions during shutdown as well as
power operations. Specifically, the horizontal directional drilling led to damage to the DC
control power cables, resulting in a loss of all non-safeguards busses, an automatic turbine
and reactor trip. The loss of all non-safeguards busses coincident with the turbine and reactor
13
trip resulted in a "SCRAM with Complications" in accordance with NEI 99-02, revision 7,
"Regulatory Assessment Performance Indicator Guideline."
Significance: The inspectors assessed the significance of the finding using IMC 0609
Appendix A, The Significance Determination Process (SDP) for Findings At-Power. The
inspectors assessed the significance of the finding using Inspection Manual Chapter (IMC) 0609, Appendix A, The Significance Determination Process (SDP) for Findings At-Power.
The inspectors used IMC 0609.04, Initial Characterization of Findings, and IMC 0609,
Appendix A, Exhibit 1, Initiating Events Screening Questions. The finding was determined to
be of very low safety significance (Green) because there was no loss of mitigating equipment
relied upon to transition the plant from the onset of the trip to a stable shutdown condition.
Cross-Cutting Aspect: H.2 - Field Presence: Leaders are commonly seen in the work areas of
the plant observing, coaching, and reinforcing standards and expectations. Deviations from
standards and expectations are corrected promptly. Senior managers ensure supervisory and
management oversight of work activities, including contractors and supplemental personnel.
Specifically, the licensee did not have nuclear business unit personnel in the field providing
oversight of supplemental workers as required.
Enforcement:
Inspectors did not identify a violation of regulatory requirements associated with this finding.
EXIT MEETINGS AND DEBRIEFS
The inspectors verified no proprietary information was retained or documented in this report.
On April 9, 2024, the inspectors presented the integrated inspection results to
Thomas Conboy and other members of the licensee staff.
14
DOCUMENTS REVIEWED
Inspection
Procedure
Type
Designation
Description or Title
Revision or
Date
2C1.2-M1
Unit 2 Startup to Mode 1
14
2C1.2-M2
Unit 2 Startup to Mode 2
10
C1B
Appendix - Reactor Startup
25
Procedures
Fig C1A-3
Estimated Critical Boron Concentration Based on
BEACON-TSM
13
Prairie Island
Maintenance Rule
Basis Document
Various Functions
Various
Dates
Miscellaneous
SP 2168.13 2R33
CE Boric Acid Indications
Procedures
PM 3122-3
Shield Bldg, Category 1 Vent Zone, Fire and Security Door
Inspection
43
Miscellaneous
Extended Operation in Lowered Inventory Operational Fous
Protection Plan
0
501000080988
Past Operability Review (POR)
02/06/2024
501000081254
Unit 1 Use of LCO 3.0.4
01/24/2024
501000081294
IST Review Mode Change and SP 1155 A/B
01/25/2024
501000081411
SP 2155A Not Complete w/in Periodicity
01/28/2024
501000081422
IST Requirements for Pumps vs 3.0.4
01/29/2024
Corrective Action
Documents
501000081503
AOC - Tech Spec Surveillance SP/ASME/IST
01/30/2024
Engineering
Changes
QF2702, Design
Equivalent
Change,
602000023965
EC 601000004330, Rev. 0, U1 NIS Drawer Replacement
1R34
12/27/2023
Engineering
Evaluations
608000001132
Evaluation of RCS for Continued Operation per Tech. Spec.
3.4.3
0
LTR-EQ-23-35
Dynamic Similarity Evaluation of NIS Source Range Drawer
Assemblies
12/14/2023
Miscellaneous
LTR-NIS-23-020
Functional Similarity Evaluation of NIS Source Range
Drawer Assemblies
12/14/2023
Procedures
MP D27.35
MSIV Closure for Maintenance or Testing
2
Miscellaneous
Technical Update
Material Color Change
03/05/2001
15
Inspection
Procedure
Type
Designation
Description or Title
Revision or
Date
01-01
501000077983
11 DC Panel Ground
01/10/2024
Corrective Action
Documents
501000078005
12 DC Panel Ground
01/10/2024
EM 4.3.1-C-6
Connectors
4
EM 4.3.1-C.7
Electrical Construction Standards Cables
6
EEQ - SPLICES RAYCHEM INLINE - CRIMP CONN
PLANNERS INSTRUCTIONS
6
H8-E.1.53.DG
EEQ - Splices EGS Compact Splice Planners Instructions
1
H8-E.1.8.DG
EEQ - Splices Raychem Inline-Crimp Conn Installers
Instructions
6
Procedures
SP 2072
Local Leakage Rate Test of Containment Penetrations
27
2M-AF-3132-1-22
Isolation, Restoration and Testing of 22 Aux Feed Pump
21
D70.12
Motor-Operated Valve Steam Lubrication
6
MP D65
Auxiliary Feedwater Overspeed TTOD Test
6
SP 1070
Reactor Coolant System Integrity Test
57
SP 1073B
Monthly Train B Shield Building Ventilation System Test
21
SP 1080.2
12 Shield Building Ventilation Filter Removal Efficiency Test
28
SP 1106B
22 Diesel Cooling Water Pump Monthly Test
109
SP 2070
Reactor Coolant System Integrity Test
53
SP 2070
Reactor Coolant System Integrity Test
53
Procedures
SP 2406
Main Steam Isolation Valve Inservice Test
6
SP 1070 Rx Coolant System Integrity Test
Troubleshoot Bkr 211J-13 and MV-32019
PM 3132-1-22: 22 TDAFWP MINOR INSP
09/27/2023
SP 2070 - Rx Coolant SYS Integrity TST
SP 2070 - RX Coolant SYS Integrity TST
01/28/2024
CV-31419 Water Leak By
SP 1155B - CC SYS QTR TEST TRN B
MV-32016 LP A MS to 11 TDAFWP Lube
Perform As-Found LLRT
SP 1106B-22 DD CL PMP (245-392) 1 M Test
Test SI NOT READY Light
Work Orders
SP 2406 - MSIV Inservice TST up from CSD
03/06/2024
16
Inspection
Procedure
Type
Designation
Description or Title
Revision or
Date
Engineering
Evaluations
602000031728
Reactor Trip Report - Unit 2
03/03/2024
QF0431, Rev. 21,
602000031268
Cause Evaluation Template, CAP ID# 501000077958, Unit 1
10/19/2023
QF0565, Revision
17
Maintenance Rule Functional and MSPI Failure Evaluation,
QA# 501000081105
12/01/2023
Miscellaneous
QF1146, Revision
5, Past
Operability
Review
CAP 501000079553
12/01/2023
2C49.5
Placing Unit 2 Condensate Filter Demineralizers On Line
12
Reactor Trip or Safety Injection
41
C58800
Remote Alarm Response Procedure
6
OP 2C28.1 AOP4
Restarting Unit 2 AFWP After Low Suction/Discharge
Pressure Trip
7
Procedures
OP 2C28.2
Unit 2 Feedwater System
46