(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
12-11-2017 | On October 16, 2017, with Unit 2 shutdown for a refueling outage, investigation into a boric acid indication identified a through wall leak at the socket weld that joins a 3/4 inch line to Loop A Reactor Coolant System ( RCS)[AB] shutdown communication line valve 2RC-8-37 )[VTV]. The leak was isolated by closed valves that would have limited primary coolant leakage to within the capacity of the charging system when the reactor coolant system was pressurized. The quantity of dry boric acid at the location was small (estimated at 1/2 teaspoon in volume). This failure constituted a welding or material defect in the primary coolant system that was not found acceptable under ASME Section Xl and an event or condition prohibited by Technical Specifications.
The cause of the leakage was determined to be stress corrosion cracking. Valve 2RC-8-37 was replaced. In addition, Prairie Island Nuclear Generating Plant intends to perform phased array ultrasonic inspections of socket welds on similar Class 1 piping containing stagnant water during future refueling outages. |
---|
|
---|
Category:Letter
MONTHYEARIR 05000282/20230042024-02-0101 February 2024 Integrated Inspection Report 05000282/2023004 and 05000306/2023004 ML23356A1232024-01-29029 January 2024 Exemption from Select Requirements of 10 CFR Part 73 (Security Notifications, Reports, and Recordkeeping and Suspicious Activity Reporting) ML24024A0722024-01-24024 January 2024 Independent Spent Fuel Storage Installation, Onticello, Supplement to Request for Exemption from Enhanced Weapons, Firearms Background Checks, and Security Event Notifications Implementation ML24017A0182024-01-19019 January 2024 Confirmation of Initial License Examination ML23356A0032024-01-17017 January 2024 Issuance of Amendments Revise Technical Specification 5.6.6, Reactor Coolant System (RCS) Pressure and Temperature Limits Report (PTLR) L-PI-23-034, Response to Request for Additional Information Regarding License Amendment Request to Revise Technical Specification 3.7.8, Cooling Water (Cl) System,2024-01-0202 January 2024 Response to Request for Additional Information Regarding License Amendment Request to Revise Technical Specification 3.7.8, Cooling Water (Cl) System, L-PI-23-035, Response to Request for Additional Information Regarding License Amendment Request to Revise Technical Specifications Section 5.6.6, Reactor Coolant System (RCS) Pressure and Temperature Limits Report2023-12-20020 December 2023 Response to Request for Additional Information Regarding License Amendment Request to Revise Technical Specifications Section 5.6.6, Reactor Coolant System (RCS) Pressure and Temperature Limits Report IR 07200010/20234012023-12-20020 December 2023 Independent Spent Fuel Storage Installation Security Inspection Report 07200010/2023401 ML23349A0572023-12-15015 December 2023 and Independent Spent Fuel Storage Installation, Revision to Correspondence Service List for Northern States Power - Minnesota ML23215A1672023-12-15015 December 2023 Acceptance of Requested Licensing Action Amendment Request to Revise Surveillance Requirement 3.8.1.2 Note 3 IR 05000282/20234012023-12-13013 December 2023 Security Baseline Inspection Report 05000282/2023401 and 05000306/2023401 L-PI-23-033, Supplement to License Amendment Request to Revise Technical Specification 3.8.1, Surveillance Requirement 3.8.1.2, Note 32023-12-0505 December 2023 Supplement to License Amendment Request to Revise Technical Specification 3.8.1, Surveillance Requirement 3.8.1.2, Note 3 ML23304A1632023-11-15015 November 2023 Supplemental Information Needed for Acceptance of Requested Licensing Action Amendment Request to Revise SR 3.8.1.2 Note 3 ML23319A3182023-11-15015 November 2023 Request for Exemption from Enhanced Weapons, Firearms Background Checks, and Security Event Notifications Implementation IR 05000282/20230032023-11-0808 November 2023 Integrated Inspection Report 05000282/2023003 and 05000306/2023003 ML23311A3572023-11-0707 November 2023 Core Operating Limits Report (COLR) for Prairie Island Nuclear Generating Plant (PINGP) Unit 2. Cycle 33. Revision 0 ML23285A3062023-10-12012 October 2023 Implementation of the Fleet Standard Emergency Plan for the Monticello Nuclear Generating Plant and the Prairie Island Nuclear Generating Plant ML23270B9022023-09-29029 September 2023 Review of Reactor Vessel Material Surveillance Program Capsule N Technical Report L-PI-23-025, License Amendment Request to Revise Technical Specification 3.8.1, Surveillance Requirement 3.8.1.2, Note 32023-09-28028 September 2023 License Amendment Request to Revise Technical Specification 3.8.1, Surveillance Requirement 3.8.1.2, Note 3 ML23265A2532023-09-26026 September 2023 Review of Reactor Vessel Material Surveillance Program Capsule N Technical Report ML23262B0372023-09-19019 September 2023 Response to NRC Request for Additional Information Regarding the 2023 Monticello and Prairie Island Plant Decommissioning Funding Status Reports ML23256A1682023-09-13013 September 2023 Independent Spent Fuel Storage Installation and Monticello Nuclear Generating Plant - Voluntary Security Clearance Program 2023 Insider Threat Program Self-Inspection L-PI-23-023, Baffle Former Bolts Alternate Aging Management Strategy2023-09-11011 September 2023 Baffle Former Bolts Alternate Aging Management Strategy IR 05000282/20230052023-08-30030 August 2023 Updated Inspected Plan for Prairie Island Nuclear Generating Plant Report 05000282/2023005 and 05000306/2023005 IR 05000282/20230102023-08-17017 August 2023 NRC Inspection Report 05000282/2023010 and 05000306/2023010 ML23222A0122023-08-10010 August 2023 Independent Spent Fuel Storage Installation and Monticello Nuclear Generating Plant - Changes in Foreign Ownership, Control or Influence IR 05000282/20230022023-08-0303 August 2023 Integrated Inspection Report 05000282/2023002 and 05000306/2023002 ML23214A2032023-08-0202 August 2023 Request for Information for an NRC Quadrennial Comprehensive Engineering Team Inspection: Inspection Report 05000282/2024010; 05000306/2024010 ML23206A2342023-07-25025 July 2023 Independent Spent Fuel Storage Installation, and Monticello Nuclear Generating Plant, Changes in Foreign Ownership, Control or Influence ML23202A0032023-07-21021 July 2023 Independent Spent Fuel and Independent Spent Fuel Storage Installation, Monticello Nuclear Generating Plant, Submittal of Quality Assurance Topical Report (NSPM-1) ML23199A0922023-07-18018 July 2023 Notification of NRC Baseline Inspection and Request for Information; Inspection Report 05000306/2023004 ML23195A1732023-07-14014 July 2023 Revision of Standard Practice Procedures Plan L-PI-23-018, License Amendment Request to Revise ISFSI Technical Specification 4.4 to Allow Use of a Code Alternative to ASME Code, NB-5130, Examination of Weld Edge Preparation Surfaces, for the TN-40HT2023-07-14014 July 2023 License Amendment Request to Revise ISFSI Technical Specification 4.4 to Allow Use of a Code Alternative to ASME Code, NB-5130, Examination of Weld Edge Preparation Surfaces, for the TN-40HT ML23181A0192023-06-30030 June 2023 Independent Spent Fuel Storage Installation, Revision to Correspondence Service List for Northern States Power - Minnesota ML23178A2422023-06-28028 June 2023 Reassignment of the U.S. Nuclear Regulatory Commission Branch Chief in the Division of Operating Reactor Licensing for Plant Licensing Branch III L-PI-23-006, License Amendment Request to Revise Technical Specification 3.7.8 Required Actions2023-06-22022 June 2023 License Amendment Request to Revise Technical Specification 3.7.8 Required Actions L-PI-23-016, 2022 10 CFR 50.46 LOCA Annual Report2023-06-14014 June 2023 2022 10 CFR 50.46 LOCA Annual Report IR 05000282/20234202023-06-0101 June 2023 Security Baseline Inspection Report 05000282/2023420 and 05000306/2023420 ML23150A1722023-05-30030 May 2023 Preparation and Scheduling of Operator Licensing Examinations 2024-02-01
[Table view] Category:Licensee Event Report (LER)
MONTHYEARML19353A4092019-12-19019 December 2019 Technical Specification 5.6.8 Special Report: Inoperable Containment Isolation Valve Indication Supplemental Report 05000306/LER-2017-0032018-01-11011 January 2018 Both Containment SEa) Pump Control Switches in Pull-out in Mode 4, LER 17-003-00 for Prairie Island Nuclear Generating Plant, Unit 2 Regarding Both Containment Spray Pump Control Switches in Pull-Out in Mode 4 05000306/LER-2017-0022017-12-11011 December 2017 Reactor Coolant System Shutdown Communication Live Vent Through Wall Defect, LER 17-002-00 for Prairie Island, Unit 2, Regarding Reactor Coolant System Shutdown Communication Live Vent Through Wall Defect 05000306/LER-2017-0012017-11-29029 November 2017 23 Containment Fan Coil Unit Operability, LER 17-001-00 for Prairie Island, Unit 2, Regarding 23 Containment Fan Coil Unit Operability 05000282/LER-2016-0062017-02-15015 February 2017 121 Motor Driven Cooling Water Pump Auto Start, LER 16-006-00 for Prairie Island Nuclear Generating Plant, Units 1 and 2 Regarding 121 Motor Driven Cooling Water Pump Auto Start 05000306/LER-2015-0022016-06-22022 June 2016 21 Feedwater Pump Lockout, Unit 2 Reactor Trip Due to Pressure Switch Failure, LER 15-002-01 for Prairie Island, Unit, Regarding 21 Feedwater Pump Lockout, Reactor Trip Due to Pressure Switch Failure 05000282/LER-2016-0042016-06-21021 June 2016 1 OF 4, LER 16-004-00 for Prairie Island, Unit 1, Regarding Missing Fire Barrier Between Fire Area (FA) 59 and 85 / Fire Hazard Analysis Drawings Do Not Match Boundary Description 05000282/LER-2016-0022016-03-25025 March 2016 Listed System Actuation - Motor-Driven Cooling Water Pump Auto-Start, LER 16-002-00 for Prairie Island, Unit 1, Regarding Listed System Actuation - Motor-Driven Cooling Water Pump Auto-Start 05000306/LER-2016-0012016-02-12012 February 2016 Unit 2 Reactor Trip due to a Ground Fault resulting in a Generator Trip, LER 16-001-00 for Prairie Island, Unit 2, Regarding Reactor Trip Due to a Ground Fault Resulting in a Generator Trip L-PI-15-071, Cancellation of License Event Report (LER)50-282/2015-001-00, 14 Fan Coil Unit Leak2015-09-0303 September 2015 Cancellation of License Event Report (LER)50-282/2015-001-00, 14 Fan Coil Unit Leak L-PI-11-023, Reinstatement of Licensee Event Reports Associated with Flooding Scenarios2011-03-31031 March 2011 Reinstatement of Licensee Event Reports Associated with Flooding Scenarios L-PI-07-101, LER 07-03-001 for Prairie Island, Unit 1 Regarding Unanalyzed Condition Due to Breached Fire Barrier2008-01-25025 January 2008 LER 07-03-001 for Prairie Island, Unit 1 Regarding Unanalyzed Condition Due to Breached Fire Barrier L-PI-06-046, Cancellation of Licensee Event Report (LER) 1-05-01, Discovery of Single Failure Vulnerability of Unit 1 Safeguards Buses2006-06-0909 June 2006 Cancellation of Licensee Event Report (LER) 1-05-01, Discovery of Single Failure Vulnerability of Unit 1 Safeguards Buses 2019-12-19
[Table view] |
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
On October 16, 2017, with Prairie Island Nuclear Generating Plant (PINGP) Unit 2 shutdown for refueling outage 2R30, an indication of leakage was found on the pipe socket weld upstream of valve 2RC-8-37 [VTV] during boric acid corrosion examinations. Valve 2RC-8-37 functions as a vent path on the normally isolated 3/4 inch Loop A shutdown communication line [AB]. Subsequent non-destructive examination confirmed a pressure boundary leak existed, which was not found acceptable under ASME Section Xl.
This event is being reported in accordance with 10 CFR 50.73(a)(2)(ii)(A), “Any event or condition that resulted in the condition of the nuclear power plant, including its principal safety barriers, being seriously degraded” because the weld defect in the primary coolant system was not found acceptable under ASME Section XI. In addition, the pressure boundary leakage exceeded the zero reactor coolant system operational leakage limit specified in Tech Spec 3.4.14 and therefore was reportable per 50.73(a)(2)(i)(B) as a condition prohibited by plant technical specifications.
There was no actual safety consequence associated with this event. The quantity of dry boric acid at the location was small (estimated at 1/2 teaspoon in volume). Even if the weld had experienced a complete circumferential failure, the leak was isolated by closed valves that would have limited primary coolant leakage to within the capacity of the charging system when the reactor coolant system was pressurized (see figure next page).
CORRECTIVE ACTIONS
Valve 2RC-8-37 and the associated weld were replaced and the reactor coolant pressure boundary was restored.
PINGP intends to perform phased array ultrasonic inspections of socket welds on similar Class 1 piping containing stagnant water during future PINGP Unit 1 and 2 refueling outages.
PREVIOUS SIMILAR OCCURRENCES
A similar boric acid deposit was previously identified during refueling outage 2R29 in 2015 on valve 2RC-8-37 at the same location. However, visual and dye penetrant testing performed in accordance with plant procedures showed no indication of flaws or an active leak. The origin of the boric acid residue on the valve at the time was incorrectly attributed to a prior leak (e.g. reactor coolant pump seal leak) or maintenance activity.
SAFETY SIGNIFICANCE
CAUSE
Laboratory analysis determined the cause of the leak to be stress corrosion cracking. Contributing causes included weld material sensitization and the presence of sulfur and oxygen on internal surfaces. Oxygen is introduced from containment air when the system is in use during outages and is not removed by the normal primary system oxygen scavenging mechanisms because the line is normally isolated / stagnant.
DESCRIPTION OF EVENT
EVENT ANALYSIS
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
Figure
|
---|
|
|
| | Reporting criterion |
---|
05000306/LER-2017-001 | 23 Containment Fan Coil Unit Operability LER 17-001-00 for Prairie Island, Unit 2, Regarding 23 Containment Fan Coil Unit Operability | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i)(b) 10 CFR 50.73(a)(2)(ii) | 05000306/LER-2017-002 | Reactor Coolant System Shutdown Communication Live Vent Through Wall Defect LER 17-002-00 for Prairie Island, Unit 2, Regarding Reactor Coolant System Shutdown Communication Live Vent Through Wall Defect | 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded | 05000306/LER-2017-003 | Both Containment SEa) Pump Control Switches in Pull-out in Mode 4 LER 17-003-00 for Prairie Island Nuclear Generating Plant, Unit 2 Regarding Both Containment Spray Pump Control Switches in Pull-Out in Mode 4 | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
|