Text

Ninety-Day 1R26 Post-Outage Report Pursuant to Generic Letter 2008-01, Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal & Containment Spray Systems
	ML100500066
Person / Time
Site:	Prairie Island
Issue date:	02/18/2010
From:	Schimmel M; Northern States Power Co, Xcel Energy
To:	; Document Control Desk, Office of Nuclear Reactor Regulation
References
	GL-08-001, L-PI-10-005
	Download: ML100500066 (14)
	v • d • e

feXcel Energya L-PI-10-005 10 CFR 50.54(f)

U S Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant Units 1 and 2 Dockets 50-282 and 50-306 License Nos. DPR-42 and DPR-60 Ninety-Day 1R26 Post-Outage Report Pursuant to Generic Letter 2008-01, "Managing Gas Accumulation in Emergencv Core Cooling, Decav Heat Removal, and Containment Sprav Systems"

References:

1. Nuclear Regulatory Commission (NRC) Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems", dated January 11, 2008, Accession Number ML072910759.

2. Nuclear Management Company, LLC, (NMC) letter to NRC RE:

Update to Three-Month Response and Request for Extension to NRC Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems", dated September 15, 2008, Accession Number ML082600139.

3. Northern States Power Company, a Minnesota corporation (NSPM),

letter to NRC RE: Nine-Month Response to NRC Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems", dated October 14, 2008, Accession Number ML082880483.

The NRC issued Generic Letter (GL) 2008-01 (Reference I ) to request that each licensee evaluate the licensing basis, design, testing, and corrective action programs for the Safety injection (SI), Residual Heat Removal (RHR), and Containment Spray (CS) systems, to ensure that gas accumulation is maintained less than the amount that challenges operability of these systems, and that appropriate action is taken when conditions adverse to quality are identified.

1717 Wakonade Drive East Welch, Minnesota 55089-9642 Telephone: 651.388.1121

Document Control Desk Page 2 In Reference 2, NMC', proposed an alternative schedule for responding to Reference 1 for Prairie Island Nuclear Generating Plant, Units 1 and 2, (PINGP) and committed to ". .

. submit results of the evaluations of the walkdowns of Unit 1 containment and RHR pits 90 days following the completion of 1R26."

In Reference 3, Enclosure Section B, Commitment 4, NSPM committed to ". . . identify corrective actions to minimize gas accumulation and its consequences for Unit 1 inside containment and the Unit 1 RHR pit areas in the 90-day 1R26 post-outage report."

The Enclosure to this letter summarizes walkdown results and corrective actions for Unit 1 inside containment areas and the Unit 1 RHR pit areas.

If there are any questions or if additional information is needed, please contact Mr. Dale Vincent, P.E., at 651-388-1121.

Summary of Commitments This letter closes the above quoted commitments made in References 2 and 3.

This letter contains no revisions to existing commitments.

This letter makes the following new commitment for resolution of GL 2008-01:

Corrective actions for three susceptible locations were identified as inverted U or dead end tee pipe configurations (Enclosure Table 2) and for six additional susceptible locations discussed in Statement 7 of the Enclosure. Unit 1 corrective actions will be completed by the end of refueling outage 1R27 in 201 1.

I declare under penalty of perjury that the foregoing is true and correct.

Executed on FEB 1 8 2010

,@L$J d@'

Mark A. Schimmel

./YAY Site Vice President, Prairie Island Nuclear Generating Plant Units 1 and 2 Northern States Power Company - Minnesota Enclosures (1) cc: Administrator, Region Ill, USNRC Project Manager, PINGP, USNRC Resident Inspector, PINGP, USNRC

' On September 22, 2008, NMC transferred its operating authority to NSPM, doing business as Xcel Energy. By letter dated September 3, 2008, NSPM assumed responsibility for actions and commitments previously submitted by NMC.

ENCLOSURE NINETY-DAY 1R26 POST-OUTAGE REPORT PURSUANT TO GENERIC LETTER 2008-01, "MANAGING GAS ACCUMULATION IN EMERGENCY CORE COOLING, DECAY HEAT REMOVAL, AND CONTAINMENT SPRAY SYSTEMS" This enclosure contains the Northern States Power Company, a Minnesota corporation (NSPM), Ninety-Day 1R26 Post-Outage Report to Nuclear Regulatory Commission (NRC) Generic Letter (GL) 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems," dated January II , 2008. In GL 2008-01, the NRC requested "that each addressee evaluate its emergency core cooling system (ECCS), decay heat removal system, and containment spray system licensing basis, design, testing, and corrective actions to ensure that gas accumulation is maintained less than the amount that challenges operability of these systems, and that appropriate action is taken when conditions adverse to quality are identified." This action was completed by submittal of an alternate course of resolution in Reference 1, which was accepted by the NRC in Reference 2, and completed by Reference 3.

The following information in this response is provided to fulfill Commitment 3 in the Reference 3, Enclosure Section B which stated, "NSPM will identify corrective actions to minimize gas accumulation and its consequences for Unit 1 inside containment and the Unit 1 RHR [Residual Heat Removal] pit areas in the 90-day 1R26 post-outage report."

Specific statements were made in Reference 3 with respect to actions that would be addressed in the 90-day 1R26 post-outage report. Each statement is repeated below in Section A and the results of the actions are provided. The Statement numbers correspond to the numbering in the Design Evaluation Section of the Enclosure to Reference 3.

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Enclosure Unit 1 90-day report A. EVALUATION RESULTS Statement I:

Statement from Nine-Month Response to NRC Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Sprav Svstems"

1. Discuss the results of the review of the design basis documents.

This discussion should include a description of any plant specific calculations or analyses that were performed to confirm the acceptability of gas accumulation in the piping of the affected systems, including any acceptance criteria if applicable. Note: This should describe the "as found" (pre Generic Letter) condition prior to any corrective or enhancement actions.

NSPM reviewed the PlNGP design basis with respect to gas accumulation in the subject systems. Various design basis documents were reviewed including design guidelines, calculations, engineering evaluations, design change packages, design basis documents and vendor technical requirements.

Design drawings provide sufficient detail regarding placement of vent, drain or test connections to fill and vent systems during return to service.

These details can also be used to adequately vent (e.g., dynamic flush) during refill operations for system piping that cannot be statically vented.

NSPM will evaluate the need for additional vent valve locations as part of the piping walkdown activities.

90-DAY 1R26 Post-Outage Report The result of the evaluation for additional vent valve locations is discussed with Statement 6 below.

Statement 4:

Statement from Nine-Month Response to NRC Generic Letter 2008-01, "Mananing Gas Accumulation in Emergencv Core Cooling, Decav Heat Removal, and Containment Spray Svstems"

4. Discuss the results of the system P&ID [piping and instrumentation diagram] and isometric drawing reviews to identify all system vents and high points.

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Enclosure Unit 1 90-day report The piping and isometric drawings for the SI [Safety Injection], RHR and CS [Containment Spray] were reviewed to identify vents, high points and susceptible void locations.

Each line that did not screen out was reviewed to determine if it could be effectively vented with an existing system vent or procedure. Horizontal line slope, horizontal line local high point information, and vent orientation details will be obtained from field walkdowns.

As identified in the NSPM 3-month response update to NRC GL 2008-01, NSPM will perform walkdowns of piping not accessible during power operation in the PlNGP Unit 1 containment and the RHR pump pits during the next Unit 1 Refueling Outage (1R26).

90-DAY 1R26 Post-Outage Report Horizontal line slope, local high point information, and vent orientation details were obtained from field walkdowns and review of isometric drawings, and the evaluation is discussed with Statement 5 below.

The NSPM nine-month response to GL 2008-01 identified several locations as susceptible void locations based on drawing review. The locations and walkdown results are provided in Table 1 and discussed further in Statement 6.

Table 1 Drawing Review Susceptible Void Locations i Unit 1 Susceptible I Description (Location ldentifier1) Void Location L-RHR pump cross-tie upstream of the RHR heat No void exchangers (12PIT-4)

RHR pump cross-tie downstream of the RHR heat No void exchangers (12PIT-2)

RHR flush line connection to the RHR pump cross- No void tie downstream of the RHR heat exchangers (12PIT-5)

I Accumulator fill line from the SI cold leg injection No voids (ISI-19, ISI-27) 1 Unique PlNGP numbers assigned to susceptible and actual void locations.

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Enclosure Unit 1 90-day report The walkdown results and subsequent Ultrasonic Testing (UT) measurements determined that these susceptible locations had no voids.

Statement 5:

Statement from Nine-Month Response to NRC Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems"

5. Identify new vent valve locations, modifications to existing vent valves, or utilization of existing vent valves, based on the drawing review, and summarize the Corrective Actions, and schedule for completion of the Corrective Actions.

NSPM drawing reviews identified susceptible void locations that are locations for potential plant modifications. However, the information is not definitive and a decision to modifv the plant will be based on the drawing reviews combined with GL 2008-01 activities and the walkdown results.

The specific piping sections associated with the susceptible void locations will be used to identify locations that mav require vents. The design change process will determine the exact number and location of vents.

NSPM will identify corrective actions to minimize gas accumulation and its consequences for Unit 1 outside containment accessible areas and Unit 2 inside and outside containment and the Unit 2 RHR pit areas in the 90-day 2R25 post-outage report. NSPM will identifv corrective actions to minimize gas accumulation and its consequences for Unit 1 inside containment and the Unit 1 RHR pit areas in the 90-day 1R26 post-outage r e ~ o r t .

90-DAY 1R26 Post-Outage Report Three locations were identified during 1R26 Unit 1 drawing reviews to be inverted U or dead end tee pipe configurations with no installed vent which were confirmed by walkdowns. These locations are summarized in Table 2.

Table 2 lnverted U and Dead End Tee Locations Based on Drawing Review Description of ~ o c a t i o n ~

Inverted U 12 SI pump injection line inside containment (ISI-22, 13-23) 1 Dead End Tee I RHR flush line (12PIT-5)

I

' These locations are in addition to the fourteen locations identified and reported in Reference 4 (2R25 90-day post-outage report).

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Enclosure Unit 1 90-day report The corrective actions currently planned for these locations are the installation of vent valves. NSPM may implement alternative corrective actions that are equally effective to resolve these locations, such as performance of analyses which demonstrate no adverse effects for a void at a particular location. These alternative corrective actions may require changes to the PINGP licensing and design bases.

The completion time frame for these Unit 1 associated corrective actions is refueling outage 1R27 scheduled for Spring 201 1.

Statement 6:

Statement from Nine-Month Response to NRC Generic Letter 2008-01, "Managing Gas Accumulation in Emergencv Core Cooling, Decav Heat Removal, and Containment Sprav Svstems"

6. Discuss the results (including the scope and acceptance criteria used) of the system confirmation walkdowns that have been completed for the portions of the systems that require venting to ensure that they are sufficiently full of water."

As committed to in the NSPM update to the 3-month response to NRC GL 2008-01, NSPM will provide the results of the walkdowns of the Unit 1 RHR pit area and the Unit I inside containment 90 days after 1R26.

90-DAY 1R26 Post-Outage Report NSPM completed walkdowns during the 1R26 outage (Fall 2009) for the Unit 1 inside containment and Unit 1 RHR pit areas.

Walkdown Summary NSPM performed walkdowns of piping in the RHR and SI systems during the 1R26 refueling outage to ensure the as-built configuration of the piping matches the design documentation and identify susceptible void locations. NSPM performed measurements during these walkdowns using work order guidance and a ZipLevelTMto determine relative pipe elevations for the RHR and SI systems. The measurements were recorded on isometric drawings that were used to identify adverse slope. Forty-eight susceptible void locations3were identified based on the walkdown results and screening criteria. Accessible susceptible void locations were measured by UT to determine if a void was 3

Additional susceptible locations have been identified outside of the 1R26 walkdowns.

Updates for these locations are provided in this report if new voids were identified where none had previously been found.

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Enclosure Unit 1 90-day report actually present. Two susceptible locations (1 1PIT-01 and 12PIT-06) were not accessible, as described below, and UT was not performed.

In addition, 10 Unit 1 locations (see Table 3 below) were selected for performing UT prior to Unit 1 entry into Mode 5 (Cold Shutdown) during plant shutdown evolutions. These locations included five orifices (locations 1SI-13, 1SI-14, 1SI-16, 13 - 1 7 and 1SI-18) to address the Unit 1 inside containment portion of commitment 3 in Reference 4. UT was performed at another five locations on 11 and 12 safety injection discharge lines (locations 1SI-19, 1SI-20, 1SI-21, 1SI-22 and ISI-23) to obtain as-found data after operating for a cycle.

Table 3 Locations UT Performed Prior to Mode 5 Entry Susceptible Location Description of Location 1 ISI-13 1 718" Orifice on line 2-SI-21A I 1 ISI-14 1 718" Orifice on line 2-51-21B I 1SI-16 19/32" Orifice on line 2-SI-22A 19/32" Orifice on line 2-SI-22B 118" Orifice on line %-I SI-7 1SI-19 11 Accumulator fill line 1-SI-30A 1SI-20 11 SI Pump injection line 3-SI-15C 1 ISI-21 I 11 SI Pump injection line 3-3-15C 1 k 1SI-22 1St-23 12 SI Pump hot leg injection line 3-SI-15D 11 SI injection line 2-SI-24A to RHR vessel injection line No gas voids were detected on either side of the five orifices. Of the other five locations, one gas void was found on 11 SI injection line to the 11 RHR vessel injection line (13-23) which is discussed below in this section.

As shown in the Table 4 below, one of these locations had an actual void as determined by the UT measurements.

This location was double assigned as both ISI-I Iand 1SI-18.

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Enclosure Unit 1 90-day report Table 4 Summary of Walkdown Results Unit 1 Inside Containment and 11 and 12 RHR Pits Susceptible Void Susceptible Locations Locations Actual Voids 1 RHR Discharge Suction Walkdown Methodology NSPM performed walkdowns of piping in the RHR and SI systems to ensure that the as-built configuration of the piping matches the design documentation and identify susceptible void locations. NSPM performed measurements during these walkdowns using work order guidance and a ZipLevelTMto determine relative pipe elevations for the RHR and SI systems. Measurements were taken "on-the-pipe" without the distorting effects of insulation on relative elevations by:

1) virtue of it being un-insulated; 2) removal of the insulation; or 3) use of a shim aid to be "on-the-pipe". These measurements were generally taken at approximately eight to ten foot intervals at marked locations (for example, hangers) where possible. The measurements were recorded on isometric drawings. Elevation sketches were developed as an aid to identify adverse slope and susceptible void locations. Susceptible void locations were identified using these drawings and sketches.

A UT was performed at each accessible location. The corrective action program was used to document voids identified by UT measurements. If a void was identified at a susceptible location, its disposition was: 1) an operability evaluation due to the voided non-conforming condition; or 2) filled and vented to correct the voided non-conforming condition.

Walkdown Results The walkdown results for the Unit 1 inside containment and Unit 1 RHR pit areas are reported below. (The walkdowns for the Unit 1 outside containment accessible areas and Unit 2 inside and outside containment and Unit 2 RHR pit areas were reported in Reference 4.)

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Enclosure Unit 1 90-day report NSPM walkdowns were performed using the methodology described above.

Unit 1 Residual Heat Removal System UT was performed on eight identified 11 PIT and 12 PIT susceptible void locations. These locations had no voids. UT could not be performed for two other susceptible locations (1 1PIT-01 and 12PIT-06). These locations are in the RHR heat exchanger cubicle approximately 12 feet above the floor in lines 8-RH-9A and 8-RH-9B (678' elevation) and cannot be reached by ladder or scaffolding without removing concrete blocks. However, when RHR is in service for shutdown cooling the flow rate is sufficiently high to flush potential voids from these lines.

RHR piping inside containment had 12 susceptible void locations (one in shield building and 11 inside containment) for which UT examinations identified no gas voids.

Unit 1 Safety Injection System UT performed on 25 identified Safety lnjection System piping (inside containment) susceptible void locations indicated no gas voids.

A void (1SI-23) was identified by UT on 9/12/09 in 11 SI injection line to 11 RHR vessel injection line on horizontal section of pipe 2-SI-24A running from check valve 3-16-7 to reactor vessel injection line 6-SI-25A. Another UT performed on 10/22/09 determined that location 1SI-23 again had a void but of a different size. The condition was again documented in the corrective action program. Prior to plant startup an operability recommendation (OPR) evaluation was performed and the condition determined to be operable but non-conforming. This void location is a local high point which may require installation of a vent valve during 1R27 as part of the corrective action.

Unit 1 Containment Spray system5 Six voids were identified by UT on 10/23/09 and 10/24/09 at susceptible locations 1CS-5, 1CS-6, 1CS-7, 1CS-8, ICS-9 and 1CS-10 in the CS and caustic addition (CA) systems while the plant was in Mode 5. These susceptible locations had been identified during previous walkdowns. The CS system is not required in Mode 5; therefore, no operability concerns existed at that time. An operability determination on 10/28/2009 classified this condition as operable but non-conforming prior to entering Mode 4.

5 Containment Spray System walkdown results were reported in 2R25 Outage 90-Day report to the NRC. This section presents the results of additional UT performed during the 1R26 outage.

Enclosure Unit 1 90-day report A void was identified that encompassed susceptible locations 1CS-4 and 1CS-14 on 12 RHR to 12 CS cross-tie line. Susceptible location 1CS-4 was reported in Reference 4 (2R25 90-Day Outage Report). Previous UT measurements had determined there was no void at this location. After venting and UT examination on 1018109, two smaller voids remained at these locations. The conditions at these locations were classified as operable but non-conforming. Follow-up UT on 10110109 determined no voids were present.

The corrective actions for these susceptible void locations on Unit 1 will be completed during refueling outage 1R27 scheduled for Spring 201 1.

Statement 7:

Statement from Nine-Month Response to NRC Generic Letter 2008-01, "Managing Gas Accumulation in Emergencv Core Cooling, Decav Heat Removal, and Containment Spray Svstems"

7. Identify new vent valve locations, modifications to existing vent valves, or utilization of existing vent valves, that resulted from the confirmatory walkdowns, and summarize the Corrective Actions, and the schedule for completion of the Corrective Actions, i.e., the walkdowns that have been completed, and the walkdowns not yet complete (refer to Reference [5] Three-Month Response to NRC Generic Letter 2008-OI)."

NSPM will perform Unit 1 walkdowns for inside containment and RHR pit areas during 1R26. The walkdown information and the drawing review information will be evaluated together to determine the need for additional corrective actions as discussed in Design Section 5. The walkdown results will be presented in the 90-day 1R26 post-outaae report.

90-Day IR26 Post-Outage Report The corrective actions currently planned for the locations discussed in Statement 6 are the installation of vent valves. NSPM may implement alternative corrective actions that are equally effective to resolve these locations, such as performance of analyses which demonstrate no adverse effects for a void at a particular location. These alternative corrective actions may require changes to the PlNGP licensing and design basis.

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Enclosure Unit 1 90-day report The locations for the corrective actions are:

One location on 11 Safety Injection line to 11 RHR Vessel injection (ISI-23)

(also identified in drawing review).

Two locations (1CS-5 and 1CS-6) in CAJCS system piping.

Two locations (1CS-4 and 1CS-14) on 12 RHR to 12 CS cross-tie line and the equivalent locations on the 11 RHR to 11 CS cross tie (ICS-3 and ICS-13).

These locations are in addition to those committed earlier to the NRC in Reference 4, commitment 3 (2R25 Outage 90-day Report).

Statement 10:

Statement from Nine-Month Response to NRC Generic Letter 2008-01, "Managing Gas Accumulation in Emergencv Core Cooling, Decav Heat Removal, and Containment Spray Systems"

10. Discuss potential gas intrusion mechanisms into each system for each piping segment that is vulnerable to gas intrusion.

NSPM identified the following potential gas intrusion mechanisms:

I . Leakage from the accumulators Tie-in points from the accumulators into the SI systems have been identified to ensure venting capability should a leakage path develop resulting in degassing from the accumulators. Piping segments within these systems at elevations higher than the accumulator tie-in points have been evaluated by drawing reviews. Plant walkdowns inside containment are being performed for Unit 2 during 2R25. Unit I walkdown is scheduled for 1 ~ 2 NSPM 6 will evaluate the need to add additional vents based on the drawing reviews and walkdowns performed durina 2R26 and 1R26.

90-Day 1R26 Post-Outane Report The accumulator fill line from SI cold leg injection was identified as a susceptible void location based on industry experience. Historically, the accumulators have not been a source of gas intrusion at PINGP. During refueling outage 1R26, susceptible locations (1SI-19 and 1SI-27) were identified on 11 accumulator fill line. UT measurements at these locations did not identify any voids. No susceptible locations were found on 12 accumulator fill line based on the walkdown results. Additional vent valve capability may be added to these locations if determined necessary.

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Enclosure Unit 1 90-day report The gas intrusion pathway at PlNGP can be from accumulator fill or accumulator test lines and valves. The valves are normally closed air operated valves that fail closed on loss of air. NSPM will evaluate isolation capability of these gas intrusion sources through the design change process. A consideration for corrective action will be the addition of a manual valve for redundant isolation capability.

B. DESCRIPTION OF NECESSARY ADDITIONAL CORRECTIVE ACTIONS

1. Additional Corrective Actions NSPM makes the following new commitment for resolution of GL 2008-01:

Corrective actions for three susceptible locations were identified as inverted U or dead end tee pipe configurations (Table 2 above) and for six additional susceptible locations discussed in Statement 7 above. Unit 1 corrective actions will be completed by the end of refueling outage 1R27 in 201 1.

2. Corrective Action Updates In partial fulfillment of Reference 4, commitment 3, NSPM performed UT inspections of five orifices that were considered susceptible void locations inside Unit 1 containment. No voids were found.

NSPM previously identified a difference between the Unit 1 and Unit 2 operating procedures for placing RHR in service during a unit cool down. The Enclosure to Reference 3 (page 15 of 18) stated that the Unit 2 procedure would be revised to incorporate the guidance that was in the Unit 1 procedure at that time. Upon further evaluation, these steps in the Unit 1 procedure have been deleted as part of compensatory measures under an OPR to maintain ECCS operability in Modes 3 and 4.

C. REFRENCES

1. Nuclear Management Company, LLC, (NMC)~letter to NRC RE: Update to Three-Month Response and Request for Extension to NRC Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems", dated September 15, 2008, Accession Number ML082600139.

2. NRC letter to NSPM RE: Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and

" On September 22, 2008, NMC transferred its operating authority to NSPM, doing business as Xcel Energy. By letter dated September 3, 2008, NSPM assumed responsibility for actions and commitments previously submitted by NMC.

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Enclosure Unit 1 90-day report Containment Spray Systems," Proposed Alternative Course of Action, dated October 8,2008, Accession Number ML082320824.

3. NSPM letter to NRC RE: Nine-Month Response to NRC Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems", dated October 14, 2008, Accession Number ML082880483.

4. NSPM letter to NRC RE: Ninety-Day 2R25 Post-Outage Report Pursuant to Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems", dated January 30, 2009, Accession Number ML090300705.

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