Text

Nine-Month Response to NRC Generic Letter 2008-01, Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems.
	ML082880662
Person / Time
Site:	Monticello
Issue date:	10/14/2008
From:	O'Connor T; Northern States Power Co, Xcel Energy
To:	; Document Control Desk, Office of Nuclear Reactor Regulation
References
	GL-08-001, L-MT-08-063, TAC MD7847
	Download: ML082880662 (21)
	v • d • e

October 14,2008 L-MT-08-063 10 CFR 50.54(f)

U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 Monticello Nuclear Generating Plant Docket 50-263 Renewed Facility Operating License No. DPR-22 Nine-Month Response to NRC Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems"

{TAC No. MD7847)

References:

1) U.S. NRC Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems," dated January 11, 2008.

2) NMC to NRC, "Generic Letter 2008-01: Three Month Response to Generic Letter 2008-01," (L-MT-08-026) dated April 11, 2008.

3) NRC to NMC, "Monticello Nuclear Generating Plant (MNGP) -

Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems," Proposed Alternative Course of Action (TAC No.

MD7847)," dated September 9, 2008.

The U.S. Nuclear Regulatory Commission (NRC) issued Generic Letter (GL) 2008-01 (Reference 1) to request that each licensee evaluate the licensing basis, design, testing, and corrective action programs for the Emergency Core Cooling Systems (ECCS), the Decay Heat Removal System, and the Containment Spray System, 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.

2807 West County Road 75 Monticello, Minnesota 55362-9637 Telephone: 763.295.5151 Fax: 763.295.1454

Document Control Desk Page 2 of 3 GL 2008-01 requested each licensee to submit a written response in accordance with 10 CFR 50.54(f) within nine months of the date of the GL to provide the information summarized below:

(a) A description of the results of evaluations that were performed pursuant to the requested actions; (b) A description of all corrective actions, including plant, programmatic, procedure, and licensing basis modifications that were determined to be necessary to assure compliance with the quality assurance criteria in Sections Ill, V, XI, XVI, and XVll of Appendix B to 10 CFR Part 50 and the licensing basis and operating license as those requirements apply to the subject systems; and, (c) A statement regarding which corrective actions were completed, the schedule for completing the remaining corrective actions, and the basis for that schedule.

The enclosure to this letter contains the Northern States Power Company, a Minnesota corporation (NSPM),(') nine-month response to NRC GL 2008-01 for the Monticello Nuclear Generating Plant (MNGP).

In summary, NSPM has concluded that the subject systems at the MNGP are in compliance with the Technical Specification (TS) definition of operability (i.e., capable of performing their intended safety functions) and that the MNGP is currently in compliance with the criteria in 10 CFR 50 Appendix B, Criteria Ill, V, XI, XVI and XVII, with respect to the concerns outlined within GL 2008-01 regarding gas accumulation in the subject systems, based upon the results of NSPM evaluations and walkdowns of the accessible portions of the piping for the subject systems.

As committed in Reference 2, NSPM will complete its assessments of the applicable inaccessible portions of these systems during the spring 2009 Refueling Outage and provide a supplement to this report with those results within 90 days from startup of that outage. Also, as requested in Reference 3, NSPM will format this supplemental report similar to this 9 month submittal in the description of evaluations and disposition of corrective actions.

1. Northern States Power Company is incorporated as a wholly owned subsidiary of Xcel Energy, Inc. Transfer of operating authority from the Nuclear Management Company, LLC to NSPM occurred on September 22, 2008.

Document Control Desk Page 3 of 3 Summary of Commitments In accordance with Reference 3, and new information obtained since NSPM provided the three month response, NSPM has clarified the first two commitments (revised below), and added a third commitment.

1. Complete the detailed walkdowns of the applicable inaccessible sections of the Generic Letter 2008-01 subject systems (does not include piping downstream of the low pressure ECCS outboard injection valves) prior to startup from the 2009 Refueling Outage.

2. NSPM will complete the evaluations of the applicable inaccessible sections of the Generic Letter 2008-01 subject systems and provide a supplement to the October 2008 response to Generic Letter 2008-01 within 90 days following return to full power from the 2009 Refueling Outage.

3. NSPM will evaluate the Technical Specification changes in the Technical Specification Task Force (TSTF) Traveler related to gas accumulation within the ECCS for applicability to the MNGP and submit a license amendment request, adjusted, as needed, to account for the MNGP plant-specific design and licensing basis, within 180 days following NRC publication of the Notice of Availability in the Federal Register.

of perjury that the foregoing is true and correct. Executed nticello Nuclear Generating Plant Company - Minnesota Enclosure cc: Administrator, Region Ill, USNRC Project Manager, Monticello, USNRC Resident Inspector, Monticello, USNRC Minnesota Department of Commerce

ENCLOSURE 1 NINE-MONTH RESPONSE TO NRC GENERIC LETTER 2008-01 MANAGING GAS ACCUMULATION IN EMERGENCY CORE COOLING, DECAY HEAT REMOVAL, AND CONTAINMENT SPRAY SYSTEMS On January 11, 2008, the U.S. Nuclear Regulatory Commission (NRC) issued Generic Letter (GL) 2008-01 (Reference I ) requesting each licensee to evaluate the licensing basis, design, testing, and corrective action programs for the Emergency Core Cooling Systems (ECCS), Decay Heat Removal System, and the Containment Spray System, 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. On April 11, 2008, the Nuclear Management Company, LLC (NMC)(') submitted a three-month response to GL 2008-01 for the Monticello Nuclear Generating Plant (MNGP) (Reference 2) and committed to provide a nine-month response to the GL, provided herein. The following information is provided in this response:

a) A description of the results of evaluations that were performed pursuant to the requested actions (see Section A of this Enclosure);

b) A description of the corrective actions determined necessary to assure compliance with the quality assurance criteria in Sections Ill, V, XI, XVI, and XVll of Appendix B to 10 CFR Part 50 and the licensing basis and operating license with respect to the subject systems (see Section B of this Enclosure);

and c) A statement regarding which corrective actions have been completed, the schedule for the corrective actions not yet complete, and the basis for that schedule (see Section C of this Enclosure).

For the MNGP the following plant systems or operating modes of certain systems were determined to be within the scope of GL 2008-01.

Emerqencv Core Cooling System (ECCS)

- Low Pressure ECCS Core Spray (CSP)

Residual Heat Removal (RHR) - Low Pressure Coolant Injection (LPCI) mode

- High Pressure ECCS(~)

High Pressure Coolant Injection (HPCI) - water side

1. Transfer of operating authority from the Nuclear Management Company, LLC to Northern States Power Company - Minnesota (NSPM), a wholly owned subsidiary of Xcel Energy, Inc., occurred on September 22, 2008.

2. Automatic Depressurization System utilizes several of the reactor safetylrelief valves to reduce reactor pressure during small breaks in the event of HPCI failure. This system, although part of ECCS, is not considered to be applicable to the GL 2008-01 response.

Page 1 of 18

ENCLOSURE 1 NINE-MONTH RESPONSE TO NRC GENERIC LETTER 2008-01 MANAGING GAS ACCUMULATION IN EMERGENCY CORE COOLING, DECAY HEAT REMOVAL, AND CONTAINMENT SPRAY SYSTEMS Decay Heat Removal

- RHR - Shutdown Cooling (SDC) mode

- RHR - Suppression Pool (Torus) Cooling (SPC) mode Both modes can utilize the RHR heat exchanger for decay heat removal. The SDC mode is the normal means for removing decay heat from the Reactor Coolant System (RCS) during shutdowns. The SPC mode is used if there is a transfer of decay heat from the reactor to the suppression pool, such as a transient resulting in safetylrelief valve opening.

Containment Spray

- RHR - Drywell Spray mode

- RHR - Suppression Pool (Torus) Spray mode The scope of the evaluation in response to this GL focused on the design, operation and management of the ECCS, Decay Heat Removal, and Containment Spray functions to limit the potential for the intrusion or excess accumulation of gas which could challenge the capability and operability of these systems to perform their intended safety-related design functions.(3)

A. EVALUATION RESULTS

1. Licensing Basis Evaluation The MNGP licensing basis was reviewed with respect to gas accumulation for the Emergency Core Cooling, Decay Heat Removal, and Containment Spray functions.

The Boiling Water Reactor (BWR) design incorporates the Decay Heat Removal and Containment Spray functions as specific modes of operation of the RHR System.

This review included the Technical Specifications (TS) and TS Bases, the MNGP Updated Safety Analysis Report (USAR), the Technical Requirements Manual (TRM) and TRM Bases, responses to NRC generic communications, regulatory commitments, and License Conditions.

3. Resolution of Generic Safety Issue (GS1)-193,"BWR ECCS Suction Concerns," is not addressed herein consistent with SECY-08-0108. Pages 23-24 of the Enclosure to the SECY states: "The initial intent to include this issue in the scope of the GL on the topic of gas accumulation in suction piping of ECCS pumps being developed by NRR proved to be impractical due to fundamental differences and the development status of the GL in relation" to the generic issue.

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ENCLOSURE I NINE-MONTH RESPONSE TO NRC GENERIC LETTER 2008-04 MANAGING GAS ACCUMULATION IN EMERGENCY CORE COOLING, DECAY HEAT REMOVAL, AND CONTAINMENT SPRAY SYSTEMS

1. Summary of Licensing Basis Review The above documents were evaluated for compliance with applicable regulatory requirements. The following is a summary of the MNGP licensing basis with respect to the concerns of GL 2008-01:

Technical Specification (TS) Surveillance Requirements (SR) SR 3.5.1.Iand SR 3.5.2.2 specify that every 31 days the following is verified for each low pressure ECCS injectionlspray subsystem:

SR 3.5.1.1 Verify, for each low pressure ECCS injectionlspray subsystem, the piping is filled with water from the pump discharge valve to the injection For the ECCS function, the MNGP licensing basis is limited to the discharge portion of the low pressure ECCS piping systems, i.e., Core Spray and the LPCl mode of RHR, with a focus on the specific piping sections between the associated pump discharge valve to the injection valve outboard of primary containment.

The TS surveillance requirements do not address gas accumulation within the following piping segments or systemlfunctions:

- ECCS suction piping

- High Pressure ECCS discharge piping

- Decay Heat Removal

- Containment Spray

2. Summary of Changes Based on Licensing Evaluation No changes have been made to the licensing basis documents as a result of this review. Opportunities for enhancements have been identified to clarify the language used in various licensing documents to describe the requirement to maintain piping systems "full of water" to preclude operability concerns. The Technical Specification Task Force (TSTF) is gathering information to develop an approved TSTF Traveler to provide guidance to individual licensees in making TS changes related to the potential for unacceptable gas accumulation.

Development of this Traveler relies on the results of evaluations of a large number of licensees to address the various plant designs and provide consistent guidance. NSPM is continuing to support the industry and Nuclear Energy

4. SR 3.5.2.2 contains the same requirements, but applies in Modes 4 and 5, shutdown and refueling.

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ENCLOSURE 1 NINE-MONTH RESPONSE TO NRC GENERIC LETTER 2008-01 MANAGING GAS ACCUMULATION IN EMERGENCY CORE COOLING, DECAY HEAT REMOVAL, AND CONTAINMENT SPRAY SYSTEMS Institute (NEI) Gas Accumulation Management Team activities regarding the resolution of generic TS changes via the TSTF Traveler process.

NSPM will evaluate the Technical Specification changes in the Technical Specification Task Force (TSTF) Traveler related to gas accumulation within the ECCS for applicability to the MNGP and submit a license amendment request, adjusted, as needed, to account for the MNGP plant-specific design and licensing basis, within 180 days following NRC publication of the Notice of Availability in the Federal Register.

Any TS Bases changes associated with these TS changes will be made as part of implementation of the license amendment, upon issuance, under the TS Bases Control Program, along with any other licensing basis document changes for consistency, such as USAR changes.

11. Desiqn Evaluation The MNGP design basis was reviewed with respect to gas accumulation for the Emergency Core Cooling, Decay Heat Removal, and Containment Spray functions.

The BWR design does not have dedicated systems for some of these functions; LPCI, Containment Spray and Decay Heat Removal are performed as specific modes of operation of the RHR System.

This included a review of design basis documents, calculations, design drawings, operating procedures, fill and vent procedures, engineering evaluations, plant operating experience, and vendor technical manuals. As part of this review, potential gas intrusion mechanisms were identified and evaluated. In addition, confirmatory plant walkdowns on accessible portions of system piping were conducted to assess as-built piping configurations and potential areas for gas accumulation. Lastly, ultrasonic testing (UT) was performed on areas susceptible to gas accumulation to evaluate for the presence of gas. The following is a description of the results of the design evaluation at the MNGP.

1. Summary of Design Review Several design features and operational practices provide assurance that the ECCS, Decay Heat Removal and Containment Spray functions will perform their safety-related design functions upon demand.

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ENCLOSURE I NINE-MONTHRESPONSE TO NRC GENERIC LETTER 2008-01 MANAGING GAS ACCUMULATION IN EMERGENCY CORE COOLING, DECAY HEAT REMOVAL, AND CONTAINMENT SPRAY SYSTEMS ECCS The Low Pressure ECCS suction piping is maintained filled by maintaining the suppression pool water level in accordance with TS surveillance requirements.

The Low Pressure ECCS also contains pressurizing stations supplied by the Condensate Service System (a type of keep-fill) to maintain the piping between the associated pump discharge valve up to the outboard injection valve pressurized.

The High Pressure ECCS (HPCI) suction is normally aligned to the Condensate Storage Tanks (CSTs). The height of water in the CSTs maintains the piping full of water up to the first closed isolation valve in the suction piping in accordance with the TS surveillance requirements. Suction automatically transfers to the suppression pool on low CST water level or high suppression pool water level.

The HPCl suppression pool suction piping is maintained filled by maintaining the suppression pool water level in accordance with TS surveillance requirements.

HPCl discharge piping has been previously evaluated for the turbulent penetration issue described in GL 2008-01. A design change was installed during the last refueling outage to utilize the Condensate System as a "keep-fill" system to maintain the HPCl discharge piping between the normally closed injection valve and the pump discharge check valve filled with water to prevent void formation. Although the keep-fill feature is not required for HPCl operability, it is normally available and HPCl operability would be evaluated, as needed, upon loss of the keep-fill.

Decav Heat Removal and Containment Spray These functions do not have any specified gas accumulation criterion as part of their design basis. The discharge sides of these systems up to the outboard injection valve experience keep-fill pressure as discussed above in Low Pressure ECCS, due to the common RHR System piping. The Decay Heat Removal and Containment Spray modes of RHR operation are manually initiated modes of operation.

The MNGP design includes keeping the section of piping between the two Drywell Spray isolation valves voided (part of Containment Spray function). The Emergency Operating Procedures that manually initiate Containment Spray direct the RHR pump(s) to be started, the outboard valve opened, then the inboard valve opened. This results in the pressurization of the voided area during the opening of the outboard valve. This condition was evaluated for operability and the pressurization transient was within allowable piping loads and relief valve setpoints, and therefore determined to be acceptable.

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ENCLOSURE 1 NINE-MONTH RESPONSE TO NRC GENERIC LETTER 2008-01 MANAGING GAS ACCUMULATION IN EMERGENCY CORE COOLING, DECAY HEAT REMOVAL, AND CONTAINMENT SPRAY SYSTEMS Vortex Concerns Sufficient margin exists in the CST vortex calculation governing the transfer of HPCl pump suction from the CST to the suppression pool to preclude vortexing concerns from the CST.

In accordance with current industry guidance discussed below, a 2 percent void fraction for continuous voiding in pump suction piping has been determined to be bounding and was applied, as needed, for this evaluation. The MNGP Emergency Operating Procedures (EOPs) rely on the prior industry guidance of NUREGICR-2772 and a 4 percent void fraction for vortex limits for the suppression pool. This difference in acceptable void fraction will require resolution and has been entered into the MNGP Corrective Action Program.

New Applicable Gas Volume Acceptance Criteria For the subject systems, it was determined that calculations and site specific analysis did not exist to support acceptance criteria for the impact of gas accumulation on system operability, with the exception of a previous evaluation for HPCl (discussed above).

NSPM has since adopted the following industry guidance to support operability.

a) Pump Suction Piping Consistent with industry guidance, gas volume acceptance criteria for ECCS pumps has been determined to be a bounding 2 percent void fraction for continuous voiding and 10 percent void fraction for up to 5 seconds. These conservative criteria will be applied in support of system operability determinations, if required, until further data supports a change. These values used in conjunction with other factors such as Net Positive Suction Head - Required (NPSHR),duration of gas flow, and transients for which the system is credited provide a basis for system operability should gas be discovered.

b) Pump Discharge Piping Susceptible to Pressure Pulsation After Pump Start A joint Owner's Group program evaluated pump discharge piping gas accumulation. Gas accumulation in the piping downstream of the pump to the first closed isolation valve or the Reactor Coolant System (RCS) pressure boundary isolation valves can result in amplified pressure pulsations after a pump start. The subsequent pressure pulsation may cause relief valves in the subject systems to lift, or result in unacceptable Page 6 of 18

ENCLOSURE 1 NINE-MONTH RESPONSE TO NRC GENERIC LETTER 2008-01 MANAGING GAS ACCUMULATION IN EMERGENCY CORE COOLING, DECAY HEAT REMOVAL, AND CONTAINMENT SPRAY SYSTEMS pipe loads, i.e., axial forces that are greater than the design rating of the axial restraint(s). The joint Owner's Group program established a method to determine the impact of gas accumulation in discharge piping. The method uses plant specific information such as piping geometry, support locations and relief valve setpoints in the subject systems to determine if there is an adverse impact on the system.

c) Low Pressure ECCS and Containment Spray Piping Downstream of Injection Valves A generic analysis of low pressure ECCS and Containment Spray piping downstream of the normally-closed injection valves has been completed and a determination made that the existence of air voids in this piping will have no adverse consequences related to accident conditions. Even if voids did exist in this piping, the pressure transient would not be greater than the normal injection pressure.

d) Effects of lnjection of Gas into the RCS Gas ingestion into the RCS as a result of voids in the ECCS piping has the potential to delay ECCS injection and subsequently impact core cooling.

A conservative "worst case" scenario evaluation for BWRs determined a bounding LOCA peak cladding temperature (PCT) heatup rate of 12"F/second for the entire U.S. BWR fleet. Applying this heatup rate, and setting a 50°F maximum allowable PCT increase, indicates that conservatively an approximate 4 seconds of additional delay in ECCS injection time can be tolerated beyond that already assumed in the current MNGP LOCA analysis@)before a "significant increase" in PCT in accordance with 10 CFR 50.46 is reached. The 4 second time delay can be translated into an equivalent void size, using the actual plant piping geometry (length of piping and nominal cross-sectional area) and required pump flowrate.

Another generic assessment of BWRs concludes that large gas voids passing through the core do not pose an additional safety concern (impact on core cooling) mainly because high void conditions are already present in the core during the LOCA blowdown phase. These voided conditions are conservatively modeled per the requirements of 10 CFR 50.46 and 10 CFR 50, Appendix K.

5. The MNGP LOCA Analysis of Record indicates that a margin of 230°F exists to the regulatory limit of 2200°F (10 CFR 50.46).

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ENCLOSURE I NINE-MONTH RESPONSE TO NRC GENERIC LETTER 2008-01 MANAGING GAS ACCUMULATION IN EMERGENCY CORE COOLING, DECAY HEAT REMOVAL, AND CONTAINMENT SPRAY SYSTEMS A generic assessment of BWRs for the Loss of Feedwater (LOFW) abnormal operating transient and Anticipated Transients Without SCRAM (ATWS) events concluded that a time delay of 5 seconds in ECCS injection would have an insignificant impact on the analysis results and the acceptance criteria in the USAR for these events would continue to be met. This same generic assessment included an evaluation for Station Blackout (SBO) events which concluded that an injection time delay of 10 seconds would not impact the ability of the water makeup system to maintain the vessel water level above the top of active fuel, the USAR acceptance criterion. Similarly, this evaluation concluded that an injection time delay of 10 seconds would have an insignificant impact on meeting the acceptance criteria for core cooling in the 10 CFR 50, Appendix R fire safe shutdown analysis.

3. Drawing Reviews A review of drawings (e.g., isometric, P&IDs, vendor component, etc.) associated with the subject systems within the scope of the GL was conducted to identify areas where gas could potentially accumulate (e.g., high points, components, and branch lines).

The systems were also evaluated for the adequacy of existing vent valve locations. The results of the drawing review identified a number of locations as areas potentially susceptible to gas accumulation. These locations were further evaluated and dispositioned by confirmatory system walkdowns.

4. Confirmatory System Walkdowns Plant walkdowns of the accessible piping sections were conducted at the MNGP.

Walkdowns were conducted to confirm the physical location and orientation of the vents and piping layout, piping slopes, component configurations with the ability to trap gas, or other susceptible areas for gas accumulation.

Piping slope was identified by taking elevation measurements along nominally horizontal sections of piping. Portions of RHR and HPCl System piping were insulated with fibrous insulation and aluminum jacketing. Measurements were taken by penetrating through the insulation and contacting the pipe. This technique was used to alleviate the need to remove insulation from significant portions of piping and to minimize dose to the workers.

From the walkdown data and drawing reviews, locations were identified for additional evaluation. These locations were comprised of piping segments that met any of the following criteria:

ENCLOSURE I NINE-MONTH RESPONSE TO NRC GENERIC LETTER 2008-01 MANAGING GAS ACCUMULATION IN EMERGENCY CORE COOLING, DECAY HEAT REMOVAL, AND CONTAINMENT SPRAY SYSTEMS

- Not sloped in the proper direction, an indication of a horizontal (nominal) run of pipe that may contain a potential local highpoint,

- Pipe tees where gas from the main flow stream could pass into a stagnant pipe section, where it may accumulate,

- Pipe diameter transitions in horizontal sections that could create void traps at the top of the larger piping or at a component such as an orifice,

- High points created by closed valves in vertical piping runs,

- Vents not in a proper location.

Based upon volume, gas removal options, and system impact, 25 areas were identified in the HPCI, Core Spray and RHR Systems piping requiring UT. The following is a general breakdown of the locations and results:

GL FunctionISystem Suction Discharqe UT Results ECCS - HPCl System 5 3 No gas accumulation found ECCS - Core Spray System 5 No gas accumulation found ECCS, Decay Heat Removal and 4 7 No gas Containment Spray - RHR System accumulation found Totals 10 15 No gas accumulations found These areas were evaluated using UT and no gas accumulations were found.

In the three month response to GL 2008-01, NSPM identified that walkdowns of inaccessible portions of the subject systems could not be performed for various reasons until the 2009 Refueling Outage and proposed the following commitment.

Complete the detailed walkdowns of the inaccessible sections of the Generic Letter 2008-01 subject systems prior to startup from the 2009 Refueling Outage.

Since that time, significant industry effort has taken place on evaluating the effects of gas accumulation. As discussed previously a generic analysis Page 9 of 18

ENCLOSURE I NINE-MONTH RESPONSE TO NRC GENERIC LETTER 2008-01 MANAGING GAS ACCUMULATION IN EMERGENCY CORE COOLING, DECAY HEAT REMOVAL, AND CONTAINMENT SPRAY SYSTEMS evaluated the piping downsteam of the Low Pressure ECCS injection valves and concluded that even if voids did exist in the discharge piping downstream of the isolation valve, the pressure transient would not be greater than that associated with an actual injection in an accident. Therefore, NSPM believes that no field walkdowns downstream of the Low Pressure ECCS injection valves (i.e.,

between the outboard injection and the reactor vessel) are necessary and proposes to revise the commitment as follows:

Complete the detailed walkdowns of the applicable inaccessible sections of the Generic Letter 2008-01 subject systems (does not include the piping downstream of the low pressure ECCS outboard injection valves) prior to startup from the 2009 Refueling Outage.

5. Procedure Reviews A review was performed of procedures and instructions with respect to system restoration, fill and vent, and gas accumulation for the subject systems.

Procedures were reviewed for adequacy of scope, sequencing of vent valves, duration of vent, need for dynamic venting, flexibility to adjust to changes in work scope, and verifications that the system was full.

Procedures for controlling alternate system line-ups and restorations were reviewed, for example returning the RHR System to the LPCl mode from the SPC mode. Such procedures were confirmed to have proper venting instructions as part of system restoration to their normal line-up. Note that surveillance procedures are evaluated under the Testing Evaluation section, below.

The post maintenance fill and vent process is controlled through restoration work instructions developed in the isolation process. The current process provides custom instructions for restoration for each maintenance task performed through the restoration instructions in the isolation process. The current process allows for the restoration instructions to be tailored to the exact isolations that are present in the field (existing standing venting procedures may be used as applicable).

Site operating experience and the confirmatory walkdowns performed demonstrate that the existing venting practices are adequate to prevent unacceptable gas accumulation in the subject systems.

6. Gas Intrusion Mechanisms The primary mechanisms for potential gas intrusion at MNGP in the subject systems are:

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ENCLOSURE 1 NINE-MONTH RESPONSE TO NRC GENERIC LETTER 2008-01 MANAGING GAS ACCUMULATION IN EMERGENCY CORE COOLING, DECAY HEAT REMOVAL, AND CONTAINMENT SPRAY SYSTEMS

- Incomplete post-maintenance fill and vent activities, and

- Conditions where local temperatures are at or above saturation temperature (turbulent penetration). The latter condition is only applicable to the HPCl dischar e piping in the vicinity of the connection to the Feedwater System. 81 Gas intrusion mechanisms that were determined to not apply at the MNGP are:

Suction piping is not connected to any pressurized gas sources that could introduce voids into the piping and flow stream for any of the GL subject systems/functions.

For the HPCl System, the CST vortex calculation for the automatic transfer from the CST to the suppression pool account for the potential for vortexing.

Containment Spray piping (discharge side) is not vulnerable to gas intrusion, although the Primary Containment is inerted with nitrogen and slightly pressurized during power operation. The Primary Containment Isolation Valves (PCIVs) in each of these piping sections are subjected to leak rate tests as part of the MNGP 10 CFR 50, Appendix J testing program. In addition, the outboard portions of the discharge piping are maintained at a higher pressure than the Primary Containment during power operation by keep-fill.

Summary of Changes Based on the Design Evaluation The following changes were identified based upon the results of the design evaluation.

a) Complete Confirmatory Walkdowns of Applicable Inaccessible Piping Sections HPCl Discharge Piping Connection to the Feedwater Svstem - Inside Main Steam Chase This is a relatively small section of piping maintained under keep-fill pressure. The section includes the HPCl discharge high point and associated vent. Based upon the fidelity of the drawing to walkdown results to date and the September 11, 2008, HPCl injection at rated flow through this line with no observed water hammer, the NSPM has high confidence that this section of piping will not accumulate an unacceptable gas void prior to system walkdown.

6. The addition of a "keep-fill" system has eliminated the forming of a steam void at this location.

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ENCLOSURE I NINE-MONTH RESPONSE TO NRC GENERIC LETTER 2008-01 MANAGING GAS ACCUMULATION IN EMERGENCY CORE COOLING, DECAY HEAT REMOVAL, AND CONTAINMENT SPRAY SYSTEMS RHR Shutdown Cooling Suction Piping Inside Containment Additional walkdowns not yet complete also include the RHR Shutdown Cooling suction piping inside Containment. Based on acceptable performance of the suction piping during operation of RHR in the Shutdown Cooling mode during the September 2008 shutdown, NSPM has high confidence that this section of piping will not accumulate an unacceptable gas void prior to system walkdown.

In accordance with commitments made in Reference 2, these inaccessible piping sections are scheduled to be walked down during the spring 2009 RFO and the results of the evaluations are to be provided to the NRC within 90 days following return to full power from the RFO.

b) Revise Order of Operation of the Containment Spray Injection Valves in the Emergency Operating Procedures (EOPs).

As discussed in Section 11.1, a procedure revision will be made to the Containment Spray EOPs. The Drywell Spray injection valves will be opened in an order that will not result in the voided section of pipe being pressurized against the closed inboard valve. The existing condition was evaluated for operability and determined to be acceptable.

This procedure change is being tracked in the MNGP Corrective Action Program and is scheduled to be complete by March 1,2009.

c) Revise Fill and Vent Procedures No instances were identified where the current procedural controls for the filling and venting of HPCI, Core Spray, and RHR Systems, following maintenance, would leave the systems in an inoperable condition.

Procedure reviews identified a number of enhancements, which include:

- Provide additional guidance for the preparation of restoration work instructions to ensure systems are filled.

- Utilize simplified system elevation drawings in the preparation of restoration work instructions.

- Provide consistent guidance on venting, such as appropriate venting duration and order.

- Incorporate system specific information identified during drawing reviews and confirmatory system walkdowns, such as additional existing vents, normally closed valves in vertical piping sections, or the use of dynamic venting.

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ENCLOSURE I NINE-MONTH RESPONSE TO NRC GENERIC LETTER 2008-01 MANAGING GAS ACCUMULATION IN EMERGENCY CORE COOLING, DECAY HEAT REMOVAL, AND CONTAINMENT SPRAY SYSTEMS

- Identify gas accumulation concerns in Design Change checklists These procedure changes are being tracked in the MNGP Corrective Action Program and are scheduled to be complete by March 1, 2009.

d) Add Gas Accumulation Guidance into the Operability Process.

Incorporate recently developed industry gas accumulation evaluation guidance into the operability process by March 1, 2009.

Based upon the above, MNGP is in conformance with its commitments to 10 CFR 50, Appendix B, Criterion Ill for Design Control, as described in the NMC Quality Assurance Topical Report (QATR) NMC-1, Revision 2.

Ill. Testing Evaluation The MNGP testing practices were reviewed with respect to gas accumulation in the ECCS, Decay Heat Removal and Containment Spray functions. This review included surveillance test procedures.

1 Procedure Reviews Various test procedures are employed at MNGP to address ECCS, Decay Heat Removal and Containment Spray functions. These procedures include fill verification of the subject systems. These procedures were reviewed for use of acceptance criteria, adequate documentation requirements and use of the MNGP Corrective Action Program.

Monthly fill verification procedures used to satisfy the requirements of SR 3.5.1.1 and SR 3.5.2.2, to verify that each low pressure ECCS injectionlspray subsystem piping is filled with water from the pump discharge valve to the outboard injection valve, were reviewed. These procedures require venting at high point locations in the respective system. The procedure for the low pressure ECCS, RHR - LPCl mode includes venting the high points of the Containment Spray system. The Decay Heat Removal function, i.e., RHR SDC discharge piping is common with the low pressure ECCS, RHR - LPCl mode piping and, therefore is also vented.

Acceptance criteria vary among the procedures but include statements such as "when water is observed flowing into drain" or "when water appears." The acceptance criteria of the periodic venting procedures are consistent with meeting the specific requirement of the SR to verify the piping system "is filled with water."

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ENCLOSURE I NINE-MONTH RESPONSE TO NRC GENERIC LETTER 2008-01 MANAGING GAS ACCUMULATION IN EMERGENCY CORE COOLING, DECAY HEAT REMOVAL, AND CONTAINMENT SPRAY SYSTEMS The procedures also require estimation of the number of seconds air venting occurred, and the value recorded. The current procedures did not specifically direct entry into the CAP for any amount of air vented; the procedures will be revised as discussed below.

2. Manual Operation of RHR in Decay Heat Removal Mode Operating procedures for placing the RHR System into the Shutdown Cooling (SDC) mode and for restoration back to the primary ECCS function, i.e., the low pressure ECCS injection, or RHR - LPCl mode were reviewed. When being aligned to SDC mode, the RHR suction piping, pumps, and a portion of the RHR discharge piping are normally vented and warmed prior to placing SDC in service. This evolution removes any potential voids that may have accumulated since the last use of SDC mode. The discharge section of piping is common with the low pressure ECCS (RHR - LPCl mode) function, and thus pressurized by the keep-fill, therefore unacceptable gas voiding is precluded. Restoration from the SDC mode to the standby ECCS (RHR - LPCl mode) lineup includes direction to vent RHR piping, sufficient to preclude unacceptable gas voiding.

3. Inadvertent Draining Relevant operating procedures for the subject systems were reviewed with respect to GL 2008-01 concerns, including system realignments. No susceptibility to gas accumulation was identified. Instructions for venting are included in many system realignment procedures, including, for example:

- Shutdown Cooling Mode - Loops A and B Startup

- Shutdown Cooling Mode - Loops A and B Shutdown

- Torus Cooling Mode - Shutdown

- Emergency Fuel Pool Cooling

4. Documentation and Trending The procedures used to perform venting in accordance with the TS surveillance requirements include steps to estimate the number of seconds air was vented from the piping system. Steps required to meet the surveillance requirements are marked at the step. Failure to meet the expected results will direct entry into the CAP.

Completion reviews of the venting surveillance procedures by the relevant system engineer provide an additional check of appropriate venting times.

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ENCLOSURE I NINE-MONTH RESPONSE TO NRC GENERIC LETTER 2008-01 MANAGING GAS ACCUMULATION IN EMERGENCY CORE COOLING, DECAY HEAT REMOVAL, AND CONTAINMENT SPRAY SYSTEMS

5. Summary of Changes Based on Testing Evaluation Revise Surveillance Procedures

- Provide consistent wording throughout testing procedures on venting, such as "solid stream of water observed flowing into drain for approximately 30 seconds."

- Add RHR Heat Exchanger vents to the surveillance venting process.

- Provide direction to enter the CAP for unanticipated gas venting.

These procedure changes are being tracked in the MNGP Corrective Action Program and are scheduled to be complete by March 1, 2009.

IV. Corrective Actions Evaluation The MNGP Corrective Action Process was reviewed with respect to gas accumulation in the Emergency Core Cooling, Decay Heat Removal and Containment Spray Systems.

This included a review of the CAP, required actions within surveillance test procedures and trending performed by plant staff.

1 Corrective Action Review The MNGP Corrective Action Program requires that conditions adverse to quality are entered into the process for resolution.

As noted in the Testing Evaluation, there were no specific requirements in the monthly surveillance test procedures to assess gas discovered during performance of a test and enter the issue into the CAP.

As part of the evaluations performed under GL 2008-01, NSPM has established guidelines for assessing voiding of the subject systems during walkdowns and for performing UT examinations. Any void, regardless of size, will be entered into the CAP for operability determinations.

No gas voids were found during the system walkdowns and UT examinations.

2. Changes Based on Corrective Action Review As identified above, procedure changes were identified for surveillance test procedures to specify the entering of the issue into the CAP if a situation requiring unanticipated venting occurs.

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ENCLOSURE I NINE-MONTH RESPONSE TO NRC GENERIC LETTER 2008-01 MANAGING GAS ACCUMULATION IN EMERGENCY CORE COOLING, DECAY HEAT REMOVAL, AND CONTAINMENT SPRAY SYSTEMS

3. Conclusion Based upon the above, NSPM has concluded that the MNGP is in conformance with its commitments to 10 CFR 50, Appendix B, Criteria Ill, V, XI, XVI, and XVII, as described in the NMC Quality Assurance Topical Report (QATR) NMC-1, Revision 2.

B. DESCRIPTION OF NECESSARY CORRECTIVE ACTIONS No corrective actions were determined necessary to assure compliance with the applicable regulations.

C. CORRECTIVE ACTION SCHEDULE As described above, the following corrective actions will be completed.

Schedule for Description Completion Basis Complete Confirmatory Walkdowns of Prior to startup Operation of the HPCl and Applicable Inaccessible Piping Sections from the RHR Systems during the (Section 11.7a), Pg. 12 ) spring 2009 unplanned September HPCl Discharge Piping Connection Refueling 2008 shutdown. HPCl to the Feedwater System - Inside Outage piping maintained under Main Steam Chase keep-fill pressure.

SDC Suction Piping Inside Containment Resolve Appropriate Void Fraction in October 14, Continuous void fraction EOPs. The MNGP EOPs (based on 2009 used in the EOPs meets BWROG guidance) utilize a 4 percent (Target Date) previous NRC guidance.

continuous void fraction for ECCS pump Current industry guidance operation and suppression pool vortex of 2 percent is conservative limits based on NUREGICR-2772. interim guidance until more Current industry guidance applied for this definitive acceptance GL specifies a 2 percent void fraction. criteria is developed.

Note that this new issue will require industry resolution and may take longer to resolve then the targeted date.

(Section II.I), Pg. 6)

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ENCLOSURE 1 NINE-MONTH RESPONSE TO NRC GENERIC LETTER 2008-01 MANAGING GAS ACCUMULATION IN EMERGENCY CORE COOLING, DECAY HEAT REMOVAL, AND CONTAINMENT SPRAY SYSTEMS Schedule for Description Completion Basis Add Gas Accumulation Guidance into the March I , 2009 UT for the 25 susceptible Operability Process locations did not detect any (Section 11.7c), Pg. 13) gas accumulations.

Therefore, need for formalized operability guidance in the interim is small.

Revise Order of Operation of the March 1, 2009 Pressurization transient Containment Spray Injection Valves in the acceptable if valves had to EOPs (Section 11.1, Pgs. 5 and 6) be opened.

Revise Fill and Vent Procedures March 1,2009 Proposed changes are (Section 11.7c), Pg. 13) enhancements. No gas accumulations found.

Present fill and vent and system operating practices are adequate.

Revise Surveillance Procedures March 1,2009 Proposed changes are (Section 111.6, Pg. 15) enhancements. No gas accumulations found.

Present surveillance procedures are adequate.

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ENCLOSURE I NINE-MONTH RESPONSE TO NRC GENERIC LETTER 2008-01 MANAGING GAS ACCUMULATION IN EMERGENCY CORE COOLING, DECAY HEAT REMOVAL, AND CONTAINMENT SPRAY SYSTEMS REFERENCES

1. U.S. NRC Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems," dated January 11,2008.

2. NMC to NRC, "Generic Letter 2008-01: Three Month Response to Generic Letter 2008-01," (L-MT-08-026) dated April 11, 2008.

3. NRC to NMC, "Monticello Nuclear Generating Plant (MNGP) - Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems," Proposed Alternative Course of Action (TAC No. MD7847),19dated September 9, 2008.

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