Text

Response to Request for Additional Information Regarding Generic Letter 2008-01
	ML093160345
Person / Time
Site:	LaSalle
Issue date:	11/03/2009
From:	Simpson P; Exelon Generation Co, Exelon Nuclear
To:	; Document Control Desk, Office of Nuclear Reactor Regulation
References
	GL-08-001, RS-09-149
	Download: ML093160345 (8)
	v • d • e

November 3,2009 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk 11555 Rockville Pike Rockville, MD 20852 LaSalle County Station, Units 1 and 2 Facility Operating License Nos. NPF-11 and NPF-18 NRC Docket Nos. 50-373 and 50-374

Subject:

Response to Request for Additional Information Regarding Generic Letter 2008-01

References:

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

dated January 11,2008

2. Letter from K. R. Jury (Exelon Generation Company, LLCIAmerGen Energy Company, LLC) to U.S. NRC, "Three Month Response to Generic Letter 2008-01," dated April 11,2008

3. Letter from K. R. Jury (Exelon Generation Company, LLCIAmerGen Energy Company, LLC) to U.S. NRC, "Nine-Month Response to Generic Letter 2008-01,"dated October 14,2008

4. Letter from P. R. Simpson (Exelon Generation Company, LLC) to U.S. NRC, "Supplemental Response to Generic Letter 2008-01," dated May 5,2009

5. Letter from C. S. Goodwin (U.S. NRC) to C. G. Pardee (Exelon Nuclear),

'IaSalle County Station, Units 1 and 2 - Request for Additional lnformation Related to Generic Letter 2008-01, 'Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems' (TAC Nos. MD7839 and MD7840)," dated September 21,2009 The NRC issued Generic Letter (GL) 2008-01 (i.e., Reference 1) to request that each licensee evaluate the licensing basis, design, testing, and corrective action programs for the Emergency Core Cooling, Decay Heat Removal, and Containment Spray systems, to ensure that gas

November 3,2009 U.S. Nuclear Regulatory Commission Page 2 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.

References 2, 3, and 4 provided the Exelon Generation Company, LLC (EGC) responses to NRC GL 2008-01 for LaSalle County Station. In Reference 5, the NRC requested additional information that is required to complete the review. In response to this request, EGC is providing the attached information.

There are no regulatory commitments contained in this letter. Should you have any questions concerning this letter, please contact Mr. Kenneth M. Nicely at (630) 657-2803.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 3rd day of November 2009.

t&' R+

Patrick R. Simpson Manager - Licensing

Attachment:

Response to Request for Additional Information cc: NRC Regional Administrator - Region Ill Senior Resident Inspector - LaSalle County Station

AnACHMENT Response to Request for Additional Information NRC Request 1 LSCS determined that the following systems are within the scope of Generic Letter (GL) 2008-01:

High Pressure Core Spray Low Pressure Core Spray Residual Heat Removal (RHR) (Suppression Pool Cooling, Low Pressure Coolant Injection, Shutdown Cooling, Drywell Spray, and Suppression Pool Spray modes of RHR).

The Reference 3 document states the above systems were evaluated with respect to the current licensing and design bases; however, it is unclear if the licensee evaluated these systems for gas intrusion under all modes of operation. Please clarify what mode or modes the above systems were evaluated.

Response

The High Pressure Core Spray (HPCS) and how Pressure Core Spray (LPCS) systems were evaluated with respect to both the full flow test and injection modes of operation. The BHW system was evaluated with respect to the full flow test, suppression pool cooling (SPC), low pressure coolant injection (LPCI), shutdown cooling (SDC), drywell spray, and suppression pool spray modes of operation. There are no other modes for these systems that provide a safety function.

NRC Request 2 The mention of systems that perform a "keep-full" function is not present in LaSalle's submittal, and is addressed in the GL as used to maintain systems full of water. Please either identify keep-full system@)as part of the scope of the GL or justify the exclusion.

Response

Since the Emergency Core Cooiing Systems (ECCSj ciisciiarge lines are elevated r;bove the suppression pool, check valves are provided near the pumps to prevent backflow from emptying the lines. To ensure leakage from the discharge lines is replaced and the lines are kept filled, a water leg pump is provided for each ECCS division. The Division 1 keep fill pump, designated to the LPCS system, supports both LPCS and the 'Ai train of RHR. The Division 2 keep fill pump is designated to the RHR system, and supports both the '6' and 'C' trains of RHR. The Division 3 keep fill pump is dedicated to the HPCS system. Continuous monitoring of discharge lines is accomplished via control room indication of keep fill pump status and annunciation of low pressure. The keep fill components were evaluated with respect to the supported systems, and were not considered a separate system.

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AmACHMENT Response to Request for Additional Information NRC Request 3 The technical specification verification of emergency core cooling system piping is "from the pump discharge valve to the injection valve every 31 days." Suction piping is not addressed.

Please justify how the current surveillance reasonably ensures the systems are and will remain operable and explain the process to determine if the frequency of surveillance needs to be changed.

Response

The suction piping was considered during the GL 2008-01 evaluations of the ECCS systems.

The suction supply for all ECCS systems is provided by the suppression pool, and is maintained full due to the static head provided by the suppression pool level. Additionally, suction piping was evaluated with respect to vortex formation creating an air intrusion path. The evaluation concluded that the level at which vortex formation was a concern was bounded by the pumps' net positive suction head lower limit. Both levels are bounded by a suppression pool water level of -18 feet, at the bottom of the indicating range.

Procedural controls require Issue Reports (IRs) to be initiated in the Corrective Action Program (CAP) if gas intrusion/accumulation issues are identified. The IR is then evaluated and dispositioned to determine the cause and identify appropriate corrective actions. If the cause is understood and can be corrected to ensure no further gas intrusions occur, adjustment of the surveillance interval may not be required. However, the need to adjust the surveillance interval is considered if the cause is not confirmed or it is determined to be necessary to confirm operability of the systems. Additionally, results of examinations for gas accumulation are trended by Engineering, and would also be used as a basis for adjusting the surveillance interval.

NRC Request 4 Provide a broad identification of surveillance locations and methods with identification and justification of excluded locations. Also, confirm if all high points are equipped with vents; and if not, justify why the location does not need vents.

As a result of the GL 2008-01 evaluations, requirements to perform periodic ultrasonic testing (UT) examinations of susceptible locations were established. The current surveillance locations are at the highest point of each ECCS systemltrain, based on evaluations that concluded these locations are the most likely for any gas to come out of solution because keepfill system pressure is the lowest.

Piping high points are equipped with vents, with the following exceptions. Piping open to and returning to the suppression pool or drywell was determined not to require high point vents.

Gas accumulation in these locations (i.e., downstream of full flow test valves and drywell spray injection valves) is expected and will not affect system function. Locations have been identified Page 2

AmACHMENT Response to Request for Additional Information where vents are not at the optimum location, and periodic UT monitoring is being performed to ensure these locations remain full of water.

NRC Request 5 It is stated that "the impact of the voids on system operability is evaluated on a case-by-case basis, with acceptable void volumes being determined as part of the evaluation." Describe the void volume determination methods and the actions that will be taken if void volume criteria are not met. The term "acceptable void volume" is unclear, please explain.

The phrase "full of water" is defined as absent of any gas voids that would adversely affect the systems from meeting their design requirements. Exelon Generation Company, LLC (EGC) also uses this definition to define the phrases "sufficiently full" and "acceptable void volumes."

Consistent with the MRC position documented in Reference 1, when voids are discovered in piping, EGC determines through an operability determination whether there is a reasonable expectation that the system in question will perform its specified safety function. Therefore, upon discovery of voids in piping, when there is a reasonable expectation that the system in question will perform its specified safety function, EGC considers the piping "full of water" or "sufficiently full" and in compliance with the associated Technical Specifications Surveillance Requirements. Actual void volumes in piping systems are typically determined via UT techniques. As discussed in the response to NRC Request 3, IRs are initiated in the CAP if gas intrusionlaccumulation issues are identified.

EGC has actively participated in the NEI Gas Accumulation Team, and the respective pressurized water reactor and boiling water reactor owners' groups, activities focused on developing suitable guidance for licensees in the evaluation of voids in the piping systems.

These groups have engaged recognized industry experts and Nuclear Steam Supply System vendors to determine the most appropriate criteria applicable to current reactor designs. The assessment of voids on the suction side, through the pump, on the discharge, and the effects on downstream piping and the reactor has been considered. The criteria are documented in eight separate reports generated to support this effort, all of which have been made available to the NRC.

Reference 2 was submitted to the NRC to summarize and focus these separate industry efforts.

The enclosure to this letter references these industry documents and provides insight on their application to evaluation of operability. This industry guidance is being used by EGC until such time that the NRC criteria can be formally issued and evaluated.

NRC Request 6 What industry guidance is being used in the void volume evaluation process?

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AmACHMENT Response to Request for Additional Information

Response

The industry guidance being used by EGC is discussed above in response to NRC Request 5.

NRC Request 7 Address the process of determining when confirmatory ultrasonic testing (UT) examinations are required as part of system restoration.

Response

Station fill and vent procedures require confirmatory UT examinations to be performed as part of system restoration at select vulnerable locations.

NRC Request 8 Explain Exelon Generation Company plans to implement a graded approach for performing periodic UT examinations. The term "graded approach" is unciear.

Response

EGC is actively supporting the industry TSTF and NEl Gas Accumulation Management Team activities regarding resolution of generic TS issues. Until such time that these issues are resolved, EGC has implemented supplemental UT inspections to ensure systems remain free of any voids that could challenge the intended safety function. This approach is described in procedure OP-AA-108-106, "Equipment Return to Service," which requires consideration of the use of UT examinations following fill and vent activities during system restoration to ensure voids have been removed.

Based on trending of the actual, recorded UT results, the monitoring frequency may be adjusted. Unexpected or unexplained gas accumulation in a system is entered into CAP for evaluation of operability and whether an increased frequency of monitoring is required.

Simiiariy, sustained gas acz~;mulat,ticnfree performance in a system is an indication that a relaxed frequency may be appropriate, after a certain confidence level has been established.

Monitoring begins at a frequency based on other TS surveillances, and relaxation should proceed incrementally, and is currently limited to not greater than six months.

NRC Reauest 9 Are all gas intrusion/accumulationdiscoveries entered in the corrective action program? If not, please justify.

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ATTACHMENT Response to Request for Additional Information

Response

All gas intrusion/accumulation discoveries are entered in the CAP. Model work orders to perform periodic UT examinations currently include the following work instructions: "If any air is identified during the UT inspection, initiate an Issue Report to document the condition."

NRC Request 10 Identify any supplementary actions to address control of voids in the subject systems that are not covered by TS requirements and the process that reasonably ensures the supplementary actions will be accomplished.

Response

As detailed in the responses to NRC Requests 7 and 8, until such time that the industry has determined the appropriate changes to TS, and these issues are resolved, EGC has implemented supplemental UT inspections where determined to be needed to ensure systems remain free of voids that could challenge the intended design function.

This approach is described in procedure OP-AA-108-106, which requires consideration of the use of UT examinations following fill and vent activities during system restoration to ensure voids have been removed. Site procedures were revised to add UT requirements following fill and vent at select vulnerable locations. In addition, the procedure that governs the modification process has been revised to include an evaluation of the potential for gas accumulation.

NRC Request 11 Training was not identified in the GL, but is considered to be a necessary part of applying procedures and other activities when addressing the issues identified in the GL. Briefly discuss training.

Response

GL 2008-01 did not require discussion of training to satisfy the 10 CFR 50.54(f) request; therefore, none was provided in the GL response for LaSalle County Station (LSCS). However, when any station procedure is modified, an assessment for training needs and change management is required in accordance with procedure AD-AA-101, "Processing of Procedures and T&RMs." The determination is typically a function of the nature of the change and the perceived impact on the organization. If the assessment concludes training is required, the training is generally accomplished prior to, or in parallel with, issuance of the procedure. For fill and vent procedure revisions, the changes have generally been minor, and have been considered enhancements. Work orders which direct the periodic examination of selected piping for the presence of air were created to draw upon pre-existing processes that provide guidance for the UT inspection of piping to verify that it is full of water. Training of personnel performing UT inspection is in accordance with corporate procedure ER-AA-335-001, "Qualification and Certification of Nondestructive Examination (NDE) Personnel."

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ATTACHMENT Response to Request for Additional Information EGC is an active participant in the NEI Gas Accumulation Team, which is currently directing the Institute of Nuclear Power Operations (INPO) in the development of generic training modules for gas accumulation and management. These training modules target the Engineering, Operations, and Maintenance disciplines. Based on this active participation, EGC plans to evaluate these training modules following completion for applicability to EGC, and may conduct training based upon modules tailored to meet EGC's needs.

References

1. Memorandum from L. D.Wert, Jr. (US. NRC) to T. B. Blount (U.S. NRC), "Task Interface Agreement - Emergency Core Cooling System (ECCS) Voiding Relative to Compliance with Surveillance Requirements (SR) 3.5.1 . I , 3.5.2.3, and 3.5.3.1 (TIA 2008-03)," dated October 21, 2008

2. Letter from J. H. Riley (Nuclear Energy Institute) to W. H. Ruland (U.S. NRC), "Industry Guidance - Evaluation of Unexpected Voids or Gas Identified in Plant ECCS and Other Systems," dated June 18, 2009 Page 6