ET 09-0020, Response to Request for Additional Information Generic Letter 2008-01, Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems

Response to Request for Additional Information Generic Letter 2008-01, Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems

ML092370297
Person / Time
Site:	Wolf Creek
Issue date:	08/17/2009
From:	Garrett T Wolf Creek
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
ET 09-0020, GL-08-001
Download: ML092370297 (10)

Text

LCREEK NUCLEAR OPERATING CORPORATION August 17, 2009 Terry J. Garrett Vice President Engineering ET 09-0020 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555

Subject:

1) Letter dated July 9, 2009, from USNRC to R. A. Muench, WCNOC, (ADAMS Accession No. ML091740391)

2) E-mail from NRC (B. Singal) to WCNOC (D. Hooper) regarding Generic Letter 2008 Request for Additional Information, dated July 14, 2009

3) Letter ET 08-0045, dated October 10, 2008, from T. J. Garrett, WCNOC, to USNRC (ADAMS Accession No. ML082950487)

4) Letter dated May 28, 2009, from USNRC to J. H. Riley, Nuclear Energy Institute, "Preliminary Assessment of Responses to Generic Letter 2008-01,

'Managing Gas Accumulation in Emergency Core

Cooling, Decay Heat

Removal, and Containment Spray Systems,' and Future NRC Staff Review Plans," (ADAMS Accession No. ML091390637).

Docket No. 50-482:

Wolf Creek Nuclear Operating Corporation Response to Request for Additional Information RE: Response to Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems" Gentlemen:

Pursuant to 10 CFR 50.54(f), this letter provides the Wolf Creek Nuclear Operating Corporation (WCNOC) response to the NRC request for additional information (RAI) (Reference 1), as supplemented by clarifications in Reference 2, regarding WCNOC's response to Generic Letter 2008-01 (Reference 3). Responses to the applicable RAI requests are included in Attachment I.

The responses were developed considering the guidance in Reference 4.

P.O. Box 411 / Burlington, KS 66839 / Phone: (620) 364-8831 An Equal Opportunity Employer M/F/HCNET

ET 09-0020 Page 2 of 3 Attachment II lists commitments made to the NRC by this letter. If you have any questions concerning this matter, please contact me at (620) 364-4084, or Mr. Richard D. Flannigan at (620) 364-4117.

Sincerely, Terry J. Garrett TJG/rlt Attachment cc:

E. E. Collins (NRC), w/a V. G. Gaddy (NRC), w/a B. K. Singal (NRC), w/a Senior Resident Inspector (NRC), w/a

ET 09-0020 Page 3 of 3 STATE OF KANSAS

)

ss COUNTY OF COFFEY )

Terry J. Garrett, of lawful age, being first duly sworn upon oath says that he is Vice President Engineering of Wolf Creek Nuclear Operating Corporation; that he has read the foregoing document and knows the contents thereof; that he has executed the same for and on behalf of said Corporation with full power and authority to do so; and that the facts therein stated are true and correct to the best of his knowledge, information and belief.

Terry J.

r0rett Vice Pr ident Engineering SUBSCRIBED and sworn to before me this f day of 2009.

rA, GAYLE SHEPHEARDl Notary jPblic Notary Public - State of KansasI My Appt. Expires

.2-01 1 E2 2

Expiration Date

'2/21

Attachment I to ET 09-0020 Page 1 of 6 Generic Letter 2008-01 Request for Additional Information Response This attachment provides the Wolf Creek Nuclear Operating Corporation (WCNOC) response to the NRC request for additional information (RAI) (Reference 1) for Wolf Creek Generating Station (WCGS), as supplemented by clarifications in Reference 2, regarding WCNOC's response to Generic Letter (GL) 2008-01 (Reference 3).

RAI Request 1:

1.

The WCNOC response to GL 2008-01 (Reference 3) stated that the safety injection (SI) accumulator level is monitored from the plant computer and a pre-determined level change causes an email alert to the system engineer. Please provide the follow-up actions the system engineer will perform if a pre-determined level change occurs in a SI accumulator and identify the process that ensures the actions.

WCNOC Response to RAI Request 1:

As described below, the appropriate response to unexpected changes to the safety injection (SI) accumulator level is governed by the requirements of procedure AP 23-006, "System Engineering Program." System-specific trending and monitoring plans have been developed for each ECCS system by the system engineer per the requirements of AP 23-006 and approved by the supervisor.

Administrative controls in procedure AP 23-006 direct system engineers to perform trending and monitoring as specified in individual trending and monitoring plans.

The trending and monitoring plan for the accumulator safety injection (SI) system includes a line item to monitor the rate of change of SI accumulator level.

This function is performed by monitoring software that compares the operating levels of all SI accumulators every hour.

If the alert set point is reached, an e-mail is sent to the system engineer. The alert set point for any SI accumulator is greater than or equal to 0.04% level change per hour.

This leakage rate corresponds to potential gas accumulation of approximately 0.03 cubic feet in the lowest pressure system location, if the gas were to accumulate at this rate for one hour.

Due to a recent assessment of this e-mail alert process, a corrective action document has been initiated to also send the e-mail alert to the on-duty shift manager. This action will ensure that corrective action is initiated if a level setpoint alert is received while the system engineer is off-shift or out of the office. This corrective action document (CR 00019016) is available for review at WCGS.

If an e-mail is received by the system engineer indicating the alert set point has been reached, the system engineer initiates a trend evaluation of the accumulator levels, SI pump starts, accumulator gas pressure, and containment temperature, per the trending and monitoring plan.

Prompt action is taken to investigate unexpected or unexplained changes in level and/or pressure. If the investigation reveals unexpected changes or other indications of a condition or circumstance that reduces the confidence that any structure, system, or component will perform satisfactorily in service, procedure AP 23-006 directs system engineers to notify their supervisor and initiate corrective action in the form of a condition report and, if necessary, a work request.

Attachment I to ET 09-0020 Page 2 of 6 Monitoring the level of each SI accumulator once per hour, combined with the administrative controls described above, provides adequate confidence that appropriate actions are initiated and completed prior to the accumulation of a volume of gas from SI accumulator leakage that could challenge ECCS system operability.

RAI Request 3:

3.

It is not apparent from the WCNOC response that actions are encompassed suitably in procedures so that an acceptable response will be obtained if a decreasing accumulator level is observed. Please clarify this item.

WCNOC Response to RAI Request 3:

The actions required in response to a decreasing accumulator level at WCGS are included in procedure AP 23-006, "System Engineering Program," as described in WCNOC's response to RAI request 1 above.

RAI Request 11:

11.

A 10-foot length of 6-inch diameter pipe could contain 0.5 cubic feet of gas if full at one end and empty at the other due to being sloped. This is inconsistent with the 0.25 cubic feet acceptance criterion that WCNOC previously stated it would apply to voids. The NRC staff uses a criterion of 4-inch diameter that avoids this discrepancy. Please discuss and provide a resolution.

WCNOC Response to RAI Request 11:

WCNOC would like to clarify the use of the term acceptance criterion relative to WCNOC's response to GL 2008-01 (Reference 3).

As stated in Section A.2.2 of Reference 3, the acceptance criterion for the WCGS systems within the scope of GL 2008-01 is "full."

The discovery of gas accumulation of any amount in systems within the scope of GL 2008-01 is considered to be a degraded condition that requires appropriate corrective action including assessing impact on system operability. The 0.25 cubic foot criterion used by WCNOC is not an acceptance criterion for use during surveillance activities, but is one of the technical criteria developed through engineering evaluation that may be used by the on-duty licensed senior reactor operators (SROs) to support a "degraded but operable" operability decision.

WCNOC used the arrangement depicted in Figure 1 below for evaluation of selection criteria for obtaining dimensional data at WCGS.

Attachment I to ET 09-0020 Page 3 of 6 Vent Pipe (10 Feet Long)

\\\\REINEN(not to scale)-

10 Figure 1. Typical arrangement for determining selection criteria for obtaining dimensional data The development of selection criteria was based on the following:

1. The vertical position tolerance for field erection of piping at WCGS is that the centerline of the pipe be at the design drawing elevation plus or minus 1.0 inch. The as-built piping configurations were verified to be within the vertical position tolerance following piping installation during the construction phase. The plus or minus 1.0 inch tolerance means that the elevation along a horizontal run of pipe can vary by as much as 2.0 inches if one point is at the positive tolerance limit and another point is at the negative tolerance limit.

2. Based on normal industry construction practices, the installation of relatively short lengths of 10 feet or less piping segments is normally accomplished with a single length of pipe with no additional welded segments between the ends.

More complex configuration arrangements with multiple welds or multiple elbows at the same elevation in a piping run less than ten feet in total length is not likely. If these more complex piping arrangements exist, consideration of normal construction practices may introduce small errors in calculated gas volumes compared to the arrangement depicted in Figure 1, but would have an insignificant impact on the conclusions of the selection criteria evaluations described below.

3. The trapped gas volume of concern for determination of selection criteria is only that volume that is between a vent or escape pathway and the adjacent upward-sloping pipe that does not have a vent or escape path. This is depicted in Figure 1. While gas could accumulate below a ventable location such as that depicted in Figure 1, WCNOC's surveillance practices and associated corrective action if.gas is found, as described in Sections A.3.2 and A.3.5 of Reference 3, provide adequate confidence that operability of affected systems will be maintained.

4. Using the configuration in Figure 1, for 10-foot pipes of various sizes sloped 2 inches from end-to-end, the calculated maximum trapped gas volumes if the run slopes up from a vent or escape path are shown in Table 1 below.

Attachment I to ET 09-0020 Page 4 of 6 Table 1. Maximum Trapped Gas Volume for 10-foot Pipe Lengths Nominal Pipe Size Maximum Trapped Gas Volume (ft3) 3" Sched 40S 0.155 4" Sched 40S 0.186 6" Sched 40S 0.239 For all nominal pipe sizes in Table 1, the maximum trapped gas volume for a 10-foot length with a linear slope away from a vent or escape path is less than 0.25 cubic feet. Even though the maximum trapped gas volume for the 6-inch size pipe is below 0.25 cubic foot, WCNOC conservatively determined that pipe diameters of 6 inches and larger should be included in the scope for dimensional data measurements regardless of the horizontal run length.

Therefore, for pipe slope dimensional data measurements, all horizontal pipes 6-inch nominal size and larger were measured regardless of length. Horizontal pipes 4-inch nominal size and smaller were measured only if they were 10 feet or greater in total length at one elevation.

Exclusion of 4 inches and smaller pipe diameters with horizontal run lengths less than 10 feet is consistent with the 0.25 cubic foot volume used by the on-duty SROs to support a "degraded but operable" operability decision.

RAI Request 13:

13.

Following vent installations, the potential cumulative unventable gas void volumes created by slopes in horizontal pipes is stated to be less than 3 cubic feet for systems discharge piping, and less than 0.5 cubic feet for suction piping. These values are inconsistent with the 0.25 cubic feet criterion. Please address and resolve these differences.

WCNOC Response to RAI Request 13:

WCNOC does not believe this is a discrepancy relative to the use of the 0.25 cubic foot engineering evaluation criterion. This criterion is not used in any engineering, maintenance or operational evaluation if accumulated gas has not been discovered.

It is used only in the evaluation of gas that has been discovered in system piping during normal surveillance testing or following maintenance activities.

The 0.25 cubic foot value is documented in an engineering document for use by operations personnel during operability determinations.

It is applicable only to a single identified trapped gas volume. Discovery of any larger gas volume or other conditions, such as several identified trapped gas volumes in close proximity, must be evaluated by engineering for potential impact on the ability of the impacted systems to perform their intended functions.

The 3 cubic feet and 0.5 cubic foot values described in Section A.2.6 of Reference 3 do not represent actual trapped gas volumes. The values represent the sum of the volumes of all piping locations that could potentially trap gas based on dimensional data measurements.

These trap locations are distributed over both trains of six different GL 2008-01 systems.

Attachment I to ET 09-0020 Page 5 of 6 The potential unventable accumulated gas volumes in system discharge piping are distributed over several hot-leg and cold-leg injection and recirculation paths. The distributed nature of the potential gas trap locations will not allow accumulation of gas that could create pressure pulsations or other effects that threaten the function of GL 2008-01 systems. Some of the potential gas volume in discharge piping is located between the last flow restriction and the reactor coolant system (RCS). Gas volumes beyond the last restriction in the flow path to the RCS cannot cause pressure pulsations greater than the RCS pressure and, thus, have no impact on GL 2008-01 system safety functions.

The less than 0.5 cubic foot of potential unventable gas volume identified by dimensional data measurements on system suction piping is distributed over both trains of six different GL 2008-01 systems. This provides high assurance that these local high points cannot create a situation that challenges the reliability of the GL 2008-01 system pumps.

RAI Request 15:

15.

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. This was identified in the NEI template (Reference 2) as an item that should be addressed in the GL responses and was discussed in the NEI workshop (Reference 5). This is not addressed in the WCNOC response. Please provide a brief description of planned training and its schedule.

WCNOC Response to RAI Request 15:

WCNOC classroom training addressing GL 2008-01 issues was presented to Engineering and Operations groups as just-in-time training in March 2008 prior to Refueling Outage 16.

WCNOC classroom training addressing gas accumulation issues identified in NRC and industry documentation such as GL 2008-01, INPO SOER 97-1 (Reference 4) and INPO SER 2-05, Rev. 1 (Reference 5) is currently planned on the following schedule.

Engineering - Fall 2010.

Mechanical Maintenance - Fall 2010 Operations - Spring 2010 WCNOC will monitor the industry-sponsored development of a gas accumulation training program and will incorporate appropriate training from the program into associated INPO accredited training programs within 120 days following issuance of the industry training program.

Attachment I to ET 09-0020 Page 6 of 6

References:

1)

Letter dated July 9, 2009, from USNRC to R. A. Muench, WCNOC, (ADAMS Accession No. ML091740391)

2)

E-mail from NRC (B. Singal) to WCNOC (D. Hooper) regarding Generic Letter 2008 Request for Additional Information, dated July 14, 2009

3)

Letter ET 08-0045, dated October 10, 2008, from T. J. Garrett, WCNOC, to USNRC (ADAMS Accession No. ML082950487)

4)

SOER 97-1, -Potential Loss of High Pressure Injection and Charging Capability from Gas Intrusion, November 28, 1997.

5)

SER 2-05, Revision 1, Gas Intrusion in Safety Systems, January 9, 2008

Attachment II to ET 09-0020 Page 1 of 1 Requlatorv Commitments The following table identifies actions committed to by Wolf Creek Nuclear Operating Corporation in this letter.

Any other statements in this letter are provided for information purposes and are not considered to be regulatory commitments.

Please direct questions regarding these commitments to Mr. Richard Flannigan, Manager Regulatory Affairs at Wolf Creek Generating Station, (620) 364-4117.

Regulatory Commitment Due Date WCNOC will monitor the industry-sponsored development of a gas 120 days following accumulation training program and will incorporate appropriate training issuance of the from the program into associated INPO accredited training programs industry-sponsored within 120 days following issuance of the industry training program.

gas accumulation training program