ULNRC-05904, Response to Request for Additional Information Pertaining to Revision of Technical Specification (TS) 3.6.6, Containment Spray and Cooling Systems, LDCN 09-0025

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Response to Request for Additional Information Pertaining to Revision of Technical Specification (TS) 3.6.6, Containment Spray and Cooling Systems, LDCN 09-0025
ML12255A040
Person / Time
Site: Callaway Ameren icon.png
Issue date: 09/10/2012
From: Maglio S
Ameren Missouri, Union Electric Co
To:
Office of Nuclear Security and Incident Response, Document Control Desk
References
TAC ME6645, ULNRC-05904
Download: ML12255A040 (12)
v • d • e


Text

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"'HAmeren Callaway Plant MISSOURI September 10, 2012 ULNRC-05904 u.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 10 CFR 50.90 Ladies and Gentlemen:

DOCKET NUMBER 50-483 CALLAWAY PLANT UNIT 1 UNION ELECTRIC CO.

FACILITY OPERATING LICENSE NPF-30 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION PERTAINING TO REVISION OF TECHNICAL SPECIFICATION (TS) 3.6.6, "CONTAINMENT SPRAY AND COOLING SYSTEMS,"

LDCN 09-0025 (T AC NO. ME6645)

References:

1. Ameren Missouri Letter ULNRC-05804, "License Amendment Request:

Proposed Revision to Technical Specification 3.6.6, 'Containment Spray and Cooling Systems,' (LDCN 09-0025)," dated June 30, 2011

2. Electronic Request for Additional Information (RAI) from NRC dated August 9,2012 (ADAMS - Pkg: ML111820367, Email: ML12220A211)

Ameren Missouri (Union Electric Company) submitted a request for an amendment to Facility Operating License Number NPF-30 for Callaway Plant per the referenced letter (Reference 1). The proposed amendment would revise Technical Specification (TS) Surveillance Requirement (SR) 3.6.6.3 for verifying the minimum required containment cooling train cooling water flow rate. Rather than require verifying that each containment cooling train has a cooling water flow rate greater than or equal to 2200 gpm, TS SR 3.6.6.3 would be revised to require verification that the flow rate is "within limits."

From the NRC staffs ongoing review of the subject license amendment request, the NRC staff has identified the need for additional information. On June 14, 2012, a teleconference was held between Callaway Plant staff and NRC staff to discuss and further clarify a proposed request for additional information. Subsequently, a formal request for additional information (RAIs) was transmitted via e-mail to the Callaway Plant staff on August 7, 2012 (Reference 2). The e-mail contained three (3) specific requests from the NRC Technical Specifications Branch and five (5) specific requests from PO Box 620 Fulton, MO 65251 AmerenMissouri.com

ULNRC-05904 September 10, 2012 Page 2 the NRC Balance-of-Plant Branch. Responses to the specific requests are hereby provided in and Enclosure 2 to this letter, respectively.

The attached responses support the revisions to TS 3.6.6 and TS 3.6.6 Bases as proposed in the amendment application (Reference 1) and therefore do not constitute changes to what is proposed.

Consequently, the responses do not require any changes to the evaluations contained in the application and are bounded by the significant hazards consideration submitted in Reference 1 pursuant to 10 CFR 50.92. Further, the conclusion in Reference 1 that an environmental assessment need not be prepared pursuant to 10 CFR 51.22(b) remains unchanged. In addition, there are no new regulatory commitments identified or contained in this letter of response or in its enclosures.

Please contact us for any additional questions you may have regarding the attached responses or Ameren Missouri's amendment application. For questions regarding the attached information, please contact Scott A. Maglio at 573-676-8719 or Tom Elwood at 573-676-6479.

Sincerely,

~~.~::?

Regulatory Affairs Manager DJW/nls

Enclosures:

1. Responses to NRC Requests for Additional Information from Technical Specifications Branch (STSB)
2. Responses to NRC Requests for Additional Information from Balance-of-Plant Branch (SBPB)

ULNRC-05904 September 10,2012 Page 3 cc: U.S. Nuclear Regulatory Commission (Original and 1 copy)

Attn: Document Control Desk Washington, DC 20555-0001 Mr. Elmo E. Collins Regional Administrator U. S. Nuclear Regulatory Commission Region IV 1600 East Lamar Boulevard Arlington, TX 76011-4511 Senior Resident Inspector Callaway Resident Office U.S. Nuclear Regulatory Commission 8201 NRC Road Steedman, MO 65077 Mr. Fred Lyon Senior Project Manager, Callaway Plant Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Mail Stop 0-8G 14 Washington, DC 20555-2738

ULNRC-05904 September 10, 2012 Page 4 Index and send hardcopy to QA File A160.0761 Hardcopy:

Certrec Corporation 4150 International Plaza Suite 820 Fort Worth, TX 76109 (Certrec receives ALL attachments as long as they are non-safeguards and may be publicly disclosed.)

Electronic distribution for the following can be made via Tech Spec ULNRC Distribution:

A. C. Heflin F. M. Diya C. O. Reasoner III D. W. Neterer L. H. Graessle J. S. Geyer S. A. Maglio R. Holmes-Bobo NSRB Secretary T. B. Elwood Mr. Bill Muilenburg (WCNOC)

Mr. Tim Hope (Luminant Power)

Mr. Ron Barnes (APS)

Mr. Tom Baldwin (PG&E)

Mr. Mike Murray (STPNOC)

Ms. Linda Conklin (SCE)

Mr. John O'Neill (Pillsbury Winthrop Shaw Pittman LLP)

Missouri Public Service Commission Mr. Dru Buntin (DNR) to ULNRC-05904 Page 1 Responses to NRC Requests for Additional Information from Technical Specifications Branch (STSB)

1. The Containment Cooling System satisfies Criterion 3 of 10 CFR 50.36(c)(2)(ii) for inclusion in the TSs. SRs, in accordance with 10 CFR 50.36(c)(3), must be included that assure that the necessary quality of the system is maintained and that the limiting condition for operation (LCO) will be met. SR 3.6.6.3, as currently structured in the TSs, provides assurance that the design flow rate necessary to provide the heat removal capability assumed in the safety analyses will be achieved and that the LCO is met. Removing the design flow rate from SR 3.6.6.3, as proposed, will create a SR that provides no assurance that the design flow rate assumed in the safety analyses will be achieved, since neither the surveillance acceptance criteria nor the methodology for determining the acceptance criteria are included in the TSs. Please state how the proposed new SR 3.6.6.3 would meet the regulatory requirements of 10 CFR 50.36(c)(3).

Response

The proposed license amendment request merely removes the specific acceptance criterion for Technical Specification (TS) Surveillance Requirement (SR) 3.6.6.3 from the TS to a licensee document controlled under the 10 CFR 50.59 Program. The Surveillance Requirement itself is not being removed from the TS. The current SR 3.6.6.3 states, "Verify each containment cooling train cooling water flow rate is 2:: 2200 gpm." The revised SR 3.6.6.3 would state, "Verify each containment cooling train cooling water flow rate is within limits." The value of the flow limit (surveillance acceptance criterion) would be maintained in a licensee document controlled under the 10 CFR 50.59 Program.

The reason for the proposed change is to ensure that the surveillance verifies each containment cooling train has a flow rate capable of removing 141.4 x 10/\6 Btu/hr as assumed in the safety analyses of record. The assumed heat removal rate has a fixed value in the safety analysis; however, the cooling water flow rate does change (or can be adjusted) based on changing system conditions/parameters (e.g. tube plugging and tube fouling). Consequently, the minimum required cooling water flow rate may need to be changed to ensure that the cooling trains provide the required heat removal rate based on the safety analyses. For this reason, the cooling water flow rate should not be quantified in the TS.

For instance, with a nominal amount of fouling of the heat exchanger tubes in the containment coolers, there is assurance that the containment cooling train heat removal rate assumed in the accident analysis can be met with a cooling water flow rate that meets the currently specified limit (2:: 2200 gpm) in SR 3.6.6.3 since a nominal fouling factor was assumed in the analysis/calculation.

However, if actual tube fouling (or tube plugging) exceeded the amount assumed for the containment coolers, but the coolers were still able to provide the required heat removal rate by increasing the cooling water flow to the coolers (via a throttle valve adjustment), the flow limit specified in SR 3.6.6.3 could be rendered non-conservative. This suggests that the flow limit to ULNRC-05904 Page 2 should be able to be adjusted, as the intent is to ensure that the required/assumed containment cooling heat removal rate is met.

10 CFR 50.36(c)(3) states, "Surveillance requirements are requirements relating to test, calibration, or inspection to assure that the necessary quality of systems and components is maintained, that facility operation will be within safety limits, and that the limiting conditions for operation will be met." The surveillance requirements of SR 3.6.6.3 would still be performed in compliance with 10 CFR 50.36(c)(3) and per Callaway's surveillance procedures with or without the flow limit specified in SR 3.6.6.3. Specifically, visual inspection and flow verification by procedures ESP-EF -0002A1B, Essential Service Water Train Flow Verification, would continue to be performed to verify that the TS Surveillance Requirement is met and that adequate cooling water flows are maintained. Attachment 6 of ESP-EF-0002A1B, which incorporates flow and differential pressure measurements for each cooler, in addition to fouling factors estimated from visual inspection (with input from Component Cooling Water HX thermal performance test), would continue to be used to determine the heat removal capability of each of the containment coolers.

In addition, the following calculations would continue to be utilized in the determination of heat removal capability given the above measured parameters:

  • Calculation 06-097, Containment Cooler Proto-HX Model Development and Design Limiting Condition Analysis,
  • Calculation 07-016, Hydraulic Analysis of Containment Cooler Tube Plugging,
  • Calculation 07-035, Containment Cooler Thermal Performance as a Function of Essential Service Water System (ESWS) Flow and Tube Blockage, and
  • Calculation 07-044, Containment Cooler Thermal Performance as a Function of Tube-Side Differential Pressure.

Proto-HX, developed by Proto-Power Corporation, a subsidiary of Zachary Nuclear Engineering Inc., is a software package that calculates temperature and heat transfer rates in heat exchangers, chillers, and air coolers. Proto-HX is recognized as the industry standard analysis software for evaluating heat exchanger performance.

These procedures and calculations are designed to ensure that the Containment Coolers are operating within their specified design limits and assure compliance with 10 CFR 50.36 (c)(3).

2. Please describe the Callaway program for complying with the guidance of Generic Letter 89-13, "Service Water Problems Affecting Safety Related Equipment," and any changes to this program necessary to be consistent with the proposed deletion of the numerical value of the emergency service water system flow rate from the Callaway technical specifications.

Enclosure I to ULNRC-05904 Page 3

Response

The proposed license amendment request merely removes the specific acceptance criterion for Technical Specification (TS) Surveillance Requirement (SR) 3.6.6.3 from the TS to a licensee document controlled under the 10 CFR 50.59 Program. The Surveillance Requirement itself is not being removed from the TS. Because the proposed change does not remove any surveillance requirement from the TS, but merely relocates the surveillance acceptance criterion to a licensee document controlled under the 10 CFR 50.59 Program, there is no impact to Callaway Plant's program for complying with the guidance of Generic Letter 89-13.

In summary, Generic Letter 89-13 provided guidance concerning plant service water systems. At Callaway, the systems corresponding to the "service water system" as defined in the Generic Letter 89-13 include the Essential Service Water (ESW) system and the Component Cooling Water (CCW) system. The Generic Letter provided the following five recommendations:

I. For open-cycle service water systems, implement and maintain an ongoing program of surveillance and control techniques to significantly reduce the incidence of flow blockage problems as a result of biofouling. An equally effective program to preclude biofouling would also be acceptable.

2. Conduct a test program, or approved, acceptable alternative, to verify the heat transfer capability of all safety-related heat exchangers cooled by service water. The test program shall include both an initial test program and a periodic test program, the frequency of which shall be based on past test results. An example of an alternative action that would be acceptable to the NRC is frequent regular maintenance of a heat exchanger in lieu of testing for degraded performance.
3. Ensure by establishing a routine inspection and maintenance program for open-cycle service water system piping and components that corrosion, erosion, protective coating failure, silting and biofouling cannot degrade the performance of safety-related systems supplied by service water.
4. Confirm that the service water system will perform its intended function in accordance with the licensing basis of the plant. The confirmation should include a review of the ability to perform required safety functions in the event of a failure of a single active component.
5. Confirm that maintenance practices, operating and emergency procedures, and training that involve the service water system are adequate to ensure that safety-related equipment cooled by the service water system will function as intended and that operators of this equipment will perform effectively.

Callaway Plant addressed Recommendations 4 and 5 with one-time actions, while Recommendations 1, 2 and 3 are on-going actions to continually verify the capability of the components to meet design safety functions related to heat removal capability of the "service water system."

At Callaway, Procedure EDP-ZZ-01112, "Heat Exchanger Predictive Performance Manual,"

provides the guidance to ensure heat transfer capability of safety-related heat exchangers supplied to ULNRC-05904 Page 4 by the Essential Service Water (ESW) and Service Water (SW) systems. The Heat Exchanger Predictive Performance Manual ensures a common approach to the inspection ofESW and Balance-of-Plant (BOP) heat exchangers and includes guidelines that may be used to predict problems with critical heat exchangers. Implementation of this program is required to satisfy NRC Generic Letter 89-13. Specific monitoring activities regarding the containment coolers currently involve either visual inspection or thermal performance testing as required by the Generic Letter at frequencies not to exceed every 5 years.

The proposed change to TS SR 3.6.6.3 would have no effect on the activities performed per EDP-ZZ-O 1112 for ensuring the heat transfer capability of applicable heat exchangers. Whether or not a value/limit is specified in SR 3.6.6.3 for the minimum containment cooling train cooling water flow rate, the containment coolers (heat exchanger) will still be monitored in accordance with EDP-ZZ-OO 112 to ensure that a heat removal rate consistent with the assumptions of the accident analysis is maintained.

3. Please discuss any changes to plant operation or procedures necessary to comply with the guidance of Generic Letter 96-06, "Assurance of Equipment Operability and Containment Integrity during Design-Basis Accident Conditions." Discuss why the possibility of problems such as water hammer and two phase flow will not be increased by this change. Are water hammer and two phase flow part of the consideration in changing the service water flow rate?

Response

Because the proposed change does not remove any surveillance requirement from the TS, but merely relocates the surveillance acceptance criterion to a licensee document controlled under the 10 CFR 50.59 Program, Callaway Plant's response to Generic Letter 96-06 is not changed.

In summary, Generic Letter 96-06 identified three issues requiring evaluation and resolution by nuclear power plant licensees: (1) water hammer in containment air cooler systems during a Loss-of-Coolant Accident (LOCA) or Main Steamline Break (MSLB) which could result in piping loads exceeding design limits; (2) two-phase flow in containment air cooling systems during a LOCA or MSLB such that heat removal capability of the system does not meet the design bases; and (3) thermally induced over-pressurization of isolated portions of piping in containment which could jeopardize the ability of systems to perform their safety functions.

At Callaway, following a MSLB or LOCA, each train of the essential service water (ESW) system (ESWS) is automatically isolated from the service water system (SWS) by motor-operated butterfly valves. Both ESW pumps are started by the emergency diesel load sequencer. Each ESW pump supplies the containment coolers through normally open motor-operated containment isolation valves. Cooling flow splits to supply the two coolers per train and rejoins prior to exiting containment. Motor-operated butterfly valves are installed at the containment exit of each train to throttle flow and maintain system flow balance. The containment cooler effluent is then mixed to ULNRC-05904 Page 5 with flow from other ESW loads and returned through a 30-inch back pressure orifice to the Ultimate Heat Sink (UHS).

The containment air coolers are normally supplied by the non-safety-related SWS. During emergency conditions, the coolers are supplied by the safety-related ESWS. A LOCA or MSLB would cause the realignment of the ESW cross-connect valves to isolate the SWS and allow flow from the ESWS. Because Callaway has an "open system" design for both the ESWS and the SWS, cooling water drains down from the containment coolers until the ESW pumps are able to re-pressurize the system. Since this creates the potential for water hammer during the switchover from SWS to ESWS, the original system was redesigned to accommodate the water hammer associated with the rejoining water column. In addition, the effect of any potential steam generation within the containment cooler coils was evaluated. Steam generation in the coils could allow steam to enter horizontal sections of cooling water piping in containment. Water hammers could then occur due to collapsing of steam inside the piping (condensation induced water hammer).

The condensation-induced water hammer and water column closure water hammer phenomena were evaluated, and from the results of those evaluations it was determined that the analyzed containment air cooling system piping stresses remain within ASME Code limits. Therefore, the containment air cooling system is adequately designed to withstand the effects of water hammers associated with LOCA or MSLB concurrent with loss of offsite power (LOOP).

Callaway also evaluated the issue of two-phase flow in the containment air cooling system in response to Generic Letter 96-06. The concern is the potential reduction in containment cooling capacity due to reduced flow caused by the increased friction of two-phase flow. The Callaway design essentially prevents two-phase flow in the coolers and associated piping. Interruption of the ESW flow to the coolers will result in some formation of steam in the tubes, however, this steam is quickly pushed from the cooler tubes and condensed. The difference in system refill time due to the presence of steam is 0.4 seconds and not significant. Once ESW flow is restored, steam in the coolers and associated piping is condensed and temperatures at all locations in the system remain below saturation temperature. Therefore two-phase flow inhibiting full design heat removal capability of the containment coolers was determined to not be an issue.

Finally, Callaway evaluated the potential for over-pressurization of piping resulting from thermal expansion of trapped fluid in isolated portions of piping systems exposed to the containment atmosphere. After a postulated accident, the possibility was considered wherein the containment atmosphere could heat exposed piping and their contents. If the fluid were isolated and restricted from expansion, the associated piping could become over pressurized and potentially jeopardize the ability of affected systems to perform their safety functions. However, all piping systems penetrating containment were evaluated, and it was determined that the containment air coolers and associated piping are not susceptible to this problem.

Again, similar to the response given to the previous question, the proposed change to TS SR 3.6.6.3 would not impact the evaluations performed in response to Generic Letter 96-06, including to ULNRC-05904 Page 6 the assumptions made in those evaluations. Assumptions made in regard to containment cooling train cooling water flow would be unchanged by a relocation of the cooling flow limit specified in SR 3.6.6.3 to a licensee-controlled procedure/document. The cooling water flow assumed in the evaluations would continue to be required to be consistent with the cooling water flow required to ensure adequate heat transfer capability of the containment cooling trains in accordance with the assumptions of the accident analyses.

Enclosure 2 to ULNRC-05904 Page 1 Responses to NRC Requests for Additional Information from Balance-of-Plant Branch (SBPB)

1. Please describe the methodology of the safety analysis where 2200 gpm was determined to provide assurance that the safety functions of the containment cooling system will be performed and provide all the design inputs and design assumptions of that safety analysis.

Response

The current methodology in Calculation 07-044 uses PROTO-HX heat exchanger modeling software. The software is used to define containment cooler thermal performance as a function of tube-side (ESWS) header differential pressure as measured locally at each containment cooler.

The evaluation is performed at a number of different fouling conditions to represent the range of possible cooler operating conditions.

Design inputs include the following: (Ref: Calculation 07-044)

a. A flow of 2000 gpm per cooler with two coolers in a train.
b. 12 working coils in each cooler.
c. Sensitivity run flows range from 1500 gpm to 2200 gpm to simplify flow balancing requirements.
d. Tube foulin~ factors of 0.002 hr-ft2- F/Btu were used to bound the design range of 0.0005-0.0015 hr-ft -F/Btu.
e. ESW inlet temperature 92.3 F
f. Containment Cooler Fan flow rates of 69,400 cfm
g. Relative humidity of 100%
h. Containment Pressure of 65.7 psia
1. Containment Temperature of277 F J. Required heat removal rate of70.7 MBtulhr for each cooler Assumptions: (Ref: Calculations07-016 and 07-035 which feed into Calculation 07-044)
a. Air density stays constant.
b. Cooler header DP will be based on worst case tube plugging conditions.
c. Air flow is evenly distributed amongst all 12 coils.
d. Air-side fouling remains zero.
2. Please describe the methodology of the safety analysis where the "within limits" flow rate will be determined to provide assurance that the safety functions of the containment cooling system will be performed and provide all the design inputs, design assumptions of that safety analysis.

Enclosure 2 to ULNRC-05904 Page 2

Response

Proto-HX software model sensitivity runs were performed using flow ranges of 1500 gpm per cooler to 2200 gpm per cooler. The sensitivity study was used to analyze and to bound any single value that any cooler could be balanced to during the performance of procedure ESP-EF-0002A/B, "Essential Service Water Train Flow Balance." (

Reference:

Calculation 07-044 mentioned above.)

3. Please identify and justify any differences in design input, design assumptions and methodology between 1 and 2 above.

Response

Proto Power Calculation 07-016 (referenced above) focuses on Containment Cooler heat removal capability with flow restrictions simulated by having various sections of the cooler disabled due to tube plugging. Proto Power Calculation 07-035 (also referenced above) focuses on Containment Cooler thermal performance based on various ranges ofESW flow blockage. Both of these calculations utilize the same modeling methodology to determine final Containment Cooler thermal performance and feed into Calculation 07-044.

4. Explain what criteria will be used to specify a change to the flow rate is "within limits" and explain how those criteria will be obtained.

Response

U sing the methodology described above, containment cooling flow rates were chosen to bound potential flow values that may result from the Essential Service Water Train Flow Balances performed as part of the Essential Service Water Train Flow Verification procedures ESP-EF-0002A/B. However, if a tube fouling or plugging condition (or a combination thereof) were identified such that the condition was not bounded by the current calculation but such that it was clear the required containment cooling heat removal rate could still be attained, then the calculation(s) and procedure would be revised to specify an appropriate cooling water flow limit that supports the required containment cooling heat removal rate.

5. Please confirm that the procedure for determining that a flow rate value must be changed and the steps to implement the change are documented in a controlled procedure.

Response

Essential Service water Flow verifications are done using procedures ESP-EF -0002A/B. These two procedures are used to document and verify Containment Cooler flows. These procedures are controlled procedures that require program reviews of any changes or modifications prior to implementation.

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