ML12241A291

UHS Meeting Slides August 29, 2012

ML12241A291
Person / Time
Site:	Callaway
Issue date:	08/29/2012
From:	Union Electric Co, Ameren Missouri
To:	Lyon C Plant Licensing Branch IV
Lyon C
References
TAC ME9234
Download: ML12241A291 (17)

Text

Overview Ameren Missouri Callaway Plant UHS Cooling Tower and Retention Pond Technical Specification Modifications August 2010 2012

AMEREN MISSOURI CALLAWAY PLANT License Amendment Request 12-0015: UHS Retention Pond LICENSEE EVENT REPORT, 2010-004-00 (ULNRC-05701), Unanalyzed Single Failure Component for Ultimate Heat Sink/Essential Service Water Follow up response:

The single failure of the UHS Cooling Tower Inlet Bypass Valve was not considered. (Identified by NRC Resident Inspector)

Single Failure analysis was not revised after Unit 2 was canceled.

Failure of the bypass valve would result in hot water flowing directly into the UHS Pond bypassing the UHS Cooling Tower Fans.

UHS Pond temperatures under worst case conditions could exceed the maximum analyzed temperature during a Design Basis Accident (LBLOCA) with a single active failure of the UHS Cooling Tower bypass valve.

2

AMEREN MISSOURI CALLAWAY PLANT ESW/UHS System Simplified Diagram 3

AMEREN MISSOURI CALLAWAY PLANT UHS Retention Pond 4

AMEREN MISSOURI CALLAWAY PLANT License Amendment Request 12-0015: UHS Retention Pond LAR will Revise SR 3.7.9.1, the maximum initial UHS Retention Pond discuss the average temperature will be reduced from 90 F to 89 F.

following:

Revise SR 3.7.9.2, the UHS Retention Pond Level will be increased from a minimum initial level of 13 - 4 to 16 of depth above pond bottom.

Addition of new SR 3.7.9.4 to verify fan auto-start on an actual or simulated actuation signal.

GOTHIC Thermal Hydraulic Model of ESW/UHS system New operator actions used in the Emergency Operating Procedures to operate the UHS system.

Remote manual bypass valve position control from the Main Control Room 5

AMEREN MISSOURI CALLAWAY PLANT License Amendment Request 12-0015: UHS Retention Pond

Background:

The UHS Cooling Tower rejected less heat from the ESW system to the atmosphere with one train of ESW operation during the worst case conditions than intended by the original design specification.

Union Electric determined to run both trains of ESW during a Design Basis Accident and perform analysis of the Cooling Tower as needed.

The analysis of record was compartmentalized. Static output data from one calculation becomes the input for the next calculation.

The FSAR credits operator actions to maintain UHS pond temperature within allowable limits during hot weather operation.

Callaway Plant needed an integrated approach when calculating the ESW heat loads to determine the dynamic thermal interactions in Containment and the UHS Retention Pond.

6

AMEREN MISSOURI CALLAWAY PLANT License Amendment Request 12-0015: UHS Retention Pond Thermal Performance Westinghouse created a GOTHIC 7.2(b)

Analysis of UHS Cooling Tower and model of the entire heat path from Retention Pond: Containment to the UHS Pond.

The model includes Containment, RHR, CCW, EDG, SFP, and the Auxiliary Building Room Cooler heat loads involved in a LBLOCA event.

The UHS Cooling Tower and Pond model includes worst-case weather and temperature conditions.

7

AMEREN MISSOURI CALLAWAY PLANT License Amendment Request 12-0015: UHS Retention Pond Issues Identified Initial Technical Specification pond through new temperature acceptance criteria challenged Thermal Design Bases Accident pond temperature Performance analyzed limit (92.3 F) margin.

Analysis:

Initial minimum pond level (TS) challenged ESW inventory for the 30-day mission time.

Control of the Cooling Tower operation was appropriately controlled in the short term but could be improved for long-term operation.

8

AMEREN MISSOURI CALLAWAY PLANT License Amendment Request 12-0015: UHS Retention Pond Two worst case scenarios Minimum Heat Transfer: A hot Summer were analyzed day with very high humidity conditions.

in the new This challenges UHS Pond temperature by Thermal minimizing the evaporative cooling rate but Performance preserves pond inventory.

Analysis -

Over a 30-day Mission Time:

Maximum Evaporation: A hot Summer day with very low humidity conditions. This maximizes forced convection cooling in the UHS Cooling Tower keeping UHS Pond temperatures low but challenges UHS Pond inventory through evaporative losses.

9

AMEREN MISSOURI CALLAWAY PLANT License Amendment Request 12-0015: UHS Retention Pond New Thermal Performance Controlling the UHS Cooling Tower off of the Analysis temperature sensor that is upstream of the tower, Impact on cycles fan speed too frequently and is not suitable UHS Cooling for long-term inventory management.

Tower Control Loop:

Controlling the UHS Cooling Tower off of bulk pond temperature is unacceptable for limiting the initial heat load transferred into the pond at the onset of the accident.

10

AMEREN MISSOURI CALLAWAY PLANT License Amendment Request 12-0015: UHS Retention Pond Required changes The maximum initial UHS Retention Pond average temperature as a result of the will be reduced from 90 F to 89 F.

New Thermal Performance Analysis: UHS Retention Pond Level will be increased from a minimum initial level of 13 - 4 to 16 of depth above pond bottom.

A manual hand switch in the Main Control Room (one per train) will swap automatic UHS system controls from the Cooling Tower inlet temperatures in the short term to bulk pond temperature for long term cooling.

Operator actions are used in the Emergency Operating Procedures to properly operate the UHS system.

11

AMEREN MISSOURI CALLAWAY PLANT License Amendment Request 12-0015: UHS Retention Pond Additional adjustments UHS Cooling Tower Fan Speed and bypass valve set-to Callaway Plant points were lowered, ESW supply temperature control implemented under loops were added, and additional bypass valve manual 10CFR50.59 for proper operation switches (providing a false high temperature UHS Cooling Tower and input that closes the bypass valves) were installed.

Retention Pond operation:

UHS Cooling Tower fan speed indication, additional valve position indications (from the new switches above), and fan trouble alarms were added to the Main Control Room.

Normal UHS Retention Pond operating level limits were modified.

Revising the Single Failure response described in the FSAR.

Clarifying the analyzed maximum UHS Retention Pond temperature in the FSAR during a LBLOCA.

12

License Amendment Request 12-0015: UHS Retention Pond THERMAL PERFORMANCE ANALYZED RESULTS :

Maximum UHS Retention Time to Pond Peak Final UHS Retention Pond Level Analysis Scenarios Pond Temperature (°F) Temperature after 30 days (ft)

Maximum Case 1 91.74 2.57 hr 3.05 Evaporation LBLOCA with Single Active Cooling Tower Bypass Valve Failure Minimum Heat Case 2 92.00 5.83 hr 8.50 Transfer Maximum Case 3 89.23 6.8 min 2.81 Evaporation LBLOCA without Single Active Tower Bypass Valve Failure Minimum Heat Case 4 89.23 6.8 min 6.80 Transfer 13

AMEREN MISSOURI CALLAWAY PLANT License Amendment Request 12-0015: UHS Retention Pond UHS UHS Cooling Tower fan speed set-points were Cooling revised.

Tower fan setpoints: Operation of the UHS Cooling Tower is Previous Fan Setpoints: automated.

High Fan Speed 114 F Low Fan Speed 104 F Valve close 91 F The Cooling Tower controls are swapped over to bulk pond temperature to protect the Cooling Current Tower Inlet Control Loop Setpoints: Tower fans and retention pond inventory during High Fan Speed 105 F the 30 day mission time.

Low Fan Speed 95 F Valve close 84 F A balanced approach has been achieved where Current Bulk Pond Control Loop Setpoints:

the UHS Cooling Tower can perform its safety High Fan Speed 89.5 F function.

Low Fan Speed 84.5 F Valve close 79 F 14

AMEREN MISSOURI CALLAWAY PLANT License Amendment Request 12-0015: UHS Retention Pond Operator With the Single Failure of the UHS Cooling Tower Timed Bypass Valve operators will verify that the valve is Actions: closed or secure the impacted train of ESW within 70 minutes from the start of the LBLOCA event.

Original Credited Without a cooling tower single failure operators will Operator Action:

Operators would secure one train of ESW within 7 days.

secure one train of ESW at 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> At 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> post LBLOCA Operators will switch UHS system automatic controls from Cooling Tower inlet temperature (ESW return) to bulk Retention Pond temperature (ESW supply).

Operators will address a single electrical failure of a Tower inlet or Pump discharge temperature sensor loop within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

15

AMEREN MISSOURI CALLAWAY PLANT License Amendment Request 12-0015: UHS Retention Pond Summary The maximum initial UHS Retention Pond average temperature (TS of Limit) will be reduced from 90 F to 89 F.

Changes Minimum initial UHS Retention Pond Level (TS Limit) will be increased from 13 - 4 to 16 of depth above pond bottom.

New SR 3.7.9.4 to be added to TS for verifying fan auto-start on an actual or simulated actuation signal.

GOTHIC Thermal Hydraulic Model of ESW/UHS system to be described in the License Amendment.

A manual hand switch in the Main Control Room (one per train) will swap automatic UHS system controls from the Cooling Tower inlet temperatures in the short term to bulk pond temperature for long term cooling. (Already implemented under 10CFR50.59.)

Operator actions are used in the Emergency Operating Procedures to properly operate the UHS system.

16

AMEREN MISSOURI CALLAWAY PLANT License Amendment Request 12-0015: UHS Retention Pond Questions?

17