ML20245J875

Suppl 2 to Evaluation of Thermal Stratification for Comanche Peak Unit 1 RHR Lines

ML20245J875
Person / Time
Site:	Comanche Peak
Issue date:	08/31/1989
From:	Matty T, Roarty D, Strauch P WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:
Shared Package
ML19292J428	List: ML20245J848 ML20245J859 ML20245J875
References
WCAP-12259-S02, WCAP-12259-S2, NUDOCS 8908180211
Download: ML20245J875 (36)

Text

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WESTINGHOUSE CLASS 3 WCAP-12259 Supplement 2 EVAL'JATION OF THERMAL STRATIFICATION FOR THE COMANCHE PEAK UNIT 1 RESIDUAL HEAT REMOVAL LINES D. H. Roarty P. L. Strauch T. J. Matty August 1989

(

Reviewed by: [) ^J W. H. Bamford l Approved by: #

5. 5. J(lusamy, hanager Structural Materials Engineering WESTINGHOUSE ELECTRIC CORPORATION Nuclear and Advanced Technology Division , !

P.O. Box 2728 ,

Pittsburgh, Pennsylvania 15230-2728

)

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"8T 8908180211 890009 E

{DR ADOCK05000445ef PNU g

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'l TABLE OF CONTENTS .I I

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i Section Title -- .Page I 1.0 LACKGROUND 1-1.

2.0 EVALUATION OF. ADDITIONAL STRATIFICATION PROFILE 2-1 2.1 Development of Temperature Profile 2-1 )

2.2 Piping System' Stress Analysis 1 2.3 ASME Section'III Fatigue Usage Factor Evaluation 2-3 a

3.0 MONITORING PROGRAM 3-1 4.0 VALVE HARDWARE - ISSUES 4-1 5.0 ,

SUMMARY

AND CONCLUSIONS 5-1 l

6.0 REFERENCES

6-1 APPENDIX A - NRC PRESENTATION VIEWGRAPHS A-1 89*

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i LIST OF FIGURES I Figure Title Page 1

2-l' RHR Stratification Profiles -

2-2 3-1 Monitoring Locations: RHR Hot Leg Loop 1.(13A) .3-2 3-2. . Monitoring Locations: RHR Hot Leg Loop 4 (138) .3-3' 1- Westinghouse EMD Drawing 8372D46 4 i 4-2 Westinghouse EMD Drawing 8373D47 4  ;

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LIST OF TABLES' Table' Tit 1e Page-2-1 1.oad Comparison Summary -

2 2-2 Summary of Fatigue'. Effects for Stratification Loading ' 2-6 at Controlling Location 3-1 Description of Monitoring Locatic'ns - Purpose 3-4 3-2 RHR Monitoring Program Acceptance Criteria 3-5 l

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SECTION 1.0 ,

BACKGROUND Report WCAP-12259 (ref. 2) addressed the issue of potential thermal stratification occurring in the Comanche Peak Unit 1 RHR suction lines. This phenomenon was discussed in NRC Bulletin 88-08, Supplement 3l " Thermal Stresses in Piping Connected to Reactor Coolant Systems" (ref.1), .which was issued following the discovery of a crack in an RHR suction line in June of 1988 at a foreign plant.

This supplemental report to WCAP-12259 provides additional information on the following subjects:

1) The potential effects of thermal stratification occurring between the reactor coolant loop and first isolation valve.  !

2) The details of the monitoring program for the RHR piping.

3) Information on the valve hardware which affects this issue.

This supplement is provided in response to NRC questions on WCAP-12259. The j content of this supplement was presented to the Staff on July 27, 1989 (Appendix A).

This supplement, in conjunction with WCAP-12259, provides'the basis for the i structural integrity and leak-before-break of the subject RHR piping, when i considering the potential effects of thermal stratification and cycling {

resulting from valve leakage. The assumptions used regarding leakage flow and  !

thermal and stress analyses for this supplement are the same as those used in the original report [2].  ;

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SECTION 2.0 EVALUA! ION OF ADDITIONAL STRATIFICATION PROFILE S:ction 1 of WCAP-12259 (reference 2) discussed the stratification profile assumed to exist in the RHR piping if leakage of RCS flow past the isolation valve were to occur. Based on experimental results it was as'sumed that

[

Ja,c.e To provide additional assurance of the structural integrity of all potentially susceptible RHR piping, it has b:en assumed that stratification could also occur in the horizontal piping b2 tween the loop hot leg and the isolation valve.

The loads and stresses resulting from this additional profile were evaluated for piping integrity (including fatigue) and leak-before-break.

2.1 Development of Temperature Profile The temperature profile for stratification beginning in the unisolable horizontal piping (piping between the reactor coolant loop and the first l isolation valve) is similar to the reference 2 profile, except that the heat transfer in the unisolable piping differs from the piping downstream of the valve, due to thicker insulation. Also, turbulent hot water at hot leg i temperature is assumed to occur only on the vertical piping. Figure 2-1 illustrates the axial temperature of the stratified flow and stagnant fluid (top and bottom of pipe) and the difference between the two (top-to-bottom AT). This figure also illustrates the original profile used in WCAP-12258.

2.2 Pipino System Stress Analysis The thermal stratification piping structural analysis was performed using the ANSYS computer program to calculate pipe, support and nozzle loads. Piping loads were used as input to the fatigue and leak-before-break evaluations.

Input to the ANSYS structural analysis was the temperature profile described in section 2.1 considering leakage and non-leakage cases. This profile has axial and tofi-to-bottom of pipe temperature variations. The ANSYS piping model was the same used in reference 2.

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i T - ~ ~ Stratification Starts at Elbow Leakage b Stratification Starts at Valve T 'F w T aI is the temperature difference 1

/ Leakage 600 -lh' '

between the fluid at the top and bottom of the inside of the pipe.

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Distance from elbow l-l 5 10 15 20 (feet) j Elbow Valve l

Figure 2-1. RHR Stratification Profiles mm..oma io 2-2

As discussed in reference 2, the RHR suction line selected for analyses was .

loop 4 [

3a,c.e The ansk sis for loop 4 is therefore conservatively applicable to loop 1.

The loads.from this analysis were considered in the evaluati6n of fatigue, leak-before-break, and nozzle evaluations. The load change, resulting from this case, was fairly small as illustrated in table 2-1. This change had no impact on leak-before-break or nozzle evaluations and therefore the summaries provided in reference 2 (table 4-7) remain valid.

The impact on the fatigue evaluation is more significant due to the increased local stresses and is discussed in more detail in section 2.3 of this report.

2.3 ASME Section III Fatigue Usage Factor Evaluation Fatigue life was calculated for the RHR line using the methods outlined in ASME Code Section III (ref. 3). The fatigue allowables were obtained using the high cycle fatigue curves for austenitic stainless steel (figures I-9.2.1 and I-9.2.2). Stresses calculated in this evaluation were intensified using the factors of table NB-3681(a)-1.

For this evaluation, a controlling location was selected [

Ja,c.e based on the point of maximum stress and ASME Code '

intensification factors. The following fatigue calculations were performed at this location. As an additional conservatism, the maximum stratification AT was assumed to occur at the controlling location.

Fatigue life of a component-is controlled by two parameters - number of cycles ,

and stress range. For this evaluation, the stress range is the difference in stress [

3a c.e Table 2.2 summarizes maximum stratification AT, number of cycles and frsquency of occurrence for the controlling location. For the maximum stratificati~on case [ 3a,c.e. the expected number of cycles is ma""c2" 2-3

[-

Ja,c.e The usage factor for this case is negligible [ la.c.e 1 If thermal cycling occurs during plant operation, the allowable fluid temperature' fluctuation.is a function of the frequency of. occurrence as shown in table 2.2.

In order to ensure that.. fatigue structural integrity is maintained,'a conservative criteria will be established for this type of loading in the monitoring program (section 3.0).

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TABLE 2-1 LOAD COMPARISON

SUMMARY

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Resultant Moment (in-kips) ,

1 Location Node Case 1 Case 2  !

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RCL Nozzle 9424 1122 1247 Valve Inlet 2180 979 1011 Containment 2680 587 523 P;netration i

Case 1: [ Ja,c.e Case 2: [ Ja,c,e j

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1 TABLE 2-2  !

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SUMMARY

.OF FATIGUE' EFFECTS FOR' STRATIFICATION LOADING AT CONTROLLING LOCATION

' Stratification (1) . Allowable Frequency of AT Fluid (*F) Cycles (2) Occurrence (3) ,

(cycles / hour) l

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1) Range of stratification AT fluid temperature from top to bottom of pipe

2) Corresponding allowable number of cycles based on'ASME fatigue curve and' usage factor of 1.0.

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3) Frequency of occurrence for allowable cycles for 40 years of continuous operation.

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SECTION 3.0 -

l MONITORING PROGRAM A monitoring program will be implemented at Comanche Peak Unit 1. The purpose j of this program is as follows: _I i (1) Check for the existence of thermal stratification and cycling.

(2) If cycling or stratification occur, provide data'for determination

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of the root cause.

(3) Provide a check for analytical assumptions.

Data will be obtained from resistance temperature detectors (RTD's) mounted on the outside of the RHR piping at selected locations, as shown in figures 3-1 '

and 3 ' (these locations will be finalized at the time of installation). Data from the plant process computer will also be used. Monitoring will begin at initial heatup (mode 4) and continue through to power operation. Monitoring I criteria are included here, based on fatigue results. l Seven locations on the RHR lines were chosen for temperature monitoring. The l purpose of each monitoring location is shown in table 3-1. Table 3-2 provides conservative acceptance criteria for the seven locations, based on the fatigue analysis results. Temperatures which exceed these criteria must be evaluated to determine the effect on fatigue usage.

The temperatures used in the acceptance criteria are less than the values J considered for the fluid temperatures in the fatigue evaluation. This was done to account for the difference between the fluid temperatures and outside wall measured temperatures, which could be significantly less depending upon l the frequency of occurrence. Therefore, a temperature of [ Ja,c e is I selected for the case of relatively low frequency of occurrence, and a temperature of ( ]"'C is selected for the case of high frequency of occurrence.

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Figure 3-2 l Monitoring Locations: RHR Hot Leg Loop 4 (13B) 3865s-073 tS910 =

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TABLE 3-1 DESCRIPTION OF MONITORING LOCATIONS - PURPOSE j RTD ID (13A, B) PURPOSE j

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.-TABLE 3-2

. RHR MONITORING PROGRAM ACCEPTANCE CRITERIA

'RTD ID (13A, B) CRITERIA PURPOSE -

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l 1)' aT is the top-to-bottom temperature difference

2) DT is ,the change in AT as' a function of time 1

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l SECTION 4.0 VALVE HARDWARE ISSUES 1

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The RHR suction lines at Comanche Peak each contain two motor operated gate j valves in series which provide isolation from the Reactor Coolant System when the RHR is not in operation. These valves are 12 inch,1525 lb. Class 1 valves, with a flexible wedge, a double set of packing, and a leakoff, built to drawings 8373D47 and 8372046. Cyclic valve leakage can potentially result from a packing leak caused by flexing of the wedge due to thermal expansion.

Proposed valve modifications to eliminato potential thermc1 cycling include drilling a hole in the wedge, or jamming the valve closed.

By drilling a small hole through the wedge, a continuous flow path into the -

bonnet cavity is established, thereby eliminating the possibility of cycling due to wedge flexing, since the wedge is always hot. This continuous flow may cause an increase in leakage through the packing, resulting in packing erosion which may require shutdown of the plant to replace the packing. In addition, I the potential for increased flow across the valve is greater, thereby increasing the chance for increased leakage and radioactivity across the  ;

second isolation valve. ,

lnereasing the required closing thrust (jamming) to provide a higher seat load may not reduce seat leakcge since seat damage may already exist which causes the leak in the first place.

1 Therefore, the proposed valve fixes may result in other problems, and not eliminate thermal cycling.

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1 SECTION 5.0

SUMMARY

AND CONCLUSIONS i

A detailed evaluation has been completed for the Comanche Peak Unit 1 Residual Heat Removal suction line, assuming that stratification can exist in the j horizontal unisolable piping upstream of the isolation valve. Load changes from reference 2 (stratification initiating at the isolation valve)'are j

j. .relatively.small. Stability and leak rate results of reference 2 are unaffected, since the loads of this evaluation were enveloped in the reference q 2 ovaluation. Fatigue results are acceptable, provided the AT and cycle d limits of table 2-1 are not exceeded.

Monitoring locations and a conservative acceptance criteria are provided in l

.t s2ction 3, based on the fatigue evaluation, to ensure piping structural integrity for the life of the unit. Should these conservative criteria be exceeded, a more detailed evaluation will be required.

I At present, the proposed fixes on the RHR isolation valve to eliminate potential thermal cycling may result in other problems. Until a final long-term solution is implemented, monitoring of the RMR piping is required. I l

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- 'I 3SH3-M330010 -

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l, SECTION 6.0-REFERENCES 2.- NRC Bulletin 88-08, Supplement 3, " Thermal Stresses in Piping. Connected to Reactor Coolant Systems," 4/11/89.

i 2. WCAP-12259, " Evaluation of Thermal Stratification for the Comanche Peak )

. Unit 1 Residual-Heat Removal Lines," W. H. Bamford, April 1989.

3. 1986 ASME Boiler and Pressure Vessel Code,. Nuclear Power Plant Components,Section III, Division 1, Appendices, and Section XI,-

Division 1. 3 l

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I APPENDIX A i i

NR: PRESENTATION VIEWGRAPHS h

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P88Se-08024410 ,

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COMANCHE PEAK UNIT 1 ADDITIONAL INFORMATION ON RHR HOT LEG THERMAL STRATIFICATION AND CYCLING DUE TO POTENTIAL VALVE LEAKAGE s

PRESENTATION TO -

US NRC JULY 27 1989 ROCKVILLE, MARYLAND D. H. ROARTY

, STRUCTURAL MATERIALS ENGINEER WESTINGHOUSE ELECTRIC CORP.

4 s.

.' A-2

l PURPOSE OF MEETING:

DISCUSS NRC QUESTIONS ON RESOLUTION OF LEAK-BEFORE-BREAK ISSUES ON CPSES UNIT 1 RHR PIPING - REF. WCAP 12258.

-EVALUATION OF ADDITIONAL STRATIFICATION CASE

-DETAILS OF MONITORING PROGRAM

-INDUSTRY ACTIVITY (EPRI SCATS)

-VALVE HARDWARE ISSUES

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REVIEW 0F ADDITIONAL STRATIFICATION CASE

-ADDITIONAL STRATIFICATION CASE EVALUATED ASSUMING POTENTIAL EXISTS FOR STRATIFICATION IN HORIZONTAL PIPING BEFORE VALVE

-CONSERVATIVE METHOD OF BOUNDING POSSIBLE STRATIFICATION SCENARIOS

_ CONCLUSIONS l

-LOAD CHANGE RELATIVELY SMALL - MOST AFFECTS ARE LOCAL FATIGUE l-STABILITY /LEAKRATENOTAFFECTED-LOADSENVELOPED

-N0ZZLE LOADS ACCEPTABLE

-FATIGUE RESULTS ACCEPTABLE 1

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A-4

FATIGUE

SUMMARY

MAXIMUM STR TIFICATION TEMPERATURE ASSUMED AT POINT OF MAXIMUM BENDING STRESSES AND FATIGUE FACTORS e,:,e

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FATIGUE CONCLUSIONS NO IMPACT ON FATIGUE USAGE EXPECTED MONITORING GUIDELINE ESTABLISHED TO CHECK ACCEPTANCE CRITERIA 1

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RHR PIPING MONITORING PROGRAM PURPOSE IS TO CHECK FOR EXISTENCE OF STRATIFICATION AND \

CYCLING, DETF"MINE ROOT CAUSE, AND PROVIDE CHECK FOR ANALYTICAL ASSUMPTIONS GENERAL DESCRIPTION:

DATA OBTAINED FROM RTD'S MOUNTED ON OUTSIDE OF PIPE AND PLANT DATA DATA TO BE OBTAINED FROM INITIAL HEATUP(MODE 4)

THROUGH TO POWER OPERATION DATA TO BE OBTAINED AT HIGH FREQENCY(2 MIN.) DURING CRITICAL TIMES 1

l DETAILED ACCEPTANCE CRITERIA DEVELOPED BASED ON l ANALYTICAL ASSUMPTIONS d*

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4 DESCRIPTION OF MONITORING LOCATIONS - PURPOSE BrCit W

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SHR MONITORING PROGRAM ACCEPTANCE CRITERIA ,,c,.

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RELATED INDUSTRY GENERIC PROGRAMS EPRI TASK GROUP ESTABLISHED:

SCATS : STRIPING, CYCLING,AND THERMAL STRATIFICATION SCATS ADVISORY COMMITTEE INCLUDES ALL USA NSSS VENDORS AND OWNER'S GROUPS PROGRAM DESCRIPTION DEVELOPED IN JULY 1989 PROGRAM OBJECTIVES INCLUDE:

DEVELOP INFORMATION BASE TO PREDICT AND EVALUATE SCATS OCCURRENCES DEVELOP SCREENING METHODOLOGY FOR IDENTIFYING LOCATIONS WHERE SCATS IS OF CONCERN PHASE 1 PROGRAM FUNDED TO EVALUATE EXISTING DATA EPRI REPORT WILL PROVIDE INFO ON SHORT AND LONG TERM FIXES AS KNOWN TODAY A-10

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IMPACT OF ADDITIONAL STRATIFICATION CASE ON N0ZZLE LOADS RCL HOT LEG N0ZZLc THERMAL CASE FORCE (KIPS) MOMENTS (IN-KIPS)

NORMAL THERMAL 11.1 1068.

STRAT. AT 15.0 1247.

VALVE OUTLET STRAT. AT 13.9 1122.

BOTTOM ELBOW CONTAINMENT PENETRATION THERMAL CASE FORCE (KIPS) MOMENTS (IN-KIPS)

NORMAL THERMAL 12.8 389.

I STRAT. AT 16.9^ -

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STRAT. AT 14.3 587.

BOTTOM ELBOW A-12

a r Cre 140NITORING LOCATIONS: RHRHOTLEGLOOP1(13A)

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1 M0lf1TORING LOCATIONS : RHR HOT LEG LOOP 4 (138)

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