ML20054M498

Pressurizer Safety & Relief Line Piping & Support Evaluation

ML20054M498
Person / Time
Site:	Farley
Issue date:	07/01/1982
From:	Chang K, Ching Ng, Laura Smith WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:
Shared Package
ML20054M488	List: ML20054M487 ML20054M492 ML20054M498
References
RTR-NUREG-0737, RTR-NUREG-737, TASK-2.D.1, TASK-TM NUDOCS 8207130516
Download: ML20054M498 (22)

Text

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WESTINGHOUSE PROPRIETARY CLASS 3 ATTACHf!EllT 2 PRESSURIZER SAFETY AND RELIEF LINE PIPING AND SUPPORT EVALUATION ALABAMA POWER COMPANY J. M. FARLEY UNIT 1 AND UNIT 2 L. C. Smith C. K. Ng July 1, 1982 1'

Approved: /

K.C. Chang,Manfr Systems Structural Analysis i

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I TABLE OF CONTENTS Section Title 1.0 Introduction 2.0 Pipe Stress Criteria 2.1 Pipe Stress Calculation - Class 1 Portion 2.2 Pipe Stress Calculation - Class NNS Portion 2.3 Load Combinations 3.0 Loading 4.0 Analytical Methods 4.1 Thermal Hydraulic Modeling 4.2 Structural Modeling 5.0 Evaluation Status

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1.0 INTRODUCTION

The Pressurizer Safety and Relief Valve (PSARV) discharge piping system for pressurizer water reactors, located on the top of the pressurizer, provides overpressure protection for tne reactor coolant system. A l water seal is maintained upstream of each pressurizer safety and relief l valve to prevent a steam interface at the valve seat. This water seal J practically eliminates the possibility of valve leakage. While this j

arrangement maximizes the plant availability, the water slug, driven by high system pressure upon actuation of the valves, generates severe I hydraulic shock loads on the piping and supports.

Under NUREG 0737,Section II.D.1, " Performance Testing of BWR and PWR

(

Relief and Safety Valves", all operating plant licensees and applicants are required to conduct testing to qualify the reactor coolant system relief and safety valves under expected operating conditions for I design-basis transients and accidents. In addition to the qualification of valves, the functionability and structural integrity of the as-built discharge piping and supports must also be demonstrated on a plant specific basis.

In response to these requirements, a program for the performance testing of PWR safety and relief valves was formulated by EPRI. The primary objective of the Test Program was to provide full scale test data con-firming the functionability of the reactor coolant system power operated relief valves and safety valves for expected operating and accident l conditions. The second objective of the program was to obtain suffi-cient piping thermal hydraulic load data to permit confirmation of models which may be utilized for plant unique analysis of safety and relief valve discharge piping systems. Based on the results of the afore.nentioned EPRI Safety and Relief Valve Test Program, additional l

thermal hydraulic analyses are required to adequately define the loads

!' on the piping system due to valve actuation.

i This report is the response of the Alabama Power Company to the July 1,1982 US NRC plant-specific submittal request for piping and support evaluation and is applicable to J. M. Farley Unit 1 and Unit 2.

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2.0 PIPE STRESS CRITERIA .

2.1 PIPE STRESS CALCULATION - CLASS 1 PORTION In general, the criteria for the structural evaluation of the Class 1 components is based upon two categories of loading. These are self-limiting loads and non-self-limiting loads. A non-self-limiting load produces a primary stress while a self-limiting load produces a secon-dary stress. In order to prevent catastrophic f ailure of the system, l primary stress criteria must be satisfied, which can be accomplished by applying Equation (9) of paragraph NB-3652 of the ASME Boiler and

Pressure Vessel Code Section III, up to and including the Summer 1971 Addenda. Fatigue f ailure may occur if the maximum stress from all loadings is so concentrated at one location that continued cycling of the loads produces a crack, which may then propagate through the wall and result in leakage. For protection against fatigue failure, cyclic stresses from both self-limiting and non-self-limiting loads must be considered. The component will cycle within acceptable limits for each specified loading combination if Equation (10), subparagraph NB-3653.1 of the Code is satisfied. This requirement insures that incremental distortion will not occur. The peak stress intensity defined by Equation (11) is then used for calculating the alternating stress intensity, S alt.

The value of S alt is then used to calculate the usage f actor for the load set under consideration. The cumulative usage

l. factor is then obtained using Miner's rule by considering all other load

sets. However, if Equation (10) is not satisfied, which means some plastic deformation occurs with each application of load, the alternate analysis, " Simplified Elastic-Plastic Discontinuity Analysis", described in subparagraph NB-3653.6 of the Code must be considered. To avoid the posibility of fatigue failure, the cumulative usage f actor should not exceed 1.0.

2.2 PIPE STRESS CALCULATION - CLASS NNS P0RTION i

The piping between the valves and the pressurizer relief tank shall be analyzed to satisfy the requirements of the appropriate equations of the 0267s:10

ANSI B31.1 Code. These equations establish limits for stresses from sustained loads and occasional loads (including earthquake), thermal expansion loads, and sustained plus thermal expansion loads, respec-tively. The allowable stresses for use with the equations were determined in accordance with the requirements of the ANSI B31.1 Code.

2.3 LOAD COMBINATIONS In order to evaluate the pressurizer safety and relief valve piping, appropriate load combinations and acceptance criteria were developed.

The load combinations and acceptance criteria are identical to those reconnended by the piping subcommittee of the PWR PSARV test program and are outlined in Table 1 and 2 with a definition of load abbreviation provided in Table 3.

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. 1 TABLE 1 l LOAD COMBINATIONS AND ACCEPTANCE CRITERIA FOR PRESSURIZER SAFETY AND RELIEF VALVE PIPING AND SUPPORTS - UPSTREAM OF VALVES Plant / System Allowable Stress Combination Operating Condition Load Combination Intensity 1 Normal N 1.5 S, 2 Upset N + OBE + SOT U

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3 Emergency N + SOT E

2.25 S,  !

4, 4 Faulted N + MS/FWPB or DBPB 3.0 S, l

+ SSE + SOT p f

5 Faulted N + LOCA + SSE + SOT p 3.0 S, NOTES: (1) Plants with an FSAR may use their original design basis in conjunction with the appropriate system operating transient definitions in Table 3; or they may use the proposed criteria contained in Tables 1 to 3.

(2) See Table 3 for SOT definitions and other load abbreviations.

(3) The bounding number of valves (and discharge sequence if r setpoints are significantly different) for the applicable system operating transient defined in Table 3 should be used.

(4) Verification of functional capability is not required, but allowable loads and accelerations for the safety-relief valves must be met.

(5) Use SRSS for combining dynamic load responses.

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TABLE 2 LOAD COMBINATIONS AND ACCEPTANCE CRITERIA FOR PRESSURIZER SAFETY AND RELIEF VALVE PIPING AND SUPPORTS - SEISMICALLY DESIGNED DOWNSTREAM PORTION Plant / System Allowable Stress l Combination Operating Condition _ Load Combination Intensity 1 Normal N 1.0 S h

2 Upset N + SOT U

1.2 S h L 3 Upset N + OBE + SOT 1.8 Sh U

l 4 Emergency N + SOT E

1.8 S h l

5 Faulted N + MS/FWPB or DBPS 2.4 S h l + SSE + SOT p 6 Faulted N + LOCA + SSE + SOT p 2.4 S h

(. NOTES: (1) Plants with an FSAR may use their original design basis in l

conjunction with the appropriate system operating transient

' definitions in Table 3; or they may use the proposed criteria contained in Tables 1 to 3.

(2) This table is applicable to the seismically designed portion of downstream non-Category I piping (and supports) necessary

- to isolate the Category I portion from the non-seismically designed piping response, and to assure acceptable valve loading on the discharge nozzle.

(3) See Table 3 for SOT definitions and other load abbreviations.

(4) The bounding number of valves (and discharge sequence if setpoints are significantly different) for the applicable system operating transient defined in Table 3 should be used.

(4) Verification of functional capability is not required, but l

allowable loads and accelerations for the safety-relief

! valves must be met.

(5) Use SRSS for combining dynamic load responses.

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TABLE 3 DEFINITIONS OF LOAD ABBREVIATIONS N = Sustained loads during normal plant operation SOT = System operating transient SOTu

= Relief valve discharge transient (1)

S0TE

= Safety valve discharge transient (1), (2)

S0Tp = Max (50T U ; S0TE

); or transition flow OBE = Operating basis earthquake SSE = Safe shutdown earthquake MS/FWPB = Main steam or feedwater pipe break DBPB = Design basis pipe break LOCA = Loss-of-coolant accident 4

Sh

= Basic material allowable stress at maximum (hot) temperature Sm

= Allowable design stress intensity (1) May also include transition flow, if determined that required operating procedures could lead to this condition.

(2) Although certain nuclear steam supply systems design transients (for example, loss of load) which are classified as upset condi-tions may actuate the safety valves, the extremely low number of actual safety valve actuations in operating pressurizer water reactors justifies the emergency condition from the ASME design philosophy and a stress analysis viewpoint. However, if actuation of safety valves would occur, a limitation must be placed to shut down the plant for examination of system integrity after an appro-priate number of actuations. This number can be determined on a plant specific basis.

NOTE: Plants with an FSAR may use their original design basis in conjunction with the appropriate system operating transient definitions in Table 3; or they may use the proposed criteria contained in Tables 1 to 3.

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3.0 LOADING i

The following loading conditions are considered in the piping stress analyses:

A. Internal pressure B. Deadweight l

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! C. Normal operating thermal moment loadings D. Additional thermal moment loadings due to the different possible l

l combinations of safety or relief valve operations l

E. Loadings due to postulated seismic events

( F. Thrust loadings due to loop seal, steam and/or water discharge during safety or relief valve operations.

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4.0 ANALYTICAL METHODS The three-dimensional piping system model which includes the effect of supports, valves and equipment are represented by an ordered set of data which numerically describes the physical system. Analytical methods used to obtain a piping deflection solution consist of the transfer matrix method and stiffness matrix formulation for the static structural analysis. All piping and piping components are assumed to behave in a linear elastic manner.

The dynamic thrust analysis is performed in two distinct steps in this analysis:

A. Generation of thermal hydraulic time history loads upon actuation of the safety and relief valves, B. Dynamic time history structural analysis of the piping system to determine the deformation and load responses due to the application of (A).

4.1 THERMAL HYDRAULIC MODELING Piping load data has been generated from the tests conducted by EPRI at the Combustion Engineering Test Facility. Pertinent tests simulating u dynamic opening of the safety valves for representative upstream envir-onments were carried out. The resulting downstream piping loadings and responses were measured. Upstream environments for particular valve opening cases of importance, which :avelope the commercial scenarios, t, are:

A. Steam discharge - steam between the pressure source and the v? ice, B. Cold water discharge followed by steam - steam between the pressure i source and the loop seal - cold loop seal between the steam and the valve, t

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I C. Hot water discharge followed by steam - steam between the pressure

! source and the loop seal - hot loop seal between the steam and the j

valve.

Specific thermal hydraulic analyses for loop seal discharges have been completed and structural modeling is in progress for the Combustion ,

Engineering Test Configuration. The capacity of the computer program for calculating the fluid-induced loads on the piping downstream of the safety and relief valves has been demonstrated by comparing the analytical results with the test data. Additionally, the capability has been shown by direct comparison to solution of classical problems.

' The thermal hydraulic analysis is performed in order to obtain transient hydraulic parameters, such as pressure mass flow rite, fluid density, etc., subsequent to initiation of valve opening. The analytical model consists of a series of single pipes joined together at one or more places by two or three way junctions. Each of the single pipes has associated with it flow area, length, elevation angle, friction factor, initial pressure and initial fluid enthalpy. The thermal hydraulic l

computer program solves the conservative equations using the method of characteristics, af ter which a post-processing program computes the unbalanced transient hydraulic forces along each straight run of pipe upstream and downstreem of the valve. These time dependent forces are then stored on magnetic tape, to be used as input to the time-history

" thrust" analysis.

f 4.2 STRUCTURAL MODELING L

The dynamic thrust analysis is performed on a time-history basis. A mathematical model consisting of node points and lumped masses connected by piping elements is developed. Supports are represented by linear and/or non-linear springs which define the restraint characteristics of supports. The time history hydraulic forces obtained from the thermal

! hydraulic analyses are then applied to the lumped mass points of the piping system. The dynamic solution is obtained by using a modified predictor-correction integration technique and normal mode theory.

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l The dynamic seismic analysis is performed using the response spectra i

method with the model established for the dynamic thrust analysis. The results generated from the seismic analysis are combined in accordance with Table 1 through Table 3 of Section 2.0.

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"O S.0 EVALUATION STATUS The J. M. Farley Unit 1 and Unit 2 safety and relief valve discharge .

piping system has received a very detailed thermal hydraulic and structural dynamic evaluation to insure the operability and structural integrity of the system. This structural evaluation, including the thermal hydraulic analysis, was based on the criteria and methods that were current prior to the availability of the data from the EPRI Test Program. The thermal hydraulic forcing functions were generated assuming simultaneous opening of either the safety valves or the -Siief valves, since they represent the worst applicable loading conditions for the piping and supports for this specific layout. These forcing func-tions were then used as input to the structural evaluation in w'hich the primary and secondary stresses were determined. The methods used and the loadings considered are consistent with Section 2.0 and Section 3.0 of this report, respectively. Results of this extensive analysis and evaluation have demonstrated that the PSARV piping meets all the applic-able design limits for the various loading cases. In addition, the acceptability of the val <e nozzles, equipment nozzles, and pressurizer shell was assured for the applied loads.

The regeneration of time history thermal hydraulic loads subsequent to the EPRI testing, is complete. Figures 1 to 4 illustrate the structural model for the J. M. Farley Unit 1 pressurizer safety and relief valve piping layout. Figures 5 to 8 show the model for Unit 2. The load combinations and acceptance criteria utilized are discussed in Tables 1 to 3.

Our evaluation of the new loadings and the old forcing functions subse-quent to relief valve discharge indicates that the relief line piping can be qualified upon completion of the structural analysis with revised

, stress calculations. For discharge of the safety valves, the revised forcing functions in the 6-inch piping imediately upstream of the i comon header are higher than previously determined. Based on engi-

{ neering judgement all piping and components between the pressurizer and 0267s:10

I relief tank, excluding the piping and branch connections near the common header, can be qualified with revised and/or refined stress calcula-tions. Additional revised and refined stress calculations may be required and/or minor system modifications such as the addition of thermal insulation in the loop seal region or the addition of supports near the branch connections. The structural analysis will quantify this.

Based on analytical work and tests to date, all acoustic pressures in the upstream piping calculated or observed prior to and during safety valve loop seal. discharge are below the maximum permissable pressure.

An evaluation of this inlet piping phenomenum was conducted and the results are documented in a report entitled " Review of Pressurizer Safety Valve Performance as Observed in the EPRI Safety and Relief Valve Test Program", WCAP-10105, dated June 1982. The piping between the pressurizer nozzle and the inlet of the safety valves is 6-inch schedule 160. The calculated maximum upstream pressure for this size of piping is below the maximum permissable pressure.

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