ML20054L493

Pressurizer & Safety Relief Line Piping & Support Evaluation & Action Plan, Interim Rept

ML20054L493
Person / Time
Site:	Wolf Creek, Callaway, 05000000
Issue date:	06/15/1982
From:	STANDARDIZED NUCLEAR UNIT POWER PLANT SYSTEM
To:
Shared Package
ML20054L487	List: ML20054L486 ML20054L493
References
RTR-NUREG-0737, RTR-NUREG-737, TASK-2.D.1, TASK-TM 0241S:10, 241S:10, NUDOCS 8207080173
Download: ML20054L493 (12)

Text

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PRESSURIZER AND SAFETY RELIEF LINE I

PIPING AND SUPPORT EVALUATION .:

AND ACT10t1 PLAfi t .

INTERIM REPORT SNUPPS UTILITIES June 15,1982 l

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TABLE OF CONTENTS Section Title 1.0 Introduction

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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 Action Plan I

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1.0 INTRODUCTION

The Pressurizer Safety and Relief Valve (PSARV) discharge piping system for pressurized water reactors, located on the top of the pressurizer, provides overpressure protection for the reactor coolant system. A water seal is maintained upstream of each pressurizer safety.'end relief yalve to prevent a steam interface at the valve seat. This water seal

- practically eliminates the possibility of valve leakage. While this arrangement maximizes the plant availability, the water slug, driven by high system pressure upon actuation of the valves, generates 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 design-basis transients and accidents. In addition to the qualification of valves, the functionability and structural'i'ntegrity 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 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 iaforementioned EPRI Safety and Relief Valve Test Program, additional (thermal hydraulic analy.s es are required to adequately define the loads on the piping system due to valve actuation. -

This report is the response of the 514UPPS Utilities to the July 1,1982 connitment to the US NRC plant-specific submittal request for piping and support evaluation and is applicable to Callaway Unit 1 and the Wolf Creek Unit.

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2.0 PIPE STRESS CRliERIA 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-

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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. 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. Fatigue failure may occur if the maximum stress from all loadings is so concentrated at one loc-ation that continued cycling of the loads produces a crack, which may uien propayale 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) of the Code is then used for calculating the alternating stress intensity, S alt.

The value of S is then used to determine the usage factor for the load set under consideration. The cumulative usage factor is obtained using Miner's rule by considering all other load sets. However, if Equation i(10) is not satisfied, which means some plastic deformation occurs with i each application of load, the alternate analysis, " Simplified klastic-Plastic Discontinuity Analysis", described in subparagraph NB-3653.6 of the Code must be considered. To avoid the possibility of fatigue fail-ure, the cumulative usage factor shou'1d not exceed 1.0.

2.2 PIPE STRESS CALCULATION - CLASS HNS PORTION The piping between the valves and the pressurizer relief tank shall be analyzed to satisfy the requirements of Equation (11), (12) and either (13) or (14) of the appropriate ANSI B31.1 Code. These equations

, establish limits for stresses from sustained loads and occasional loads

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(including earthquakQ, thermal expansion loads, and sustained plus thermal expansion loads, respectively. The allowable stresses for use with Equation (11), (12), and (13) or (14) were determined in accordance with the requirements of Section 102.3.1C 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 recommended by the piping subconnittee 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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_ TABLE 2 .' '

LOAD COMBlNATIONS AND ACCEPTANCE CRITERIA FOR PRESSURIZER SAFETY AND RELIEF VALVE PIPING AND SUPPORTS - SEISMICAll.Y DESIGNED DOWNSTREAM PORTION ,

Plant / System Service Streps Allowable Stress Combination. ' 'Uperating Condition Load Combination -

Limit Intensity 1 Normal N A 1.0 S H 2 Upset N + S0TU B 1.2 S h 3 Upset N + 00E + S0TU C 1.8 S h 4 Emergency N + S0T C 1.8 S h E

6 Faulted N + MS/FWPB or DDPB D 2.4 S h ,

+ SSE + SOT p 6 Faulted N + LOCA + SSE + 50T p D 2.4 S h NOTES:

(1) Plants with an FSAR may use their original design, basis in conjunction with the appropriate system operating transient defini'tions in Table 3, or they may use the proposed criteria contained in Tables 1-3.

(2) This table is applicable to the seismically designed portion of downstream non-l Category I piping (and supports) necessary to isolate the Category I portion from the non-seismically designed piping response, and to assure acceptable valve lo,ajngonthedischargenozzle.

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

i (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 l

be used.

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

(6) Use SRSS for combining dynamic load responses.

TABLE 1 LOAD COMBINATIONS AND ACCEPTANCE CRITERIA FOR PRESSURIZER SAFETY AND REllEF VALVE PIPING AND SyPPORTS - CLASS 1 PORTION -

Plant / System Service Stress Allowable Stress Combination Operating Condition Load Combination -

Limit Intensity 1 Normal N A 1.5Sm 2 Upset N + OBE + S0T B Min (1.8 h ,1.5Sy ]

U 3 Emergency N + SOT C Min (2.25Sm .1.8S)

E 4 Faulted N + MS/FWPB or DBPB D 3.0 Sm

+ SSE + SOT F

5 Faulted N + LOCA + SSE + S0T p D 3.0 Sm NOTES:

(lflants 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 1-3.

(2)See Table 3 for 50T definitions and other load abbreviations.

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

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

(5)Use SRSS for combining dynamic load responses.

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

A. Internal pressure  :

B. Deadweight C. Normal operating thermal moment loadings D. Additional thermal moment loadings due to the different possible combinations of safety or relief valve operations E. Loadings due to postulated seismic events C. Thr>:t leadings 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. Dyn e.it time history structural analysis of the piping system to determine the deformation and load resporises 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 -

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 envelope the commercial scenarios, are:

. A. Steam discharge - steam between the pressure source and the valve, B. Cold water discharge followed by steam - steam between the pressure source and the loop seal - cold loop seal between the steam and the valve, 0241s:10

C. Hot water discharge followed by steam - steam between the pressure source and the loop ' seal - hot loop seal between the steam and the valve.

Specific thermal hydraulic analyses for loop seal discharges,have been

. completed and structural modeling is in progress for the ComSustien

.-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 rate, 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 associatedwithitflowarea, length,elevatioi, angle,frictionfactor, initial pressure and initial fluid enthalpy. The thermal hydraulic ~

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 dovmstream of the valve. These time dependent forces are-then stored on magnetic tape, to be used as input to the time-hist'ory '_ ; 'T ,

" thrust" analysis.

4.2 STRUCTURAL MODELING The dynamic thrust analysis is performed on a time-history basis. A mathematical model consisting of node points and lumped masses connected

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i.by piping elements is developed. Supports are represented by linear '

' and/cr non-linear springs which define the restraint characteristics of g supports. The time history hydraulic forces obtained from the thermal hydraulic analyses are t'm applied to the lumped mass points of the piping system. The dynamic selution is obtained by using a modified predictor-correction integraticn technique and normal mode theory.

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5.0 ACTIOff PLAN A detailed dynamic analysis and code evaluation was performed prior to the availability of all test data resulting from the EPRI tests. All pertinent prior results will be used in a re-evaluation of the piping and support , system including the computer models and all previous s,

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-deadweight, ther.Ta1 and seismic analyses. ,

A.- The thermal hydraulic analysis will be performed 'as noted in Section 4.0.

B. One dynamic - time history structural analysis will be performed for each set of transient thermal hydraulic loads developed in (A) to obtain stresses on piping components and loads on all supports and

_. ' quipment nozzles.

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C. The results deadweight, thermal and seismic analyses pre-viously peri..ined will be combined, as de'f'ined in Section 2.0, with

^the thermal hydreulic results developed in (B) to obtain pipe stresses throug50ut the piping system from the pressurizer to the pressurizer relidf tank. In addition to the pipe stress evaluation, equipment nozzhs, vUve nozzle loads and accelerations are eval-uated for operability pnd structural integrity limits.

D. If,.the evaluation".in (B) and (C) indicates all pertinent stress intensities are within the allowable limits, the support loads will

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be tabulated. Inde. pendent evaluation will be performed.

E. In the event of system overstresses resulting from either '(C) or (D), system modifications baieRon analytical results an'd engi-'

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,- neering' judgement, which potgntially would resolve all overstress or

- overload problems, yill be prop) sed.

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The dynamic seismic analysis s 'is), performed using the t espcase spectra i method with the model established for the dynamic thrust rnalysis. The ,

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results generated from the seismic analysis are combined '.n accordance i

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