W3F1-2019-0054, Response to U.S. Nuclear Regulatory Commission Request for Additional Information Regarding Relief Number WF3-RR-19-2, Proposed Alternative to Code Case N-666-1

Response to U.S. Nuclear Regulatory Commission Request for Additional Information Regarding Relief Number WF3-RR-19-2, Proposed Alternative to Code Case N-666-1

ML19203A365
Person / Time
Site:	Waterford
Issue date:	07/22/2019
From:	Gaston R Entergy Operations
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
W3F1-2019-0054
Download: ML19203A365 (31)

Text

CALCULATION PACKAGE File No.:

1900769.30 2 Project No.:

1 900769 Quality Program Type: Nuclear Commercial PROJECT NAME:

Waterford Code Case N

-513 Evaluation of Leaking Class 2 Line CONTRACT NO.:

10585075 CLIENT: Entergy Nuclear PLANT: Waterford Steam Electric Station, Unit 3 CALCULATION TITLE:

Evaluation of Weld Overlay Repair of Socket Weld Region Document Revision Affected Pages Revision Description Project Manager Approval Signature & Date Preparer(s) & Checker(s)

Signatures & Date 0 1 - 8 Initial Issue Eric Houston 7/18/19 Prepare r: Andrew Collins 7/18/19 Checker: .Stephen Parker 7/18/19 File No.:

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Table of Contents 1.0 OBJECTIVE ..............................................................................................................

3 2.0 METHODOLOGY

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3 2.1 Criteria for Hoop Stress

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3 2.2 Criteria for Axial Stress

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4 3.0 DESIGN INPUTS

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5 4.0 ASSUMPTIONS

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6 5.0 CALCULATIONS

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6 6.0 RESULTS OF ANALYSIS

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7

7.0 CONCLUSION

S

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7

8.0 REFERENCES

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8

List of Tables

Table 1: Applied Moment Loads

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6 Table 2: Minimum Thickness Results

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7

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1.0 OBJECTIVE A leaking flaw was recently discovered at the Waterford Steam Electric Station, Unit 3 (Waterford) in the Chemical and Volume Control (CVC) system. The Class 2 leaking pipe is upstream of valve CVCMVAAA186 (CVC-186). The objective of this calculation is to determine the minimum required wall thickness for the repaired section of piping with a weld overlay repair.

2.0METHODOLOGY The structural suitability of a weld overlay repair is accomplished by verifying that the thickness of the weld buildup meets the required minimum thickness for the operational condition.

The methodology of this calculation uses the equations for hoop stress and axial stress along with allowable stresses from Section III, 1971 Edition with Addenda through Winter 1972 Code of Construction [

1].

The hoop stress limit is defined by the Code of Construction [

1 , NC-3641.1 Equation 3] and calculates the minimum required wall thickness due to internal pressure, t

m. The axial stress limits are defined as a series of stress limits based on pressure and piping loads:

Equation 8, Longitudinal Stresses due to Sustained Loads [

1 , NC-3652.1] Equation 9, Longitudinal Stresses due to Occasional Loads [

1 , NC-3652.2] Equation 10, Longitudinal Thermal Expansion Stresses [

1 , NC-3652.3(a)]

Equation 11, Longitudinal Thermal Expansion and Sustained Loads Stress [

1 , NC-3652.3(b)]

The smallest wall thickness that satisfies both the hoop and axial stress limits is defined as the minimum

wall thickness, tmin. Note that only Equation 10 or Equation 11 is required to be met, not both [

1 , NC-3652.3]. Therefore, only Equation 10 is evaluated herein.

For this evaluation, the tmin value will be conservatively calculated using the dimensions of the weld buildup over the socket welded connections and ignoring the structural benefit of the unflawed existing base pipe material.

2.1Criteria for Hoop Stress The minimum thickness required based on hoop stress, Equation 3 [1 , NC-3641.1], assures against gross structural failure due to primary membrane pressure loading. Equation 3 is written as a design thickness calculation based on the maximum allowable stress. The minimum thickness required for design pressure, t m, is defined by Equation 3 as: P = Internal design pressure, psi D o = Outside pipe diameter, in S = Maximum allowable stress at design temperature, psi E = Longitudinal weld joint efficiency factor (1.0 for seamless pipe) y = Pressure coefficient

= 0.4 [1 , NB-3641.1] A = Additional thickness, in

The additional thickness value, A, is taken as zero.

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2.2Criteria for Axial Stress Equations 8, 9, and 10

[1 , NC-3652] are intended to show that the calculated axial stresses in the piping component, due to pressure and piping loads, meet the Code of Construction stress limits. An iterated uniform wall thickness is used to calculate the piping stresses in these equations, which are compared to an allowable stress for design purposes.

The thickness that results in a stress equal to th e allowable stress is taken as the minimum thickness for that condition.

The Longitudinal Stresses Due to Sustained Loads , S SL, must satisfy the following requirement [

1 , NC-3652.1 , Equation 8

]: P = Internal design pressure, psi D o = Outside pipe diameter, in t n = Nominal wall thickness, in i = Stress intensification factor (Note: 0.75i may not be less than 1.0)

(see [1 , NC-3673.2(b)])

M A = Resultant moment due to sustained loads, in

-lb (see [1, NC-3654]) Z = Section modulus, in 3 (see [1, NC-3654]) S h = Allowable stress at design temperature (equivalent to S for this evaluation), psi

The Longitudinal Stresses Due to Occasional Loads , S OL, must satisfy the following requiremen t 1 , NC-3652.2, Equation 9]: Pmax = Peak pressure (taken as operating pressure), psi D o = Outside pipe diameter, in t n = Nominal wall thickness, in i = Stress intensification factor (Note: 0.75i may not be less than 1.0)

(see [1 , NC-3673.2(b)])

M A = Resultant moment due to sustained loads, in

-lb (see [1, NC-3654]) M R = Resultant moment due to occasional loads, in

-lb (see [1, NC-3652.4]) Z = Section modulus, in 3 (see [1, NC-3654]) S h = Allowable stress at design temperature (equivalent to S for this evaluation), psi

The Thermal Expansion Stress es , S E, must satisfy the following requirement [

1 , NC-3652.3(a), Equation 10]: i = Stress intensification factor M C = Range of resultant moment due to thermal expansion, in

-lb (see [1, NC-3652.2]) Z = Section modulus, in 3 (see [1, NC-3654]) S A = Allowable stress range for expansion stresses, psi

The allowable stress range, S A, is defined as S A=f (1.25S c+0.25S h) [1 , NC-3611.1(b)(3)], where f is defined as the stress range reduction factor for full temperature thermal cycles. S c is the basic material allowable File No.:

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stress at minimum (cold) temperature. For this evaluation, the reduction factor is assumed to be equal to 1.0 since the number of thermal expansion cycles is expected to be below 7,000 (see Section 4.0 , Assumption No.

2). Therefore, S A is equal to 1.5S h as S c and S h are equivalent for this evaluation.

3.0DESIGN INPUTS The following design inputs were provided by Entergy personnel to be used in the analysis:

1.Pipe Material =

SA-376, TP-304 [2] 2.Pipe Nominal Size = 1-inch Schedule 80 [

2] 3.Maximum Operating Temperature = 120

°F [3] 4.Design Temperature = 250

°F [3] 5.Maximum Operating Pressure = 85 psig [

3] 6.System Code of Construction = ASME Section III, 1971 Edition with Addenda through Winter 1972

[3] 7.Code Allowable Stress, interpolated at 120°F, = 18.6 ksi [

1, Table I-7.2] 8.Material Yield Strength = 30 ksi [1, Table I-7.2] 9.Material Ultimate Strength = 75 ksi [

1, Table I-7.2] The pipe outside diameter (1.315 inches) and nominal thickness (0.179 inch) are obtained from readily available industry information based on the pipe size and schedule.

The OD of the socket welded elbow and coupling are assumed to be those of 3000 lb fittings from

[5], which have a maximum fitting OD of 1.8125 inches. Piping loads are taken from the design basis stress report [

4]. The location of interest is at Node 403, but the bounding load s used in the evaluation are taken from Node 402, which is the branch of the socket welded connection to the 4

-inch run piping. The methodology requires moment loads as input, which are obtained from the Reference [

4] nodal outputs for each load case. Three load cases are utilized: thermal expansion (TH), sustained (DW), and operating basis earthquake (OBE). OBE is the only seismic loading evaluated in the stress report and is, therefore, the only seismic loading evaluated herein.

The component moments at Node 402 are taken from each load case in the Reference [

4] output. The square root sum of squares (SRSS) moments are calculated for each load.

Constrained thermal expansion stress in a simple system is roughly linear over small ranges of changes in temperature (T), with slight non

-linearities introduced due to temperature depended material properties. Complex system s, such as piping systems, are not strictly linear due to geometric effects and the potential influence of mixed metals. The design basis stress report only evaluates thermal expansion loading for the design temperature of 250°F. If the reference temperature for thermal expansion stress is taken as 70°F (see Assumption 1), the evaluated T is 180°F. The maximum operating temperature is only 120°F, which represents a T of 50°F. Rather than use the thermal expansion loading for the full 180

°F T, the thermal expansion loads are scaled by a factor of 0.5. This represents an evaluated T of approximately 90°F , which is still considered conservative when the actual T is nearly half that amount.

To conservatively account for the stress intensification due to the weld overlay repair, a stress intensification factor (SIF) of 1.3 is used in the analysis. This SIF is consistent with Figure NC

-3672.9(a)-1 from the Code of Construction for socket welded connections [1]. Application of this SIF to the analysis is conservative as the stress intensification created by the original socket welded joint will be reduced with the addition of the repair weld metal. The geometric configuration of the weld overlay will result in a design that File No.:

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is similar to a butt welded connection, which have an SIF of 1.0 per Figure NC

-3672.9(a)-1 from the Code of Construction [1]. The loads for the analysis, derived from Reference [

4], are shown in Table 1. Table 1: Applied Moment Loads From Stress Report (ft

-lbs) Resultant T Scale Factor Applied Evaluated Loads X Y Z (in-lbs) (in-lbs) (in-lbs) DW 19 1 8 248 --- 248 OBE 21 13 16 353 --- 353 TH 53 170 42 2195 1098 1098 4.0ASSUMPTIONS The following assumptions are used in the evaluation.

1.It is assumed that 70°F is used as the reference temperature (i.e., the zero-stress state) in the design basis thermal expansion stress analysis [

4]. The stress report then evaluates the change in temperature from 70°F to 250°F. Use of 70°F is typical for such an evaluation. Use of a different reference temperature would result in a change in the resulting stress (higher stress for a lower reference temperature, lower stress for a higher reference temperature). However, use of a significantly different reference temperature does not have a meaningful impact on the results of the analysis, and there is no basis for evaluating from a different reference temperature. 2.It is assumed that the full thermal cycles for the piping system total less than 7,000 cycles. Given the operation of the system, this assumption is appropriate for determining the stress range reduction factor (f) for this analysis. 3.The evaluation assumes no structural benefits from the existing base pipe material. This is reasonable and conservative for analyzing the acceptance of the weld overlay buildup.

5.0CALCULATIONS For longitudinal stresses, the thickness , t n, is iterated for Equations 8, 9, and 10 until the calculated stress is equal to the allowable stress, as defined for each equation.

This calculation provides a resulting m inimum thickness necessary that meets the Code of Construction requirements based on the dimensions of the added weld overlay material. T he section modulus of the weld overlay cross section is also iterated as function of the evaluated thickness.

The minimum thickness necessary for hoop stresses is calculated directly from Equation

3.

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6.0RESULTS OF ANALYSIS The resulting tmin for each loading condition is shown in Table 2. Table 2: Minimum Thickness Results Loading Condition Minimum Required Thickness (inch) Equation 3

- Hoop Stress 0.004 Equation 8 - Sustained Load

- Deadweight 0.00 8 Equation 9

- Occasional Load - OBE 0.01 3 Equation 10

- Thermal Expansion 0.0 2 1 The Code of Construction minimum required wall thickness for these conditions is taken as the maximum of the resulting thicknesses tabulated in Table 2. Therefore, the minimum required wall thickness for the weld overlay design is 0.021 inch and is limited by thermal expansion.

7.0CONCLUSION

S This evaluation calculates the minimum required thicknesses of the Waterford Steam Electric Station, Unit 3 CVC system Class 2 piping region upstream of valve CVCMVAAA186 (CVC-1 86) in support of a Code Case N

-666-1 weld overlay repair. The Code of Construction minimum required wall thickness for the weld overlay repair is 0.021-inch. This minimum thickness is based on the dimensions of the socket welded fittings and the resulting weld overlay and conservatively ignores the structural benefit of the existing unflawed base pipe material.

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8.0REFERENCES

1.ASME Boiler and Pressure Vessel Code,Section III, 1971 Edition with Addenda through Winter 1972. 2.Waterford Drawing No. 4305-3913, SI File No. 1900769.205.

3.Email from T. House (Entergy) to E. Houston (SI), Subject "RE: SI Contact Information," July 2, 2019, SI File No. 1900769.208.

4.Waterford Stress Report No. SA

-2869-2, Revision 2, "Stress Analy sis of CH-Piping per SMP

-1743 'A s-Buil t'," SI File No. 1900769.201.

5.Ladish General Catalog No. 55, Forged and Seamless Welding Pipe Fittings,1954, SI File No.

1900769.209.