Development of the Environmental Fatigue Evaluation ... to the difference in material and thickness...

© Copyright by DOOSAN Heavy Industries & Construction Co. 2009

All Rights Reserved.

Younghun Heo, Junghun Lee, Sungho Chung

Doosan Heavy Industries & Construction, Korea

KEPIC/ASME Joint Seminar

Sep. 4-7, 2017

Development of

the Environmental Fatigue Evaluation Technology

for PPG Charging Inlet Nozzle

in Application with RG 1.207

1

Table of Contents

I. Overview of Environmental Fatigue Evaluation

II. Charging Inlet Nozzle Introduction

III. Environmental Fatigue Evaluation

IV. Evaluation Results

V. Conclusion

2

1. Background of Environmental Fatigue Evaluation


1) Fatigue Evaluation in Air Environment

- The ASME Code provides fatigue curve for materials used in nuclear power plant design

- The fatigue curve of the ASME Code is determined by determining the optimum S-N line from

the fatigue test data obtained in the laboratory air environment and then applying

the 2 and 20 adjustment factors to the stress and cycle number.

- The fatigue curve of the ASME Code indirectly corrects the difference between the test environment and

the use environment through the adjustment factor.

2) Fatigue Evaluation in Reactor Coolant Environment

- The coolant environment fatigue test was conducted steadily to check whether the adjustment factors applied to

the ASME Code reflect the environmental impact of the reactor coolant sufficiently.

- From the fatigue test of the coolant environment, the adjustment factor was found to be insufficient,

and the need to improve the design fatigue evaluation was raised.

- The United States approved that regulatory guideline to consider the coolant environment

when evaluating the fatigue of new nuclear power plants.

3

2. Environmental Fatigue Evaluation Method


1) Fatigue Curve Evaluation Method

- The method to calculate partial usage factor directly using fatigue curve reflecting environmental impact.

2) Evaluation Method of Environmental Correction Factor

- The method to calibrate the fatigue life difference between the air environment and the coolant environment

by applying the environmental correction factor instead of using the fatigue curve based on the air environment

Cold Leg (p-5)

SG

RV

Pump

Charging Inlet Nozzle

To RV

From Pump

4

1. Location and Function


- The primary piping charge inlet nozzle is attached to the cold leg pipe located between the RCP pump and the

reactor vessel and connected to the branch piping of the 2 inch 160 SCH to provide a passage for the fluid entering

the chemical and volume control system.

5

2. Nozzle Characteristic


- Due to the difference in material and thickness of the nozzle and the safe end, large thermal stress can be

generated by thermal loading.

- There are many events with severe thermal hydraulic curve.

Sefe End

Nozzle

6

1. Regulatory Requirements and Technical Standards


1) USNRC RG 1.207

- US regulatory guidelines that require consideration of coolant environmental impacts in

equipment and piping fatigue evaluations within reactor coolant pressure boundaries.

- The environmental fatigue evaluation should be performed by applying S-N curve and

Environmental Fatigue Correction Factor(Fen) correlation equations presented in NUREG/CR-6909 and

fatigue evaluation procedure described in ASME B&PV Code Section III Subsection NB.

2) NUREG/CR-6909

- In February 2007, the USNRC published a report on the major environmental impact factors

affecting fatigue damage in the reactor coolant environment, the Fen correlation equations and detailed

derivation process, and overall environmental fatigue evaluation methods and procedures.

- Use the S-N curve and environmental correction factor(Fen) correlation equation for each material

presented in Appendix A of NUREG / CR-6909 for environmental fatigue evaluation

as specified in RG 1.207.

7

1. Regulatory Requirements and Technical Standards (Con’t)


3) ASME P&PV Code Section III

- The method for calculating the air usage factor during the environmental fatigue evaluation is

the same as the fatigue evaluation method and procedure of the existing ASME B & PV Code

Section III Subsection NB-3000 except for the S-N curve.

PRIMARY + SECONDARY STRESS

STRESS CONCENTRATION FACTOR PEAK STRESS

STRESS DIFFERENCE

ALTERNATING STRESS INTENSITIES

MULTIPLY E RATIO

ALLOWABLE NUMBER OF CYCLE

CALCULATE USAGE FACTOR U < 1 END

8

1. Regulatory Requirements and Technical Standards (Con’t)


4) Reference Technical Standards

- RG 1.207 and NUREG / CR-6909 provide the Fen correlation equations and the overall calculation procedure,

but there is no detailed method for determining the main variables of the Fen correlation equations,

so refer to the results of ASME and EPRI R & D activities for detailed methodology .

ASME Strain Rate Code Case : Detailed method for determining strain rate as a parameter of Fen correlation

equation

EPRI Report-1025823(Guidelines for Addressing Environmental Effects in Fatigue Usage Calculations) : Applying

method for Fen to dynamic load

9

2. Geometry and Cut Information of Charging Inlet Nozzle


918

840

762

761

756

754

753

743

713

672

671

706

716

752

732

712

696

690 768

846

852

868

888

908

689

686

667

557

469

582

474 402

342

258

78

24

6

12

18

1 7 13 73

253

337 397

668

1

PIPING CHARGING INLET NOZZLE (3-D)

1

CVCS CHARGING INLET NOZZLE

10

3. Finite Element Model


1) Stress calculation model by pressure : 3-D Plane Symmetric Model

2) Stress calculation model by thermal load : 2-D Axisymmetric Model

11

4. Applied Loads


1) Pressure and Thermal Load : Thermal Hydraulic Curve in Transients

T/H data examples

Proprietary Information

12

4. Applied Loads (Cont’d)


2) Mechanical load : Main and branch piping reaction force against thermal expansion,

earthquake, dynamic load

Proprietary Information

Sefe End

(S/S)

Nozzle

(C/S)

Clad

(S/S)

Sefe End

(Ni-Cr-Fe)

Nozzle

(C/S)

Clad

(Ni-Cr-Fe)

Material of Case 1 Material of Case 2

13

5. Applicable Meterial


1) Nozzle and Cold Leg Pipe : Carbon Steel

2) Safe end and Clad

- Case 1 : Stainless Steel

- Case 2 : Ni-Cr-Fe Alloy

14

2. 환경피로해석 절차 (계속)


Alternating stress intensity (Salt) calculation

(ASME Code Sec III. procedure)

Partial usage factor (Ui) calculation

(CR-6909/S-N Curve)

Environmental correction factor (Fen) calculation

(Fen : CR-6909)

(έ : Strain Rate Code Case)

Environmental fatigue usage factor(Uen)

(Uen= ∑ Ui x Fen)

NUREG/CR-6909

(a) Carbon Steel

Fen,i = [exp (0.632 - 0.101S*T*0*έ*)]

(c) Low Alloy Steel

Fen,i = [exp (0.702 - 0.101S*T*0*έ*)]

(b) Austenitic Stainless Steels (wrought and cast)

Fen,i = [exp (0.734 - T*0*έ*)]

(c) Ni-Cr-Fe Alloys

Fen,i = [exp (-T*0*έ*)]

Strain Rate Code Case, Rev.18

Includes detailed procedures to determine Strain Rate

15


1. Comparison of Safe end Environmental Fatigue Analysis Results

Result of Case 1 Result of Case 2

16


1. Comparison of Safe end Environmental Fatigue Analysis Results (Cont’d)


17


2. Comparison of Clad Environmental Fatigue Analysis Results


18


2. Comparison of Clad Environmental Fatigue Analysis Results (Cont’d)


19


3. Comparison of Environmental Fatigue Analysis Results for Major Cuts

Criteria Cut CASE 1 CASE 2

Uen

A 1.9374 0.4061

B 2.2934 0.3460

Ec 1.7326 0.5744

Fc 1.5120 0.6744

20

V. Conclusion

1. For the same design load, Ni-Cr-Fe alloys show better thermal conduction and

environmental fatigue correction factor than stainless steel.

2. For the above reasons, if stainless steel is applied to areas where high fatigue is

expected in design considering environmental impact, substitution with Ni-Cr-Fe

alloy may be considered.

As a result of the analysis of environmental fatigue by changing the safe end and clad

material of the charging inlet nozzle, the following conclusions were obtained.

21

Thank You.

[email protected]

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Development of the Environmental Fatigue Evaluation ... to the difference in material and thickness...

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