KievKiev, , UkraineUkraine

19-21 September19-21 September 20020077

Stress State Simulation Stress State Simulation for Reactor and Steam Generator Pressure Vesselsfor Reactor and Steam Generator Pressure Vessels

Kharchenko V. Kharchenko V.

G.S.Pisarenko Institute for Problems of Strength G.S.Pisarenko Institute for Problems of Strength

22nd Hungarian-Ukrainian Joint Conference onnd Hungarian-Ukrainian Joint Conference on ««Safety-Reliability and Risk of Engineering Plants and ComponentsSafety-Reliability and Risk of Engineering Plants and Components»»

- Reactor pressure vessel;

- Steam generators;

- Pipelines

Primary Circuit of WWER NPP

INTEGRITY AND LIFETIME ASSESSMENT OF NPP COMPONENTS

Stress intensity factor versus crack-tip temperature (plastic calculation) for RPV under PTS, from NUREG/CR-6651, Task

T1C2

The stress and SIF values and peculiarities of its variation in space and time are affected by a large number of factors:

loading conditions; sizes and locations of cracks; metal characteristics; accuracy methods and schemes for calculations;and so on.

When assessing the RPV or SG structural integrity,

the accuracy of determination of changes in the stress state and stress intensity factor (SIF) values under thermo-mechanical loading also plays an important part.

Not only materials characteristics are big scatter, stress state and FM parameters often have big differences too

Development of the methods and software for the stress-strain state calculations

for complex three-dimensional structuresMixed schemes of the finite-element method (MFEM)for the thermoelasticity and thermoplasticity

Original 2D and 3D Software RELAX, SPACE, PIPE, and other packages

Various Tests:•Pure bending of the beam•Three-point bending of the

beam with the edge crack, etc

Comparisons with commercial software (ANSYS and so on), analytical and exp. results

n

Examples of the Test Tasks Solution

Error in the SIF determination

Error in the stress determination Pure bending of the beam

Three-point bending of the beam with the edge crack

Our MFEM

Accuracy Evaluation of the Software

3D Stress Calculation

0,00

0,35

0,70

1,05

1,40

Время

Нап

ряже

ние

-узел соединения “горячего” коллектора и патрубка ПГ

Crack placeExperimental Data

on-line

Integrity and Lifetime Assessment

Structural Integrity and Lifetime of Steam Generator Elements

Elements with damage:

-Heat-change tubes

- Collectors

Key problems analysis experimental data stress calculation

3-D calculation models

Evaluation of the Validity and Accuracy of the Schemes for Modeling

Different FE Meshes

•Stresses σZ on the outer surface of the welded joint in the region of strain gage mounting:•1 – numerical calculation (P1/P2 = 16/6 MPa, M = 2.279 MHm);•2 – data of full-scale strain measurements

Accuracy of Different Software and Meshes

Comparison of Calculation

and Measurements

Comparison of calculations results

150

200

250

300

350

400

0 30 60 90 120 150 180 210 240 270 300 330 360

θград

σМПа

Distribution of the stresses acting on the “pocket” surface on the side of the nozzle 20 mm away from its bottom under hydrotest

•- EDO Gidropress, software ANSYS�- our results, software SPACE

•Распределение по окружности патрубка ПГ напряжений z на стенке кармана на высоте 20 мм от дна.

•Напряжения 1-3 на стенке кармана в области галтельного перехода: 1 – 16/6 МПа + 2,279 МНм, угол 4,10 рад.; 2 - 25/11 МПа + 1,082 МНм, угол 4,32 рад.; 3 – 18/8 МПа + 0,977 МНм, угол 4,32 рад.; 4 -16/6 МПа + 0,827 МНм, угол 4,32 рад.

Local Stress State of Steam Generator Element Ours 3D Schemes

Different2D

Schemes

Stress state under different loading

•Распределение по окружности патрубка ПГ напряжений z на стенке кармана на высоте 20 мм от дна.

•Напряжения 1-3 на стенке кармана в области галтельного перехода: 1 – 16/6 МПа + 2,279 МНм, угол 4,10 рад.; 2 - 25/11 МПа + 1,082 МНм, угол 4,32 рад.; 3 – 18/8 МПа + 0,977 МНм, угол 4,32 рад.; 4 -16/6 МПа + 0,827 МНм, угол 4,32 рад.

Influence of structural design on stresss state

Распределение по окружности патрубка ПГ напряжений z в стенке «кармана» на высоте 20 мм от его дна, вызванное совместным действием теплоносителя и изгибающего момента при НУЭ (а) и ГИ на плотность (б): - «малая» серия; - «большая» серия

•Рис. 1. Схемы подсоединения к ПГ «горячей» ветки ГЦТ в случае блоков «малой» (а) и «большой» (б) серий (вид сверху и сбоку): 1 – ПГ; 2 – труба «горячей» ветки ГЦТ; 3 – КР, 4 – опорный бурт; 5 – патрубок «холодной» ветки; А – место разрушения

•а •б

Modelling of stress-strain state of a Welded Joint of Hot Collector to Nozzle of SG PGV-1000

during Local Heat Treatment after Repair

Temperature

distribution

Schematic of the SG Element and mounting of heating elements: 1 - steam generator shell with heat insulation; 2 – nozzle; 3 – “pocket”; 4 – heat insulation; 5- welded joint; 6 – heating elements; 7 –collector; 8 – heat insulation plugs

0

50

100

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250 270 290 310 330 350 370

z, ммН

апр

яж

ени

я,

МП

а

Sf, малая серия Sz, малая серия Si, малая серияSf, большая серия Sz, большая серия Si, большая серия

Residual stresses (φ = π)

Residual Stresses of the SG Element after Local Thermal Treatment

а) - φ = π; b) - φ = 0

Equivalent Stresses

Resume:Local Stresses are High Levelin SG Elementafter Local Thermal Treatment and under Service Loads

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100

150

200

250

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400

0 1 2 3 4 5 6Угловая координата, рад

Нап

ря

жен

ия

, М

Па

Sf, малая серия Sz, малая серия Si, малая серияSf, большая серия Sz, большая серия Si, большая серия

Distribution of the residual stresses acting on the “pocket” surface on the side of the nozzle 20 mm away from its bottom

VTT INDUSTRIAL SY STEMS

TEMPERATURE (°C)

FRA

CTU

RE

ME

CH

AN

ICA

LP

AR

AM

ETE

R

Loadingparameter KJ

Safety margin

Fracturetoughness KJC

Transition temperatureshift due to irradiation

KJ < KJC

Safety requirements

Conditions of in-service

thermomechanical loading,

specifically in emergency events – thermal shock

STRENGTH AND LIFE CALCULATIONof reactor pressure vessels of NPPs

Strength of RPVs with cracks- limit state criteria;- postulation of cracks- calculation of SIF KJ

- fracture toughness KJС

Stress state, temperature fields, thermal hydraulics,

Neutron fluence in pressure vessel wall Ф(x, y, z)

Residual stresses

Mechanical propertiesof base metal, welds, cladding

and their in-service degradation

Defects (actual and hypothetical)

Key issues

Stress State in RPV under PTS

3D FE Model

We use original 2D and 3D Software RELAX, SPACE and schemes with and without built-in cracks

We analysed accuracy of stress and FM parameters ( SIF, COD) determination for linear and non-linear cases

Input data for 3D accidents cases

as function of time and space:

- coolant temperature in the downcomer

- heat transfer coefficient

- primary circuit pressure

SIF Calculations

To calculate the SIF, we considered two basic options :– engineering methods, whereby use is made of

analytic formulae or tabulated collections of stress intensity values for given defect and vessel geometries;

– cracked body finite element analyses, in which the crack is directly modelled in the mesh and subjected to the appropriate loadings

RPV with a built-in crack

WWER 1000 RPV FEM model with surface or sub cladding crack (a=11 or 19 mm, a/c=1/3 or 2/3) in weld 4

Crack location area

Temperature and Stress State Comparison of Temperature in RPV wall

(EDO Gidropress, Marc and IPS, SPACE)

Comparison of Stresses in RPV wall for Different

FE Meshes

3D Distribution of Temperature at t=500 s

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100

150

200

250

300

0 20 40 60 80 100 120 140 160 180 200Линейный размер, мм

Тем

пр

атур

а, С

ОКБ ГИДРОПРЕСС; время 1000 с ИПП; время 1000 сОКБ ГИДРОПРЕСС, время 1500 с ИПП; время 1500 с

2,00E+02

2,50E+02

3,00E+02

3,50E+02

4,00E+02

4,50E+02

5,00E+02

0 5 10 15 20 25 30 35 40Линейный размер, мм

Нап

ря

жен

ие,

МП

а

ИПП, сетка со сгущением (11 узлов в ОМ)ИПП, густая сетка со сгущением (21 узел в ОМ)ИПП, редкая сетка (7 узлов в ОМ) со сгущением (ГП)ИПП, регулярная густая сетка (21 узел в ОМ)

Stress Distributions

with and wthout residual stress

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40

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80

100

120

0 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08

Crack front length, m

К1,

МP

а*m

^0

,5

600 s

1000 s

2000 s

3000 s

4000 s

Variation in the stress intensity factor KI along the longitudinal half-elliptical crack front under PTS a/c = 2/3, a/t = 1/10

SIF comparisons by different procedures (WPF and EVI)

SIF Distribution along Crack

Comparison of SIF calculations( EDO Gidropress, Marc and IPS, SPACE)

Small Primary Leak (D36 mm). Weld 4. Circumferential cracks,

a=11 and 19 mm, а/с=2/3 .

0,0

20,0

40,0

60,0

80,0

100,0

0 40 80 120 160 200 240 280 320

Температура, ОС

КИ

Н,

МП

а м

1/2

ИПП, а=11 мм, без ОН, петля 3 ИПП, а=19 мм, без ОН, петля 3a=11mm a=19mm

0

20

40

60

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100

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0 40 80 120 160 200 240 280 320

Температура, ОС

КИ

Н, М

Па

м1

/2a=11 мм; ОКБ ГИДРОПРЕССa=19 мм; ОКБ ГИДРОПРЕССa=11 мм; ИППa=19 мм; ИПП

[KI]3=35+53e0,0217(T-Tка)

, Tка= 79,4 O

C

Intermediate Primary Leak (Break of SG Collector Head). Weld 4.

Circumferential cracks,

a=11 and 19 mm, а/с=2/3 .

Crack Open Displacement

Elastic caseElasto-plastic caseElasto-plastic case with residual stresses

Conclusions• Methods and software have been improved for the calculation of the stress state of

complex spatial structures with cracks, which is based on the mixed schemes of the finite element method;

• Various numerical and engineering procedures for determining the stress intensity

factors for a reactor pressure vessel have been compared

• Comparison of the results of the stress state calculation for RPV and SG elements obtained by the authors and at the Design Bureau “GIDROPRESS” revealed a good correspondence and confirmed the applicability of the developed computational schemes, calculation procedures, and software;

• The development of 3D models for the SG welded joint and their application for

calculations made it possible to establish a nonmonotonic stress distribution along the circumference of the welded joint with two maxima. The maximum (comparable to the yield stress) levels of tensile stresses are reached in the local region at the fillet for various regimes of post-repair heat treatment and operation conditions. The level of the maximum stress is influenced appreciably by the bending moment induced by thermal expansion of the Main Circulation Pipeline

Thank YouFor Attention !