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MiskolcMiskolc , , HungaryHungary
AprilApril 20020066
Numerical Modelling Numerical Modelling of Deformation and Fracture Processes of Deformation and Fracture Processes
of NPP Equipment Elementsof NPP Equipment Elements
Моделирование процессов деформирования и Моделирование процессов деформирования и разрушения материалов и элементов оборудования АЭСразрушения материалов и элементов оборудования АЭС
Kharchenko V. Kharchenko V. Харченко В.В.Харченко В.В.
G.S.Pisarenko Institute for Problems of Strength G.S.Pisarenko Institute for Problems of Strength Институт проблем прочности им. Г.С. Писаренко НАН Институт проблем прочности им. Г.С. Писаренко НАН УкраиныУкраины
1st Hungarian-Ukrainian Joint Conference on1st Hungarian-Ukrainian Joint Conference on ««Safety-Reliability and Risk of Engineering Plants and ComponentsSafety-Reliability and Risk of Engineering Plants and Components»»
About 50% of the electric power produced in Ukraine is generated by the NPPs.
Now there are 15 units—13 VVER-1000 and 2 VVER-440—operated in Ukraine.
But, as seen from Table, half of the units have been operated for over 20 years.
So, Extension of the NPP Service Life is one of the most important strategical tasks of the nuclear industry
Operating reliability and extension of the NPP service life depend on the solution of the problems concerning the structural strength of equipment
Creation of the scientific fundamentals for determining the strength and life of NPP equipmentA great deal has been done by the Institutes of the National Academy of Sciences of Ukraine for the development of the nuclear science and technology including the following: •Development of the procedures and unique equipment for testing NPP structural materials, including those under irradiation conditions
•Development of the procedures and software packages for simulation of NPP equipment elements
•Investigation of deformation and fracture, determination of the mechanical properties of structural steels under various conditions of thermo-mechanical loading and a complex stress state
•Investigation of the stress-strain state of materials and NPP equipment elements
•Development of the strength (fracture) criteria
Now we’ll say about IPS results of numerical modeling
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 Software RELAX, SPACE, PIPE, ИМПРО, and other packages
Tests:•Pure bending of the beam•Three-point bending of the
beam with the edge crack, etc
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
Evaluation of the Validity and Accuracy of the Modeling Schemes
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
Modeling of the Behavior of Materials and Structural Elements
• Modeling of material testing
under static, cyclic and dynamic loadings
(tension, compression, impact toughness)
• Modeling of the strain-stress state kinetics in the processes of manufacture and maintenance
(cutting, pipe pressing-in, thermal treatment)
• Modeling of behavior of NPP equipment elements (reactor pressure vessel, steam generator, protective structures) under service loads
Numerical modeling of material testing. Various schemes of dynamic testing
Calculation scheme
Specimens
Specimen with concentrator R2
0 0.1 0.2 0.3 0.4 0.5 0.6 0.70
200
400
600
800
1000
1200
1400
1600
1800
Удлинение, мм
Уси
лие, кг
с
Упруго-пластическая модельУпруго-пластическая модель с GTNЭкспериментЭксперимент
Tension Testing Modelling
0 1 2 3 4 5 6 70
200
400
600
800
1000
1200
1400
Удлинение, мм
Усилие, кгс
ЭкспериментЭкспериментУпруго-пластическая модель с GTNУпруго-пластическая модель
Smooth cylindrical specimen
CalculationExperiment
Charpy Testing Modelling
Time variation of the load on the knife-edge
loading unloading
The variation of the stress state at the crack (or concentrator) tip indicated that the plastic deformation region changes its shape and the accumulation of residual plastic strains occurs after each cycle.Further investigation will deal with the analysis of damage accumulation at the crack (or concentrator) tip and assessment of the applicability of various fracture criteria under such loading conditions.
Repeated Loading Modelling
-300
-200
-100
0
100
200
300
400
500
0,596 0,597 0,598 0,599 0,6
X (m)
S (МПа)
•2
•3
•4
•1
•5
STRESS-STRAIN STATE FEATURES OF STEAM GENERATOR ELEMENT WITH THE CONCENTRATOR
UNDER REPEATED-STATIC LOADING
Stress Distribution in the region of a concentrator 1mm in depth under pressures P1 and P2: 1 – radial stresses, 2 – axial stresses, 3 – tangential stresses, 4 – equivalent stresses under loading, 5 – axial stresses under unloading.
Modeling scheme for the steam generator component and the fragment of the finite element meshing in the defect region.
- Reactor pressure vessel;
- Steam generators;
- Pipelines
Primary Circuit of WWER NPP
MATERIAL TESTING AND NUMERICAL MODELLING FOR INTEGRITY AND LIFETIME ASSESSMENT OF NPP COMPONENT
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
Temperature and Stresses in RPV
3D Model
Temperature in RPV wall Stress in RPV wall
Stress in RPV weld
Stress intensity factor versus crack-tip temperature (plastic calculation), from NUREG/CR-6651, Task T1C2
The SIF value and peculiarities of its variation in time are affected by a large number of factors:
sizes and locations of cracks; loading conditions; metal characteristics; accuracy of calculation methods and schemes;and so on.
When assessing the RPV structural integrity,
the accuracy of determination of changes in the stress intensity factor (SIF) value under thermal shock conditions also plays an important part.
Geometrical model
Finite element grid:
a) –in the vicinity of the crack;
b) – in the cross section of the crack front
Crack location area
RPV with a built-in crack
20
40
60
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
Hoop strains in the zone of the built-in longitudinal half-elliptical crack
Crack location area
RPV with a built-in crack
•1 •2
•3•4
•1
•2
•3•4
•1
•2
•3
•4
•Si, Sy, Ey in crack tip: 1 – t=0.3ms, 2 – t=0.5ms, 3 – t=0.66ms, 4 – t=0.83ms.
Crack propagation and arrest in RPV wall under PTS
Crack velocity.
3D Calculation Scheme
0,00
0,35
0,70
1,05
1,40
Время
Нап
ряже
ние
-Weld 111
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 Models for Stress Modeling of the SG Element
Evaluation of the Validity and Accuracy of the Modeling Schemes
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
•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
Simulation of the Stress-Strain State Kinetics in Manufacturing and Maintenance
Pressing-in of pipes into the steam generator collector
Local thermal treatment of the SG shell and collector assembly after maintenance
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
Residual Stresses of the SG Element after Local Thermal Treatment
0
50
100
150
200
250
300
350
400
450
0 0,5 1 1,5 2 2,5 3
Угол, рад
Напряж
ение, М
Па
1
2
3
Distribution of the residual stresses acting on the “pocket” surface on the side of the nozzle 20 mm away from its bottom (from the results of three-dimensional computations): tangential stresses (1); axial stresses Z (2); i (3)
а) - φ = π; b) - φ = 0
Equivalent Stresses
Resume:Local Stresses are High Levelin SG Elementafter Local Thermal Treatment and under Service Loads
Conclusions
In our opinion the important research directions are as follows :
•Development and harmonization of standards for the structural integrity and lifetime assessment
•Development of procedures for structural integrity and lifetime calculation (including those taking into account crack propagation and arrest)
•Improvement of strength (fracture) criteria•Development of experimental methods for determining metal
degradation and obtaining additional information•Improvement of correlation dependences between mechanical
metal characteristics obtained by various methods•Improvement of calculation methods for assessment of strain-
stress state, fracture mechanics parameters and their application to problems of structural integrity and to risk-based methods
Summary
Thank You
For Attention !
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