Introducing advanced ISI
Transcript of Introducing advanced ISI
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Introducing advanced ISI requirements at
Paks NPP for supporting the LTO
P. Trampus1, S. Rátkai2 1Trampus Consulting & Engineering, Hungary
2MVM Paks Nuclear Power Plant, Hungary
3rd Int. Conf.
Nuclear Power Plant Life Management 14 – 18 May 2012, Salt Lake City, USA
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Outline
• Paks Nuclear Power Plant
• Operational life extension project
• ASME BPVC adoption
• Regulatory framework
• Advanced ISI requirements
– General aspects
– Periodic NDE program
– Acceptance standards
– Pressure tests
• Economic benefit
• Summary
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Paks NPP, Hungary • Hungary’s sole NPP
• 4 Russian design VVER-440s model 213
• Design life of the units: 30 years
• Expiration of design life: 2012 to 2017
• LTO: 20 more years
• Currently:
• license renewal of Unit 1 in progress
• other units under preparation for LTO
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Overall LTO Strategy (1)
• Maintaining business interest of owner / operator
• Completing engineering work needed to
demonstrate safe LTO
• Performing work required by licensing procedure
Engineering and operational practice should integrate
• up-to-date knowledge on ageing phenomena
• vigilance through ageing management and condition monitoring
• ability to recognize unexpected
• application of best practice
• learning from experience
• consideration of VVER-440 features
• graded approach concerning SSC safety relevance
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Overall LTO Strategy (2)
• All SSCs have to be covered by a specific plant
program (AM, maintenance, scheduled
replacement,…)
• Safety classified SSCs: programs should comply
with regulations
• Not safety classified SSCs: programs depend on
importance for power production
• All ageing processes should be considered
• All plant activities should be taken into
consideration (synergy of routine activities and
LTO specific ones)
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KI < KIc or
Pt < 5∙10-6/y
Change in material
properties (e.g.
embrittlement)
Structural
integrity
assessment
Crack
propagation
(e.g. fatigue,
corrosion)
Decrease
in safety
margin
Loading,
environment
Material properties Flaws
Role of ISI
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Goals for ASME BPVC Section XI Adoption
• To facilitate the implementation of
–ISI and IST,
–repair and replacement,
–strength and fracture mechanics analyses
•with state-of-the-art methods, and give the possibility
for their direct comparison with current methods and
requirements SAFETY GOAL
• To serve for the plant life extension
– technically (to make it possible the extension of current
4-year ISI cycle (Class 1 components) up to an 8-year
one COST-EFFECTIVENESS
–„politically” (to support international acceptance of life
extension)
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Regulatory Environment
• Current ISI program differs from BPVC Section XI one – based on Russian normative documents (PK-1514; PNAE G-7-008
and 010)
– narrower in its scope
• Major elements: – periodic NDE
– in-service examination (structural examination) equivalent to VT-3
– system pressure test
• No single ISI document like Section XI, instead: – individual documents for various systems (Technical Inspection
Plans)
– NDE framework programs
– acceptance criteria
– NDE procedures (no regulatory license needed)
• Component classification do not show remarkable difference from BPVC Section III
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Concept of Introducing Advanced ISI Requirements
• Keeping proven practice as much as possible
• Technical Inspection Plans replaced by ISI Programs
– keeping basic structure (proved in practice)
– integrating concept and requirements of Section XI
– more emphasis on ageing management
• In-service examination
– remains but supplemented by relevant examinations
• ISI interval:
– Currently 4 years for Class 1 components & piping and
Class 2 components; 8 years for secondary circuit
components & piping
– Future: 8 years (instead of 10 as of Section XI)
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Periodic NDE
• Appropriate framework programs supplemented by
– IWB-2500 B-M-1 examinations (valve bodies)
– IWC-2500 C-C (welded attachments) and C-G
examinations (valve & pump casing welds)
• In-service examination supplemented by
– IWD-2500 D-A examinations (attachments of welded
components and pipes)
• NDE procedures (not bound by regulatory license)
upgraded to comply with BPVC Section V
• Inspection qualification (instead of performance
demonstration, Appendix VIII)
– requirement for current operating license
– European approach (ENIQ)
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Subject NDE
Equipment
NDE
Procedure
NDE
Personnel
Qualifications completed
SG Primary Collector (mechanized UT) + +
SG Heat Exchanger Tube (mechanized ET) + + + *
RPV Welds, Cladding, Nozzle Inner Radius (simplified
mechanized UT from ID) + +
RPV Main Loop Nozzle dissimilar weld (simplified
mechanized UT from ID) + +
RPV Cladding (simplified mechanized ET from ID) + +
Main Loop Circumferential Weld (mechanized UT) + +
Main Loop Longitudinal Weld (mechanized UT) + +
MCP Stud (MT) + +
Small Diameter Tube (PT) + +
Pressurizer Nozzle Dissimilar Weld (mechanized UT) + +
SG Collector Dissimilar Weld (mechanized UT) + +
RPV Welds (mechanized UT from OD) + +
SG Threaded hole (mechanized ET ) + +
MCP Threaded hole (mechanized ET ) + +
RPV Main Loop Nozzle dissimilar weld (mechanized UT
from OD) + +
RPV Safety Injection Nozzle dissimilar weld (mechanized UT
from OD) + +
RPV Stud (mechanized ET and UT) + +
RPV Threaded hole (mechanized ET) + +
Qualifications in progress SG Stud (mechanized ET ) + +
MCP Stud (mechanized ET ) + +
Generic Procedure for PT of nuclear components + +
Status of Inspection Qualification
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Registration level
Reference level
(recording level)
Acceptance level (quality control)
Acceptance level
(fitness-for-service)
In
dic
atio
n s
ize
Fla
w s
ize
LEVEL
Evaluation based on flaw
characteristics
Recording
Repair/replacement, or
fracture mechanics analysis
Quality Control Fitness-for-Service
100% PRR (FBH)
+12 dB
20% DAC (SDH)
100% DAC (SDH)
siz
ing
Critical
Not-allowable
Allowable
Acceptance Standards
Current approach Future approach
siz
ing
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Level 1 evaluation
Allowable?
Is sizing possible?
Sizing and Level 2
evaluation
Allowable?
Fracture mechanics
calculation
Allowable?
Measures
NDE
OPERATION
Y
N
Y
Y
N
N
Y
N Y
Current standard
IWB, C, D-3000
IWB, C, D-3600
Two-level
evaluation
concept
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Pressure Test
• Biggest debate with regulator
• Test pressure of primary coolant circuit:
– 19.1 MPa (until 1993); 16.4 MPa (currently)
– operating pressure: 12.2 MPa
• Fail safe design / operation
– resistance against operation, accident and test loads (flaw size
will not change during hydrotest)
– leakage test (operating pressure)
• Test at elevated pressure:
– no added value to integrity
assessment
– contribution to fatigue
– risk increase
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Estimation of Economic Benefit
• Impact of ISI interval extension: USD 300 to 600 M
– NDE volume increase (+) due to ageing management
– longer interval
– outage reduction
• Inspection qualification – usually not quantifiable – allows to use simpler (less time-consuming) NDE
– more reliable NDE – longer inspection interval
– defect repair can be optimized (in earlier stage)
• Risk informed ISI – under consideration
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Summary
• To support LTO of Paks NPP
– a complete revision and
– a substantial modification of ISI program
was performed
• Content of ISI program achieved a good agreement
with ASME BPVC Section XI requirements
• ISI program shows more and more features of an
effective ISI (see IAEA-TECDOC 1400)
• Acceptance criteria meet technical requirements of
life extension
– fracture mechanics calculation
– decisions on repair / replacement
• Licensing is under way