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

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

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

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

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)

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

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)

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

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)

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)

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

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

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

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

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

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