Management of Pressure Tube In-service Deformation in CANDU NPPs

Management of Pressure Tube In-service Deformation in CANDU NPPs -Perspectives of Regulatory Staff Yong-Zhi Wang,

Operational Engineering Assessment Division Directorate of Assessment and Analysis Canadian Nuclear Safety Commission IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, 16-18 November 2011, Vienna, Austria

Outline of Presentation • Introduction • Canadian Nuclear Regulatory Authority • Nuclear Power in Canada

• CANDU Reactors: • Fuel Channels • Pressure Tube in-service Degradation

• Management of PT in-service Deformation • CSA N285.4 requirements • Licensee's F/C lifecycle management Strategy and plan • Current Status and Recent development

• Conclusions

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Canadian Nuclear Safety Commission

Established May 2000, under the Nuclear Safety and Control Act Replaced the AECB, established in 1946, Atomic Energy Control Act Canada’s Independent Nuclear Regulator 65 Years Of Experience IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Nuclear Power In Canada For Canada and Other Countries… 120

80 70

100

60 80

50

60

40 30

40

20 20

10

0

0 France Ukraine Sweden South Finland Japan U.S. Russia Canada U.K. Korea Source: World Nuclear Association, May 2010

… Nuclear is already part of the mix IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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% of Energy Mix

Number of Operable Reactors

World nuclear reactors and share of electricity

Nuclear Power In Canada

Refurbishments and New Builds  Design Reviews • • • •

ACR-1000 – phase III completed 31 December 2010 AP1000 – phase I complete EPR –phase I on hold EC-6 – phase I complete; phase II in progress

Bruce • • •

Station A, Units 1 and 2 Refurbishments on-going Station A, Units 3 and 4 ISR in progress Station B, Units 5-8 in early planning

EPR

EC‐6

AP1000

ACR‐1000

Point Lepreau •

Refurbishment underway; project experiencing delays

Gentilly-2 •

Refurbishment planned in 2011 postponed to 2012

Pickering • •

$300 million for 10 more years of Pickering B operation, then decommissioning Pickering A shuts down at same time as PB

Darlington • •

Refurbishment scheduled for 2016 New nuclear plant Joint Review Panel site selected, design tbd

Saskatchewan, Alberta ? Canadian Nuclear Safety Commission

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria 5

Fuel Channel: Rolled Joint, Coolant/PT reaction

Pressure Tube dimensions Length: ~ 6.4m Inner diameter: 103.4 mm Thickness: 4.2 mm IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Typical Coolant in CANDU PHTS -the working conditions of a pressure tube Inside: Pressurized Heavy Water (D2O) – – – –

~ 250 to 315˚C; Outlet header pressure: 8.7 ~ 9.9 MPa pHa: 10.2 ~ 10.8; Dissolved oxygen concentration < 5μg(O2)/kg (D2O); – Neutron fluxes up to 3.7 x 1013 n/cm2 /s – Fluences up to 3 x 1022 n/cm2 (in 30 years of 80% capacity)

Outside: dry CO2 annulus gas, ~60 ˚C

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Pressure Tube Degradation Mechanisms • Delayed Hydride Cracking – Corrosion and Deuterium Ingress – Hydride precipitate – Flaws acting as stress raisers: Debris, Fuel-bundle Bearing Pad Fretting, crevice corrosion –leading to DHC initiation – Hydride Blisters, due to PT/CT contact, can initiate long DHC cracks and lead to PT rupture

• Irradiation Enhanced Deformation (Creep) – Axial growth, diametral growth, sag, wall thinning

• Changes in Material Properties: reduction in ductility and fracture toughness – Irradiation Embrittlement – Deuterium ingress IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Pressure Tube deformation:

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Canadian NPP Aging Management • Aging is an issue to be accounted for in any nuclear facility, existing or new builds, at all the stages, from cradle to grave. • Both industry and regulator have to work together to address it • CNSC adopted a comprehensive and systematic strategy to Aging Management including: 9 Regulatory requirements and documents (RDs, GDs), national and international codes and standards 9 Implementation plans 9 Compliance verification 9 Necessity for Research and Support (R&S) Projects – independent – joint with the industry – joint with international community

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Regulatory Framework - CSA Standards (Relevant to SSC Aging Management) CSA N285.0

General requirements for Pressure Retaining Systems and Components for CANDU NPP including appendix: Materials requirements for Pressure Retaining Systems and Components for CANDU NPP (formerly CSA N285.6)

• CSA N285.4

ASME Boiler & Pressure Vessel Code, Section III, Div. 1 Periodic Inspection of CANDU NPP Components (clause 12 specifies PIP requirements for pressure tubes)

CSA N285.5

Periodic Inspection of CANDU NPP Containment Components

CSA N285.8

Technical Requirements for In-Service Evaluation of Zirconium Alloy Pressure Tubes in CANDU (fitness- for-service assessment guidelines)

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Systematic Aging Management Process: Know–Plan-Do-Check-Act Application to Pressure Tubes 2. Planning, Coordination • Life cycle management strategy and plan, update regularly, site specific •Industry-wide R&D projects, via COG •PIP to meet License conditions •Long Term Operation •Organization & resources • Data requirements

Improve AMP

ACT

1. Understanding Aging • Material properties and dimension changes • Mechanisms •Stressors, indicators, locations. e..g rolled joints •Significance to other SSC and consequences if not managed •FFSG methodology and improvement •Inspection and maintenance tooling • OPEX, R&D, Standards

5. Maintenance • Tube shift •Spacer relocation •PT or F/C replacement: single or large scale

Mitigate degradation

Canadian Nuclear Safety Commission

PLAN Minimize expected degradation

DO 3. Operation •Strainer for commissioning •Temperature / pressure envelop for heat-up/ cooldown •Chemistry and environments control

4. Inspection, Monitoring, Check for Condition Assessment CHECK • volumetric, dimensional, replication: degradation flaws and sag •Gap bwt PT & CT •[H] and other material properties, vis surveillance program •Fitness for service evaluations, inc. core assess. IAEA Workshop on the Prediction of Axial and Radial Creep in • Disposition HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria •Condition assessments (ISR) 12

Pressure Tube Deformation Management

• CNSC license Requirement – CSA N 285.4*

• Licensee activities – Current status – Measurements and trends

*N285.4-05 with update 1 for OPG and BP; N285.4-09 for Point Lepreau

.

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Pressure tube deformation management: License Requirements

• CSA N285.4 requirements – Baseline: manufacturing and/or installation inspection records can be used – PIP inspection • ~every 6 years • minimum 10 channels (5 of them repeat) • including: internal diameter, wall thickness, PT/CT gap, position on bearings, channel length, tube deflection (sag); and the rate of change of these parameters IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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CSA N285.4 requirements – PIP inspection • acceptance criteria: at the next planned inspection:

Elongation:

Channel remains on bearing

Diametral Expansion:

Internal diameter within the design maximum

Wall Thinning:

Wall thickness no less than the design minimum

PT Sag:

No PT/CT contact

F/C Sag:

No contact bwn F/C and other internal components

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Pressure Tube Deformation Management: Licensee Activities • Comprehensive FC lifecycle management plan developed, implemented; • Reasonable size of database established enabling empirical equations for trending and prediction; • R&D funded for mechanistic understanding and developing robust constitutive relations.

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Overview of licensee’s FC Lifecycle Management Process Fuel Channel Life Cycle Management Plan

Outage Scope Definition

•R&D Program •OPEX •Fuel and Fuel Channel Program

•Inspection •Surveillance •Maintenance Fitness for Service Assessment including Probabilistic Core Assessment (CSA N285.8 )

Risk-Based Inspection Requirements Canadian Nuclear Safety Commission

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria 17

A licensee’s strategy for Pressure tube deformation management (template)

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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A licensee’s FC management plan for a particular unit (template)

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Pressure tube deformation (current status) : Axial Elongation • Off-bearing could limit the operation life of an unit; • Under-estimated in early design in the bearing travel limit; Corrected in later designs; • Monitored/measured by STEM regularly; • Re-configuration the fixed/free ends for whole unit; shifting of some to accommodate; • Predicted on-bearing till planned operation life for the majority; limited defueling for some;

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Pressure Tube Deformation (Current Status) : Diametral Expansion • The amount diametral change is dependant on fast flux, temperature, material and stress. • Diametral expansion limit can be defined either (1) exceeding ASME III allowable stresses in full crept state (accounting for end of life diametral growth and wall thinning), or (2) “nip-up” of spacer between crept PT and CT. • Coolant by-pass could lead to power de-rating; • Also, “nip-up” affects spacer integrity. • Measured by CIGAR/ANDE. • Remain within the limits until the planned operation life.

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Pressure Tube Deformation (Current Status): Wall Thinning

• A consequence of irradiation creep/growth; • Measured regularly; • Not a PT life limiting factor.

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Pressure Tube deformation (current status): Sag • May cause PT/CT contact between spacers; potential risk of hydride blister formation; • May affect fuel passage and interfere with fuelling, inspection and maintenance tooling. • Regularly monitored; Tool for gap measurement in progress. • SLAR operation to mitigate. IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Elongation Rate of A CANDU Reactor (mm/7000 EFPH, 2008)

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Elongation Rate of A CANDU Reactor, mm/7000 EFPH, 2011, a repeat measurement of the same unit of the previous slide

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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On-Bearing Predictions of the CANDU Reactor (EFPH, based on the Elongation Rate, 2008)

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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On-Bearing Predictions of the CANDU Reactor (EFPH, based on the Elongation Rate, 2011, same unit of the previous)

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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A CANDU Reactor Measured Pressure Tube Maximum Mean Internal Diameter Data, 2011 Correlation with Normalized EFPH

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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The Measured Pressure Tube Maximum Mean Internal Diameter Data for whole Station Correlation with Normalized EFPH

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Comparison of Pressure Tube Diameter in Repeat Inspection Channels with Linear Regression

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Comparison of PT Measured Mean ID with Predicted Mean ID at Mid Bundle Position using the HTS Aging Model at the time of 2011 outage

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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A CANDU Reactor Measured Pressure Tube Minimum Wall Thickness Data Correlation with Normalized EFPH, 2011

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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A CANDU NPP Measured Pressure Tube Minimum Wall Thickness Data Correlation with Normalized EFPH, 2011

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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A CANDU Reactor Measured Pressure Tube Maximum Sag Data Correlation with Normalized EFPH, 2011

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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A CANDU NPP Measured Pressure Tube Maximum Sag Data Correlation with Normalized EFPH, 2011

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Recent developments in PT Aging Management • More DHC resistant material developed and used for new CANDU NPPs and retubing • More sophisticated FFSG Methodology • Inspection and Surveillance program updating • Site Specific F/C Life Cycle Management Strategy and Plan (living document, update annually) • CANDU Owners Group (COG) Fuel Channel Life Management Project (FCLMP) to address issues related to long term operation

IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Issues related to PT deformation management • Inspection: Gap measurement system with CIGAR- developed, applied and successful rate improved • Mitigation: Shift-plus project in progress, safety analysis conducted • Assessment: – proposal of use tube specific data rather the upper bound for prediction – probabilistic approach • Standard: CSA N285.4 initiative on after-retube PIP requirements IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Conclusions: Pressure Tube Aging deformation Management • Systematic approaches have been applied in Canadian NPPs to the management of pressure tube deformation, as part of the FC Lifecycle Management Plan. • Sufficient inspection database has been established and reasonably mechanistic understanding of the issues are achieved. • Pressure tube deformation has been reasonably managed such that it alone could not cause a safety or structural integrity concern for fuel channels. • Assessment methodology and prediction capacity enables NPP safe operation with certain conservatism. • A coordinated research project could lead to further improvement in mechanistic understanding and in prediction accurate and thus benefit optimizing operation, especially long term operation. IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Acknowledgments: The author would like to thank • The Canadian nuclear power industry for permission to use the materials presented and useful discussions, particularly Mr. N. van den Brekel of OPG and Mr. D. Cho of Bruce Power. • Colleagues of CNSC for useful discussions and suggestions during the preparation, particularly Dr. N. Christodoulou, J Mok…. IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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Thank You For Your Attention

Canada’s Nuclear Energy Profile Pickering ON A1

A2

A3

In service  In service  In service  1971/2005 1972 Safe  1971 Safe  Mwe 515 storage state storage state B5

B6

B7

In service  1983 Mwe 516

In service  1984 Mwe 516

In service  1985 Mwe 516

Darlington ON A4

1

In service  1971/2003 Mwe 515

In service  1992 Mwe 881

B8

3

In service  1986 Mwe 516

In service  1993 Mwe 881

2

In service  1990 Mwe 881 4

In service  1993 Mwe 881

Typical share of nuclear energy in total electricity generation

Canada ‐ 14.7%

Quebec ‐ 3%

Ontario ‐ 52%

New Brunswick ‐ 30%

Bruce ON A1

In service  1977 Mwe 750 B5

In service  1985 Mwe 882

A2

A3

Point  Lepreau NB

In service  1983 Mwe 635

In service  1983 Mwe 635

A4

In service  1978/2003 Mwe 750

In service  1979/2003 Mwe 750

B6

B7

B8

In service  1984 Mwe 882

In service  1986 Mwe 882

In service  1977 Mwe 750

Gentilly QC

In service  1987 Mwe 882

Operable status (Average age – 25 Years) In service within design life In service / Returned to service Safe storage state In refurbishment IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria

Canadian Nuclear Safety Commission

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Nuclear Power in Canada

source: Nuclear Energy in the 21 Century

note hydro plays a dominant role, and nuclear is almost as the same as coal in electricity generation in Canada. IAEA Workshop on the Prediction of Axial and Radial Creep in HWR Pressure Tubes, Nov. 16-18, 2011, Vienna Austria Canadian Nuclear Safety Commission

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