ASME graphite code development

Technical Meeting on High-Temperature Qualification

of High Temperature Gas-Cooled Reactor Materials

10-13 June 2014, IAEA Vienna

M W Davies

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Content

Original ‘design’ codes for graphite components

Currently used design/assessment codes

ASME Sub-group on Graphite Core Components

Main sections of new code

Mandatory appendices

Non-mandatory appendices

Benchmark exercises

Assessment methodologies (for design)

Still to do for graphite…..

Ceramics code and in-service inspection

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Original ‘design’ codes for graphite components

Original ASME code for core support structures (in Section III, Division 2, Sub-section CE, of Boiler and Pressure Vessel Code)

– Incomplete draft produced in late 80s/early 90s

– Deterministic (compared stress with critical strength and used a factor of 4)

– Does not cover irradiated components

– Does not cover graphite data and assessment methodology

– Intended to cover materials, design, manufacture, installation etc

German KTA 3232 rule

– Complete draft produced in late 80s/early 90s but never adopted

– Simplified version (deterministic)

– Full version (probabilistic)

– Does cover irradiated components

– Partially covers graphite data and assessment methodology

– Covered materials, design, manufacture, installation etc

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Currently used design/assessment codes

South Africa (PBMR)

– Used it’s own design code called the Regulation for the Design and Manufacture of Ceramic Internals (RDMCI), which is based on the full version of the KTA 3232 rule

– Adopts a Probability of Failure approach using a design strength based on Weibull parameters for the graphite (tail of distribution)

Japan

– Uses modified version of the original ASME code

– Adopts a strength vs stress methodology and criterion for estimating component integrity. (Calculates a strength based on material variability, then applies a factor)

UK

– Uses Compendium of CAGR Core and Sleeve Data and Methods (which includes full details of graphite data and assessment methodology)

– Adopts a Fractional Remanent Strength criterion for determining component integrity. (Critical strength from FE analysis of component loaded to failure)

Aim is to unify/consolidate into the ASME code for graphite core components

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ASME Subgroup on Graphite Core Components

UK - Mike Davies (AMEC)

US - Tim Burchell (ORNL)

RSA - Mark Mitchell (BUFO Technology)

Japan - Taiju Shibata (JAEA)

Korea – Se-Hwan Chi (KAERI)

Others from UK, France, US, RSA, Japan and Korea have also participated

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ASME Subgroup on Graphite Core Components

Committee Charter

The committee shall establish codes, standards and guides for materials selection and

qualification, design, fabrication, testing, installation, examination, inspection,

certification, and the preparation of reports for manufacture and installation of nonmetallic

internal components for graphite-moderated fission reactors, where non-metallic

internal components are defined as components, including control rods and assemblies,

contained within a graphite-moderated fission reactor pressure vessel and manufactured

from graphite, carbon, carbon/carbon composites, ceramics, or ceramic matrix

composites. The codes, standards and guides shall apply to non-metallic components as

defined above. The codes, standards and guides shall not apply to graphite fuel matrix

materials, fuel compacts, fuel pebbles, bushings, bearings, seals, blanket materials,

instrumentation, or components internal to the reactor other than those defined above.

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Subgroup web-page

http://cstools.asme.org/csconnect/CommitteePages.cfm?Committee=N20070900&Action=18619&ChooseTemplate=3477

Contents of ASME code for graphite core components

Code is part of Section III of B&PV code, Division 5

Subsection HA - General Requirements, Subpart B - Graphite Materials

(Drafted with help of Subgroup on General Requirements

Article HAB-1000 Introduction

Article HAB-2000 Classification of Graphite Core Components

Article HAB-3000 Responsibilities and Duties

Article HAB-4000 Quality Assurance

Article HAB-5000 Authorised Inspection

Article HAB-7000 Reference Standards

Article HAB-8000 Certificates and Data Reports

Article HAB-9000 Glossary

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Contents of ASME code for graphite core components

Subsection HH – Class A Non-metallic Core Support Structures, Subpart A - Graphite Materials

Article HHA-1000 Introduction

Article HHA-2000 Materials

Article HHA-3000 Design

Article HHA-4000 Machining and Installation

Article HHA-5000 Examination

Article HHA-6000 Testing

Article HHA-7000 Not used

Article HHA-8000 Stamping and Reporting

Article HHA-9000 Glossary

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Contents of ASME code for graphite core components

Mandatory Appendices

– Article HHA-I Graphite material specifications. ASTM D7219-05 ‘Standard

specification for isotropic and near-isotropic graphites’, and ASTM D7301-08

‘Standard specification for nuclear graphite suitable for components subjected

to low neutron irradiation dose)

– Article HHA-II Requirements for preparation of a material data sheet

– Article HHA-III Requirements for generation of design data for graphite grades

– Article HHA-IV Cleanliness requirements (Drafted – submitted for comment and

review)

Non-mandatory Appendices

– I Graphite as a structural material. (Completed)

– II Recommended practices for the stress analysis of irradiated parts. (Partially

drafted)

‘White Papers’

– These will be produce as required to support code recommendations etc

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Assessment methodologies for Article HHA-3000

(Design)

Deterministic assessment methodologies, primarily comparing a stress to a ‘critical’ strength using a factor

– Draft ASME Section III, Division 2, Subsection CE, 1990.

– JAERI modified Draft ASME Section III, Division 2, Subsection CE, 1990.

– Draft KTA-3232 , 1992 (Germany) - Simplified assessment methodology.

Probabilistic assessment methodologies

– Classical Weibull (with Principle of Independent Action )

– Modified Weibull, Draft KTA-3232 , 1992

– Batdorf (CARES) – developed by NASA

– Burchell

Other possible approaches

– Continuum damage methods (Manchester University)

– Fracture mechanics

Carrying out a number of benchmark exercises to compare methods

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Benchmark exercises (1)

(1) Predict the mean, 4 point bending strength from the tensile strength test data.

(2) Predict failure loads for rectangular tensile specimens with different notch radii.

(3) Predict failure load of ring specimens subject to internal pressure.

(4) Predict failure load of ring specimens subject to diametral compression.

(5) Predict failure load of large beam with drilled holes.

(6) Predict failure loads of ‘L-shaped’ beams with different root radii.

(7) Predict failure loads of AGR fuel brick slice tests loaded through keyways

(8) Predict failure loads of AGR fuel brick slice tests loaded through pure bending

(9) Predict failure loads of initially unstressed AGR full brick tests loaded through keyways

(10) Predict failure loads of initially stressed AGR full brick tests loaded through keyways

(11) Predict failure loads for biaxially loaded specimen (axial tension/compression plus internal pressure

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Benchmark exercises 2, 3, 4, 5 and 6

L

L

L

L

L

L

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Benchmark exercise 7 and 8

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Strength/stress comparison (1)

Japanese method

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Strength/stress comparison (2)

StSm

Fixed

Margin

Material

Dependent

Su

Design Margin

Old ASME code Germany/PBMR

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Still to do for graphite……

Complete benchmark exercises to compare the different design methods

Complete balloting of Articles HHA-4000, 5000 and 6000 and mandatory appendices on Cleanliness Requirements

Produce ‘G’ forms General Requirements for Graphite (Equivalent to ‘N’ forms for pressure vessels)

Complete non-mandatory Appendices

Produce additional ‘White Papers’ as necessary

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Ceramics Code and In-service Inspection

The Sub-group is currently producing the equivalent code for ceramic

components – e.g. for core restraints, supports and control rods. Much of it

will be based on the graphite code. Most difficult area is seen as the Design

and Fabrication

ASME may be looking to include in-service inspection (ISI) requirements for

reactor internals (non-pressure retaining parts) in Section XI. Meetings will

have to be held with representatives from the Subcommittee on Nuclear In-

service Inspection (Section XI) to discuss ISI requirements/techniques for

graphite cores