Slide 1

ASME B&PV III, Div. 5 Section H

Code on Nuclear Graphite Core

Components

Technical Meeting on High-Temperature Qualification of

High-Temperature Gas Cooled Reactor Materials

IAEA, Vienna

Jan 10-13, 2014

Tim Burchell, Mark Mitchell and Mike Davies, BPC-III Working

Group Graphite & Composite Design

Acknowledgements

This work is sponsored by the

U.S. Department of Energy, Office of Nuclear Energy, Advanced Reactor

Technology Program, under contract DE-AC05-00OR22725 with Oak Ridge

National Laboratory, managed by UT-Battelle, LLC

Slide 3

Contents

Here we present some information on the rules for the design and construction of graphite core components of a High Temperature Reactor.

Contents: HTRs and their Graphite Core Components (GCC)

Progress and structure of the code

proposed criteria for the design of Graphite Core Components

Introduction (GCC In Safety Case)

Modes of failure, Stress categories and Stress Limits

Design Margin Comparison

Verification of methods

New verification exercise/methodology

Conclusion

Slide 4

Graphite Core Components Prism Type

HTR (HTTR)

Slide 5

Graphite Core Components Pebble Type

HTR (PBMR)

Slide 6

Overview of the code documents

Part HAB: General Requirements for Graphite Core Components HAB-1000 Introduction

HAB-2000 Classification of Graphite Core Components

HAB-3000 Responsibilities and Duties

HAB-4000 Quality Assurance

HAB-5000 Authorized Inspection

HAB-7000 Reference Standards

HAB-8000 Certificates and Data reports

Part HHA: Technical Requirements for Design and Construction of Non Metallic Core Support Structures (Graphite GB- HHA 1000 Introduction

HHA -2000 Materials

HHA -3000 Design

HHA -4000 Machining and installation

HHA -5000 Examination

HHA -6000 Testing

HHA -8000 Nameplates, Stamping and Reporting

Appendix HHA-I Graphite Material Specifications

Appendix HHA-II Requirements for creation of a material datasheet

Appendix HHA-III Requirements for Generation of Design Data for Graphite Grades

Appendix HHA-IV contamination control requirements for graphite core components and core assemblies

Appendix HHA-A Graphite as a structural material

Slide 7

Major Design Code Issues

Selected design methodology Probabilistic:

Design margin related to material uncertainty.

Defined in Appendix 3 Material Qualification, not prescribed in the code

Core Component vs. assembly design, catering for damage tolerance assessment.

Designer selection and classification of parts for structural reliability.

Design for effect of environmental effects over operating life (Irradiation, Oxidation)

Graphite Data and ASME Code Development

8

Application of the AGC Data to the ASME B&PV Code, Division III, Sect 5:HTRs, Rules for

Construction of Nuclear Facility Components

HHA-2220 IRRADIATED MATERIALS PROPERTIES

(a) The Materials Data Sheet shall include the properties specified in Mandatory Appendix

HHA-II. Fast neutron irradiation effects on the following properties shall be required for

compliance with this Subpart:

1) Dimensional change

2) Creep coefficient

3) Coefficient of thermal expansion

4) Strength

5) Thermal conductivity

6) Elastic modulus

(b) The magnitude of the material property change depends on the damage dose and

irradiation temperature. The damage dose and temperature range for the measurements shall

cover the qualification envelope range of HHA-2131(a), or as required in the application of the

graphite grade in the Graphite Core Assembly

Graphite Data and ASME Code Development

9

HHA-3142 Irradiation Effects

Neutron Fast Fluence

Limit

(DPA)

Condition Design Analysis Requirement

0.001 Irradiated Effect on thermal

conductivity shall be

considered (thermal

stress and stress

gradients)

>0.25 Irradiated Full viscoelastic

analysis.

Full effects of neutron

irradiation (HHA-2220)

Graphite Data and ASME Code Development

10

HHA 3142.3 Internal Stresses Due to Irradiation

The internal stresses in a graphite core component [that exceed the dose limits described in

HHA-3142.1(c)] shall be calculated. This calculation shall be completed by viscoelastic

modeling of the material behavior.

(a) Irradiation induced property changes creep and changes in properties (elastic modulus,

CTE, thermal conductivity) shall be accounted for in this analysis. The interaction between

irradiation creep and the CTE shall be included in this assessment.

(b) The analysis shall account for stress concentrations resulting from Graphite Core

Component geometry.

(c) The stress analysis shall account for superposition of stresses resulting from all of the

loads that a Graphite Core Component is exposed to simultaneously.

HHA-3142.4 Graphite Cohesive Life Limit

A temperature-dependent cohesive life limit is to be defined for the graphite grade used for

the Graphite Core Components. Material that exceed this life limit is considered to provide

no contribution to the structural performance (stiffness and strength) of the Graphite Core

Component. This fluence limit shall be set to the fluence at which the material experiences a

+10% linear dimensional change in the with-grain direction. For full assessment (HHA-

3230) this material shall not be included in the volume of the Graphite Core Component

assessed.

Graphite Data and ASME Code Development

11

MANDATORY APPENDIX HHA-III

REQUIREMENTS FOR GENERATION OF DESIGN DATA FOR GRAPHITE GRADES

HHA-III-3300 IRRADIATED GRAPHITE

For irradiated graphite [HHA-3132.1(b) and (c)] the following properties shall be determined:

(a) thermal conductivity temperature dependent

(b) dimensional change [HHA-3132.1(c) only]

(c) creep coefficients [HHA-3132.1(c) only]

(d) CTE temperature dependent [HHA-3132.1(c) only]

(e) strength [HHA-3132.1(c) only]

(f) elastic modulus [HHA-3132.1(c) only]

Test data shall represent and envelope the irradiation conditions in service, i.e., they shall

mimic reactor neutron fluence and temperature ranges. Data shall be reported in accordance

with ASTM C625.

FORM MDS-1 MATERIALS DATA SHEET (SI UNITS)

This form provides a template for the required graphite properties.

Hope to accumulate data by grade/property (or algorithm) and incorporate as ASME Code

cases

Slide 12

HHA-3000: TABLE OF CONTENTS HHA-3100 GENERAL DESIGN

HHA-3110 Graphite core components

HHA-3120 Loading Criteria (Design & Service loadings)

HHA-3130 Nomenclature

HHA-3140 SPECIAL CONSIDERATIONS HHA-3141 Oxidation

HHA-3142 Irradiation Effects

HHA-3143 Abrasion and Erosion

HHA 3144 Fatigue (on ballett)

HHA-3145 Compressive Load

HHA-3200 DESIGN BY ANALYSIS HHA-3210 DESIGN CRITERIA

HHA-3211 Requirements for acceptability

HHA-3212 General Design Requirements for Graphite Core Components

HHA-3213 Basis for Determining Stresses

HHA3214 Terms Relating to Stress Analysis

HHA-3215 Stress Analysis

HHA-3220 Stress Limits for GCC Simplified Assessment (Stress intensity based limits. These are related to the failure probability limits in the next section.)

HHA-3230 Probability of Failure Limits for GCC Full Assessment (Failure probability limits and how to assess to them.)

HHA-3240 Experimental limits - Design by test (For both static and fatigue strength.)

HHA-3300 REQUIREMENTS FOR DESIGN OF GRAPHITE CORE ASSEMBLY

Slide 13

Design Criteria for GCC

Brief overview of the criteria for the design of the

GCC. Supporting Article HHA-3000.

Key concepts: Role of GCC in A HTR Safety Case.

Modes of Failure addressed

Determination of Limits

Material Reliability Curve

Probabilistic Assessment Simplified Assessment

Probabilistic Method Full Assessment

Comparison of Margins

Verification (current & planned)

Slide 14

GCC In safety Case Graphite is quasi-brittle.

Graphite Strength shows a high variability.

It is not necessarily possible to ensure against cracking of graphite components.

A Graphite Core Assembly design shall ensure that the Failure (cracking) of a GCC does not result in loss of functional integrity of the Graphite Core Assembly.

As opposed to a pressure vessel, damage tolerance in GCA in ensured by limiting the consequence of failure of a single GCC, thus damage tolerance is ensured by assemblies of many components where no single component is critical to the functional integrity of the component.

Slide 15

Modes of failure

The identified modes of failure for graphite are:

Brittle fracture

Based on small numbers of parts cracking. Related to loss of function. Material dependent.

Fatigue

Buckling (Elastic Instability)

Environmental effects.

Oxidation

Water vapour

Irra