Presented to SYMPOSIUM 13: International Symposium on Advanced Ceramics and Composites for Sustainable Nuclear Energy and Fusion Energy Several high-temperature reactors have been designed, built and operated successfully using conventional materials. This application invariably pushed the materials to the edge of their envelope. Over the last 20 years it has become clear that unlocking the use of advanced materials – such as ceramic matrix composites and carbon-carbon composites – will enable significant improvements in the performance of high-temperature reactors. This presentation provided an overview of some of the work completed to enable the use of these materials in various reactor development programmes, and explained the current work that is being completed in the ASME Boiler and Pressure Vessel Code committees to establish codes and standards for this application.

1. Development of a Standard for the
use of composites in a High
Temperature Reactor
6 May 2015
Mitchell, Mark N.; Katoh, Yutai; Gonczy,
Stephen T.
Presented to: SYMPOSIUM 13:
International Symposium on Advanced
Ceramics and Composites for
Sustainable Nuclear Energy and Fusion
Energy

2. 6 May, 2015 / 2 © 2015 – EON Consulting (Pty) Ltd
Introduction
• Provide an overview of the need for and progress developing ASME code for
Ceramic Matrix Composites (CMC) components in High Temperature Reactors
• Specifically we are targeting two composite systems: SiC-SiC and CFRC.
–Why do we consider CMC for High Temperature Reactors?
–What CMC applications are being considered?
–What are we doing from a code and standards perspective to enable this?

3. 6 May, 2015 / 3 © 2015 – EON Consulting (Pty) Ltd
Why do we consider Ceramic Matrix Composites
for High Temperature Reactors
• Increase the range of applications that
the reactor system can be used for:
–Example: Process heat for hydrogen
production using a sulphur iodine cycle
• Environmental Effects
–Notably high Irradiation resistance – SiC
based materials.
• High Temperature:
–Allows for the operation of the reactor
system at higher temperature (leading to
higher power and efficiencies)
Why use these materials?
Rachael Elder*, Ray Allen, 2009, Nuclear heat for hydrogen production: Coupling a very high/high temperature reactor to a hydrogen production plant, Progress in Nuclear Energy 51
(2009) 500–525

4. 6 May, 2015 / 4 © 2015 – EON Consulting (Pty) Ltd
What are the benefits of higher temperatures?
• Rector component temperature limits
limit the reactor power due to
temperatures during loss of active
cooling.
Power Density
• Higher reactor outlet temperature
allows for higher specific power output
for essentially the same equipment.
Specific Power Output
Failure due to
imperfect particles?
Failure material in
perfect particles?
• Temperature limits of relatively few components limit the highest
temperature.
• Increasing temperature can lead to significant increase in power output
• Worth investing: Rough estimate, for a 400MW plant, a 10% power increase
will be worth more the $1bn for single Reactor over life.

5. 6 May, 2015 / 5 © 2015 – EON Consulting (Pty) Ltd
What are the main elements of the reactor system
design for these reactors
• The key items are identified in the figure
below
• General design principles such as
enveloping hot components in cold gas
ensure that the majority of the components
are never exposed to the highest
temperatures
Reactor Unit Power Conversion
Gas Turbine
Heat Exchanger
Interconnecting
Duct
Reactor Vessel
Reactor Core
Control Rod
Graphite Core
Assembly

6. 6 May, 2015 / 6 © 2015 – EON Consulting (Pty) Ltd
What are the main elements of the reactor
system design for these reactors
Reactivity Control
System (RCS)
Reserve
Shutdown
System (RSS)
Core
Unloading
Device (CUD)
Core
Structures
(CS)
Reactor
Pressure Vessel
(RPV)

7. 6 May, 2015 / 7 © 2015 – EON Consulting (Pty) Ltd
What has been done or in the past?
• Reactor Components
• Structural components
• Tie Rods
• Straps
• Control Rods
• Outlet duct
• Power Conversion
• Heat Exchangers
• Turbine components
Reactor Unit Interconnecting Duct
Power Conversion
Control Rods
Example HTTR
CFRC Control Rod
Tie Rods Restraint Straps Hot Gas Duct
HP Turbine
Blisk
Heat
Exchangers
Ø1.5 m

8. 6 May, 2015 / 8 © 2015 – EON Consulting (Pty) Ltd
What are we doing to develop Codes and
Standards to support future development
• ASME has been working on the
development of codes for the
incorporation of these materials since
August 2011.
• This will be incorporated into the Boiler
and Pressure Vessel Code, Section III,
Division 5.
• Development parallels the graphite
code
–Subsection HH Subpart A: Graphite Core
Components
–Subsection HA Subpart B: General
Requirements
• This forms one part of the broader
standardisation effort.

9. 6 May, 2015 / 9 © 2015 – EON Consulting (Pty) Ltd
Development of a code for Ceramic Matrix
Composite Core Components
• HHB-1000: Introduction
• HHB-2000: Materials
• HHB-3000: Design
• HHB-4000: Machining and Installation
• HHB-5000: Examination
• HHB-6000: Testing
• Appendix
–HHB-I: Material Specifications
–HHB-II: Material Datasheet
–HHB-III: Design Data
Subsection HH Subpart B
• HAC-1000: Introduction
• HAC-2000: Classification
• HAC-3000: Responsibilities and
Duties
• HAC-4000: Quality Assurance
• HAC-5000: Authorised Inspection
• HAC-7000: Reference Standards
• HAC-8000: Certificates and Data
Reports
Subsection HA Subpart C
Draft in process of review and
approval.
To be published in the 2017 Code.
Development to start based on HAB
for graphite.
Publication date not fixed.

10. 6 May, 2015 / 10 © 2015 – EON Consulting (Pty) Ltd
Some key concepts introduce in the draft HHB
code
• Structured the code to allow for multiple
applications and continual development
• To allow for future applications and the
unique nature of the material, the code is
process based
–Guidance for permissibility of the materials,
how to specify, how to qualify
• Design provides for two design approaches
–Simplified (Design by Analysis)
–Design by test
This code approach captures industry good
practice and aligns with other industry
standards (Like MIL-HDBK-17 Volume 5)
• The standards development
challenge:
• CMCs are Less mature then
graphite in terms of nuclear
applications and track record.
• No strong lead applications
–Need to be flexible
• A lot of standards mostly in
material test area
.

11. 6 May, 2015 / 11 © 2015 – EON Consulting (Pty) Ltd
General Design Requirements
• The standard is based on the principle of minimizing risk. General requirements
provide guidance by means of a set of conditions that the designer should
consider:
–Avoid use in highly irradiated condition (CFRC 2-4 1020 /cm2 (EDN), SiC-SiC significantly
higher)
–Design with high margin
–Design for redundancy
–Design for inspection and replacement
–Use of Commercial Grade Material
• The design code provides for classification of components into two classes:
–SRC-1: Structural
–SRC-3: Other (Insulation, ducting, fittings, Control Rods, …)
Snead (2007)

12. 6 May, 2015 / 12 © 2015 – EON Consulting (Pty) Ltd
Design By Analysis
• Design By Analysis Requirements
–The parts have simple geometry
–The part material properties are simple
and well understood
–The loading on the part is simple.
–The design margin on the part is high.
• If any of the above do not apply,
Design by Testing shall be done.
When is it applicable?
• Failure mode related allowable stress
value (Sgm). Not only for simple stress
modes (Tension , Bending)
• Design margin determined based on
statistical analysis of test data.
Key Concepts?

13. 6 May, 2015 / 13 © 2015 – EON Consulting (Pty) Ltd
What does CMC strength test data look like?
• Typical modes:
– Linear Elastic to Failure
– Linear until proportional limit
– Non-linear
• For the purpose of design we assume
that some portion of the strain in the
material after the proportional limit
involves irreversible damage to the
material.
A B
A
B
B
? Note that the material behaviour
may differ depending on the
material system, fibre orientation
and the mode of loading
strain
Stress

14. 6 May, 2015 / 14 © 2015 – EON Consulting (Pty) Ltd
Material Reliability Curve
The variability in material
strength is
characterised by the
material reliability
curve.
–Proposed. Use a Weibull
Distribution to characterise
the material strength (Ho,
Schmidt, Nemeth & Bratton)
–Conservatism introduced
using 95% confidence limits.
Slide 14

15. 6 May, 2015 / 15 © 2015 – EON Consulting (Pty) Ltd
Simplified Assessment
StSm
Material Dependent,
Based on POF Required
Design Margin
Conservative 95%
CI based on data availability
Simplified assessment:
–Compare the highest stress calculated in the
part to a design stress value, calculated from
the Material reliability curve and the target POF
for the part for this service level.
Using Weibull:
Slide 15
  
   
 
1
m
allowS Sc ln 1 POF
Note: The Allowable stress is now a function of material quality.

16. 6 May, 2015 / 16 © 2015 – EON Consulting (Pty) Ltd
How do we determine the Design Allowable
Stress (Sgm) for the CMCs
• The Design Allowable
Stress (Sgm) is based on
a statistically determined
margin from both the
proportional and ultimate
strengths.
• The minimum value for
both of these is to be
considered.
A
B
MIN
= Sgm

17. 6 May, 2015 / 17 © 2015 – EON Consulting (Pty) Ltd
Design by Test
• Design by focuses on components
• Similar requirements to the derivation
of Sgm
–Multiple components
–Close similarity to actual components
–May adjust for temperature and other
environmental conditions
• Applicable where components or
loading are too complex to be able to
rely on Design by Analysis

18. 6 May, 2015 / 18 © 2015 – EON Consulting (Pty) Ltd
Case Study: PBMR DPP400 Top Reflector CFRC
Tie Rod Design
• Function of Tie Rod: Support the
Top Reflector (TR) in its intended
position throughout all operating
conditions.
• SRC-1 (Load carrying function)
• Max design load = 32kN (including
design margin)
• Design allowable values:
A Rambharos; M van Wyk; M Mitchell (2008)
SRC LOC A LOC B
SRC-1 Sgm (10-4) Sgm (10-3)
This meets the code requirements.

19. 6 May, 2015 / 19 © 2015 – EON Consulting (Pty) Ltd
Conclusion
• There are clear applications for Ceramic Matrix Composites in the future
development of high temperature reactors.
• Initial work complete to design and demonstrate rector components show
promise.
• There is probably a very good business case to be made to support further
development.
• The ASME code committees are working with others to establish a codes and
standards environment that will support this..

20. Thank you
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.
Mark N. Mitchell
+27 83 458 5304
mark.mitchell@eon.co.za