ASTM C781-08(2014)
(Practice)Standard Practice for Testing Graphite and Boronated Graphite Materials for High-Temperature Gas-Cooled Nuclear Reactor Components
Standard Practice for Testing Graphite and Boronated Graphite Materials for High-Temperature Gas-Cooled Nuclear Reactor Components
SIGNIFICANCE AND USE
4.1 Property data obtained with the recommended test methods identified herein may be used for research and development, design, manufacturing control, specifications, performance evaluation, and regulatory statutes pertaining to high temperature gas-cooled reactors.
4.2 The test methods are applicable primarily to specimens in the non-irradiated and non-oxidized state. Many are also applicable to specimens in the irradiated or oxidized state, or both, provided the specimens meet all requirements of the test method. The user is cautioned to consider the instructions given in the test methods.
4.3 Additional test methods are in preparation and will be incorporated. The user is cautioned to employ the latest revision.
SCOPE
1.1 This practice covers the test methods for measuring the properties of graphite and boronated graphite materials. These properties may be used for the design and evaluation of high-temperature gas-cooled reactor components.
1.2 The test methods referenced herein are applicable to materials used for replaceable and permanent components as defined in Section 7 and Section 9, and includes fuel elements; removable reflector elements and blocks; permanent side reflector elements and blocks; core support pedestals and elements; control rod, reserve shutdown, and burnable poison compacts; and neutron shield material.
1.3 This practice includes test methods that have been selected from existing ASTM standards, ASTM standards that have been modified, and new ASTM standards that are specific to the testing of materials listed in 1.2. Comments on individual test methods for graphite and boronated graphite components are given in Sections 8 and 10, respectively. The test methods are summarized in Tables 1 and 2.
1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: C781 − 08 (Reapproved 2014) An American National Standard
Standard Practice for
Testing Graphite and Boronated Graphite Materials for High-
Temperature Gas-Cooled Nuclear Reactor Components
This standard is issued under the fixed designation C781; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope ments of Manufactured Carbon and Graphite Articles
C561 Test Method for Ash in a Graphite Sample
1.1 This practice covers the test methods for measuring the
C577 Test Method for Permeability of Refractories
properties of graphite and boronated graphite materials. These
C611 TestMethodforElectricalResistivityofManufactured
properties may be used for the design and evaluation of
Carbon and Graphite Articles at Room Temperature
high-temperature gas-cooled reactor components.
C625 Practice for Reporting Irradiation Results on Graphite
1.2 The test methods referenced herein are applicable to
C651 Test Method for Flexural Strength of Manufactured
materials used for replaceable and permanent components as
CarbonandGraphiteArticlesUsingFour-PointLoadingat
defined in Section 7 and Section 9, and includes fuel elements;
Room Temperature
removable reflector elements and blocks; permanent side
C695 Test Method for Compressive Strength of Carbon and
reflector elements and blocks; core support pedestals and
Graphite
elements; control rod, reserve shutdown, and burnable poison
C709 Terminology Relating to Manufactured Carbon and
compacts; and neutron shield material.
Graphite
1.3 This practice includes test methods that have been
C747 Test Method for Moduli of Elasticity and Fundamental
selected from existing ASTM standards, ASTM standards that
Frequencies of Carbon and Graphite Materials by Sonic
have been modified, and newASTM standards that are specific
Resonance
tothetestingofmaterialslistedin1.2.Commentsonindividual
C749 Test Method for Tensile Stress-Strain of Carbon and
test methods for graphite and boronated graphite components
Graphite
are given in Sections 8 and 10, respectively. The test methods
C769 Test Method for Sonic Velocity in Manufactured
are summarized in Tables 1 and 2.
Carbon and Graphite Materials for Use in Obtaining
1.4 The values stated in SI units are to be regarded as
Young’s Modulus
standard. The values given in parentheses are for information
C816 Test Method for Sulfur in Graphite by Combustion-
only.
Iodometric Titration Method
1.5 This standard does not purport to address all of the C838 Test Method for Bulk Density of As-Manufactured
safety concerns, if any, associated with its use. It is the Carbon and Graphite Shapes
responsibility of the user of this standard to establish appro- C1039 Test Methods for Apparent Porosity, Apparent Spe-
priate safety and health practices and determine the applica- cific Gravity, and Bulk Density of Graphite Electrodes
bility of regulatory limitations prior to use.
C1179 Test Method for Oxidation Mass Loss of Manufac-
tured Carbon and Graphite Materials in Air
2. Referenced Documents
C1233 Practice for Determining Equivalent Boron Contents
of Nuclear Materials
2.1 ASTM Standards:
C1274 Test Method forAdvanced Ceramic Specific Surface
C559 Test Method for Bulk Density by Physical Measure-
Area by Physical Adsorption
D346 Practice for Collection and Preparation of Coke
Samples for Laboratory Analysis
This practice is under the jurisdiction of ASTM Committee D02 on Petroleum
Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcom-
D1193 Specification for Reagent Water
mittee D02.F0 on Manufactured Carbon and Graphite Products.
D2854 Test Method for Apparent Density of Activated
CurrenteditionapprovedMay1,2014.PublishedJuly2014.Originallyapproved
Carbon
in 1977. Last previous edition approved in 2008 as C781 – 08. DOI: 10.1520/
C0781-08R14.
D2862 Test Method for Particle Size Distribution of Granu-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
lar Activated Carbon
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
D3104 Test Method for Softening Point of Pitches (Mettler
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. Softening Point Method)
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C781 − 08 (2014)
TABLE 1 Summary of Test Methods for Graphite Components
NOTE 1—Designations under preparation will be added when approved.
Fuel, Removable Reflector,
and Core Support Elements; Permanent Side
Core Support Pedestals
Pebble Bed Reflector, Reflector Elements
and Dowels
Key and Sleeves; and Dowel Pins
and Dowel Pins
Fabrication
As Manufactured Bulk Density C838 C838 C838
Mechanical Properties
Compressive Strength C695 C695 C695
A A A
Tensile Properties C749 C749 C749
B B B
Poisson’s Ratio E132 E132 E132
A A A
Flexural Strength C651 C651 C651
BB B
Fracture Toughness
Modulus of Elasticity C747 C747 C747
Physical Properties
Bulk Density–Machined Specimens C559 C559 C559
Surface Area (BET) C1274 C1274 C1274
A,B A,B A,B
Permeability C577 C577 C577
Apparent Porosity C1039 C1039 C1039
BB B
Spectroscopic Analysis
Electrical Resistivity C611 C611 C611
Thermal Properties
A
Linear Thermal Expansion E228
A A A
Thermal Conductivity E1461 E1461 E1461
Chemical Properties
B B B
Oxidative Mass Loss C1179 C1179 C1179
Sulfur Concentration C816 C816 C816
A A A
Ash Content C561 C561 C561
A AC
Equivalent Boron Content C1233 C1233
A
Modification of this test method is required. See Section 8 for details.
B
New test methods are required. See Section 8 for details.
C
There is no identified need for determining this property.
TABLE 2 Summary of Test Methods for Boronated Graphite
E11 Specification for Woven Wire Test Sieve Cloth and Test
Components
Sieves
E132 Test Method for Poisson’s Ratio at Room Temperature
NOTE 1—Designations under preparation will be added when approved.
E228 Test Method for Linear Thermal Expansion of Solid
Compacts
Neutron
Materials With a Push-Rod Dilatometer
Shield
Control Burnable Reserve
Material
Rod Poison Shutdown
E261 Practice for Determining Neutron Fluence, Fluence
Bulk Density C838 C838 C838 D4292 Rate, and Spectra by Radioactivation Techniques
A A AB
Linear Thermal Expansion E228 E228
E639 Test Method for Measuring Total-Radiance Tempera-
CC C
Particle Size D2862
ture of Heated Surfaces Using a Radiation Pyrometer
Mechanical Strength:
A A AB 3
Compressive Strength C695 C695 C695
(Withdrawn 2011)
BB B C
Impact Performance
E1461 Test Method for Thermal Diffusivity by the Flash
Chemical Properties:
CC C C
Method
Sulfur Concentration
CC C C
Hafnium Concentration
CC C C
Relative Oxidation Rate
3. Terminology
Boron Analysis:
CC C C
3.1 Definitions—Terminology C709 shall be considered as
Total Boron
CC C C
Boron as Oxide
applying to the terms used in this practice.
D D D D
B C Particle Size D2862 D2862 D2862 D2862
A
Modification of this test method is required. See Section 10 for details.
4. Significance and Use
B
There is no identified need for determining this property.
C
New test methods are required. See Section 10 for details. 4.1 Property data obtained with the recommended test
D
Additional test methods are required. See Section 10 for details.
methods identified herein may be used for research and
development, design, manufacturing control, specifications,
performance evaluation, and regulatory statutes pertaining to
high temperature gas-cooled reactors.
D4292 Test Method for Determination of Vibrated Bulk
4.2 The test methods are applicable primarily to specimens
Density of Calcined Petroleum Coke
in the non-irradiated and non-oxidized state. Many are also
D5600 Test Method for Trace Metals in Petroleum Coke by
applicable to specimens in the irradiated or oxidized state, or
Inductively Coupled Plasma Atomic Emission Spectrom-
etry (ICP-AES)
D7219 Specification for Isotropic and Near-isotropic
The last approved version of this historical standard is referenced on
Nuclear Graphites www.astm.org.
C781 − 08 (2014)
both, provided the specimens meet all requirements of the test 7.1.5 Except for support, guide, and containment of fuel
method. The user is cautioned to consider the instructions material, removable reflector elements may also serve any of
given in the test methods.
the functions listed in 7.1.2.
4.3 Additional test methods are in preparation and will be
7.2 Permanent Side Reflector Element:
incorporated. The user is cautioned to employ the latest
7.2.1 Apermanent side reflector element is a graphite block
revision.
that is designed to remain permanently in the core but may be
removed for inspection and replacement, if necessary. A
5. Sample Selection
permanent side reflector element contains channels for align-
ment dowel pins. It may also contain channels for neutron flux
5.1 All test specimens should be selected from materials
control materials (boronated steel pins) and nuclear
that are representative of those to be used in the intended
instrumentation,andrecessedareasalongitslengthonitsouter
application.
periphery to provide channels for the passage of coolant gas
between the element and the metallic lateral restraint for the
6. Test Reports
reactor core.
6.1 Test results should be reported in accordance with the
7.2.2 The permanent side reflector elements encircle the
reporting requirements included in the applicable test method.
active (fuel) elements and passive (removable reflector) ele-
Where relevant, information on grade designation, lot number,
ments of the reactor core and serve multiple functions, includ-
billet number, orientation, and location (position of sample in
ing (1) vertical and lateral mechanical support for the perma-
the original billet) shall be provided.
nent side reflector elements above and beside them, (2) lateral
6.2 Information on specimen irradiation conditions shall be
mechanical support for the fuel, removable reflector, and core
reported in accordance with Practices C625 and E261 or
support elements, (3) moderation of fast neutrons within the
referenced to source information of equivalent content.
reflectorregion, (4)reflectionofthermalneutronsbackintothe
core region, and (5) support, guide, and containment of nuclear
GRAPHITE COMPONENTS
instrumentation and neutron flux control materials (boronated
steel pins) for reducing the neutron flux to metallic structures
7. Description and Function
outside the permanent side reflector boundary.
7.1 Fuel and Removable Reflector Elements:
7.3 Core Support Pedestals and Elements:
7.1.1 A fuel element is a removable graphite element that
7.3.1 A core support pedestal is a graphite column that is
contains channels for the passage of coolant gas, the fuel
designedtoremainpermanentlyinthecorebutcanberemoved
material (typically in the form of a compact containing coated
for inspection and replacement, if necessary. A core support
particle fuel), the alignment dowel pins, and the insertion of a
pedestal has a central reduced cross-section (dog bone shape)
handling machine pickup head. A fuel element may also
that at its upper end contains channels for the passage of
contain channels for reactivity control material (control rods),
coolant gas, alignment dowel pins, and the insertion of a
reserve shutdown compacts, and burnable poison compacts,
handling machine pickup head, and at its lower end contains a
and nuclear instrumentation.
recessed region for locating it with respect to the metallic
7.1.2 The fuel elements serve multiple functions, including
structure that supports the graphite core support assembly. A
(1)verticalandlateralmechanicalsupportforthefuelelements
core support element is a graphite element that contains
and removable reflector elements above and adjacent to them,
channels for alignment dowel pins and the insertion of a
and for the fuel, reactivity control materials, and nuclear
handling machine pickup head.The core support elements may
instrumentation within them, (2) moderation of fast neutrons
also contain channels for the passage of coolant gas, neutron
within the core region, (3) a thermal reservoir and conductor
flux control materials, and nuclear instrumentation.
for nuclear heat generated in the fuel, (4) a physical constraint
7.3.2 The primary function of the core support pedestals is
for the flow of coolant gases, and (5) a guide for and
to provide for vertical mechanical support for core support
containment of fuel material, reactivity control materials, and
elements and permanent side reflector elements above them. In
nuclear instrumentation.
addition, core support pedestals provide for lateral mechanical
7.1.3 Aremovable reflector element is a removable graphite
support for adjacent core support pedestals and permanent side
element that contains channels for the alignment dowel pins
reflector elements and physical constraint for the flow of
and the insertion of a handling machine pickup head. A
coolant gases. The primary function of the core support
removable reflector element may also contain channels for the
elements is to provide for vertical mechanical support for core
passage of coolant gas, reactivity control materials (control
support, fuel, and removable reflector elements above them. In
rods), neutron flux control materials (neutron shield materials),
addition, core support elements provide for lateral mechanical
and nuclear instrumentation.
support for adjacent core support and permanent side reflector
7.1.4 The primary function of the removable reflector ele-
elementsandmayprovideforthephysicalconstraintofcoolant
ments that are located at the boundaries of the active reactor
gases and for the support, guide, and containment of neutron
core (fuel elements) is to provide for moderation of fast
flux control materials and nuclear instrumentation.
neutronsescapingfromandreflectionofthermalneutronsback
into the active core region. 7.4 Pebble Bed Modular Reactor Reflector Blocks:
C781 − 08 (2014)
7.4.1 The fuel form of a pebble bed reactor is typically a 8.2.3 Flexural Strength—Determine flexural strength in ac-
60 mm diameter sphere (pebble) containing graphite-carbon cordance with Test Method C651.
matrix and coated particle fuel.
8.2.4 Fracture Toughness—A test method for determining
7.4.2 The Pebble Bed reactor core structure consists of a fracture toughness is in preparation.
graphite reflector supported and surrounded by a metallic core
8.2.5 Modulus of Elasticity—Determine modulus of elastic
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C781 − 08 C781 − 08 (Reapproved 2014) An American National Standard
Standard Practice for
Testing Graphite and Boronated Graphite Materials for High-
Temperature Gas-Cooled Nuclear Reactor Components
This standard is issued under the fixed designation C781; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*Scope
1.1 This practice covers the test methods for measuring the properties of graphite and boronated graphite materials. These
properties may be used for the design and evaluation of high-temperature gas-cooled reactor components.
1.2 The test methods referenced herein are applicable to materials used for replaceable and permanent components as defined
in Section 7 and Section 9, and includes fuel elements; removable reflector elements and blocks; permanent side reflector elements
and blocks; core support pedestals and elements; control rod, reserve shutdown, and burnable poison compacts; and neutron shield
material.
1.3 This practice includes test methods that have been selected from existing ASTM standards, ASTM standards that have been
modified, and new ASTM standards that are specific to the testing of materials listed in 1.2. Comments on individual test methods
for graphite and boronated graphite components are given in Sections 8 and 10, respectively. The test methods are summarized
in Tables 1 and 2.
1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
C559 Test Method for Bulk Density by Physical Measurements of Manufactured Carbon and Graphite Articles
C561 Test Method for Ash in a Graphite Sample
C577 Test Method for Permeability of Refractories
C611 Test Method for Electrical Resistivity of Manufactured Carbon and Graphite Articles at Room Temperature
C625 Practice for Reporting Irradiation Results on Graphite
C651 Test Method for Flexural Strength of Manufactured Carbon and Graphite Articles Using Four-Point Loading at Room
Temperature
C695 Test Method for Compressive Strength of Carbon and Graphite
C709 Terminology Relating to Manufactured Carbon and Graphite
C747 Test Method for Moduli of Elasticity and Fundamental Frequencies of Carbon and Graphite Materials by Sonic Resonance
C749 Test Method for Tensile Stress-Strain of Carbon and Graphite
C769 Test Method for Sonic Velocity in Manufactured Carbon and Graphite Materials for Use in Obtaining Young’s Modulus
C816 Test Method for Sulfur in Graphite by Combustion-Iodometric Titration Method
C838 Test Method for Bulk Density of As-Manufactured Carbon and Graphite Shapes
C1039 Test Methods for Apparent Porosity, Apparent Specific Gravity, and Bulk Density of Graphite Electrodes
C1179 Test Method for Oxidation Mass Loss of Manufactured Carbon and Graphite Materials in Air
C1233 Practice for Determining Equivalent Boron Contents of Nuclear Materials
C1274 Test Method for Advanced Ceramic Specific Surface Area by Physical Adsorption
This practice is under the jurisdiction of ASTM Committee D02 on Petroleum Products Products, Liquid Fuels, and Lubricants and is the direct responsibility of
Subcommittee D02.F0 on Manufactured Carbon and Graphite Products.
Current edition approved Sept. 1, 2008May 1, 2014. Published October 2008July 2014. Originally approved in 1977. Last previous edition approved in 20022008 as
C781C781 – 08.–02. DOI: 10.1520/C0781-08.10.1520/C0781-08R14.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C781 − 08 (2014)
TABLE 1 Summary of Test Methods for Graphite Components
NOTE 1—Designations under preparation will be added when approved.
Fuel, Removable Reflector,
and Core Support Elements; Permanent Side
Core Support Pedestals
Pebble Bed Reflector, Reflector Elements
and Dowels
Key and Sleeves; and Dowel Pins
and Dowel Pins
Fabrication
As Manufactured Bulk Density C838 C838 C838
Mechanical Properties
Compressive Strength C695 C695 C695
A A A
Tensile Properties C749 C749 C749
B B B
Poisson’s Ratio E132 E132 E132
A A A
Flexural Strength C651 C651 C651
B B B
Fracture Toughness
Modulus of Elasticity C747 C747 C747
Physical Properties
Bulk Density–Machined Specimens C559 C559 C559
Surface Area (BET) C1274 C1274 C1274
A,B A,B A,B
Permeability C577 C577 C577
Apparent Porosity C1039 C1039 C1039
B B B
Spectroscopic Analysis
Electrical Resistivity C611 C611 C611
Thermal Properties
A
Linear Thermal Expansion E228
A A A
Thermal Conductivity E1461 E1461 E1461
Chemical Properties
B B B
Oxidative Mass Loss C1179 C1179 C1179
Sulfur Concentration C816 C816 C816
A A A
Ash Content C561 C561 C561
A A C
Equivalent Boron Content C1233 C1233
A
Modification of this test method is required. See Section 8 for details.
B
New test methods are required. See Section 8 for details.
C
There is no identified need for determining this property.
TABLE 2 Summary of Test Methods for Boronated Graphite
Components
NOTE 1—Designations under preparation will be added when approved.
Compacts
Neutron
Shield
Control Burnable Reserve
Material
Rod Poison Shutdown
Bulk Density C838 C838 C838 D4292
A A A B
Linear Thermal Expansion E228 E228
C C C
Particle Size D2862
Mechanical Strength:
A A A B
Compressive Strength C695 C695 C695
B B B C
Impact Performance
Chemical Properties:
C C C C
Sulfur Concentration
C C C C
Hafnium Concentration
C C C C
Relative Oxidation Rate
Boron Analysis:
C C C C
Total Boron
C C C C
Boron as Oxide
D D D D
B C Particle Size D2862 D2862 D2862 D2862
A
Modification of this test method is required. See Section 10 for details.
B
There is no identified need for determining this property.
C
New test methods are required. See Section 10 for details.
D
Additional test methods are required. See Section 10 for details.
D346 Practice for Collection and Preparation of Coke Samples for Laboratory Analysis
D1193 Specification for Reagent Water
D2854 Test Method for Apparent Density of Activated Carbon
D2862 Test Method for Particle Size Distribution of Granular Activated Carbon
D3104 Test Method for Softening Point of Pitches (Mettler Softening Point Method)
D4292 Test Method for Determination of Vibrated Bulk Density of Calcined Petroleum Coke
D5600 Test Method for Trace Metals in Petroleum Coke by Inductively Coupled Plasma Atomic Emission Spectrometry
(ICP-AES)
C781 − 08 (2014)
D7219 Specification for Isotropic and Near-isotropic Nuclear Graphites
E11 Specification for Woven Wire Test Sieve Cloth and Test Sieves
E132 Test Method for Poisson’s Ratio at Room Temperature
E228 Test Method for Linear Thermal Expansion of Solid Materials With a Push-Rod Dilatometer
E261 Practice for Determining Neutron Fluence, Fluence Rate, and Spectra by Radioactivation Techniques
E639 Test Method for Measuring Total-Radiance Temperature of Heated Surfaces Using a Radiation Pyrometer (Withdrawn
2011)
E1461 Test Method for Thermal Diffusivity by the Flash Method
3. Terminology
3.1 Definitions—Terminology C709 shall be considered as applying to the terms used in this practice.
4. Significance and Use
4.1 Property data obtained with the recommended test methods identified herein may be used for research and development,
design, manufacturing control, specifications, performance evaluation, and regulatory statutes pertaining to high temperature
gas-cooled reactors.
4.2 The test methods are applicable primarily to specimens in the non-irradiated and non-oxidized state. Many are also
applicable to specimens in the irradiated or oxidized state, or both, provided the specimens meet all requirements of the test
method. The user is cautioned to consider the instructions given in the test methods.
4.3 Additional test methods are in preparation and will be incorporated. The user is cautioned to employ the latest revision.
5. Sample Selection
5.1 All test specimens should be selected from materials that are representative of those to be used in the intended application.
6. Test Reports
6.1 Test results should be reported in accordance with the reporting requirements included in the applicable test method. Where
relevant, information on grade designation, lot number, billet number, orientation, and location (position of sample in the original
billet) shall be provided.
6.2 Information on specimen irradiation conditions shall be reported in accordance with Practices C625 and E261 or referenced
to source information of equivalent content.
GRAPHITE COMPONENTS
7. Description and Function
7.1 Fuel and Removable Reflector Elements:
7.1.1 A fuel element is a removable graphite element that contains channels for the passage of coolant gas, the fuel material
(typically in the form of a compact containing coated particle fuel), the alignment dowel pins, and the insertion of a handling
machine pickup head. A fuel element may also contain channels for reactivity control material (control rods), reserve shutdown
compacts, and burnable poison compacts, and nuclear instrumentation.
7.1.2 The fuel elements serve multiple functions, including (1) vertical and lateral mechanical support for the fuel elements and
removable reflector elements above and adjacent to them, and for the fuel, reactivity control materials, and nuclear instrumentation
within them, (2) moderation of fast neutrons within the core region, (3) a thermal reservoir and conductor for nuclear heat
generated in the fuel, (4) a physical constraint for the flow of coolant gases, and (5) a guide for and containment of fuel material,
reactivity control materials, and nuclear instrumentation.
7.1.3 A removable reflector element is a removable graphite element that contains channels for the alignment dowel pins and
the insertion of a handling machine pickup head. A removable reflector element may also contain channels for the passage of
coolant gas, reactivity control materials (control rods), neutron flux control materials (neutron shield materials), and nuclear
instrumentation.
7.1.4 The primary function of the removable reflector elements that are located at the boundaries of the active reactor core (fuel
elements) is to provide for moderation of fast neutrons escaping from and reflection of thermal neutrons back into the active core
region.
7.1.5 Except for support, guide, and containment of fuel material, removable reflector elements may also serve any of the
functions listed in 7.1.2.
7.2 Permanent Side Reflector Element:
The last approved version of this historical standard is referenced on www.astm.org.
C781 − 08 (2014)
7.2.1 A permanent side reflector element is a graphite block that is designed to remain permanently in the core but may be
removed for inspection and replacement, if necessary. A permanent side reflector element contains channels for alignment dowel
pins. It may also contain channels for neutron flux control materials (boronated steel pins) and nuclear instrumentation, and
recessed areas along its length on its outer periphery to provide channels for the passage of coolant gas between the element and
the metallic lateral restraint for the reactor core.
7.2.2 The permanent side reflector elements encircle the active (fuel) elements and passive (removable reflector) elements of
the reactor core and serve multiple functions, including (1) vertical and lateral mechanical support for the permanent side reflector
elements above and beside them, (2) lateral mechanical support for the fuel, removable reflector, and core support elements, (3)
moderation of fast neutrons within the reflector region, (4) reflection of thermal neutrons back into the core region, and (5) support,
guide, and containment of nuclear instrumentation and neutron flux control materials (boronated steel pins) for reducing the
neutron flux to metallic structures outside the permanent side reflector boundary.
7.3 Core Support Pedestals and Elements:
7.3.1 A core support pedestal is a graphite column that is designed to remain permanently in the core but can be removed for
inspection and replacement, if necessary. A core support pedestal has a central reduced cross-section (dog bone shape) that at its
upper end contains channels for the passage of coolant gas, alignment dowel pins, and the insertion of a handling machine pickup
head, and at its lower end contains a recessed region for locating it with respect to the metallic structure that supports the graphite
core support assembly. A core support element is a graphite element that contains channels for alignment dowel pins and the
insertion of a handling machine pickup head. The core support elements may also contain channels for the passage of coolant gas,
neutron flux control materials, and nuclear instrumentation.
7.3.2 The primary function of the core support pedestals is to provide for vertical mechanical support for core support elements
and permanent side reflector elements above them. In addition, core support pedestals provide for lateral mechanical support for
adjacent core support pedestals and permanent side reflector elements and physical constraint for the flow of coolant gases. The
primary function of the core support elements is to provide for vertical mechanical support for core support, fuel, and removable
reflector elements above them. In addition, core support elements provide for lateral mechanical support for adjacent core support
and permanent side reflector elements and may provide for the physical constraint of coolant gases and for the support, guide, and
containment of neutron flux control materials and nuclear instrumentation.
7.4 Pebble Bed Modular Reactor Reflector Blocks:
7.4.1 The fu
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