ASTM C776-17(2022)

Standard Specification for Sintered Uranium Dioxide Pellets for Light Water Reactors

ABSTRACT
This specification covers sintered uranium dioxide pellets containing 235U for use in nuclear reactors. Chemical requirements include uranium content, impurity content, stoichiometry, and moisture content. Maximum concentration limits are specified for impurity elements such as: aluminum, carbon, calcium+magnesium, chlorine, chromium, cobalt, fluorine, hydrogen, iron, nickel, nitrogen, silicon, and thorium. Chemical analyses shall be performed. Nuclear requirements include isotopic content and equivalent boron content. The following are physical characteristics of the material: dimensions, pellet density, grain size and pore morphology, pellet integrity –
SCOPE
1.1 This specification is for finished sintered UO2 pellets. It applies to UO2 pellets containing uranium (U) of any  235U concentration for use in nuclear reactors.  
1.2 This specification recognizes the presence of reprocessed U in the fuel cycle and consequently defines isotopic limits for UO2 pellets made from commercial grade UO2. Such commercial grade UO2 is defined so that, regarding fuel design and manufacture, the product is essentially equivalent to that made from unirradiated U. UO2 falling outside these limits cannot necessarily be regarded as equivalent and may thus need special provisions at the fuel fabrication plant or in the fuel design.  
1.3 This specification does not include (a) provisions for preventing criticality accidents, (b) requirements for health and safety, (c) avoidance of hazards, or (d) shipping precautions and controls. Observance of this specification does not relieve the user of the obligation to be aware of and conform to all federal, state, and local regulations pertaining to possessing, shipping, processing, or using source or special nuclear material. Examples of U.S. Government documents are Code of Federal Regulations (Latest Edition), Title 10, Part 50, Title 10, Part 70, Title 10, Part 71, and Title 49, Part 173.  
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.5 The following precautionary caveat pertains only to the technical requirements portion, Section 4, of this specification:  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, health, and environmental practices and determine the applicability or regulatory limitations prior to use.  
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Jun-2022
• ICS: 27.120.30 - Fissile materials and nuclear fuel technology
• Technical Committee: C26 - Nuclear Fuel Cycle
• Drafting Committee: C26.02 - Fuel and Fertile Material Specifications

Relations

• Refers: ASTM C859-24 - Standard Terminology Relating to Nuclear Materials
• Effective Date: 01-Jan-2024
• Refers: ASTM C996-20 - Standard Specification for Uranium Hexafluoride Enriched to Less Than 5&#x2009;%&#x2009;<sup > 235</sup>U
• Effective Date: 01-Mar-2020
• Refers: ASTM C696-19 - Standard Test Methods for Chemical, Mass Spectrometric, and Spectrochemical Analysis of Nuclear-Grade Uranium Dioxide Powders and Pellets
• Effective Date: 01-Nov-2019
• Refers: ASTM C753-16 - Standard Specification for Nuclear-Grade, Sinterable Uranium Dioxide Powder
• Effective Date: 01-Feb-2016
• Refers: ASTM C996-15 - Standard Specification for Uranium Hexafluoride Enriched to Less Than 5 % ²³⁵U
• Effective Date: 01-Jul-2015
• Refers: ASTM C859-14a - Standard Terminology Relating to Nuclear Materials
• Effective Date: 15-Jun-2014
• Refers: ASTM C859-14 - Standard Terminology Relating to Nuclear Materials
• Effective Date: 15-Jan-2014
• Refers: ASTM C859-13a - Standard Terminology Relating to Nuclear Materials
• Effective Date: 01-Jun-2013
• Refers: ASTM C859-13 - Standard Terminology Relating to Nuclear Materials
• Effective Date: 01-May-2013
• Refers: ASTM E112-12 - Standard Test Methods for Determining Average Grain Size
• Effective Date: 15-Nov-2012
• Refers: ASTM C696-11 - Standard Test Methods for Chemical, Mass Spectrometric, and Spectrochemical Analysis of Nuclear-Grade Uranium Dioxide Powders and Pellets
• Effective Date: 01-Sep-2011
• Refers: ASTM E112-10 - Standard Test Methods for Determining Average Grain Size
• Effective Date: 01-Nov-2010
• Refers: ASTM C859-10b - Standard Terminology Relating to Nuclear Materials
• Effective Date: 01-Nov-2010
• Refers: ASTM E105-10 - Standard Practice for Probability Sampling Of Materials
• Effective Date: 01-Oct-2010
• Refers: ASTM C996-10 - Standard Specification for Uranium Hexafluoride Enriched to Less Than 5 % ²³⁵U
• Effective Date: 01-Oct-2010

Overview

ASTM C776-17(2022) is the internationally recognized standard specification for sintered uranium dioxide (UO₂) pellets used in light water reactors. Developed by ASTM International, this standard aims to ensure the consistent quality, safety, and performance of nuclear fuel pellets containing any concentration of uranium-235. Covering chemical, nuclear, and physical requirements, ASTM C776 details the criteria that finished UO₂ pellets must meet before being placed into service within nuclear fuel assemblies.

The specification applies to both freshly enriched uranium as well as reprocessed uranium dioxide, provided isotopic requirements are met. It is a crucial reference for manufacturers, suppliers, and operators within the nuclear energy sector who design, fabricate, and qualify nuclear fuel for light water reactor applications.

Key Topics

• Chemical Requirements

  • Specifies minimum uranium content and maximum allowable concentration of impurities such as aluminum, carbon, calcium-magnesium, chlorine, chromium, cobalt, fluorine, hydrogen, iron, nickel, nitrogen, silicon, and thorium.
  • Emphasizes the importance of using validated chemical analysis methods.
  • Defines acceptable stoichiometry (oxygen-to-uranium ratio) and moisture content limits.

• Nuclear Requirements

  • Includes precise limits for isotopic content, especially relevant to U-235 enrichment.
  • Establishes the maximum acceptable equivalent boron content for reactor safety.

• Physical Characteristics

  • Requires pellets to meet criteria for dimensions, density, grain size, and pore morphology.
  • Describes inspection and sorting requirements to maintain pellet integrity, including checks for chips, cracks, inclusions, and surface cleanliness.

• Quality Assurance and Testing

  • Outlines procedures for sampling, testing, and certification of pellet lots.
  • Stipulates documentation and retention practices for quality control.
  • Addresses packaging and labeling for compliance with regulatory and safety requirements.

Applications

ASTM C776 is fundamental for organizations involved in manufacturing, quality assurance, procurement, and licensing of uranium dioxide pellets for nuclear fuel. Key applications include:

• Nuclear Fuel Fabrication: Ensuring UO₂ pellets meet strict chemical and physical specifications before assembly into fuel rods.
• Quality Assurance Programs: Establishing repeatable procedures for sampling, analysis, and certification to comply with safety and regulatory standards.
• Supplier-Buyer Agreements: Defining mutually agreed acceptance criteria, testing protocols, and documentation for pellet lots.
• Regulatory Compliance: Providing supporting evidence for licensing activities and adherence to federal, state, or international nuclear regulations.
• Fuel Design and Optimization: Supporting reactor operators and designers with consistent, reliable fuel performance data.

By adhering to ASTM C776, stakeholders can reduce the risk of fuel failure, enhance operational safety, and streamline regulatory approvals in nuclear power generation.

Related Standards

Understanding and correctly applying ASTM C776-17(2022) often requires referencing additional standards and regulatory documents, including:

• ASTM C696 – Test Methods for Chemical, Mass Spectrometric, and Spectrochemical Analysis of Nuclear-Grade Uranium Dioxide Powders and Pellets.
• ASTM C753 – Specification for Nuclear-Grade, Sinterable Uranium Dioxide Powder.
• ASTM C996 – Specification for Uranium Hexafluoride Enriched to Less Than 5% U-235.
• ASTM C1233 – Practice for Determining Equivalent Boron Contents of Nuclear Materials.
• ASME NQA-1 – Quality Assurance Requirements for Nuclear Facility Applications.
• CFR Title 10 Parts 50, 70, 71, and Title 49 Part 173 – U.S. Code of Federal Regulations covering nuclear materials licensing, safety, packaging, and transport.
• Regulatory Guide NUREG 1.126 – Guidance on fuel pellet densification and analysis methods.

Conclusion

ASTM C776-17(2022) is critical for maintaining the quality and safety of uranium dioxide pellets in light water reactors, providing a comprehensive framework for chemical, nuclear, and physical requirements. Its adoption helps nuclear fuel manufacturers and reactor operators achieve operational reliability, regulatory compliance, and industry best practices in nuclear fuel cycle management.

Keywords: ASTM C776, uranium dioxide pellets, light water reactors, nuclear fuel, nuclear standards, UO₂ pellet specification, fuel manufacturing, pellet quality assurance.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation:C776 −17 (Reapproved 2022)
Standard Specification for
Sintered Uranium Dioxide Pellets for Light Water Reactors
This standard is issued under the fixed designation C776; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
This specification is intended to provide the nuclear industry with a general standard for uranium
dioxide(UO )pelletsforlightwaterreactoruse.Itrecognizesthediversityofmanufacturingmethods
by which UO pellets are produced and the many special requirements for chemical and physical
characterization which may be imposed by the operating conditions to which the pellets will be
subjected in different light water reactors. Therefore, it is anticipated that the purchaser may
supplement this specification with additional requirements for specific applications.
1. Scope 1.5 The following precautionary caveat pertains only to the
technical requirements portion, Section 4, of this specification:
1.1 This specification is for finished sintered UO pellets. It
235 This standard does not purport to address all of the safety
applies to UO pellets containing uranium (U) of any U
concerns, if any, associated with its use. It is the responsibility
concentration for use in nuclear reactors.
of the user of this standard to establish appropriate safety,
1.2 This specification recognizes the presence of repro-
health, and environmental practices and determine the appli-
cessed U in the fuel cycle and consequently defines isotopic
cability or regulatory limitations prior to use.
limitsforUO pelletsmadefromcommercialgradeUO .Such
2 2
1.6 This international standard was developed in accor-
commercialgradeUO isdefinedsothat,regardingfueldesign
dance with internationally recognized principles on standard-
and manufacture, the product is essentially equivalent to that
ization established in the Decision on Principles for the
made from unirradiated U. UO falling outside these limits
Development of International Standards, Guides and Recom-
cannot necessarily be regarded as equivalent and may thus
mendations issued by the World Trade Organization Technical
need special provisions at the fuel fabrication plant or in the
Barriers to Trade (TBT) Committee.
fuel design.
2. Referenced Documents
1.3 This specification does not include (a) provisions for
preventingcriticalityaccidents,(b)requirementsforhealthand
2.1 ASTM Standards:
safety, (c) avoidance of hazards, or (d) shipping precautions
C696Test Methods for Chemical, Mass Spectrometric, and
and controls. Observance of this specification does not relieve
SpectrochemicalAnalysis of Nuclear-Grade Uranium Di-
the user of the obligation to be aware of and conform to all
oxide Powders and Pellets
federal, state, and local regulations pertaining to possessing,
C753Specification for Nuclear-Grade, Sinterable Uranium
shipping, processing, or using source or special nuclear mate-
Dioxide Powder
rial. Examples of U.S. Government documents are Code of
C859Terminology Relating to Nuclear Materials
FederalRegulations(LatestEdition),Title10,Part50,Title10,
C996Specification for Uranium Hexafluoride Enriched to
Part 70, Title 10, Part 71, and Title 49, Part 173.
Less Than 5% U
C1233Practice for Determining Equivalent Boron Contents
1.4 The values stated in SI units are to be regarded as
of Nuclear Materials
standard. No other units of measurement are included in this
E105Guide for Probability Sampling of Materials
standard.
E112Test Methods for Determining Average Grain Size
This specification is under the jurisdiction of ASTM Committee C26 on
NuclearFuelCycleandisthedirectresponsibilityofSubcommitteeC26.02onFuel
and Fertile Material Specifications. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
CurrenteditionapprovedJuly1,2022.PublishedJuly2022.Originallyapproved contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
in 1976. Last previous edition approved in 2017 as C776–17. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
C0776-17R22. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C776−17 (2022)
2.2 ASME Standard: If an element analysis is reported as “less than” a given
ASMENQA-1QualityAssuranceRequirementsforNuclear concentration, this “less than” value shall be used in the
Facility Applications determination of total impurities.
2.3 U.S. Government Documents:
4.1.3 Stoichiometry—The oxygen-to-uranium ratio of sin-
Code of Federal Regulations (Latest Edition), Title 10, Part tered fuel pellets shall be within the range from 1.99 to 2.02.
50Domestic Licensing of Production and Utilization Fa-
4.1.4 Moisture Content—The moisture content limit is in-
cilities
cluded in the total hydrogen limit (see Table 1).
Code of Federal Regulations, Title 10, Part 70Domestic
4 4.2 Nuclear Requirements:
Licensing of Special Nuclear Material
4.2.1 Isotopic Content:
Code of Federal Regulations, Title 10, Part 71Packaging
4.2.1.1 For UO pellets with an isotopic content of U
and Transportation of Radioactive Material
below 5%, the isotopic limits of Specification C996 shall
Code of Federal Regulations, Title 49, Part 173General
apply,unlessotherwiseagreeduponbetweenthebuyerandthe
Requirements for Shipments and Packaging
seller. If the U content is greater than the Enriched Com-
Regulatory Guide NUREG 1.126AnAcceptable Model and
mercial Grade UF requirements, the isotopic analysis require-
Related Statistical Methods for the Analysis of Fuel 6
ments of Specification C996 shall apply. The specific isotopic
Densification, Rev. 1 March 1978
measurements required by Specification C996 may be waived,
3. Terminology provided that the seller can demonstrate compliance with
Specification C996, for instance, through the seller’s quality
3.1 Definitions—For definitions of terms, refer to Terminol-
assurance records.
ogy C859.
4.2.1.2 For UO pellets not having an assay in the range set
forth in 4.2.1.1, the isotopic requirements shall be as agreed
TABLE 1 Impurity Elements and Maximum Concentration Limits
upon between the buyer and the seller.
Maximum Concentration
Element 4.2.2 Equivalent Boron Content—For light water reactor
Limit (µg/g U)
use, the total equivalent boron content (EBC) shall not exceed
Aluminum (Al) 250
4.0 µg/g on a U basis. The total EBC is the sum of the
Carbon (C) 100
Calcium (Ca) + magnesium (Mg) 200
individualEBCvalues.ForpurposeofEBCcalculationB,Gd,
Chlorine (Cl) 25
Eu, Dy, Sm, and Cd shall be included in addition to elements
Chromium (Cr) 250
Cobalt (Co) 100 listed in Table 1. The method of performing the calculation
Fluorine (F) 15
shallbeasindicatedinPracticeC1233.Forfastreactoruse,the
Hydrogen (H, total from all sources) 1.3
above limitation on EBC does not apply.
Iron (Fe) 500
Nickel (Ni) 250
4.3 Physical Characteristics:
Nitrogen (N) 75
Silicon (Si) 500 4.3.1 Dimensions—The dimensions of the pellet and their
Thorium (Th) 10
tolerances shall be specified by the buyer. These shall include
diameter, length, perpendicularity, and, as agreed upon be-
tweenthebuyerandseller,otherparametersincludingend-face
4. Technical Requirements
configuration and surface finish. The diameter can be deter-
minedbythree(3)multiple-pointmeasurementsataminimum:
4.1 Chemical Requirements—Allchemicalanalysesshallbe
middle and the two extremities of the pellet. Length measure-
performedonportionsoftherepresentativesamplepreparedin
ments shall be made between the furthest extremities of the
accordance with Section 6.Analytical chemistry methods used
pellet on the land area.
shall be as stated in Test Methods C696 (latest edition) or
4.3.2 Pellet Density—The density and tolerance of sintered
demonstrated equivalent as mutually agreed upon between the
pellets shall be as specified by the buyer. The theoretical
seller and the buyer.
density (TD) for UO shall be considered as 10.96 g/cm .
4.1.1 Uranium Content—TheUcontentshallbeaminimum
Density measurements shall be made by the method stated in
of87.7 weight% ona
...