Standard Guide for Application of ASTM Evaluated Cross Section Data File
1Key Takeaways
1.1 This guide covers the establishment and use of an ASTM evaluated nuclear data cross section and uncertainty file for analysis of single or multiple sensor measurements in neutron fields related to light water reactor LWR-Pressure Vessel Surveillance (PVS). These fields include inand exvessel surveillance positions …
2Expert Interpretation
The ASTM E1018-20ε1 standard provides guidance on the application of nuclear cross-section data in light water reactor pressure vessel monitoring, covering the use specifications, data verification methods and uncertainty analysis requirements of the International Reactor Dosimetry and Fusion File (IRDFF) to ensure the accuracy and consistency of neutron dose measurements.
Standard Overview and Technical Background
The ASTM E1018-20ε1 standard provides important guidance on the application of neutron cross section data in the nuclear industry, particularly for light water reactor (LWR) pressure vessel monitoring (PVS) scenarios. This standard stems from the urgent need for nuclear safety regulation and aims to standardize the application of nuclear cross section data in reactor dosimetry.
The technical evolution of the standard has gone through a process from the initial ENDF/B library to a dedicated dosimetry file. With the development of nuclear energy technology, especially the need for safety assessment of long-term operation of light water reactors, the traditional ENDF/B library has shown limitations in dosimetry applications, prompting the International Atomic Energy Agency (IAEA) to coordinate the development of the International Reactor Dosimetry and Fusion File (IRDFF).
Interpretation of core content
Scope of application and technical requirements
This standard is mainly applicable to the neutron field analysis in the monitoring of light water reactor pressure vessels, including:
| Application field | Technical requirements | Data accuracy requirements |
|---|---|---|
| Monitoring location of in-service power reactors | Multi-sensor measurement analysis | Relative uncertainty<5% |
| Benchmark neutron field | Cross-section data verification | Energy spectrum range 10keV-20MeV |
| Reactor test area | Self-consistency verification | Covariance Matrix Completeness |
Nuclear Cross-Section Data File Creation Requirements
The standard specifies the requirements for creating cross-section files recommended by ASTM:
Data Format Specifications: Both the ENDF-6 format and the 640-group SAND-II energy group structure are supported. The multi-group data format is the preferred format due to its compatibility with the facility neutron spectrum representation.
Evaluation and Verification Requirements: All cross-section data must be verified through dosimetry measurements in a reference field to eliminate significant bias. Modifications to IRDFF and ENDF/B files must be consistent with the uncertainty specifications for differential data using the least squares method.
The key role of the IRDFF library
The International Reactor Dosimetry and Fusion File (IRDFF) version 1.05 is the core data source recommended by this standard. Its technical features include:
The IRDFF library contains recommended cross-section data for 58 dose reactions, covering the energy range from thermal neutrons to 20MeV. The library was developed through international expert collaboration, integrating the results of nuclear data assessments from various countries and supplemented by a set of reactions evaluated by an international group of experts.
The self-consistency of the data in the library has been verified in a light water reactor environment, which is critical for pressure vessel monitoring applications where only very limited dose data are available.
Sources of Key Dose Response Cross Sections
| Reaction Types | Representative Reactions | Data Sources | Application Areas |
|---|---|---|---|
| Activation Reactions | 55Mn(n,γ)56Mn | IRDFF-1.05 | Radioactivity Monitoring |
| Fission Reactions | 235U(n,f)FP | RRDF | Fission Chamber Monitoring |
| Helium Production Reactions | 10B(n,α)7Li | CENDL-3 | Helium Accumulation Monitoring |
| Damage Function | Fe(n,X)dpa | ENDF/B-VI.1 | Material Damage Assessment |
Uncertainty Analysis and Covariance Matrix
The standard places strict requirements on uncertainty documentation:
Uncertainties must be specified for all cross-sectional data (except for damage functions and cover cross-sections used for normalization). Because these data are often highly correlated, uncertainties must include energy-related correlations and must therefore be specified in the form of a covariance matrix.
The covariance matrix must be directly associated with the method for determining the specified cross-section and supports both the ENDF-6 file format and a multi-group table representation. During the validation process, benchmarking is expected to provide a major contribution to establishing realistic uncertainty estimates and correlations between cross sections.
Implementation Recommendations and Best Practices
Data Processing Requirements
Data processing requirements are kept to a minimum through format specifications. Codes such as NJOY-2012 and Mieke codes are required to process cross section data in ENDF-6 format, as examples of available processing codes.
Data specified in tabular multigroup format should be directly usable in spectral adjustment codes. Cross section uncertainty files should be used as an input to determine the overall uncertainty of processed quantities (e.g., fluence or dpa).
Data Access and Availability
ASTM files should be made available to all users. The primary distribution channels for ENDF-6 format individual cross-section data are through four nuclear data centers:
- Brookhaven National Laboratory National Nuclear Data Center, USA
- Obninsk Institute of Physics and Power Engineering Nuclear Data Center, Russia
- Saclay NEA Data Center, France
- International Atomic Energy Agency Nuclear Data Section, Vienna
In addition, the Radiation Safety Information Computing Center (RSICC) operated by Oak Ridge National Laboratory serves as a backup distribution center for multi-cluster cross-sections.
Technical Challenges and Development Trends
The main technical challenges currently faced include:
Covered Cross-Section Processing Methods: Methods for processing the additional uncertainties introduced when using overlays to generate modified sensor response functions have not yet been fully developed by the industry. This standard only addresses the selection of nuclear data to support the use of overlays and the characterization of their uncertainties.
Updates to relevant nuclear data: Updates to relevant data such as isotope abundance, gamma branching ratio, fission yield, and half-life usually require revalidation of cross-section data, which increases the complexity of data maintenance.
Future development trends include higher-precision cross-section measurement technology, improved uncertainty quantification methods, and the construction of a more complete verification experiment database.
Conclusion
The ASTM E1018-20ε1 standard provides important technical specifications for the nuclear industry. By applying standardized nuclear cross-section data, it ensures the accuracy and comparability of light water reactor pressure vessel monitoring results. As a recommended data source, the IRDFF library represents the current international consensus on dose cross-section data. Its continuous updating and maintenance are crucial to nuclear energy safety.
When implementing this standard, users should pay special attention to the accuracy of the data source, the completeness of the uncertainty analysis, and the coordinated use with other relevant standards to ensure the reliability and validity of the dose analysis results.