United States Nuclear Regulatory Commission - Protecting People and the Environment

Review and Assessment of Codes and Procedures for HTGR Components (NUREG/CR-6816, ANL-02/36)

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Publication Information

Manuscript Completed: February 2003
Date Published: June 2003

Prepared by:
V.N. Shah, S. Majumdar, and K. Natesan
Argonne National Laboratory
9700 South Cass Avenue
Argonne, Illinois 60439

C.A. Greene, NRC Program Manager

Prepared for:
Division of Engineering Technology
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

NRC Job Code Y6537

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The report reviews and evaluates currently available national and international codes and procedures for use in the design of high-temperature gas-cooled reactors (HTGRs) including, but not limited to, the Gas Turbine-Modular Helium Reactor (GT-MHR) and the Pebble Bed Modular Reactor (PMBR). It includes an evaluation of the applicability of the codes, standards, and procedures to the materials that have been used or recommended for HTGRs, taking into account the HTGR operating temperature and environments. Seven codes and procedures, including five ASME Codes and Code Cases, one French Code (RCC-MR), and one British Procedure, were reviewed and evaluated. The ASME Codes and Code Cases included Section III, Subsection NB and Subsection NH; Code Cases N-499-1, N-201-4; and the draft Code Case for Alloy 617. Major findings of the evaluation are the following. (1) Most of the materials needed for HTGR are not included in the code cases. New code cases are needed for these materials. (2) The maximum temperature permitted by the codes and code cases for the materials acceptable for HTGR components is lower (760°C) than the maximum temperature (850°C or higher) that these components may experience in reactor service. The scope of the code and code cases needs to be expanded to include materials with allowable temperatures of ≥850°C. (3) The codes and code cases do not provide specific guidelines for environmental effects, especially the effect of impure helium, on the high-temperature behavior (e.g., creep and creep-fatigue) of the materials considered. The needed data on environmental effects should be collected or generated, if not available, so that the specific guidelines for these effects can be developed. Although the linear damage rule has been adopted by many design codes for estimating creep-fatigue damage, other potentially superior predictive models need to be evaluated and further developed for HTGR components operating under helium environment. The linear damage rule is not a good description of behavior if environmental effects (e.g., surface cracking) play an important role in high-temperature fatigue. Life predictive models for surface cracking have to be developed for this type of damage.

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