Development of methods for generating design allowable limits for the HTTR High-Temperature Structural Design Code

This report gives methods for generating the design allowable limits for the High-Temperature Structural Design Code for the Class 1 Components of the HTTR and their values generated. Structural materials involved are the HTTR specification of a normalized and tempered (NT) material of 2 1/4 Cr-1Mo steel, a nickel-base helium-gas corrosion-resistant and heat-resistant superalloy Hastelloy XR, and two kinds of austenitic stainless steels SUS321TB and SUS316. The design allowable limits for the 2 1/4Cr-1Mo steel NT-material HTTR-spec. and the austenitic stainless steels are reproduced from the Design Allowable Limits for the Elevated Temperature Structural Design Guide for the Prototype Fast Breeder Reactor 'Monju' (FBR Code), through examining the applicability of the these values for 2 1/4Cr-1Mo steel NT-material to its HTTR-specification in which contents of some impurities are lowered so as to maintain sufficient fracture toughness. For Hastelloy XR, the material properties are reviewed at first and then the principles are established for generating the design allowable limits, because this material is not involved in the FBR Code. Special considerations were taken into dynamic recrystallization which is developed at high temperatures above about 850degC and in a high strain rate range, statistical treatment method of creep rupture life data, and a method for developing a creep equation (i.e., a correlation of creep data from uniaxial creep tests). An evaluation guideline for helium environmental effects is also specified. The design allowable limits for Hastelloy XR are generated from available material data with using a computer code 'Data MAC-HTTR' for managing and analyzing material properties data. (author)