Development of 2012 Edition of JSME Code for Design and Construction of Fast Reactors: (6) Design Margin Assessment for the New Materials to the Rules

Abstract

New 2012 edition of JSME code for design and construction of fast reactors (FRs code) was published by Japan society of mechanical engineers (JSME). Main topic of the current JSME FRs code 2012 edition is registration of the two new materials, 316FR and Mod.9Cr-1Mo steel. Besides the allowable strength values and material properties were standardized for the registration, the design margins for the new materials to the rules for the components and piping serviced at elevated temperature described in the JSME FRs code were assessed. To confirm the design margins, a series of the assessment program for the new materials to the conventional design rules was performed using the evaluation of the experimental data and finite element analysis. Namely, the design margin including the evaluation procedure of creep-fatigue damage, strain range and the others were assessed based on the background concept of the conventional JSME FRs code. Since a number of the evaluation procedures described in the JSME FRs code were investigated, a several topical assessments of these are reported in this paper. Besides the assessed results of the evaluation of the accumulated creep-fatigue damage and enhanced creep strain are reported, the assessments results of the design margin including the concept of the elastic follow-up originally applied in the JSME FRs code were covered in this paper. Through these assessments, the enough design margins for new materials to the rules were confirmed.

Creep–fatigue evaluation method for weld joints of Mod.9Cr–1Mo steel. Part I: Proposal of the evaluation method based on finite element analysis and uniaxial testing

“…3) The elastic follow-up factor in the uniaxial test specimen during the creep-fatigue test was estimated to be less than 3. Gauge length, L Tables Table 1 Chemical composition and heat treatment condition of the weld joint Table 2 Material properties assumed for the three materials used in the FEA Table A1 Cyclic stress-strain equation of Mod.9Cr-1Mo steel [3] Table A1 Fatigue life Table A2[2] = BM 1.1 × ε t in Table A1 Creep life Table A3[2] α R = 10 in Table A3 = BM…”

“…The material properties for the BM were obtained from the JSME FRs code [2] and its supporting documentation [3]. The material properties of the HAZ were experimentally obtained using uniaxial tests.…”

“…With respect to the creep damage calculations, in the JSME FRs code, the initial stress for creep relaxation in each cycle is defined by the strain range to estimate the fatigue damage; namely, the initial stress was determined from the tensile curve entered at estimated strain range, ε t , in equation (3). The tensile curve was applied to consider the cyclic softening characteristics of Mod.9Cr-1Mo steel [3]. A comparison of the creep damages estimated for the BM, HAZ, and WM calculated using the elastic follow-up method is shown in Fig.19.…”

“…In addition to standardizing the allowable strength values and material properties for the registration, the evaluation procedures for creep-fatigue damage and other rules were defined. Moreover, the margins for the Mod.9Cr-1Mo steel with respect to the rules were assessed to confirm that the magnitudes of the margins were appropriate for the new materials [3].…”

Creep-fatigue evaluation method for weld joint of Mod.9Cr-1Mo steel Part II: Plate bending test and proposal of a simplified evaluation method

“…In addition to standardizing the allowable strength values and material properties for registration, the creep-fatigue evaluation procedures and other rules for these new materials were defined. Moreover, the margins for the new materials with respect to the rules were assessed to confirm that the magnitudes of the margins are appropriate for the new materials [3].…”