iter structural design criteria for in-vessel components (sdc-ic)

ITER G 74 MA 8 01-05-28 W0.2
B3000 DESIGN RULES FOR SINGLE-LAYER
HOMOGENEOUS STRUCTURES
The applicable rules depend on whether or not the effects of thermal creep are negligible. If
they are negligible, then the low temperature design rules (IC 3100) apply. If not, hightemperature
rules (IC 3600) are applicable.
B 3020 Methods of analysis
Two alternative types of analyses are permissible - elastic and inelastic. Elastic analysis
should be the method of first choice because it is much simpler. Inelastic analysis is more
complex and likely to encounter problems with convergence, accuracy, etc. Furthermore, the
validation of inelastic analysis methods, particularly those dealing with cyclic stresses in a
nonlinear material, requires extensive theoretical and experimental work.
The criteria to be used in conjunction with elastic analyses are purposely selected to be fairly
conservative. Other methods of analysis could be pursued if elastic analysis fails to
demonstrate compliance with the criteria.
In general, inelastic analyses methods should be adopted if the criteria based on elastic
analyses cannot be satisfied. These might include inelastic finite element analysis and
simplified inelastic analysis methods. Guidelines for satisfying limits for inelastic analysis
using simplified inelastic analysis methods are given in this chapter. Other simplified
analysis methods could be used provided they can be justified and shown to yield
conservative results. In general, inelastic finite element analyses should be conducted if the
simplified inelastic analysis methods fail to satisfy the criteria for inelastic analysis.
In general, elastic analysis is used to satisfy stress limits while inelastic analysis is used to
satisfy strain limits. This is because elastic analysis cannot calculate plastic strains directly,
rendering stress (and the equivalent elastic strain) as its only useful measure. Also, when an
inelastic analysis is performed in the range of interest, significant plastic strains can occur
with only small variation of stress, rendering strain a more useful measure. In addition to the
stress and strain limits needed to ensure structural integrity, fast fracture limits, fatigue limits,
buckling limit, and deformation limits for functional adequacy must be satisfied for both
types of analyses.
Both elastic and inelastic analyses may be conducted on the assumption that the
displacements and strain are infinitesimal (geometric linearity). However, the analyst should
verify that this assumption is reasonable, particularly in the presence of irradiation-induced
swelling and creep, because the design rules do not explicitly put a limit on these strains.
Guidance for verifying this assumption is given in B 3021. If the strains and displacements
become significant, an elasto-visco-plastic analysis, including finite deformation effects may
be needed.
The design rules have been separated into two classes - low-temperature rules (thermal creep
effects can be neglected) and high-temperature rules (thermal creep effects cannot be
neglected). To determine which rules are applicable, a test for negligible thermal creep
(IC3050) has been included.
Strain rate or time-dependent strain (or creep) effects are considered explicitly in the hightemperature
rules, with or without irradiation-induced swelling and creep. Generally, strain-
SDC-IC, Appendix B. Guidelines for Analysis page 20