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

ITER G 74 MA 8 01-05-28 W0.2
from all sources should be limited to satisfy the deformation limits for functional adequacy
(IC 3040).
Since irradiation-induced swelling and creep are time-dependent phenomena, deformations
and stress intensities are necessarily time-dependent. Generally, irradiation-induced creep
changes the initial elastic stress distribution by relaxing secondary (e.g., thermal or
constrained swelling stress) or peak stresses with accumulating neutron fluence. The relaxed
part of the secondary and peak stresses will reappear with reversed sign when the reactor is
shut down and the incremental loading is applied in reverse. These changes in stress
distribution should be accounted for in satisfying fatigue, ratchet, and buckling limits.
Constitutive equations for irradiation-induced creep and swelling for the ITER structural
materials are given in the ITER MPH-IV 2 . These equations should be used in a finiteelement
elastic-creep analysis of the component. In some cases, simplified constitutive
equations for irradiation-induced swelling and creep may be used, provided they can be
shown to give conservative results. Two such cases where stresses evolve with time are
discussed - one for swelling-induced stress (B 3024.1.1.1) and the other for relaxation of
thermal stress by irradiation-induced creep (B 3024.1.1.2).
B 3024.1.1.1 Swelling induced stress value
If the negligible swelling test of B 3022 is not satisfied, then stresses due to constrained
irradiation-induced swelling (B 2513) have to be considered. For computing stresses due to
fluence-dependent swelling, the relaxing effects of irradiation-induced creep has to be taken
into account irrespective of whether the negligible irradiation-induced creep test of B 3101 is
satisfied or not, because otherwise the elastically calculated swelling stresses could become
unrealistically large. Swelling strains, when constrained, give rise to stresses that, in general,
increase with fluence and ultimately reach steady-state values that are the results of a
dynamic equilibrium between the elastically driven constrained swelling stresses and the
relaxation effects of irradiation-induced creep. Such constrained swelling stresses are
classified as secondary stresses (ICÊ2525). In general, solving for constrained swelling
stresses would require an incremental thermal-elastic-creep analysis of the component. For
some isotropic materials, such as type 316 austenitic stainless steel, the constitutive equations
for the fluence driven creep and swelling strains can be approximated by
and
e
ij creep
( ft)
= BT ( , f)
S
3
2
eij
swelling 1 1 V 1
= d = AT ( , f) d
( ft)
3 V ( ft) 3
where
V = the volume,
ij
ij ij
A(T, f) and B(T, f) are coefficients for irradiation-induced swelling and
creep equations (see A.MAT.4.2 and A.MAT.4.3 of appendix
A), with T as temperature and f as neutron flux,
SDC-IC, Appendix B. Guidelines for Analysis page 24
(1)
(2)