Irradiation creep

Graphite will creep imder neutron irradiation and stress at temperatures where thermal creep is normally negligible. The phenomenon of irradiation creep has been widely studied because of its significance to the operation of graphite moderated fission reactors. Indeed, if irradiation induced stresses in graphite moderators could not relax via radiation creep, rapid core disintegration would result. The observed creep strain has traditionally been separated into a primary reversible component ( ,) and a secondary irreversible component (Ej), both proportional to stress and to the appropriate unirradiated elastic compliance (inverse modulus) [69]. The total irradiation-induced creep strain (ej is thus ... 

Kelly, B.T. and Burchell, T.D., The analysis of irradiation creep experiments on nuclear reactor graphites. Carbon, 1994, 32, 119 125. 

Due to these interactions, the macroscopic swelling results in crystal lattice, which in turn affects the lattice parameter. The swelling may be associated with plastic flow (irradiation creep) that occurs in response to the ion implantation stress (Primak 1976, Volkert 1991, Brenier 1993). Expansion of lattice volumes in association with macroscopic swelling is already evidenced from the XRD results that the lattice parameter increases with irradiation fluence. However, phase transition does not occur for the present irradiation dosages investigated in the present study. 

Babovich et al. [63] studied creep and stress relaxation of low-density polyethylene film cross-linked with beta radiation as a function of irradiation dose. They showed that both storage modulus and alpha relaxation were influenced by irradiation. Creep results showed an increase in the creep strain when the polymer was irradiated with a dose below 4 Mrad, in comparison with a nonirradiated low-density polyethylene. This increase corresponded to a disorientation in the amorphous phase, which took place as a result of the film heating during irradiation. 

In Paper 12 it is Implied that Irradiation creep may limit the life of some of the Douglas Point pressure tubes to about 15 years. Could the Author explain whether this estimate is based on a certain limiting creep strain, and if so how has this been chosen ... 

Describe the main factors which hmit components hfetime and underlying phenomena interaction with coolant high temperatures radiation effects irradiation creep . .. 

Uehira, A., et al., 1999. Evaluation of Swelling and Irradiation Creep Properties of High Strength Ferritic/Martensitic Steel (PNC-fms). JNC report No.TN9400 99—022. Japan Nuclear Cycle Development Institute, Iharaki (Japan) (in Japanese). 

The dimensional stability under irradiation controlled by swelling and irradiation creep phenomena has to be as high as possible ... 

In the mechanism of corrosion due to MOX—clad interaction the fission product tellurium plays a dominant role, but several interdependent parameters can interfere among which on one hand, the critical pin bum-up rate (5—6%) having to be reached to generate the necessary chemical conditions to activate the Te-assisted corrosion and, on the other hand, the in-pile clad deformation via swelling and irradiation creep that produces an overheating of the fuel and thus an acceleration of the corrosion as shown in Fig. 8.3 [19]. 

Swelling and irradiation creep properties of reference austenitic steels... 

General insight about swelling, irradiation creep phenomena... 

In fire presence of a mechanical load, for example the fission gas pressure in a fuel pin or the sodium pressure inside a hexagonal can, another irradiation-induced type of deformation can occur the so-called irradiation creep phenomenon that is a macroscopic plastic strain occurring along the direction of the stress. Irradiation swelling and creep are correlated because both of these phenomena are exclusively related to the evolution toward the point defects of the sinks of the vacancies and interstitials generated in the atomic colhsion cascades produced inside the crystal lattice by the... 

When there is no primary stress, voids grow by absorption of vacancies, dislocations climb in aU directions and the material simply increases in volume with an isotropic volume expansion this is the swelling phenomenon. But in the presence of a stress and independently of thermal creep, a plastic creep strain is also observed under irradiation in the direction of the applied stress [29]. Several, but mainly two, irradiation creep mechanisms caused by dislocation motion are invoked depending on whether they involve pure dislocation climb, or slip controlled by climb... 

After several decades of research on the subject, plenty of work has been done on the understanding and modeling of swelling and irradiation creep, but the accurate inreactor behavior prediction of core stractures made of alloys as complex as the steels studied here is still far from fully satisfactory. 

A. MaiUard, et al.. Swelling and irradiation creep of neutron-irradiated 316Ti and 15-15Ti steels, in Effect of Radiation on Materials, 16th Conference, ASTM STP 1175, Aurora, 1994, pp. 824-837. 

E.A. Gamer, M.B. Toloczko, B.H. Sencer, Comparison of swelling and irradiation creep behavior of ECC-austenitic and BCC-ferritic/martensitic alloys at high neutron exposure, J. Nucl. Mater. 276 (2000) 123-142. 

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