22.08.2015   Comprehensive nuclear materials

Creep Models and Theories

It is unfortunate that a validated set of graphite irra­diation creep data covering the range oftemperatures and fluences of interest for power producing reactors, as well as radiolytic oxidation in the case of carbon dioxide-cooled reactors, does not exist. In addition, there are no microstructural studies available to give an insight into the mechanism involved in irradiation creep in graphite. This has lead to much speculation and several model proposals.

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Figure 59 Synergy between changes in coefficient of thermal expansion in irradiation creep specimens and change in unirradiated, stressed graphite. (a) additional change in CTE as a function of creep strain and (b) change in CTE in unirradiated stressed samples.

 

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0 8 — SM1-24 (axial), irradiation temperature = 850-9200C

Подпись: (D D) C 03 J= О 0.0MPa (Capsule 76M-18A) О 0.0MPa (Capsule 77M-10A) 04 _ ■ 3.3MPa (Capsule 76M-18A) □ 3.3MPa (Capsule 77M-10A)

4.5MPa (Capsule 76M-18A) Д 4.5MPa (Capsule 77M-10A) 6.5MPa (Capsule 76M-18A) О 6.5MPa (Capsule 77M-10A)

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Fluence (1024 ncm-2, E > 29fJ)

Figure 60 Changes in Young’s modulus in tensile crept and uncrept specimens. Reproduced from Oku, T.; Fujisaki, K.; Eto, M. J. Nucl. Mater. 1988, 152(2-3), 225-234.

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(a) Compressive stress (MNm )

 

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(b) Compressive creep strain (%)

Figure 61 Changes in Young’s modulus in irradiated-creep experiments. (a) changes to Young’s modulus as a function of stress and fast neutron fluence and (b) normalized Young’s modulus as a function of creep strain. Modified from Brocklehurst, J. E.; Kelly, B. T. A review of irradiation induced creep in graphite under CAGR conditions; UKAEA, ND-R-1406(S); 1989.