22.08.2015   Comprehensive nuclear materials

. Radiation-Induced Changes in Dimension

One of the most challenging engineering conse­quences of neutron irradiation is the development of dimensional instability, whereby a structural com­ponent can shrink or grow in volume and where it can be distorted in shape, often with both processes occurring at the same time. There are two major categories of such changes: conservative of volume and nonconservative of volume. A distinction can also be made between processes that distribute the resulting strains isotropically or anisotropically. Additionally, a further distinction can be made con­cerning whether the process to the first-order is stress-driven or not, or whether it is stress-sensitive to the second-order.

Depending on the crystal structure there are a variety of such distortion processes, some more prominent than others in a given crystal system. For austenitic stainless steels the phenomenon of radiation-induced growth (volume-conservative, an­isotropic distribution ofstrains in the absence ofstress) is not an issue, whereas for hexagonal close packed alloys based on zirconium and rhenium growth is often a dominant process.9,106 Austenitic steels also

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Swelling (%) Swelling (%)

Figure 39 (Left) Correlation between ductility loss and swelling in several heats of irradiated Ti-modified steels in PHENIX. At ~5% swelling the total and uniform elongations converge and by ~10% no ductility remains. (Right) Correlation of swelling and embrittlement in Charpy impact tests of cold-worked Ti-modified 316 steel irradiated in PHENIX.

Reproduced from Fissolo, A.; Cauvin, R.; Hugot, J. P. Levy, V. In Effects of Radiation on Materials: 14th International Symposium; STP 1046; 1990; Vol. II; pp 700-713.

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Figure 40 Failure during mounting in a vise of severely void-embrittled 316 stainless steel creep tube irradiated in the EBR-II fast reactor to 130 dpa at ~400 °C with a hoop stress of 276 MPa. Reproduced from Porter, D. L.;

Garner, F. A. J. Nucl. Mater. 1988, 159, 114-121. Swelling at the initial failure point was ~14%.

 

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Figure 41 Void-induced embrittlement of an annealed 304 steel EBR-II assembly duct after ~54 dpa at ~400°C. Reproduced from Flinn, J. E.; Krajcinovic, D.; Phipps, R. D.; Franklin, D. G.; Miller, S. C. Evaluation of Ex-Reactor Loading Event on High-fluence EBR-II Control-rod Thimble 5E3, ANL/EBR-068, February 1973. The duct broke during routine handling in the hot cell.

 

are not very prone to significant transmutation — induced changes in lattice parameter as sometimes observed in alloys based on rhenium and vana­dium.106107 See also Chapter 4.01, Radiation Effects in Zirconium Alloys.

Stainless steels experience three general cate­gories of radiation-induced strain processes. These are precipitation-related strains, void swelling, and
irradiation creep. In general, these three processes are not fully independent but are interrelated and often synergistic.