Sunday, June 6, 2010

Replies to comments

Meredith asked: "In metals at high temp, you can expect the dpa-induced structural problems to anneal out, at least to some extent. Will they anneal out in the non-oxide ceramics?"

Ceramics aren't my field of expertise, but I believe the answer is "yes." SiC, graphite, and related materials are being examined for high-DPA applications.

Anonymous asked: "Isn't one of the advantages of the MSR designs the fact that they are not 'fast' reactors but thermal ones, which hence implies that the neutrons are themselves slower when they hit the containment material than their fast reactor cousins?"

Different reactor designs will suffer more or less neutron damage due to their neutron energy, but even a "thermal" reactor has a fair number of fast neutrons flying about.

1 comment:

  1. Currently, two composites types are being developed for incore application: carbon fiber carbon composite (CFC), and silicon carbide fiber composite (SiC/SiC.) Irradiation effects studies have been carried out over the past few decades yielding radiation-tolerant CFC’s and a composite of SiC/SiC with no apparent degradation in mechanical properties to very high neutron exposure. While CFC's can be engineered with significantly higher thermal conductivity, and a slight advantage in manufacturability than SiC/SiC, they do have a neutron irradiation-limited lifetime. The SiC composite, while possessing lower thermal conductivity (especially following irradiation), appears to have mechanical properties insensitive to irradiation.

    As I'm sure you are all aware, material engineering is a largely a mater of compromise as one tries to balance cost and various aspects of performance. It may be that materials like ceramics will be the best choice even if they do not have superior qualities to exotic alloys simply because of cost. A shorter service life may be acceptable if it permits higher operating temperatures or it may be that ceramic reactor pots (for MSR types) will be easier to dispose of when they are time-x.

    All of these factors will be weighted during the materials selection stage of the process, and neutron radiation resistance will just be one of the parameters considered.

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It's been pointed out to me that using a cartoon character's screen name while disabling anonymous comments would be a pot//kettle//black situation. So let's try the "anonymous allowed, all moderated" paradigm. Please be aware that moderation will occur at most once per day, every other day might be more likely. Please be patient. (I also notice some FireFox related comment-leaving problems; perhaps Google is getting angry at Mozilla users?)