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Some questions about neutron shielding in fast reactors

  1. Dec 27, 2013 #1
    I've been reading about fast reactor designs lately (not necessarily ones that have actually been built). A few articles I've come across < https://drive.google.com/folderview?id=0B-MNeRy61MgpTVExcUQ3T3ZWWG8&usp=sharing > discuss the possibility of building fast reactors, fueled with molten U, TRU chlorides diluted in Alkali/Alkaline chlorides (not including Li or Be), w/ and w/o a possible Th/U chloride/fluoride breeding blanket. It is claimed, in some of these articles, that fast molten salt reactors (FSMSRs) would not have the need for constant on line removal of fission products (other than more easily removed volatile and noble metal fission products), like thermal molten salt reactors would. One technical problem discussed in these articles that FSMSRs would face (at least for FSMSRs w/o a fertile blanket) is the need to shield the reactor vessel (RPV) from high fast neutron flux; it is suggested in at least one of the articles that ferritic/martensitic steels, which cannot stand the high temperatures of FSMSRs (or any molten salt reactor), coated w/ a nickle based alloy resistant to corrosion (but not fast neutron flux) at high temperatures, are perhaps the only suitable neutron shield for the RPV of a FSMSR w/o a fertile blanket, and that the neutron shields would need to be replaced, perhaps multiple times, during an FSMSR's life time. In one article, document titled: ANL-6792.pdf, w/ most references from 1960s or earlier, it is claimed that INOR (a nickle based alloy?) would be a suitable separator of the fissile core from the fertile blanket. If INOR (or some other nickle based high temperature alloy) were used only as a separator of the fertile blanket from the fissile core, and not as neutron shielding for the RPV, would the embrittlement of the material from the high neutron flux not be a problem (i.e. not prevent the material from chemically separating the fertile blanket from the fissile core)? Also, for a FSMSR w/ a molten salt breeding blanket, would the need for solid material to shield the RPV from fast neutrons be greatly reduced or perhaps eliminated?
  2. jcsd
  3. Dec 27, 2013 #2


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    Fast reactors would likely use a blanket/reflector, or perhaps a moderating shield in order to drop the fast flux in the vicinity of the core baffle/shroud. Liquid metal fast reactor fuel typically uses shrouds/channels on the individual fuel assemblies.

    The blanket/reflector fuel would be of low enrichment in order to mitigate the fission reactions, which is the source of fast flux.

    INOR alloys are apparently Ni-Mo-Cr alloys

    INOR-8 is Ni, 17% Mo, 7% Cr, 5% max Fe, with traces of Mn, Si, W, Co, Ti/Al, Cu

    http://web.ornl.gov/info/reports/1961/3445606041761.pdf [Broken]

    See page 183 of this text for other INOR compositions.

    An article on Chemical Considerations for the Selection of the Coolant for the Advanced High-Temperature Reactor

    https://inlportal.inl.gov/portal/server.pt/gateway/PTARGS_0_2_3310_277_2604_43/http%3B/inlpublisher%3B7087/publishedcontent/publish/communities/inl_gov/about_inl/gen_iv___technical_documents/chemical_considerations_4.pdf [Broken]
    Last edited by a moderator: May 6, 2017
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