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Control Rod Materials

  1. Mar 9, 2015 #1
    Hi Masters.

    I'm searching for control rod materials and so far I got the ones listed below. I know that the material selected for control rods should have a good absorption cross section for neutrons and have a long lifetime as an absorber. I just wonder the materials and compounds used in control rods other than listed below.

    - Boron ( as B-10 and B-11)
    - Boron carbide (B4C)
    - Boron-stainless steel (B-SS)
    - Cadmium (Cd-113)
    - Silver (Ag-105, Ag-107)
    - Hafnium (Hf-174, Hf-176, Hf-177, Hf-178, Hf-179, Hf-180)
    - HfB2
    - Indium (In-115)
    - Europium
    - Stellite (cobalt-chromium alloys)
    - Gd2O3 (Gadolinium)
    - Eu2O3 (Europium oxide)
    - Dysprosium titanate (Dy2TiO5 - Is this correct ? Some sources says it is Dy2TiO7 and some other says it is Dy2TiO9)

    Please inform me if any of the listed materials are wrong or if there any other materials.

    I suppose there should be more compounds but I can just arrange the ones listed.

    Also, if anyone knows please indicates the percentage of the compounds. For an example, if I am correct, there exist
    - Ag-In-Cd as 80% Ag, 15% In, and 5% Cd

  2. jcsd
  3. Mar 9, 2015 #2


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    Here is some background - http://www-pub.iaea.org/MTCD/publications/PDF/te_1132_prn.pdf
    I used to work with some of the authors of some of the papers.

    Ag-In-Cd (80-15-5) is pretty common in PWRs, but some do use B4C, which is enriched in 10B. Russians have experience with Dy2TiO5. Hf was tried in the US briefly, but the Hf absorbed hydrogen and swelled, so Hf-RCCAs were removed from service.

    BWR control elements use B4C enriched in 10B and Hf.

    Gd and Eu are not used in commercial control elements. They are rather expensive, and boron is cheaper.

    The structural materials as mostly high purity SS 304L (with 308 endplugs) and 316L, although some suppliers have used Inconel 625 or SS 321, 347, 348.

    In PWRs, the absorbers have to be compatible with hydrogen.
    Last edited: Mar 17, 2015
  4. Mar 10, 2015 #3
    Thanks a lot Dear Astronuc.

    From the document you shared, I reached the following documents IAEA-TECDOS-813 and IAEA-TECDOC-884.

    Do you recommend those too ?
  5. Mar 10, 2015 #4


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    TECDOC 813 and 884 are older, but it's good background material.
  6. Mar 11, 2015 #5
    Briefly looking at the list I noticed that you didn't include cobalt. I know that it has been used in CANDU reactors (in fact the Co-60 that is produced can actually be sold). A quick google turned this wiki page up.

  7. Mar 13, 2015 #6
    Gd does get used in BWR fuel assemblies as a burnable poison. This has allowed for the elimination of shaper rods in the core (control rods inserted purely to manage axial shape) and can extend cycle length as well as help manage thermal limits.
  8. Mar 14, 2015 #7


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    In the case of Hope Creek, some fuel rods in an assembly are replaced by special target rods containing cobalt, and there are a small number of assemblies in a given reload. As for control rods, one would not normally use Co-59.

    Stellite materials were used in some nuclear plants, but were removed because the cobalt became activated, and Co-60 in an alloy has higher disposal costs. In addition, Co-60 could leach into the coolant and cause an increase in the radiation field, so low-Co materials were developed to replace Co-bearing alloys.

    Gadolinia is a 'burnable' absorber, meaning that its effect is reduced with irradiation. The odd-number isotopes, Gd-155 and Gd-157, are transmuted to Gd-156 and Gd-158, respectively, and the even-number isotopes have much lower absorption cross-sections. Gadolinia is the absorber of choice in BWRs, and some PWRs, but many PWR fuel assemblies use ZrB2. Erbia has been used as well, since it has lower residual, but it has largely been replaced.
  9. Mar 17, 2015 #8
    Hey master,

    So I made a basic final list as below. Please inform me if I missed any.

  10. Mar 22, 2015 #9


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    While most elements on the list are strong neutron absorbers, most are not used in control rods.

    Silver-Indium-Cadmium (AIC) is commonly used in PWRs, but some B4C is used in so-called hybrid designs. Hf was tried, but swelling due to hydrogen absorption made it's application in LWRs unfeasible.

    B4C and Hf are used in BWR control blades. Hf is typically used on the edges and in the tips of the active zone.

    Boron is relatively inexpensive compared to rare earth elements.

    Dysprosia titanate has been used by Russians in their VVER control rods. I don't know how widespread the application though.

    Gd and Er in the form of gadolinia and erbia, respectively, as used as 'burnable absorbers' in the fuel. ZrB2 is also used as burnable absorber in the fuel of a particular supplier. Also, burnable poison assemblies containing boron-bearing pyrex or alumina-B4C can be used in guide tube locations of fuel assemblies (in uncontrolled assemblies, i.e., assemblies not located under control rods), or even in place of fuel rods.

    Other materials, e.g., stainless steel and Inconels, are used as 'structural' materials, but do not play a significant part in absorbing neutrons.
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