Control Rod Materials: List & Compounds Explained

[parazit]

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

Best.

 

[Astronuc]

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.

 

[parazit]

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 it 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.

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 ?

 

[Astronuc]

TECDOC 813 and 884 are older, but it's good background material.

 

[Hologram0110]

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.

The CANDU reactors can be used to activate 59Co, by substituting the stainless steel control rods with cobalt rods.[9] In the United States, it is now being produced in a BWR at Hope Creek Nuclear Generating Station. The cobalt targets are substituted here for a small number of fuel assemblies.[10]

 

[Hiddencamper]

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.

 

[Astronuc]

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.

 

[parazit]

Hey master,

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

-B
-Eu
-Cd
-Sm
-Hf
-I
-Ag
-Co
-Dy
-Gd
-Er
-ZrB₂
-TiB₂
-HfB₂
-Dy₂TiO₅
-Gd₂Ti₂O₇
-HfC
-B₄C
-Hafaloy-M/-N/-MN
-Gd₂O₃
-HfO₂
-Eu₂O₃
-Dy₂O₃
-Sm₂O₃
-Er₂O₃
-Eu₂TiO₅
-Dy₂O₃HfO₂

 

[Astronuc]

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.