Principle of Zr radiation resistance

[wulianlian]

I am a graduate student specialising in Nuclear Material. Could somebody give me some suggestions on the principle of high Radiation Resistance of Zirconium from the viewpoint of an expert?

Thanks!

 

[Astronuc]

I am a graduate student specialising in Nuclear Material. Could somebody give me some suggestions on the principle of high Radiation Resistance of Zirconium from the viewpoint of an expert?

Thanks!

What does one mean by high radiation resistance of zirconium?

Like any material, zirconium undergoes irradation damage in the lattice. Radiation produces dislocations in the microstructure, and under typical environmental conditions, zirconium allows experience creep and growth. Normally, Zr alloys are used at temperatures below about 350°C, or less than 0.3 of T_melt.

Zirconium is an hcp metal, so fabricated products have a texture, and the creep and growth are anisotropic. The texture can be tailored according to the mechanical and thermal treatments during manufacture.

Zirconium is typically used in an alloy form - often a dilute alloy contain varying levels of Sn, Nb, Fe, Cr, Ni, and a few others. Impurities are kept quite low - preferably in low ppm range.

One must also consider the irradiation environment. Most zirconium alloys are used in LWRs and CANDUs. The outer surface of cladding tubes (and endplugs) and the surfaces of spacer grids are exposed to high temperature water (and various cations = corrosion products). So waterside corrosion is a concern with respect to operating lifetime and safety. A consequence of corrosion in an aqueous environment is hydrogen pickup whereby some hydrogen from the reaction Zr + 2 H₂O => ZrO₂ + 2H₂ is absorbed into the Zr matrix where it forms ZrH_x, where x varies locally according to the bulk H content. Zr hydrides embrittle Zr alloys, so the corrosion (oxidation) and hydrogen pickup must be limited.


The best sources of information on Zr and alloy technology are found in the ASTM STPs containing the proceedings of Zirconium in the Nuclear Industry: --th International Symposium

 

[rmattila]

I think the question might be about the low neutron capture rate at Zr, compared to some other structural materials? This is due to the fact - which ultimately is based on the quantum-mechanical properties of Zr nuclei - that the neutron reaction cross sections of Zr nuclei are small, i.e. they do not capture neutrons passing-by as eagerly as e.g. iron tends to.

 

[wizwom]

Zircalloy is used because it enhances (or at least does not detract) from moderation. As you note, the very low absorption cross section is unusual; this is because Zr90 is on the N=50 stability line.