Gallium reactors

snorkack

How useful are reactors cooled by gallium alloys?

Ga has cross section for neutrons of 2,9 barns. Somewhat high - but K has 2,1 barns, and NaK is mostly (76 %) K.

Pure Ga melts under +30 Celsius. The reactor may freeze - but it is much easier to melt than Pb/Bi eutectic (+125 Celsius).

Ga melting point can be further lowered by alloying. While In, Cd and Hg are neutron poisons, the other low melting metals are reasonable - Pb, Bi, also Sn (0,62 barns) and Zn (1,1 barns).

Would a reactor with Ga-Sn coolant be convenient to handle? Ga/Sn melt is nowhere as reactive as Na/K melt, and also not poisonous until irradiated....

Astronuc

Gallium's price has been on the order of $650/kg but could be has high as $750 to $970/kg as compared to sodium at around $150/kg.

In a reactor, liquid metal embrittlement with fuel and structural materials is an issue. Liquid metals are usually used for fast reactors.

snorkack

Clementine managed to work with mercury coolant - despite its huge neutron cross-section.

How does the quoted price of gallium compare with the price of highly enriched uranium 235, or plutonium 239? These are presumably priceless because no one wants to sell them....

Astronuc

It depends on the enrichment. One could develop a price based on the quantity of natural U (0.7%) needed to provide a particular enrichment and the cost of the separative work unit (SWU) to enrich it. Cost of Pu239 depends on cost of starting material (U), irradiation, and separation.