Breeding of ^242mAm in a Fast Reactor

There is growing interest in the use of ^242mAm as a nuclear fuel. Since the thermal absorption cross section of ^242mAm is very high (_a = 8950 b), the best way to obtain ^242mAm is by the capture of fast or epithermal neutrons in ²⁴¹Am. As a result, we have considered replacing the radial blanket of a fast reactor, which is usually depleted uranium, with ²⁴¹AmO₂.

We chose a 714-MW(thermal) MONJU reactor, and we replaced some of the radial blanket and the outer core assemblies with 10 676 kg of ²⁴¹AmO₂ fuel. We calculated the reactor core by using the MCNP Monte Carlo code.

The total amount of ^242mAm becomes stabilized after 16 yr, but the enrichment does not. In our calculation, ~7.2% enrichment is obtained after 18 yr. Obtaining higher enrichments might indicate that ^242mAm nuclear fuel can be used without further enrichment in many cases.

The results presented in this paper are considered an upper limit scenario. In particular the target ²⁴¹Am loading is not likely to be available soon, but ^242mAm production from lesser amounts is easily scaled down proportional to the actual mass irradiated.