03/25/2013 - 13:19

Taking a fresh look

This Roundtable discussion has been very thought-provoking, and has encouraged me to look with new eyes at certain issues that surround the conversion of Kazakhstan's research reactors from highly enriched uranium (HEU) to low-enriched uranium (LEU).

The two active research reactors owned by Kazakhstan's National Nuclear Center (NNC) don't require refueling very often. Partly for this reason, Kazakhstan has never developed the capability to manufacture reactor fuel. If Kazakh research reactors convert to low-enriched uranium, this dependence on foreign fuel manufacturers seems likely to persist. At first glance, then, it would seem natural for the Russian firm that now manufactures fuel for the center's reactors to provide LEU fuel after conversion occurs.

But maybe this isn't as natural as it appears at first. This is because LEU fuel, by definition, is enriched to a lower level than HEU fuel; therefore, in order for low-enriched fuel to provide performance approximating that of highly enriched fuel, the density of the uranium in the fuel matrix must be increased. But this carries implications for fuel fabrication -- the stage of the process at which enriched fuel is converted into assemblies suitable for use in a reactor. That is, existing technologies for producing HEU fuel may not, even after they are modified for low-enriched uranium, be compatible with existing processes for LEU fuel fabrication. This implies that fabrication techniques for low-enriched fuel would probably have to be designed from scratch.

With conversion requiring so many changes, the firm that now manufactures fuel for Kazakh research reactors would appear to enjoy no advantage over competing firms, other than its history of working with Kazakhstan. Thus it seems appropriate for Kazakh authorities, if conversion goes forward, to make an objective assessment of the entire market for LEU fuel suppliers, and not confer any special status on the existing fuel supplier.

Another issue to which I have devoted thought as a result of this Roundtable is the exact manner in which conversion at Kazakh reactors might be carried out. The reactors owned by the NNC are in constant use for research projects, mostly involving nuclear energy (including fusion). The center has reached agreements with customers on work schedules through 2018, and proposals have come in for projects as far in the future as 2020. These programs, of course, play a significant role in the NNC's budget. Any reactor shutdown would be undesirable because the center would inevitably sustain financial losses during conversion and, even if conversion were very successful, building up the reactors' business again would take time.

Therefore, if conversion is to proceed, disruptions to research projects must be minimized. How could this be achieved? One option, if it proves technically possible, would be to replace HEU fuel with LEU fuel only gradually, during planned refuelings. The NNC might be able to implement this approach at its IVG reactor, where preliminary studies have shown that conversion would not require changes to some of the reactor's systems -- for example, to its control and protection systems. However, this approach would require Kazakh authorities and international partners such as Argonne National Laboratory and the US National Nuclear Security Administration to reach agreement on a conversion schedule. Also, these partners would need to make decisions about providing compensation for financial losses associated with conversion.

Not much point. My colleagues Pablo Cristini and Charles Piani have conducted a discussion on whether the widely accepted cut-off between low-enriched and highly enriched uranium should be maintained where it is, at 20 percent uranium 235, or whether it should be increased. To my mind, the existing cut-off is based on reasonable criteria. Any attempt to change the cut-off would have to win acceptance from the international nuclear community and various regulatory bodies -- but the chances of this happening are very low, so I see little point in calling for an increase. In my view, then, there is only one option for converting reactors to LEU, and that is to do so with the cut-off of 20 percent in mind.