Future US enrichment needs require clarification: GAO

19 February 2018

The US Department of Energy's National Nuclear Security Administration (NNSA) has extended its supply of low-enriched uranium (LEU) for national security needs for at least the next two decades but should clarify its longer term enrichment needs, the US Government Accountability Office (GAO) has found.

 ACR 100 centrifuges at the American Centrifuge demonstration plant (Image: Centrus)

The NNSA is responsible for securing so-called unobligated LEU needed for purposes including the production of the tritium used in nuclear weapons. Tritium has a relatively short half-life of 12.3 years and decays at a rate of about 5.5% per year, so must be periodically replenished to maintain the designed capability of the weapons, the GAO notes. Some tritium may be recycled from dismantled weapons, but the inventory must also be replenished through the production of new tritium.

At present, NNSA produces tritium through the use of one of the Tennessee Valley Authority's electricity-producing nuclear reactors fuelled with unobligated LEU. The uranium, technology and equipment used to produce such LEU must therefore be of US origin.

America has had no uranium enrichment capability to meet such military needs since the 2013 closure of the Paducah enrichment plant, at which time the NNSA had projected that its supply would run out in 2027.

The NNSA has now taken or plans to take four actions to extend its inventories of unobligated LEU to 2038 or 2041, the GAO found. It has reviewed those actions, two of which involve preserving supplies of LEU and two which involve diluting HEU with lower enriched forms of uranium. Actual costs and schedules for those actions taken to date generally align with estimates, the GAO found.

However, the GAO's assessment found the NNSA had not "clearly defined" longer term enriched uranium needs. It also found that NNSA's preliminary cost estimates for building a new enrichment capability were "not reliable".

The NNSA has identified two uranium enrichment technologies as the most feasible options to supply unobligated LEU for tritium production: the AC100 centrifuge, which has been demonstrated by Centrus at the American Centrifuge Plant in Ohio, and a "small centrifuge", the first prototype of which has now been built at the Oak Ridge National Laboratory. However, both of these options face challenges to deployment, the GAO found.

It questioned the NNSA's preference to build a new uranium enrichment capability without including other technology options for analysis. The GAO said the scope of the mission need statement underpinning the analysis of alternatives was "unclear" and also inconsistent with the requirement that the mission need should be "independent of a particular solution and not be defined by a technological solution or physical end-item". It also found the scope of the NNSA's cost estimates to be limited in that they do not reflect the full cost of building a uranium enrichment facility that could meet a range of enriched uranium needs. Cost-estimating best practices indicate that the scope of preliminary cost estimates should reflect full life-cycle costs, the GAO said.

The GAO recommended that the NNSA revise the scope of its mission need to clarify its long-term requirements. It should then ensure that its cost estimates for "whichever options it considers going forward" are aligned with the revised statement while developing estimates consistent with best practices.

Researched and written
by World Nuclear News