Uranium Market - The SWU (separative Work Unit)

The SWU (separative Work Unit)

Separative Work Unit (SWU) is a complex unit which is a function of the amount of uranium processed and the degree to which it is enriched, i.e. the extent of increase in the concentration of the 235U isotope relative to the remainder. Separative work is expressed in SWUs, kg SW, or kg UTA (from the German Urantrennarbeit )

The unit is strictly: Kilogram Separative Work Unit, and it measures the quantity of separative work (indicative of energy used in enrichment) when feed, tails and product quantities are expressed in kilograms.

The number of Separative Work Units provided by an enrichment facility is directly related to the amount of energy that the facility consumes. Modern gaseous diffusion plants typically require 2,400 to 2,500 kilowatt-hours of electricity per SWU while gas centrifuge plants require just 50 to 60 kilowatt-hours of electricity per SWU.

Example:

A large nuclear power station with a net electrical capacity of 1,300 MW requires about 25,000 kg of enriched uranium annually with a 235U concentration of 3.75%. This quantity is produced from about 210,000 kg of raw uranium using about 120,000 SWU. An enrichment plant with a capacity of 1,000 kSWU/year is, therefore, able to enrich the uranium needed to fuel about eight large nuclear power stations

Cost Issues

In addition to the Separative Work Units provided by an enrichment facility, the other important parameter that must be considered is the mass of raw uranium that is needed in to order to yield a desired mass of enriched uranium. As with the number of SWUs, the amount of feed material required will also depend on the level of enrichment desired and upon the amount of 235U that ends up in the depleted uranium. However, unlike the number of SWUs required during enrichment which increases with decreasing levels of 235U in the depleted stream, the amount of raw uranium needed will decrease with decreasing levels of 235U that end up in the tails.

Example:

In the production of enriched uranium for use in a light water reactor it is typical for the enriched stream to contain 3.6% 235U (as compared to 0.7% in raw uranium) while the depleted stream contains 0.2% to 0.3% 235U. In order to produce one kilogram of this enriched uranium it would require approximately 8 kilograms of raw uranium and 4.5 SWU if the tails stream was allowed to have 0.3% 235U. On the other hand, if the depleted stream had only 0.2% 235U, then it would require just 6.7 kilograms of raw uranium, but nearly 5.7 SWU of enrichment. Because the amount of raw uranium required and the number of SWUs required during enrichment change in opposite directions, if raw uranium is cheap and enrichment services are more expensive, then the operators will typically choose to allow more 235U to be left in the tails stream whereas if raw uranium is more expensive and enrichment is less so, then they would choose the opposite.

• Uranium Enrichment Calculator designed by: the WISE Uranium Project