Uranium Enrichment Safeguards: Uranium Enrichment Concepts


This video will introduce and explain some basic uranium enrichment concepts. To successfully apply safeguards to a uranium
enrichment facility, we must first understand how enrichment works. Although there are many enrichment technologies,
and an even greater number of facility designs, there are some concepts that hold for all
enrichment facilities, no matter what technology is used to accomplish the enrichment process. The most basic component of the enrichment
process is the separation element. This is a basic element that receives a single
input stream at a certain level of enrichment and produces two outgoing streams: one that
is enriched relative to the input stream and another that is depleted relative to the input
stream. The input stream is referred to as the Feed. In the diagram we see here, it has a mass
flow rate of F kilograms per unit time. The enriched stream is referred to as the
Product, with a mass flow rate of P kilograms per unit time. The depleted stream is referred to as the
Waste (or Tails) with a mass flow rate of W kilograms per unit time. NF, NP and NW represent the uranium-235 fraction
in the Feed, Product, and Waste streams respectively. When we look at a single separation element,
we want to know how effective that separation element is at increasing the enrichment level
of the feed stream. This effectiveness is known as the separation
factor, and we calculate it by taking the ratio of the concentration of the product
stream to the concentration of the waste stream, as we see in this equation. Another key characteristic of our separation
element is its throughput. This is the mass flow rate at which the uranium
feed can be processed. It is the total mass of material passing through
the separation element per unit time. For most enrichment technologies, the throughput
of a single separation element is very small, meaning that one separation element is unable
to process large amounts of material at a time. When we see pictures of gas centrifuge enrichment
facilities, we almost always see large numbers of centrifuge elements interconnected into
complicated configurations. Separation elements are first arranged in
parallel, allowing material to be enriched simultaneously. This is done to increase the material throughput. These parallel arrangements of separation
elements are called stages. Stages are then connected in series to form
cascades. Basically, the enriched output stream of each stage
becomes the feed stream for the next stage in the series and so forth. As the stages increase the throughput of the
enrichment process, cascades allow for a multiplication of the separation factors of the separation
elements in order to achieve a higher product enrichment. One final concept we should discuss before
we go on to compare the different enrichment technologies is the separative work unit,
or SWU, which represents the electrical, mechanical, and chemical work that goes into the enrichment
process. The energy consumption of an enrichment facility
is usually given in kilowatt hours per SWU. Generally speaking, it takes approximately
100,000 SWU to produce enough low enriched uranium to fuel a light water reactor for
a year of operation. It takes around 200 SWU to produce a kg of
uranium enriched to 90% and approximately 5000 SWU to produce a significant quantity
of weapons-grade material. This means that an enrichment facility intended
for the peaceful uses of nuclear energy has more than enough capacity to produce materials
for nuclear weapons. This is part of why it is so critical to safeguard
commercial uranium enrichment plants to ensure that plant material is not being enriched beyond
the limits imposed.

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