Uranium Enrichment Safeguards: Material Flow

Now let’s take a look at how material flows
through an enrichment plant. Material enters the enrichment plant in the
form of Uranium hexafluoride. Commercial uranium enrichment facilities typically
receive the uranium hexafluoride in large drums that can hold up to 12,500 kg. This UF6 is transported from the conversion
plant to the enrichment plant via truck or rail. When it arrives at the plant, the material
is weighed. Then, depending upon the facility, this material
may undergo non-destructive assay analysis or statistical sampling to verify the purity
and isotopic concentration. The material is then put into a storage queue
awaiting processing. If we look at a simplified uranium enrichment
plant diagram, we see that the material is received here. In general, safeguards for uranium enrichment
facilities are based around two broad material balance areas. The first material balance area covers shipping,
receiving, and any storage areas. The second MBA covers the process areas including
the cascade/enrichment halls. Since we are weighing, and possibly analyzing,
the concentration of the material at the point at which it is received, we will place a key
measurement point or KMP at this point, before it enters the storage area. The UF6 as it is stored is in a solid, crystalline
form. This form is easy to handle and weigh. After it enters the feed input area, it will
generally be heated to a gas state to be fed into the cascades. The process for this will depend on the type
of enrichment plant, but the end result is a gas product being fed into the cascade hall. There will also be some small amount of waste
as a result of this process, so we need to monitor the material entering the cascade
halls to have an accurate measurement of the UF6 gas that enters the enrichment area. This could be accomplished using an online
flow monitor, for instance. As it undergoes the enrichment process, there
is a constant withdrawal of both product and tails from the cascades, and those streams
are then cooled back down to a solid state and transferred into storage. There is another Key Measurement Point here,
at the point where both of these streams are weighed and sampled once again before being
moved into storage. In the case of the tails, this material is
generally put into long-term storage at the facility. The product is put into short-term storage
and then possibly blended and homogenized in the weighing and sampling area before ultimately
being shipped to a customer, which is generally the fuel fabrication facility. As we can see here, we place Key Measurement
Points at basically every point where the material stream enters or exits one of the
two main material balance areas.

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