With the end of the Cold War, the United States and the former Soviet Union began dismantling thousands of nuclear weapons. This dismantlement resulted in large quantities of surplus weapons-usable highly enriched uranium and plutonium. This creates a huge problem – plutonium is one of the most expensive materials on earth, by far the most dangerous in the wrong hands and short of sending it into the sun you can’t just get rid of it!
To reduce the threat of terrorists or rogue nations obtaining nuclear weapon materials, the United States and Russia agreed to dispose of 68 metric tons of surplus weapon-grade plutonium. By one sources calculation, that is equivalent to over 7000 warheads! Disposal is accomplished by converting it to mixed oxide (MOX) fuel for use in existing nuclear reactors. Once the MOX fuel is used in the nuclear reactors, it is no longer usable for nuclear weapons.
Mixed oxide fuel contains a mixture of approximately 95 percent uranium and 5 percent plutonium. Low enriched nuclear fuel that is normally used in U.S. commercial power plants only contains uranium.
The Department of Energy signed a contract with a consortium comprised of Duke Energy, COGEMA, and Stone & Webster (DCS) to:
- Design and operate a Mixed Oxide Fuel Fabrication Facility (MFFF)
- Design the commercial MOX fuel
The Russian Federation agreed to use the DCS design of the U.S. facility in implementing the Russian Federation’s disposition program. Time became a critical factor because any delays in the US program would also delay the Russian Federation’s program.
Although the facility was to be based on the successful Melox and LaHague facilities in France, there were enough differences in material compositions and US Federal requirements that forced much of the process to be reconsidered.
The MFFF is an incredible investment with 500,000-square feet, over 150,000 cubic yards of concrete, 31,900 tons of reinforcing steel, 3,366,000 linear feet of power and control cable, and 70 miles of piping. Getting the process and facility correct was critical.
After months of preliminary design, and recognizing that static calculations would not be adequate, DCS turned to ProcessModel Consulting Services to build a simulated model of the proposed process. During a three week period, ProcessModel worked closely with DCS engineers to create a model that would represent real world production capabilities.
The model provided incredible insight to the operation of a facility that has completely new characteristics. Many of the pre-simulation calculations where inadequate in predicting the capacity and the throughput of the facility. These static calculations did not work because of internal dependencies, change-over’s and natural cycles of the system.
The simulation model showed that machines previously thought to have ample capacity and be under-utilized, would become the bottleneck. Typical operations research calculations did not take into account that the MFFF system requires higher capacity for short periods of time. While other times, processing is delayed waiting for components of the mixture to be produced. These delays rendered the bottleneck machine idle; further reducing its effective capacity. Several machines exhibited the same bottlenecking behavior which further complicated the manual throughput calculations. This system is impossible to analyze with manual calculations. It is like jiggling one of many spoons in a bowl of Jell-O. When one spoon is jiggled they all jiggle. This facility behaved the same way. Every part of the system is connected, and adjusting one part affects every other part.
The model also helped to establish internal scheduling. Three materials are being produced through a series of steps that cross a common set of machines. Machine changeovers are time consuming while final production requires all three products. While the balance was almost impossible to predict before the model, the schedule requirements became clear after the model was validated.
The model was indispensable in teaching engineers about the system’s operation and the effects one area had on the others. Scott P. Baird, president of ProcessModel said, “The insight gained from simulating a system prior to actual creation can save millions of dollars and months of rework. The DCS project is typical of our customer’s projects. When the tool is used in capable hands the very nature of project changes. You can see things that are invisible to everyone else. It allows you to have insight and understand what will make the system function at peak performance.”
This is one more example of how manufacturing facilities can be optimized through the use of simulation. In addition, ProcessModel has been used on projects by General Electric, 3M, NASA, Motorola and thousands of others.
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