Process Simulation Helps Superfund Site Cleanup

After 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!

Problem with Nuclear Waste Disposal

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 7,000 warheads!

Proposed Solution to Nuclear Waste Disposal

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.

Disposal Process & Requirements

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.

The contract was to support the cleanup of a multi-billion dollar superfund site, and was designed to examine the fleet and to move 750,000 cubic yards of low-level radioactive waste in one year. The waste is to be transported via over-the-road truck and trailers. Low-level hazardous wastes are removed from a riverside location to an inland place and buried in huge lined pits. The contract negotiated with the truck drivers restricts driving to daylight hours. The contract also requires inspecting any trailer after dumping to ensure a complete clean-out before any long haul. There is a penalty of $100,000 per day for failing to achieve the dump quota of 150 trailer loads per day. To meet the contract requirements, the union deemed it prudent to set up separate tractors for loading, hauling, and dumping. Company management required the process sized to handle 10% more than the minimum load requirements.

Why Process Simulation Was Needed

The initial process did not meet spreadsheet projections. After months of preliminary design, and recognizing that static calculations would not be adequate, DCS turned to ProcessModel Lean Consulting Service 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 old process could have been configured to meet the contract’s requirements. However, the first comment that every trucking company made was “why is every load being passed between three tractors?“ The old process required six load or unload activities for every round trip. 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 problem required a process simulation model to be built, to understand real needs before returning to re-negotiate with the truck drivers union.

How Processmodel Lean Consulting Helped

ProcessModel lean consultants reviewed the process, and then, with the input of team leaders, created a model, a digital-twin of the current process. The model provided incredible insight to the operation of a facility that has completely new characteristics. 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.

The Superfund Site Cleanup Logistics Model

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.

Results from Using Process Simulation

The model became an indispensable tool in teaching engineers about the system’s operation and the effects one area had on the others. When the management team were showed the new approach, they were stunned by the efficiency gain. They were originally sold on the old process to gain efficiency based on the storage’s providing a buffer to smooth production. But the unnecessary hand-offs required more equipment, people, and time. With the ability to see the possible gains on the on-screen statistics.

“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 a