Case Study 4: Nuclear Site Cleanup
Not Enough Throughput
Washington Closure Hanford (WCH, LLC) won a contract with the Federal government to clean up low risk toxic waste at a retired nuclear site in the United States. Efficient use of resources, and optimizing the overall process was critical because of the stringent federal regulations and extreme fines imposed for delays in meeting defined objectives. Those fines could range anywhere from $250K to $1M per day.
One aspect of the cleanup project involved collecting contaminated soil and moving it to a storage site approximately 40 miles away. The project was expected to cost $10B over a 10 year period. Because of process inefficiencies the company was at risk of losing the project if significant changes weren’t made.
This procedure seemed fairly simple. A track hoe would fill containers at the cleanup site with the contaminated
soil. The containers would then be moved to a dump site for further processing. The logistics of moving the containers is where the problems came in. There were several stages in which containers were loaded and unloaded from trucks in multiple locations. An empty container would be loaded on a short haul truck at the cleanup site, loaded with dirt, and then moved to a transfer station.
From there the containers were loaded onto long haul trucks for the 40 mile trip to the dump site. There another transfer would take place in which full containers were exchanged for empty ones. The long haul trucks then returned to the collection site.
The full containers at the dump site were loaded on short haul trucks where they would be emptied. The empty containers would be reloaded on the long haul trucks as mentioned above and returned to the cleanup sites for the next cycle through the process.
In order to keep the contract and avoid very costly fines, the company needed to maximize the daily tonnage of soil removed from each of several collection sites. It also needed to find and eliminate as many delays in the system as possible.
Several questions needed to be answered before the goal could be met. However, in order to simplify the issues for the purposes of this case study, we won’t get into the political issues, union concerns, etc. We will just focus on the logistical concerns.
• How many trucks should be used at each location?
• How many containers should be used?
• Where are the bottlenecks in the operation?
• How can the most soil be transported in the least amount of time in order to reduce or eliminate fines and the risk of losing the contract?
• Is the current method the best approach for this job or does there need to be a dramatic change to increase throughput?
Several cleanup sites were involved. However, for simplicity we have limited the model to use a single cleanup site, long haul transfer, and the dump site.
Normally entities are processed and the system collects statistics on them as they exit. However, in this case, trucks and containers are continuously reused, never exiting the model. So the approach taken to solve this problem is slightly different than what would normally be used. Container entities are “attached” to truck entities to represent the loading step, then “detached” representing the unload step. Since nothing actually leaves the model, normal statistics are not collected. User-defined variables are used to gather each of the critical statistics to measure model performance. The routes shown in red contain action logic where variables are used to collect the needed statistics
Your 1st Assignment
Download Case Study 4 – Nuclear Site Cleanup model here.
Install the Case Study 4 – Nuclear Site Cleanup model package and review the model.
Note the variables used, and where they are located (on the red routes). Scenario Parameters are also used in the model. These parameters control the number of trucks and containers which arrive initially. By using scenario parameters, the values you will be changing as you work with this model will all be centrally located for ease of access.
Click the Simulation menu, then select Define Scenarios and click the Scenario Parameters tab.
You will need to determine how the number of trucks and containers used can be altered in order to improve performance and meet the goal specified above.
Your 2nd Assignment
As you watch the model simulate, observe where the delays are occurring in the system. Is there a way to eliminate those delays? Using the original model with its activities, times, capacities, etc., design your own model to alter the overall process in a way that reduces the wait times experienced. Remember you want to get as much throughput (soil moved) as possible, eliminate wasted time, and reduce costs as much as possible.
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