PNNL

Ever watched a building being demolished? Then you know about the dust it can raise—which alone can create a breathing hazard for those nearby without the right precautions. But what if the building is also highly radioactive? And that dust is contaminated? That’s the challenge for the Department of Energy in protecting workers tearing down old nuclear facilities at the Hanford Site.

To help, PNNL researchers are using integrated air dispersion modeling to predict dust exposure for workers tearing down Hanford’s Plutonium Finishing Plant (PFP), providing vital data to create a safe work environment at this highly contaminated site that began undergoing demolition in fall of 2016.

"To develop a model, we use many years’ worth of meteorological data from the site, a design of the facility, a plan for tearing it down, and estimates of what would be released when they tear it down."

-Bruce Napier

A Complex Challenge

Used to prepare plutonium for nuclear weapons during the Cold War, the PFP completed its mission in 1989 and has been a focus of DOE cleanup efforts for the past 20 years. Not only is the PFP one of Hanford’s most contaminated facilities, it’s also the most complex modeling job PNNL’s Bruce Napier, Jeremy Rishel, Eva Mart and have taken on.

What makes it so complicated? The sheer number of factors, according to Napier, a 39-year PNNL veteran who has been developing air dispersion models for the Hanford Site since 2006. The PFP complex consists of more than 60 individual buildings, some of which contain unremovable, contaminated equipment. Demolition must proceed carefully and with safety in mind.

For nearly seven years the PNNL team has worked on models in preparation for PFP demolition efforts, giving the demolition contractor CH2M Hill Plateau Remediation Company (CHPRC) information they need to keep the dust released at safe levels. Tom Bratvold, Vice President for the PFP Closure Project, recently described PNNL’s efforts as the most sophisticated work of its kind ever performed, enabling CHPRC to conduct the work with a high assurance of worker safety.

Factoring It All In

Predicting the spread and hazards of radioactive dust during demolition is no small chore. Consider the following, which are just the tip of the iceberg: How contaminated is the facility? What is it contaminated with? What materials were used to build it? How will it be torn down? How long will that take? Is dust suppression being used? How close are workers to the demolition?

Add in uncontrollable factors like wind, precipitation, and temperature, which can change hourly or even by the minute, and it may seem like too much to account for—but not for experienced air dispersion modelers like the PNNL team.

“Our job is to predict the emission rates from the various facilities as you tear them down,” Napier says. “To develop a model, we use many years’ worth of meteorological data from the site, a design of the facility, a plan for tearing it down, and estimates of what would be released when they tear it down. For some of the highest emission periods we go through several thousand hours of meteorology data.”

The data are used as input to a key output of the model: plume maps that show, under various conditions, how far the dust will spread, the direction it will travel, and how contaminated it will be. These maps and other data help to guide important decisions like when to perform demolition tasks, how quickly to proceed, and what demolition techniques to use to minimize dust exposure—all of which play a part in helping Hanford Site demolition workers to breathe easier.