Shifting Radioactivity Risks:

A Case Study of Waste Management at the Fernald Nuclear Weapons Site

By Annie Makhijani and Arjun Makhijani[1]

Since the late 1990s, the U.S. Department of Energy has produced several versions of ⌠accelerated■ cleanup schemes of its nuclear weapons sites.  This has led to more rapid decommissioning of two large weapons plants √ notably the Rocky Flats Plant in Colorado, where plutonium pits for nuclear weapons were mass produced, and the Fernald Plant near Cincinnati, Ohio, where uranium metal was produced, mainly for plutonium production reactors. These sites are considered flagship sites in the federal government▓s effort to ⌠clean up■ and ⌠close■ some of the most contaminated sites in the country.

⌠Accelerated■ has not necessarily meant better or lower-risk.  To examine the effects of hasty cleanup, where timetables were tied to bonuses without reference to radiation doses to future generations, we did a case study of some radioactive waste at the Fernald plant.

The specific wastes we studied derived from the extraction of high-grade uranium ores.  Some of these ores were processed during the World War II Manhattan Project and in the immediate post-war years at the Mallinckrodt Chemical Works in St. Louis.  Others were processed at Fernald.  Besides uranium itself, uranium ore contains thorium-230 and radium-226, which are decay products of uranium-238, the main isotope of natural uranium. (See uranium decay chain below.) Since the ores in question were high-grade, they were also concentrated in radium-226 and thorium-230, which are long-lived, bone-seeking radionuclides.  The highest grade ores, up to two-thirds uranium oxide content, were known as ⌠pitchblende■ and came from the ⌠Belgian Congo,■ so called because the region was then a Belgian colony.

The wastes from the processing of uranium ores and uranium concentrates (yellow cake) were stored in three large concrete structures called silos.  Silos 1 and 2, which were emptied and demolished last year, stored radium-containing wastes from the processing of the ⌠Belgian Congo■ pitchblende.  Silo 1 contained only waste produced at Mallinckrodt.  Silo 2 contained waste produced at Mallinckrodt and Fernald.  Silos 1 and 2 were also known as the ⌠K-65■ silos after the name of the process used to extract the uranium from the ore. 

Silo 3, which also has been emptied and demolished, contained radioactive waste from the processing of uranium concentrates.  Silo 3 wastes are less radioactive than the K-65 silo waste and have far more thorium-230 than radium-226. 

This article examines the silo cleanup decisions made by the U.S. Department of Energy (DOE), how they changed over time, how they were implemented, and what their long-term radiological implications are likely to be. It summarizes our August 2006 report, Shifting Radioactivity Risks: A Case Study of the K-65 Silos and Silo 3 Remediation and Waste Management at the Fernald Nuclear Weapons Site.  The full report, including references for this article, can be found online at www.ieer.org/reports/fernald/.

We have chosen to study the significant problems and failures associated with the management of these wastes because they illustrate problems in remediation and long-term stewardship that hold lessons for other sites.

The Fernald site

The Feed Materials Production Center (FMPC), now called the Fernald Closure Project Site, covered 1,050 acres and operated from 1952 to 1989. During these years it produced about 1.3 billion pounds of uranium metal to support the U.S. nuclear weapons program.  Its main function was to provide reactor fuel and target rods for plutonium production at the Hanford Plant in Washington state and the Savannah River Plant in South Carolina.  Fernald operations resulted in the contamination onsite and offsite of air, soil and water.

The radium and thorium waste that was stored in the three silos posed the most immediate risk to the workers and the offsite residents in two ways: (1) radon emissions, created by the decay of radium-226 into radon-222, and (2) the potential for the roofs of Silos 1 and 2 to collapse and release radioactive waste into the environment.  Emptying the silos and putting the waste into a form that would not be prone to dispersal in the short term and that would be stable in the long term was recognized to be a challenging and critical task in the decommissioning of Fernald.

The silo waste

Table 1 shows the concentrations of the various radionuclides in Fernald silo waste.  Table 2 shows the silos▓ radioactivity content from some radionuclides. The contents of Silos 1 and 2 were similar because they were generated from high-grade ores. It is important to note that while the concentration of radium-226 is far higher than that of thorium-230, the latter has a much longer half-life √ 1,600 years, and about 75,000 years, respectively. 

Moreover, thorium-230 decays into radium-226, so over a period of a few thousand years their concentrations become approximately equal. They are approximately in equilibrium at times far longer than the half-life of radium-226 but far shorter than that of thorium-230.  Hence the half-life of thorium-230 controls the rate of decay of the waste over the very long term.  Moreover, when inhaled, the radiation doses to most organs are considerably larger per unit of radioactivity for thorium-230 than for radium-226.

The main radionuclide of concern for Silo 3 waste is thorium-230.  However, radium-226 will build up over the millennia to approximately equal the concentration of thorium-230 for a time.   Silo 3 also contains arsenic, cadmium, chromium, and selenium.  It is common for ore processing wastes to contain significant heavy metal contamination.  Lead-210 and polonium-210 are decay products of radon-222, which is a decay product of radium-226.

Table 1: Estimated Radionuclide Content of Silos 1, 2, and 3 Waste

Source: Adapted from the 1997 IEER report, Containing the Cold War Mess, on the Web at www.ieer.org/reports/cleanup/, citing D. Paine (Silos Project Manager), Operable Unit 4: Project History and Status Presentation, Fernald, OH: Meeting of Independent Review Team, November 14, 1996, pages 8 and 11.

Notes: Volumes (V) for Silos 1 and 2 do not include 357 and 314 cubic meters (m³), respectively, of bentonite clay added in the 1990s to reduce radon emissions. Bentonite clay was not added to Silo 3.  There is a slight discrepancy between the volumes cited in Paine for Silos 1 and 2 (3,240 + 2,845 = 6,085 cubic meters) and the total volume listed in the Record of Decision (6,120 cubic meters).  

Table 2: Radioactivity in Silos 1, 2, and 3 Waste

Source: 1994 Record of Decision for OU4, and Safety of the High-Level Uranium Ore Residues at the Niagara Falls Storage Site, Lewiston, New York (Washington, DC: National Academy Press, 1995).

Note: 28 metric tons of natural uranium correspond to less than 20 curies.

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Published by Alla Yaroshinskaya