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Declassification of Today's and Historical Inventory Differences for Highly Enriched Uranium at the Y-12 Plant in Oak Ridge, Tennessee

U.S. Department of Energy, Office of the Press Secretary, Washington, DC 20585

Declassification of Today's and Historical Inventory Differences for Highly Enriched Uranium at the Y-12 Plant in Oak Ridge, Tennessee

Table of Contents

Who Are the Key Stakeholders?
Questions and Answers

The Department of Energy has declassified today's and historical inventory differences for highly enriched uranium at the Y-12 Plant in Oak Ridge, Tennessee. Highly enriched uranium is defined as uranium having an enrichment above 20 percent of the fissionable isotope uranium-235.




Who Are the Key Stakeholders?


U.S. Department of Energy
Office of Public Affairs
Contact: Sam Grizzle
(202) 586-5806


Inventory Difference Is Book Inventory Less Physical Inventory

Historical Highly Enriched Uranium Inventory Difference at the Y-12 Plant

U.S. Department of Energy, Office of the Press Secretary, Washington, DC 20585


Q. Does the highly enriched uranium inventory difference represent material that is missing?

A. The highly enriched uranium related to inventory differences is not "missing." Inventory differences result from reconciling "book inventories" and physical inventories, after adjustments for transactions, removals, decays, corrections, transmutation, and production. The size of the inventory differences results from remeasurements, high measurement uncertainty of material in holdup resulting from processing, and data rounding and input errors. The unavailability of highly precise and accurate measurement capabilities and less rigorous accounting practices prior to the mid-1970's, all of which have largely been overcome today, have significantly contributed to the differences observed during this period.

Q. Do the storage and use of chemicals such as uranium, lithium, and the release of radioactive materials at the Y-12 Plant represent a health hazard to the workers or the public?

A. The Department of Energy is addressing the question of health hazards from exposures to chemicals and radioactive materials by sponsoring a comprehensive package of health studies of Oak Ridge workers and community residents.

The medical surveillance program examines workers exposed to chemicals and radioactive materials to identify signs of organ damage known to be associated with metals, such as beryllium, mercury and uranium. The National Institute for Occupational Safety and Health is managing a special study of mercury workers.

The Department of Energy has established a special medical monitoring program for beryllium workers at the Oak Ridge Y-12 Plant. In 1991, two beryllium workers who had been diagnosed with other lung diseases were determined to have chronic beryllium disease. In 1993, 146 current beryllium workers were provided a blood lymphocyte proliferation test for immunologic sensitivity to beryllium. Six cases of chronic beryllium disease were diagnosed among those with abnormal blood test results. In 1994, 383 former beryllium workers have been provided the blood test, 12 have been found to be abnormal, and 1 case of chronic beryllium disease has been diagnosed. One individual with an abnormal blood test was found not to have chronic beryllium disease and ten others are scheduled for, or in the process of, receiving diagnostic medical examinations.

The Department of Energy conducted mortality studies of workers at various facilities on the Oak Ridge reservation. The studies included industrial exposures to nonradioactive chemicals such as elemental mercury, and to ionizing radiation primarily through exposure to uranium. A mortality study of 2,133 white male workers exposed to elemental mercury at Y-12 and an unexposed group was published in 1984. The mercury exposed workers did not have any statistically significant causes of death, whereas the control group exhibited two cancer categories with more deaths than expected. In a related study, a group of 247 workers heavily exposed to elemental mercury and a control group were studied for clinical evidence of mercury toxicity. The results of this study, published in 1988, determined that the mercury workers had few clinically significant abnormalities except for the increased prevalence of tremor. The Oak Ridge Institute for Science and Education and Emory University are updating this study under a contract with the National Institute for Occupational Safety and Health.

A Y-12 mortality study, published in 1981, included 18,869 white males employed for more than 2 days between June 1943 and May 1947. No personnel dosimetry data was available, although radiation exposure was primarily due to uranium dust. The vital status of the workers was followed through 1973. The elevated risk of lung cancer was statistically significant among men hired at age 45 or older and exposed to uranium dust. Employees in this cohort who were exposed to phosgene were also the subjects of two separate mortality studies published in 1980 and 1985. Exposure to phosgene is associated with increased deaths due to lung diseases, including lung cancer, but there was no observed excess of lung cancer and only a slight increase in respiratory disease mortality through 1985. A special study of 27 cases of central nervous system cancers among Y-12 workers was published in 1987. No association between the risk of these tumors and internal exposure (using the lung dose from uranium as the surrogate for brain dose) or external radiation was found.

A mortality study of 6,781 white males employed at Y-12 for at least 30 days between 1947 and 1974 was published in 1988. This study examined the mortality of workers exposed to ionizing radiation from uranium compounds. The death rate for lung cancer was statistically significantly elevated when compared with U.S. death rates. There was evidence that the risk of lung cancer increased with increasing exposure to ionizing radiation. There was no excess rate of death among workers when compared with Tennessee death rates. This study has been updated through 1990 and the report is expected in 1994 after review by the National Institute for Occupational Safety and Health who currently manage Department of Energy analytic epidemiology studies.

Y-12 workers are also part of other Oak Ridge studies in progress that focus on statistical methodology rather than risk of disease. A mortality study of the Oak Ridge workers was published in 1985. The vital status of 8,375 white males who worked at least 1 month between 1943 and 1972 at Oak Ridge National Laboratory was followed. This study included mortality through 1977. Statistically significant decreases of cancer deaths were noted for 6 of the 23 categories of cause of death and none had statistically significant increases. Deaths due to leukemia, Hodgkin's disease, and prostate cancer were slightly elevated. Leukemia death rates were highest among men employed ten or more years or involved in engineering activities.

A second study of the Oak Ridge National Laboratory cohort was published in 1991. The study found a statistically significant excess death rate from all leukemia combined although there was no correlation with the amount of ionizing radiation encountered in the workplace. The overall cancer death rate increased with increasing exposure to ionizing radiation. The statistical tables in the 1991 publication were in error, but the conclusions remained unchanged. In 1992, a second publication analyzed associations between cancer mortality and occupation. The author concluded that isotope production, chemical operations and exposures to mercury, beryllium and lead may be associated with higher cancer risks. The vital status of the workers included in the Oak Ridge National Laboratory study is expected to be updated through 1990.

The results of these studies were published and the information was provided to workers.

A community dose reconstruction study to estimate chemical and radiation doses to community residents is being initiated this year by the State of Tennessee under a State Health Agreement. It will assess releases of materials to the environment and the pathways leading to human exposure.

The State Health Agreement also supports quality assurance activities to enhance the operations of the Tennessee cancer registration program. The registration of cancer cases in a surveillance system will help detect unusual patterns or clusters of cancer in workers or residents living near the site. The clusters can then be examined for potential associations with site operations or releases.

The State Health Agreement supports a birth defects registry in Tennessee. The registry provides information about any reproductive outcomes so that those can be analyzed to determine if they are associated with the Department of Energy operations in Tennessee.

The following information is a summary of bioassay (medical surveillance) programs at the Oak Ridge National Laboratory facilities:

Workers at the Oak Ridge Y-12 Plant

During calendar year 1993, 1,978 workers at Y-12 were monitored for potential exposure to uranium. The number of positive doses in that group was 687. Five hundred and seventy-two of these represented doses between 1-10 mrem committed effective dose equivalent. Committed effective dose equivalent is the dose that the individual will receive from the uptake that is delivered to body tissue over the next 50 years. Ninety-three doses fell within the range of 10-30 mrem committed effective dose equivalent. Eighteen doses fell within the range of 31-100 mrem committed effective dose equivalent. One dose fell within the range of 101-150 mrem committed effective dose equivalent and the highest was in the range of 201-250 mrem committed effective dose equivalent. There was no reported exposure to either plutonium or tritium. The majority of the doses at Y-12 are chronic exposures. Thus, there is little distinction between historical and current exposures.

Workers at Oak Ridge National Laboratory (X-10)

During calendar year 1993, 1,245 personnel were monitored at the Oak Ridge National Laboratory (X-10) for potential internal dose. Of these about 95 percent were monitored for plutonium, tritium or uranium. There were no positive plutonium doses. Two positive tritium doses ranged from 1-2 mrem committed effective dose equivalent. Seven positive uranium doses ranged from 2-66 mrem committed effective dose equivalent.

Historical burdens are being followed for three individuals for plutonium, two for uranium and none for tritium.

Workers at the Oak Ridge K-25 Plant

During calendar year 1993, 1,339 individuals were monitored (all for uranium). The number of individuals with positive uranium doses was 64. The range of the uranium uptakes was 1-16 mrem committed effective dose equivalent. This range could change as 14 of these dose assignments are under current analyses update.

Q. Is it possible that holdup of uranium could cause a nuclear reaction or explosion?

A. No. If the material were in a significantly large enough quantity in any one location, it would be easily detected by routine radiation surveys. We monitor our facilities for radiation for just this purpose.

Q. Has highly enriched uranium been released into the environment at Oak Ridge?

A. Small quantities have been released to the environment through sewers and ventilation stacks. However, the releases have not exceeded the limits established by the Environmental Protection Agency and the Department of Energy. Both Department of Energy and external regulators routinely review the enriched uranium processing and storage programs at Oak Ridge. For example, the State of Tennessee is initiating a detailed study of historical releases of radionuclides and chemicals from the Department of Energy's Oak Ridge sites. During their recently completed Phase I Feasibility Study, researchers did not recommend that uranium from the Y-12 Plant and the other two Oak Ridge Sites be included as materials of concern for dose reconstruction studies. The historical releases identified by the researchers for further study are radioactive iodine from the X-10 reactor and fuel reprocessing facilities during the 1940's and 1950's, cesium-137 to surface waters through the 1960's, mercury from the Y-12 Plant in the 1950's and 1960's, and releases of polychlorinated biphenyl's, primarily from Y-12 and K-25. The researchers had access to classified data.

Q. How can you assure us that someone did not steal or divert the material?

A. Stringent security measures have made theft or diversion highly improbable. Physical security will respond to threats based on specific events and intelligence assessments. These threats include terrorists, nuclear weapon proliferants, and criminals. These threats, in addition to those related to malevolent insiders, have been drivers behind the type and level of safeguards and security measures in place at Departmental nuclear facilities. These measures have been designed to prevent, deter, detect, and respond to losses of nuclear material.

Deterrence and detection are achieved through a combination of personnel security, material access controls, materials accountability, and physical security. Response capabilities exist to interrupt or stop malevolent acts such as diversion/theft of nuclear materials. These safeguards and security measures give us high confidence that no plutonium and highly enriched uranium was stolen or diverted and that, if these acts were attempted or had occurred, they would have been detected.

Q. Didn't inventory difference used to be called "material unaccounted for," or "MUF?"

A. Yes, however, the term "inventory difference" is more descriptive of the actual situation, namely differences between accounting records and inventory by physical identification and measurements. Each inventory difference accounting transaction is investigated and resolved per Department of Energy Orders. The term "MUF" does not accurately convey this process and procedure.

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