U.S. Department of Energy, Office of the Press Secretary, Washington, DC 20585
Declassification of Today's and Historical Inventory Differences for Weapon-Grade Plutonium and Highly Enriched Uranium at the Rocky Flats Plant, near Denver, Colorado
Table of Contents
SpecificallyBackground
Benefits
Who Are the Key Stakeholders?
Contact
Attachments
Questions and Answers
The Department of Energy has declassified today's and historical inventory differences for weapon-grade plutonium and highly enriched uranium at the Rocky Flats Plant near Denver, Colorado. Highly enriched uranium is defined as uranium having an enrichment above 20 percent of the fissionable isotope uranium-235. Weapon-grade plutonium contains less than 7 percent of the isotope plutonium-240.
- The declassified inventory differences are the totals for each year from 1953 to 1993. All future inventory differences will be declassified every 6 months as they are for the rest of the Department of Energy complex.
- Department of Energy Order 5633.3A, defines the "inventory difference" as the "book inventory" minus the "physical inventory." The "book inventory" is the quantity of material present at a given time as reflected by accounting records. The "physical inventory" is the quantity determined to be on hand by first physically ascertaining its presence and then using techniques that include measuring, sampling, weighing, and analysis.
- The "book inventory" may not reflect all holdup material (see background for definition) or material in waste when the waste has been written off the books. More accurate values for material in holdup will be obtained during decontamination of buildings and equipment. Although material in waste has been written off the books and is not contained in the "book inventory" retrieval of this information is possible through significant effort.
Specifically
- Today's total inventory difference at the Rocky Flats Plant for weapon-grade plutonium represents a decrease from the "book inventory" of 1191 kilograms. Yearly values varied between an increase from the "book inventory" of 192 kilograms and a decrease of 198 kilograms (see attached chart).
- Today's total inventory difference at the Rocky Flats Plant for highly enriched uranium represents a decrease in the total inventory of 313 kilograms of uranium-235. Yearly values varied between an increase in the inventory of 96 kilograms and a decrease of 27 kilograms of uranium-235 (see attached chart).
- The total inventory differences for weapon-grade plutonium and highly enriched uranium are expected to be reduced by materials that will be recovered during decontamination of buildings and equipment.
- Most of the inventory differences were accumulated prior to 1971 when measurement technologies were less precise and accurate.
- The attached maps show today's cumulative inventory differences for plutonium and highly enriched uranium at the Department of Energy sites. Today's and historical inventory differences for weapon-grade plutonium and highly enriched uranium at the Rocky Flats Plant and for highly enriched uranium at the Y-12 Plant were recently declassified. Inventory differences for other Department of Energy sites are declassified 6 months after their generation. Future inventory differences for the Rocky Flats Plant and the Y-12 Plant will be declassified in the same way as all other Department of Energy sites.
Background
- Data on the annual inventory differences at Rocky Flats, for each year since the plant opened in 1952, were classified to protect estimates of the amount of plutonium or highly enriched uranium in weapon parts, weapon design information, fluctuations in weapon production, and approximate numbers of weapons produced.
- "Holdup" is material that has adhered to gloveboxes, ducts, etc., over the years. While the majority of holdup in the complex is booked based on measurements or engineering estimates, the uncertainty of these values is high. Verification of these values or the establishment of more accurate values cannot be achieved until large-scale dismantlement and recovery.
- The most likely cause of the increase in plutonium inventory difference at the Rocky Flats Plant for the years prior to 1966 was the buildup and high measurement uncertainty of plant holdup. Plutonium is a material that "clings" tenaciously to anything and everything such as glovebox walls, ducts between the gloveboxes and filters, pipes for transferring solution, etc.
- Inventory differences are the result of reconciling book inventories and physical inventories after adjustments for transactions, removals, decays, corrections, transmutations, and production. If any of these adjustments have a large uncertainty, a large contribution to inventory difference can occur. In addition, inventory differences can result from such actions as remeasurements, high measurement uncertainty of holdup of material resulting from processing, rounding to the nearest gram, and data input errors. After analysis and verification of inventory differences, the "book inventory" is adjusted so as to represent the amount of material present.
- The quantity of enriched uranium or plutonium in waste cannot be measured or estimated very well, i.e., it has a large uncertainty. Since the waste is written off from the inventory, any understatement of the quantity will reflect in an inventory difference representing a decrease in inventory.
- Future inventory differences at Rocky Flats will be made public in the same way they are for all other facilities, that is, they will be declassified every year for a 12-month timeframe starting 18 months prior to the date of the declassification. The delay permits investigation into the reasons for each inventory difference. The delay also prevents an adversary from using the information to make a claim about the material represented by the inventory difference while the facility is still investigating the reasons for the inventory difference.
- A number of things contribute to inventory difference values. Contributors include: (1) high measurement uncertainty of plant "holdup;" (2) measurement uncertainties because of the wide variations of the matrix containing the materials; (3) measurement uncertainties because of the statistical variations in the measurement itself; (4) in the early years, technology had not been developed to measure the material adequately; (5) measurements for waste are still very uncertain because often small quantities of plutonium or uranium are mixed in with a variety of other materials so variable that it is not possible to make accurate calibration sources for measurements; (6) losses from operations, such as accidental spills where accurate measurements were not made before the spill; (7) corrections of human errors in the input of data into the accounting system; and (8) rounding errors.
- In many situations, plutonium and highly enriched uranium are not in forms that can be easily inventoried. They are often in solutions or oxides that are similar in properties to talcum powder. The amount of material in the solution or in the powder has to be measured by volume or weight.
- The quantity listed here is based on the evaluation of the records available. The quantity may be updated or revised in the future after re-evaluation of the methodology used originally.
Benefits
- As part of the Secretary of Energy's Openness Initiative, the Department of Energy is declassifying the information regarding the amount of inventory differences for plutonium and highly enriched uranium at the Rocky Flats Plant for each year that the plant has been in operation. As a result of this declassification, the American public will have more information relating to the current debate over proper management and handling of plutonium and enriched uranium at the Rocky Flats Plant. This declassification should encourage other nations to release similar information.
- With these declassifications, and similar ones for the Oak Ridge Y-12 facility, inventory differences at all Department of Energy facilities will be treated in the same manner as far as classification is concerned.
Who Are the Key Stakeholders?
- Regulators. The Colorado Department of Health and the Defense Nuclear Safety Board.
- The Public. Present and former employees at the Rocky Flats Plant, local citizens, others who are following information about the Rocky Flats Plant.
- Public Interest Organizations. Stakeholders include environmental, safety and health groups, historians, archivists, researchers, scientists and industrial workers, as well as State and Federal personnel. With this declassification, those interested in oversight of plutonium and highly enriched uranium related activities will have additional information regarding today's and historical inventory differences for weapon-grade plutonium and highly enriched uranium at the Rocky Flats Plant near Denver, Colorado. Public interest organizations which have expressed such an interest include (but are not limited to): American Friends Service Committee; Citizens Advisory Board; Colorado Council on Rocky Flats; Energy Research Foundation; Environmental Information Network; Friends of the Earth; Greenpeace; League of Women Voters; Military Production Network; National Security Archive; Natural Resources Defense Council; Physicians for Social Responsibility; Plutonium Challenge; Rocky Flats Cleanup Commission; Rocky Flats Local Impacts Initiative; Rocky Mountain Peace Center; Sierra Club; and Western States Legal Foundation.
Contact
U.S. Department of Energy
Office of Public Affairs
Contact: Sam Grizzle
(202) 586-5806
Attachments
U.S. Department of Energy, Office of the Press Secretary, Washington, DC 20585
QUESTIONS AND ANSWERS
Q. Is the plutonium and highly enriched uranium missing? If it is not missing, can you account for it?
A. The plutonium and highly enriched uranium related to inventory differences are 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 holdup of material 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. If you do not know where the material is, isn't it possible that holdup material could undergo a nuclear reaction or explosion?
A. If the material were in any one location in a sufficiently large quantity, it would be easily detected by routine radiation surveys. We monitor our facilities for radiation for just this purpose.
Q. How can you assure us that the material did not go into the environment?
A. Onsite reviews indicate that the material did not go into the environment. The contributions to inventory differences are many. The total amount for any time period is the sum of many smaller differences. Each one arises for one or more of the reasons enumerated. Each inventory difference is investigated to assign its cause and to help assure that no loss, diversion, theft or environmental contamination occurred. Any substantial loss to the environment would be identified by routine radiological surveys.
Q. Why do you think that you will "find" a large quantity of this material when you decontaminate and decommission the plant?
A. From past experience with such actions both here and at other facilities, we find that a large part of the cumulative inventory difference is regained from such extensive cleanup actions. We cannot do such complete cleanup when a facility is in operation because it requires the dismantlement of the facility.
Q. How can you assure us that someone did not steal or divert the material?
A. Stringent security measures have made theft or diversion unlikely. Physical security will respond to design-basis threats based upon 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 today. These measures prevent, deter, detect, and respond to losses of nuclear material. Prevention measures include barriers and protective forces.
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 that have negative consequences on national security. 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 differences 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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