Doctoral Dissertations

Paul C. Stumb

Date of Award

8-1996

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Engineering Science

Major Professor

Elden L. DePorter

Committee Members

Milt Russell, Wayne Davis, Doug Hutchinson

Abstract

As a by-product of its uranium enrichment activities, the United States Department of Energy (DOE) has generated and currently manages more than one billion pounds of depleted uranium hexafluoride (DUF6), which is stored in nearly 50,000 large (10 and 14-ton) carbon steel cylinders, many of which have physically corroded to the point that they exist in a very deteriorated condition. Unless specific and timely actions are taken to protect the cylinder walls from further corrosion and thus extend the life expectancy of these containment vessels, it is projected that as many as 20,000 or 40% of the cylinders could breach by the year 2020. In 1995, a cross-functional team of technical professionals agreed that the exposed cylinder surfaces should be cleaned and re-coated with a penetrating epoxy paint to extend the cylinder life expectancy. The problem of how to optimally accomplish this re-coating has several important characteristics including:

1. multiple, conflicting, and non-commensurable (i.e. dissimilarly dimensioned) objectives

2. a large and continuous versus small and/or discrete decision space

3. soft or imprecisely defined goals and constraint limits. As part of this research, the technique known as Fuzzy Goal Programming (FOP) is identified as the best approach for a problem with these characteristics and a detailed FGP model is developed and applied against several subsets of the total cylinder population. Ultimately, this research accomplishes several very important objectives. It produces a customized set of recommendations for optimally applying a limited number of resources to recondition the large and growing population of UF6 cylinders in a manner that simultaneously considers (and attempts to balance) cost and risk to human health and the environment. It extends the envelope of previous FGP applications to the growing and dynamic environmental arena, as well as to a much larger and more complex problem than those heretofore addressed with this methodology. Also, and perhaps most significantly, it produces a robust and flexible model that may be subsequently applied to a substantial and increasing number of other important environmental issues or concerns that face our nation and world today.

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