Pu-Bearing Materials - From Fundamental Science To Storage Standards
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1104-NN03-08
Pu-Bearing Materials - From Fundamental Science To Storage Standards Shiu-Wing Tam, and Yung Liu Decision & Information Sciences Div., Argonne National Laboratory, 9700 S. Cass Avenue, Bldg. 900, MS-12, Argonne, IL, 60439 ABSTRACT The behavior of plutonium (Pu) oxides in the presence of water/moisture in a confined space and the associated issues of hydrogen and oxygen generation due to radiolysis have important implications for the storage and transportation of Pu-bearing materials. This paper reviews the results of recent studies of gas generation in the Pu-O-H system, including the determination of release rates via engineering-scale measurement. The observations of the significant differences in gas generation behavior between “pure” Pu-bearing materials and those that contain salt impurities are addressed. In conjunction with the discussion of these empirical observations, this work also addresses recent scientific advances in the investigations of the Pu-O-H system using state-of-the-art ab initio electronic structure calculations, as well as advanced synchrotron techniques to determine the electronic structure of the various Pu-containing phases. The role of oxidizing species such as the hydroxyl radical from the radiolysis of water is examined. Discussed also is the challenge in the predictive ab-initio calculations of the electronic structure of the Pu-H-O system, due to the nature of the 5f valence electrons in Pu. Coupled with the continuing material surveillance program, it is anticipated that this work may help determine the electronic structure of the various Pu-containing phases and the role of impurity salts on gas generation and the long-term stability of oxygen/hydrogen-containing plutonium oxides beyond PuO2. INTRODUCTION There are two U.S. Department of Energy (DOE) standards for long-term (i.e., up to 50 years) storage of nuclear materials: STD-3028-2000 for uranium-233-bearing materials, and STD-3013-2004 for plutonium (Pu)-bearing materials [1,2]. DOE-STD-3013-2004 was developed over a period of 10 years, with significant revisions in 1996, 1999, 2000, and 2004. It covers stabilization, packaging, and storage of Pu-bearing materials, including metals and oxides. In this paper, we will focus on Pu oxide materials. Some of these oxide materials may contain chloride (salt) impurities in up to tens of weight percent. These chloride-containing Pu oxides are considered impure. DOE-STD-3013-2004 does not limit the chloride content of the Pu oxide materials. Impure Pu oxides turn out to be important because of gas generation issues over time within the containers storing the Pu-bearing materials. Packaging of the Pu-bearing materials after stabilization (see discussion below) relies on the use of a minimum of two individually welded, nested stainless-steel containers known as 3013 cans. These ductile, corrosion resistant, 300-series stainless-steel cans provide isolation of the contents from the environment. Stabilization is a process of calcining the oxide materials at 950 oC for at lea
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