Up Close: Immobilization of High-Level Nuclear Waste at the Savannah River Plant
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At the Savannah River Plant (SRP), construction of what will be the world's largest solidification facility for nuclear waste has been under way since 1983. Beginning in 1990, the nearly 100 million liters of liquid high-level nuclear waste now stored on the site will be made into a durable borosilicate glass in this Defense Waste Processing Facility (DWPF).M In developing a slurry-fed melting process for the DWPF, we made advances in understanding both glass processing and glass durability. This article focuses on what we learned and what further advances are likely to be made.
AL REMOVAL "•
AND
SLUDGE WASHING
INSOLUBLE SLUDGE
ORGANIC REMOVAL FRIT ADDITION FEED PREPARATION
SOLUBLE SALTS PRECIPITATION -•
4S ®
AND
VITRIFICATION
FILTRATION
CONTAINERIZATION
Glass Technology and Waste Vitrification
Generally speaking, the goal of any glass technologist is to make a. good glass and to make it well. In the glass industry a good product is whatever people will buy. To make it well means, above all, to make the product as economically as possible. Thus, the commercial glass technologist will control the composition of the melter feed material very closely to ensure that only the components necessary for glass performance are included, and in the least expensive form possible.. The commercial glass technologist may also tolerate low yields or specify several stages of post-melt processing if it is necessary to produce a product to demanding specifications. To the nuclear waste glass technologist, however, a good product is one which will be stable in geologic environments for millions of years. In this case, to make it well means to have a highly reliable process that will immobilize most of the elements of the periodic table in a durable glass form. The nuclear waste glass technologist has much less control over his glass composition because an important part of his feed material — the waste — may vary widely in composition (Table I). In addition, the waste contains many elements never encountered in processing commercial glasses. Even those waste components familiar to commercial glass technologists, such as iron or manganese, are present at levels very different than those commonly encountered, and in unusual forms.5 The process designed by the nuclear waste glass technologist must also be highly reliable because it will be run in an environment where maintenance is very difficult and releases of hazardous materi-
33FBNSE WASTE' PROCESSING FACILITY
EFFLUENT CONTROL
±
ON-SITE BURIAL OF DECONTAMINATED SALT
CANISTERS OF GLASS TO REPOSITORY
Figure 1. Immobilization of SRP high-level nuclear waste.
als are intolerable. Low yields also cannot be tolerated because of the difficulty of reprocessing poor glass.6 Thus, while the nuclear waste glass technologist utilizes conventional glass technology whenever possible, sometimes problems cannot be solved by conventional means. SRP is solving those problems in
Table I: Variations in Composition of SRP Insoluble Waste •
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Component Fe(OH)3 . AI(OH)3 Mn0 2 U02(O
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