Cementitious Radioactive Waste Hosts Formed under Elevated Temperatures and Pressures (FUETAP Concretes)
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CEMENTITIOUS RADIOACTIVE WASTE HOSTS FORMED UNDER ELEVATED TEMPERATURES AND PRESSURES (FUETAP CONCRETES) *
L. R. DOLE, J. G. MOORE, G. C. ROGERS, G. A. WEST, H. E. DEVANEY, M. T. MORGAN, E. W. McDANIEL, AND J. H. KESSLER Oak Ridge National Laboratory, P.O. Box Y, Oak Ridge, Tennessee 37830
ABSTRACT Concretes formed under elevated temperatures and pressures (FUETAP concretes) are effective hosts for transuranic (TRU) and high-level defense and commercial wastes. Tailored cement formulations developed at Oak Ridge National Laboratory (ORNL) use Portland cement, fly ash, sand, and clay additives. These FUETAP concretes are cured under mild autoclave conditions, then the unbound water is removed. This paper summarizes the FUETAP development program. These continuous studies address the major questions concerning the performance of radioactive waste forms.
INTRODUCTION Concretes formed under elevated temperatures and pressures (FUETAP concretes) are effective hosts for TRU and high-level defense and commercial radioactive wastes [1-8]. These tailored concretes, developed at Oak Ridge National Laboratory (ORNL), are prepared from common Portland cements, fly ash, sand clays, and waste products by accelerated curing under mild autoclave conditions (100'C, 1 atm gage). These solids are subsequently dewatered at 0 250 C for 24 h, producing strong (40-100 MPa compressive strength), leach 2 resistant (Pu 10-11 g/cm .d), and radiolytically stable monolithic waste forms. Figure 1 illustrates one of the proposed flow sheets for a FUETAP concrete developed for the Savannah River Plant (SRP) high-level defense waste [9). 3 Specimens are cast in sizes from 1 cm to 75 L for the evaluations of leaching, tensile and compressive strengths, thermal conductivity, porosity, permeability, density, and dewatering kinetics. Only pourable mixes requiring light vibration to fill the molds uniformly and to remove entrained air are selected for study. This paper discusses briefly the processing, Materials Characterization Center (MCC)-l static leach tests, a-radiolysis, phase characterization, and thermal expansion of FUETAP concretes and will summarize their status as a host for radioactive wastes.
PROCESSING:
MIXING AND SET TIME
An advantage of FUETAP as a radioactive waste disposal alternative is its ease of processing. For example, one FUETAP flow sheet for the SRP defense
Research sponsored by the Office of Waste Operations and Technology, U.S. Department of Energy under contract W-7405-eng-26 with the Union Carbide Corporation.
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ASH 11%, 15 psig
100"C
WATER 18%F-
90%
e80
2)24h
O(MIX
PRESSURE CURE
16% VATER
770 Ib GROSS WEIGHT
®CAP, COOL AND STORE
(®241h OVEN DRY
Fig. 1. Flow sheet for FUETAP concrete developed for the Savannah River Plant high-level defense wastes.
high-level waste requires 2 h to add 2 t of dry solids to a full charge of water and set-retarder in a ribbon mixer. To assess the consequences of possible accidents affecting this step, s
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