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Title: Remediation on off-gas system deposits in a radioactive waste glass melter

Abstract

Since the early 1980`s, research glass melters have been used at the Savannah River Laboratory (SRL) to develop the reference vitrification process for immobilization of high level radioactive waste. One of the operating concerns for these melters has been the pluggage of the off-gas system with solid deposits. Samples of these deposits were analyzed to be mixture of alkali-rich chlorides, sulfates, borates, and fluorides with entrained Fe{sub 2}O{sub 3} spinel, and frit particles. The spatial distribution of these deposits throughout the off-gas system indicates that they form by vapor-phase transport and subsequently condensation. Condensation of the alkali-rich phases cements entrained particulates causing the off-gas line to plug. It is concluded that off-gas system pluggage can be effectively controlled by maintaining the off-gas velocity above 16 m/s, while maintaining the off-gas temperature as high as practical below the glass softening point. This paper summarizes the results of chemical and physical analyses of off-gas deposit samples from various melters at SRL. Recent design changes made to the Defense Waste Processing Facility (DWPF) at the Savannah River Site (SRS) to alleviate the pluggage problem are also discussed.

Authors:
; ;
Publication Date:
Research Org.:
Westinghouse Savannah River Co., Aiken, SC (United States)
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
10129557
Report Number(s):
WSRC-MS-91-400; CONF-911040-12
ON: DE92008827
DOE Contract Number:
AC09-89SR18035
Resource Type:
Conference
Resource Relation:
Conference: International waste management conference,Seoul (Korea, Republic of),21-26 Oct 1991; Other Information: PBD: [1991]
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; OFF-GAS SYSTEMS; BUILDUP; CERAMIC MELTERS; RADIOACTIVE WASTE PROCESSING; REMEDIAL ACTION; VITRIFICATION; CHEMICAL ANALYSIS; IRON OXIDES; SPINELS; BORATES; SAVANNAH RIVER PLANT; CHLORIDES; FLUORIDES; SULFATES; 052001; WASTE PROCESSING

Citation Formats

Jantzen, C.M., Choi, A.S., and Randall, C.T. Remediation on off-gas system deposits in a radioactive waste glass melter. United States: N. p., 1991. Web.
Jantzen, C.M., Choi, A.S., & Randall, C.T. Remediation on off-gas system deposits in a radioactive waste glass melter. United States.
Jantzen, C.M., Choi, A.S., and Randall, C.T. 1991. "Remediation on off-gas system deposits in a radioactive waste glass melter". United States. doi:. https://www.osti.gov/servlets/purl/10129557.
@article{osti_10129557,
title = {Remediation on off-gas system deposits in a radioactive waste glass melter},
author = {Jantzen, C.M. and Choi, A.S. and Randall, C.T.},
abstractNote = {Since the early 1980`s, research glass melters have been used at the Savannah River Laboratory (SRL) to develop the reference vitrification process for immobilization of high level radioactive waste. One of the operating concerns for these melters has been the pluggage of the off-gas system with solid deposits. Samples of these deposits were analyzed to be mixture of alkali-rich chlorides, sulfates, borates, and fluorides with entrained Fe{sub 2}O{sub 3} spinel, and frit particles. The spatial distribution of these deposits throughout the off-gas system indicates that they form by vapor-phase transport and subsequently condensation. Condensation of the alkali-rich phases cements entrained particulates causing the off-gas line to plug. It is concluded that off-gas system pluggage can be effectively controlled by maintaining the off-gas velocity above 16 m/s, while maintaining the off-gas temperature as high as practical below the glass softening point. This paper summarizes the results of chemical and physical analyses of off-gas deposit samples from various melters at SRL. Recent design changes made to the Defense Waste Processing Facility (DWPF) at the Savannah River Site (SRS) to alleviate the pluggage problem are also discussed.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1991,
month =
}

Conference:
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  • Since the early 1980's, research glass melters have been used at the Savannah River Laboratory (SRL) to develop the reference vitrification process for immobilization of high level radioactive waste. One of the operating concerns for these melters has been the pluggage of the off-gas system with solid deposits. Samples of these deposits were analyzed to be mixture of alkali-rich chlorides, sulfates, borates, and fluorides with entrained Fe{sub 2}O{sub 3} spinel, and frit particles. The spatial distribution of these deposits throughout the off-gas system indicates that they form by vapor-phase transport and subsequently condensation. Condensation of the alkali-rich phases cements entrainedmore » particulates causing the off-gas line to plug. It is concluded that off-gas system pluggage can be effectively controlled by maintaining the off-gas velocity above 16 m/s, while maintaining the off-gas temperature as high as practical below the glass softening point. This paper summarizes the results of chemical and physical analyses of off-gas deposit samples from various melters at SRL. Recent design changes made to the Defense Waste Processing Facility (DWPF) at the Savannah River Site (SRS) to alleviate the pluggage problem are also discussed.« less
  • Radioactive liquid waste from nuclear materials production processes wi11 be vitrified in the Defense Waste Process Facility (DWPF) melter. The melter borescope outer housing, fabricated from N06690, was severely degraded by the combined effects of corrosion and oxidation after only five months of non radioactive operation. The melter was idled and not being fed over 85% of the time during the cold run operations. The borescope was designed to perform in an oxygen rich, chloride containing environment with temperatures approaching 900{degree}C (1650{degree}F). The housing was designed for a minimum of two years of continuous service in the DWPF melter. Airmore » and steam were purged through the borescope and swept over the optics assembly to keep molten glass and volatile gases from depositing on the lens cover. Upon exiting the borescope the air passes through a N06690 orifice and enters the melter. Severe oxidation was observed around the orifice. Extensive material loss was also observed on the side of the outer housing which protrudes through the dome of the melter. Redesign of the borescope is currently underway and will include a new set of optics that will allow the size of the orifice to be significantly decreased, thus reducing the amount of air necessary to keep the lens cover clean. Application of a duplex diffusion coating, consisting of chromium and aluminum, on the end of the borescope outer housing and the use of an inert gas purge are also being considered.« less
  • Corrosion coupons were exposed in a scale demonstration melter system in order to evaluate the performance of alternate materials for use as top head and off gas components in the Defense Waste Processing Facility (DWPF) melter at the DOE`s Savannah River Site. The demonstration system is a 1/10 scale prototypic version of the DWPF melter. In DWPF, high activity radioactive waste will be vitrified and encapsulated for long-term storage. Fifteen different nickel and cobalt base alloys were exposed for five months to corrosive vapors and molten glass, characteristic of the DWPF melter except for radioactivity. Process conditions included temperatures approachingmore » 900{degree}C and a synthetic acid waste containing formates, halides, sulfates, phosphates, nitrates, and mercury. Severe oxidation of the N06625 in both the splash zone and vapor space was attributed to the formation of MoO{sub 3}. Cobalt containing alloys experienced significant degradation in this environment. Results of the metallurgical examination showed that alloys containing 50 wt % Ni, 25 wt % Cr, and additions of 2 to 3 wt % of either aluminum or silicon performed comparably or better than the N06690 in both the splash zone and in the vapor space near the lid. Corrosion rates for these alloys did not exceed 0.2 mm per year (8 mpy).« less
  • Liquid high-level nuclear waste will be immobilized at the Savannah River Site (SRS) by vitrification in borosilicate glass. Experimental glass melters, used to develop the vitrification process, have occasionally experienced problems with pluggage of the off-gas line with solid deposits. The deposits were determined to be mixtures of alkali rich chlorides, sulfates, borates, and fluorides with entrained insoluble particles of Fe{sub 2}O{sub 3} spinel, and frit. The distribution and location of the alkali deposits throughout the off-gas system indicate that the deposits form by vapor-phase transport and condensation. Condensation of the alkali-rich phases cements the entrained particulates causing the off-gasmore » system pluggages. The identification of vapor phase transport as the operational mechanism causing off-gas system pluggages indicates that deposition can be effectively eliminated by increasing the off-gas velocity. The cementitious alkali borates, halides, and sulfates comprising the off-gas line deposits were determined to be water soluble. Thus pluggage can be effectively removed with water and/or steam.« less
  • Liquid high-level nuclear waste will be immobilized at the Savannah River Site (SRS) by vitrification in borosilicate glass. Experimental glass melters, used to develop the vitrification process, have occasionally experienced problems with pluggage of the off-gas line with solid deposits. The deposits were determined to be mixtures of alkali rich chlorides, sulfates, borates, and fluorides with entrained insoluble particles of Fe{sub 2}O{sub 3} spinel, and frit. The distribution and location of the alkali deposits throughout the off-gas system indicate that the deposits form by vapor-phase transport and condensation. Condensation of the alkali-rich phases cements the entrained particulates causing the off-gasmore » system pluggages. The identification of vapor phase transport as the operational mechanism causing off-gas system pluggages indicates that deposition can be effectively eliminated by increasing the off-gas velocity. The cementitious alkali borates, halides, and sulfates comprising the off-gas line deposits were determined to be water soluble. Thus pluggage can be effectively removed with water and/or steam.« less