Two thermoplastic processes for improved treatment of radioactive, hazardous, and mixed wastes were developed from bench scale through technology demonstration: polyethylene encapsulation and modified sulfur cement encapsulation. The steps required to bring technologies from the research and development stage through full scale implementation are described. Both systems result in durable waste forms that meet current Nuclear Regulatory Commission and Environmental Protection Agency regulatory criteria and provide significant improvements over conventional solidification systems such as hydraulic cement. For example, the polyethylene process can encapsulate up to 70 wt pct. nitrate salt, compared with a maximum of about 20 wt pct. for the best hydraulic cement formulation. Modified sulfur cement waste forms containing as much as 43 wt pct. incinerator fly ash were formulated, whereas the maximum quantity of this waste in hydraulic cement is 16 wt pct

Colombo, Peter

Kalb, Paul D.

English

NASA Technical Reports Server

N92-22456
WASTE MANAGEMENT TECHNOLOGY DEVELOPMENT AND DEMONSTRATION PROGRAMS
AT BROOKHAVEN NATIONAL LABORATORY
Paul D. Kalb
Research Engineer
Brookhaven National Laboratory
Upton NY, 11973
Peter Colombo
Technical Program Manager
Brookhaven National Laboratory
Upton NY, 11973
ABSTRACT
Two thermoplastic processes for improved treatment of radioactive, hazardous, and mixed wastes
have been developed from bench-scale through technology demonstration: polyethylene encapsulation and
modified sulfur cement encapsulation. The steps required to bring technologies from the research and
development stage through full-scale implementation are described. Both systems result ill durable waste
forms that meet current Nuclear Regulatory Commission and Environmental Protection Agency regulatory
criteria and provide significant improvements over conventional solidification systems such as hydraulic
cement. For example, the polyethylene process can encapsulate up to 70 wt% nitrate salt, compared with
a maximum of about 20 wt% for the best hydraulic cement formulation. Modified sulfur cement waste forms
containing as much as 43 wt% incinerator fly ash have been formulated, whereas the maxinmm quantity of
this waste in hydraulic cement is 16 wt%.
INTRODUCTION
The Department of Energy (DOE) has generated large volumes of low-level radioactive (LLW),
hazardous, and mixed waste as a result of its research and defense activities over the last 50 years. These
include a broad range of waste types encompassing diverse chemical and physical properties. The total
volume of DOE LLW alone, (either buried or disposed) through 1987 is estimated at 2.4 x 106 cubic meters,
and these wastes continue to be generated at an estimated annual rate of 1.5 x 105 cubic meters [1]. Sources
of commercial LLW and mixed wastes include nuclear power fuel cycle activities (60%), and
industrial/institutional sources (40%) such as hospitals, universities, and radionuclide manufacturers. About
1.5 x 10_ cubic meters of commercial LLW has been generated, and the current generation rate is estimated
at 5.5 x l& cubic meters/year. Figure 1 compares current sources of both DOE and commercial LLW.
Much of this waste requires solidification/stabilization (S/S) before final disposal to reduce the
mobility of contaminants into the accessible environment. The most common practice at DOE and
commercial facilities is to solidify waste using hydraulic cement such as portland cement, llistorically, cement
processes (also known as grouting) were the first methods for S/S of wastes. They continue to bc widely used
primarily because they are relatively inexpensive (material costs of $0.10/lb or less), readily available, and easy
to process. Cement solidification processes are limited however, because cement hardens by means of a
chemical hydration reaction that is susceptible to interferences with the waste. For example, many inorganic
salts and heavy metals present in LLW and mixed wastes are known to inhibit cement hydration [2]. These
*This work was sponsored by the U.S. Department of Energy under contract No. DE-AC02-76CiI00016.
283
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https://ntrs.nasa.gov/search.jsp?R=19920013213 2020-03-17T12:01:54+00:00Z
Power Reactors/
Government (non-. _/ 2.66E*04 m 3
3.70E*03
Indus ./Instit.t *
.... 2.19E*04 m 3
DOE/Defense
9.95E+04 m 3
• Induetrisl/Inetltutlonsl wsete
Figure 1 Comparison of DOE and commercial low-level radioactive waste volumes generated annually
(1987 data) [1].
interactions reduce the amount of waste that can be incorporated and/or result in poor quality waste forms
that do not successfully withstand disposal conditions. Low material costs for hydraulic cement are offset by
poor waste loading efficiency (amount of waste per drum) and potentially poor performance of waste forms
in disposal. In addition, small variations in waste chemistry over time can necessitate frequent process
modifications and quality assurance testing. This seemingly straightforward process can actually prove
complex and labor-intensive.
Thus, work conducted at Brookhaven National Laboratory, sponsored by the U.S. Department of
Energy Office of Technology Development (DOE OTD), is focusing on the development and demonstration
of new and innovative techniques for encapsulation of "problem" wastes. In keeping with OTD's policy of
fostering "faster, better, cheaper, and safer technologies," the objectives of this effort are to develop materials
and processes that:
have the potential to encapsulate "problem" LLW and mixed wastes where current practices are
inadequate,
• minimize the potential for release of toxic materials to the environment,
• result in-durable waste forms that can withstand anticipated conditions during storage,
transportation, and disposal,
• are simple to operate, easy to maintain, and economical.
284
Process development efforts at BNL begin with bench-scale research and development that progresses in
logical stages:
1) Waste characterization--Waste composition is analyzed and physical properties
relevant to treatment and processing are identified.
2) Investigation of Potential Materials and Processes---A large field of potential
systems is examined and the list of preferred candidates is narrowed based on
known properties and behavior.
3) Waste-Specific Treatability Studies--Feasibility is investigated based on compatibility
of the waste and binder. Preliminary formulations are developed and tested
according to broad acceptance criteria (e.g., process results in a monolithic solid
waste form with minimum strength characteristics).
4) Formulation Development--The most promising candidates progress to this next
phase of R & D in which waste/binder ratios are optimized to provide the best
combination of loading efficiency and waste form performance (see below). Often,
these two factors represent a trade-off and final formulations must reflect a balance
between meeting minimum performance criteria and producing an economical
process.
5) Performance Testing--Optimized waste form formulations are subjected to a
complete set of waste form property and performance tests to provide a means of
comparison among potential S/S options. Performance testing also provides
necessary data for predicting long-term behavior of waste forms in storage and
disposal. These tests can reveal areas where potential performance improvements
are achievable by means of additional waste treatment, modifying formulations, or
use of specific additives. In these cases, performance testing and formulation
development comprise all iterative process.
6) Economic Feasibility--Overall system cost-effectiveness is examined and compared
with conventional and alternative technologies.
Bench-scale systems shown to have potential technical and economic benefits are candidates for
process scale-up and technology demonstration activities. The ultimate goal of full-scale technology
demonstration is accomplished through the following steps:
1) Site Selection--Appropriate waste generating sites are selected based on types and
volumes of waste generated. Cooperation of site personnel is solicited.
2) Feasibility Assessment--Scale-up feasibility is confirmed by means of pilot- or full-
scale testing using sinmlated wastes. Resulting process data are compared with
laboratory data and engineering estimates to corroborate scale-up of process
parameters. Quality assurance testing of products is conducted to verify proper
metering, mixing, and overall product performance.
3) Equipment Acquisition and Installation--Site-specific needs are considered prior to
final equipment specification and acquisition.
4) Technology Demonstration--Upon completion of installation, start-up, calibration,
and preliminary testing, the technology demonstration is held under actual plant
conditions. To provide maximum impact, personnel from throughout the DOE
complex, related regulatory agencies, and from the commercial sector are invited to
attend.
285
5)
6)
Process Evaluation--Data collected during the technology demonstration is then
reviewed to ascertain compliance with quality assurance (QA) requirements and to
compare with bench-scale data. Waste form properties of the resulting product are
also tested against QA and performance criteria.
Technology Transfer---_l necessary information for the successful implementation
of developed technologies is transferred to target sites within the DOE complex.
SELECTION OF BINDER MATERIALS
Research and development efforts have encompassed waste streams that are common within DOE
(e.g., nitrate salts), the commercial sector (e.g., evaporator concentrates, ion exchange resins) or both (e.g.,
sludges, incinerator ash). Potential S/S binder materials surveyed are listed in Table 1. Because of the
inherent problems with using hydraulic cement for solidifying and stabilizing waste discussed above, two
thermoplastic materials were selected for further development: low-density polyethylene and modified sulfur
cement. These materials can be melted, mixed with waste to form a homogenous mixture and then allowed
to cool, resulting in a monolithic solid waste form. Contaminants are immobilized by micro-encapsulation.
Since no chemical reaction is required for solidifying, they are compatible with a wider range of waste types
and can encapsulate more waste per drum than conventional processes. Process temperatures are relatively
low (melting temperature of both materials is - 120°C) so volatilization of contaminants is negligible.
Table 1
Cements
Portland
Masonry Cement
Cement-Sodium Silicate
Pozzolanic
Itigh Alumina
Blast-Furnace Slag
Polymer Modified Gypsum
Polymer Impregnated Concrete
Glass
Soda-l,ime
Phosphate
Slag
Potential Encapsulation Materials
Thermoplastic
Bitumen
Polystyrene
Polypropylene
Polyethylene
Modified Sulfur Cement
Thermosetting
Vinyl-Ester Styrene
Polyester Styrene
Water Extendable
Polyester
286
Polyethylene is an organic polymer of crystalline-amorphous structure available ill a wide range of
densities and molecular weights. These properties, in turn, affect basic material properties such as inch
temperature, viscosity, hardness, and permeability. Polyethylene has been shown to withstand conditions that
may be encountered in disposal including harsh chemicals, radiation, microbial degradation, freeze-thaw
cycling, and saturated conditions [3]. Modified sulfur cement was developed by the U.S. Bureau of Mines
about 20 years ago as a means of util_ing by-product sulfur for construction [4]. The supply of sulfur by-
products from flue gas de-sulfurization and petroleum refining is growing. More than 5 x 106 tolls of waste
sulfur are projected to be produced annually by the year 2000. Modified sulfur cement is made by reacting
elemental sulfur with organic modifiers that increase its stability by suppressing unstable phase
transformations. Results of testing have shown that modified sulfur cement is also durable under anticipated
disposal conditions [5].
PROCESS DEVELOPMENT AND PERFORMANCE TESTING
Formulation and process development studies have been performed E_r polyethylene and modified
sulfur cement encapsulation of a wide range of waste types. These studies determine the maximum waste
loadings for each binder, while still nmintaining adequate waste form performance [6,7,8]. Existing waste
form performance criteria established by the Nuclear Regulatory Commission (NRC) for demonstrating Iollg-
term durability of commercial low-level radioactive waste forms and by the Environmental Protection Agency
(EPA) for the toxic leachability of hazardous wastes were applied. Maximum waste Ioadings achieved for
polyethylene and hydraulic cement encapsulation are compared in Figures 2 and 3 (weight % and volunlc,
respectively). Figures 4 and 5 present similar data for modified sulfur cement. Significant improvements in
waste loading are attained in each case using these thermoplastic binders when compared with convcntioual
cement systems.
80
70
60
50
40
30
20
10
0
Wa#te Loadings, dry wt_
70
Sodium Nitrate Sodium Sulfate
7O
................ 7t Encapsulation Matrix
rt  ort,an 
s0
e0
s
Boric Acid Incinerator Ash I.X. Resins
Waste Types
Figure 2 Maximum waste Ioadings (wt%) for polyethylene encapsulation compared with hydraulic cement
processes.
287
Figure 3
Waste Types
Sodium Nitrate
Sodium Sulfate
Boric Acid
Incinerator Ash
LX. Resins
Waste Loading, kg/55 gal drum
0 50 100 150 200 250
.... 1_ ! I J !
J 508
141
-- ] 552
61
] 248
._j 238
_\_'_ _6o
-- I 139
i • I I I
0 100 200 300 400 500
Waste Loading, Ibs/55 gal drum
300
J
I
600 700
Polyethylene Hydraulic cement
Maximum waste/drum for polyethylene encapsulation compared with hydraulic cement processes.
50
40
3O
2O
10
0
Waste Loading, dry wt%
40
9
43 43
40 40
15
Sodium Sulfate Boric Acid Bottom Ash
Waste Types
Incinerator Fly Ash
i Modified Sulfur _ Hydraulic Cement
Figure 4 Maximum waste Ioadings (wt%) for modified sulfur cement compared with hydraulic cement
processes.
288
Waste Types
Sodium Sulfate
Boric Acid
Bottom Ash
Incinerator Fly Ash
0
Waste Loading, kg/55 gal drum
50 100 150 200
l L J ........ _ ....
366
61
253
360
430
I I I I
0 100 200 300 400 500
Waste Loading, Ibs/55 gal drum
l Modified Sulfur _ Hydraulic Cement
Figure 5 Maximum waste/drum for modified sulfur cement compared with hydraulic cement processes.
PROCESS SCALE-UP AND DEMONSTRATION
On satisfactory completion of bench-scale R & D, scale-up feasibility was investigated for
polyethylene encapsulation of nitrate salt wastes. A production-scale feasibility test was conducted using a
commercial-grade polyethylene extruder with a 4.5 in. (114 mm) diameter screw and an output capacity of
about 2,000 lbs/hr (900 kghlr). Technical grade sodium nitrate was used to simulate actual mixed waste
nitrate salts at a waste loading of 60 wt%. Figure 6 is a process flow diagram for the production-scale test
indicating typical parameters. A 30 gallon drum (114 liter) of encapsulated "waste" was filled in about 25
minutes for an average flow rate of about 72 gal/hr (273 l/hr). The resulting product was sectioned to inspect
for potential void formation, verify homogenous mixing and provide test specimens for additional
confirmatory performance testing. Results of the feasibility test and performance testing are presented in
Reference [3], but can be summarized in the following points:
Polyethylene encapsulation of at least 60 wt% nitrate salt wastes can successfully be accomplished
using a production-scale extruder,
• Bench- and production-scale process data are in close agreement,
QA/performance testing of the 30 gal. waste form demonstrates that a homogenous product with
excellent performance properties can be produced using off-the-shelf production equipment.
Based on these results, a production-scale extruder was procured for a technology demonstration to
be held at BNL during this fiscal year. The demonstration will be conducted using either actual mixed waste
from a DOE facility or surrogate waste that closely approximates actual waste in both chemical and physical
composition. This demonstration will be open to all interested parties including those from DOE, NRC,
EPA, and the commercial sector.
Scale-up activities for the modified sulfur cement process are continuing and demonstration of
production-scale feasibility is planned by the end of FY-1992. The focus of this demonstration will be
treatment of mixed waste incinerator fly ash generated at both DOE and commercial facilities.
289
Output: 1800 Ibs/hl
Melt Ternp: 300
romp: 325 F Temp: 300 F Temp: 000 F
Press'. 1240 psi Press: 0 psl Press:880 psi
Temp: 300 F Temp: 000 F
PreSs: 2000 psi Press: 0 pSI
Figure 6 Process flow diagram for full-scale polyethylene encapsulation system.
SUMMARY AND CONCLUSIONS
Waste management technology development and demonstration efforts conducted at BNL are aimed
at providing improved methods of treating radioactive, hazardous, and mixed wastes. In keeping with DOE
OTD policy, processes must be "better, faster, cheaper, and safer" than conventional technologies. Two
systems developed to date (polyethylene and modified sulfur cement encapsulation) have been shown to
provide better waste form performance under long-term disposal conditions and improved waste loadings,
on a cost-effective basis.
29O
REFERENCES
.
.
.
.
°
.
.
.
U.S. Department of Energy, "Integrated Data Base for 1988: Spent Fuel and Radioactive Waste
Inventories, Projections, and Characteristics," DOE/RW-0006, Rcv. 4, Oak Ridge National
Laboratory, Oak Ridge, TN, September 1988.
Kalb, P.D., J.II. lleiser, and P. Colombo, "Comparison of Modified Sulfur Cement and l lydraulic
Cement for Encapsulation of Radioactive and Mixed Wastes," Proceedings of thc Twelfth Annual
U.S. DOE Low-Level Waste Management Cxmfcrence, CONF-9008119-Proc., Chicago, II., August
28-29, 1990.
Kalb, P.D., J.tI. lleiser, and P. Colombo, "Polyethylene Encapsulation of Nitrate Salt Waste: Waste
Form Stability, Process Scale-Up, and Economics," BNI.-52293, Brookhavcn National l.aboratory,
Upton, NY, July 1991.
McBee, W.C., T.A. Sullivan, and B.W. Jong, "Development and Testing of Superior Sulfur
Concretes," RI-8160, Bureau of Mines, U.S. l)cpt, of Interior, Washington, I)(', 1976.
Kalb, P.D., J.ll. lleiser, and P. Colombo, "l)urability of Incinerator Ash Waste I:.ncapsul:ltcd in
Modified Sulfur Cement," Thcrnml Treatment of Radioactive, llazardous Chemical, Mixed and
Medical Wastcs, Procccdings of the 1991 Incineration Conference, Knoxville, TN, May 13-15, 199 I.
Kalb, P.D., and P. Colombo, "Polycthylcnc Solidification of l.ow-l.cvcl Wastes, Topical I_,cport,"
BNI.-51867, Brookhavcn National l.aboratory, Upton, NY, October 1984.
Franz, E.M., J.ll. lleiser, and P. Coloml×_, "Solidification of l_roblcm Wastes, Annual Progrcss
Report," BNI.-52078, Brookhaven National l.aboratory, Upton, NY, February 1987.
Kalb, P.D. and P. Colombo, "Modificd Sulfur Cement Solidification of lx_w-l.cvcl Wastes, Topical
Report," BNL-51923, Brookhavcn National Laboratory, Upton, NY, October 1985.
291


Waste management technology development and demonstration programs at Brookhaven National Laboratory

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