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Comparing the Carbon Footprints of Low-Activity Radioactive Waste Immobilization Techniques

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29 July 2026

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30 July 2026

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Abstract
Between 1943 and 1989, the Hanford Nuclear Site produced weapons-grade plutonium and accumulated 212,000 cubic meters of mixed radioactive and hazardous chemical waste, stored in 177 aging underground tanks. It is estimated that 90% of this waste is “Low Activity Waste” after the cesium, strontium, and transuranics are removed. In late 2025, the Direct Feed Low Activity Waste facility began vitrification, which involves mixing liquid waste with molten glass at 1150 °C to destroy hazardous organic chemicals, at an average rate of 15 metric tons per day. Maintaining heat in the two 300-ton melters requires about 200,000 megawatt-hours of electricity each year. Over 40 years, this electricity use results in about 3,000,000 tonnes of carbon dioxide emissions. To mitigate this carbon footprint, a significant portion of the waste could be “grouted” with a mixture of Portland cement, granulated slag, fly ash, and batch-specific chemicals. Vitrifying LAW has a carbon footprint of about 32 tCO2e per cubic meter (m3), whereas grouting LAW and shipping it out-of-state by truck involves about 6 tCO2e/m3, and shipping it by rail involves about 2.5 tCO2e/m3. Adding a rail spur to a grouting facility is key to Hanford’s net-zero approach.
Keywords: 
vitrification
;  
grouting
;  
radioactive waste
;  
hazardous waste
;  
carbon dioxide
;  
greenhouse gases
;  
hanford nuclear site
Subject: 
Environmental and Earth Sciences  -   Waste Management and Disposal

1. Introduction: What is to be done with Hanford’s Low Activity Waste?

From 1943 to 1945, the Hanford Nuclear Site hosted the Manhattan Project’s plutonium production facilities, which supplied the fissile material for the Nagasaki bomb in August 1945. During the Cold War, Hanford was a key site for plutonium production, operating nine reactors and five reprocessing plants (Colburn and Petersen, 2020). Reprocessing technologies included the bismuth phosphate process (1944–1956), the reduction-oxidation (REDOX) process (1952–1967), and the plutonium uranium extraction (PUREX) process (1952–1988), each employing a distinct set of chemicals. Smaller quantities of plutonium were also produced at Idaho National Laboratory and Savannah River National Laboratory (SNRL). By 1989, 212,000 cubic meters (m3, about 56 million gallons) of radioactive and hazardous waste had been stored in 177 underground tanks at Hanford.
In 1989, the U.S. Department of Energy (DOE), the U.S. Environmental Protection Agency (EPA), and the Washington State Department of Ecology signed the Tri-Party Agreement (TPA) to set milestones for cleaning up Hanford tank waste. The Waste Treatment and Immobilization Plant (WTP), to process the waste, has been under construction since 2002. The TPA was revised again in 2025 (DOE, 2025).
As shown in Table 1, Westesen et al. (2026, p. 1) report, “Of the 56 million gallons, 23 million gallons are comprised of saltcake, 21 million gallons are supernatant [liquids], and the remaining 12 million gallons are insoluble sludge [Colburn and Petersen, 2020].” It is estimated that about 90% of this waste (Hanford Vit Plant, 2025a), roughly 190,800 m3 (about 50.4 million gallons of supernatant, saltcake, and some sludge), could be “Low Activity Waste” (LAW) after cesium, strontium, and transuranics have been removed through the Tank-Side Cesium Removal (TSCR) facility. Further, Wells et al. (2011) note,
“These tanks contain a mixture of sludge, saltcake, and supernatant liquids… The saltcake, generated by extensive evaporation of aqueous solutions, consists primarily of dried sodium salts. The supernates consist of concentrated (5-15 M) aqueous solutions of sodium and potassium salts.”
Each liter of the liquid contains 5 to 15 moles of dissolved salts, making it dense and chemically active. Hill and Langton (2025, p. 4) assume that 1 liter of post-TSCR-processed supernatant liquid weighs 1250 g, and Wells et al. (2002) assume that 1 liter of diluted saltcake weighs 1580 g. The saltcake can be diluted, for example, with DFLAW (Direct Feed Low Activity Waste) secondary waste liquids, to pass through TSCR and DFLAW. According to GAO (2026, p. 1), 24,000,000 gallons of LAW (90,800 m3) could be grouted. If 90,800 m3 is to be grouted, then 99,900 m3 will need to be vitrified. Within LAW, it is assumed that (1) 79,900 m3 (21,120,000 gallons) is liquid that will be evaporated in DFLAW and must be treated as secondary waste, and (2) 20,000 m3 are solids. To these solids, about 79,900 m3 of glass-forming compounds (GFCs) are added to produce 99,900 m3 of immobilized LAW (ILAW) glass.
The Hanford Field Office of DOE-Environmental Management manages the WTP construction and operations contracts. The WTP includes the High-Level Waste (HLW) facility, the Pre-Treatment facility, the DFLAW facility (GAO, 2022), the Analytical Laboratory (LAB), and the Balance of Facilities (BOF, including TSCR). GAO (2026, p. 4) discusses the limitations of DFLAW: “this facility is only designed to treat about 60 percent of Hanford’s LAW, and DOE [has] not yet determined how it will treat the remaining 40 percent of the LAW,” hence the term “supplemental” LAW. GAO (2026, p. 14) also notes.
“However, one industry expert we interviewed stated that vitrifying 1 gallon of LAW could generate significantly more than 3 gallons of secondary waste that DOE would need to treat and dispose of. DOE officials explained that any plans to continue grouting waste must therefore also address the treatment and disposal of this additional waste stream.”
Because the liquid supernatant contains approximately 1 liter of liquid (1 kg) and 250 g of solids, the liquid evaporates upon contact with the molten glass. If no evaporation occurs after passing through the TSCR, there could be 3 to 4 liters of off-gas (steam and other gases) for each liter of LAW. Given these secondary wastes and the presence of hazardous chemicals, it is naïve to believe that liquid LAW could be shipped across several States and grouted offsite.
In late 2025, the DFLAW facility began vitrification, blending waste with molten glass at 1150 °C (2100 °F). According to Beaver (2026), “[T]he U.S. DOE has until Oct. 15, 2028, to have the facility running at 70% capacity, equivalent to producing 21 metric tons of vitrified waste per day, to meet a legally binding consent decree.” (The nominal capacity of DFLAW is 21 tonnes per day, but the expected capacity is only 15 tonnes per day.) This process not only stabilizes the waste but also destroys hazardous chemicals. Once fully operational in 2028, the facility is expected to fill about 1,100 stainless-steel canisters with vitrified waste annually. Each canister holds roughly 2.67 m3 (about 6 tonnes) of glass and will be disposed of onsite in the Integrated Disposal Facility (IDF).
The DFLAW setup includes two “300-ton” melters (the largest globally, approximately 6.1 meters by 9.1 meters and 4.9 meters high) and an off-gas treatment system. The “300-ton” label refers to the melter’s weight, including its refractory lining and steel casing, not its processing capacity. These are liquid-fed Joule-Heated Ceramic Melters (JHCM) that use submerged electrodes to pass current directly through the molten glass.
Suneel (2019) details this technology and compares it with the other vitrification methods at plants in Table 2. In the 1970s, pilot plants tested batch vitrification at Marcoule, France (Vernazm and Bruezière, 2014). These pilot plants were scaled up at the Atelier de Vitrification de Marcoule in the late 1970s and at the R7 and T7 plants at La Hague in the late 1980s and 1990s. Plants at the West Valley Demonstration Project in New York and the Defense Waste Processing Facility (DWPF) at the Savannah River Site began operations in 1996. In parallel, countries including Russia, India, the UK, Japan, and China adopted borosilicate glass matrices for high-level waste immobilization. More recently, Cold Crucible Induction Melters (CCIM) have been shown to handle higher temperatures and more corrosive waste streams.
To accelerate disposal at Hanford, the latest TPA envisions “grouting” (Rakhimova, 2022) to solidify supplemental LAW by mixing it with concrete-like materials for offsite disposal, e.g., at the Waste Control Specialists’ facility in Texas. (At present, the Clive Radioactive Waste Disposal Facility in Utah can only accept Class A radioactive waste.) In the scientific literature, grouting is referred to as “cementitious grouting,” and in documents such as PNNL and SRNL (2013), grout is referred to as “cast stone.” See NASEM (2023), which reviews Bates et al. (2023).
Yet there is disagreement over whether grouting is “as good as glass” (NASEM, 2019). Although the Washington State Department of Ecology does not consider grouting as effective as vitrification for long-term storage, particularly near the Columbia River and its associated water table, it has agreed in principle to grout supplemental LAW for off-site disposal. According to GAO (2026, p. 1), “DOE is pursuing options to grout about 24 million gallons [90,800 m3] of LAW ([plus] liquid added during the retrieval and pretreatment process) from 22 tanks in Hanford’s 200 West Area and dispose of this waste offsite by 2040, as outlined in the 2025 Holistic [TPA] Agreement.” Further, as noted in GAO (2026, p. 6),
“In general, such organics and nitrates—another hazardous contaminant of concern—could prevent grout from setting, thereby reducing the grout’s effectiveness. To address this, organics and nitrates will need to be destroyed using one of two processes—chemical treatment or a thermal, high-heat procedure—prior to grouting. Estimates from industry representatives we interviewed varied on the percentage of LAW in the 22 tanks that may require organic treatment, ranging from an estimated 5 percent to up to 33 percent.”
Vitrification requires keeping the melters operating continuously at 1150 °C for about five years (the melters are replaced every five years). In contrast, grouting occurs at room temperature (about 25 °C), and grout curing is exothermic. Grouting blends the liquid LAW with dry materials to produce a concrete-like product (in which gravel is replaced by recycled ground slag from steel production and sand is replaced by fly ash from coal combustion). Bates et al. (2023, p. 34) state, “The grout is poured into containers, assumed to be 10 yd3 [2,020 gallons or 7.7 m3, approximately 2m x 2m x 2m] steel boxes that can be disassembled and reused, each with a heavy-duty polypropylene bag liner.”
Before 2017, debates about grouting Hanford LAW generally assumed that vitrification would have a life-cycle cost of roughly $53 billion and that grouting would cost around $5.5 billion (see GAO, 2017, p. 40). The $40B estimate for the “Estimated operating cost for vitrification at Hanford” is accompanied by a footnote stating,
“DOE does not have an estimate for the cost to treat LAW. However, according to contractor estimates [Bechtel National, Inc., BNI], the cost for commissioning and operating the LAW facility and associated support systems is currently estimated at about $600 million per year… DOE is currently planning to begin operating the facility in 2022, and treatment is not expected to finish until 2061 (39 years) (about $20 billion total).”
Although the DFLAW facility did not begin operations until late 2025, it remains unclear whether the earlier estimates account for inflation, escalation, or discounting (Rothwell, 2025). However, the U.S. GAO (2023, p. 1) later re-estimated the cost of vitrification: “The Hanford Site in Washington State is one of the largest and most expensive environmental cleanup projects worldwide. We estimated in 2022 that the cleanup will cost between $300 billion and $640 billion and take decades.” DOE-RL (2019, p. D-14) estimated that “Radioactive Liquid Tank Waste Disposition” would cost $213.9 billion (see discussion in Rothwell, 2026). Congressional funding for fiscal year 2026 was $460 million.
Numerous estimates have been made to determine these costs. However, no analysis has been published on the greenhouse gas (GHG) emissions associated with vitrification or grouting LAW. Clayton et al. (2024) point out,
“This review analyses the landscape of life cycle assessment (LCA) within the nuclear sector, focusing on radioactive waste management, decommissioning, and disposal. A literature search yielded 225 journal articles plus additional grey literature, yet only eight relevant LCAs were identified.”
Of the articles cited by Clayton et al. (2024), only Nian et al. (2014) and Sheldon et al. (2015) discuss GHG emissions in commercial nuclear fuel cycles, and none discuss emissions from nuclear weapons fuel cycles.
The present paper seeks to address a small piece of this research gap by examining the carbon dioxide equivalent (CO2e) footprint of LAW immobilization at Hanford. Ideally, a complete LCA of Hanford tank waste would account for the environmental impacts of constructing treatment facilities, treating secondary waste forms, and long-term disposal. This initial comparison of LAW vitrification and grouting will focus on the CO2e footprint of facility operations and the production and transportation of inputs and outputs, assuming (for now) that vitrification and grouting facilities and infrastructures have similar carbon footprints.
Because vitrification has a carbon footprint 5 to 12 times larger than that of grouting (not considering the destruction of hazardous chemicals that could be present in grouted LAW), and because multiple estimates of carbon dioxide emissions per cubic meter of the inputs are found in the literature, the higher estimate is used when considering grout and the lower estimate is used when considering vitrification (unless otherwise indicated, as in Table 4, where averages are used).

2. Methods: What are the sources of CO2 emissions?

This analysis begins by estimating the megawatt-hours consumed by DFLAW and grouting. First, electricity consumption data for the two 300-ton melters, the largest of their kind, are not publicly available. DOE (2012, p. S-154/S-156) states, “Emissions from employee vehicles and indirect emissions from electricity use were not estimated… Operation of the WTP HLW and LAW melters, for example, would require a significant amount of electric power.” DOE (2024) adds,
“When the WTP begins operating, it will roughly double Hanford’s energy demands. Addressing emissions at these facilities is key to Hanford’s net-zero approach and helps create a waste treatment process less impactful to global climate change.” (emphasis added)
The explicit assumption here is that DFLAW operates in equilibrium. (Electricity use during commissioning and startup is excluded from these calculations.)
The Glass Material Oxidation and Dissolution System (GMODS) was evaluated as a potential technology for treating surplus fissile materials and spent nuclear fuel at the Savannah River Site (SRS). It was designed to convert various fuel types directly into glass forms and potentially integrate with the SRS DWPF. Forsberg et al. (1995, p. 13) described the construction and operation of the GMODS facility: “This site plan is essentially identical to the DWPF at the SRS because the GMODS facility would be about the same size and produce similar quantities of [High-Level Waste] glass.”
The DWPF uses a 75-ton JHCM melter to mix radioactive sludge with glass frit and pour the molten mixture into stainless-steel canisters. Since March 1996, it has produced over 4000 canisters. The two DFLAW melters are 4 times larger than the DWPF and the proposed GMODS. Following Forsberg et al. (1995, p. 45), the DFLAW’s annual electricity consumption can be estimated at 200,000 MWh to fill about 1,100 canisters. Over the 40-year lifespan of the two melters (each replaced roughly every 5 years), this totals approximately 8,000,000 MWh and supports filling about 44,000 canisters. This estimate excludes electricity used by the DFLAW off-gas recovery system, the Effluent Management Facility (which handles gases and liquids emitted during vitrification), and other support systems.
Although low-CO2 sources of electric power are nearby, including a nuclear power plant and hydroelectric dams on the Columbia River, DFLAW’s electricity comes from the regional grid. According to the Energy Information Administration (EIA) carbon calculator, producing one MWh of electricity in the U.S. typically results in 0.37 metric tonnes of CO2 (tCO2) (EIA, 2024). Using this rate, vitrification at DFLAW with 8,000,000 MWh would generate roughly 3,000,000 tCO2. (In the spreadsheet model presented below, 7,982,600 MWh are required, producing 2,946,200 tCO2e; see Table 5.) Since many subsystems in the grouting alternative, shown in Table 3, are also necessary for vitrification, their electricity use is excluded from the carbon calculations because they cancel out when the two methods are compared.
Table 3. A Hypothetical Grouting Complex at Hanford.
Table 3. A Hypothetical Grouting Complex at Hanford.
(based on the DFLAW complex, Rothwell, 2026, Table 4)
Facility Function
Tank Farm Double-shell Tank SY-XXX feeds liquid waste to TSCR
TSCR TSCR filters cesium, strontium, and transuranic solids from liquid waste
IXC Ion Exchange Column (IXC) Storage Pad stores wastes removed by TSCR
HLW-Vit The High-Level Waste Vitrification facility will vitrify waste from IXC and ETF
Tank Farm TSCR treated LAW stored in Tank SY-ZZZ, then transferred to the GROUT Facility
222-S Lab Analyzes the LAW batch and determines the proper recipe for grouting
ETF Treats contaminated Hanford liquids and provides decontaminated water to GROUT
GROUT Mixes LAW with cement, blast furnace slag, fly ash, and chemicals, increasing volume and weight, then pours wet grout into steel boxes (assumed to be 7.7 m3 that can be disassembled), each with a heavy-duty polypropylene bag liner (Bates et al., 2023, p.34)
LAB Provides laboratory services to confirm the GROUT facility is operating properly
SHIP Cured containers are shipped to Waste Control Specialists in Andrews County, TX
BOF Provides necessary services to support GROUT system operations
Notes: SY refers to the 4200-cubic-meter (1,000,000-gallon) double-shelled tanks at the Hanford tank farm, constructed between 1974 and 1976; TSCR is the Tank Side Cesium Removal facility; ETF is the Effluent Treatment Facility; and IDF is about 900,000 m3. Source: based on Bates et al. (2023) and Rothwell (2026, Table 4).
Table 4. Glass Forming Component Masses Added to Tank AP-107 Waste.
Table 4. Glass Forming Component Masses Added to Tank AP-107 Waste.
Glass GFCs for
Forming one m3 of CO2e
Chem Components (GFCs) LAW % emitted Source
SiO2 Silica 350.71 kg 39% 7.96 kg US Silica
H3B3₃ Boric Acid 171.08 kg 19% 186.48 kg Alfa Aesar
CaSiO3 Calcium Silicate 77.41 kg 9% 53.22 kg NYCO Minerals
Al2Si5₅ Aluminum Silicate 69.06 kg 8% 24.17 kg Kyanite Mineral Company
C122211₂₂O₁₁ Sucrose 60.04 kg 7% 26.16 kg C & H Sugar Company
Fe23₃ Iron Oxide 50.37 kg 6% 51.66 kg JT Baker
ZrSiO4 Zircon Silicate 43.08 kg 5% 13.79 kg Prince Minerals
ZnO Zinc Oxide 33.85 kg 4% 98.50 kg Zinc Corp. of America
Mg2Si4₄ Magnesium Silicate 28.39 kg 3% 22.65 kg Unimin Corporation
TiO2 Titanium Oxide 13.44 kg 1% 65.10 kg Chemalloy
Li2C3₃ Lithium Carbonate 12.04 kg 1% 37.88 kg Foote Mineral Company
Totals 909.47 kg 100% 587.57 kg
Source: Dixon et al. (2019, p. 2-6). Note: Answers from Google AI to the question, “What are the CO2 equivalent emissions from producing X kg of Y component?” If more than one kg value was given, the average was used in this table.
Table 5. Vitrification Components.
Table 5. Vitrification Components.
Vitrification Components US units Metric Number tCO2e
Additives (m3, tCO2e) 96,700 58,000
S-S Canister (ft3, m3) 94.25 2.67
Stainless steel (ft2, m2) 119.38 11.12
Stainless steel weight per container (t) 0.93 0.84
S-S trucking (million t-km)+returns 69.41 8,050
Canister Volume (gals, m3, t) 705 2.67 7
Canisters required (t, #, tCO2e) 34,900 41,600 185,100
Canisters per year at 95% capacity 1,045
CO2 emissions to produce canisters 193,200
Number of years required 39.8
Weight of ILAW glass-filled canisters 317,800
Canisters to IDF (M t-km) by truck 1.27 147
Electricity (MWh) per year 0.00 200,000
Total electricity (MWh) 7,962,600 2,946,200
Total tCO2e ILAW glass 3,197,500
Total tCO2e for m3 of ILAW glass 32.0
Note: A 95% capacity factor is assumed, yielding approximately 40 years. Sources: Société de Calcul Mathématique SA (2009), Post-Guillen (2014), Dixon et al. (2019), Marcial et al. (2024), and Hanford Vit Plant (2025c).
Second, although the literature on electricity consumption for mixing LAW cementitious grout is non-existent, some publications address the electric power requirements for mixing concrete with varying levels of granulated blast-furnace slag (GBFS) and coal-combustion fly ash. For a cubic meter of grout, electricity consumption is distributed across several systems in a grouting facility (Arularasi et al., 2022): the main mixer motor consumes about 4 kWh per cubic meter of grout; the material conveyors and pumps require about 5 kWh; the compressors consume about 3 kWh to manage valves and pressure; and control instrumentation uses about 1.5 kWh. In radioactive grout mixing, additional electricity is required for air filtration (High-Efficiency Particulate Air, HEPA), remote handling systems, and extended homogenization (radioactive waste often requires longer mixing times to ensure complete chemical bonding). In total, assuming 50 kWh per cubic meter of grout and 161,000 m3 of LAW and additives, mixing could require up to 8000 MWh of electricity. Using EIA’s carbon calculator, producing 8000 MWh of electricity in the U.S. would generate about 3000 tCO2e.
Electric energy is one of the most carbon-dioxide-intensive inputs for radioactive waste immobilization. In DFLAW vitrification, the ILAW is poured into stainless-steel canisters after the addition of GFCs. Both the stainless-steel canisters and their transportation to the site generate CO2, or its equivalent, as do the GFCs. Grout involves using Portland cement, pouring the mixture into polypropylene-lined reusable steel boxes, and transporting the grout out of state; all of these activities generate CO2. On the other hand, recycling slag and fly ash, both of which may contain heavy metals and other contaminants, generate carbon dioxide credits by removing them from the environment.

3. Results: CO2 emissions of LAW immobilization at Hanford

Section 2 examined one aspect of CO2 emissions from LAW immobilization at Hanford: electricity use. This section examines the carbon footprint of the compounds added to LAW after it has passed through the TSCR facility, whether for vitrification or grouting.

3.1. CO2 Emissions from Vitrifying Liquid Low Activity Waste

Although many compounds are used to vitrify LAW, the primary component is silica (SiO2, silicon dioxide), which can make up to 50% of the mixture (Hanford Vit Plant, 2025b). The glass product consists of about 20% LAW and 80% additives (Hanford Vit Plant, 2025c). The glass is poured into stainless-steel (S-S) canisters that hold about 6 tonnes of glass and weigh about 7 tonnes when filled. As in Marcial et al. (2024, p. 5),
“The glass melt is cast by airlift through one of two pour spouts into 304L stainless-steel containers, where it cools and solidifies to form an ILAW glass. Each melter discharges roughly 15 t of glass per day, filling almost three containers … with 6 t of glass each. Meanwhile, process gases exit the top of the melters into the LAW off-gas process... The 2.29 m (7.5 ft) tall and 1.22 m (4 ft) diameter stainless steel containers are filled to over 90 vol% level with nominally 6 t of glass. If the glass fill level is insufficient, an optional inert material (SiO2) backfill is added to bring the total fill volume to ≥90 vol%.”
Table 4 presents one recipe prepared for a small amount of LAW, as discussed in Dixon et al. (2019). (Treatment recipes for each batch of LAW can vary depending on the chemicals in a particular batch.) In Table 4, the amounts of the GFCs were scaled up to one cubic meter of LAW input. For each cubic meter, approximately one metric ton of additives is used. The production of these additives emitted approximately 600 kg of CO2e. The first line in Table 5 assumes that for every cubic meter of additives used in the vitrification process, the emissions are 0.6 tCO2e, i.e., about 58,000 tCO2e are generated in producing the GFCs. In addition to those in Table 4, other additives include borax, sodium carbonate, and zirconium silicate (Hanford Vit Plant, 2025a).
The ILAW is poured into stainless-steel (S-S) canisters. According to Post-Guillen (2014), “The containers and canisters are fabricated from 3/8” (9.525 mm) thick 304L stainless steel.” Each canister weighs about 0.84 tonnes (see https://www.onealsteel.com/resources/metal-calculator/). Each holds about 1.2 tonnes of LAW solids and 4.8 tonnes of additives. In total, Table 5 shows that 41,600 canisters are required for 99,900 m3 and that they are fabricated with about 34,900 tonnes of S-S. According to Société de Calcul Mathématique SA (2009, p. 3), “5.3 tons of CO2 are emitted to produce one ton of [S-S] using only raw materials.” The carbon footprint of the S-S used in the canisters is about 185,100 tCO2e. Hanford Vit Plant (2020) reports that BNI awarded a contract to Peterson, Inc. of Ogden, Utah, to produce the canisters. It is reasonable to assume that Peterson purchases its S-S from local manufacturers, such as Norfolk Iron & Metal and/or PCC Structurals in Utah.
Shipping the canisters from Ogden to Hanford involves moving about 34,900 tonnes of S-S over about 1,000 km (617 miles), i.e., 69.41 million tonne-km, with empty backhauls (backhauls are assumed to require two-thirds of the tonne-km of the headhauls, BTS, 2017). Because there are no remaining rail spurs at Hanford, the canisters are assumed to be trucked from Ogden to Hanford. According to the EPA’s SmartWay Framework (EPA, 2026), approximately 186 tCO2e are produced per million tonne-km, i.e., 8050 tCO2e. Therefore, excluding the S-S fabrication inputs and their transportation to Ogden, the carbon dioxide footprint of the DFLAW S-S canisters is approximately 193,200 tCO2e.
Finally, canisters weighing 317,800 tonnes would be transported about 4 km from DFLAW to the on-site IDF, resulting in 1.27 million tonne-km of transport, or approximately 147 tCO2e. Excluding the transportation of vitrification inputs, the carbon dioxide equivalent of vitrifying LAW would be about 2,946,200 tCO2e for electricity, 193,200 tCO2e for the stainless steel canisters, 58,000 tCO2e for GFCs, and 147 tCO2e for moving the canisters to the IDF, yielding a total of about 3,197,500 tCO2e, or 32.0 tCO2e/m3. These calculations do not include disposal of secondary liquid or gas waste (DOE-EM, 2026).

3.2. CO2 Emissions from Grouting Liquid Low Activity Waste

Regarding the number of years to grout 90,800 m3 of LAW, GAO (2026, p. 9) states,
“Schedule: DOE will need to consider the schedule implications associated with constructing a new facility. DOE officials we interviewed estimated that it would take about 2-4 years to finish construction of such a facility and begin the grouting process. These officials expressed confidence in the agency’s ability to complete retrieval of the waste by 2040.”
This implies that the grouting facility would be operational by 2030 and could grout about 90,800 m3 over 10 years, or 9,080 m3 per year. See Table 6. Additionally, GAO (2026, p. 12) assumes that (1) a single container would be shipped per truck trip and (2) three containers would be shipped per flatbed rail car.
The cost of grouting LAW at Hanford is based on a specific grouting technique used to treat LAW at SRS. According to research at SRS (Hill and Langton, 2025, p. 4), mixing one liter (1250 g) of liquid LAW (after cesium, strontium, and transuranics have been removed) with Portland cement (55.5 ml, 172 g), GBFS (348.5 ml, 1010.5 g), and fly ash (368 ml, 967.5 g) yields a total volume of 1.772 liters and a total mass of 3.4 kg.
According to Arbeláez Pérez et al. (2024), 1 kg of Portland cement yields, on average, 826 g of CO2 from the production and transportation of inputs and the manufacture and transportation of the cement. Therefore, grouting 90,800 m3 (112,800 tonnes) of LAW with Portland cement would generate approximately 12,600 tCO2e. On the other hand, Lee and Park (2005) calculated that “The use of GBFS as raw material for slag cement resulted in the highest environmental credit, [−0.8439 tCO2/t GBFS].” Assuming an equivalent calculation could be made for grouting, 112,800 tonnes of LAW would require about 114,000 tonnes of slag, resulting in a carbon credit of approximately −96,200 tCO2e.
Fly ash is the residue left after coal combustion. If the coal contains heavy metals or other hazardous chemicals, the fly ash cannot be disposed of in a landfill. Hou et al. (2023, p. 1) find that “The results confirm the possibility of fly ash resource utilization for synergetic pollution and carbon reduction and demonstrate the synergetic emission reduction potential of the solid waste resource utilization supply chain.” Regarding carbon dioxide reduction, Hou et al. (2023, p. 4) conclude, “If 1 ton of fly ash is used as an admixture in cement production, the GHG emission reduction compared to producing the same amount of ordinary Portland cement is 650.2 kg CO2 eq.” If 112,800 tonnes of LAW requires 109,100 tonnes of fly ash, this results in a carbon credit of approximately −71,000 tCO2e. However, grout is not ordinary concrete; additional technical research is required to determine the carbon credits of combining slag and fly ash in LAW grouting.
Assume the polypropylene sheeting lining the reusable steel boxes, into which the grout is poured, weighs 900 kg/m2. Approximately 12 m2 of polypropylene is required to line each box, yielding a polypropylene weight of 11 tonnes per box with a volume of 7.65 m3. According to Alsabri et al. (2021, p. 1), producing 1 tonne of polypropylene emits 1.58 tCO2e, i.e., 17.3 tCO2e per box. Assume these boxes are made of ¼-inch steel and weigh 1.16 tonnes; for 90.800 m3 of grout, 18,700 boxes will need to be shipped out of state. The polypropylene in those boxes will produce about 324,700 tCO2e. The weight of each container is about 30 tonnes, including the grout, polypropylene, and steel box.
Assuming 99,800 m3 of LAW is grouted, the volume would increase to 161,000 m3, and the mass to 355,300 tonnes. The most recent TPA agreement requires moving this grout 2560 km (1590 miles) off-site to Texas (852 million tonne-km). The total carbon footprint of moving grout by truck is 374,600 tCO2e. Hauling one container at a time by truck and returning the reusable steel box would result in a total of 548,700 tCO2e, or about 6.0 tCO2e/m3 of LAW, i.e., about 19% of the carbon footprint of ILAW glass. On the other hand, if the demolished rail spurs at Hanford were replaced and all grouted LAW were moved out of state by rail, the total carbon footprint of rail transport of grout would be 57,900 tCO2e. Using trains to haul at least three containers at a time and return the reusable steel boxes would result in a total of 232,000 tCO2e, or about 2.5 tCO2e/m3 of LAW, i.e., about 8% of the carbon footprint of ILAW glass.

4. Discussion and Conclusions

Although not all aspects of carbon dioxide emissions from immobilizing low-activity radioactive waste at Hanford using DFLAW vitrification and proposed grouting technologies have been identified, it is reasonable to conclude that vitrification is much more carbon-intensive than grouting and that trucking grout to Texas is more carbon-intensive than shipping it by train. The difference between vitrification and grouting would be even greater if the resulting grout could be shipped to the Clive Radioactive Waste Disposal Facility in Utah. It is also likely that vitrification facilities are more capital-intensive than grouting facilities, and that more capital-intensive facilities are more carbon-intensive. Therefore, adding more detail about the construction and operation of these immobilization technologies is unlikely to alter their comparative carbon intensities greatly.
However, because of the complexity of the LAW’s chemical composition, it is unlikely that States would allow the transfer of LAW liquids across their roads or rails. This complexity also makes it unlikely that LAW liquids would be accepted for grouting at out-of-state locations. It is reasonable to conclude that adding a rail spur to a grouting facility is key to Hanford’s net-zero approach. Therefore, the Department of Energy-Office of Environmental Management should begin planning the infrastructure for rail shipments from Hanford’s grouting facility.
Given the chemical complexity of LAW and the fact that each of the 177 waste tanks contains a different mixture of radioactive and hazardous chemicals (inventories were not recorded when the tanks were filled), more effort should be directed toward harnessing machine learning to determine optimal recipes for vitrifying and grouting LAW (Selvam et al., 2025). Much of this work is underway at PNNL (Lu et al., 2026). As Sanchez et al. (2025) point out,
“However, thermal treatment followed by disposal as HLW can be challenging because of high cost, material handling challenges, and the absence of a geologic repository. Alternative disposal pathways may be viable in the future as either Class C or [Greater than Class C] radioactive waste when incorporated in grout wasteforms. However, these waste streams differ in composition and physical-chemical properties from other DOE wastes that are currently grouted. Thus, grout performance objectives and conforming formulations will be developed (Objective 2) to enable further consideration of potential grout disposal pathways.”
This research on Low Activity Waste immobilization should help address some of the technical challenges associated with the handling and disposal of High Level Waste.
This analysis must be extended when more information becomes available regarding (1) how all the secondary waste streams from DFLAW will be managed and (2) how the hazardous chemicals will be managed in the grouting process. Finally, there is the contentious issue of whether GHG emissions should be discounted over time to the present. One could argue that the sooner emissions are reduced, the lower the damage from climate change. However, there is no consensus on how to discount emissions or credits in a life-cycle analysis, or how to evaluate the trade-offs between GHG emissions and radioactive waste remediation. In fact, as noted in NASEM (2023), there has been no estimate of the value of cleaning up Hanford tank waste, as would be appropriate for a cost-benefit analysis of the Waste Treatment and Immobilization Plant program. Therefore, much more work remains to be done on comparing vitrification and grouting, and their respective carbon footprints,

Author Contributions

Geoffrey Rothwell is responsible for conceptualization, methodology, investigation, writing—original draft preparation, review, and editing.

Funding

This research received no external funding.

Data Availability Statement

No new data were created.

Acknowledgments

This research is based on committee work for the National Academies of Sciences, Engineering, and Medicine (NASEM). All errors are the author’s responsibility. The author thanks N. Anderson, J. Applegate, G.E. Gibson, R. Graber, D. Korn, C. Pescatore, W.G. Ramsey, T. Wood, and committee members for their comments and support, as well as the reviewers of this and companion papers. This paper reflects the views and conclusions of the author, not those of NASEM committee members or staff. Google AI was used to determine the CO2-equivalent values in Table 4. An earlier draft of this paper is available at https://www.researchgate.net/publication/408477517_The_Carbon_Footprint_of_Radioactive_Waste_Immobilization.

Conflicts of Interest

The author declares no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
DFLAW Direct Feed Low Activity Waste facility
HLW High Level Waste
IDF Integrated Disposal Facility
ILAW Immobilized Low Activity Waste
JHCM Joule-Heated Ceramic Melters
LAW Low Activity Waste
TPA Tri-Party Agreement
WTP Waste Treatment and Immobilization Plant

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Table 1. Hanford Tank Waste by Type and Disposition.
Table 1. Hanford Tank Waste by Type and Disposition.
Type of Mixed Radioactive Waste Gallons m3 tonnes
Supernate (liquid) 21,000,000 79,500 99,400
Saltcake 23,000,000 87,100 137,600
Sludge 12,000,000 45,400 72,700
Total Tank Waste 56,000,000 212,000 309,600
HLW (=10% of total tank waste) 5,600,000 21,200 33,900
LAW 50,400,000 190,800 236,900
LAW Vit 26,400,000 99,900 124,100
LAW Vit liquids (secondary waste) 21,120,000 79,900 99,900
LAW Vit solids 5,280,000 20,000 24,200
Additives 21,120,000 79,900 96,700
Total LAW glass (ILAW) 26,400,000 99,900 120,900
LAW grout 24,000,000 90,800 112,800
Liquid in LAW grout 19,200,000 72,700 90,200
Solids in LAW grout 4,800,000 18,200 22,600
LAW grout with additives 42,528,000 161,000 306,900
Sources: Dixon et al. (2019), Hill and Langton (2025), Westesen et al. (2026), and GAO (2026).
Table 2. Vitrification Facilities.
Table 2. Vitrification Facilities.
Waste Melting Operating
Facility Location Type Process Period
Atelier Vitrification de Marcoule Marcoule, France HLLW IHM 1978-2008
PAMELA Mol, Belgium HLLW JHCM 1985-1991
EP-100-1 Mayak, Russia HLLW JHCM 1987-1988
R7 La Hague, France HLW IHM/CCIM 1989+
Advanced Vitrification System Tarapur, India HLW JHCM 1990+
EP-500-1 Mayak, Russia HLLW JHCM 1991-1997
Waste Vitrification Plant Sellafield, UK HLLW IHM 1991+
T7 La Hague, France HLW IHM/CCIM 1992+
Tokai Vitrification Facility Tokai, Japan HLLW JHCM 1995-2006
West Valley Demonstration Project West Valley, NY, USA HLLW JHCM 1996-2002
Defense Waste Processing Facility Savannah River Site, GA, USA HLLW JHCM 1996+
Waste Immobilization Plant Kalpakkam, India HLW JHCM 1998+
Waste Immobilization Plant Trombay, India HLW IHM 2002+
EP-250/6 Mayak, Russia HLLW JHCM 2025+
Direct Feed Low Activity Waste Hanford, WA, USA LAW JHCM 2025+
Rokkasho Vitrification Facility Rokkasho, Japan HLLW IHM 2026?
Notes: HLLW is High-Level Liquid Waste; HLW is High-Level Waste; JHCM is Joule-Heated Ceramic Melters; IHM is Induction-Heated Melter; CCIM is Cold-Crucible Induction Melters. Sources: based on Suneel (2019, p. 29) and Goel et al. (2026).
Table 6. Grouting Components.
Table 6. Grouting Components.
Grouting Components Gallons m3 tonnes number tCO2e
LAW grout 24,000,000 90,800 112,800
Portland cement total 1,332,000 5,000 19,400 12,600
Slag total 8,364,000 31,700 114,000 -96,200
Fly ash total 8,832,000 33,400 109,100 -71,000
Total grout mixture 42,528,000 161,000 355,300
Electricity for mixing grout (50 kWh/m3) 8 000 3 000
Totals for grout production -151,600
Annual production for 10 years 3,772,800 14,300 33,300
Grout container size (gal, m3, t) 2020 7.65 17.82
Grout containers, # 18,700
Polypropylene wrapping per container (m2, t) 8.40 11.00
Polypropylene wrapping (t, tCO2e) 205,500 324,700
Reusable steel containers for 3 months, # 470
Reusable steel box for transportation (t, tCO2e) 1.16
Reusable steel boxes, # 542 1 000
Total tonnes to transport 538,300
Average tonnes per container 30.00
Truck transport (million t-km)+returns 2,320 374,600
Train transport (million t-km)+returns 2,320 57,900
Totals for trucks 548,700
Totals for trains 232,000
tCO2e per m3 of LAW grout, truck 6.0
tCO2e per m3 of LAW grout. train 2.5
Sources: Alsabri et al. (2021), Bates et al. (2023), Hill and Langton (2025), EPA (2026), and GAO (2026).
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