Glass-contact refractory of the nuclear waste vitrification melters in the United States: a review of corrosion data and melter life

Figures & data

Figure 1. Cross-sectional view of Defense Waste Processing Facility (DWPF) melter representing a typical JHCM design. Reprinted with permission from Ref. [40].

Table 1. Major U.S. nuclear waste treatment projects using JHCM for vitrification. Monofrax® K-3 is used as the refractory lining of all the JHCMs in the table.

Project	Waste inventory	Operation timeline	Melter size and production rate in metric tons of glass per day (t/day)	Waste glass produced	Inspection of melter refractory	Notes
West Valley Demonstration Project (WVDP), near West Valley, New York [1, 4-9]	4 tanks, 2,200 m^3 HLW with high Fe, Al	1995-2002 Melter began non-radioactive operations in October 1995 and radioactive operations began in June 1996.	Glass pool surface area: 2.2 m^2 (23.7 ft^2, rectangular) Operation Volume: 0.86 m^3 Production rate: 0.7-1.2 t/day	∼ 570 t of glass was produced in 275 canisters (∼ 2.1 t glass per canister).	Cross-sectioning samples of the Monofrax^® K-3 bricks were taken for analysis. See section “Refractory corrosion in production melters”	Zeolite was used to remove the Cs-137 from the liquid waste (salt solution) separated from HLW; the effluent solution was concentrated and processed into cement waste form which was deposed as LLW.
Defense Waste Processing Facility (DWPF) at Savannah River Site (SRS), near Aiken, South Carolina [1, 4, 5, 11-14, 55]	51 tanks, 148,000 m^3 HLW with high Fe, Al	1994-present Melter began non-radioactive operations in April 1994 and radioactive operations began in March1996. Melter 1 serviced from 1994 to 2002; Melter 2 serviced from 2003 to 2017; and Melter 3 was installed in 2017 and is currently in service	Glass pool surface area: 2.6 m^2 (6 ft diameter cylindrical) Operation Volume: 2.2 m^3 Production rate: 2.2 t/day (1.3-1.4 t/day before bubblers installed in 2010)	As of 2022, over 7,700 t glass had been produced in 4313 vitrified waste canisters (∼ 1.8 t glass per canister). The total number of canisters needed to vitrify all the DWPF waste estimated by model is 8,170.	Both DWPF Melter 1 and Melter 2 were visually inspected after service. See section “Refractory corrosion in production melters”	The liquid waste (salt solution) separated from HLW is immobilized into grout form (salt stone)
Waste Treatment and Immobilization Plant (WTP) at Hanford Site, near Hanford, Washington [1, 11, 15-17]	177 tanks, 210,000 m^3 HLW with various chemical compositions in different tanks	The first phase of LAW vitrification, i.e., direct feed LAW (DFLAW), is projected to start in 2023 Vitrification of HLW is anticipated to start in 2033	LAW Melter: Glass pool surface area: 10 m^2 (rectangular) Production rate (estimated average): 15 t/day	N/A	N/A	The HLW and LAW (salt solution separated from HLW) will be vitrified in two separate facilities. There will be two parallel-operating LAW melter systems for the LAW vitrification facility and two parallel-operating HLW melters for the HLW vitrification facility.
			HLW Melter: Glass pool surface area: 3.75 m^2 (rectangular) Production rate (estimated average): 4.2 t/day
Vitrification Pilot Plant (VITPP) at Fernald Site, near Fernald, Ohio [4, 5, 31-35]	9,000 m^3 Geological mill tailings include high sulfur and high lead wastes	1996 Melter was “baked up” in May 1996; and failed after processing non-radioactive surrogate waste for seven months.	Glass pool surface area: 0.84 m^2 (3 ft by 3 ft rectangular) Operation Volume: 0.76 m^3 Production rate: 1 t/day	N/A	The leakage was caused by dissolution of molybdenum disilicide bubbler tubes installed in the melter floor and the molten glass flowed through the bubbler hole in the Monofrax^® K-3 layer. The inspection did not indicate any problems with the Monofrax^® K-3 layer in contact with the glass.	The operating temperature was 1350-1450 °C, while other vitrification melters worked at 1150 °C. After the melter failed, the waste that was planned to be vitrified was shipped off-site.
SRS M-area melter at Savannah River Site (SRS), near Aiken, South Carolina [4, 5, 36]	2,500 m^3 Mixed low-level waste	1996-1999 The first melter DM5000 was replaced after 5 months of operation to avoid potential glass penetration; the new melter DM5000A served from 1997 to 1999, which successfully completed the mission.	Glass pool surface area: 5 m^2 (rectangular) Production rate: 5-15 t/day	Over 4,500 m^3 (1.2 million gallons) of feed was processed and ∼ 1,000 t (2.2 million pounds) of glass was produced.	Visual inspections indicated that hot spots formed in the DM5000 melter were a result of refractory corrosion by molten glass near the refractory joints. Molten liquid had leaked from the refractory assembly (i.e., joints) during non-radioactive startup testing. The feeding of anhydrous borax directly to the melter when the melter was at high temperatures (1000 °C) resulted in the borax migrating, causing electrical shorts, localized joule heating, and damage to the refractory. DM5000A melter was inspected after service. See section “Refractory corrosion in production melters”

Table 2. Compositions of Monofrax® K-3 [64–66].

	Wt-%	Note
Chemical Composition
Al2O3	58.6
Cr2O3	27.1
Fe2O3	5.9	Analysis showed that the measured redox ratio Fe(2+)/ΣFe ≈ 92–94%, that is 5.4–5.5 wt-% of FeO of the reported 5.9 wt-% Fe2O3 [64].
MgO	6.1
SiO2	1.6
Phase Composition
Major Phase I: Cr2O3-Al2O3 solid solution (corundum structure)	60 - 65	18 wt-% none-spinel Cr2O3
Major Phase II: Complex spinel	35 - 40

Figure 2. Representation of typical wear in refractories described in the literature [58, 71].

Figure 3. Schematic representation of general crucible test method. (a) crucible setup (b) cross-section of the altered refractory test coupon after material loss. The measured ‘neck loss’ is calculated by $Gc=(G-g)/2$, where Gc is the neck corrosion, G is the width of the coupon before test, and g is the width of the coupon at the melt line after test.

Table 3. Monofrax^® K-3 Corrosion data from crucible tests with glass formulations typical for DWPF HLW following the ASTM-C621 methods.

Reference	Test condition		Mass% of components of interest. wt %		Monofrax^® K-3 neck loss at melt line, average loss rate (μm/day) **
	Temperature (°C)	Time (days)	Na2O	Li2O
[60]	1100	6	13.4	2.9	0.00
	1200				14.82
					4.23
					8.47
	1300				25.40
					8.47
					8.47
[62]	1150	NA	13.7	4.1	16.26
[96, 99, 100]	1150	7	11-13	Not specified	16.26
					18.54
					5.84
					17.27
		5			20.07
					39.88
[96]*	1150	0.167			151.89
		1			37.34
		5			40.89
		0.167			182.88
		1			70.36
		5			24.64
		0.167			253.24
		1			114.81
		5			52.32
		0.167			223.27
		1			58.67
		5			23.88
		0.167			254.00
		1			46.23
		5			28.19

*Reducing additives were included in the batch to control the redox.

** The average loss rate data were calculated based on the originally reported data in non-SI units.

Table 4. Monofrax^® K-3 Corrosion data from crucible tests with a molten salt phase.

Reference	Test condition		Salt phase	Monofrax^® K-3 neck loss at melt line, average loss rate (μm/day) ***
	Temperature (°C)	Time (days)
[85]*	1100	3	0.7 wt% sulfate in feed	73.07
	1300			430.76
	1100		0.5 wt% chloride in feed	160.05
	1300			707.72
	1100		1.5 wt% chloride in feed	218.51
	1300			522.61
	1100		0.7 wt% sulfate, 1.5 wt% chloride, 4.5 wt% phosphate, and 0.6 wt% chromate in feed	50.80
	1300			527.48
[86]**	1208	3	∼ 50 wt % sulfate mixed with a pre-melted glass	151.81
				87.50
		6	Sulfate layer formed by SO2 bubbling in the glass melt	88.69
				26.33
				16.51

*The change of salt layer was not described during the tests.

**Two necks distinguishable in one coupon; one at the air/salt interface and one at the salt/glass melt interface.

***The average loss rate data were calculated based on the originally reported data in non-SI units.

Figure 4. Monofrax_® K-3 corrosion rate and normalized alkali oxide in mass % of the LAW glasses in the datasets of WTP baseline and ORP [126].

Table 5. Summary of Monofrax® K-3 corrosion data by a modified ASTM C621 method tested at 1208°C for 6 days with air bubbling in the glass melt. The average corrosion rate was converted from the reported 6-day corrosion depth at the neck/melt line in inch [126].

Dataset (number of tests)	Monofrax® K-3 corrosion rate (neck loss), μm/day			Mass% of components of interest
	minimum	maximum	median	Na2O	NAlk*	SO3	Cr2O3	Cl
All (344)	4	592	120	2.5–26	14.3–27.2	≤ 2.5	≤ 0.6	≤ 1.2
WTP Baseline (157)	4	494	98	2.5–25	14.3–26.2	0.01–2.5	≤ 0.6	≤ 1.2
ORP (178)	4	592	130	5.0–26.0	16.7–26.5	0.16–1.5	≤ 0.6	0.01–0.73
DFHLW (9)	63	539	143	17.1–24.1	21.5–27.2	≤ 0.57	≤ 0.2	≤ 0.19

* NAlk (normalized alkali oxide in mass %) = Na₂O + 0.66 K₂O + 2.07Li₂O.

Figure 5. Monofrax® K-3 refractory from disassembled scaled melters. (a) PNL-LFCM. Cross-section of the glass discharge showing glass penetration into the refractory brick joints and cracks [61]. (b) DM3300. View of the inside of the melter after the melter lid was removed. Picture shows the plenum refractory, tuckstone (yellow brick on ledge) and the K-3 refractory (black brick). The bubblers and temporary riser can also be seen [135]. (c) DM3300. K-3 glass contact refractory that was broken during the removal process. Picture shows approximately 10 cm (4 inches, the measuring tape is in inch) of loss at the melt line [135]. Reprinted with permission from refs [61] and [135].

Table 6. Refractory corrosion data from scaled melter Tests.

Melter*	Glass Pool Surface Area	Operational time (not continuous) of the inspected Monofrax® K-3 refractory		Average corrosion rate		Glass Composition
				Neck (melt line)	Riser/pour spout
PNL-LFCM [37, 61]	1.05 m^2 (rectangular, 122 cm × 86 cm)	3 years	1977–1980	23 μm/day (0.85 cm/year)	52 μm/day (1.9 cm/year)	Simulant DWPF HLW glasses (11–14 wt-% Na2O)
Project 1941 [66, 67, 94, 129]	1.17 m^2 (cylindrical, 4 ft diameter)	2 years	1978–1981	Not measured	70 μm/day (2.5 cm/year)
SCM [66, 67, 129, 130]	0.12 m^2 (roughly octagonal, 1.3 ft^2)	2 years	1979–1982	191 μm/day (7 cm/year)	279–330 μm/day (10-12 cm/year)
LSFM [66, 67, 129, 131]	1.17 m^2 (octagonal, 4 ft diameter)	2 years	1982–1985	25 μm/day (0.91 cm/year)	Not measured
SGM [66, 67, 129]	1.17 m^2 (cylindrical, 4 ft diameter)	2 years	1986–1988	found slight deform of the bottom	Not measured
IDMS [66, 67, 129]	0.29 m^2 (cylindrical, 2 ft diameter)	7 years	1988–1995	Not measured	As much as 5 cm (2 inch) Monofrax® K-3 loss was found near the drain valve
DM1200 [132, 133]	1.2 m^2 (rectangular, 34 inch × 54 inch)	5 years	2001–2006	Good condition	Not measured	Simulant WTP HLW and WTP LAW glasses
DM3300 [36, 134, 135]	3.3 m^2 (rectangular, 80 inch × 64 inch)	5 years	1998–2003	70 μm/day (10-13 cm in 5 years)	Not measured	Simulant WTP LAW glasses
RSM [136–139]	0.017 m^2 (circular, 15.2 cm diameter)**	11 weeks	2016	No measurable neck	Not measured	Simulant high Fe-Ni HLW glass

* PNL-LFCM = Pacific Northwest Laboratory – Liquid Fed Ceramic Melter, Project 1941 = a prototype melter system tested at SRS, SCM = Small Cylindrical Melter (SRS), LSFM = Large Slurry Fed Melter (SRS), SGM = Scale Glass Melter (SRS), IDMS = Integrated DWPF Melter System (SRS), DM1200 = HLW Pilot Melter (VSL/Duratek), DM3300 = LAW Pilot Melter (VSL/Duratek), RSM = Research-Scale Melter (PNNL).

** The Monofrax® K-3 lining of the RSM is exchangeable. The melter diameter is 15.2–25.4 cm (6-10 inch) surface area is 0.017–0.05 m² when using different sizes of linings.

Figure 6. Average corrosion rate (neck or melt line corrosion depth per day) as a function of time in SRNL’s crucible tests [60, 62, 96, 99, 100] and scaled melter tests [61, 66, 129, 131]. Results of crucible tests with different glass at 1100–1200°C and scaled melter tests are shown, with the rates averaged over time.

Figure 7. Corrosion of the Monofrax® K-3 refractory lining of production melters. (a) DWPF Melter 2, reprinted with permission from ref [151]. (b) SRS M-Area DM5000A, reprinted with permission from Ref. [36].

Figure 8. Summary of Monofrax® K-3 refractory corrosion data from melter and crucible tests [36, 60–62, 66, 96, 99, 100, 126, 129, 131, 149–151]. The limits of corrosion rate are shown in both of the long-term melter data plot (top, > 300 days) and the short-term crucible data plot (bottom, ≤ 7 days) for comparison. The non-SI unit inch is used in the plots as it is used in all the data source reports. The DWPF design basis of 0.0075 inch/day equals to 191 µm/day and the proposed limit of crucible test of 0.0067 inch/day equals to 169 µm/day. It should be noted that the two DWPF data points are very roughly estimated based on visual inspection of DWPF Melter 1 [149, 150] and DWPF Melter 2 [151] after end of their service.

Figure 9. Example of empirical models of Monofrax® K-3 corrosion by crucible test. (a) linear mixture model fit. (b) machine learning fit. (c) response trace plot for 13-Term reduced partial quadratic mixture model on the naturallogarithm of melt line corrosion depth. Data adapted from Muller et al. [126], Vienna et al. [127], and Smith-Gray et al. [128]. The non-SI unit inch is used in the plots as it is used in all the data source reports.

Figure 10. Diagram of dissolution at surface (a) neck corrosion on sample (1: solid, 2: liquid, 3: gas) and (b) Marangoni flow schematic showing development of corrosion groove. Adopted from Hrma [152] and Pötschke and Brüggmann [154].

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