PSFC/RR-16-5

Filling Granite and Basalt Boreholes with Rock and Nuclear Waste Glass Melts

Paul Woskov and Ken Oglesby*

*Imapact Technologies, LLC, Tulsa, OK

January 2017

Plasma Science and Fusion Center Massachusetts Institute of Technology

Cambridge MA 02139 USA This work was supported by the U. S. Department of Energy DE-SC0012308 Reproduction, translation, publication, use and disposal, in whole or in part, by or for the United States government is permitted.

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Filling Granite and Basalt Boreholes with Rock and Nuclear Waste Glass Melts

Paul Woskov and Ken Oglesby1

1Imapact Technologies, LLC, Tulsa, OK

Abstract Directed energy millimeter-wave beam melted granite, basalt, and two nuclear waste glass matrixes where used for sealing experiments of 51 mm diameter predrilled boreholes of about 200 mm depth in granite and basalt. A 28 GHz, 32 mm diameter launched diverging beam capable of 5 kW on target was used, but was generally limited to less than 4 kW due to plasma breakdown in high temperature, atmospheric pressure air. Heating times of up to 20 minutes in situ per inch (25 mm) depth caused thermal damage to the original borehole walls that was greater in granite than basalt. Basalt melt fill in a basalt borehole showed the least damage. The lower melting temperature nuclear glass waste matrix melt fills, which could be achieved with about 2 kW in 8 minutes per inch (25 mm) showed little or no wall damage.

Experiment Description

There is currently much interest in deep borehole storage of nuclear waste in basement crystalline rock formations [1, 2]. Reliably sealing the borehole after the waste is deposited is a key technological requirement. A Number approaches and studies are being investigated using grouts and clays [3–4]. Sealing with melted rock using an electric heater has also been proposed [5]. Here we investigate using a directed beam of millimeter-wave (MMW) energy to melt rock and nuclear waste glass compositions to seal a borehole.

Borehole sealing experiments using MMW beam melted rock and nuclear waste glass melts were carried out in predrilled axial boreholes in two granite and two basalt cylindrical rock specimens encased in steel pipe prepared by Impact Technologies. The directed energy heat source was the 28 GHz gyrotron system at MIT that could deliver up to a 5 kW beam on target, but power was generally limited to below the maximum by plasma breakdown. The rock cylinders were 10” (25.4 cm) in diameter, 12“ (30.5 cm) long and encased by 3/8” (0.95 cm) thick wall steel pipe. The steel casing was necessary to reinforce the rock against thermal stress breakup and is in effect representative of lithostatic constraining pressure that would be present in a deep rock formation. The boreholes were 2“ (5.1 cm) in diameter and about 8” (20.3 cm) long in the two granite specimens and in one of basalt specimens. The second basalt cylinder was completely drilled completely through with a 1” (2.54 cm) borehole. Figure 1 shows the basalt specimen with the 1 inch drilled hole sitting in the test chamber before it was exposed to the gyrotron beam.

Figure 1. View of cylindrical basalt sample with 1” (25 mm) drilled bore hole in steel casing inside test

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The gyrotron beam was a circularly polarized TE11 cylindrical beam launched from a 1.27“ (32.5 mm) internal diameter copper waveguide. The launched beam diverges as it propagates from the launch aperture and it was typically necessary to locate the target surface 2 – 3” (5.1 – 7.6 cm) from the launch aperture to adequately heat a 2” (5.1 cm) diameter surface area. The rock specimens were exposed to the gyrotron beam in a completely enclosed steel test chamber with internal Teflon water tubing to trap all the millimeter-wave radiation for energy balance measurements and to prevent exposure of millimeter-waves to personnel. Figure 2 shows the setup with the 1.66” (4.22 cm) outside diameter copper waveguide going in through the top of the test chamber. The main body of the test chamber was 32” (81.3 cm) in diameter and 24” (61.0 cm) tall with 36“ (91.4 cm) square bottom and top covers. The test chamber was placed on a hydraulic lift to insert and withdraw the waveguide and adjust its distance to the target surface.

The 2” (5.1 cm) diameter boreholes were filled in small batch increments. Typically a small cube of basalt or granite about 1” (2.54 cm) on a side was placed in the hole, heated to melting after which the gyrotron was turned off, the test chamber lowered, another cube of material loaded into the hole, the test chamber raised back into position, and the gyrotron turned on again. This was repeated as many times as necessary to fill the hole. Figure 3 shows a basalt cube inside the 2” (5.1 cm) borehole in the basalt specimen resting on top of previously melted basalt cubes.

Figure 2. Test chamber on a hydraulic lift with copper waveguide entering from top.

Figure 3. 1” (25 mm) square basalt cube inside 2” (5.1 cm) diameter borehole in basalt resting on previously melted cubes that cooled into a black glass.

Figure 4. 20 mm diameter green glass spheres inside 2” (5.1 cm) diameter borehole in granite resting on previously melted glass still glowing.

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In the case of the nuclear waste glass compositions, two type of nuclear glass waste matrix were used to fill parts of the 2” (5.1 cm) diameter borehole in one of the granite specimens. One was a green glass matrix analyzed at the Savannah River Technology Center (SRTC), with the composition listed in Appendix 1 and the other was a Hanford #8 high level waste (HLW) black glass matrix prepared at Hanford Site with composition listed in Appendix 2. The green glass came in the form of 2 cm (0.787”) spheres that were loaded into the borehole 3 – 7 at a time and the Hanford #8 black glass was in the form of a granular frit that was loaded at 30 – 60 grams per batch. Figure 4 shows seven green glass spheres loaded into a granite borehole resting on top of previously melted glass spheres that are still glowing incandescent.

Recorded Data

The test setup was instrumented for various power and temperature measurements to record the power incident on the specimen, temperatures that were achieved, and to determine the emissivity (how well the millimeter-waves were absorbed) throughout the high temperature range studied. The main data signals recorded were:

1. 28 GHz Beam forward power by a schottky diode sensor at the gyrotron output calibrated to the actual power transmitted into the test chamber and incident on the specimens.

2. Thermal emission (product of temperature and emissivity) of the heated surface by a 137 GHz heterodyne receiver radiometer view collinear with the heating beam and calibrated to the temperature at the waveguide launch aperture.

3. 28 GHz Beam power scattered (unabsorbed by the rock) into the test chamber by the Teflon water coil inside the test chamber. This was also used to calibrate forward power into the test chamber when no specimen was present.

4. 28 GHz Beam power reflected back up the waveguide to a reflected power isolator that prevents reflections going all the way back to the gyrotron.

5. Infrared radiated thermal emission from the heated specimen by a copper water coil inside the top of the test chamber. The copper reflects the 28 GHz millimeter-waves.

6. Temperature of the outside of the cylindrical test specimen about half way between the top and bottom by a type k thermocouple.

The actual signals for the power measurements using the water coils inside the test chamber and reflected power isolator were not direct but achieved by measuring the temperature rise of the water in each coil by differential thermocouples and the water flow volume with flowmeters and then calculating the power deposited into the water. The test chamber Teflon coil and the reflected power isolator Teflon coils were in series on one flowmeter, which caused a spurious spike in the calculated isolator power in the data presented below whenever there was a rapid change in the test chamber coil absorbed power that caused a temporary temperature gradient in the water flow through the to the isolator.

The 137 GHz radiometer was calibrated within an inch (2.54 cm) distance from the waveguide launch aperture with a black body (emissivity equal to 1.0) filling the radiometer field of view with a known temperature. The temperatures plotted below are for this calibration and do not correct for the rock/ melt emissivity of less than 1.0 or for the divergence of the field of view, which would include cooler regions at distances greater than one inch (2.54 cm) from the waveguide. Consequently, the plotted temperatures are lower limits to actual peak temperatures achieved, which could be as much as 40 to 50% higher.

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Basalt Cube Melt Pretest

One basalt cube was first melted on a flat slab of granite to determine if the beam power and exposure times to be used would be sufficient to completely melt the cube and if the melt would flow enough to fill a 2” (5.1 cm) diameter borehole area. The result of this test is shown in Figure 5 and the recorded data is plotted in Figure 6. The approximately 1” (2.54 cm) dimensioned basalt cube was placed on a 1” (2.54 cm) thick, 4”(10 cm) square granite slab that was located inside the test chamber on top of one of the cylindrical test specimens as shown in Figure 1. The waveguide launch aperture was brought to about 1” (2.54 cm) distance from the top of the basalt.

The 15 minute MMW beam exposure starting at an incident power of about 0.8 kW and stepping up to a maximum power of 3.9 kW for about 2 minutes at the end was sufficient to mostly melt the cube and flow occurred to a maximum of 3.75” (7 cm) in one dimension. The melt flow was helped by a waveguide flow of air collinear with the heating beam of about 490 scfh. A small layer of unmelted basalt about 4 mm thick under the visible melt in Figure 5 was found. Inside a deep borehole heat would be trapped and with preheating of the hole this level of beam exposure or longer would be sufficient for the planned tests.

The radiometer temperature plot in the middle graph in Figure 6 shows a rather complex behavior indicative of several process going in within its field of view. Sharp upward spikes on a relatively slow changing base temperature are interpreted as plasma breakdown events with some longer lasting events after about 900 seconds. Concern for more arcing limited the exposure time and power level.

The main temperature level also

fluctuates after 900 seconds when the basalt cube is melting, flowing, and receding from the waveguide. Note that at these later

Figure 6. Data for melting a 1” (25 mm) basalt cube on top of a granite slab. Top: incident gyrotron power and unabsorbed powers, Middle: 137 GHz radiometer temperature and basalt emissivity, Bottom: heat to test chamber top and thermocouple below granite slab.

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Figure 5. A 1” (25 mm) basalt cube melted on a granite slab.

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times the lower level radiometer temperature is only about 1000 °C. The melting temperate of basalt is known to be about 1200 °C confirming that the radiometer calibration with a black body at the waveguide launch aperture underestimates the actual peak surface temperatures.

The emissivity at 28 GHz, or how well this power was absorbed, by the melting basalt was

determined by subtracting the unabsorbed power measured by the test chamber and refection isolator water coils and subtracting from the incident power and then dividing by the incident power. These measured powers are plotted in the top graph of figure 5 and the resulting emissivity is plotted in the middle graph along with the radiometer temperature. The test chamber power plot was corrected for the background temperature rise as measured by the copper coil and thermocouple temperatures plotted in bottom graph. The 28 GHz emissivity generally decreases with temperature to a value near 0.7 in this test (the upward bumps coincident with incident power changes a spurious). Assuming that the emissivity is the same at the 137 GHz radiometer frequency, then the 1000 °C black body calibrated temperature would be about 1400 °C. This temperature would still be too low because the melt surface has receded from the waveguide and the hot area does not fill the receiver field of view.

Granite Borehole Filled with Basalt

The first cylindrical rock specimen filled with rock melt was a granite cylinder with a 2 inch (5 cm) diameter borehole, 8” (20 cm) deep. It took 17 basalt cubes to fill this hole over two days heating one cube at a time. The data for the third basalt cube when the cubes were still deep inside the hole is shown in Figure 7. For this basalt cube the MMW beam exposure lasted a total of 19 minutes at a power of 1 kW for the first 3 minutes and then was mostly over 3 kW with a maximum of 3.9 kW for the last 2 minutes. The unabsorbed power, plotted in the top graph, was almost zero as measured by the water loads in the test chamber and reflected power isolator. This would be expected by power trapping inside the hole. The resulting 28 GHz emissivity was high, slowly dropping with temperature to 0.91 at its lowest as shown in the middle graph. The radiometer temperature also showed the characteristic noisy signature of breakdown after 750 seconds.

The data for the 17th and final basalt cube that was used to finish the fill of the granite borehole

is shown is Figure 8. The MMW beam exposure for this cube was turned on for 1 hour with the first 30 minutes at about 1 kW after which it was stepped up to 4.9 kW for the last 9 minutes. The waveguide launch aperture was located 3 “(7.6 cm) above the basalt cube at the start so that after melting the target surface was 4” (10.2 cm) from the waveguide. The unabsorbed power is much larger now that the incident surface is not inside the borehole. The resulting 28 GHz emissivity decreases to a low of about 0.70.

The observed MMW surface temperature in the middle graph is lower than inside the borehole

because the radiometer field of view expands to include cooler areas. Also there is in no indication of plasma breakdown. This is likely due to the 4” (10.2 cm) beam divergence distance from the waveguide to the heated spot, reducing incident intensity, and the continued 490 scfh airflow through the waveguide directed at the surface.

A slice of the core 4” (10.2 cm) below the top is shown in Figure 10. The original 2” (5.1 cm)

diameter borehole wall was damaged by the heat applied to melt the basalt fill. The diameter of the pre drilled granite hole was increased to a slight oval of about 2 9/16” (6.5 cm) by 2 3/8” (6.0 cm). The material coming off the wall formed a 5/16” (0.8 cm) maximum of loose sand-like rubble between the

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basalt plug and the undamaged granite. In addition, the basalt plug is fractured, and there is a small fragment missing near the center that occurred during slicing.

Figure 7. Data for the 3rd basalt fill cube of the 2” diameter hole in granite.

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Figure 9. Top view of the granite specimen with a 2” (5.1 cm) borehole filled with melted basalt.

Figure 10. Slice 4”( 10.4 cm) below top the of granite specimen with the basalt melt filled borehole.

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After the borehole was filled with the 17 melted basalt cubes, a 5 5/8” (14.3 cm) core from the

original 10” (25.4 cm) diameter granite was cut and sliced for examination. The top of the filled hole is shown in Figure 9. It has a smooth concave appearance caused by the impinging airflow on the surface.

Basalt Borehole Filled with Basalt

The basalt cylinder with a 2” (5.1 cm) diameter borehole was filled next. Its depth was a little over 8” (20.3 cm) taking 19 basalt cubes to fill. Two 14 minute MMW beam exposures were necessary to melt the first basalt cube after it was found that the first exposure did not completely melt the cube. The test chamber was lowered about 1” (2.54 cm) for the second exposure increasing the distance from the waveguide launch aperture to 3” (7.6 cm) from the top of the original height of the cube to allow MMW beam divergence to increase beam size on target.

The data for the second MMW beam exposure is shown in Figure 11. The MMW beam power

was turned on at 1.3 kW for the first 1.5 minutes and then increased to 2.8 to 3.1 kW for the rest of the exposure. Examination after the second exposure revealed that the basalt was well melted across the borehole diameter. There was no MMW beam scatted power into the test chamber from the deep borehole, but the reflected power isolator in the waveguide did receiver receive sufficient power to reduce the 28 GHz emissivity to about 0.79 at the highest temperature. The MMW radiometer temperature rapidly increased to a maximum of about 1900 °C, corrected for emissivity only, and showed numerous instances of breakdown sparking.

Figure 11. Data for second exposure of the first basalt cube in the 2” ( 5.1 cm) diameter basalt borehole.

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Figure 12. Data for 19th and final basalt fill cube of the 2” ( 5.1cm) diameter basalt borehole.

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The data for the 19th and final basalt cube used to fill the 2” (5.1 cm) diameter basalt borehole is shown is Figure 12. The MMW beam was on for a total of 15 minutes, staring at about 1.5 kW for the first 2 minutes and then increased to between 3.2 to 3.6 kW for the rest of the exposure. The waveguide launch aperture distance from the top of the basalt cube was maintained at about 3” (7.6 cm) as for the previous basalt fill cubes. Unabsorbed 28 GHz beam power scattered into the test chamber was observed with the waveguide launch aperture raised outside the borehole, but a somewhat lower level was detected in the reflected power isolator resulting in a 28 GHz emissivity not much lower than inside the borehole. The 28 GHz emissivity was at about 0.76 at the highest temperature. The surface MMW radiometer temperatures were much lower than inside the borehole demonstrating the divergence of the radiometer field of view to see cooler regions outside the borehole.

The resulting borehole basalt melt fill after cool down, coring, and slicing is shown in Figures 13 and 14. The slice was made 4” (10.2 cm) below the top of the borehole. Figure 13 is looking up toward the top of the borehole and Figure 14 is looking down on the same cut. The surfaces are displaced along the borehole by the thickness of the cutting blade of 1/8” (3 mm). There is less damage to the basalt borehole wall compared to the granite. However, the diameter of the original borehole has increased to 2 5/16” (5.9 cm) and there is a thin weaker melt annulus about 1/16 -1/8” (1 - 3 mm) thick between the melt plug and original basalt rock that was more easily chipped by the slice cut. Also, the basalt parent rock and the melt core plug both have many thermal stress fractures. In order to prevent the core from breaking apart along these fractures during the slicing cut, the core was wrapped in duct tape (red in photos) before cutting.

Granite Filled with Granite and Nuclear Waste Glasses

The second granite cylinder with a 2” (5.1 cm) diameter borehole was filled with three different melts (from the bottom up in the following order): 1” (2.54 cm) cubes of granite, 2 cm (0.787”) diameter spheres of green glass nuclear waste matrix (Appendix 1), and Hanford #8 nuclear glass frit (Appendix 2).

Figure 13. Slice 4” below the top of the basalt specimen with a 2” borehole filled with basalt melt looking upward.

Figure 14. Same slice as in Fig. 13, but looking down.

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The borehole was 8 3/8” (21.3 cm) deep. Six granite cubes where used for the bottom 5 1/8” (13 cm) length of the borehole, 20 spheres of the green glass were used for the next 1 7/8” (4.8 cm), and 239.6 grams of Hanford #8 glass frit where used for the top 1 3/8” (3.5 cm) length of the borehole.

In general it proved harder to melt the graphite cubes than the basalt and the granite melt did not flow well to completely fill the 2” (5.2 cm) diameter borehole. The data for the 6th and last granite cube still deep in the borehole is shown in Figure 15. The MMW beam power was on for a total of 20 minutes, starting at a power level of 1.8 kW and stepped up to 3.7 kW for the last 4 minutes. Longer exposure times and higher power levels would have been desirable, but plasma breakdown was occurring, as seen in the MMW radiometer temperature plot. Higher power for longer times into the plasma would just cause more damage to the borehole wall and possibly the waveguide. The 28 GHz power absorption was good as shown by the emissivity trace with a low value of 0.93.

The nuclear waste glass matrixes where much easier to melt and flow than basalt and granite, taking much less MMW beam power and exposure times. These glasses have been formulated to melt at low temperatures (~ 1100 °C) to be compatible with joule heated melters using inconel electrodes. Twenty spheres of the green glass matrix (Appendix 1) where melted in batches of 3 to 7 spheres (7 spheres are seen in Figure 4) at a time. The data for the finial 6 sphere batch is shown in Figure 16. The MMW beam was on for 8 minutes at an incident power of about 2 kW. A good level melt filling the 2” (5.1 cm) diameter borehole was produced. The uncorrected MMW radiometer temperature is almost half that observed with basalt and granite melts inside a borehole and the 28 GHz emissivity at maximum temperature was 0.93.

The data for the Hanford #8 is shown in Figure 17 for the last 30 gram batch of fill at the top of the borehole. The MMW beam was on for

Figure 15. Data for the 6th granite cube melt inside the 2” (5.1 cm) diameter borehole in granite.

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Figure 16. Data for a 6 sphere batch of green nuclear waste glass matrix melted inside the 2” 95.1 cm) diameter granite borehole.

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about 9 minutes staring at a power level of 2 kW and increasing to 2.7 kW for the last 3 minutes. The uncorrected MMW radiometer temperature is lower than pervious results for basalt on top of filled boreholes, but the observed 28 GHz emissivity at maximum temperatures is similar at 0.73.

After coring and slicing 5” (12.7 cm) below the top surface of the cylindrical granite specimen, the granite melt fill in the borehole is shown in Figure 18. The melted granite only filled about the central 1 11/16” (4.3 cm) diameter of the borehole. It did not flow to the walls. The longer MMW beam exposures with higher power in plasma breakdown mode only caused more erosion of the borehole wall, which increased its size to about a 2 5/8” x 2 1/8” (6.7 cm x 5.4 cm) oval. The annular region between the cooled hard melt and the undamaged granite is just loose granular fill. The loss of directed

energy with plasma breakdown prevented raising the melt temperature higher to decrease viscosity and reemitted the heat to the surroundings eroding the wall.

An axial slice of the top 5” (15.7 cm) length of the granite specimen offset 7/8” (22 mm) from the center of the borehole was made to expose the three different melt fills. This slice is shown in Figure 19. It is evident as we move up the borehole from granite melt to green glass melt and Hanford #8 glass that the borehole wall damage decreases to zero as seen by the lighter colored boundary between the melts and the granite that tapers down in thickness to nothing at the Hanford #8 melt. The lower melting temperature of the nuclear waste glass matrixes reduced the MMW beam power and exposure times that prevent plasma breakdown and damaging heat to the borehole wall. The damage seen opposite the green glass was caused when melting the granite cubes when the waveguide launch aperture was located just above the green glass layer.

Figure 17. Data for final 30 gr batch of Hanford #8 glass melt complete to fill of the 2” (5.1 cm) diameter granite borehole.

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Basalt with 1 inch Through Borehole Enlarging Attempt

The 4th cylindrical test specimen exposed to the gyrotron beam was the basalt with a 1” (2.5 cm) borehole going completely through the 12” (30.5 cm) long sample. The goal of this test was to increase the size of the hole with the larger diameter gyrotron beam using the 1” (2.5 cm) diameter borehole to provide a path for the basalt melt to flow out the bottom. The data for the first exposure is shown in Figure 20. The MMW beam power was on for a total of 84 minutes, staring at a power level of about 1 kW for the first 20 minutes and then increased rapidly to a maximum power of 4.9 kW, but encountering a large plasma breakdown as seen in the radiometer temperature plot. The power was backed off to 3.9 kW for 8 minutes allowing the plasma to die down and then increased to about 4.5 kW for about 18 minutes before being stepped down to shut off over the last 29 minutes. The 28 GHz emissivity decreased to a minimum of about 0.79 at maximum temperature and was higher at the beginning and end of the of the MMW beam exposure at lower temperatures.

Examination of the top of this sample after the MMW beam exposure showed a melt carter about 2” (5.1 cm) diameter and about ¾” (2 cm) deep in the center. Additional beam exposures on this end of the specimen and flipped to the other side did not produce a lager borehole, but instead plugged the original 1” (2.5 cm) diameter hole with a larger 2” (5.1 cm) diameter melt cater visible at each end where the MMW beam was incident.

The cored specimen is shown in Figure 21. The view is toward the top of the first surface

exposed, which is seen in Figure 1 before exposure. The basalt was fractured throughout by the thermal stresses and large fragments broke completely of he ends after the coring tool was removed. Another view after drying and more breakoff exposing a ½” (1.3 cm) leak hole that was originally 1.5” (3.8 cm) below the top of the basalt specimen is shown in Figure 22. The use of water pressure to help extract

Figure 18. Slice 5” below top of granite specimen with 2” diameter borehole showing fill with granite melt

Figure 19. Axial slice of the top 5” length of the granite borehole, 7/8” (22 mm) off center of the 2” diameter. Glass melts from top: Hanford #8, green glass, granite.

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the core from the coring tool accentuates the factures with wetted surfaces that followed the cracks. This can be clearly seen in the side view of Figure 23.

Leak holes ½” (1.3 cm) in diameter were drilled into the side of this basalt cylinder, as seen in Figs. 22 and 23, to help the melted basalt flow from the beam, but where the melt reached these holes near the ends of the specimen the flow only went about 1.25” (3.2 cm) in before it froze up. The melt flow in the 1“ (2.5 cm) diameter axial borehole, after slicing the core in half, was observed to only penetrated about 4” (10.2 cm) from either end before freezing. It is apparent that the surrounding rock is too cold to sustain a slow melt flow too far under the influence of only gravity.

Figure 20. Data for the basalt cylinder with a 1” (2.54 cm) diameter through borehole.

Figure 21. Top view of the basalt specimen with 1” (2.54 cm) diameter through hole after MMW beam exposure and coring. See Fig. 1 for before exposure view.

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Conclusions

It is apparent from these experiments, done at atmospheric pressure and at 20 °C temperature, that melting basalt or granite as a plug material at approximately 15 – 20 minute per inch inside granite or basalt boreholes causes damage to the original borehole wall. The wall damage is much more significant in the large mineral grained granite than in the more homogeneous fine grained basalt, but the basalt suffers much more from thermal fracturing in the body of the rock going away from the borehole. In these tests basalt as the melt plug material worked better than granite because it flowed better (lower viscosity) than granite to fill the borehole cross section. The longer MMW beam time periods needed to try to make the granite flow out to the wall caused much more wall damage as seem in Figure 18 as compared to Figure 10.

It is possible that under high deep subsurface pressures, temperature generated borehole over

pressures, and with higher beam intensities that such damage could be mitigated. At higher pressures higher beam intensities would be possible because plasma breakdown threshold increases with pressure. With the higher power shorter beam exposures could be used to melt the plug material while reducing energy to the walls. Borehole over pressure could compress and seal any wall damage, repairing what is seen in these open hole laboratory experiments. Further study would be needed in a pressurized test chamber to study this possibility.

Much more success with plugging and reducing borehole wall damage under laboratory

conditions was seen with the nuclear waste glass matrixes. These glass formulations were designed to melt at lower temperatures and were also observed here to flow better (lower viscosity) that allowed using lower power and shorter MMW beam exposure times. This represents a possible new option to sealing deep nuclear storage boreholes by using the same nuclear waste vitrification matrix outside the waste canisters that is used inside.

Figure 22. Another view of end shown in Fig. 21 after more break off.

Figure 23. Side view of basalt core with original 1” (2.5 cm) diameter through borehole after MMW beam exposure, coring, and extraction from coring tool with water pressure.

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References

1. Bill W. Arnold, Patrick V. Brady, and Robert J. MacKinnon, ‘Deep Borehole Disposal of Nuclear Waste”, Trans. of the American Nuclear Soc., Vol. 109, 921-922, Washington, D.C., 2013.

2. E.A. Bates, M.J. Driscoll, R.K. Lester, B.W. Arnold, “Can deep boreholes solve America's nuclear waste problem?” Energy Policy, Vol. 72, 186-189, 2014.

3. Nicholas C. Collier, Neil B. Milestone, Karl P. Travis, Fergus G.F. Gibb, “The effect of organic retarders on grout thickening and setting during deep borehole disposal of high-level radioactive waste”, Progress in Nuclear Energy, Vol. 90, 19-26, 2016.

4. E. A. Bates, A. Salazar, M. J. Driscoll, E. Baglietto, and J. Buongiorno, “Plug Design for Deep Borehole Disposal of High-Level Nuclear Waste”, Nuclear Technology, Vol. 188 280-291, 2014.

5. Fergus G. F. Gibb and Karl P. Travis, “Sealing Deep Borehole Disposals of Radioactive Waste by ’ROCK WELDING’ ”, 5th International High-Level Radioactive Waste Management Conference 2015, IHLRWM 2015, 401-406, 2015.

Acknowledgment

Supported by the U. S. Department of Energy DE-SC0012308.

15

Appendix 1

Green Glass

16

Appendix 2

Hanford #8 Glass