US-12626828-B1 - Tritium-compatible cryogenic pellet gas gun

Abstract

A tritium-compatible pellet gas gun for a deuterium-tritium (D-T) pellet fueling apparatus is provided. In one aspect, the tritium-compatible pellet gas gun includes a pellet sizer assembly that provides in situ adjustment of pellet length during injector operation. The pellet sizer assembly includes a guillotine slide that is actuated by a pusher tube, the guillotine slide being operable to restrict the orifice of the extruder nozzle to reduce pellet length with fine resolution. The tritium-compatible pellet gas gun also includes dual flexible metal bellows seals that maintain hermetic separation between the D-T fuel region, a guard vacuum, and the ambient environment, while still permitting linear motion. This configuration allows the pellet length to be reduced by up to 50% without venting or warming the D-T pellet fueling apparatus.

Inventors

• Larry R. Baylor
• Steven J. Meitner
• William D. McGinnis

Assignees

• UT-BATTELLE, LLC

Dates

Publication Date

20260512

Application Date

20250930

Claims (17)

1. 1 . A tritium-compatible gas gun for producing cryogenic fusion fuel pellets from a solid extrusion ribbon as the solid extrusion ribbon is discharged from an extruder through an extruder nozzle opening, the gas gun comprising: a pellet sizer assembly including an adjustable guillotine slide that is configured to restrict the extruder nozzle opening, the guillotine slide being an elongated rectangular member, the pellet sizer assembly further including a first flexible metal bellows seal and a second flexible metal bellows seal; wherein the first flexible metal bellows seal includes series-connected bellows on either side of a first flange, the second flexible metal bellows seal includes series-connected bellows on either side of a second flange, the first flange being coupled to the second flange via a pusher tube, and the second flange being rigidly coupled to the guillotine slide, such that lateral movement of the first flange causes lateral movement of the second flange via the pusher tube, thereby causing lateral movement of the guillotine slide to at least partially restrict the extruder nozzle opening; a cutter assembly including a cutter solenoid housing, a cutter tube, a plunger operatively coupled to a first solenoid coil, and a spring assembly to absorb return shock from the plunger; a gun barrel concentrically disposed within the pusher tube and configured to receive pellets that have been cut from the solid extrusion ribbon by the cutter tube; and a propellant valve assembly including a valve body, a second solenoid coil, a shuttle armature that is operatively coupled to a valve tip such that energization of the second solenoid coil causes the valve tip to unseat from a valve seat, and a return spring configured to reseat the valve tip and maintain seal tightness when the second solenoid coil is deenergized.
2. 2 . The gas gun of claim 1 , wherein the pusher tube extends outside of a guard vacuum chamber for positioning the guillotine slide.
3. 3 . The gas gun of claim 1 , wherein the adjustable guillotine slide of the pellet sizer assembly is configured to reduce fuel pellet length by up to 50%.
4. 4 . The gas gun of claim 1 , wherein the first flexible metal bellows seal is positioned to separate a guard vacuum from an ambient environment.
5. 5 . The gas gun of claim 4 , wherein the second flexible metal bellows seal is positioned adjacent the extruder to separate the guard vacuum from a deuterium-tritium (D-T) fuel environment.
6. 6 . The gas gun of claim 1 , wherein the spring assembly includes a metal wave spring and metal washer, the metal wave spring being positioned to absorb return shock from the plunger.
7. 7 . The gas gun of claim 1 , wherein the shuttle armature of the propellant valve assembly is free-floating relative to the valve tip.
8. 8 . The gas gun of claim 1 , wherein the valve body of the propellant valve assembly consists entirely of stainless steel.
9. 9 . The gas gun of claim 1 , wherein the valve body of the propellant valve assembly includes a first end portion joined to a second end portion by a square groove weld.
10. 10 . A method of producing and injecting cryogenic fusion fuel pellets with a tritium-compatible gas gun, the method comprising: sizing a pellet by actuating an adjustable guillotine slide to restrict an orifice of an extruder nozzle, the guillotine slide being sealed by a first metal bellows seal and a second metal bellows seal, wherein the guillotine slide is an elongated rectangular member, and wherein each of the first metal bellows seal and the second metal bellows seal includes series-connected bellows on either side of a flange, the flange of the first metal bellow seal being coupled to the flange of the second metal bellows seal by a pusher tube that surrounds a gun barrel, such that lateral movement of the first metal bellows seal causes lateral movement of the second metal bellows seal via the pusher tube, thereby causing lateral movement of the guillotine slide; cutting the pellet from a solid extrusion by plunging a cutter tube into the solid extrusion and absorbing a return shock of the cutter tube with a metal spring assembly; and propelling the pellet through the gun barrel, the gun barrel being concentrically disposed within the pusher tube, by energizing a solenoid coil to draw a shuttle armature toward a valve body to lift a valve tip from a valve seat, and thereafter reseating the valve tip with a return spring when the solenoid coil is deenergized to maintain seal tightness.
11. 11 . The method of claim 10 , wherein the first metal bellows seal separates a guard vacuum from an ambient environment.
12. 12 . The method of claim 11 , wherein the second flexible metal bellows seal separates the guard vacuum from a deuterium-tritium (D-T) fuel environment.
13. 13 . The method of claim 10 , wherein the guillotine slide is actuated to reduce pellet length by up to 50%.
14. 14 . The method of claim 10 , wherein absorbing the return shock comprises compressing a metal wave spring disposed in the cutter assembly.
15. 15 . The method of claim 10 , wherein the shuttle armature of the propellant valve assembly is maintained free-floating relative to a valve tip.
16. 16 . The method of claim 10 , wherein the valve body of the propellant valve assembly is formed entirely of stainless steel.
17. 17 . The method of claim 10 , further comprising monitoring cutter operation by measuring shock loads with a shock accelerometer coupled to the cutter assembly.

Description

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT This invention was made with government support under Contract No. DE-AC05-00OR22725 awarded by the U.S. Department of Energy. The government has certain rights in the invention. FIELD OF THE INVENTION The present invention relates to cryogenic fueling systems for deuterium-tritium fusion reactors and other applications. BACKGROUND OF THE INVENTION Deuterium-tritium (D-T) fusion reactors require the continuous injection of solid cryogenic fuel pellets into a plasma. This operation generally requires accelerating pellets that are cut from a continuous extrusion composed of frozen hydrogen isotopes. Gas gun pellet injectors were developed specifically for deuterium-deuterium (D-D) fusion experiments, however several shortcomings remain for use with D-T fusion reactors. The original gas gun pellet injector developed at Oak Ridge National Laboratory used a moving barrel to cut and chamber pellets. However, this configuration allowed misalignment between the barrel and a downstream injection line guide tube. A later gas gun pellet injector design improved reliability by using a solenoid-driven cutting tube and a fixed barrel. In operation, the cutting tube punches out and chambers a pellet into the barrel, after which a fast-opening solenoid valve releases high-pressure propellant gas (helium, hydrogen, deuterium, or tritium) to accelerate the pellet to speeds up to 1 km/s, with demonstrated injection frequencies above 5 Hz. Despite these advances, existing gas gun pellet injectors suffer from several shortcomings for use with a D-T fusion reactor. The pellet size is fixed by the cutter diameter and extrusion nozzle dimensions, requiring system warm-up and component replacement for adjustment. Long-term tritium compatibility is also limited by: solenoid coil insulation, neoprene bump stops, and polymer seals that degrade in a tritium environment, creating debris, leaks, or electrical failures. Mechanical stresses on brazed joints between the plunger and the cutter tube can cause fatigue and separation, halting pellet cutting and operation of the injector. Furthermore, the propellant valve and its solenoid housing includes welds and dissimilar metal joints that are difficult to qualify under emerging tritium boundary standards, which require 100% volumetric inspection of primary boundary welds. Fillet welds and dissimilar joints, commonly used in prior designs, are not acceptable for such qualification. Accordingly, there remains a continued need for an improved cryogenic pellet gas gun that provides tritium compatibility for D-T pellet injection. In particular, there remains a continued need for an improved pellet gas gun that can operate with tritium and meets tritium boundary standards for long pulse fusion power production and for other applications involving long-pulse, high density magnetically-confined plasmas for energy production. SUMMARY OF THE INVENTION A tritium-compatible pellet gas gun for a D-T pellet fueling apparatus is provided. In one aspect, the tritium-compatible pellet gas gun includes a pellet sizer assembly that provides in situ adjustment of pellet length during injector operation. The pellet sizer assembly includes a guillotine slide that is actuated by a pusher tube, the guillotine slide being operable to restrict the orifice of the extruder nozzle that feeds that gas gun to to provide adjustment of pellet length with fine resolution. The tritium-compatible pellet gas gun also includes dual flexible metal bellows seals that maintain hermetic separation between the D-T fuel region, a guard vacuum cryostat, and the ambient environment, while still permitting linear sizer motion. This configuration allows the pellet length to be reduced without venting or warming the system. In another aspect, the tritium-compatible pellet gas gun includes a cutter assembly within a solenoid coil located outside of the D-T gas boundary of a pellet fueling apparatus. A stainless-steel solenoid housing functions as a magnetic insulator, while high-permeability steel components complete the magnetic circuit. A cutter plunger that is actuated by the solenoid is secured to a hollow actuator rod with a threaded and brazed connection, and return shock is absorbed by an all-metal bump stop with a wave spring, thereby eliminating tritium-incompatible polymer materials. The actuator rod is coupled to a cutter tube that is machined from stainless steel. The actuator rod is actuated by the plunger to drive the cutter tube forward. When driven forward, the cutter tube cuts a cylindrical pellet from the solid extrusion and chambers the cylindrical pellet into the gun barrel. The cutter tube is spring loaded to return the plunger against the stop when the solenoid electrical pulse actuation ends. In a further aspect, the tritium-compatible pellet gas gun includes a propellant valve assembly having a valve body, optionally constructed of stainless steel. The