Patent Number: 
Section: claims

1. A subcritical aqueous assembly having a negative coefficient of reactivity, the aqueous assembly comprising:a vessel;an aqueous solution, including a fissile solute including uranium, supported in the vessel;a neutron source for maintaining a fission reaction with the fissile solute at a subcritical level within the vessel; anda reactivity stabilizer disposed within the aqueous solution to reduce a magnitude of the negative coefficient of reactivity of the subcritical aqueous assembly during operation of the subcritical aqueous assembly, wherein the reactivity stabilizer includes boric acid. 2. The aqueous assembly of claim 1, wherein the coefficient of reactivity is a solution temperature coefficient of reactivity. 3. The aqueous assembly of claim 1, wherein the coefficient of reactivity is a solution void coefficient of reactivity. 4. The aqueous assembly of claim 1, wherein the fissile solute includes at least one of uranyl nitrate, uranyl sulfate, and uranyl fluoride. 5. The aqueous assembly of claim 1, wherein the reactivity stabilizer includes boron-10. 6. The aqueous assembly of claim 1, wherein the reactivity stabilizer further includes at least one of gadolinium-155 and gadolinium-157. 7. The aqueous assembly of claim 1, further comprising a control rod, at least a portion of the control rod being selectively disposed within the aqueous solution to at least partially control a reactivity within the aqueous solution. 8. A method of operating a subcritical aqueous assembly having a negative coefficient of reactivity with a magnitude, the method comprising:adding an aqueous solution, including a fissile solute including uranium, to a vessel;adding a reactivity stabilizer to the aqueous solution, wherein the reactivity stabilizer includes boric acid;operating a neutron source to sustain a fission reaction with the fissile solute of the aqueous solution at a subcritical level; andreducing the magnitude of the negative coefficient of reactivity of the subcritical aqueous assembly during operation of the subcritical aqueous assembly. 9. The method of claim 8, further comprising withdrawing a control rod until the aqueous solution achieves criticality. 10. The method of claim 8, wherein the reactivity stabilizer includes boron-10. 11. The method of claim 8, wherein the reactivity stabilizer further includes at least one of gadolinium-155 and gadolinium-157. 12. The method of claim 8, wherein reducing the magnitude of the coefficient of reactivity includes reducing a magnitude of a negative temperature coefficient of reactivity. 13. The method of claim 8, wherein reducing the magnitude of the coefficient of reactivity includes reducing a magnitude of a negative void coefficient of reactivity. 14. A subcritical aqueous assembly having a negative coefficient of reactivity, the aqueous assembly comprising:a vessel;an aqueous solution, including a fissile solute including uranium, supported in the vessel;a neutron source for maintaining a fission reaction with the fissile solute at a subcritical level within the vessel; anda reactivity stabilizer disposed within the aqueous solution to reduce a magnitude of the negative coefficient of reactivity of the subcritical aqueous assembly during operation of the subcritical aqueous assembly, wherein the reactivity stabilizer is a solute of the aqueous solution. 15. The aqueous assembly of claim 14, wherein the coefficient of reactivity is a solution temperature coefficient of reactivity. 16. The aqueous assembly of claim 14, wherein the coefficient of reactivity is a solution void coefficient of reactivity. 17. The aqueous assembly of claim 14, wherein the fissile solute includes at least one of uranyl nitrate, uranyl sulfate, and uranyl fluoride. 18. The aqueous assembly of claim 14, wherein the reactivity stabilizer includes at least one of boron-10, gadolinium-155, and gadolinium-157. 19. The aqueous assembly of claim 14, further comprising a control rod, at least a portion of the control rod being selectively disposed within the aqueous solution to at least partially control a reactivity within the aqueous solution. 20. A method of operating a subcritical aqueous assembly having a negative coefficient of reactivity with a magnitude, the method comprising:adding an aqueous solution, including a fissile solute including uranium, to a vessel;adding a reactivity stabilizer to the aqueous solution, wherein the reactivity stabilizer is a solute of the aqueous solution;operating a neutron source to sustain a fission reaction with the fissile solute of the aqueous solution at a subcritical level; andreducing the magnitude of the negative coefficient of reactivity of the subcritical aqueous assembly during operation of the subcritical aqueous assembly. 21. The method of claim 20, further comprising withdrawing a control rod until the aqueous solution achieves criticality. 22. The method of claim 20, wherein the reactivity stabilizer includes at least one of boron-10, gadolinium-155, and gadolinium-157. 23. The method of claim 20, wherein reducing the magnitude of the coefficient of reactivity includes reducing a magnitude of a negative temperature coefficient of reactivity. 24. The method of claim 20, wherein reducing the magnitude of the coefficient of reactivity includes reducing a magnitude of a negative void coefficient of reactivity.