COMBINED AMMONIA-BASED MODERATOR AND PROPELLANT FOR NUCLEAR THERMAL PROPULSION STAGES
Combined moderator-propellant technologies allow a dual-purpose fluid to act as both a nuclear moderator as well as a propellant in a nuclear reactor system, such as a nuclear thermal propulsion (NTP) system. By increasing the mass efficiency of the NTP system and improving the overall performance during operation, the combined moderator-propellant technologies improve valuable payload efficiency in the NTP system. Advantageously, the combined moderator-propellant technologies require little to no dedicated storage space for the majority of NTP system operation. For example, the combined moderator-propellant is ammonia (NH 3 ), which satisfies moderation requirements as well as propulsion requirements for the NTP system.
1 . A nuclear thermal propulsion system comprising:
a pressure vessel; and
a nuclear reactor core disposed in the pressure vessel, including:
a moderator region configured to flow a combined moderator-propellant; and
an array of fuel assemblies disposed within the moderator region, wherein each fuel assembly includes:
a nuclear fuel, and
an array of coolant channels formed within the nuclear fuel and coupled to the moderator region to flow the combined moderator-propellant to a thrust chamber.
2 . The nuclear thermal propulsion system of claim 1 , wherein:
the combined moderator-propellant includes ammonia (NH 3 ).
3 . The nuclear thermal propulsion system of claim 1 , wherein each fuel assembly further includes:
an insulator layer surrounding the nuclear fuel and the array of coolant channels;
an inner can surrounding the insulator layer;
a combined moderator-propellant return surrounding the inner can; and
an outer can, wherein the combined moderator-propellant return is located between the inner can and the outer can.
4 . The nuclear thermal propulsion system of claim 3 , wherein:
the outer can is directly coupled to the moderator region.
5 . The nuclear thermal propulsion system of claim 3 , wherein:
the insulator layer is formed of zirconium carbide (ZrC).
6 . The nuclear thermal propulsion system of claim 3 , wherein:
the pressure vessel is formed of a titanium alloy, an aluminum stainless steel alloy, or a nickel-chromium based superalloy.
7 . The nuclear thermal propulsion system of claim 3 , wherein:
the inner can is formed of a silicon carbide/silicon carbide (SiC—SiC) composite or a zirconium alloy; and
the outer can is formed of the SiC—SiC composite, a beryllium (Be) composite, or a stainless steel alloy.
8 . The nuclear thermal propulsion system of claim 3 , wherein:
the nuclear fuel is comprised of coated fuel particles embedded inside a high-temperature matrix; and
the high-temperature matrix includes silicon carbide, zirconium carbide, titanium carbide, niobium carbide, tungsten, molybdenum, or a combination thereof.
9 . The nuclear thermal propulsion system of claim 8 , wherein:
the coated fuel particles include tristructural-isotropic (TRISO) fuel particles, bistructural-isotropic (BISO) fuel particles, or TRIZO fuel particles.
10 . The nuclear thermal propulsion system of claim 9 , wherein:
the BISO fuel particles include a fuel kernel formed of uranium nitride (UN).
11 . The nuclear thermal propulsion system of claim 1 , further comprising a reflector region disposed between the moderator region and the pressure vessel.
12 . The nuclear thermal propulsion system of claim 11 , wherein the reflector region is formed of a solid reflector material.
13 . The nuclear thermal propulsion system of claim 12 , wherein the solid reflector material is formed of beryllium (Be) or beryllium oxide (BeO).
14 . The nuclear thermal propulsion system of claim 11 , wherein the reflector region is configured to flow the combined moderator-propellant.
15 . The nuclear thermal propulsion system of claim 14 , further comprising:
a moderator reflector separator disposed between the moderator region and the reflector region,
wherein the moderator reflector separator is formed of a silicon carbide/silicon carbide (SiC—SiC) composite, beryllium (Be), or a stainless steel alloy.
16 . The nuclear thermal propulsion system of claim 1 , further comprising:
a coolant plenum located inside the pressure vessel and coupled to the moderator region to store and flow the combined moderator-propellant to the moderator region.
17 . The nuclear thermal propulsion system of claim 16 , further comprising a combined moderator-propellant pump, wherein:
the combined moderator-propellant pump is configured to:
pump the combined moderator-propellant from the coolant plenum to the moderator region; and
pump the combined moderator-propellant from the moderator region to the array of fuel assemblies.
18 . The nuclear thermal propulsion system of claim 1 , further comprising:
a plurality of circumferential control drums surrounding the moderator region,
wherein each of the control drums includes a reflector portion within a first portion of an outer surface and an absorber material within a second portion of the outer surface.
19 . The nuclear thermal propulsion system of claim 18 , wherein the reflector portion is formed of a solid reflector material.
20 . The nuclear thermal propulsion system of claim 19 , wherein the solid reflector material is formed of beryllium (Be) or beryllium oxide (BeO).
21 . The nuclear thermal propulsion system of claim 18 , wherein the reflector portion includes a control drum reflector chamber configured to flow the combined moderator-propellant.
22 . The nuclear thermal propulsion system of claim 21 , wherein the control drum reflector chamber is configured to flow the combined moderator-propellant while the combined moderator-propellant is in a pressurized or a supercritical state.