Radial in-flow particle bed nuclear rocket engine and method

A system comprising:

• a pump configured to pump a propellant from a propellant reservoir;
• a set of fuel elements, each fuel element in the set of fuel elements defining a cylindrical geometry of concentric layers comprising:
• a cold shell defining a first array of perforations configured to direct the propellant radially through the cold shell;
• a fuel bed containing a set of low enriched uranium fuel particles;
• a hot shell defining a second array of perforations configured to direct the propellant radially through the hot shell;
• and
• an interior chamber configured to direct propellant axially out of the fuel element toward a thrust nozzle;
• a moderator:
• defining a set of fuel bores, each fuel bore in the set of fuel bores:
• fluidly coupled to a warm propellant inflow manifold;
• occupied by a fuel element;
• and
• configured to direct warm propellant axially downward from the warm propellant inflow manifold along a length of the fuel element;
• and
• defining a set of moderator coolant channels, each moderator coolant channel:
• fluidly isolated from the set of fuel bores;
• defining a set of moderator coolant inlets fluidly coupled to the thrust-coolant valve;
• defining a set of moderator coolant outlets fluidly coupled to the pump bypass valve;
• and
• configured to pass propellant through the moderator to cool the moderator;
• a reflector arranged on a perimeter of the moderator:
• comprising:
• a neutron-reflecting material;
• and
• a reflector coolant channel arranged within the reflector configured to exchange thermal energy with propellant pumped through the reflector coolant channel;
• operable in:
• a first position to reflect a first proportion of incident neutrons toward the set of fuel elements;
• and
• a second position to release a second proportion of incident neutrons to an external environment;
• and
• the thrust nozzle configured to outlet propellant to produce thrust:
• comprising a nozzle coolant channel arranged within a wall of the thrust nozzle configured to exchange thermal energy with propellant pumped through the nozzle coolant channel.

A system comprising:

• a pump configured to pump a propellant;
• a set of fuel elements, each fuel element of the set of fuel elements comprising:
• a set of low enriched uranium fuel particles defining a set of interstitial volumes through which the pump pumps the propellant;
• a moderator:
• defining a set of fuel bores, each fuel bore in the set of fuel bores occupied by a fuel element;
• and
• defining a set of moderator coolant channels, each moderator coolant channel:
• fluidly isolated from the set of fuel bores;
• and
• configured to pass propellant through the moderator to cool the moderator;
• a reflector arranged on a perimeter of the moderator:
• comprising a neutron-reflecting material;
• and
• operable in:
• an open position to release neutrons to an external environment;
• and
• a closed position to reflect incident neutrons back into the set of fuel elements;
• and
• a thrust nozzle:
• configured to outlet propellant to produce thrust;
• and
• comprising a nozzle coolant channel arranged within a wall of the thrust nozzle configured to exchange thermal energy with propellant pumped through the nozzle coolant channel.