An aqueous assembly has a negative coefficient of reactivity with a magnitude. The aqueous assembly includes a vessel and an aqueous solution, with a fissile solute, supported in the vessel. A reactivity stabilizer is disposed within the aqueous solution to reduce the magnitude of the negative coefficient of reactivity of the aqueous assembly during operation of the aqueous assembly.

A first system for producing a high flux of neutrons for non-destructive testing includes a dense plasma focus device neutronically coupled to a subcritical or sub-prompt critical fission assembly. The dense plasma focus device is a source of initiating neutrons for the fission assembly, and the fission assembly is configured to multiply a number of the initiating neutrons via inducing fission. A second system for producing a high flux of neutrons includes a gas-target neutron generator neutronically coupled to a subcritical or sub-prompt critical fission assembly. The gas-target neutron generator is a source of initiating neutrons for the fission assembly, and the fission assembly is configured to multiply a number of the initiating neutrons via inducing fission.

A first system for producing a high flux of neutrons for non-destructive testing includes a dense plasma focus device neutronically coupled to a subcritical or sub-prompt critical fission assembly. The dense plasma focus device is a source of initiating neutrons for the fission assembly, and the fission assembly is configured to multiply a number of the initiating neutrons via inducing fission. A second system for producing a high flux of neutrons includes a gas-target neutron generator neutronically coupled to a subcritical or sub-prompt critical fission assembly. The gas-target neutron generator is a source of initiating neutrons for the fission assembly, and the fission assembly is configured to multiply a number of the initiating neutrons via inducing fission.

A target irradiation system for irradiating a radioisotope target in a vessel penetration of a fission reactor, including a target delivery assembly including a body defining a central bore, a basket that is slidably receivable within the central bore of the body, and a winch that is connected to the basket by a cable, the target delivery assembly being affixed to the vessel penetration of the reactor, and a target passage that is in fluid communication with the target delivery assembly, wherein the basket is configured to receive the radioisotope target therein via the target passage and be lowered into the vessel penetration of the reactor when irradiating the radioisotope target, and the target delivery system forms a portion of the pressure boundary of the reactor when in fluid communication with the reactor.

A hybrid nuclear reactor that is operable to produce a medical isotope includes an ion source operable to produce an ion beam from a gas, a target chamber including a target that interacts with the ion beam to produce neutrons, and an activation cell positioned proximate the target chamber and including a parent material that interacts with the neutrons to produce the medical isotope via a fission reaction. An attenuator is positioned proximate the activation cell and selected to maintain the fission reaction at a subcritical level, a reflector is positioned proximate the target chamber and selected to reflect neutrons toward the activation cell, and a moderator substantially surrounds the activation cell, the attenuator, and the reflector.

A target irradiation system for irradiating a radioisotope target in a vessel penetration of a fission reactor, includes a target delivery assembly with a body defining a central bore, a basket that is slidably receivable within the central bore of the body, and a winch that is connected to the basket by a cable. The target delivery assembly is affixed to the vessel penetration of the reactor; and a target passage is in fluid communication with the target delivery assembly. The basket is configured to receive a radioisotope target therein via the target passage and be lowered into the vessel penetration of the reactor when irradiating the radioisotope target. The target delivery system forms a portion of the pressure boundary of the reactor when in fluid communication with the reactor.

A hybrid nuclear reactor that is operable to produce a medical isotope includes an ion source operable to produce an ion beam from a gas, a target chamber including a target that interacts with the ion beam to produce neutrons, and an activation cell positioned proximate the target chamber and including a parent material that interacts with the neutrons to produce the medical isotope via a fission reaction. An attenuator is positioned proximate the activation cell and selected to maintain the fission reaction at a subcritical level, a reflector is positioned proximate the target chamber and selected to reflect neutrons toward the activation cell, and a moderator substantially surrounds the activation cell, the attenuator, and the reflector.

An aqueous assembly has a negative coefficient of reactivity with a magnitude. The aqueous assembly includes a vessel and an aqueous solution, with a fissile solute, supported in the vessel. A reactivity stabilizer is disposed within the aqueous solution to reduce the magnitude of the negative coefficient of reactivity of the aqueous assembly during operation of the aqueous assembly.

An aqueous assembly has a negative coefficient of reactivity with a magnitude. The aqueous assembly includes a vessel and an aqueous solution, with a fissile solute, supported in the vessel. A reactivity stabilizer is disposed within the aqueous solution to reduce the magnitude of the negative coefficient of reactivity of the aqueous assembly during operation of the aqueous assembly.

A method to determine a global core reactivity bias and the corresponding estimated critical conditions of a nuclear reactor core prior to achieving reactor criticality. The method first requires collection and evaluation of the inverse count rate ratio (ICRR) data; specifically, fitting measured ICRR vs. predicted ICRR data. The global core reactivity bias is then determined as the amount of uniform reactivity adjustment to the prediction that produces an ideal comparison between the measurement and the prediction.