A reactor core includes an inner core region that extends in a vertical direction, and has a plurality of first fuel pins accommodating an inner core fuel; an outer core region that extends in the vertical direction, is arranged to surround the inner core region from an outer peripheral side, and has a plurality of second fuel pins accommodating an outer core fuel; and a sodium plenum provided above the inner core region and the outer core region, in which a dimension of the outer core fuel in the vertical direction is larger than a dimension of the inner core fuel in the vertical direction, and the position of a center of the outer core fuel in the vertical direction is higher than the position of a center of the inner core fuel in the vertical direction.

A reactor core includes an inner core region that extends in a vertical direction, and has a plurality of first fuel pins accommodating an inner core fuel; an outer core region that extends in the vertical direction, is arranged to surround the inner core region from an outer peripheral side, and has a plurality of second fuel pins accommodating an outer core fuel; and a sodium plenum provided above the inner core region and the outer core region, in which a dimension of the outer core fuel in the vertical direction is larger than a dimension of the inner core fuel in the vertical direction, and the position of a center of the outer core fuel in the vertical direction is higher than the position of a center of the inner core fuel in the vertical direction.

The invention relates generally to nuclear engineering and more particularly to controlled reactor start-up. The invention improves reliability of an operational neutron source by creating additional safety barriers between the coolant and the source active part materials. The operational neutron source is designed as a steel enclosure housing an ampule containing antimony and beryllium with separate antimony and beryllium cavities positioned coaxially. The antimony is contained in the central enclosure made of a niobium-based alloy unreactive with antimony. A beryllium powder bed is located between the antimony enclosure and the ampule enclosure. The ampule enclosure is made of martensite-ferrite steel poorly reacting with beryllium. An upper gas collector is located above the ampule, which serves as a compensation volume collecting gaseous fission products. At the bottom, the ampule is supported by a reflector and a bottom gas collector. The gas collectors, reflector and washers are made of martensite-ferrite grade steel.

A breech-loading neutron gun (12A) providing neutrons to stimulate the release of energy from nuclear materials (18) in a containment vessel (14) in a regulated fashion includes a chamber (34A) among a plurality of chambers (34A-D) located in a breech (32) where one or more of the plurality of chambers are configured and arranged to load with a neutron source (58), and a mechanism for controllably moving the breech or the chamber relative to an access cavity (16A) of the containment vessel and exposing the nuclear materials to neutrons from the chamber when the chamber containing the neutron source aligns with the access cavity.

A breech-loading neutron gun (12A) providing neutrons to stimulate the release of energy from nuclear materials (18) in a containment vessel (14) in a regulated fashion includes a chamber (34A) among a plurality of chambers (34A-D) located in a breech (32) where one or more of the plurality of chambers are configured and arranged to load with a neutron source (58), and a mechanism for controllably moving the breech or the chamber relative to an access cavity (16A) of the containment vessel and exposing the nuclear materials to neutrons from the chamber when the chamber containing the neutron source aligns with the access cavity.

A breech-loading neutron gun providing neutrons to stimulate the release of energy from nuclear materials in a containment vessel in a regulated fashion includes a chamber among a plurality of chambers located in a breech where one or more of the plurality of chambers are configured and arranged to load with a neutron source, and a mechanism for controllably moving the breech or the chamber relative to an access cavity of the containment vessel and exposing the nuclear materials to neutrons from the chamber when the chamber containing the neutron source aligns with the access cavity.

A breech-loading neutron gun providing neutrons to stimulate the release of energy from nuclear materials in a containment vessel in a regulated fashion includes a chamber among a plurality of chambers located in a breech where one or more of the plurality of chambers are configured and arranged to load with a neutron source, and a mechanism for controllably moving the breech or the chamber relative to an access cavity of the containment vessel and exposing the nuclear materials to neutrons from the chamber when the chamber containing the neutron source aligns with the access cavity.

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 Control Neutron Absorber (CNA) assembly for a microreactor that produces nuclear energy is disclosed. The CNA assembly includes a housing, a CNA rod, and a burnable absorber. The housing includes an inner housing and an outer housing. The inner housing is configured to receive a CNA rod. The outer housing extends coaxially with the inner housing and is positioned radially outward and offset from the inner housing defining a cavity therebetween. The CNA rod includes a neutron absorbing rod including a first neutron absorbing material. The neutron absorbing rod is positioned within the inner housing and is configured to move axially relative to the inner housing. The burnable absorber includes a second neutron absorbing material, exhibits a neutron absorbing strength that is less than that of the neutron absorbing rod, is positioned within the inner housing, and is configured to receive the neutron absorbing rod therein.