Patent Number: 
Section: claims

1. A single fluid molten salt nuclear reactor comprising:a vessel having a central region and a vessel wall, a vessel height and a vessel width;a support structure;a neutron moderator secured to the support structure and located in the central region of the vessel, the neutron moderator having a neutron moderator height and a neutron moderator width, the vessel height being greater than the neutron moderator height by a factor comprised between two and four, the vessel width being greater than the neutron moderator width by a factor comprised between two and four such that an under-moderated zone is defined between the neutron moderator and the vessel wall, the neutron moderator having at least one through hole defined therein that is in fluid communication with the under-moderated zone; anda pump to circulate a molten salt in the vessel, the support structure, the neutron moderator, and the pump being arranged to circulate the molten salt through the at least one through hole of the neutron moderator and the under-moderated zone between the neutron moderator and the vessel wall;wherein a space between the neutron moderator and the vessel wall is free of any neutron reflector. 2. The nuclear reactor of claim 1 wherein the support structure is also a guide structure to guide the molten salt therethrough, the support structure, the neutron moderator, and the pump being arranged to circulate the molten salt first through the support structure, then through the at least one through hole of the neutron moderator, and subsequently between the neutron moderator and the vessel wall. 3. The nuclear reactor of claim 1 wherein the support structure is also a guide structure to guide the molten salt therethrough, the support structure, the neutron moderator, and the pump being arranged to circulate the molten salt first between the neutron moderator and the vessel wall, then through the at least one through hole of the neutron moderator, and subsequently through the guide structure. 4. The nuclear reactor of claim 1 wherein the neutron moderator is a cylinder-shaped neutron moderator, the at least one through hole being parallel to a height of the cylinder-shaped neutron moderator. 5. The nuclear reactor of claim 1 wherein the at least one through hole is perpendicular to the neutron moderator width. 6. The nuclear reactor of claim 1 wherein the vessel has a vessel height and the neutron moderator has a neutron moderator height, the at least one through hole being parallel to the neutron moderator height. 7. A single fluid molten salt nuclear reactor comprising:a vessel having a central region and a vessel wall, a vessel height and a vessel width;two opposite walls disposed at opposite ends of the vessel;a support structure;a neutron moderator secured to the support structure and located in the central region of the vessel, the neutron moderator having a neutron moderator height and a neutron moderator width, the vessel height being greater than the neutron moderator height by a factor comprised between two and four, the vessel width being greater than the neutron moderator width by a factor comprised between two and four such that an under-moderated zone is defined between the neutron moderator and the vessel wall, the neutron moderator having at least one through hole defined therein that is in fluid communication with the under-moderated zone;a molten salt inlet formed on one of the two opposite walls;a molten outlet formed on the other of the two opposite walls; anda pump operationally connected to the molten salt inlet and to the molten salt outlet, the pump to circulate a molten salt in the vessel, through the at least one through hole of the neutron moderator and the under-moderated zone between the neutron moderator and the vessel wall;wherein a space between the neutron moderator and the vessel wall is free of any neutron reflector. 8. The nuclear reactor of claim 1 wherein the neutron moderator includes at least one of graphite and of clad beryllium compound. 9. The nuclear reactor of claim 1 wherein the neutron moderator is one of graphite, a clad beryllium compound, and a clad graphite powder. 10. The nuclear reactor of claim 7 wherein the neutron moderator includes at least one of graphite and of clad beryllium compound. 11. The nuclear reactor of claim 7 wherein the neutron moderator is one of graphite, a clad beryllium compound, and a clad graphite powder. 12. A single fluid molten salt nuclear reactor comprising:a vessel having a central region and a vessel wall, the vessel wall being free of any graphite neutron reflector, the vessel having a vessel height and a vessel width;a neutron moderator positioned a central region of the vessel, the neutron moderator having a neutron moderator height and a neutron moderator width, the vessel height being greater than the neutron moderator height by a factor comprised between two and four, the vessel width being greater than the neutron moderator width by a factor comprised between two and four such that an under-moderated zone is defined between the neutron moderator and the vessel wall, the neutron moderator having at least one through hole defined therein that is in fluid communication with the under-moderated zone; anda pump to circulate a molten salt in the vessel, the neutron moderator and the pump being arranged to circulate the molten salt through the at least one through hole of the neutron moderator and the under-moderated zone between the neutron moderator and the vessel wall such that the molten salt in the under-moderated zone reduces a neutron flux at the vessel wall to reduce damage to the vessel wall;wherein a space between the neutron moderator and the vessel wall is free of any neutron reflector. 13. The nuclear reactor of claim 12 wherein the neutron moderator:is a graphite neutron moderator,has a width comprised between one meter and two meters, andhas a height that matches the width of the neutron moderator. 14. The nuclear reactor of claim 12 further comprising a support structure that positions the neutron moderator at the central region of the vessel, the support structure having a conduit portion, the support structure, the neutron moderator, and the pump being configured to circulate the molten salt first through the conduit portion of the support structure, then through the at least one through hole of the neutron moderator, and subsequently between the neutron moderator and the vessel wall. 15. The nuclear reactor of claim 12 wherein the support structure is also a guide structure to guide the molten salt therethrough, the support structure, the neutron moderator, and the pump being arranged to circulate the molten salt first between the neutron moderator and the vessel wall, then through the at least one through hole of the neutron moderator, and subsequently through the guide structure. 16. The nuclear reactor of claim 12 wherein the neutron moderator is a cylinder-shaped neutron moderator, the at least one through hole being parallel to a height of the cylinder-shaped neutron moderator. 17. The nuclear reactor of claim 12 wherein the neutron moderator includes at least one of graphite and of clad beryllium compound. 18. The nuclear reactor of claim 12 wherein the neutron moderator is one of graphite, a clad beryllium compound, and a clad graphite powder.