Patent Description:
The concept of utilizing nuclear thermal propulsion (NTP) to propel spacecraft during space travel is known. In developing the technology related to propelling spacecraft in this manner, it is necessary to be able to test the NTP engines and be able to both assemble and disassemble the engines so that their internal components can be inspected. Preferably, nuclear reactors for NTP engines are compact, lightweight, and due to the extreme conditions in which the nuclear reactors must function, readily assembled and disassembled for rigorous testing during the developmental phase. Various issues exist with regard to existing NTP engine designs, such as Nuclear Engine for Rocket Vehicle Application (NERVA). Specifically, the assembly and disassembly of existing designs is known to be both complicated and time consuming, and free-standing internal plumbing from the outside of the reactor vessel to the internal moderator components within the nuclear core assembly can lead to flow induced vibrations and, therefore, undesired wear of the components.

As noted above, it is important to have the ability to disassemble an NTP engine's reactor vessel after performing hot and cold fire tests to determine the integrity of the internal reactor components. Existing NTP engine designs often require welding operations and, therefore, weld inspection operations when reassembling a previously inspected nuclear reactor. During normal operations of NTP engines, thrust generated from the nozzle is transferred to the reactor vessel, to the reactor head, and onto a thrust vector control structure which interfaces with the spacecraft that is being propelled. During launch of the reactor assembly into space, the reactor vessel must support the weight of the reactor core assembly, such as fuel elements and moderators, as well as launch acceleration loads. As shown in <FIG>, in some known NTP engine designs, the weight of the core <NUM> is hung from the support structure <NUM> and transferred to the reactor vessel by a support plate <NUM> that is welded into the inner diameter of the reactor vessel <NUM>. As such, when disassembling the nuclear reactor for inspection, various internal components, such as control drums, are often not removable.

As well, routing of coolant from outside known nuclear reactors to the plenums located in the support structure <NUM> above the core often requires either penetrations through the reactor vessel <NUM> or through the reactor vessel head <NUM>. When plumbing is routed horizontally (not shown) through a side of the reactor vessel <NUM>, the plumbing must be welded to both the reactor vessel <NUM> and the support structure <NUM>. This welding locks the support structure <NUM> to the reactor vessel <NUM> and does not allow replacement of components below the support plate unless these welds are first cut, possibly damaging the reactor vessel/support structure. The known solution to this routing issue involves routing coolant lines <NUM> to the top of the reactor internals and interior dome and passing them vertically out through the reactor head, as shown in <FIG>. The coolant lines <NUM> are then threaded into a mating flange that is then bolted to the reactor head thereby making a gas seal. High velocity coolant gas used to cool the reactor head flows between the outside of the interior dome and the inside of the reactor head. As such, the coolant gas lines <NUM>, as shown in <FIG>, are susceptible to flow induced vibration which can lead to tube cracks and ultimately tube failure.

There at least remains a need, therefore, for improved devices for NTP engines that can be more easily assembled and disassembled for inspection and maintenance purposes during testing operations. <CIT> discloses a nuclear reactor having a penetration seal ring interposed between the reactor vessel flange and a mating flange on the reactor vessel head. <CIT> discloses a suspended basket includes a plurality of plates, tie rods, and adjustable length threaded tie rod couplings connecting threaded ends of the tie rods with threaded features of the plates.

One embodiment of the present invention includes an internal interface structure for a nuclear thermal propulsion nuclear reactor including a reactor vessel and a reactor head. The interface structure includes a substantially cylindrical body having a top end, a bottom end, an inner surface, and an outer surface, and an annular flange extending radially-outwardly from the outer surface of the cylindrical body, wherein the annular flange of the interface structure is configured to be mounted between an upper flange of the reactor vessel and a bottom flange of the reactor head.

The internal interface structure further comprises: a pathway extending through the annular flange and having an inlet formed in an outer perimeter of the annular flange and an outlet formed in the inner surface of the cylindrical body; a first annular ledge formed on the inner surface of the cylindrical body; a second annular ledge formed on the inner surface of the body; and a third annular ledge formed on the inner surface of the cylindrical body, wherein the first annular ledge is disposed between the top end of the cylindrical body and the outlet of the pathway, the second ledge is disposed between the bottom end of the cylindrical body and the outlet of the pathway, and the third ledge is disposed between the second ledge and the bottom end of the cylindrical body. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with the description, serve to explain the principles of the invention.

The invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not, all embodiments of the invention are shown. Indeed, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements.

Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention according to the disclosure.

The invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not, all embodiments of the invention are shown. Indeed, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. As used in the specification, and in the appended claims, the singular forms "a", "an", "the", include plural referents unless the context clearly dictates otherwise.

Referring now to the figures, an internal interface structure <NUM> in accordance with the present disclosure is shown in <FIG> and <FIG>. The interface structure <NUM> is designed and configured to be used in a nuclear reactor <NUM> of a nuclear thermal propulsion (NTP) rocket engine <NUM>, as shown in <FIG> and <FIG>. The interface structure <NUM> is a single component including a substantially cylindrical body <NUM> and an annular flange <NUM> extending radially-outwardly therefrom. The annular flange <NUM> lies in a plane that is transverse to a longitudinal center axis <NUM> of the cylindrical body <NUM> and is configured to be mounted between an upper flange <NUM> of a corresponding reactor vessel <NUM> and a lower flange <NUM> of a corresponding reactor head <NUM>, as best seen in <FIG>. As shown in <FIG>, the body <NUM> of interface structure <NUM> extends above and below the annular flange <NUM> and functions as a cylindrical pressure vessel that supports the internal reactor core components, shielding components, reactor controls, and provides pathways for the reactor coolant gas and instrumentation pathways.

As shown in <FIG>, the interior of the pressure vessel <NUM> provides mounting surfaces at <NUM>, <NUM>, and <NUM> for the interior plenum lid <NUM>, interior gamma shield <NUM>, interior neutron shield <NUM>, respectively, and provides a coolant gas barrier, as discussed in greater detail below. Coolant gas from a turbo pump <NUM> (<FIG>), passes through the interior plenum lid <NUM> and accumulates prior to entering the coolant holes <NUM> and <NUM> of the gamma and neutron shields <NUM> and <NUM>, respectively, located below the interior plenum lid <NUM>. The gamma and neutron shields <NUM> and <NUM>, respectively, are mounted to the annular ledges that form the mounting surfaces <NUM> and <NUM> and are disposed on the inner wall of the pressure vessel <NUM>. The coolant gas passes through the coolant holes <NUM> and <NUM> in both shields, thereby removing heat from the shielding material.

Referring additionally to <FIG>, the interface structure <NUM> also supports and provides cooling pathways through exterior gamma and neutron shields <NUM> and <NUM>, respectively, located adjacent the outer surface of the pressure vessel <NUM>. Coolant holes <NUM> and <NUM> of the exterior gamma and neutron shields <NUM> and <NUM>, respectively, are aligned with corresponding coolant holes <NUM> that are formed in the annular flange <NUM>, as best shown in <FIG>.

Referring now to <FIG>, a plurality of annular ledges <NUM>, <NUM> and <NUM> is provided on the inner surface of the pressure vessel <NUM> inwardly of the annular flange <NUM>. Each annular ledge supports a corresponding plenum plate <NUM>, <NUM>, and <NUM>, the plenum plates <NUM>, <NUM>, and <NUM> dividing the coolant gas supply for the moderator and fuel elements. Unlike the fuel elements which only require gas to flow through them, the moderators require plenums to provide coolant gas both into and out of the moderator. Coolant for the moderators is supplied by plumbing that is disposed externally of the reactor vessel. A coolant supply line <NUM> is formed within the annular flange <NUM> and allows for a non-welded pathway to the interior of the reactor at the moderator entrance plenum <NUM>. After coolant passes through the moderator, the coolant exits the moderator and enters a moderator exit plenum <NUM>. The moderator coolant gas exits the moderator plenum <NUM> through penetrations <NUM> in the pressure vessel wall, as best seen in <FIG> and <FIG>.

Referring now to <FIG>, a radial reflector <NUM> surrounds the reactor core and reflects neutrons back into the core. The radial reflector <NUM> is located below the annular flange <NUM> adjacent the outer surface of the pressure vessel <NUM>. An annular ledge <NUM> is disposed on the outer surface of the pressure vessel <NUM> beneath the annular flange <NUM>, the annular ledge <NUM> being configured to abut an upper surface of the reflector <NUM>, thereby holding it in place. The bottom <NUM> of the radial reflector <NUM> is supported by the reactor vessel <NUM> once the reactor vessel <NUM> is attached to the bottom of the annular flange <NUM>, as best seen in <FIG>. The radial reflector <NUM> houses a plurality of control drums <NUM> that are used to control the criticality of the nuclear reactor. Control drum drive motors <NUM> (<FIG>) are located on the outside of the reactor head and are connected to the control drums <NUM> by shafts <NUM> that pass through the annular flange <NUM>. Referring additionally to <FIG>, the annular flange <NUM> provides alignment holes <NUM> and surfaces for supporting bearings <NUM> for each control drum shaft <NUM>.

As best seen in <FIG>, the coolant pathway <NUM> through the annular flange <NUM> is the only location that which the full flange thickness 140a is required from the cylindrical pressure vessel <NUM> to the outer perimeter of the annular flange <NUM>. Preferably, most of the remaining material between the mating surfaces of the reactor vessel <NUM> and reactor head <NUM>, and the interior pressure vessel <NUM> wall is removed. An annular recess <NUM> formed by this removal of material becomes an internal coolant mixing area for mixing the coolant exiting from the moderator exit plenum <NUM> (<FIG>) and the coolant exiting the radial reflector <NUM> and control drums <NUM> shown in <FIG>. The mixed coolant then exits through coolant holes <NUM> that are defined by annular flange <NUM>.

Referring again to <FIG>, the lower surface <NUM> of the interface structure's pressure vessel <NUM> is used to provide a vapor barrier from the interior gas flow through the core and the higher pressure coolant through the radial reflector <NUM> and control drums <NUM>. A seal <NUM> located at the thrust chamber assembly interface to the reactor vessel <NUM> provides the vapor barrier. Additionally, the lower portion of the pressure vessel <NUM> provides a secondary load path to the annular flange <NUM> from the thrust exiting the nozzle of the rocket engine (<FIG> and <FIG>).

Instrumentation required within the reactor vessel for monitoring temperature, pressure, ionizing radiation, structural loading, etc., can be routed by way of direct pathways <NUM> through the annular flange <NUM> to the interior of the reactor, as shown in <FIG>. In prior art designs, instrumentation that was routed either through the reactor head or reactor vessel had to be disconnected when removing or installing the reactor head and/or the reactor vessel. By preferably routing instrumentation cabling through the annular flange <NUM>, the instrumentation cables may be hardwired directly to the corresponding instrument with the first connection being located outside of the pressure boundary. Multiple ports <NUM> can be radially placed through the circular flange that do not interfere with the cooling holes <NUM>, control drum supports <NUM>/<NUM>, and reactor head/vessel mounting holes <NUM>.

As described above, the interface structure <NUM> allows the internal reactor components to be mounted directly thereto. The components are attached by bolted structures and require no welding. Thus, interior reactor components and parts may be disassembled after testing of the reactor for inspection without having to cut welds. As well, by routing coolant to the moderator through the annular flange <NUM>, coolant penetrations to both the reactor vessel and the reactor head may be avoided. As well, by routing the coolant through the annular flange <NUM>, flow induced vibration issues commonly found in prior art designs may be avoided.

Referring now to <FIG>, <FIG> and <FIG>, the coolant flow paths through an NTP rocket engine <NUM> having an interface structure in accordance with the present disclosure is described. As shown, coolant from an external turbo pump <NUM> enters the nozzle <NUM> at <NUM>, coolant from the nozzle enters reactor vessel at <NUM>, through holes <NUM> (<FIG>) in the bottom of reactor vessel <NUM>, coolant passes through the reflector and the control drums at <NUM>, coolant exits the reflector and the control drums and enters upper plenum at <NUM>, where internal mixing of the coolant form the nozzle and moderator occurs. Additionally, coolant from the external turbo pump <NUM> enters coolant pathway <NUM> of interface structure at <NUM>, coolant next enters moderator entrance plenum at <NUM>, the coolant next enters moderator inlet tube at <NUM>, the coolant next flows through the moderator at <NUM>, after a <NUM>° change in the direction of flow, the coolant passes upwardly through the moderator into the moderator exit plenum <NUM> and out the moderator exit plenum at <NUM> through holes <NUM>, enters the upper plenum where it undergoes internal mixing at <NUM> with the coolant that entered through the nozzle <NUM>. The coolant passes upwardly through the holes <NUM> in the annular flange of the interface structure and through the holes <NUM> and <NUM> of the neutron and gamma shields at <NUM>, passes upwardly through reactor head at <NUM> into the inlet of a turbo pump <NUM>, the coolant exits the turbo pump at <NUM> and enters the central dome at <NUM>, after passing through the internal neutron and gamma shields at <NUM>, the coolant enters the fuel element plenum at <NUM>, and passes next into the fuel element inlet tube at <NUM>, ultimately passing through the fuel elements at <NUM> and exiting the NTP rocket engine nozzle <NUM> as exhaust at <NUM>.

Claim 1:
An internal interface structure (<NUM>) for a nuclear thermal propulsion nuclear reactor (<NUM>) including a reactor vessel (<NUM>) and a reactor head (<NUM>), the internal interface structure (<NUM>) comprising:
a substantially cylindrical body (<NUM>) having a top end, a bottom end, an inner surface, and an outer surface;
an annular flange (<NUM>) extending radially-outwardly from the outer surface of the cylindrical body (<NUM>), wherein the annular flange (<NUM>) of the interface structure (<NUM>) is configured to be mounted between an upper flange of the reactor vessel (<NUM>) and a bottom flange of the reactor head (<NUM>); and
a pathway extending through the annular flange (<NUM>) and having an inlet formed in an outer perimeter of the annular flange (<NUM>) and an outlet formed in the inner surface of the cylindrical body (<NUM>);
characterized by
a first annular ledge (<NUM>) formed on the inner surface of the cylindrical body (<NUM>); a second annular ledge (<NUM>) formed on the inner surface of the cylindrical body (<NUM>); and
a third annular ledge (<NUM>) formed on the inner surface of the cylindrical body (<NUM>),
wherein the first annular ledge (<NUM>) is disposed between the top end of the cylindrical body (<NUM>) and the outlet of the pathway, the second annular ledge (<NUM>) is disposed between the bottom end of the cylindrical body (<NUM>) and the outlet of the pathway, and the third annular ledge (<NUM>) is disposed between the second annular ledge (<NUM>) and the bottom end of the cylindrical body (<NUM>).