TECHNICAL FIELD

The presently-disclosed invention relates generally to systems and methods of use thereof for controlling reactor power levels in nuclear reactors and, more specifically, to systems and methods of use thereof for controlling the operation of multiple control drums for nuclear thermal propulsion space reactors.

BACKGROUND

The reactivity of nuclear reactors, specifically nuclear thermal space reactors, may be controlled by various techniques, such as core barrels and control drums, in-core control rods, movable fuel and reflector segments, burnable poisons and poisons that are dispersed in the core. The majority of space nuclear reactors use ex-core control systems. The present disclosure pertains to the ex-core reactor control systems, specifically control drums

Space nuclear reactors are controlled by the amount of neutrons reflected back into the reactor core in order to either increase or decrease the neutron flux, the number of neutrons that split further uranium atoms. Ex-core reactor controllers are either a form of control drums or control barrels. Ex-core control barrels control the reactor's criticality by the amount of neutrons that are reflected back into the reactor core to fission the uranium atoms. As shown inFIG. 1, the basic rotating control barrel design consists of an inner stationary barrel10and an outer rotating barrel12. Both barrels10and12contain both reflector material segments14and open segments16. As shown, the inner barrel10is the stationary barrel and the outer barrel12rotates. The outer control barrel12inFIG. 1is in the full “on” position such that the reflecting material segments14in the outer barrel overlap, or block, the open segments16of the inner barrel10in order to reflect all the neutrons (arrows18) back into the core20.

To shut down the nuclear reactor11, the outer control barrel12is rotated to the full “off” position such that the outer barrel's reflector segments14are aligned with the stationary inner barrel's reflector segments14, while both the inner and outer barrel10and12, respectively, open segments16are aligned. By aligning the open segments16, more neutrons escape (arrows22) than are required to keep the reactor core20critical, thus shutting down the reactor11. Reactor power control is accomplished by positioning the outer barrel reflector segments14between the full on position shown inFIG. 1and the shutdown position shown inFIG. 2.

In yet another ex-core control system, rotating control drums assemblies24surround the reactor core20and consist of rotating drum cylinders26inserted within the ex-core radial reflector28, as shown inFIGS. 3 through 5. As shown, each control drum assembly24includes a control drum cylinder26that is driven by way of a drive shaft32by its own individual control drum drive motor (CDDM)30. The control drum cylinder26is made of the same material as the radial reflector28material with a section of absorber material34(or neutron poison) that consists of neutron absorbing material. Each drive shaft32connects a drum cylinder26to the corresponding CDDM30. Each CDDM30, which positions the corresponding drum cylinder26, can be powered either electrically, hydraulically or with pneumatics.

Referring now to the left-hand side ofFIG. 6, during normal reactor operation conditions, the control drums cylinders26are positioned such that the reflecting material36is pointing toward the core20, thereby directing the neutrons38back into the reactor core20(left side ofFIG. 6). During shutdown, each control drum cylinder26is rotated so that the neutron absorbing material34is pointing toward the core20, thereby absorbing enough neutrons38to shut down the nuclear reactor11, as shown on the right side ofFIG. 6.

Referring additionally toFIG. 7, in known systems, each control drum cylinder26is controlled by its own CDDM30. As expected, the use of an independent CDDM30for each control drum cylinder26increases the chances for the failure of a sole CDDM30, and the subsequent inability to operate the corresponding control drum cylinder26. The present disclosure pertains to eliminating the requirement of having an individual CDDM30for each control drum.

As such, there at least remains a need, therefore, for systems and methods for controlling reactor power levels in nuclear space reactors, to include nuclear thermal space reactors.

SUMMARY OF INVENTION

One embodiment of the present disclosure provides a control drum system for a nuclear reactor including a reactor core, comprising an ex-core reflector including a cylindrical outer wall, a cylindrical inner wall that is concentric with the outer wall and defines a cylindrical center bore, and a plurality of cylindrical apertures disposed between the outer and inner walls, a plurality of control drum assemblies, each control drum assembly including a drive shaft having a top end and a bottom end, a drum cylinder affixed to the bottom end of the drive shaft, and a planetary gear attached to the top end of the drive shaft, wherein the drum cylinder of each control drum assembly is rotatably received in a corresponding cylindrical aperture of the ex-core reflector, a first control drum drive motor operably connected to the top end of the first control drum assembly of the plurality of the control drum assemblies so that the first control drum motor rotates the drum cylinder of the first control drum assembly within the corresponding cylindrical aperture of the ex-core reflector, and an annular ring gear that is operably connected to the planetary gear of each of the control drum assemblies so that all the control drum assemblies rotate simultaneously.

Another embodiment of the present disclosure provides a nuclear reactor having a reactor core, an ex-core reflector including a cylindrical outer wall, a cylindrical inner wall that is concentric with the outer wall and defines a cylindrical center bore, and a plurality of cylindrical apertures disposed between the outer and inner walls, the reactor core being disposed within the center bore, a plurality of control drum assemblies, each control drum assembly including a drive shaft having a top end and a bottom end, a drum cylinder affixed to the bottom end of the drive shaft, and a planetary gear attached to the top end of the drive shaft, wherein the drum cylinder of each control drum assembly is rotatably received in a corresponding cylindrical aperture of the ex-core reflector, a first control drum drive motor operably connected to the top end of a first control drum assembly of the plurality of the control drum assemblies so that the first control drum motor rotates the drum cylinder of the first control drum assembly within the corresponding cylindrical aperture of the ex-core reflector, and a synchronizing element that is operably connected to the planetary gear of each of the control drum assemblies so that all the control drum assemblies rotate simultaneously.

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.

