Induced nuclear reactions: processes – systems – and elements – With control of reactor – By movement of control element or by release of neutron...
Reexamination Certificate
1999-03-12
2001-05-08
Carone, Michael J. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
With control of reactor
By movement of control element or by release of neutron...
C376S233000
Reexamination Certificate
active
06229867
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a control rod for a nuclear reactor and particularly relates to a control system including a cable-controlled spring assembly for controlling the movement of the control rod into and out of the reactor core.
BACKGROUND OF THE INVENTION
Control rods in a nuclear reactor perform the functions of power distribution, shaping and reactivity control. This is accomplished generally by providing a plurality of control rods containing material for neutron absorption and manipulating the control rods within the reactor core and between the fuel bundle assemblies. Typically, each control rod employed in a boiling water reactor is provided in a cruciform cross-sectional shape and extends in complementary cruciform-shaped interstices between the fuel bundles.
Generally, control rod guide tubes are located inside the pressure vessel and extend from the top of the control rod drive housing through the core support. Typically, each tube is designed as a lateral guide for a control rod and as a vertical support for a four-lobed fuel support piece and the fuel assemblies surrounding the control rod. The bottom of each guide tube is supported by the control rod drive housing which, in turn, transmits the weight of the guide tube, fuel support piece and fuel assemblies to the reactor vessel bottom head. Linear hydraulic systems are employed to drive the control rods. These drive systems, however, involve complicated control systems, as well as space for accumulators, valves, piping and controls.
BRIEF SUMMARY OF THE INVENTION
In accordance with an embodiment of the present invention, there is provided a spring-actuated cable controlled control rod drive system which, among other advantages, eliminates the fluid systems and ancillary equipment necessary for operation of the fluid systems previously employed, as well as saving building space in which such equipment would otherwise reside. Particularly, the present control rod drive system includes a control rod support disposed in the control rod guide tube. The support includes a support element to which the lower end of the control rod is connected and to which is connected a spring set for supplying SCRAM energy. More particularly, the spring set is disposed between the support element and the opposite end of the support guide tube and includes a set of springs, at least two of which springs are series connected lying in compression and a third spring which lies between the series connected springs and lies in tension. Consequently, the weight of the control rod is supported at all times by the springs. Also, the springs at all times bias the support element in a direction to displace the control rod toward the core.
A take-up cable connected at one end to a winch and extending through the control rod guide tube is coupled to the support element. By taking up the cable on the winch, the support element is withdrawn in the guide tube against the bias of the spring set to displace the control rod in a direction away from the reactor core. The spring loading on the spring set at the fully inserted position of the control rod into the core is greater than the weight of the control rod by a predetermined amount. Consequently, as the control rod is withdrawn, energy is stored in the spring set which SCRAMS the control rod upon release of a ratchet on the cable drum. Stops are provided in the guide tube for limiting the travel of the springs. Control rod over-travel is limited by the cable stretching against a limit stop on the drum.
In a preferred embodiment according to the present invention, there is provided an assembly for selectively positioning a control rod along a vertical axis in a nuclear reactor core disposed inside a reactor pressure vessel, comprising a control rod guide tube, a control rod support within the tube for supporting the control rod and movable along the tube, the support including a support element and a spring within the tube biasing the support element for movement in a vertical direction along the axis toward the reactor core, a cable received within the tube and coupled to the support element, a cable control device including a drive for retracting and releasing the cable and a control connected to the drive for selectively retracting the cable and the support element within the tube to move the control rod support element in a direction away from the core against the bias of the spring and releasing the cable enabling the spring to displace the control rod into the core.
In a further preferred embodiment according to the present invention, there is provided a nuclear reactor comprising a pressure vessel, a core containing a plurality of nuclear fuel assemblies and disposed within the pressure vessel, a plurality of control rods mounted for vertical movement within the core, a control rod guide tube for each of the control rods, a control rod support within the guide tube for supporting the control rod and for movement therewith, the control rod support including a support element and a spring within each of the tubes biasing the support element for movement in a vertical direction toward the core, a cable received within each tube and connected to the support, the cable penetrating through the pressure vessel and a cable control device including a drive for each cable outside the pressure vessel for selectively retracting the cable and support element within the tube to move the control rod support element in a direction away from the core against the bias of the spring and releasing the cable enabling the spring to displace the control rod into the core.
REFERENCES:
patent: 4076584 (1978-02-01), Golden et al.
patent: 4219384 (1980-08-01), Cramer et al.
patent: 4585608 (1986-04-01), Day
patent: 4624825 (1986-11-01), Martin et al.
patent: 5200140 (1993-04-01), Kobsa et al.
patent: 54-045483 (1979-04-01), None
patent: 2-098687 (1990-04-01), None
Carone Michael J.
General Electric Company
Keith Jack
Nixon & Vanderhye
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