Patent Number: 
Section: claims

1. A control rod drive system controlling operation by supplying a hydraulic pressure to control rod drive mechanisms, comprising:a plurality of first hydraulic control units;a plurality of control rod drive mechanisms respectively corresponding to the plurality of first hydraulic control units;a second hydraulic control unit, which has a same configuration as the plurality of first hydraulic control units;first piping connecting each first hydraulic control unit with each respectively corresponding control rod drive mechanism; anda plurality of valves, each on a flow path of the first piping,wherein the second hydraulic control unit is connected to each control rod drive mechanism via second piping that is connected to each of the plurality of valves,wherein water does not flow directly between the second hydraulic control unit and any of the first hydraulic control units, andwherein a flow path of supplying hydraulic pressure to a control rod drive mechanism is switched from a respective first hydraulic control unit to the second hydraulic control unit via a valve. 2. The control rod drive system according to claim 1,wherein each a three-way selector valve, anda first inlet of each three-way selector valve is connected to a respective discharge port of a respective first hydraulic control unit, a second inlet of each three-way selector value is connected to a respective discharge port of the second hydraulic control unit, and an outlet of each three-way selector valve is connected to a respective control rod drive mechanism. 3. The control rod drive system according to claim 1,wherein each valve includes a tee and a gate valve, anda first opening of each tee is connected to a respective discharge port of the first hydraulic control unit, a second opening of each tee is connected to a respective discharge port of the second hydraulic control unit though the gate valve, and a third opening of each tee is connected to a respective given control rod drive mechanism. 4. The control rod drive system according to claim 1,wherein the second hydraulic control unit is detachably connected to each valve. 5. The control rod drive system according to claim 4,wherein the second hydraulic control unit is detachably connected to each valve through flange joints. 6. The control rod drive system according to claim 5,wherein the second hydraulic control unit is mobile upon disconnection from the valves. 7. The control rod drive system according to claim 1, wherein each first hydraulic control unit and the second hydraulic control unit each comprise:an air operated scram valve,a scram pilot valve that opens/closes the scram valve,downstream-side gate valves positioned on a downstream side of the scram valve,an upstream-side gate valve positioned on an upstream side of the scram valve,a pressure device positioned between the scram valve and the upstream-side gate valve and configured to pressurize an internal pipe, anda solenoid valve positioned between the scram valve and the downstream-side gate valves and configured to supply purge water. 8. The control rod drive system according to claim 2, wherein each first hydraulic control unit and the second hydraulic control unit each comprise:an air operated scram valve,a scram pilot valve that opens/closes the scram valve,downstream-side gate valves positioned on a downstream side of the scram valve,an upstream-side gate valve positioned on an upstream side of the scram valve,a pressure device positioned between the scram valve and the upstream-side gate valve and configured to pressurize an internal pipe, anda solenoid valve positioned between the scram valve and the downstream-side gate valves and configured to supply purge water. 9. The control rod drive system according to claim 3, wherein each first hydraulic control unit and the second hydraulic control unit each comprise:an air operated scram valve,a scram pilot valve that opens/closes the scram valve,downstream-side gate valves positioned on a downstream side of the scram valve,an upstream-side gate valve positioned on an upstream side of the scram valve,a pressure device positioned between the scram valve and the upstream-side gate valve and configured to pressurize an internal pipe, anda solenoid valve positioned between the scram valve and the downstream-side gate valves and configured to supply purge water. 10. The control rod drive system according to claim 4, wherein each first hydraulic control unit and the second hydraulic control unit each comprise:an air operated scram valve,a scram pilot valve that opens/closes the scram valve,downstream-side gate valves positioned on a downstream side of the scram valve,an upstream-side gate valve positioned on an upstream side of the scram valve,a pressure device positioned between the scram valve and the upstream-side gate valve and configured to pressurize an internal pipe, anda solenoid valve positioned between the scram valve and the downstream-side gate valves and configured to supply purge water. 11. The control rod drive system according to claim 5, wherein each first hydraulic control unit and the second hydraulic control unit each comprise:an air operated scram valve,a scram pilot valve that opens/closes the scram valve,downstream-side gate valves positioned on a downstream side of the scram valve,an upstream-side gate valve positioned on an upstream side of the scram valve,a pressure device positioned between the scram valve and the upstream-side gate valve and configured to pressurize an internal pipe, anda solenoid valve positioned between the scram valve and the downstream-side gate valves and configured to supply purge water. 12. The control rod drive system according to claim 6, wherein each first hydraulic control unit and the second hydraulic control unit each comprise:an air operated scram valve,a scram pilot valve that opens/closes the scram valve,downstream-side gate valves positioned on a downstream side of the scram valve,an upstream-side gate valve positioned on an upstream side of the scram valve,a pressure device positioned between the scram valve and the upstream-side gate valve and configured to pressurize an internal pipe, anda solenoid valve positioned between the scram valve and the downstream-side gate valves and configured to supply purge water.