Patent Number: 061852686
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a main steam pressure disturbance preventing apparatus of a nuclear power plant which is so constructed as to be able to prevent pressure disturbance produced due to the disturbance of the liquid level of a pressure detection pipe or a water level detector generated when hydrogen and oxygen contained in vapor generated as a result of radiolysis of core cooling water in a main steam system or a drain system at a nuclear power plant are dissolved into liquid phase of the pressure detection pipe or the water level detector and the dissolved gas is evaporated due to the decrease of the process pressure, and thus, maintain pressure and water level measurements in the satisfactory state. 2. Description of the Related Art At a boiling water reactor power plant, a main steam pipe is connected to a reactor pressure vessel in order to lead steam generated in a reactor core directly to a turbine. Assuming the possible break of the main steam pipe, main steam separation valves are provided at the inside and the outside of a reactor container, respectively to form a reactor coolant pressure boundary. The outline of the main steam system and the drain system of a boiling water reactor power plant will be briefly explained referring to FIG. 10. Steam generated in a reactor 1 is sent to a steam turbine 3 by passing through a main steam pipe 2 of the main steam system along with hydrogen and oxygen produced as a result of the radiolysis. Part of the steam worked in steam turbine 3 is sent to a feed-water heater 5 by passing through a turbine bleeding pipe 4. On the other hand, the remainder of the steam worked in steam turbine 3 is condensed in a condenser 6, boosted by a feed-water pump 7 and sent to feed-water heater 5. In this feed-water heater 5, feed-water from feed-water pump 7 is heated by the steam worked in steam turbine 3, and this heated feed-water is sent to reactor 1 by passing through a feed-water pipe 9. The steam that was heat exchanged in feed-water heater 5 is condensed to drain and recovered by condenser 6 after passing through a drain pipe 8 of the drain system. As the steam generated in reactor 1 is accompanied with hydrogen and oxygen produced as a result of the radiolysis, hydrogen and oxygen exist in the small amount in the main steam system and the drain system, as described above. For measuring pressure in main steam pipe 2 of the main steam system, as shown in FIG. 11, a detection pipe 10 is connected to a pressure detection seat (not shown) of main steam pipe 2, and a main instrumentation valve 11 and an upward detection pipe 12 are connected to detection pipe 10 and a pressure detector 13 is connected to detection pipe 10 at the downstream side. Here, as hydrogen and oxygen exist in main steam pipe 2 as described above, hydrogen and oxygen having lower specific gravity than steam may possibly be accumulated in upward detection pipe 12. In detection pipe 10, water is filled so as to give a prescribed hydrostatic head to pressure detector 13. Accumulated hydrogen and oxygen are dissolved into the liquid phase of detection pipe 10. When the process side pressure is decreased, the hydrogen and oxygen dissolved in the liquid phase of detection pipe 10 are boiled under the reduced pressure. The hydrostatic head applied to pressure detector 13 is changed due to the disturbance of the liquid phase of detection pipe 10 by the boiling under the reduced pressure. The thus caused disturbance of the liquid level appears as the disturbance to the output signal of pressure detector 13. As a result of this disturbance, there are such problems that the supervision and control of the nuclear power plant are adversely affected. SUMMARY OF THE INVENTION Accordingly, one object of this invention is to provide a main steam pressure disturbance preventing apparatus of a nuclear power plant, which is capable of recombining hydrogen and oxygen gradually by catalyst and removing them in a pressure detector or a water level detector connected to a steam system or a drain system, preventing thereby pressure disturbance, and thus maintaining the pressure and water level measurements in a satisfactory state. Another object of this invention is to provide a main steam pressure disturbance preventing apparatus of a nuclear power plant, which is capable of recombining hydrogen and oxygen gradually by catalyst and removing them in an instrumentation pipe for connecting a pressure detector or a water level detector to a steam system or a drain system, preventing thereby pressure disturbance, and thus maintaining the pressure and water level measurements in a satisfactory state. Still another object of this invention is to provide a main steam pressure disturbance preventing apparatus of a nuclear power plant, which is capable of recombining hydrogen and oxygen gradually by catalyst provided on a catalyst plated layer on a thin disc-state plate and removing them in a pressure detector or a water level detector connected to a steam system or a drain system, preventing the drain containing metals dropped from the upper space of a detection container of the pressure detector or the water level detector from adhering to the surface of the thin disc-state plate, and thereby preventing the drop of performance of catalyst due to the adhered drain containing metals. These and other objects of this invention can be achieved by providing a main steam pressure disturbance preventing apparatus of a nuclear power plant including, one of a pressure detector and a water level detector provided in one of a steam system from a reactor of the nuclear power plant and a drain system connected to the steam system, an instrumentation pipe connected between one of the pressure detector and the water level detector and one of the steam system and the drain system, and catalyst installed in one of the pressure detector, the water level detector and the instrumentation pipe for recombining hydrogen and oxygen. According to one aspect of this invention, there is provided a main steam pressure disturbance preventing apparatus of a nuclear power plant including, one of a pressure detector and a water level detector provided in one of a steam system from a reactor of the nuclear power plant and a drain system connected to the steam system, an instrumentation pipe connected between one of the pressure detector and the water level detector and one of the steam system and the drain system, and a cylindrical thin plate inserted in the instrumentation pipe with a catalyst plated layer plated on an inner surface of the cylindrical thin plate with a catalyst for recombining hydrogen and oxygen. According to another aspect of this invention, there is provided a main steam pressure disturbance preventing apparatus of a nuclear power plant including, one of a pressure detector and a water level detector provided in one of a steam system from a reactor of the nuclear power plant and a drain system connected to the steam system, an instrumentation pipe connected between one of the pressure detector and the water level detector and one of the steam system and the drain system, and a thin disc plate provided at an inner surface of an upper lid of a detection container of one of the pressure detector and the water level detector. The thin disc plate is provided with a center hole and a small cylindrical projection with a curved surface rising from around the center hole, and the thin disc plate is provided with a catalyst plated layer plated on an under surface of the thin disc plate and on an outer surface of the small cylindrical projection with a catalyst for recombining hydrogen and oxygen. According to still another aspect of this invention, there is provided a main steam pressure disturbance preventing apparatus of a nuclear power plant including, one of a pressure detector and a water level detector provided in one of a steam system from a reactor of the nuclear power plant and a drain system connected to the steam system, an instrumentation pipe connected between one of the pressure detector and the water level detector and one of the steam system and the drain system, and a thin disc plate provided at an inner surface of an upper lid of a detection container of one of the pressure detector and the water level detector. The thin disc plate is provided with a center hole, a small cylinder and a thin ring plate at an under surface of the thin disc plate, and the thin ring plate has a catalyst plated layer plated on an under surface of the thin ring plate with a catalyst for recombining hydrogen and oxygen. According to a further aspect of this invention, there is provided a main steam pressure disturbance preventing apparatus of a nuclear power plant including, one of a pressure detector and a water level detector provided in one of a steam system from a reactor of the nuclear power plant and a drain system connected to the steam system, an instrumentation pipe connected between one of the pressure detector and the water level detector and one of the steam system and the drain system, and a tapered thin plate provided at an inner surface of an upper lid of a detection container of one of the pressure detector and the water level detector. The tapered thin plate is thicker at a central portion than at a peripheral portion, and is provided with a center hole and a catalyst plated layer plated on an under surface of the tapered thin plate with a catalyst for recombining hydrogen and oxygen. According to another aspect of this invention, there is provided a main steam pressure disturbance preventing apparatus of a nuclear power plant including, one of a pressure detector and a water level detector provided in one of a steam system from a reactor of the nuclear power plant and a drain system connected to the steam system, an instrumentation pipe connected between one of the pressure detector and the water level detector and one of the steam system and the drain system, and a thin disc plate provided at an inner surface of an upper lid of a detection container of one of the pressure detector and the water level detector. The thin disc plate is provided with a center hole, a catalyst plated layer plated on an under surface of the thin disc plate with a catalyst for recombining hydrogen and oxygen, and a ring for preventing drain adherence on the under surface of the thin disc plate around the center hole. According to still another aspect of this invention there is provided a main steam pressure disturbance preventing apparatus of a nuclear power plant including: one of a pressure detector and a water level detector provided in one of a steam system from a reactor of the nuclear power plant and a drain system connected to the steam system, an instrumentation pipe connected between one of the pressure detector and the water level detector and one of the steam system and the drain system, and a float stem penetrating through an upper lid of a detection container of one of the pressure detector and the water level detector. The float stem is provided with a catalyst plated layer plated on a surface of the float stem with a catalyst for recombining hydrogen and oxygen. To prevent the pressure disturbance that is caused by the accumulated hydrogen and oxygen, it is necessary to remove hydrogen and oxygen before their densities increase. To remove hydrogen and oxygen, it will be effective to install a catalyst to accelerate the recombination of hydrogen and oxygen as proposed in this invention and gradually recombine them before their densities become high. Further, for instance, when steam flows into the upper space of a pressure detector or a water level detector and is condensed in the upper space of the detector, and the generated drain drops to a detecting container of the detector, the drain may possibly adhere to the surface of a thin disc-state plate having a catalyst plated layer of platinum (Pt), etc. attached to the upper lid of the detection container. If metals such as chrome, etc. contained in a float stem, etc. are melted into this drain, such metals are separated from the drain adhered to the catalyst plated layer of platinum (Pt), etc. provided at the surface of the thin disc-state plate, and may cover the surface of the catalyst plated layer. However, even when the drain is adhered to the surface of the catalyst plated layer and metals melted in the drain are separated, according to the present invention it is possible to prevent the drop of the recombination function of hydrogen and oxygen without reducing the contacting area of hydrogen, oxygen and catalyst in a detection container.