Patent Number: 056573600
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a reactor container provided with a dry well cooling system according to the present invention will be described hereunder with reference to FIG. 1. In FIG. 1, denoted by reference numeral 1 is a reactor container which is divided to define a dry well 2 and a wet well therein. An in-dry-well heat exchanger 3 is disposed in the dry well 2, and an in-dry-well blower 4 is provided on and connected to the primary side of the in-dry-well heat exchanger 3. The wet well is not shown in FIGS. 1-13 in connection with first to thirteenth embodiments of the present invention, but it will be easily understood by persons skilled in the art that the wet well is disposed below the dry well 2 in the reactor container 1 such as located in a reactor container of FIGS. 14 to 17. A circulation pipe 9 is connected to the secondary side, i.e., a heat transfer pipe, of the in-dry-well heat exchanger 3, and a normal cooling system 6 is connected to the circulation pipe 9. The normal cooling system 6 includes an equipment cooling pump 7, an equipment cooling heat exchanger 8, and a seawater pump 13. A standby cooling system 14 is branched from the circulating pipe 9 at an intermediate portion between the reactor container 1 and the normal cooling system 6. The standby cooling system 14 is intended to flow cooling water into the heat transfer pipe of the in-dry-well heat exchanger 3 for cooling the same. The cooling water is introduced by a standby cooling pump 15 to a standby cooling heat exchanger 16 where the water is cooled. Then, the cooling water is conveyed to the heat transfer pipe of the in-dry-well heat exchanger 3. In other words, the standby cooling system 14 comprises the standby cooling pump 15, the standby cooling heat exchanger 16, and a standby seawater pump 17 for supplying seawater 12 from the sea 5 as cooling water to the secondary side of the standby cooling heat exchanger 16. A second embodiment of the present invention shown in FIG. 2 is basically similar to the above first embodiment except that the standby cooling pump 15 and the standby cooling heat exchanger 16 are omitted. The standby cooling system 14 is constituted as a direct seawater cooling system which acts to directly supply the seawater 12 to the in-dry-well heat exchanger 3 by using only the seawater pump 17. More specifically, a standby cooling discharge pipe 14a and a supply pipe 14b are connected, as seawater circulation line in communication with the sea 5, to respective lines of the circulation pipe 9, and the standby seawater pump 17 is connected to the supply pipe 14b. With the first and second embodiments explained above, even when the normal cooling system 6 is brought into an outage due to failure or inspection, the in-dry-well heat exchanger 3 can be cooled by operating the standby cooling system 14 and the interior of the dry well 2 can be cooled by the in-dry-well blower 4. As a result, the reliability of the dry well cooling system can be improved. With the following embodiments, the present invention will be described with reference to structure different from that of the first or second embodiment by adding new reference numerals and like reference numerals to portions or members corresponding to those shown in FIGS. 1 and 2 and the explanations thereof are omitted herein. A third embodiment of the present invention will be described hereunder with reference to FIG. 3. In the third embodiment, the standby cooling system 14 is likewise connected to the circulation pipe 9, but it comprises a standby cooling pump 14c and an air cooler 14d connected to each other. With this third embodiment, therefore, the standby cooling system can be operated with no need of operating the seawater pump. Accordingly, even during the periodic inspection of the seawater cooling system, the dry well cooling system can be operated by using the standby cooling system. A fourth embodiment of the present invention will be described hereunder with reference to FIG. 4. The fourth embodiment is different from the above first embodiment in that electric power necessary for operating various equipment can be supplied from not only a normal power supply 18 under ordinary condition, but also an emergency power supply 19 at need. With the fourth embodiment, therefore, even when the normal power supply 18 is disabled due to the outage of the external power source, the dry well cooling system can be operated by the electric power supplied from the emergency power supply 19 to remove the heat from the reactor container. A fifth embodiment of the present invention will be described hereunder with reference to FIG. 5. In the fifth embodiment, the normal cooling system 6 in the above first embodiment is disconnected from the in-dry-well heat exchanger 3 and constituted as a separate system, whereas a dedicated cooling system 20 is provided on and connected to the secondary side of the in-dry-well heat exchanger 3. The dedicated cooling system 20 comprises a dedicated cooling pump 21, a dedicated cooling heat exchanger 22, and a dedicated cooling seawater pump 23. With this embodiment, even when the RHR system is failed and its cooling function is disabled, the cooling system in the dry well can be operated so that the function of the dry well cooler for removing the heat from the reactor container is ensured. A sixth embodiment of the present invention will now be described with reference to FIG. 6. In the sixth embodiment, the in-dry-well blower 4 and heat exchanger 3 disposed in the dry well 2 inside the reactor container 1 are associated with an environmental condition resistance maintaining equipment 24 to maintain their performance so that the blower 4 and the heat exchanger 3 can endure against serious environmental conditions, i.e., high-temperature, high-pressure, high-humidity and aqueous atmosphere, in an anticipation of a severe accident, thereby enabling the dry well cooling system to operate. With this sixth embodiment, even if the atmosphere in the dry well 2 should exceed conventional design conditions, i.e., a temperature of 200.degree. C., pressure of 10 Kg/cm.sup.2 and humidity of 100%, in the event of a severe accident, the performance of the dry well cooling system can be maintained to ensure sufficient heat removal from the reactor container. Also, even when an atmosphere of sprayed water droplets is produced in the dry well 2 by a reactor container spray, not shown in FIG. 6, the dry well cooling system can be operated to effect sufficient heat removal. Therefore, even if the heat removal function of the RHR system should be disabled in the event of a severe accident, the dry well cooling system can remove the heat from the reactor container with the sufficient reliability. A seventh embodiment of the present invention will be described hereunder with reference to FIG. 7. In the seventh embodiment, an extra-dry-well blower 4a is mounted outside the reactor container 1 through a pipe 4b communicating with the dry well 2 of the reactor container 1, and the delivery side of the extra-dry-well blower 4a is connected to an inlet pipe 3b on the primary side of an extra-dry-well heat exchanger 3a. A return pipe 3c on the primary side of the extra-dry-well heat exchanger 3a is connected to the reactor container 1 to be communicated with the dry well 2. An emergency dry well cooling system equipment cooling system 25 is connected to a circulating pipe 3d on the secondary side of the extra-dry-well heat exchanger 3a. The emergency dry well cooling system equipment cooling system 25 comprises an emergency dry well cooling system equipment cooling pump 26, an emergency dry well cooling system equipment cooling heat exchanger 27, and an emergency dry well cooling system equipment cooling seawater pump 28, which are operatively connected to each other. Thus, the seventh embodiment of the present invention shown in FIG. 7 includes a system dedicated for secondary cooling of the extra-dry-well heat exchanger 3a, i.e., the emergency dry well cooling system equipment cooling system 25. In this embodiment, the emergency dry well cooling system equipment cooling pump 26 conveys cooling water from the extra-dry-well heat exchanger 3a to the emergency dry well cooling system equipment cooling heat exchanger 27, and the emergency dry well cooling system equipment cooling seawater pump 28 conveys the seawater 12 to the emergency dry well cooling system equipment cooling heat exchanger 27, thereby cooling the heat in the dry well 2. An eighth embodiment of the present invention will be described hereunder with reference to FIG. 8. This eighth embodiment is of the same arrangements as the above seventh embodiment except that an emergency dry well cooling system equipment air cooling system 26 is provided in place of the emergency dry well cooling system equipment cooling system 25. The eighth embodiment of the present invention shown in FIG. 8 includes an emergency dry well cooling system equipment air cooling pump 26 and an air cooler 31 for cooling the secondary side of the extra-dry-well heat exchanger 3a. With this embodiment, the emergency dry well cooling system equipment cooling system can be operated with no need of operating the seawater pump. As a result, even during inspection of the seawater cooling system, the emergency dry well cooling system can be operated. A ninth embodiment of the present invention will be described hereunder with reference to FIG. 9. The ninth embodiment is different from the seventh embodiment in that not only the normal power supply 18 but also the emergency power supply 19 are electrically connected to the extra-dry-well blower 4a, the emergency dry well cooling system equipment cooling pump 26, and the emergency dry well cooling system equipment cooling seawater pump 28. In the ninth embodiment of the present invention shown in FIG. 9, electric power can be supplied from an emergency diesel generator (EDG), i.e., the emergency power supply 19, to the emergency dry well cooling system and the emergency dry well cooling system equipment cooling system. With this embodiment, therefore, even when the normal power supply is disabled due to outage of the external power source, the emergency dry well cooling system can be operated by electric power supplied from the emergency power supply 19 to remove the heat from the reactor container. A tenth embodiment of the present invention will be described hereunder with reference to FIG. 10. The tenth embodiment is different from the seventh embodiment in that a pressure sensor 32 and a temperature sensor 33 are disposed in the reactor container 1, and an emergency dry well cooling system automatic start-up circuit 34 is installed which detects an abnormal temperature or pressure increase in the dry well 2 by receiving an output signal from the sensor 32 or 33, also detects a function outage of a residual heat removing (RHR) system 35 by receiving a function outage signal output from the same, and then automatically starts up the emergency dry well cooling system. The emergency dry well cooling system automatic start-up circuit 34 is electrically connected to the extra-dry-well blower 4a, the emergency dry well cooling system equipment cooling pump 26, and the emergency dry well cooling system equipment cooling seawater pump 28 via signal lines 37 for delivering output signals over the respective signal lines. With this embodiment, even in a case where the residual heat removing system 35 should fail to start up operation and the operator should miss the failure of the RHR system 35, the emergency dry well cooling system is automatically started up on condition that the temperature or pressure in the dry well 2 exceeds a threshold, or the function of the RHR system is disabled, making it possible to ensure integrity of the reactor container 1. An eleventh embodiment of the present invention will be described hereunder with reference to FIG. 11. The eleventh embodiment is different from the seventh embodiment in that the extra-dry-well blower 4a is connected to the return pipe 3c on the primary side of the extra-dry-well heat exchanger 3a. Stated otherwise, in the eleventh embodiment, the extra-dry-well blower 4a is disposed downstream of the extra-dry-well heat exchanger 3a. With this embodiment, since the extra-dry-well blower 4a is not exposed to the atmosphere having the temperature raised in the dry well 2, the function of the extra-dry-well blower 4a will not be deteriorated and the soundness of the reactor container can be maintained more surely. A twelfth embodiment of the present invention will be described hereunder with reference to FIG. 12. The twelfth embodiment is different from the seventh embodiment in that a header 38 is installed in the dry well 2 and the return pipe 3c on the primary side of the extra-dry-well blower 4a is connected to the header 38. With this embodiment, since the emergency dry well cooling system is provided with the header 38 at its delivery port, the atmosphere in the dry well 2 can be cooled with higher efficiency. A thirteenth embodiment of the present invention will be described hereunder with reference to FIG. 13. The thirteenth embodiment is different from the seventh embodiment in that a branch pipe 39 is connected to the pipe 4b interconnecting the reactor container 1 and the extra-dry-well heat exchanger 3a, a safety valve 40 is connected to the branch pipe 39, a discharge pipe 41 is connected to the safety valve 40, and a vent line 42 is connected to the discharge pipe 41. With this embodiment, in the event of a severe accident such as anticipated transient without scram (ATWS) sequence, if the pressure in the dry well is abruptly raised in excess of the design pressure of the reactor container, the safety valve 40 is opened at a preset pressure and, therefore, the atmosphere in the dry well can be introduced to the vent line 42 to keep soundness of the reactor container 1. According to the present invention, as described above, the heat removal from the dry well in the event of a severe accident can be performed by the normal dry well cooling system and the emergency dry well cooling system with high reliability and, at the same time, the pressure in the reactor container can also be reduced. As a result, it is possible to prevent breakage of the reactor container in the event of a severe accident. A reactor container vent system which has been contemplated to be installed in the past is problematic in that because the atmosphere in the reactor container is directly discharged to open air for pressure reduction, fission products, though a very small amount, may be discharged to the environment and heat removal from the reactor container cannot be expected. By contrast, according to the present invention, it is possible to safely settle down a severe accident without discharging fission products. According to the present invention, there are further provided the following embodiments which are represented by FIGS. 14 to 17, respectively, as fourteenth, fifteenth, sixteenth and seventeenth embodiments, in which like reference numerals are added to common members or equipments. The fourteenth embodiment will be described hereunder with reference to FIGS. 14. Referring to FIG. 14, a reference numeral 101 denotes a reactor container the inside of which is divided into an upper dry well 102a and a lower wet well 102b, and a pipe line 105 is communicated with the dry well 102a and the wet well 102b, respectively. An extra-dry-well heat exchanger 103 is also connected to the pipe line 105 and an extra-dry-well blower 104 is connected to the downstream side of the heat exchanger 103. A primary cooling circulation pipe 106 is connected to a secondary side of the heat exchanger 103 and a primary cooling system is connected to the primary cooling circulation pipe 106. The primary cooling system comprises a primary cooling pump 107, a cooling system heat exchanger 108, a secondary cooling seawater circulation pipe 109 and a secondary cooling seawater pump 110, which are operatively associated with each other. FIG. 15 represents the fifteenth embodiment of the present invention, which is similar to the fourteenth embodiment but different in an arrangement that the cooling system is composed of a direct seawater cooling system capable of supplying the seawater 111 directly to the heat exchanger 103 only through a seawater circulation pipe 112 and a seawater pump 113. According to the fourteenth and fifteenth embodiments, even in a time when an equipment is damaged through a failure of the RHR system at an accident, the atmosphere in the reactor container 101 is guided to the heat exchanger through the operation of the blower 104 to thereby perform the cooling function, thus surely maintaining the soundness of the reactor container. FIG. 16 represents the sixteenth embodiment of the present invention, in which there is located a cooling pool 118 opened to the atmosphere as a heat sink and a heat exchanger 117 is located in the cooling pool 118 filled up with water. The heat exchanger 117 is connected to the pipe line 105 and the blower 104. According to this embodiment, there is no need of any dynamic equipment such as pump for the operation of the cooling system, and because of this reason, the reactor container can be cooled with high reliability at a time of an occurrence of a severe accident. FIG. 17 represents the seventeenth embodiment of the present invention, which is different from the fourteenth embodiment in a location of a blower duct 125 in the reactor container 101. The blower duct 125 is connected to the pipe line 105. According to this embodiment, since the blower duct 125 is connected to a discharge side of the emergency dry well cooling system, the atmosphere in the reactor container 101 can be effectively cooled. As can be seen from the above disclosure and drawings of FIGS. 14-17, according to the fourteenth to seventeenth embodiments, the pipe line 105 is connected to both the dry well and wet will, which is different from the former embodiments in which the pipe line is connected only to the dry well. In a case where an accident occurs in a normal operation condition, the reactor scrams, and thereafter, vapor in the RPV is flown out in the vent tube or into the suppression pool through a safety relief valve. At this time, the vapor is condensed by the water in the suppression pool and a fission product contained in the vapor is captured in the suppression pool water through a scrubbing effect and transferred to the wet well gas phase. According to these embodiments of the present invention, the atmosphere in the wet well is circulated to the suppression pool liquid phase through the cooling system, the dry well and the vent tube, thus the fission product in the suppression pool gas phase being scrubbed more effectively. When the accident occurs during the normal operation, the reactor is shut-down and the core is cooled. Thereafter, when the reactor container is cooled, by the RHR system through one of the suppression pool cooling mode and the dry well spray mode. In the prior art technology, the suppression pool cooling means is not provided, but according to the present invention, the safeness of the reactor can be realized with high performance. Further, it will be easily understood that the first to thirteenth embodiments may be selectively applicable to the fourteenth to seventeenth embodiments of the present invention by persons skilled in the art without specifically describing herein through drawings. It is also to be noted that the present invention will be described hereinbefore with reference to the preferred embodiments but it is not limited to them and many changes and modifications may be made without departing from the subjects and scopes of the appended claims.