Patent Number: 
Section: claims

1. An apparatus comprising:a nuclear reactor comprising an upper head, a reactor vessel shell coupled to the upper head, the reactor vessel shell comprising a cylindrical shape, a lower head provided on a lower portion of the reactor vessel shell, and a core located within an interior of the nuclear reactor;a steam generator surrounding a circumference of the reactor vessel shell, the steam generator comprising a first penetration hole in fluid communication with the interior of the nuclear reactor such that a fluid flows between the interior of the nuclear reactor and an interior of the steam generator; anda steam drum surrounding a circumference of the steam generator and comprising a second penetration hole in fluid communication with an interior of the steam generator such that a fluid flows between an interior of the steam drum and the interior of the steam generator, wherein the steam generator further comprises:a steam generator inner shell connected to or formed in one piece with the reactor vessel shell and surrounding 360 degrees the circumference of the reactor vessel shell, wherein the steam generator inner shell shares a portion with the reactor vessel shell and extends in a longitudinal direction of the reactor vessel shell; anda steam generator outer shell spaced apart from the steam generator inner shell and surrounding 360 degrees the circumference of the reactor vessel shell, wherein the steam generator outer shell extends in the longitudinal direction of the reactor vessel shell,wherein the steam drum further comprises:a steam drum inner shell connected to or formed in one piece with the steam generator outer shell and surrounding 360 degrees the circumference of the steam generator, wherein the steam drum inner shell shares a portion with the steam generator outer shell and extends in the longitudinal direction of the reactor vessel shell; anda steam drum outer shell spaced apart from the steam drum inner shell and surrounding 360 degrees the circumference of the steam generator, the steam drum outer shell extending in the longitudinal direction of the reactor vessel shell,wherein the first penetration hole is provided in a region in which the reactor vessel shell and the steam generator inner shell are connected to or formed in one piece with each other and is used as a flow path allowing a fluid to flow between the interior of the nuclear reactor and the interior of the steam generator,wherein the second penetration hole is provided in a region in which the steam generator outer shell and the steam drum inner shell are connected to or formed in one piece with each other and is used as a flow path allowing a fluid to flow between the interior of the steam generator and the interior of the steam drum. 2. The apparatus of claim 1, wherein the steam generator further comprises:a steam generator upper head connecting an upper portion of the steam generator inner shell to an upper portion of the steam generator outer shell; anda steam generator lower head connecting a lower portion of the steam generator outer shell to the reactor vessel shell,wherein the steam generator upper head has a semicircular or semielliptical cross section and extends in a ring shape along the circumference of the steam generator, and the steam generator lower head has a circular-arc cross section and extends in a ring shape along the circumference of the steam generator. 3. The apparatus of claim 2, wherein a manway is detachably coupled to the steam generator upper head or the steam generator lower head. 4. The apparatus of claim 1, wherein a plurality of first partition plates are arranged at intervals inside the steam generator along the circumference of the steam generator, and steam generator modules each comprising a high-temperature part and a low-temperature part are provided in spaces separated by the first partition plates, andeach of the steam generator modules comprises a second partition plate separating the high-temperature part and the low-temperature part from each other. 5. The apparatus of claim 4, wherein the first penetration hole comprises a first entrance penetration hole communicating with the high-temperature part and a first exit penetration hole communicating with the low-temperature part;a cylindrical core support barrel assembly extending in the longitudinal direction of the reactor vessel shell and accommodating the core is provided inside the nuclear reactor; andthe core support barrel assembly comprises a core penetration hole communicating with the first entrance penetration hole, and the first exit penetration hole communicates with a space between the reactor vessel shell and the core support barrel assembly. 6. The apparatus of claim 1, wherein a lower heat transfer tube sheet is provided in a lower portion of the steam generator, the lower heat transfer tube sheet being coupled to the steam generator inner shell and the steam generator outer shell and having a plate shape along the circumference of the steam generator;an upper heat transfer tube sheet is provided in an upper portion of the steam generator, the upper heat transfer tube sheet being coupled to the steam generator inner shell and the steam generator outer shell having a plate shape along the circumference of the steam generator; andthe externally integrated steam generator type small modular reactor further comprises a heat transfer tube coupled to the lower heat transfer tube sheet and the upper heat transfer tube sheet and extending straight from the lower heat transfer tube sheet to the upper heat transfer tube sheet. 7. The apparatus of claim 6, wherein the lower heat transfer tube sheet or the upper heat transfer tube sheet is connected to or formed in one piece with the steam generator inner shell and the steam generator outer shell. 8. The apparatus of claim 1, wherein the steam drum further comprises:a steam drum upper head connecting an upper portion of the steam drum inner shell to an upper portion of the steam drum outer shell; anda steam drum lower head connecting a lower portion of the steam drum outer shell to the steam generator outer shell,wherein the steam drum upper head has a semicircular or semielliptical cross section and extends in a ring shape along a circumference of the steam drum, and the steam drum lower head has a circular-arc cross section and extends in a ring shape along the circumference of the steam drum. 9. The apparatus of claim 8, wherein a steam outlet nozzle is formed in the steam drum upper head. 10. The apparatus of claim 8, wherein a moisture separator and a steam dryer are provided in the steam drum. 11. The apparatus of claim 8, further comprising a circular-arc shaped shroud extending from an inside of the steam drum lower head to an inside of the steam generator outer shell, the shroud extending in a ring shape along a circumference of the steam drum lower head and a circumference of the steam generator outer shell. 12. The apparatus of claim 1, wherein a pressurizer plate in which a surge hole is formed to allow a fluid to pass therethrough and an electric heater is installed to heat a fluid is provided in the nuclear reactor. 13. The apparatus of claim 12, wherein a protrusion protruding inward from the nuclear reactor and having a stud bolt hole is provided on the nuclear reactor, andthe pressurizer plate is coupled to the protrusion using a stud bolt. 14. The apparatus of claim 1, wherein a cylindrical shell flange protrudes inward from the reactor vessel shell and comprises a stud bolt hole,an upper head flange protrudes outward from the upper head and comprises a stud bolt hole, andthe upper head and the reactor vessel shell are coupled to each other by joining the cylindrical shell flange and the upper head flange using a stud bolt. 15. The apparatus of claim 1, wherein the apparatus is manufactured by coupling a plurality of forged members to each other. 16. The apparatus of claim 1, wherein a space formed on an upper portion of the reactor vessel shell and surrounded by the steam generator inner shell is configured to be filled with a fluid.