Patent Number: 
Section: claims

1. A sealing mechanism for a nuclear reactor vessel cable penetration tube, the sealing mechanism comprising:a penetration tubeconfigured to penetrate a nuclear reactor vessel from an outside to advance to an inside thereof andcomprising an axially extending penetration hole for communication with the inside of the nuclear reactor vessel;a cable configured to be inserted to the inside of the nuclear reactor vessel through the penetration hole of the penetration tube; anda thimble placed between the cable and the penetration tube such that the thimble surrounds the cable within the penetration tube,the thimble comprising a dimple groove extending in a direction from an outer surface of the thimble toward the cable,wherein a diameter of the penetration hole at a first end portion of the penetration tube and a diameter of the penetration hole at a second end portion of the penetration tube are both smaller than a diameter of the penetration hole at a middle portion of the penetration tube,wherein the thimble is supported by the first end portion and the second end portion of the penetration tube,wherein the thimble is axially shorter than the penetration hole, wherein a thermal expansion space is defined between one or more of the thimble and the first end portion of the penetration tube or the thimble and the second end portion of the penetration tube, andwherein the penetration tube is provided in a lateral side of the nuclear reactor vessel. 2. The sealing mechanism of claim 1, wherein the dimple groove portion has a round groove shape. 3. The sealing mechanism of claim 1, further comprising a guide tube protruding from an end of the penetration tube, the guide tube comprising a guide hole communicating with the penetration hole to receive the cable. 4. The sealing mechanism of claim 1, further comprising a guide tube and a Swagelok fitting,wherein the guide tube protrudes from an end of the penetration tube and comprises a guide hole communicating with the penetration hole to receive the cable, andthe Swagelok fitting is installed on the end of the penetration tube or an end of the guide tube. 5. The sealing mechanism of claim 1,wherein the thimble comprises a thimble protrusionbetween the first end portion and the middle portion of the penetration tube orbetween the second end portion and the middle portion of the penetration tube.