Patent Number: 
Section: claims

1. A boiling water type nuclear reactor use control rod which comprises a tie rod having substantially cross shaped cross section, a plurality of sheathes having substantially U shape cross section and attached to the respective sides of the tie rod, a plurality of neutron absorption rods disposed inside the respective sheathes, a handle which is disposed at one ends of the sheathes in the axial direction of the control rod and a lower portion supporting plate or a dropping speed limiter which is disposed at the other ends of the sheathes in the axial direction of the control rod, wherein at least one of the handle, the lower portion supporting plate and the dropping speed limiter is provided with a sliding structural body which is constituted by a pin, a pin hole into which the pin is inserted and a roller which rotates around the pin in the axial direction, and at least one groove is sized to promote water flow in a clearance between the pin and the pin hole and is arranged adjacent the clearance. 2. A boiling water type nuclear reactor use control rod according to  claim 1 , wherein the at least one groove is provided either at the outside or at the inside of the clearance. claim 1 3. A boiling water type nuclear reactor use control rod according to  claim 2 , wherein the at least one groove is provided at an upstream axial side and at a downstream axial side. claim 2 4. A boiling water type nuclear reactor use control rod according to  claim 3 , wherein the at least one groove is formed so as to extend near to end portions of the pin. claim 3 5. A boiling water type nuclear reactor use control rod according to  claim 4 , wherein the handle is provided with an opening near the end portions of the pin. claim 4 6. A boiling water type nuclear reactor use control rod which comprises a tie rod having a substantially cross shaped in its cross section, a plurality of sheathes having substantially U shape in its cross section each being attached to the respective four sides of the tie rod, a plurality of neutron absorption rods disposed inside the respective sheathes, a handle disposed at the upper ends of the sheathes and a lower supporting plate or a dropping speed limiter disposed at the lower ends of the sheathes, wherein each of four wings which constitute the handle is provided with a guide use roller constituted by a pin, a pin hole into which the pin is inserted and a roller which rotates in the axial direction around the pin, and a groove is sized to promote water flow in a clearance between the pin and the pin hole and is arranged at two positions adjacent the clearance. 7. A boiling water type nuclear reactor use control rod according to  claim 6 , wherein at least one of the lower portion supporting plate and the dropping speed limiter is provided with a second guide use roller constituted by a pin, a pin hole into which the pin is insertably arranged and a roller which rotates in the axial direction around the pin, and a groove which promotes water flow in a clearance between the pin and the pin hole is provided at two positions adjacent to the clearance of the second guide use roller. claim 6 8. A boiling water type nuclear reactor use control rod which comprises a tie rod having a substantially cross shaped in its cross section, a plurality of sheathes having substantially U shape in its cross section each being attached to the respective four sides of the tie rod, a plurality of neutron absorption rods disposed inside the respective sheathes, a handle disposed at the upper ends of the sheathes and a guide use roller which is provided at the handle and permits sliding of the control rod in an axial direction thereof, wherein a groove is sized to promote water flow in a clearance between the pin and the pin hole in the guide use roller and is provided adjacent the clearance at an upstream axial side and at a downstream axial side so as to communicate with the clearance.