Patent Number: 055531067
Section: claims

1. A residual stress improving method for members in reactor pressure vessel, comprising: a first step of ejecting, toward a first region in a surface of members in reactor pressure vessel submerged in reactor water, a water jet in the form of a high speed submerged water jet at temperature lower than any temperatures of said reactor water and said members in reactor pressure vessel from a nozzle to impinge against said first region in water environment; and  a second step of stopping the impingement of said water jet against said first region, allowing said first region to be heated again. 2. A residual stress improving method for members in reactor pressure vessel according to claim 1, wherein said second step comprises moving said nozzle while ejecting said water jet from said nozzle such that said water jet impinges toward a second region different from said first region of members in reactor pressure vessel. 3. A residual stress improving method for members in reactor pressure vessel according to claim 1, wherein said second step comprises stopping the ejection of said water jet from said nozzle. 4. A residual stress improving method for members in reactor pressure vessel according to claim 1, 2 or 3, wherein an initial ejection speed of said water jet from said nozzle is not less than 100 m/s, but not larger than 700 m/s. 5. A residual stress improving method for members in reactor pressure vessel according to claim 1, 2 or 3, wherein an initial ejection speed of said water jet from said nozzle is not less than 200 m/s, but not larger than 400 m/s. 6. A residual stress improving method for members in reactor pressure vessel according to claim 1, 2 or 3, wherein an initial ejection speed of said water jet from said nozzle is not less than 250 m/s, but not larger than 350 m/s. 7. A residual stress improving method for members in reactor pressure vessel according to claim 1, 2 or 3, wherein a source of said water jet is low temperature water obtained by cooling said reactor water and pumping the same under pressure. 8. A residual stress improving method for members in reactor pressure vessel according to claim 1, 2 or 3, wherein a source of said water jet is low temperature water prepared outside the reactor and pumped under pressure. 9. A residual stress improving method for members in reactor pressure vessel according to claim 1, 2 or 3, wherein a source of said water jet is low temperature pure water prepared outside the reactor plant and pumped under pressure. 10. A residual stress improving method for members in reactor pressure vessel according to claim 1, 2 or 3, wherein said water jet is high speed jet water including cavitation bubbles. 11. A residual stress improving method for members in reactor pressure vessel according to claim 1, 2 or 3, wherein said nozzle is a an elbow-shaped nozzle for ejecting said high speed submerged water jet at a predetermined angle with respect to the inflow direction of high pressure water supplied to said nozzle.