Apparatus for ultrasonic inspection of reactor pressure vessel

A method for inspecting a weld zone of a control rod drive housing and an area in proximity to the weld zone in a reactor pressure vessel, said method comprising the steps of:

• mounting an ultrasonic probe onto a probe holding unit of an inspection apparatus for inspecting weld zones which comprises the probe holding unit for holding the probe such that an ultrasonic wave transmitting surface of the probe is kept in direct contact with or at a constant distance from an outer surface of the reactor pressure vessel, a pressing unit for pressing the probe holding unit parallel to a central axis of the control rod drive housing against the reactor pressure vessel, a rotator for rotating the probe holding unit and the pressing unit around the central axis of the control rod drive housing, an elevator for moving the probe, the probe holding unit, the pressing unit, and the rotator along the control rod drive housing up and down, a size of the ultrasonic wave transmitting surface of the probe being a value selected from 35 mm to 120 mm in order that an effective focus area, within a range of −6 dB from a maximum sound pressure height, reaches an area to be inspected ranging from 150 mm to 200 mm;
• setting a focus position of the probe;
• mounting the inspection apparatus to the control rod drive housing;
• pressing the probe against the reactor pressure vessel by raising the elevator so that the pressing unit is brought into the most contracted state;
• rotating the probe around the control rod drive housing by rotating the rotator;
• performing the inspection;
• lowering the probe to a lower portion of the reactor pressure vessel by lowering the elevator after completion of the inspection;
• and
• removing the inspection apparatus from the control rod drive housing.