Monitoring acoustic emission at in-service hydrotest in nuclear power plant Paks

Acoustic emission offers potential for nondestructive testing of nuclear power plant components and systems, particularly in monitoring crack growth in the reactor pressure vessel. The most important centre of acoustic emission research and instrument development in Hungary is the Central Research Institute for Physics, where activities are more and more focused on applications in the Paks nuclear power plant (PWR 4x440 MW). The hydrotests of the reactor pressure vessels of units 1 and 2 of the Paks plant were two main steps in this program. The research program was commenced by extensive studies of reactor steels and small size test vessels with respect to the relation of fracture mechanics behavior to acoustic emission phenomena. Acoustic emission was interpreted as the result of the growth of the plastic zone at the crack tip. These studies were followed by acoustic emission experiments of the first in-service hydrotest in Paks on the reactor vessel of the first unit in 1987, after a period of 4 years of service. This experiment was performed in the region of the nozzles. 12 sensors were used. During the second hydrotest (in 1988, unit 2 of NPP Paks) acoustic emission sensors were installed in three regions of the vessel: 12 in the zone of nozzles, 3 on the primary tubes, 8 on one of the welding regions. Remote-controlled manipulators were employed for installing some of them. Measurements were carried out using multichannel acoustic emission systems (Defectophone NEZ-220), developed and manufactured by the Central Research Institute for Physics. No active defect was detected. (author). 8 figs., 3 refs