NDTsi 2001 Session: Structural Integrity and NDE I-II
In-Service Inspection Practice at Paks NPP
J. Pinczés, D. Szabó, G. Takács, J. Palásti, L. Sárközi, Paks NPP, Hungary
ABSTRACT
The Paks Nuclear Power Plant consists of four reactor units with 440 MW electric power each. The plant was designed in the former Soviet Union; the construction was started in 1974. The first unit of the Paks NPP was started up in 1982 and the unit-4 in 1987. The four pressurised water type reactors give nearly 50% of electric power generated in Hungary; consequently the plant plays significant role in Hungarian electricity production. The load factors of the units are remarkable on the world scale. Regarding the availability for the whole lifetime all units of Paks are among the top twenty-five. According to the Hungarian NPP Safety Rules, the primary loop components have to be inspected in 4-year intervals. For the performance of the in-service inspection program the Material Testing Section of the plant is responsible having qualified inspection personnel. During the outages this staff as well as other competent companies carry out the in-service inspections. Among the non-destructive testing methods used for in-service inspection the UT plays significant role. After detection of cracking in 1992 in primary collector flange at the surroundings of threaded hole N°17 of SG N°5 on Unit 3 first a comprehensive strength analysis has been performed. On the basis of this the Hungarian Atomic Energy Authority allowed a further limited operation with the degraded collector head. After 6 months operation with cracks, the flange has been changed. The cut flange has been examined by metallography. At this stage it was decided to improve the effectiveness of non-destructive examination by exchanging manual ultrasonic inspections for mechanised examinations using advanced UT technique. Up to the present time all 48 SG collectors at least two times have already been inspected. From 1995 the primary collector welds are also inspected in 12-year interval with the same UT equipment. The RPV mechanised UT inspection performed from both sides. The owner uses every effort to improve the OD inspection system for all critical area. The first Mechanised UT inspection on the primary circuit tube-system is performed in 2001. Practical result shows that using the large Phased Array Probes Park, which was established at Paks in the last years, the inspections can be performed. The planned live time extension program ad to the importance of Mechanised In-service Inspections.
Publication Source: 3nd International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurized Components, November 14-16, 2001, Seville Spain. Publisher: Tecnatom s.a. - [Homepage]
