PSI - Issue 16

Peter Trampus / Procedia Structural Integrity 16 (2019) 161–168

166

Peter Trampus / Structural Integrity Procedia 00 (2019) 000 – 000

6

6. Life extension and NDE at Paks NPP, Hungary

Paks, Hungary’s sole NPP consisting of four Russian designed VVER-440 model 213 units, was commissioned in the 80s, and originally licensed for 30 years. VVER is a Russian designed PWR; 440 refers to the nominal electric capacity in MW; model 213 means that it is the second generation of the VVER-440s. In early years of this century the plant owner decided on the operational life extension of the units up to 50 years. The life extension’s cornerstones in association with NDE were the followings:

6.1. Introduction of new NDE acceptance standards

The Hungarian licensing legislation for the extended operating period shows a vast similarity to the US approach in NPP license renewal. To ensure the consistency with this approach as well as to strengthen a Europe wide acceptability of the life extension program, it was decided to adapt the ASME Inspection Code requirements. ISI in conformance with ASME requirements provided an opportunity to compare these activities with worldwide acceptable safety requirements. Also, it allowed to extend the former four-year inspection interval (for Class 1 components) up to a ten-year one, which contributed to a more cost-efficient operation. The Hungarian regulatory rules supported the adaptation of the ASME Inspection Code requirements. The term of adaptation refers to the ASME requirements fitted in a special situation because Paks NPP has not been constructed, commissioned and operated previously in line with the relevant ASME Code sections. This procedure was not unique in the world; however, it was far from being routine and could not be applied for each code criterion as well, Trampus and Babics (2016). One of the biggest differences between the Hungarian ISI/NDE rules and the ASME Inspection Code was in the conceptual difference of the acceptance standards. Evaluation of UT has formerly been based on the comparison between the amplitude and the amplitude given by an artificial reflector. The reference reflectors were usually Flat BottomHoles (FBHs). Thus, the acceptance level was characterized by an equivalent FBH diameter. A real acceptance level has to be formulated in the language of fracture mechanics (i.e. flaw size). This means that there was no fitness for-service type acceptance level in the former Hungarian ISI/NDE rule. The aforementioned are shown in Fig. 4.

Quality Control

Fitness-for-Service

Critical

LEVEL

Repair/replacement, or fracture mechanics analysis

Not-allowable

Acceptance level (fitness-for-service)

Allowable

Flaw size

+12 dB

sizing

Acceptance level (quality control)

100% DAC (SDH)

Indication size Recording

sizing

100% PRR (FBH)

Reference level (recording level)

20% DAC (SDH)

Evaluation based on flaw characteristics

Registration level

Former (Russian) approach

ASME approach

Fig. 4. Different evaluation concepts of the former Hungarian ISI/NDE rules and ASME Inspection Code.