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High-Temperature Ultrasound NDE Systems for Continuous Monitoring of Critical Points in Nuclear Power Plants Structures

Petar Mateljak ; INETEC - Institute for nuclear technology Ltd. Dolenica 28, 10250 Lučko, Croatia
Marko Budimir ; INETEC - Institute for nuclear technology Ltd. Dolenica 28, 10250 Lučko, Croatia
Mario Koštan ; Brunel Innovation Centre, Brunel University Granta Park, Great Abington, Cambridge CB21 6AL, United Kingdom
Abbas Mohimi ; Brunel Innovation Centre, Brunel University Granta Park, Great Abington, Cambridge CB21 6AL, United Kingdom

Sažetak

High temperature pipe cracks are the root of a steam power failure in the EU typically every 4
years, resulting in loss of human life, serious accidents and massive financial losses. According to
IAEA’s Reference Technology Database, such an event on a nuclear power plant has an average
cost of €120 million, including outage costs, emergency repair costs, insurance and legal costs.
Since only one growing crack is needed to cause a major failure, they have to be inspected and
monitored thoroughly.
Breakdowns at extreme conditions (e.g. 580°C, 400 bar) are a result of two major weld failure
modes: a) creep cracks near pipe welds; b) fatigue cracks on pipe welds. Current maintenance
practice is to proceed with repairs on a detected crack according to its severity. For cost reasons,
cracks that are not judged as severe enough will not be repaired. Crack severity judgement is based
on its probability to cause a failure and this probability is derived taking into account the crack size
and operational lifetime. More variables such as operating temperature and vibrations may rarely be
found in other studies. Recent data from fracture mechanics statistical studies shows this connection
between the size of a crack on a nuclear power plant pipe and its probability to lead to a failure.
To deal with the above problems two Structural Health Monitoring (SHM) systems have been
developed and they are presented in this work. These systems are able to achieve continuous
operation for an extended time period at operating temperatures of nuclear power plants. The
developed systems employ novel phased array (PA) ultrasonic and ultrasound guided wave (UGW)
probes able to withstand and continuously operate even up to 580 °C. The systems are designed to
be permanently mounted on superheated steam pipes, at locations of known defects and to
continuously monitor their size. However, this supposes that defects will have already been detected
by a traditional method during an outage. The PA transducers are placed according to the Time-of-
Flight Diffraction (TOFD) technique’s topology, thus creating a novel configuration, while the
UGW transducers are placed on a stainless steel ring in a circular array configuration. These
configurations can enable continuous tracking of cracks growth with high accuracy, enabling
maintenance crews to estimate the severity directly and not through statistics.

Ključne riječi

nuclear power plants; high temperature ultrasound; phased array; guided waves; signal analysis

Hrčak ID:

199624

URI

https://hrcak.srce.hr/199624

Datum izdavanja:

15.10.2017.

Posjeta: 642 *