While the demand on electric power is consistently increasing, public concerns and
regulations for the construction of new nuclear power plants are getting restrict, and also operating
nuclear power plants are gradually ageing. For this reason, the interest on lifetime extension for
operating nuclear power plants by applying lifetime management system is increasing. The 40-year
design life concept was originally introduced on the basis of economic and safety considerations. In
other words, it was not determined by technological evaluations. Also, the transient design data
which were applied for fatigue damage evaluation were overly conservative in comparison with
actual transient data. Therefore, the accumulation of fatigue damage may result in a big difference
between the actual data and the design data. The lifetime of nuclear power plants is mostly dependent
on the fatigue life of a reactor pressure vessel, and thus, the exact evaluation of fatigue life on a
reactor pressure vessel is a crucial factor in determining the extension of operating life. The purpose
of this paper is to introduce a real-time fatigue monitoring system for an operating reactor pressure
vessel which can be used for the lifetime extension. In order to satisfy the objectives, a web-based
transient acquisition system was developed, thereby, real-time thermal-hydraulic data were reserved
for 18 operating reactor pressure vessels. A series of finite element analyses was carried out to obtain
the stress data due to actual transient. The fatigue life evaluation has been performed based on the
stress analysis results and, finally, a web-based fatigue life evaluation system was introduced by
combining analysis results and on-line monitoring system. Comparison of the stress analysis results
between operating transients and design transients showed a considerable amount of benefits in terms
of fatigue life. Therefore, it is anticipated that the developed web-based system can be utilized as an
efficient tool for fatigue life estimation of reactor pressure vessel.
In general, the fatigue life of major nuclear components has been evaluated based on design
codes conservatively. However, sometimes, more exact fatigue life evaluation is required for
continued operation beyond the endorsed life. The purpose of this paper is to carry out 3-D stress and
fatigue analyses reflecting full geometry as well as actual operating data. The actual operating data
acquired through a monitoring system were filtered and assessed. Then, temperature and stress
transfer Green’s functions were developed and applied to critical locations of reactor pressure vessel.
The finite element analyses results for representative design transients were verified through
comparison to reference solution and showed that the conservatism of current 2-D evaluation.
Therefore, it is anticipated that the proposed scheme adopting Green’s function and real operating
histories can be utilized for remaining life time evaluation of major components.
Steam generators working in nuclear power plants convert water into steam from heat produced in the reactor core and each of them contains from 3,000 to 16,000 tubes. Since these tubes constitute one of primary barriers under radioactive and high pressure condition, the integrity should be maintained carefully during the operation. The objective of this research is to introduce an integrity evaluation system for steam generator tubes as a substitute of well-trained engineers or experts. For this purpose, a couplet examination has been carried out on the complicated evaluation procedure and an efficient system named as STiES was developed employing three representative integrity evaluation methods: fracture mechanics analysis (crack driving force diagram and J-integral/Tearing modulus method) and limit load method. Exemplary analyses for steam generator tubes with various types of flaws showed good applicability of the proposed integrity evaluation system. So, it is anticipated that the system can be used for the calculation of reference pressure to decide either the continued operation or repair until next outage.
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