Abstract: In this paper, as a fundamental study to evaluate fracture characteristics and material
degradation by corrosion, evaluated electrochemical corrosion and corrosion fatigue characteristics
of CF8A steel using as a material of the piping system in nuclear power plant. CF8A steel was
artificially degraded at 400°C for 3 months. The environmental test condition is 3.5wt.% NaCl
solution of room temperature. Corrosion rate of degraded CF8A steel in NaCl solution of room
temperature increases with concentration of NaCl solution increase. However, concentration of
NaCl solution will be more than 4.0wt.%, it shows decreasing tendency. Crack growth rates of
degraded and not-degraded CF8A steel in air condition do not show remarkable difference.
However, in 3.5wt.% NaCl solution, crack growth rates of them showed higher than ones in air.
Particularly, crack growth rate of degraded material remarkably increases compare to one of notdegraded
Abstract: It is known that fracture characteristics are changed due to the geometric configuration.
Also, it is known that toughness data obtained from the standard specimen test are conservative to
predict fracture behavior of the real piping. Thus fracture behavior by tests of pipes would to be
applied to the integrity evaluation for the piping system. However, fracture test with real pipe is not
only difficult to perform but also very expensive, and requires lots of experience. So an estimation
method of pipe’s fracture behavior is necessary to solve this problem. The objective of this thesis is to
propose a method to estimate the fracture behavior of a pipe from the result of the standard specimen
fracture test. For this, fracture tests for standard specimens and pipes are conducted. The resultant
load - load-line displacement record of the standard specimen was transformed to that of a pipe by
load separation method. To begin with, the load versus load-line displacement curve of a standard
specimen extracted from a pipe is normalized by a geometry function of the CT specimen. Then this
normalized curve was converted to pipe’s load versus displacement curve by a geometry function of
pipe. To verify the constraint factor and the geometric function of pipe, finite element analyses were
performed. To demonstrate the proposed method, experimental results of pipes are compared with
predicted results. Calculated results from CT specimens are similar to experimental results of pipes.
Therefore the transformability from a CT specimen to a pipe by load separation method is proved.
Consequently the applicability of the proposed method was proved.
Abstract: Various hold periods in a cyclic wave of fatigue load were introduced to investigate
loading frequency effects on crack growth behavior and microstructural damage. The crack growth
path and microstructural damage characteristics at 600°C in tempered martensitic 9Cr-2W (P92)
HAZ of welded steel were studied. Generally, low frequency effect with increasing hold periods
affects microstructural damage with microvoids/cavities nucleation due to the effect of creep. Results
showed that the fatigue crack growth behavior was sensitive to the loading frequency. As frequency
decreased, the fatigue crack growth rate increased and the crack path mode changed from
transgranular to intergranular in terms of microstructural damage. As the loading frequency
decreased, it was found that the microvoids /cavities and microcracks that formed along the prior
austenite grain boundaries ahead of the main crack contributed to the intergranular crack growth.
Abstract: 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.
Abstract: Pressure tubes are major component of nuclear reactor, but only selected samples are
periodically examined due to numerous numbers of tubes. Pressure tube material gradually pick up
deuterium, as such are susceptible to a crack initiation and propagation process called delayed hydride
cracking (DHC), which is the characteristic of pressure tube integrity evaluation. If cracks are not
detected, such a cracking mechanism could lead to unstable rupture of the pressure tube. Up to this
time, integrity evaluations are performed using conventional deterministic approaches. So it is
expected that the results obtained are too conservative to perform a rational evaluation of lifetime. In
this respect, a probabilistic safety assessment method is more appropriate for the assessment of
overall pressure tube safety. This paper describes failure probability estimation of the pressure tubes
using probabilistic fracture mechanics. Failure assessment diagram (FAD) of pressure tube material is
proposed and applied in the probabilistic analysis. In all the analyses, failure probabilities are
calculated using the Monte Carlo simulation. As a result of analysis, failure probabilities for various
conditions are calculated, and examined application of FAD and LBB concept.