Shigeki Suzuki

The development of a diagnostic and monitoring system for vibrating pipe branches

Abstract This paper deals with a diagnostic and monitoring system for assessing the integrity of pipe branches, during the operation of the nuclear power plant. This system have been developed under the concept of “easy to use without any sophisticated analysis” and “portable”. The accuracy of the diagnosis is based on the model optimization subsystem, which automatically modifies the numerical vibration model so as to fit its natural frequency to the actual natural frequency. The information obtained by this system may be reflected to a maintenance program of the plant to assure more reliable operation of the plant.

Applicability of the Modified Rate Approach Method Under Various Conditions Simulating Actual Plant Conditions

The fatigue life in elevated temperature water is strongly affected by water chemistry, temperature and strain rate. The effects of these parameters on fatigue life reduction have been investigated experimentally. In transient condition in an actual plant, however, such parameters as temperature and strain rate are not constant. In order to evaluate fatigue damage in actual plant on the basis of experimental results under constant temperature and strain rate condition, the modified rate approach method was developed. As a part of the EFT (Environmental Fatigue Tests) project, the study was conducted in order to evaluate the applicability of the modified rate approach to the case where temperature and strain rate varied simultaneously. It was reported in the previous papers (1,2) that the accuracy of modified rate approach is about factor of 2. Various kinds of transient have to be taken into account of in actual plant fatigue evaluation, and stress cycle of several ranges of amplitude has to be considered in assessing damage from fatigue. Generally, cumulative usage factor is applied in this type of evaluation. In this study, in order to confirm applicability of modified rate approach method together with cumulative usage factor, tests were carried out by combining stress cycle blocks of different strain amplitude levels, in which temperature changes in response to strain change in a simulated PWR environment.Copyright

Fatigue Crack Growth Curve for Austenitic Stainless Steels in PWR Environment

Reference fatigue crack growth rate curves for austenitic stainless steels in pressurized water reactors (PWR) environments were prescribed in JSME S NA1-2004(1) in Japan. The reference fatigue crack growth curve in PWR environment had been determined as a function of stress intensity factor range, temperature, load rising time and stress ratio. In order to confirm the applicability of the reference fatigue crack growth rate curve under high stress ratio, low rising time and low stress intensity range, fatigue crack propagation tests of austenitic stainless steels 316, 316 weld metal, 304 and 304 weld metal were carried out. It is concluded that the reference fatigue crack growth curve in PWR environment is applicable to predict fatigue crack growth rate of this study test conditions.© 2006 ASME

Effect of Factors on Fatigue Life in PWR Water Environment

It is known that the fatigue life in elevated temperature water is substantially reduced compared with that in the air (1–4) . Although the key parameters that have an effect on fatigue lives are strain rate and temperature in PWR water environment, it is necessary to consider the other factors on fatigue life for accurate evaluation. The effects of many factors on fatigue life have been investigated experimentally in the EFT project of Japan Nuclear Energy Safety Organization (JNES). Many tests have been done for carbon, low alloy, stainless steel and nickel-based alloy, and the environmental fatigue life equation that evaluates quantitative factor influencing the fatigue life has been proposed. In this paper, in order to evaluate effects of material structure difference between base metal and weld metal, strain amplitude, strain rate, strain ratio, temperature, sulfur content in steel, aging, water flow rate and strain holding, fatigue tests were performed in simulated PWR water environment.Copyright