[en] Purpose: To improve the scram accuracy and realize the avoid of reactor scram upon earthquakes of small magnitude by considering vibration characteristics of earthquakes, and equipments and pipeways. Constitution: The scram conditions are determined not by the maximum acceleration values for nuclear reactor building floors as in the prior art but they are set to natural frequencies of main equipments. Further, frequency analysis for seismic waves is conducted currently upon occurrence of earthquakes and compared with scram setting values. If an acceleration value at a certain frequency exceeds a scram setting value, a scram signal is generated. According to the present invention, if earthquakes of any frequency component are inputted to nuclear power plant buildings, since scram values are set considering the vibration characteristics of each of equipments and pipeways, and the seismic waves are currently subjected to frequency analysis and monitored in comparison with the scram values safety countermeasure can be taken. (Kamimura, M.)

[en] Currently many systems used to safeguard processes in industry use a combination of hardware and software. Many of the analysis techniques applied in this field, however, quantify aspects of hardware only. This paper presents a technique that is used to quantify the safety of safeguarding systems as a whole, including hardware and software. The techniques used bases itself on a combination of simulation and fault injection techniques. This paper will present this new technique and will demonstrate that it is possible using this ''Random Intelligent Failure Injection Technique'' to analyze and optimize practical safeguarding systems

No abstract available

[en] The extensive use of judgement in risk studies creates several issues related to the perception of probabilities and the value of formal theories for uncertainty analysis. The direct assessment of probability distributions may lead to biased curves that do not represent the state of knowledge of the assessors. The use of formal methods and the calibration of the analysts help alleviate some of these biases. Case studies involving the assessment of probability distributions for human error rates and for failure rates of components exemplify the importance of the careful use of expert opinions in risk studies. (orig.)

[en] An emergency shutdown system for a liquid metal cooled reactor is presented. This is a device containing neutron absorbing balls. When the reactor is working normally, the balls are in high position in the column carried by the coolant. In the event of reduced flow, the balls drop to the lower part facing the reactor core and thereby reduce its reactivity

No abstract available

[en] It is estimated that the cumulative financial impact of reactor scrams on U.S. nuclear plants approaches one-half billion dollars per year. At the current scram rate in the U.S., the incremental affect on power generation costs is estimated to be almost 1 Mill/KWhr. These figures involve calculations which were reinforced by input from a simple questionnaire used to gather information about the financial impacts of reactor scrams. The financial impact of reactor scrams is expanding into new areas and involves both obvious and hidden elements. Some are felt immediately while others may not be felt for 20 years or more. In addition to the visible financial impacts, the organizational disruption resulting from a reactor scram is widespread

No abstract available

[en] The Westinghouse Owners Group is nearing completion of the first phase of its Trip Reduction and Assessment Programme (Trap). Trap has already not only analysed the root causes of automatic trips, but also pointed to ways in which they can be avoided. (author)

No abstract available