[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

[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] 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

[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

[en] Anticipated Transients Without Scram (ATWS) would occur on failure of all the control and shutdown assemblies to insert into the core following an automatic reactor trip. The major concern of the ATWS derives from consequences of the high primary system pressure which is the characteristic of the transients. According to section 2.4 of YVL guides which are Finnish regulations for safety of nuclear power plants (NPP), the acceptance criterion for the ATWS analysis is that the pressure of the protected item does not exceed a pressure limit that is 1.3 times the design pressure. The main purpose of this paper is to assess its impact on the APR1400 preliminarily, for Europe regulatory environments by applying European Utility Requirements (EUR) for Light Water Reactor Nuclear Power Plants

[en] This paper deals with the drop modelling of rod cluster control assembly(RCCA) and the prediction of drop time and impact velocity of RCCA at scram event. On the scram, RCCA, dropping into the guide thimble of fuel assembly by the gravity, is subject to retarding forces such as hydraulic resistance, mechanical friction and buoyancy. Considering these retarding forces RCCA dynamic equation is derived and computerized it to solve the equation in conjunction with fluid equation which is coupled with the motion of the RCCA. Because the equation is nonlinear, coupled with fluid equations, the program is written in FORTRAN using numerical method in order to calculate the drop distance and velocity with time increment. To verify the program, its results are compared with those of other fuel vendors. Predicting identical tendency as other fuel vendors and the deviation is insignificant in values this program is expected to be used for predicting the drop time and impact velocity of RCCA when the parameters affecting the control rod drop time and impact velocity changes are occurred

[en] The reactor protection system of a nuclear power plant must be periodically checked. The manual testing method used till recently by the French power plants required considerable time and personnel investments. An automatic testing system has been developed which does not show these disadvantages any more. It will be installed in all French 900 MW nuclear power plants. 6 figs

[en] Purpose: To shorten the time required for the reactor shutdown and improve the reliability and safety of gas cooled reactors. Constitution: A valve is engaged to close the falling port of a neutron absorber storing hopper. A bridge preventive member is attached at the lower end of the valve body. When an emergency actuation signal is issued from a reactor guard system, a drive motor is rotated to rise a connection plate and a connection rod by means of ball threads. Then, when the connection plate abuts against a limit switch, the drive motor rotates reversely to lower the connection plate, connection rod and the valve body. Then, when the connection plate abuts against a limit switch for actuation point, the drive motor rotates again. Such vertical reciprocation of the valve body and vertical reciprocation of the bridge preventive member accompanying therewith can prevent the bridging effect of the neutron absorbers to rapidly fall the absorbers. (Moriyama, K.)