Introduction to GO-FLOW Method and Comparison to RGGG Method Lab Seminar Dec. 13th, 2010 Seung Ki Shin

Korea Advanced Institute of Science and Technology Contents Introduction GO-FLOW Methodology Simple example Phased mission problem Comparison of GO-FLOW to RGGG Summary & Conclusions 1/15

Korea Advanced Institute of Science and Technology References T. Matsuoka, M. Kobayashi, “GO-FLOW: A new reliability analysis methodology”, Nuclear Science and Engineering, T. Matsuoka, “GO-FLOW methodology – Basic concept and integrated analysis framework for its applications, Nuclear Safety and Simulation, M. Yang, Z. Zhang, H. Yoshikawa, S. Yan, “Dynamic reliability analysis by GO-FLOW for ECCS systems of PWR nuclear power plant, Proceedings of the First International Symposium of Global COE Program, Kyoto, Japan, /15

Korea Advanced Institute of Science and Technology Introduction GO methodology is a success-oriented system analysis technique which was developed to be an alternative to fault tree analysis. It was originally developed to analyze the safety and reliability of nuclear weapons and missile systems. It has been modified and refined for nuclear systems. (EPRI NP-765, 1978) Disadvantages It finds out the time when a system changes state, but cannot treat a system that has multiple state changes. It cannot easily perform a time-dependent system analysis. Development of GO-FLOW was motivated by the disadvantages of GO methodology. (T. Matsuoka, 1988) The modeling method and calculation procedure are similar to those of the GO method. The meaning of the signal and the definitions of operators are essentially different. 3/15

Korea Advanced Institute of Science and Technology GO-FLOW Methodology 4/15 The GO-FLOW uses a set of standardized operators to describe the logic operation, interaction, and combination of physical equipment. They are numbered greater than 20 to avoid being confused with the operators in the GO method. The operators in the GO-FLOW chart are connected by signal lines, which identify the inputs and outputs to the operators. A finite number of discrete time points are required for expressing the system operation sequence. The time values do not necessarily represent real time but correspond to it and represent an ordering.

Korea Advanced Institute of Science and Technology GO-FLOW Methodology 5/15 Signal A signal represents some physical quantity or information. Fluid flow in a pipe, electric current in wire, pneumatic pressure, demand signal for operation, operating period, etc. It does not represent a “change of condition” or “occurrence”. A quantity called “intensity” is associated with a signal. In most cases, the intensity represents the probability of signal existence. If a signal is a subinput signal to the type-35, 37, or 38 operator, the intensity is used for representing a time interval between the successive time points. Time point If a system alters its state with time, it is necessary to introduce “time” to express the changes of system state. The smallest time point (1) is usually used to indicate a time before the system starts to operate. If the intensities of final signals are obtained at every time point, the time-dependent characteristic of a system will be obtained.

Korea Advanced Institute of Science and Technology GO-FLOW Methodology 6/15 Operators Three types of signals are connected to an operator. Main input signal (S), Subinput signal (P), Output signal (R) Each operator has a logic for combining the inputs properly and producing the output.

Korea Advanced Institute of Science and Technology GO-FLOW Methodology Summary of the functions of GO-FLOW Operators 7/15 P g = prob. for successful operationO(t) = prob. for valve in open state P p = prob. for premature operationT’ = time point immediately before the time point t P o = prob. for valve successfully openP c = prob. for valve successfully close

Korea Advanced Institute of Science and Technology GO-FLOW Methodology Simple example The system consists of a battery, two switches, and two lights. Initially, the battery is connected to the circuit, a little later S1 is actuated, and 10h later S2 is actuated. Our interest is the probability that at least one light comes on. 8/15

Korea Advanced Institute of Science and Technology GO-FLOW Methodology Six time points are declared. Calculation steps 9/15 Time pointSystem configuration 1Initial time 2Battery is connected 3Switch S1 is demanded to close 410h after time point 3 5Switch S2 is demanded to close 610h after time point 5 Light 1 Light 2 At least one light

Korea Advanced Institute of Science and Technology GO-FLOW Methodology Phased mission problem Emergency core cooling system (ECCS) of a BWR is considered. It consists of eight sub-systems. High pressure core spray (HPCS) system Low pressure core spray (LPCS) system Three low pressure core injection (LPCI) systems Automatic depressurization system (ADS) Two heat exchangers After a LOCA has occurred, three phases for the ECCS can be identified. Initial core cooling (0.0 ~ 0.5 h) Suppression pool cooling (0.5 ~ 36.5 h) Residual heat removal (36.5 ~ h) 10/15

Korea Advanced Institute of Science and Technology GO-FLOW Methodology 11/15

Korea Advanced Institute of Science and Technology Comparison of GO-FLOW to RGGG The RGGG (Reliability Graph with General Gates) method can be utilized in the analysis of the phased mission problems. Each phase needs each RGGG and each input data. 12/15

Korea Advanced Institute of Science and Technology Comparison of GO-FLOW to RGGG Comparison of the results 13/15 Time pointSystem configuration 1Initial time 2Battery is connected 3Switch S1 is demanded to close 410h after time point 3 5Switch S2 is demanded to close 610h after time point 5 Light 1 Light 2 At least one light Time point 2 Time point 3 Time point 6

Korea Advanced Institute of Science and Technology Comparison of GO-FLOW to RGGG In GO-FLOW method, time to failure of various components are independent. It is the major difference between the GO-FLOW and dynamic RGGG method. 14/15 Backup Battery Backup S1 S2 L1 L2 OR w Spare

Korea Advanced Institute of Science and Technology Summary & Conclusions GO-FLOW charts are constructed from engineering blueprints or flow diagrams. This makes it easy to validate and interpret the charts. Alterations and updates to a GO-FLOW chart are readily accomplished. Adding or deleting operators or altering the logical combinations of signal lines can be accommodated without extensive alterations to the basic chart structure. GO-FLOW models system functions and operational logic, so it contains all possible system operational states. The phased mission problem that the failures of components are interdependent could be analyzed by the integration of GO-FOW and dynamic RGGG. 15/15