Patent Number: 043080995
Section: summary

TECHNICAL FIELD This invention relates to nuclear reactor safety systems in general and in particular to such systems having digital computing modules which accept data in parallel for continuous and repetitive calculation of parallel functions indicative of percentage of reactor maximum power load. BACKGROUND ART Safety systems for nuclear reactors are known which implement digital computing modules as part of the reactor protection system. These modules implement standard digital techniques such as are used in computers. The essence of these techniques is the conversion of input signal to digital form, storage in memory, the use of a stored program to manipulate the stored data and the presentation of an output. All of these functions are essentially performed serially in the time domain by a single central computer. The disadvantage of such prior art systems is the length of time required to do the calculations in sequence and the complexity of a program that has to manipulate in serial fashion the individual measured parameters. The normal sequence involves the taking in of data parameters to perform series of calculations and at the end of the calculations to produce data which determines whether or not the reactor is in a safe operating posture. Another problem of such prior art devices comes from the nature of digital computers operating in this fashion causing data to lose identity except for address location. Hence the tracing of programs or the debugging of faults in the system becomes time consuming and difficult. The serial computer system in order to be continuously and exhaustively tested and retested to assure proper safety control require that each of the measured parameters affecting safety have every possible value or state relative to all the other parameters. For example, if possible reactor temperatures could have 4000 different possible values and pressure have 4000 different possible values between and liquid flow 4000 possible values the number of possible input states to the serial calculating machine would be 4000 to the third power. To exhaustively test this, even at the rate of one every tenth second, would require the order of hundreds of years. Thus, other means have been employed to assure that there are no flaws in programs for safety systems. This involves extensive review and checking by independent technical groups and regulatory authorities. SUMMARY OF THE INVENTION The present invention solves the problems associated with the prior art systems as well as others by providing a safety system for a nuclear reactor which uses a parallel combination of computing modules each of which receives data on a particular parameter and each of which produces functions which are added together. Each individual function of the parallel set is therefore composed of a combination of a single parameter and a set of constants. Each parameter is independently converted to a function of that parameter so that a check can be made between the parameter and the output using all possible states of that parameter. Using the previous example of each parameter having 4000 possible states, the number of possible combination states that have to be tested becomes not 4000 to the third power but 4000 plus 4000 plus 4000 or 12,000 possible states. At the rate of testing of one per tenth second, testing would take roughly 30 minutes. Thus, the system can be exhaustively tested with all possible values of the parameter being applied at the input and tested to determine that all functions of that parameter at an analog output are correct. This permits both input and output to be tested in analog form for each individual parameter. Another advantage of the present invention is the ease with which parameters may be changed or added by changing a set of constants going into the computing module performing the function calculation. With these changes function can be adjusted to any desired value. Thus, in view of the foregoing, it will be seen that one aspect of the present invention is to provide a safety system for a nuclear reactor which individually calculates functions of various parameters affecting the safety of the nuclear reactor to produce a safety control signal therefrom. Another aspect of the present invention is to provide a safety system for a nuclear reactor which can be exhaustively tested with all possible values of the parameters affecting the safety of the system. These and other aspects of the present invention will be more clearly understood after a review of the following description of the preferred embodiment when considered with the drawings.