Patent Number: 053176065
Section: summary

BACKGROUND OF THE INVENTION This invention relates to an automation system for nuclear power plants, and more particularly to an automation system for nuclear power plants, which is suitable for application to boiling water type nuclear power generation plants and which becomes effective when the plant condition deviates from the normal operation range. Starting of the nuclear power plant or adjusting the control rod pattern have been done according to an operation plan prepared beforehand. If the nuclear power generation plant is in the state as prearranged in the operation plan, there is no problem in operating the plant according to the operation plan. However, when the process quantities such as reactor power, core flow rate, neutron flux, core temperature, core performance which is a thermal characteristic of the reactor core or the operating condition of the equipment such as the pump and control rods differs from the plan, the operators of the plant usually make various decision-making operations. In the load follow-up operation of the boiling water reactor (BWR), a technique of preventing the core from deviating from the operational limit condition or a technique regarding the remedial actions for the deviation is disclosed in JP-A-57-189097 entitled "Operation Control System of Boiling Water Reactor." This Japanese patent publication describes with regard to the load follow-up operation (1) when a decision is made that data used for calculating the core performance (core flow rate, core pressure, core temperature, neutron flux, etc.) or the calculated values of core performance deviate from the operational limit condition, a method for avoiding the deviation from the operational limit condition is considered (the load follow-up plan is revised) and (2) when the above-mentioned plant data or the calculated values of core performance have deviated from the operational limit condition, the recirculation flow rate control system is blocked, and then, an operation plan to bring the above-mentioned data or the like back within the limit condition or an operation plan after the data has returned within the limit condition is prepared. Blocking the recirculation flow rate control system is meant here to maintain the current condition without changing the recirculation flow rate (more specifically, not to change the set value of the recirculation pump speed or the recirculation flow rate). SUMMARY OF THE INVENTION The object of this invention is to provide a nuclear power plant automation system for improving the operating rate of the nuclear power plant, lessening the burden on the operators and engineers in abnormal plant condition, and achieving the reduction of labor requirement. This invention comprises: operation plan making means for, after the nuclear power plant has been operated according to an operation plan under abnormal condition, making an operation plan to return to the normal operating condition, which had existed before the plant condition deviated from the normal operation range, from the condition that the operation according to the operation plan under abnormal condition has been finished; PA1 means for storing the operation plan under abnormal condition to decrease the reactor power to a power level within the normal operation range when the operating condition of the nuclear power plant deviates from the normal operation range; PA1 means for deciding from detected plant data whether or not to perform an operation according to the operation plan under abnormal condition; PA1 control and arithmetic means for outputting control commands according to the operation plan; PA1 means for transmitting the operation plan under abnormal condition to the control and arithmetic means when the decision means makes a decision to perform an operation according to the operation plan under abnormal condition; PA1 supervisory control means having the control and arithmetic means for outputting control commands according to the new operation plan mentioned above when the operation plan under abnormal condition has been executed; and PA1 control means for controlling automatically controlled object according to the control commands. To be more specific, in a start operation, stop operation, load follow-up operation, rated-power operation or control rod pattern adjusting operation, the supervisory control means has stored therein a plurality of operation plans under abnormal condition to decrease the reactor power to a power level within the normal operation range when the operating condition of the nuclear power plant deviates from the normal operation range, decides from detected plant data whether or not to apply the above-mentioned operation plan under abnormal condition, and when it has made a decision to perform an operation according to the operation plan under abnormal condition, controls the reactor operation to interrupt the increase in the reactor power or decrease the reactor power by the recirculation flow rate control means and/or control rod operation control means. An operation plan after the operation according to the above-mentioned operation plan under abnormal condition is prepared by an operation plan unit. Preferably, the operation plan under abnormal condition has a plurality of remedial actions to use according to the degree of deviation of the plant condition from the normal operation range, and includes an operation plan to interrupt the increase in the reactor power when the degree of the deviation of the plant condition from the normal operation range is small, and decreases the reactor power to automatically bring the reactor power back within the normal operation range when the above-mentioned degree becomes large. The operation plan under abnormal condition includes an automatic action for a violation of the operation range related to the reactor power and the core flow rate, an automatic action for abnormality in the reactor feed water system, an automatic action for abnormality in the thermal characteristic of the core, an automatic action for abnormality frequency increase of the power system, an automatic action for abnormal drop in the vacuum of the condenser, an automatic action for abnormality in the neutron flux, and an automatic action for abnormal change rate of the reactor temperature. Each of those automatic actions includes an action to interrupt the increase in the reactor power and/or an action to automatically decrease the reactor power by a predetermined value or to a predetermined level. In order to shorten the time for decision as to whether or not to apply an operation plan under abnormal operation, it is desirable to limit kinds of decision about application of an operation plan under abnormal condition according to the reactor conditions (operation modes, for example). Since the probability of operating the reactor according to an operation plan under abnormal condition is low, it is uneconomical to install one operation plan making means for each power generation plant. Therefore, an operation plan making means may be installed for a plurality of plants. This operation plan making means is capable of making operation plans of a plurality of plants as occasion demands. The operation plan making means should preferably receive a desired value of the reactor power or the generator power from the engineers, infers, by using knowledge engineering methods, manipulated variables (e.g., a core flow rate value, control rod pattern) for achieving a desirable reactor power or generator power according to knowledge about operation plan formulation, stored beforehand, evaluates the adequacy of an operation plan resulting from the inference by a simulator which simulates the reactor characteristics, and shows the evaluation result on the display unit. Incidentally, when making an operation plan, if one wishes to quantitatively decide values of the flow rate, for example, only by knowledge (rules), a huge number of items of knowledge will be required. In order to avoid this, the manipulated variables of the plant operation is inferred from knowledge about the formulation of operation plans and a simple simulator for simulating the outline of the reactor characteristics. Then, the adequacy of the operation plan is evaluated by a simulator (three-dimentional simulator, for example) capable of more detailed simulation of the reactor characteristics that the simple simulator mentioned above. Therefore, the aspects of this invention which differ greatly from the conventional technique are that when the plant condition deviates from the normal operation range, the plant condition are made to automatically return within the normal operation range by decreasing the reactor power by a predetermined range or to a predetermined level, that there are a plurality of remedial actions to apply according to the degree of deviation from the normal operation range, that not only the recirculation flow rate but also the control rods are operated automatically, and that an operation plan after an automatic action under abnormal condition is taken is an operation plan which starts within the normal operation range and does not include an operation plan to bring the plant out of the condition of disobeying some operational limit condition back within the limit condition. The conventional technique does not reveal how an operation plan is made, but in an embodiment of this invention, an operation plan is made by using methods of knowledge engineering and a simulator for simulating the reactor characteristics, which is operated when necessary. The supervisory control means has stored therein a normal operation plan corresponding to any one of the plant start operation, stop operation, load follow-up operation, rated power operation, control rod pattern adjusting operation. Therefore, the plant is operated according to this operation plan. The supervisory control means has stored therein a plurality of operation plans under abnormal condition, related to automatic actions under abnormal plant condition, to prevent a reactor scram by decreasing the reactor power to automatically return to the normal operation range when the plant condition deviates from the normal operation range, and decides whether or not to apply an operation plan under abnormal condition mentioned above according to data obtained by measurement of the plant. If the supervisory control means decides that an operation should be performed according to an operation under abnormal condition, the plant is controlled by switching from a normal operation plan to an operation plan under abnormal condition (for example, by switching a normal set value of the recirculation pump speed to a set value under abnormal plant condition). As a result, the plant condition automatically settles down to a desirable condition (i.e., within the normal operation range) that the reactor power is at a low level. When an operation was done according to an operation plan under abnormal condition mentioned above, the plant condition differs from that under normal plan, the operation plan making means prepares an operation plan to return to the operating condition in which it was (100% of the rated value of the reactor power). Consequently, an operation plan is produced to, for example, gradually increase the reactor power from a normal operation range to the rated value and keep the reactor power at this level. Then, to return to the previous normal operating condition (before the deviation from the normal operation range) after the plant was operated according to the operation plan under abnormal condition, the plant is controlled by switching from the operation plan under abnormal condition to the above-mentioned operation plan prepared by the operation plan making means (e.g., the pump speed is switched from a set value under abnormal condition to a set value under normal condition). Therefore, if the plant condition deviates from the normal operation range, the plant operating condition automatically and temporarily moves into a desirable condition (normal operation range) that sufficiently satisfies the operation standard by decreasing the reactor power, for example, and an operation plan for a subsequent rise in the reactor power can be prepared easily and efficiently, so that the operation can be resumed with ease. As a result, it is possible to improve the operating rate and the operation reliability by avoiding a scram of the reactor, and mitigate the burden on the operators and engineers and reduce the operational labor requirement by use of automatic actions which are taken when abnormality occurs in the plant and also by support of operation plans which are made by an operation plan unit. In other words, various abnormal conditions of the plant are dealt with automatically and the plant temporarily and automatically moves into a normal operation range, thus preventing a scram of the plant from occurring. In this respect, the operating rate and the operation reliability can be improved. In addition, after the plant is operated according to a plan under abnormal condition, an operation plan can be prepared efficiently which restores a desirable operating condition, so that the operating rate can be improved, the burden on the operators can be reduced and a reduction in labor can be achieved.