Patent Number: 052001393
Section: description

DETAILED DESCRIPTION As shown in FIG. 2, the present invention is applicable in general terms to a reactor comprising the following components: A core 2 containing fuel rods in which a nuclear reaction takes place, giving off nuclear power which is distributed between the top and the bottom of the core and which is transformed into heat. A heat exchange circuit 4, 6, 8 for causing a heat exchange fluid to enter the core via an inlet duct 4, to flow through the core under the action of a primary pump 8, and to leave the core via an outlet duct 6, thereby removing said heat. The circuit delivers the heat to an external heat receiver 10 having varying needs, and which is conventionally constituted by a steam generator 10 which transfers the power to a secondary circuit. Control clusters 12 driven by mechanisms 13 for penetrating on command into the core from the top in order to control the nuclear reaction therein. At least one power measurement system 14 for providing a total power signal DT representative of the nuclear power. This system takes the difference between the temperatures measured by two temperature detectors 20 and 30 disposed respectively on the inlet duct 4 and the outlet duct 6. A power difference measuring system 16 for providing a power difference signal DI representative of axial nuclear power difference between the top and the bottom of the core. This system has two inputs connected to neutron detectors 15 and 17 disposed respectively facing the top and the bottom of the core 2. A temperature measurement system 18 for providing an operating temperature signal representative of an operating temperature which is the temperature of said cooling fluid. This system takes the average of the temperatures measured by the detectors 20 and 22. In conventional manner, the system for controlling the reactor comprises: A power control system 24 acting on some of the control clusters 12 as a function, in particular, of the varying needs of the heat receiver 10, thereby ensuring that said receiver receives heat power which corresponds, at least approximately, to its needs. A reference temperature defining circuit which receives a power signal SP representative of the nuclear power and delivered by a detector 28, said circuit generating a temperature reference signal TR representative of a reference temperature which depends on the nuclear power and which is such that the reactor operates under optimum conditions when, for each value of nuclear power, the operating temperature is equal to the reference temperature. The temperature regulation system 30 which receives the operating temperature signal ST and the temperature reference signal TR and which acts on a temperature regulation group constituted by some of the control clusters 12, in a manner which is distinct from the power control system 24 and for the purpose of at least limiting the difference between the operating temperature and the reference temperature. According to the present invention, the apparatus further includes a temperature regulation inhibit system 36 which receives the total power signal DT and the power difference signal DI and which combines them to obtain a combination which defines a composite power based on these signals, the temperature regulation inhibit system inhibiting the temperature regulation system 30 whenever said composite power exceeds a predetermined inhibit threshold. This threshold B1 is symbolically supplied in FIG. 2 by a generator 38. The inhibit circuit preferably includes a multiplier 40 for multiplying at least one of the total power signal DT and the power difference signal DI by a positive coefficient B.sub.2 so as to obtain a positive linear combination of the coefficients DT+B.sub.2.DI. Filtering is preferably performed on at least one of these signals with composite power being defined after such filtering. The filtering is performed by circuits 32 and 34 having transfer functions of the type (1+T.sub.2 p)/(1+T.sub.1 p) for said power difference signal DI, and of the type 1/(1+T.sub.3 p) for said total power signal DT, where T.sub.1, T.sub.2, and T.sub.3 are time constants specific to the nuclear reactor being controlled, as are the coefficients such as B.sub.2 and the inhibit threshold B.sub.1. In FIG. 1, the nuclear power corresponding to the inhibit threshold is represented by a straight line having the equation: EQU DT=B.sub.1 -B.sub.2 .multidot.DI By implementing the present invention, the evolution of the above-mentioned cooling transient becomes as shown by the succession of segments C1 and C3. In a practical implementation of the invention, nuclear power is represented as mentioned above by the measured temperature difference DT between the hot outlet duct 6 and the cool inlet duct 4. An inhibit signal SB (see FIG. 2) is generated when this power, after filtering, exceeds a limit value defined on the basis of the signal DI as filtered at 32. This is defined as follows: EQU DT/(1+T.sub.3 p).gtoreq.DI.multidot.(B.sub.1 -B.sub.2).multidot.(1+T.sub.1 p)/(1+T.sub.2 p) Where the fractions involving T.sub.x p designate transfer functions representative of the effects of the filter circuits 34 and 32, respectively. The advance/retard filter 32 may anticipate the evolution of the signal DI. The filter 34 eliminates measurement noise from the signal DT. The reference values B.sub.1 and B.sub.2 and the time constants T.sub.1 to T.sub.3 need to be optimized as a function of the boiler in question and of its authorized operating domain. In general, this inhibit instruction is preferably designed so that even in the event of a single failure in any one of the parts of the apparatus, the inhibit instruction is nevertheless performed by virtue of a redundant system. Further, in order to avoid inhibition taking place when not necessary, an effective inhibit instruction is preferably a secondary instruction delivered at the output from a 2 out of n logic circuit where n is the number of parallel systems for generating primary inhibit signals. Initial simulations of the operation of the above-described apparatus in the event of cooling accidents has shown that protection is ensured in satisfactory manner. It enables non-negligible margins to be obtained relative to core safety criteria. These margins may be made use of in fuel management, thereby facilitating the definition of loading planes.