Control method for a pressurized water nuclear reactor

Abstract

This invention relates to a control method for a pressurized water nuclear reactor, which comprises a core generating thermal power and means of acquiring magnitudes representative of core operating conditions. The method comprises a step to regulate the temperature of the primary coolant, if the temperature of the primary coolant for a given thermal power is outside a predefined set temperature interval (TREF) depending on the reactor power. The set temperature interval (TREF) is characterized by variable amplitude (T) on a thermal power range between N % and 100% nominal power, where N is between 0 and 100 and comprises a zero amplitude at 100% nominal power, a zero amplitude at N % nominal power.

Claims

1. A method of controlling a pressurized water nuclear reactor, said reactor comprising a core generating thermal power cooled by a primary coolant and instrumentation lines for measurement of representative data of a thermal power and for measurement of a temperature of the primary coolant; said method comprising: acquiring data corresponding to at least a thermal power and a temperature of the primary coolant of the core operating conditions via the instrumentation lines, and adjusting the temperature of the primary coolant responsive to the temperature of the primary coolant, for a given thermal power, being outside a predefined set temperature interval (TREF) which is based on the thermal power, wherein said set temperature interval (TREF) comprises: a variable temperature amplitude (T) within a thermal power range between N % and 100% of a nominal power, where N is between 0 and 100, inclusive of 0 and exclusive of 100; a zero amplitude at 100% nominal power; a zero amplitude at N % of the nominal power.

2. The method of controlling a pressurized water nuclear reactor according to claim 1, wherein the set temperature interval (TREF) has a maximum temperature amplitude (T) for a thermal power or range of thermal powers on which frequency regulation is done for a nuclear reactor.

3. The method of controlling a pressurized water nuclear reactor according to claim 1, wherein the temperature amplitude (T) of said interval (TREF) is maximum between 40% and 80% of the nominal power.

4. The method of controlling a pressurized water nuclear reactor according to claim 2, wherein the temperature amplitude (T) of said interval (TREF) is maximum between 80% and 100% exclusive of the nominal power.

5. The method of controlling a pressurized water nuclear reactor according to claim 1, wherein said set temperature interval (TREF) lies within a zone (ZH) in which the lower limit corresponds to the set temperature at 0% nominal power (TREFMIN) and the upper limit corresponds to the set temperature at 100% nominal power (TREFMAX).

6. The method of controlling a pressurized water nuclear reactor according to claim 1 further comprising adjusting at least one other core operating condition selected from the group consisting of an axial power distribution (AO) and a capacity for instantaneous return to power (Pmax), when the primary coolant temperature is within the set temperature interval (TREF).

7. The method of controlling a pressurized water nuclear reactor according to claim 1, wherein said temperature interval (TREF) has a variable amplitude (T) at least over a thermal power range of between 50% and 100% nominal power.

8. The method of controlling a pressurized water nuclear reactor according to claim 1, wherein said set temperature interval (TREF) is surrounded by a dead band (BM).

Description

(1) Other characteristics and advantages of the invention will become clear after reading the description given below for guidance and in no way imitative, with reference to the appended drawings among which:

(2) FIG. 1, already described, shows a set temperature profile for the primary coolant as a function of the thermal power of a pressurised water nuclear reactor;

(3) FIG. 2, already described, shows a programmed variation profile of the reference temperature during load following of a pressurised water nuclear reactor;

(4) FIG. 3 shows a first example of a variable amplitude set temperature range as a function of the thermal power according to the invention;

(5) FIG. 4 shows a second example of a variable amplitude set temperature range as a function of the thermal power according to the invention;

(6) FIG. 5a is a graph showing an example variation of the nominal reactor power as a function of time during operation in frequency regulation;

(7) FIG. 5b is a graph showing temperature variations as a function of time obtained by use of the control method according to the invention, during operating in frequency regulation shown in FIG. 5a, in comparison with temperature variations as a function of time obtained by use of the control method according to the state of the art;

(8) FIG. 5c is a graph showing variations of the position of a group of control clusters obtained by use of the control method according to the invention during operation in frequency regulation shown in FIG. 5a, in comparison with variations in the position of a group of control clusters obtained by the use of a control method according to the state of the art;

(9) FIG. 6a is a graph showing an example variation of the nominal reactor power as a function of time during load following;

(10) FIG. 6b is a graph showing the variation of the Xenon effect during load following shown in FIG. 6a;

(11) FIG. 6c is a graph showing temperature variations as a function of time obtained by use of the method according to the invention during operation in load following shown in FIG. 6a, in comparison with temperature variations as a function of time obtained by use of a control method according to the state of the art;

(12) FIG. 6d is a graph showing variations in the boron concentration obtained by use of the method according to the invention during operation in load following shown in FIG. 6a, in comparison with variations in the boron concentration obtained by use of a control method according to the state of the art.

(13) FIG. 3 shows a first example embodiment of a set temperature range made on the temperature program of a nuclear reactor operating in load following. It is considered that load variations are most frequently made between 50% or 60% nominal power (PN) and 100% PN, therefore this is the variation range in which the maximum gain should be made on control cluster displacements.

(14) At 0% PN and 100% PN, the set temperature is defined by a single value of the set temperature (i.e. by a zero temperature amplitude) rather than a set temperature range. Set temperature values TREF.sub.MIN at 0% PN and TREF.sub.MAX at 100% PN are conventionally defined so as to minimise any impacts on accident studies and taking account of the capability of producing a sufficient steam pressure for the turbine. In general, the set temperature values TREF.sub.MIN at 0% PN and TREF.sub.MAX at 100% PN according to the invention are identical to the set temperature values according to the state of the art for these same thermal power values.

(15) From 0% to 35% PN, the set temperature is conventionally made by a set temperature varying linearly as a function of the reactor power, a single value of the set temperature being associated with a given thermal power of the reactor.

(16) Between 35% and 100% nominal power (PN), the set temperature is defined by a temperature range 10 composed of a plurality of set temperature intervals TREF with variable amplitudes as a function of the thermal power, the temperature range 10 being delimited by a high threshold value T.sub.CMAX and a low threshold value T.sub.CMIN.

(17) Between 60% and 100% PN, the maximum limiting value of set temperature intervals TREF is constant and corresponds to the set temperature at 100% PN, namely T.sub.CMAX.

(18) Between 35% and 60% PN, the minimum limiting value of set temperature intervals TREF is constant and corresponds to the set temperature at 25%, namely T.sub.CMIN.

(19) The set temperature range 10 thus shown as an example allows a maximum temperature variation of the primary coolant at a thermal power of 60% PN. Thus, no temperature regulation actions are initiated as long as the temperature of the primary coolant is within the range (within a dead band .sub.BM around the set temperature interval TREF).

(20) Thus, the temperature range 10 shown in FIG. 3 minimises actions, for example such as displacements of control clusters, during operation of a nuclear reactor operating in load following and for which load variations due to frequency regulation (for example 5%) are usually made around 60% nominal power.

(21) FIG. 4 shows a second example embodiment of a set temperature range 20 made on the temperature program of a nuclear reactor operating in load following. This second set temperature range is defined to allow a maximum variation of the primary coolant temperature at 50% PN, a value at which frequency regulation is preferred. In the same way as for the first example described above, the set temperatures at 0% PN and at 100% PN is defined by a single set value TREF.sub.MIB (at 0% PN) and TREF.sub.MAX (at 100% PN) so as to minimise any impacts on accident studies and to take account of the steam pressure demanded by the turbine. Values of set temperatures TREF.sub.MIN at 0% PN and TREF.sub.MAX at 100% PN are identical to the set temperature values according to the state of the art for these same values of the thermal power, the variation of the set temperature TREF as a function of the thermal power according to the state of the art being shown as a dashed straight line reference TREF in FIG. 4 for comparison purposes.

(22) According to another embodiment (not shown), the temperature range may also include: a first part, for example between 0% and 35% nominal power, in which temperature intervals have a variable amplitude that increases as a function of the power, a second part, for example between 35% and 70% nominal power, in which temperature intervals have a constant non-zero maximum amplitude, and; a third part, for example between 70% and 100% nominal power, in which temperature intervals have a variable amplitude that decreases as a function of the power.

(23) This temperature range thus described is particularly suitable for nuclear reactors operating in load following with low load levels (between 35% and 70% PN) different from the level at which the frequency regulation is done.

(24) In parallel with this regulation to maintain the primary coolant temperature within a set temperature interval, the other core parameters, namely the axial power distribution (axial offset) and the capacity for instantaneous power buildup (P.sub.max) are always controlled in parallel, by varying the positions of the control clusters and the boron concentration of the primary coolant.

(25) FIGS. 5a, 5b and 5c show temperature variations of the reactor and the position of a group of control clusters resulting from use of the control method according to the invention during operation in frequency regulation shown particularly by the graph in FIG. 5a.

(26) FIG. 5b more particularly shows free temperature variations (curve T2) in the set temperature interval TREF delimited by threshold values T.sub.CMAX and T.sub.CMIN.

(27) For comparison, the graph also shows temperature variations (curve T1) resulting from a temperature regulation relative to a reference temperature TREF for the same operation in frequency regulation.

(28) Therefore free variation of the primary coolant temperature will compensate for power variations. Thus, the method according to the invention can eliminate the compensation of power variations by a very large number of movements of control clusters so as to keep the primary coolant temperature as close as possible to the reference set temperature TREF.

(29) FIG. 5c shows the gain in cluster movements obtained by use of the method according to the invention, for the example of operation in frequency regulation shown in FIG. 5a. Curve P1 shows cluster movements necessary to maintain the temperature of the primary coolant as close as possible to the reference set temperature TREF (application of a control according to the state of the art), and curve P2 shows cluster movements necessary to maintain the temperature of the primary coolant within the set temperature interval.

(30) Thus, the use of the set temperature range to regulate the temperature of the nuclear reactor during operation in frequency regulation can significantly reduce or even eliminate control cluster movements.

(31) The use of a temperature range according to the invention also has the advantage that it reduces effluent volumes during operation of the nuclear reactor in load following.

(32) Thus, during operation in load following as shown as an example by the graph in FIG. 6a, free variation of temperature within the set interval makes it possible to correct the effects of reactivity by taking account of the Xenon effect (shown by the graph in FIG. 6b) to reduce the number of steps of control cluster control mechanisms (not shown) and reduce the volumes of effluents (shown in FIG. 6d).

(33) To achieve this, FIG. 6c shows temperature variations during load following shown in FIG. 6a and FIG. 6d shows variations in the boron concentration during this same load following.

(34) The graph shown in FIG. 6c more particularly shows free temperature variations (curve T2) within the set temperature interval TREF delimited by threshold values T.sub.CMAX and T.sub.CMIN resulting from use of the control method according to the invention. For comparison, the graph also shows temperature variations (curve T1) resulting from a temperature regulation relative to a reference temperature TREF resulting from use of a control method according to the state of the art.

(35) The graph shown in FIG. 6d more particularly shows the variations in the boron concentration (curve C2) during load following resulting from use of the control method according to the invention. For comparison, the graph also shows variations in the boron concentration (curve C1) during the same load following resulting from the use of a control method according to the state of the art.

(36) As shown in FIG. 6d, the free temperature variation within the set temperature interval can retard the beginning of dilution (curve C2). When the temperature reaches a threshold value of the set temperature interval (T.sub.CMIN at time t3), regulation is necessary to keep the temperature within the set temperature interval TREF (from time t3 to time t4). Therefore this regulation is made by dilution starting from t3. At time t4, the reactor temperature returns within the set temperature interval TREF and dilution is stopped. Starting from time t5, boration is applied to compensate for the temperature that reaches the threshold value T.sub.CMAX and it is continued starting from t6 so as to compensate for the reduction in Xenon that can be seen on the curve in FIG. 6b.

(37) Thus, FIG. 6d shows the reduction in effluent volumes generated during a load following as an example (curve C2) compared with volumes of effluents generated by use of a control method according to the state of the art (curve C1).

(38) The invention has been described particularly for application with control mode T; however, the invention is also applicable to all control modes known to those skilled in the art and not only to the control modes mentioned in this application.