Patent Grant
8654916
The invention relates in general to the methods applicable for controlling nuclear reactors.
More specifically, the invention relates to a method for regulation of operational parameters of the core of a pressurised water nuclear reactor, this nuclear reactor comprising:
A method is known from document FR-2 493 582 wherein the temperature of the primary fluid is regulated automatically by displacement of the groups of control rods according to the power required from the turbine, the current temperature value and a reference temperature. The axial distribution of thermal power (and neutron flux distribution) is regulated automatically by displacing certain groups, selected in an appropriate manner. Finally, the parameter which is representative of the capacity to increase the power of the reactor is controlled by an operator, by adjusting the concentration of boron in the primary fluid by injection either of pure water, or of a concentrated boron solution.
According to this method, a group must be kept inserted permanently in the low part of the core, in order to be able to assure control of the axial distribution of power. This constraint is impossible to meet when the reactor is operating with high power, since all the groups of control rods are then situated in the high part of the core. In this case, the operators must inhibit the automatic regulation of the temperature and of the axial distribution of power in accordance with the above-described method, and must change it over to another operating mode which permits only automatic regulation of the temperature.
This changeover requires stabilisation of the nuclear reactor: the above-described method for regulation of the core therefore does not make it possible to vary the power of the turbine automatically when the sets are situated in the zone of changeover between the two regulation modes. Operation of the reactor “with frequency regulation” is not possible in this zone, since this functioning consists of modulating the power of the turbine in order to maintain the frequency of the electrical network which is supplied by the reactor at 50 Hertz.
In this context, the object of the invention is to propose a method for regulation of the core of a nuclear reactor which makes it possible to carry out efficient automatic control of the three aforementioned operational parameters (temperature of the primary fluid, axial distribution of power, capacity to increase the power) over a greater range of operating power of the reactor.
For this purpose, the invention relates to a method for regulation of the operational parameters of the core of a pressurised water nuclear reactor, wherein it comprises:
The method can also have one or more of the following characteristics, considered individually or according to all the combinations technically possible:
Other characteristics and advantages of the invention will become apparent from the description which is provided of it hereinafter by way of indication which is in no way limiting, with reference to the attached figures, in which:
The method which is shown schematically in
This reactor 8 is shown symbolically in
The core 10 produces variable thermal power. It is divided into a high zone and a low zone.
The primary circuit 30 can assure circulation through the core 10 of a primary cooling fluid, comprising substantially water and dissolved boron, this liquid heating up in contact with the nuclear fuel assemblies, then yielding its heat by passing into the steam generator. The secondary circuit can assure the circulation of a secondary cooling fluid, comprising substantially water, this fluid being vaporised in the steam generator by the heat yielded by the primary fluid. The steam drives the turbine, and is then re-condensed and returned to the steam generator.
The generator provides the network with electric power which is variable according to the demand from the network. The reactor is controlled such as to adapt the thermal power supplied by the core continually to the electric power demanded by the network, by varying the reactivity within the core of the reactor.
For this purpose, the reactor is equipped with the following means:
The boron in solution in the primary fluid absorbs the neutrons emitted by the nuclear fuel assemblies, such that the reactivity of the core 10 decreases when the concentration of boron increases.
In a pressurised water nuclear reactor, the nuclear fuel assemblies each comprise a bundle of tubes with long lengths containing pellets of fissile material, known as fuel rods. These fuel rods are disposed vertically, parallel to one another, and are assembled by bracing grids. In certain assemblies a plurality of fuel rods is replaced by hollow tubes known as guide tubes.
The control rods each comprise a bundle of tubes containing a material which absorbs the neutrons. These tubes have the same length as the fuel assemblies. They are connected to one another such as to constitute a cluster which is mobile in a single piece in a vertical direction. Each cluster can be inserted in the guide tubes of a fuel assembly, such that the tubes made of material which absorbs the neutrons are interposed in the network of fuel rods containing the fuel pellets. The reactivity of the core decreases when a control rod is inserted. The lower the control rod, i.e. the further it is from its high position, the lower the reactivity of the core is.
The values which are representative of the thermal powers produced in the high and low parts of the core are the neutron fluxes FH and FB in the high and low parts of the core, which are measured by means of sensors disposed at different heights in the core.
The regulation method shown in
The parameters which are regulated comprise at least the mean temperature of the primary cooling fluid in the core Tmoy, the axial distribution of thermal power between the high and low zones of the core AO, and a parameter {circumflex over (P)} max which is representative of the capacity to increase the power of the reactor Pmax.
The concentration of boron in the primary fluid and the positions of the groups of rods P1 to P5 are modified automatically in order to regulate the operational parameters, without intervention by the operators, or with very limited interventions by the operators, for example in order to modify the control set points, or to validate the commands for displacement of the groups of rods or for modification of the concentration of boron planned according to the regulation method.
The capacity to increase the power Pmax corresponds to the thermal power which can be produced by the core when the groups of rods P1 to P5 are raised rapidly to the top of the core, in the vicinity of their high position.
The axial distribution of power AO is expressed by means of the following ratio:
AO=(FH−FB)/(FH+FB) (1)
wherein FH and FB are the neutron fluxes respectively in the high and low parts of the core.
The temperature Tmoy is expressed by means of the following ratio:
Tmoy=(TBC+TBF)/2 (2)
The set points for controlling of the core comprise a value Pc which is representative of the secondary power to be supplied by the turbine, a set point for the capacity to increase the power of the reactor Pmaxc, and a set point for axial distribution of thermal power between the high and low zones of the core AOc. The value which is representative of the secondary power Pc is for example a thermal power measurement supplied by the secondary circuit of the reactor. As a variant, the set point used can be a set point for the electrical power supplied by the generator to the network.
As shown in
These different steps are shown in a detailed manner in
The first step 1 comprises the sub-steps 11 to 13 illustrated in
In the sub-step 11, the mean temperature set point for the primary cooling fluid in the core Tmoyc is calculated according to the power set point Pc determined by the operator. For this purpose, use is made for example of a predetermined curve which provides the value Tmoyc directly according to Pc.
In the sub-step 12, the groups of rods P1 to P5 are distributed in a sub-set Pi for control of the mean temperature of the primary cooling fluid in the core Tmoy and a heavy sub-set H which is inserted to a slight extent, thus assuring substantially the control of the axial distribution of power AO.
As shown by
When the reactor is close to its nominal power, the control sub-set Pi contains only one group (group P1 in
On the other hand, when the power of the reactor is low, the control sub-assembly Pi contains a plurality of groups (3 groups in
Hereinafter in the text, Zi will designate collectively the positions Z1, Z2, etc of the different groups of the sub-set Pi, and Zh will designate the unique position of the groups of the heavy sub-set H.
The set point {circumflex over (P)} maxc of the parameter {circumflex over (P)} max which represents the capacity to increase the power Pmax of the reactor is calculated in the sub-step 13.
The parameter {circumflex over (P)} max corresponds to the vector which has as co-ordinates the positions of insertion Zi of the groups of rods of the sub-set Pi. It is determined by calculation software, on the basis of Pmax and the actual primary power Ppe. The actual primary power Ppe is estimated by means of the following formula:
Ppe=C·Q·(TBC−TBF) (3)
C being the calorific capacity of the primary fluid.
The software estimates the variation of the primary power which can be obtained by sequential displacement of the groups of the sub-set Pi upwards or downwards, on the basis of the actual situation of the core (actual concentration of boron in the primary fluid, actual position of the groups), according to the sequential insertion procedure described hereinafter. When the actual primary power Ppe and the curve of variation of the primary power according to the positions Zi are known, it is possible to associate a position vector Zi with a value for capacity to increase the power Pmax.
The set point {circumflex over (P)} maxc thus corresponds to a set point Zic for the positions of insertion of the groups of rods of the sub-set Pi. The values Zic are theoretical positions of the groups of rods of the sub-set Pi which make it possible to obtain both actual primary power equal to Ppe and a capacity to increase the power of the reactor which is equal to the set point Pmaxc.
The sequential insertion procedure for the groups of the sub-set Pi is described hereinafter.
As shown in
In the second step 2, the neutron fluxes FH and FB in the high and low parts of the core, the temperatures TBC and TBF of the primary cooling fluid in the hot and cold branches of the primary circuit and the flow Q of primary fluid in the primary circuit are acquired. These values are measured by means of the measuring systems of the reactor, or are picked in the system for operating the reactor.
In the third step 3, the actual values Tmoye, AOe, {circumflex over (P)} maxe of the operational parameters Tmoy, AO and {circumflex over (P)} max are evaluated. The actual value of the axial distribution of power AOe is calculated by means of the above formula (1), according to the values of the neutron fluxes FH and FB acquired in the second step. The actual value Tmoye of the temperature Tmoy is calculated by means of the above formula (2), according to the temperature values TBC and TBF acquired in the second step. The actual value {circumflex over (P)} maxe of the parameter representative of Pmax is calculated on the basis of the actual positions of insertion Zie of the groups of rods of the control sub-set Pi and of the actual primary power Ppe. These positions Zie are picked for example in the computer which controls the means for insertion of the groups of rods. The power Ppe is calculated by means of the above formula (3), in accordance with the temperature values TBF and TBC and with the primary flow value Q acquired in the second step.
In the fourth step 4, the first control law is selected when at least one group of rods is in an insertion position lower than a predetermined position Zref, and the second control law is selected in the opposite case.
The second law is thus used in particular when all the groups P1 to P5 are in the high part of the reactor, i.e. when the reactor is operating at power close to the nominal power.
The first control law is used when at least one of the groups is in the low part of the reactor, i.e. when the reactor is operatin at power which is for example less than 90% of the nominal power, or during operating with partial power with the groups of rods in the high part of the core.
The step for regulation 5 of the method when the first control law is used is broken down in the left-hand part of
The step for regulation 5 by means of the first control law comprises a module 51 for regulation of the temperature Tmoy, a module 52 for regulation of the axial distribution of power AO, and a module 53 for regulation of the capacity to increase the power Pmax.
The module 51 for regulation of Tmoy is broken down into:
The module 52 for regulation of the distribution of power AO is broken down into:
As previously described, the difference between the actual value Tmoye and the set point Tmoyc for the mean temperature of the cooling fluid is used in the calculation of the displacements of the sub-sets Pi and H.
In addition, the control sub-et Pi and the heavy sub-set H are preferably displaced in opposite directions in order to regulate the axial distribution of thermal power AO, so as not to disrupt the temperature of the primary fluid Tmoy. This is true in particular when Tmoy is in a dead band around its set point Tmoyc.
The grey area represents the field in which AO and Tmoy are each in a dead band around their respective set points, and in this case the modules for regulation of the temperature Tmoy and for the distribution of power AO do not include any action on the control groups.
It can be seen that, when AO is in its dead band and Tmoy is out of its band, the control sub-set Pi is displaced by the module for regulation of Tmoy in a direction which makes it possible to bring Tmoy into the dead band.
Conversely, when Tmoy is in its dead band and AO is out of its band, the module for regulation of the distribution of power commands the displacement either of the sub-et Pi or of the heavy sub-set H, according to the sign of the temperature difference. For example, if ΔAO>L2 and ΔTmoy is positive, with ΔAO=AOe−AOc and ΔTmoy=Tmoye−Tmoyc, the sub-set H is displaced downwards. This has the effect of bringing the axial distribution of power towards the set point, and also of decreasing Tmoy, such that ΔTmoy becomes negative. The situation then arises in which ΔAO>L2 and ΔTmoy is negative. The module for regulation of the distribution of power then displaces the sub-set Pi upwards, as shown in
On the other hand, when AO and Tmoy are out of their respective dead bands at the same time, the control strategy for AO is different. The sub-set Pi is displaced according to the sign of the temperature difference ΔTmoy by the module for regulation of the temperature. The heavy sub-set H is displaced by the module for regulation of the distribution of power, such as to bring AO towards its set point, but this displacement is inhibited if it goes in the direction of increasing the deviation of Tmoy relative to the set point. Thus, when ΔAO>L2 and ΔTmoy<−L1, the sub-set Pi is displaced upwards in order to make Tmoy increase. The heavy sub-set H should be displaced downwards in order to bring AO towards its set point, but this displacement is inhibited, since it would lead to a decrease in Tmoy, and would therefore move the temperature away from its set point. The heavy sub-set H is therefore not displaced in this case. The displacement of the heavy sub-set H is also inhibited when ΔAO<−L2 and ΔTmoy>L1. On the other hand, the displacement of the heavy sub-set H is not inhibited in the other cases, i.e. when ΔAO<−L2 and ΔTmoy<−L1 (
The module 53 for regulation of the capacity to increase the power of the reactor Pmax is broken down into:
In fact, when {circumflex over (P)} max is lower than a dead band centred on the set point {circumflex over (P)} maxc (groups of the sub-set Pi not inserted far enough), the module for regulation of Pmax gives rise to dilution of the primary fluid by injection of water which does not contain boron. The concentration of boron decreases, which gives rise to an increase in the reactivity in the core, and therefore to an increase in the temperature of the primary fluid Tmoy. The module for control of Tmoy then displaces the control sub-set Pi downwards in order to decrease Tmoy, as previously explained, such that {circumflex over (P)} max, which corresponds to the vector of the insertion positions Zi, is brought into its dead band.
Conversely, when {circumflex over (P)} max is greater than its dead band (groups of the sub-set Pi inserted too far), the module for regulation of Pmax gives rise to injection of concentrated boron into the primary fluid. The reactivity of the core decreases, which gives rise to a decrease of Tmoy and causes displacement of the control sub-set Pi upwards by means of the module for control of Tmoy.
In a variant embodiment, in order to minimise the effluents, the module for regulation of Pmax 53 is partially or totally inhibited during power transient. Thus, in the embodiment in
At 100% of the nominal power (
When the reactor reaches 50% of the nominal power (
During the stage at 50% of the nominal power, xenon is produced inside the fuel rods which constitute the fuel assemblies under the effect of the nuclear reactions, which has the effect of decreasing the reactivity of the core and decreasing the temperature Tmoy. The module for control of Tmoy then gives rise to the displacement of the control sub-set Pi upwards, such as to counterbalance the effects of the xenon and to keep Tmoy constant. The thermal power produced by the core also remains constant. Thus, the raising of the sub-set Pi reduces Pmax, since it is no longer possible to revert to 100% of the nominal power by bringing the groups P1 and P2 up to the high position.
When the sub-set Pi reaches the position set point Zic corresponding to the set point {circumflex over (P)} maxc, the module for control of Pmax gives rise to dilution of the primary fluid such as to stop the raising of the sub-set Pi under the effect of the production of xenon (
The step of regulation 5 of the method when the second control law is used is broken down in the right-hand part of
As previously stated, the second law is used when all the groups P1 to P5 are in the high part of the reactor, i.e. when the reactor is functioning at a power level which is close to the nominal power or during functioning at partial power with the clusters extracted. Consequently, the control sub-set Pi contains only the group P1, and the heavy sub-set H comprises the four other groups. In this case {circumflex over (P)} max=Z1. In fact, the set point {circumflex over (P)} maxc is a position set point of P1, noted as Z1c in the following paragraphs. Similarly, the actual value {circumflex over (P)} maxe of the parameter {circumflex over (P)} max is in fact the actual position Z1e of the group P1.
As in the case of the first control law, the regulation step comprises a module 54 for regulation of the temperature Tmoy, a module 55 for regulation of the axial distribution of power AO, and a module 56 for regulation of the capacity to increase the power Pmax.
The module 54 for regulation of Tmoy comprises:
The group P1 is displaced as a priority in order to regulate Tmoy, within the limits of a dead band which is centred on the position set point Z1c. The heavy sub-set H is displaced when the group P1 reaches the limits of the dead band.
This control strategy is shown in
It can be read in the central band of the table that when P1 in is a dead band centred on the set point Z1c and ΔTmoy<−L1, the group P1 is displaced upwards. When ΔZ1 reaches L2, the heavy sub-set H is displaced upwards.
Similarly, when P1 is in the dead band which is centred on the set point Z1c and ΔTmoy>L1, the group P1 is displaced downwards. When ΔZ1 reaches −L2, the heavy sub-set H is displaced downwards.
The module 55 for regulation of the axial power distribution comprises:
More specifically, when AO is greater than the set point AOc, the module for regulation of AO commands dilution of the primary cooling fluid by injection of water which does not contain boron. This dilution has the effect of increasing the reactivity of the core, and thus the temperature Tmoy, which gives rise to the intervention of the module for control of Tmoy. The latter will then command the insertion of the group P1 and/or of the sub-set H, as previously described, which gives rise to decrease of the thermal power in the high part of the reactor, and thus to the decrease of AO.
Conversely, when AO is lower than the set point AOc, the module for regulation of AO commands injection of a concentrated boron solution in the primary fluid. This injection has the effect of decreasing the reactivity of the core and thus the temperature Tmoy, which gives rise to the withdrawal of the group P1 and/or of the sub-set H, by means of the module for control of Tmoy. The thermal power in the high part of the reactor increases, which gives rise to the increase of AO.
The module 56 for regulation of Pmax comprises:
The control of Tmoy by means of the second control law means that the group P1 remains in its dead band since, as previously described, H is displaced when P1 reaches the limit of its dead band. The regulation of Pmax is therefore only rarely required. This regulation is described hereinafter.
Thus, when the mean temperature Tmoy is in its dead band around its set point Tmoye, the control sub-set Pi and the heavy sub-set H are displaced in inverse directions in order to keep the control sub-set in its dead band around its position set point Zic.
It will be noted that the difference between the actual value Tmoye and the set point Tmoyc of the mean temperature is taken into account in the calculation of the displacements of the sub-sets Pi and H.
The method previously described makes it possible to control power transient. During a power transient, the power required from the turbine goes progressively from a value V1 to a value V2.
In the case when V1>V2, the thermal power discharged by the secondary circuit decreases, and, in a first stage, becomes less than the thermal power supplied by the core of the reactor. The temperature Tmoy of the primary fluid thus increases, which gives rise to the intervention of the module for control of Tmoy 51 or 54, depending on the circumstances. This module commands the displacement of the groups of control rods P1 to P5 downwards, which makes it possible to return Tmoy to its set point, whilst keeping the thermal power supplied by the core towards a level which is compatible with the power discharged by the secondary circuit.
The fact of implementing two control laws which are different from one another makes it possible to carry out efficient and fully automatic control of three operational parameters of the reactor (primary fluid temperature Tmoy, axial distribution of thermal power AO, parameter {circumflex over (P)} max which is representative of the capacity to increase the power of the reactor Pmax), irrespective of the power set point, and in particular up to 100% of the nominal power of the reactor.
The fact of selecting the control law according to the position of the groups of control rods makes it possible to use two different laws, i.e. a first law which is adapted to the case in which at least one group is inserted in the low part of the core, and a second law which is adapted to the case in which all the groups are in the high part of the core.
The particular embodiment previously described also has other advantages which will now be described. However, it will be noted that the associated characteristics are optional.
In the two laws, the control of Tmoy is obtained by distributing the control groups into a control sub-set and a heavy sub-set, the groups of the control sub-set being inserted sequentially for the purpose of controlling Tmoy.
Also in the two laws, the set point for Pmax is translated into a position set point Zic for the control sub-set Pi, which permits automatic controlling of this parameter.
In the first law, the axial distribution of power AO is regulated to its set point by displacing the groups of rods P1 to P5. When the temperature Tmoy is in a dead band around its set point Tmoye, the sub-sets Pi and H are displaced in inverse directions. In addition, the parameter {circumflex over (P)} max which is representative of the capacity to increase the power of the reactor Pmax is regulated to its set point {circumflex over (P)} maxc by adjusting the concentration of boron in the primary fluid. This method for controlling AO is efficient only if at least one group is inserted in the low part of the core.
Consequently, in the situation in which all the groups are in the high part of the core, i.e. when the second law is used, there is automatic inversion of the modes for controlling the axial distribution of power AO and the capacity to increase the power Pmax. AO is regulated to its set point by adjusting the concentration of boron. Pi normally remains in its dead band since the sub-set H is acted upon when Pi reaches the limit of its dead band. However, if Pi is outside its dead band, the parameter representative of the capacity to increase the power of the reactor is regulated to its set point by displacing the groups of rods P1 to P5. When the temperature Tmoy is in a dead band around its set point Tmoyc, the sub-sets Pi and H are displaced in inverse directions. The control of AO is thus efficient, even when the reactor is close to its nominal thermal power.
The control method makes it possible to make the reactor function with frequency regulation at high power, without placing excessive demands on the control groups P1 to P5 in the form of displacements which are too frequent.
It should be noted that the procedure for sequential insertion of the groups of the sub-set Pi, wherein a difference of a half-core is maintained between the positions of two groups inserted in succession, makes it possible to maintain at least one group in the low part of the core for a very wide range of power of the reactor.
The method has been described for a reactor, the control clusters of which are distributed into five groups P1 to P5, but it also applies to the control of a reactor, the control clusters of which are distributed in more or less than five groups.
Similarly, the second control law has been described in the case in which the control sub-set contained only a single group. However, the second control law could also apply to the case in which the control sub-set contains two groups or more.
The parameter {circumflex over (P)} max which is representative of the capacity to increase the power could take into account not only the positions of insertion Zi of the groups of the sub-set Pi, but also the position of insertion Zh of the heavy sub-set H, which would constitute an additional co-ordinate of the vector {circumflex over (P)} max. In this case, the set point {circumflex over (P)} maxc would be established in the sub-step 13, by “fixing” Zh in its actual position. The position set points Zic associated with the set point {circumflex over (P)}maxc would thus be dependent on the actual position Zh of the heavy sub-set H.
The method previously described is implemented by one or more computers which control automatic means for modification of the concentration of boron and for displacement of the groups of rods.
| Number | Date | Country | Kind |
|---|---|---|---|
| 06 04572 | May 2006 | FR | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4470949 | Deroubaix et al. | Sep 1984 | A |
| 4844856 | Cohen et al. | Jul 1989 | A |
| Number | Date | Country |
|---|---|---|
| 24 46 247 | Apr 1976 | DE |
| 0 128 834 | Dec 1984 | EP |
| 0 336 338 | Oct 1989 | EP |
| 2 493 582 | May 1982 | FR |
| 2 544 907 | Oct 1984 | FR |
| Number | Date | Country | |
|---|---|---|---|
| 20080069288 A1 | Mar 2008 | US |
