LIGHT WATER NUCLEAR REACTOR (LWR), IN PARTICULAR PRESSURIZED WATER REACTOR (PWR) OR BOILING WATER REACTOR (BWR), WITH A HEAT SINK ON THE GROUND AND INCORPORATING AN AUTONOMOUS DECAY HEAT REMOVAL (DHR) SYSTEM

Abstract

An ORC engine and an additional water reservoir, separate from the pool, the energy stored in the pool being the heat source for the evaporator of the ORC, the additional water reservoir directly supplying the condenser of the ORC via a dedicated pump in order to constitute the heat sink for the condenser of the ORC.

Claims

1. A light water nuclear reactor (LWR), comprising: a reactor core; a cooling circuit comprising a heat exchange device connected in a closed loop to a take-off device for taking off steam from the primary or secondary circuit of the reactor and a first pump for supplying the take-off device of the primary or secondary circuit with water from the heat exchange device; a system for removing at least a part of the decay heat of the reactor core, the system comprising: a first water reservoir or pool, arranged below the steam generator, wherein the heat exchange device is immersed so that the water contained therein cools the steam coming from the take-off device; an organic Rankine cycle (ORC) engine comprising: an expander; a condenser, a second pump; an evaporator arranged in contact with the pool so that the latter constitutes the heat source of the ORC; a fluidic circuit wherein a working fluid flows in a closed loop, the fluidic circuit connecting the expander to the condenser the condenser to the second pump, the second pump to the evaporator, and the evaporator to the expander; a second water reservoir, separate from the pool, and a third pump connected to the second water reservoir and to the condenser of the ORC in order to supply the latter with water, as the heat sink of the ORC.

2. The water nuclear reactor according to claim 1, comprising a cooling circuit comprising a steam generator and a water condenser immersed in the pool and connected in a closed loop to the steam generator.

3. The water nuclear reactor according to claim 1, the device for withdrawing the decay heat present in the primary circuit being a liquid/liquid exchanger, and the heat exchange device being a water exchanger immersed in the pool, so that the water contained in the latter cools the water of the primary circuit flowing in the liquid/liquid exchanger.

4. The water nuclear reactor according to claim 1, comprising a cooling circuit comprising: a take-off of primary steam from the supply line to the turbine of the reactor; a water condenser immersed in the pool and connected in a closed loop to the steam take-off.

5. The water nuclear reactor according to claim 1, the device for removing the decay heat coming from the core of the reactor being a system for depressurizing the steam present in the containment building, and the heat exchange device being a water exchanger immersed in the pool or a direct take-off of the water of the pool on one hand, and on the other hand a containment wall condenser in direct contact with the steam present in the containment building of the reactor.

6. The nuclear reactor according to claim 1, the first water reservoir or pool being arranged on or in the ground.

7. The nuclear reactor according to claim 1, the second water reservoir being arranged on or in the ground.

8. The nuclear reactor according to claim 1, the evaporator being immersed in the pool or remote therefrom.

9. The nuclear reactor according to claim 8, the immersed evaporator being a tube exchanger.

10. The nuclear reactor according to claim 8, the immersed evaporator being a plate exchanger.

11. The nuclear reactor according to claim 1, furthermore comprising a refrigeration cycle comprising: a compressor; a condenser connected to the third pump in order to supply the latter with water; a pressure reduction member; an air evaporator, a fluidic circuit wherein a working fluid flows in a closed loop, the fluidic circuit connecting the compressor to the condenser, the condenser to the pressure reduction member, the pressure reduction member to the air evaporator, and the air evaporator to the compressor.

12. The nuclear reactor according to claim 11, the condenser of the refrigeration cycle being the condenser of the ORC.

13. The nuclear reactor according to claim 11, the working fluid of the refrigeration cycle being that of the ORC.

14. The nuclear reactor according to claim 11, the shaft of the ORC expander being coupled to the shaft of the compressor of the refrigeration cycle.

15. The nuclear reactor according to claim 1, comprising an injector arranged in a lower part of the system and connected to the third pump arranged in an upper part of the system, the injector being configured to prime the third pump.

16. The nuclear reactor according to claim 1, comprising batteries configured for the electrical start-up of the pumps, of the electrical components of the ORC and optionally of the refrigeration cycle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0137] FIG. 1 illustrates in the form of a curve the decrease as a function of time of the decay heat of a nuclear reactor according to the prior art, known by the designation VVER TOI.

[0138] FIG. 2 is a schematic view of a passive system for removing the decay heat of a nuclear reactor core of the PWR type according to the prior art.

[0139] FIG. 3 is a schematic view of a nuclear reactor of the PWR type with a water pool on the ground and a passive system and for removing the decay heat of a reactor core according to the prior art.

[0140] FIG. 4 is a schematic view of a nuclear reactor of the PWR type with a water pool on the ground and a passive system and for removing the decay heat of a reactor core according to the invention.

[0141] FIG. 5 is a schematic view illustrating one embodiment of the invention furthermore comprising a refrigeration cycle.

[0142] FIG. 6 is a T-s entropy diagram of the ORC and of the refrigeration cycle of a system such as according to FIG. 5.

[0143] FIG. 7 is a schematic view illustrating a first variant of a system according to the invention.

[0144] FIG. 8 is a view illustrating a second variant of a system according to the invention.

[0145] FIG. 9 is a schematic view illustrating another embodiment according to the invention with a system for depressurizing the steam present in the containment building of a BWR or PWR.

[0146] FIG. 10 is a schematic view illustrating a first variant of a heat exchange means according to the invention for a BWR or PWR.

[0147] FIG. 11 is a schematic view illustrating a first variant of a heat exchange means according to the invention for a BWR or PWR.

DETAILED DESCRIPTION

[0148] Throughout the present application, the terms “vertical”, “lower”, “upper”, “down”, “up”, “below” and “above” are to be understood by reference with respect to a water-filled cooling pool of a nuclear reactor, such as is in a horizontal operating configuration and arranged on the ground, that is to say buried or “above ground”, supported on the ground.

[0149] FIGS. 1 to 3 have already been described in detail in the preamble, and will therefore not be discussed below.

[0150] For the sake of clarity, a given element according to the invention and according to the prior art will be denoted by the same numerical reference in all of FIGS. 1 to 8.

[0151] It is to be pointed out that in FIGS. 4 to 8, which relate to the invention, only a part of the cooling system of a PWR nuclear reactor core is represented, namely the steam generator connected in a closed loop to an exchanger immersed in the cooling pool.

[0152] It is also to be pointed out that the dashed lines denote the electrical supply lines of the various electrical components, while the solid lines denote the fluidic lines.

[0153] FIG. 4 illustrates an autonomous system for removing at least a part at a time of the decay heat of a PWR according to the invention.

[0154] The system firstly comprises the cooling pool 5 arranged on the ground, a water condenser 4 immersed in the pool so that the water contained in the latter cools the steam coming from the secondary circuit of the reactor, and a first pump 30 for supplying the steam generator with water from the water condenser.

[0155] It also comprises an organic Rankine cycle (ORC) engine 6 comprising: [0156] an expander 60; [0157] a condenser 61, [0158] a second pump, referred to as the ORC pump, which is a working fluid pump 62; [0159] an evaporator 63 arranged relative to the pool 5 so that the latter constitutes the heat source of the ORC; [0160] a fluidic circuit 64 in which a working fluid flows in a closed loop.

[0161] As illustrated, according to the invention the fluidic circuit 64 connects the expander 60 to the condenser 61, the condenser 61 to the pump 62, the pump 62 to the evaporator 63, and the evaporator 63 to the expander 60.

[0162] A second water reservoir forming a general pool 7 contains all of the heat sink dedicated to cooling the reactor, and supplies the pool 5 which is dedicated to the operation of the ORC and contains the safety condenser 4 and the ORC evaporator 63.

[0163] The water coming from the pool 7 is used as a heat sink for the exchanger condenser 61.

[0164] The water coming from the pool 7 is heated slightly by the condenser 61 before being injected into the pool 5 by means of a third pump 8, which is a water pump. This pump 8 supplies a dedicated fluidic line 65 for overcoming the evaporation of the pool 5 receiving the reactor decay heat.

[0165] The expander 60 may typically be a turbine, or a pressure reducer with coils, screws, pistons, etc.

[0166] The condenser 61 is typically a plate condenser.

[0167] The pump 62 is typically a centrifugal pump or membrane pump, screw pump, etc.

[0168] The engine 6 may comprise a buffer tank 66, that is to say a reservoir of a quantity of working fluid which in particular allows adequate operation of the ORC in a variable regime. As illustrated in FIG. 4, this buffer tank 66 may be arranged upstream of the pump 62.

[0169] In the embodiment illustrated in FIG. 4, the evaporator 63 is a tube evaporator immersed vertically in the pool 5.

[0170] In the advantageous embodiment of FIG. 5, a refrigeration cycle 9 comprising the following is furthermore provided: [0171] a compressor 90; [0172] a condenser 61, which is that of the ORC, connected to the water pump 8 in order to supply it with water; [0173] a pressure reduction member 92; [0174] an air evaporator 93, [0175] a fluidic circuit 94 in which a working fluid flows in a closed loop.

[0176] The fluidic circuit 94 connects the compressor 90 to the condenser 61, the condenser 61 of the ORC to the pressure reduction member 92, the pressure reduction member to the air evaporator 93, and the air evaporator 93 to the compressor 90.

[0177] The pressure reduction member 92 may be a valve, preferably a turbine, an ejector, etc.

[0178] Like the ORC 6, the refrigeration cycle 9 may also comprise a buffer tank forming a reservoir of working fluid in this cycle.

[0179] Batteries 10 may be provided for the electrical start-up of the various pumps 30, 62, 8, of the electrical components of the ORC and optionally of the refrigeration cycle 9. More precisely, the batteries may be used firstly to supply the pump 30 of the cooling circuit, then secondly, when the water reservoir 5 is boiling, to allow start-up of the ORC, that is to say start-up of the pump 62 and of the filling pump 8.

[0180] An example of dimensioning, according to an accident situation in the case of a PWR with a power of 3200 MWth, is provided below.

[0181] The working fluid of the ORC is an organic fluid, the evaporation temperature of which is lower than that of the boiling water by about 100° C. at atmospheric pressure. In particular, Novec649, HFE7000, HFE7100, etc. may be mentioned. Numerous other organic fluids may be envisioned, such as alkanes, HFC, HFO, HFCO, HFE, as well as some other fluids (NH.sub.3, CO.sub.2) and all mixtures thereof.

[0182] The fluid used in the dimensioning simulation is HFE7100, and it is advantageously used both in the ORC 6 and in the refrigeration cycle 9.

[0183] In this example, sensors of temperature or water level of the pool 5 make it possible to detect the state of complete saturation of the pool 5 and the start of the loss of liquid level by boiling. The indicated value of 50 m.sup.3 corresponds to a typical delay of 5 minutes of operation of a condenser removing 60 MW from the SG. At that moment, the pump 8 injects a flow rate corresponding exactly, by dimensioning, to replacement of the water evaporated in the pool 5, i.e. the evaporation produced by the 60 MW exchanged.

[0184] The pump 30 is regulated in flow rate in order to produce the 60 MW of heat exchange of the condenser 4, and the pumps 8 and 30 are thus linked by the power transfer function of the condenser 4, given that the boiling of 1 kilogram of water of the pool 5 requires about 2.25 MW of thermal power delivered by the condenser 4.

[0185] The dimensioning relating to the pool 5 and the water reservoir 7 is summarized in Table 1 below.

TABLE-US-00001 TABLE 1 Dimension Value Total volume of the pool 5 .sup. 50 m.sup.3 Water reservoir 7 as a function of the maximum autonomy of autonomous operation of the reactor Height difference between 30 m the pool 5 and the steam generator 2

[0186] The information relating to the operating time of the pool is summarized in Table 2 below.

TABLE-US-00002 TABLE 2 Operation Duration (min) Pool 5 enters saturation T0 + 5 in a 60 MW condenser operating regime Start-up of the ORC T0 + 5 + a few seconds

[0187] The flow rates are given in the following Table 3:

TABLE-US-00003 TABLE 3 Flow rate Value (kg/s) Flow rate of the working fluid of the ORC 3.5 Flow rate of pumped water (heat sink) 30 Flow rate of the working fluid of the 0.2 refrigeration cycle dedicated to the ORC

[0188] The correspondence between the flow rates of the pumps 8 and 30 will now be indicated.

[0189] In this dimensioning example, the condenser 61 without subcooling of the condensates is operated at a power of 60 MWth by the command control of the plant, which stipulates reactor cooling by x degrees/h at an SG steam pressure of 60 bar.

[0190] The flow rate of the pump 30 is equal to the ratio between the power and the latent heat at saturation under 60 bar, that is to say equal to 60 MW/1.57 MJ/kg, i.e. 38.2 kg/s. That is to say a volume flow rate of the pump 30 of 180 m.sup.3/h.

[0191] Considering a pump output overpressure of 3 bar to raise the condensates and the head losses in the circuit, this gives a hydraulic power of 15 kW, i.e. with a pump efficiency equal to 0.7, an electrical supply power of 22 kWe. The battery associated with the operation of the pump 30 therefore needs to be able to supply 22 kWe for at least 5 minutes, before the ORC steps in.

[0192] The flow rate, associated with this operating point, of the pump 8 is derived directly by the relationship: the flow rate of water pumped is equal to the ratio between the power and the latent heat at atmospheric pressure, that is to say equal to 60 MW/2.25 MJ/kg, i.e. 27 kg/s. The associated volume flow rate of the pump 8 is therefore about 100 m.sup.3/h. This pump needs to be battery-supplied for the start-up of the ORC (heat sink provisioning).

[0193] The external temperatures are given in the following Table 4:

TABLE-US-00004 TABLE 4 Temperature Value (° C.) Average temperature of the heat source 100 Temperature of the heat sink 30 Temperature of the heat sink (output of the ORC) 34

[0194] The internal pressures are given in the following Table 5:

TABLE-US-00005 TABLE 5 Pressure Value (bar) High cycle pressure of ORC 6 2.4 Low cycle pressure of ORC 6 0.45

[0195] The powers of the exchangers are given in the following Table 6:

TABLE-US-00006 TABLE 6 Powers Value (kW) Power of ORC condenser (61) 600 Power of ORC evaporator (63) 550

[0196] The electrical powers are given in the following Table 7:

TABLE-US-00007 TABLE 7 Electrical powers Value (kW) Power of ORC pump (62) 1.4 Power of water pump (8) 0.6 Power of water pump (30) 33 Power of electrical turbine (60) 35

[0197] Thus, under all these operating conditions, the volume of the exchangers to be dimensioned is summarized in the following Table 8:

TABLE-US-00008 TABLE 8 Volumes Value (m.sup.3) Volume of ORC condenser (HFE7100/water) 0.02 Volume of ORC evaporator (HFE7100/water) 3.66

[0198] The T-s diagram of the ORC and the refrigeration cycle is shown in FIG. 6.

[0199] One of the possible variants of the configuration according to FIG. 5 consists in coupling the shaft 11 of the turbine 60 of the ORC 6 and the shaft of the compressor of the refrigeration cycle. This configuration, which is shown in FIG. 7, makes it possible to avoid the need for electrically supplying the compressor of the refrigeration cycle, and thus makes it possible to save on energy (electromechanical conversions).

[0200] A second variant of the system consists in sharing more components between the ORC and the refrigeration cycle: the working fluid, a part of the pipework, the condenser 61, as already illustrated.

[0201] Another possible variant is not to use an immersed tube evaporator as shown in FIG. 4 but instead a remote evaporator, for example of the plate type. In order to do this, it is necessary to convey water from the reservoir in a conduit via a pump 14, as shown in FIG. 8. This configuration makes it possible to reduce the volume of the hot exchanger, to reduce the workload for installing the exchanger on the pool, or allows the possibility, as in the previous configuration, of operating the ORC by using an ancillary heat source. It should be noted that returning the water at the exit of the evaporator while mixing it with that coming from the ORC condenser means that only a single tap from the pool is needed, instead of two in the other variants and configurations.

[0202] The invention is not limited to the examples which have just been described; in particular, characteristics of the examples illustrated may be combined with one another within variants which are not illustrated.

[0203] Other variants and embodiments may be envisioned without thereby departing from the scope of the invention.

[0204] The DHR system which has just been described in connection with a pressurized water nuclear reactor may equally be implemented in a boiling water nuclear reactor (BWR).

[0205] In general, the invention applies to any pool 5 which can constitute the heat sink intended for cooling a PWR core or a BWR core, or for cooling and/or depressurizing the primary containment building of a PWR or of a BWR.

[0206] Thus, in the examples illustrated, the means for removing the decay heat coming from the core of the reactor passes through the steam generator, and this means may equally well be a condenser installed in the containment building whether for a PWR or for a BWR.

[0207] For a PWR, for example, reference may be made to the configuration of the ambience condenser panels of the HPR1000 project (“Passive containment heat removal”) or to publication [6], which describes an optimized condenser mounted against the containment building wall (“Passive containment cooling system”). For a BWR, reference may be made to the configuration of the KERENA advanced reactor of the cooling condensers (“Containment cooling condensers”) of the building.

[0208] More generally, for a PWR or a BWR, the means for removing the decay heat coming from the core of the reactor may be a system for depressurizing the steam present in the containment building (FIG. 9), and the heat exchange means may be a water exchanger 4 immersed in the pool 5 (closed-loop configuration of FIG. 11, taken from reference [6]) or a direct take-off of the water of the pool 5 (closed-loop configuration of FIG. 10, taken from reference [6]) on the one hand, and a “containment wall condenser” 11 in direct contact with the steam present in the containment building 100 of the reactor on the other hand.

[0209] The pool 5 may be the supply source of a spray header of a containment spray (CS) circuit which, in the event of an accident leading to a significant increase in the pressure in the building of the reactor, makes it possible to reduce this pressure and thus preserve the integrity of the containment building. For a PWR, reference may be made to the configuration of spray headers internal to the primary containment building of the HPR 1000 project or external to the primary containment of the AP1000 project.

[0210] The pool 5 may be an overpressure pool of a BWR, for example a torically shaped steel pool in a Mark I type reactor, the water steam accidentally coming from the core of the reactor being condensed.

[0211] The pool 5 may also be a pool of the security injection circuit of a PWR, such as that of the HPR-1000 project, with the acronym IRWST (“In containment Refueling Water System Tank”).

LIST OF REFERENCES CITED

[0212] [1]: https://www-pub.iaea.org/MTCD/Publications/PDF/TE-1785_web.pdf. [0213] [2]: S. Kadalev et al., 2014, Annals of Nuclear Energy, vol. 72, p. 182-188; [0214] [3]: D. C. Sun, Y. Li, Z. Xi, Y. F. Zan, P. Z. Li, W. B. Zhuo, “Experimental evaluation of safety performance of emergency passive residual heat removal system in HPR1000”, Nuclear Engineering and Design, Volume 318, 2017, Pages 54-60, ISSN 0029-5493, https://doi.org/10.1016/j.nucengdes.2017.04.003. [0215] [4]: Mikhail Maltsev, 2015, “Additional information on modern VVER Gen III technology” https://www.oecd-nea.org/upload/docs/application/pdf/2020-07/ii-1a-maltesev.pdf [0216] [5]: David Hinds and Chris Maslak, “Next-generation nuclear energy: The ESBWR” Nuclear News. January 2006. [0217] [6]: https://www-pub.iaea.org/MTCD/Publications/PDF/te_1624_web.pdf