LIGHT-WATER NUCLEAR REACTOR (LWR), IN PARTICULAR A PRESSURISED WATER REACTOR (PWR) OR BOILING WATER REACTOR (BWR), INCORPORATING AN INTEGRAL, AUTONOMOUS, PASSIVE DECAY HEAT REMOVAL SYSTEM

Abstract

An organic Rankine cycle machine and a supplementary reservoir of water, distinct from the pool, the energy stored in the pool being the hot source for the organic Rankine cycle evaporator, the supplementary reservoir of water feeding the organic Rankine cycle condenser directly via a dedicated pump to constitute the cold source of the organic Rankine cycle condenser.

Claims

1. A light water nuclear reactor (LWR), comprising: a reactor core; a system for evacuation of at least some of the decay heat from the reactor core, the system including: a first reservoir of water or pool arranged above the reactor core; a heat exchange device submerged in the pool so that the water contained in the latter cools the steam coming from a steam intake device of the primary or secondary circuit of the reactor; an organic Rankine cycle (ORC) machine including: an expander; a condenser; a first pump; an evaporator arranged in contact with the pool so that the latter constitutes the hot source of the organic Rankine cycle; a fluidic circuit wherein a working fluid circulates in a closed loop, the fluidic circuit connecting the expander to the condenser, the condenser to the first pump, the first pump to the evaporator, and the evaporator to the expander; a second reservoir of water, distinct from the pool, and a second pump connected to the second reservoir of water and to the organic Rankine cycle condenser to feed the latter with water as the cold source of the organic Rankine cycle.

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

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

4. The water nuclear reactor according to claim 1, including comprising a cooling circuit including: an intake of primary steam on the line feeding the turbine of the reactor; a water condenser submerged in the pool and connected to the steam intake in a closed loop.

5. The water nuclear reactor according to claim 1, the system for removing decay heat from the core of the reactor being a system for depressurisation of the steam present in the containment enclosure and the heat exchange device may be a water exchanger submerged in the pool or a direct intake of water from the pool on the one hand, and a containment wall condenser in direct contact with the steam present in the containment vessel of the reactor on the other hand.

6. The water nuclear reactor according to claim 1, the second reservoir of water being arranged in a part lower than the pool, advantageously on or in the ground.

7. The water nuclear reactor according to claim 1, the evaporator being submerged in or located remotely from the pool.

8. The water nuclear reactor according to claim 6, the submerged evaporator being a tubular exchanger.

9. The water nuclear reactor according to claim 6, the submerged evaporator being a plate exchanger.

10. The water nuclear reactor according to claim 1, further including comprising a cooling cycle including: a compressor; a condenser connected to the second pump to feed the latter with water; an expansion member; an air evaporator; a fluidic circuit wherein a working fluid circulates in a closed loop, the fluidic circuit connecting the compressor to the condenser the condenser to the expansion member, the expansion member to the air evaporator, and the air evaporator to the compressor.

11. The water nuclear reactor according to claim 9, the cooling cycle condenser being the organic Rankine cycle condenser.

12. The water nuclear reactor according to claim 9, the working fluid of the cooling cycle being that of the organic Rankine cycle.

13. The water nuclear reactor according to claim 9, the shaft of the organic Rankine cycle expander being coupled to the shaft of the cooling cycle compressor.

14. The water nuclear reactor according to claim 1, the organic Rankine cycle machine and where applicable the cooling cycle being arranged in a lower part of the system, below the pool.

15. The water nuclear reactor according to claim 1, comprising an injector arranged in a lower part of the system and connected to the second pump arranged in a higher part of the system, the injector being adapted to prime the second pump.

16. The water nuclear reactor according to claim 1, comprising batteries for electrically starting the first pump, electric components of the organic Rankine cycle and where applicable of the cooling cycle, as well as the second pump.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0124] FIG. 1 illustrates in the form of a curve the decrease over time of the decay heat of a prior art nuclear reactor known as a VVER TOI reactor.

[0125] FIG. 2 is a schematic view of a passive decay heat removal system for a prior art pressurised water reactor-type nuclear reactor core.

[0126] FIG. 3 is a schematic view of a passive system for decay heat removal from a pressurised water reactor-type reactor core according to one embodiment of the invention.

[0127] FIG. 4 is a T-s entropy diagram of the organic Rankine cycle and of the cooling cycle of a system like that in FIG. 3.

[0128] FIG. 5 is a schematic view illustrating a first variant of a system according to the invention.

[0129] FIG. 6 is a schematic view illustrating a second variant of a system according to the invention.

[0130] FIG. 7 is a schematic view illustrating a third variant of a system according to the invention.

[0131] FIG. 8 is a schematic view illustrating another embodiment of the invention with a system for depressurisation of the steam present in the containment vessel of a boiling water or pressurised water reactor.

[0132] FIG. 9 is a schematic view illustrating a first variant of a heat exchange means according to the invention for a boiling water or pressurised water reactor.

[0133] FIG. 10 is a schematic view illustrating a first variant of a heat exchange means according to the invention for a boiling water or pressurised water reactor.

DETAILED DESCRIPTION

[0134] Throughout the present application the terms “vertical”, “lower”, “upper”, “low”, “high”, “under” and “over” are to be understood with reference to a cooling pool of a nuclear reactor filled with water, as it is in a horizontal operating configuration, arranged above the reactor core.

[0135] FIGS. 1 and 2 have already been described in the preamble and will therefore not be commented on hereinafter.

[0136] Elements common to the invention and to the prior art are designated by the same reference number in all of FIGS. 1 to 10.

[0137] In FIGS. 3 to 7 relating to the invention only a part of the system for cooling a pressurised water nuclear reactor core is represented, namely the steam generator connected in a closed loop to a water exchanger submerged in the cooling pool.

[0138] The dashed lines denote electrical power lines of the various electrical components while solid lines denote fluid lines.

[0139] There has been illustrated in FIG. 3 an autonomous system according to the invention for evacuation of at least some decay heat from a pressurised water reactor.

[0140] The system includes firstly the cooling pool 5 arranged above the reactor core and a water condenser 4 submerged in the pool so that the water contained in the latter cools the steam issuing from the secondary circuit of the reactor.

[0141] It also includes an organic Rankine cycle (ORC) machine 6 including: [0142] an expander 60; [0143] a condenser 61; [0144] a first pump 62, for a working fluid; [0145] an evaporator 63 arranged relative to the pool 5 so that the latter constitutes the hot source of the organic Rankine cycle; [0146] a fluidic circuit 64 in which a working fluid circulates in a closed loop.

[0147] As illustrated, and according to the invention, the fluidic circuit 64 connects the expander 60 to the condenser 61, the condenser 61 to the first pump, termed the pump 62 of the organic Rankine cycle, the pump 62 of the organic Rankine cycle to the evaporator 63, and the evaporator 63 to the expander 60.

[0148] A second reservoir of water forming a general pool 7 contains all of the cold source dedicated to cooling the reactor and feeds the pool 5 dedicated to the organic Rankine cycle and containing the safety condenser 4 and the organic Rankine cycle evaporator 63.

[0149] The water from the pool 7 serves as a cold source for the exchanger condenser 61. The water from the pool 7 is slightly heated by the condenser 60 before being injected into the pool 5 by means of a second pump, which is a water supply pump 8. This pump 8 feeds a dedicated fluidic line 65 to palliate the evaporation of the pool 5 receiving the reactor decay heat.

[0150] The expander 60 may typically be a turbine, a spiral, screw, piston, etc. pressure regulator.

[0151] The condenser 61 is typically a plate condenser.

[0152] The organic Rankin cycle pump 62 is typically a centrifugal, or membrane, screw, etc. pump.

[0153] The machine 6 may include a surge tank 66, that is to say a reserve of a quantity of working fluid enabling in particular adequate functioning of the organic Rankine cycle under varying conditions. As illustrated in FIG. 3, this surge tank 66 can be arranged upstream of the organic Rankine cycle pump 62.

[0154] In the embodiment illustrated in FIG. 3 the evaporator 63 is a tubular evaporator submerged vertically in the pool 5.

[0155] The system also includes a second reservoir 7 of water, distinct from the pool, and a water pump 8 connected to the second water reservoir and to the condenser 61 of the organic Rankine cycle to supply the latter with water, as the cold source of the organic Rankine cycle.

[0156] In the advantageous embodiment from FIG. 3 there is further provided a cooling cycle 9 including: [0157] a compressor 90; [0158] a condenser 61, which is that of the organic Rankine cycle, connected to the water pump 8, to supply the latter with water; [0159] an expansion member 92; [0160] an air evaporator 93; [0161] a fluidic circuit 94 in which a working fluid circulates in a closed loop.

[0162] The fluidic circuit 94 connects the compressor 90 to the organic Rankine cycle condenser 61, the condenser 61 to the expansion member 92, the expansion member to the air evaporator 93, and the air evaporator 93 to the compressor 90.

[0163] The expansion member 92 may be a valve or preferably a turbine, an ejector, etc.

[0164] Like the organic Rankine cycle 6, the cooling cycle 9 may also include a surge tank forming a reservoir of working fluid in this cycle.

[0165] Batteries 10 may be provided for electrically starting the various pumps 62, 8, the organic Rankine cycle electrical components, and where applicable the cooling cycle 9. To be more precise, the batteries may serve for the function of starting the organic Rankine cycle, that is to say starting the organic Rankine cycle pump 62 and activating the submerged pump 8 that feeds the cold source to the pool 5, thus making it possible to provide the cold source of the organic Rankine cycle (condenser exchanger).

[0166] An example of dimensions for an accident situation in the case of a pressurised water reactor with a power rating of 3200 MWth is given below.

[0167] The working fluid of the organic Rankine cycle is an organic fluid the evaporation temperature of which is lower than that of boiling water, approximately 100° C. at atmospheric pressure. There may in particular be cited Novec649, HFE7000, HFE7100, etc.

[0168] Numerous other organic fluids may be envisaged such as alkanes, HFC, HFO, HFCO, HFE, as well as other fluids (NH.sub.3, CO.sub.2) and all mixtures thereof.

[0169] The fluid used in the simulation of setting dimensions is HFE7100 and is advantageously used both in the organic Rankine cycle 6 and in the cooling cycle 9.

[0170] In this example temperature sensors or sensors of the level of water in the pool 5 enable detection of the complete saturation state of the pool 5 and the commencement of loss of liquid level by boiling off.

[0171] There is a delay for the pool 5 to be half-emptied before starting the filling pump 8. For reliability, the flowrate of the pump 8 is fixed at the flowrate of loss by evaporation from the pool, at the moment it is started.

[0172] Knowing that the residual power of the reactor core decreases with time, from the moment at which the pump 8 is started the pool 5 gains in water inventory.

[0173] Dimensions in relation to the pool are summarised in table 1 below.

TABLE-US-00001 TABLE 1 Dimension Value Total volume of pool 5 1000 m.sup.3 Height of pool 5  10 m Height difference between pool 5 and water reservoir 7  50 m

[0174] Information relating to the time for which the pool functions is summarised in table 2 below.

TABLE-US-00002 TABLE 2 Functioning of pool Duration (h) Pool 5 becomes saturated 1.5 Pool 5 is half-empty/organic Rankine cycle 6 starts 20 Pool 5 refilled 90

[0175] The flowrates are given in table 3 below:

TABLE-US-00003 TABLE 3 Flowrate Value (kg/s) Flowrate of organic Rankine cycle working fluid 1 Flowrate of pumped water (cold source) 6 Flowrate of cooling cycle working fluid 0.02

[0176] The outside temperatures are given in table 4 below:

TABLE-US-00004 TABLE 4 Temperature Value (° C.) Mean temperature of the hot source 100 Temperature of the cold source 30 Temperature of the cold source (exit from cooling cycle) 30 Temperature of the cold source (exit from organic Rankine cycle) 38

[0177] The internal pressures are given in table 5 below:

TABLE-US-00005 TABLE 5 Pressure Value (bar) Organic Rankine cycle 6 high pressure 2.7 Organic Rankine cycle 6 low pressure 0.5 Cooling cycle 9 high pressure 2.0 Cooling cycle 9 low pressure 0.1

[0178] The powers of the exchangers are given in table 6 below:

TABLE-US-00006 TABLE 6 Power Value (kW) Organic Rankine cycle condenser (61) power 170 Organic Rankine cycle evaporator (63) power 180 Cooling condenser (61) power 3 Cooling evaporator (93) power 2

[0179] The electrical powers are given in table 7 below:

TABLE-US-00007 TABLE 7 Electrical power Value (kW) Organic Rankine cycle pump (62) 0.5 Water pump (8) 7.5 Compressor (90) 0.7 Electric turbine (60) 8.6

[0180] Thus under all the above operating conditions the volume of the exchangers to be set dimensions is summarised in table 8 below:

TABLE-US-00008 TABLE 8 Volume Value (m.sup.3) Organic Rankine cycle condenser volume 0.01 (HFE7100/Water) Cooling cycle condenser volume 0.0005 (HFE7100/Water) Organic Rankine cycle evaporator volume 0.5 (HFE7100/Water)

[0181] The T-s diagram of the organic Rankine cycle and the cooling cycle is shown in FIG. 4.

[0182] One possible variant of the FIG. 3 configuration consists in coupling the shaft 11 of the turbine 60 of the organic Rankine cycle 6 and the shaft of the compressor of the cooling cycle. This configuration shown in FIG. 5 makes it possible not to need to supply the compressor of the cooling cycle with electrical power and therefore saves energy (electromechanical conversions).

[0183] A second variant of the system consists in pooling the advantages of components between the organic Rankine cycle and the cooling cycle: the working fluid, some of the pipework, the condenser 61 as already illustrated.

[0184] Another variant of this system consists in placing the organic Rankine cycle and the cooling cycle in the lower part of the system, thanks to the presence of an intermediate circuit, which makes it possible to couple to the same shaft the organic Rankine cycle turbine and the pump 8 for feeding water from the lower part to the higher part. This enables improved reliability of the system, as in fact the transmission of power between the turbine and the water pump 8 is purely mechanical: there is no conversion of mechanical energy into electrical energy. However, this disposition obliges the organic Rankine cycle to be in the lower part, which renders it vulnerable to numerous accident situations: flooding, etc. Moreover, it is necessary to take heat energy from the pool in the lower part. This in particular also enables facilitated access for maintenance and surveillance by the operating personnel.

[0185] As shown in FIG. 6 it is also possible to place the organic Rankine cycle in the lower part, thanks to an intermediate circuit, without coupling the water pump 8 to the organic Rankine cycle turbine 60. This intermediate circuit then includes a supplementary evaporator 67 fed by means of a third pump 68. The advantage of this configuration will be the possibility of having the organic Rankine cycle function via an ancillary hot source 12 and valves 13 to enable maintenance/testing of the system to increase its reliability.

[0186] Another possible variant is not to use a submerged tubular evaporator as shown in FIG. 3 but a remotely located evaporator for example of plate type. To this end, it is necessary to feed the water from the reservoir in a pipe, via a pump 14 as shown in FIG. 7. This configuration enables reduction of the volume of the hot exchanger, reduction of the work of installing the exchanger over the pool or, as in the preceding configuration, the organic Rankine cycle functioning thanks to an ancillary hot source. It is to be noted that mixing water at the exit from the evaporator with that coming from the organic Rankine cycle condenser requires only a single intake from the pool instead of two in the other configurations and variants.

[0187] Another possible variant of this technology is to place a condensation injector in the lower part of the installation. It would thus be possible to position the water pump 8 in the upper part of the structure by actuating the pumping movement by means of the injector in the lower part. This configuration would make it possible to have the whole of the organic Rankine cycle and of the pump 8 in the upper part (and therefore safer from external aggression, flooding, etc.). This injector would enable priming of the system: being fed by a reserve of low-capacity thermal energy, this injector would direct into the intake pipe of the pump 8 a sufficient quantity of water to prime it.

[0188] The invention is not limited to the examples that have just been described; in particular features of the examples illustrated may be combined with one another in variants that are not illustrated.

[0189] Other variants and embodiments may be envisaged that do not depart from the scope of the invention.

[0190] The decay heat removal system that has just been described with reference to a pressurised water nuclear reactor may be used in a boiling water nuclear reactor (BWR).

[0191] Generally speaking, the invention applies to any pool 5 that can constitute the cold source intended to cool a pressurised water reactor core or a boiling water reactor core or to cool and/or depressurise the primary containment vessel of a pressurised water reactor or a boiling water reactor.

[0192] Accordingly, although in the examples illustrated the means for evacuation of decay heat from the core of the reactor include the steam generator, this means may equally well be a condenser installed in the containment vessel whether for a pressurised water reactor or for a boiling water reactor.

[0193] For example, for a pressurised water reactor reference may be had to the ambient condenser panels of the HPR1000 project (“Passive containment heat removal”) or to publication [6] which describes an optimised condenser mounted against the containment vessel wall (“Passive containment cooling system”). For a boiling water reactor see the configuration in the KERENA reactor of the containment cooling condensers.

[0194] More generally, for a pressurised water reactor or a boiling water reactor the means for evacuation of decay heat from the core of the reactor may be a system for depressurisation of the steam present in the containment vessel (FIG. 8) and the heat exchange means may be a water exchanger 4 submerged in the pool 5 (closed loop configuration from FIG. 10, taken from reference [7]) or taking water directly from the pool 5 (closed loop configuration of FIG. 9, taken from reference [7]) on the one hand and of a containment wall condenser 11 in direct contact with the steam present in the containment vessel 100 of the reactor on the other hand.

[0195] The pool 5 may be a source feeding a sprinkler manifold of an enclosure sprinkler circuit which in an accident situation leading to a significant increase of pressure in the reactor building enables this pressure to be decreased and thus preserves the integrity of the containment vessel. For a pressurised water reactor see the configuration of internal sprinkler manifolds in the primary containment vessel of the HPR1000 project or external to the primary vessel of the AP1000 project.

LIST OF CITED REFERENCES

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