EP2707882A1

EP2707882A1 - Nuclear reactor with device for injecting nanoparticles in the event of an accident

Info

Publication number: EP2707882A1
Application number: EP12720184.6A
Authority: EP
Inventors: Mehdi Moussavi; Mickaël GUILLODO; Marylise CARON-CHARLES
Original assignee: Areva SA
Current assignee: Areva SA
Priority date: 2011-05-11
Filing date: 2012-05-10
Publication date: 2014-03-19
Also published as: FR2975215A1; KR20140059759A; FR2975215B1; US20140079172A1; CN103620692A; JP2014514584A; WO2012152883A1

Abstract

The nuclear reactor comprises: - a core having nuclear fuel assemblies; - a core cooling circuit in which a coolant circulates; and - a device designed to inject nanoparticles into the coolant. The nanoparticles comprise first nanoparticles (82) of a first type having a first form factor lower than two and second nanoparticles (84) of a second type different from the first type and having a second form factor greater than two, the nanoparticles containing between 10 wt% and 90 wt% of the first nanoparticles (82) and between 90 wt% and 10 wt% of the second nanoparticles (84).

Description

Nuclear reactor with nano particle injection device in case of accident

The present invention generally relates to nuclear reactors, in particular the dissipation of heat in such reactors during an accident of the LOCA type (loss of coolant accident).

More specifically, the invention relates to a nuclear reactor of the type comprising:

a core having nuclear fuel assemblies;

- A cooling circuit of the core in which circulates a cooling fluid;

- A device for injecting nano particles into the cooling fluid.

Such a nuclear reactor is described in US 2008/0212733. A LOCA-type accident in a nuclear reactor typically corresponds to a leak occurring in the core cooling circuit, such that a portion of the primary coolant flows out of the cooling circuit and is collected at the bottom of the reactor. the reactor cavity. As a result, the nuclear fuel assemblies are no longer adequately cooled, and the temperature in the reactor core increases. This increase in temperature can cause the heart to melt. In type PWR and BWR reactors, a LOCA type of accident corresponds, for example, to the rupture of the main steam line connecting the reactor vessel to the steam generator or the turbine, respectively.

The above US document provides for the injection of nanoparticles into the primary coolant in the case of LOCA, with a view to increasing the heat exchange in the cooling circuit. This injection is performed as soon as the loss of coolant is detected.

To effectively increase heat exchange in the core cooling circuit, the nanoparticles must disperse in the coolant and remain in suspension without sedimentation.

In this context, the invention aims to propose a nuclear reactor in which the injection of the nanoparticles makes it possible to increase the heat exchange in the cooling circuit of the core in an efficient and sustainable manner, in the event of a LOCA-type accident.

To this end, the invention relates to a nuclear reactor of the aforementioned type, characterized in that the nanoparticles comprise first nano particles of a first type having a first form factor of less than 2, and second nano particles of a second type different from the first type having a second form factor greater than 2, the nano particles comprising between 10% and 90% by weight of the first nanoparticles and between 90% and 10% by weight of the second nanoparticles.

The first nanoparticles, having a lower form factor, are more resistant to thermal shocks and sediment less, because they have a higher uniformly distributed surface charge. The second nanoparticles, having a higher form factor, have a higher thermal conductivity in solution but sediment more quickly. Surprisingly, the mixed use of nanoparticles of both types makes it possible to benefit from the advantages of the two types of nanoparticles. The coolant containing the mixture of the first and second nanoparticles has excellent thermal conductivity. The nanoparticles hardly sediment, and the turbulence resulting from the circulation of the cooling fluid is enough to keep them in suspension.

The nuclear reactor is a PWR type reactor, or a BWR type reactor, or any other type of reactor in which the core is cooled by circulation of a heat transfer liquid. This cooling fluid is typically water, but could be another coolant.

The nanoparticles are typically nano powders of metal oxides or diamonds.

Such nano particles are for example described in the article "Surface wettability change during pool boiling of nanofluids and its effect on critical heat flow" by Kim et al, published in International Journal of Heat and Mass Transfer, 50 (2007) 40105- 401 16; or else in the article "A feasabililty assessment of the use of nanofluids to enhance the in-vessel retention capability in light water reactors", by Buongiorno et al, published in Nuclear Engineering and Design 239 (2009) 941 -948 or in "Effects of nano particles deposition on surface wettability influencing boiling heat transfer in nanofluids" by Kim et al published in Applied Physics Letters 89, 153107 (2006).

The first nano particles are in a material identical to the material constituting the second nano particles. Alternatively, the first nanoparticles and the second nano particles are in respective materials different from each other.

Preferably, the first nanoparticles are in a mineral oxide, typically selected from Al ₂ O ₃ , ZnO, CeO ₂ , or Fe ₂ O ₃ . The second nanoparticles are also in a mineral oxide, typically selected from Al ₂ O ₃ , ZnO, CeO ₂ or Fe ₂ O ₃ .

The first nanoparticles have a form factor of less than 2, preferably between 1 and 1.5, more preferably between 1 and 1.2. By form factor is meant here the ratio between the length of the nanoparticle and its width. The length corresponds to the largest dimension of the nanoparticle, this dimension being taken along a longitudinal direction of the particle. The width corresponds to the smallest dimension of the particle, taken in a plane perpendicular to the longitudinal direction.

Thus, for a sphere, the form factor is rigorously equal to 1. Preferably, the first nanoparticles are spherical or pseudospherical.

Typically, at least 50% of the first nanoparticles have a form factor of between 1 and 1.5, preferably at least 75% of the first nanoparticles, and even more preferably at least 90% of the first nanoparticles.

The second nanoparticles have a second form factor greater than 2. The form factor is defined as before.

Preferably, the second nanoparticles have a form factor of between 2 and 5, and more preferably of between 2 and 3. For example, the second nanoparticles are in the form of rods, each rod having an elongated shape according to a longitudinal direction.

Typically, at least half of the second nanoparticles have a form factor of between 2 and 5, preferably at least 75% of the second nanoparticles and more preferably at least 90% of the second nanoparticles.

The nanoparticles intended to be injected into the cooling fluid comprise between 10 and 90% by weight of the first nanoparticles, preferably between 30 and 70% by weight of the first nanoparticles, and even more preferably between 40 and 60% by weight. first nano particles. In contrast, the nanoparticles comprise between 90% and 10% by weight of second nanoparticles, preferably between 70% and 30% by weight of second nanoparticles, and even more preferably between 60% and 40% by weight of nanoparticles. second nano particles. For example, the nanoparticles comprise 50% by weight of first nanoparticles and 50% by weight of second nanoparticles.

Typically, the nanoparticles comprise only first nanoparticles and second nanoparticles, and do not comprise nanoparticles of another type.

The nanoparticles mainly have sizes of between 50 nanometers and 250 nanometers, before being agglomerated to each other as described below. Preferably, at least 75% of the nanoparticles have sizes of between 50 and 250 nanometers, and even more preferably 90% of the nanoparticles. Preferably, the nanoparticles have predominantly sizes of between 75 and 150 nanometers, and more preferably between 90 and 1 10 nanometers.

Here, the size of a nanoparticle is the largest dimension of said nanoparticle.

The nanoparticles, before injection, are in the form of agglomerates, each agglomerate comprising both first nanoparticles and second nanoparticles. Thus, each agglomerate is an assembly comprising a plurality of first nanoparticles and a plurality of second nano particles, integral with each other. Each agglomerate is therefore a monolithic set of small size. After injection of the nanoparticles into the cooling fluid, the agglomerates are dispersed and form a suspension. Agglomerates, within the cooling fluid, remain in one piece, the nanoparticles constituting each agglomerate remaining normally integral with each other. The agglomerates can break on the other hand under the effect of shocks, after a certain period of circulation in the cooling fluid.

The agglomerates predominantly have sizes of between 150 nanometers and 400 nanometers. Preferably, at least 75% of the agglomerates have a size of between 150 and 400 nanometers, and even more preferably 90% of the agglomerates. Preferably, the majority of agglomerates have sizes of between 200 and 300 nanometers, and even more preferably between 200 and 250 nanometers.

The agglomerates have a general zigzag shape, as represented for example in FIG. 4 and in FIG. 7. By this is meant that the agglomerate has a general broken line shape. In other words, the agglomerate has a general shape that has several sections with respective inclinations different from each other. The sections are integral with each other.

The general zigzag shape, the size and the constitution of the agglomerates are different elements which each contribute to obtaining the desired properties once the nanoparticles have been dispersed in the cooling fluid. The agglomerates are self-dispersing, i.e., mix substantially instantaneously with the coolant, to form a homogeneous suspension. Agglomerates sediment only slowly. The circulation of the cooling fluid in the cooling circuit, even in the case of LOCA, is sufficient to maintain almost all the agglomerates in suspension. Finally, when the agglomerates are dispersed in the cooling fluid, the heat dissipation in the cooling circuit increases very significantly. By this is meant that the thermal power released by the nuclear fuel assemblies is better transferred to the cooling fluid, the assemblies thus being maintained at a lower temperature. Likewise, the coolant yields more readily its thermal energy, and is kept at a moderate temperature. The thermal conductivity of a cooling liquid comprising water and 30% by weight of agglomerates is about 10 to 25% higher than the thermal conductivity of pure water.

Preferably, the nanoparticles are injected into the cooling fluid with a mass content of between 10 and 50%, preferably between 20 and 40%, and being for example 30%.

According to another aspect of the invention, the nanoparticles before injection are stored in solid form. They are also injected in solid form into the coolant in the event of an accident. Thus, the device provided for the injection of the nanoparticles comprises a storage of said nanoparticles in solid form, and an injection member of the nanoparticles in solid form from the storage directly in the primary liquid. The nanoparticle injection member comprises, for example, a device for dosing the quantity of nanoparticles to be injected, and a means for driving the nanoparticles from the dosing member into the cooling circuit. The entrainment of the nanoparticles is done for example by means of a compressed neutral gas.

The invention has been described above in the context of a LOCA-type accident, the nanoparticles being in this case injected into the fluid circulating directly in the reactor core. However, nanoparticles can also be injected when other types of accidents occur, which hinder or prevent the cooling of the reactor core: rupture of a secondary circuit piping of a PWR type reactor or other, connecting the steam generator at the turbine; leak on the secondary cooling circuit; rupture of one or more steam generator tubes; blocking of control rods; etc. In other words, the invention applies in all cases where it is necessary to increase the efficiency with which the thermal power released by the nuclear fuel assemblies is discharged out of the core.

The nanoparticles are preferably injected into the so-called primary cooling fluid, which circulates in the reactor core. However, it is possible to provide a suitable device for injection in the primary cooling circuit, and / or in the secondary cooling circuit, and / or in a possible tertiary cooling circuit of the reactor. The secondary and tertiary circuits are circuits of cooling of the heart, since they help to evacuate the heat released in the heart.

Other features and advantages of the invention will emerge from the detailed description given below, for information only and in no way limitative, with reference to the appended figures, among which:

FIG. 1 is a simplified schematic representation of a nuclear reactor according to the invention;

FIG. 2 is a schematic representation of first nano particles of different types;

FIG. 3 is a simplified schematic representation of second nano particles of different types;

FIG. 4 is a simplified schematic representation of an agglomerate of nanoparticles; and

FIGS. 5 to 7 illustrate successive steps in the process for producing agglomerates of nanoparticles.

The reactor 1 shown in FIG. 1 is a PWR type reactor. The reactor 1 comprises a tank 10, in which are placed the nuclear fuel assemblies forming the core of the reactor, a cooling circuit 20 of the reactor core in which circulates a cooling fluid, a steam generator 30 inserted in the reactor circuit. cooling 20, a coolant circulation pump 40 also inserted into the cooling circuit, and a device 50 for injecting nano particles into the cooling fluid.

The steam generator 30 has a primary side in which circulates the cooling fluid of the core, and a secondary side in which circulates a secondary heat transfer fluid. The core coolant transfers its heat to the secondary fluid through the steam generator 30.

The circulation pump 40 is placed downstream of the steam generator 30 in the direction of circulation of the cooling fluid. The cooling circuit 20 comprises a hot leg 22 connecting a cooling fluid outlet 12 of the tank to a cooling fluid inlet 32 of the steam generator, an intermediate branch 24 connecting a cooling fluid outlet 34 of the steam generator at a suction inlet of the primary pump 40, and a cold branch 26 connecting a discharge outlet of the primary pump 40 to an inlet 14 of the primary liquid of the tank. The cooling circuit 20 further comprises one or more pressurizers 70. The device 50 intended for the injection of the nanoparticles comprises a storage 52 of said nanoparticles in solid form, and a device 54 for injecting the nanoparticles in solid form from the storage 52 directly into the cooling liquid. The storage 52 is of any suitable type. It may comprise a tank under pressure of an inert gas in which the nanoparticles, a hopper, etc. are stored. The nanoparticles are in the form of agglomerates in the storage 52.

The injection member 54 typically comprises a nano-particle injecting device 56, a means 57 for driving the nanoparticles of the metering member 56 into the cooling circuit 20 and one or more transfer lines 58. nanoparticles, connecting the metering member 56 to the cooling circuit 20.

The metering member 56 has an inlet communicating with the storage 52. A closure member, interposed between the storage 52 and the inlet of the metering member 56, selectively allows communication or isolation of the storage 52 of the metering member 56. The metering member can be of all types adapted. The metering member 56 is for example a receptacle mounted on a weighing cell adapted to measure the mass of charged nanoparticles in the receptacle.

The means 57 for driving the nanoparticles from the metering member 56 into the primary circuit comprises, for example, a supply of a high-pressure inert gas connected to a gas inlet of the metering member 56. A valve, or any other suitable means, selectively trigger or interrupt the supply of high pressure gas in the metering member 56. The transfer lines 58 connect an output of the metering member 56 to one or more taps 59 of the cooling circuit 20. Valves placed on the lines 58 make it possible to selectively connect or isolate the metering member 56 of the cooling circuit 20.

The taps 59 are placed at selected points of the cooling circuit to allow a dispersion of nanoparticles as fast and efficient as possible in the coolant. For example, one of the taps 59 is placed immediately downstream of the outlet 12 of the tank. Another stitching 59 may be placed on the cold branch 26, immediately upstream of the inlet 14 of the tank. Another stitch 59 can be placed in the cold branch 26, away from the circulation pump 40 and away from the tank 10.

The device 50 is controlled by a computer not shown.

To perform the injection of nanoparticles in the cooling circuit, the computer first controls the transfer of nanoparticles from the storage 52 up to the metering member 56, and then isolates the metering member 56 from the storage 52. It then triggers the supply of the metering member 56 to inert gas via the means 57, and the transfer of the nano particles from the metering member 56 into the primary circuit 20 via the lines 58. The inert gas pressure supplied by the means 57 is greater than the coolant pressure in the primary circuit.

As illustrated in FIG. 2, the first nano particles are spherical (example a) or quasi-spherical (example b). When they are almost spherical, they can have an ovoid shape. The first nanoparticles may still have an irregular shape, as illustrated in Example c of Figure 2.

As can be seen in FIG. 3, the second nanoparticles have the shape of elongated rods in a longitudinal direction. In example a, the rods have a substantially constant cross section perpendicular to the longitudinal direction. For example, the section is round, or rectangular, or any other shape. In example b of Figure 3, the rod may have an irregular cross section in a plane perpendicular to its longitudinal direction.

As shown diagrammatically in FIG. 4, the agglomerates each comprise a plurality of first nano-particles 82 and a plurality of second nano-particles 84 integral with each other. The agglomerate has a general zigzag shape. By this is meant that the nano particles are arranged so as to constitute several branches oriented in respective directions different from each other. The branches are connected to each other. Each branch consists of first nanoparticles and / or second nanoparticles. The branches are distinct from each other.

The different branches are referenced 86 in FIG.

Figures 5 to 7 illustrate different steps of a first method adapted to produce agglomerates from the first and second nanoparticles. In the first step, shown in FIG. 5, the rods 88 of polyvinyl alcohol (PVA) are mixed with the first and second nano particles 82 and 84.

In the second step, shown in FIG. 6, the mixture is quenched at a temperature of at least about 180 ^° C. To do this, a metered amount of water is added to the mixture, the nanoparticles and the PVA rods are dispersed in water, and this dispersion is brought to the temperature of -180 ° C. The nano particles 82 and 84 are then compressed at the interface of the ice crystals 90. The PVA 88 sticks act as a plasticizer. The agglomerates of nanoparticles are formed during the quenching step, due to the compression between the ice crystals. The water is then removed by lyophilization, this step being carried out under cold conditions, at a temperature below 0 ° C. Finally, after the end of the lyophilization step, the nanoparticles are dispersed in water. Most of the PVA is separated from the nanoparticles either at the vacuum lyophilization stage or at the final dispersion stage.

A second method will now be described. It is particularly suitable for producing agglomerates whose first and second particles are both ZnO.

The second method comprises the following steps.

1 °) Preparation of colloidal sols of nano-particles of zinc oxides

Two colloidal sols are prepared, the colloidal sol of ZnO marketed by Nyacol under the reference Nyacol DP5370 and that marketed by Evonik under the reference: VP DISP ZnO 20 DW. Both soils are 35% by mass and contain crystallized nanoparticles. The major difference between them is the shape and size of the nanoparticles: spherical from 30 to 50 nm for Nyacol, and in the form of rods and elongated platelets for Evonik (diameter less than 50 nm, 500 to 750 nm in length). Both soils are sold in stabilized form and must be washed to remove organic products and stabilizing salts (dialysis 5 days on a dialysis membrane of 14000 MWCO cellulose against 90 liters of water Dl). The efficiency of the dialysis is measured by the measurements of the conductivity of the buffer water and the final ZnO titre is measured gravimetrically after heating at 1000 ° C. After washing, the ZnO mass titers are respectively 17%. for Nyacol and 14.5% for Evonik.

2 °) Preparation of agglomerates

First example: agglomerates having 60% ZnO Nyacol + 40% ZnO Evonik, by mass.

0.92 g of PVA (Fluka: 4-88) is added to 25 g of DI water. The mixture is stirred at room temperature until complete dissolution of the PVA. The PVA solution is added at room temperature to a mixture of 22.2 g of the aqueous dialyzed ZnO Nyacol sol prepared in the preceding step (17% by mass ZnO) and 17.35 g of the aqueous sol of dialyzed ZnO Evonik prepared in the previous step (14.5% by weight in ZnO). The reaction medium is milky white, very homogeneous without formation of precipitate.

The reaction medium is then added dropwise in liquid nitrogen (DEWAR 5 I), the diameter of the drops is about 5 mm. The agglomerates obtained after quenching in liquid nitrogen are then filtered on a plastic Buchner. They are weighed and freeze-dried for 48 hours. Lyophilization usually lasts 48 hours. After 36 hours, the lyophilization is stopped and the agglomerates are weighed. They are then left to freeze dry for 12 hours, then they are reweighed. We consider that lyophilization is complete if the mass variation between 36 hours and 48 hours does not exceed 0.5 g per 100 g of material involved. The agglomerates are then conditioned under argon and stored at room temperature.

Second example: agglomerates having 80% ZnO Nyacol + 20% ZnO Evonik, by mass.

0.92 g of PVA (Fluka: 4-88) is added to 25 g of DI water. The mixture is stirred at room temperature until complete dissolution of the PVA. The PVA solution is added at ambient temperature to a mixture of 29.6 g of the aqueous dialyzed ZnO Nyacol sol prepared in the preceding step (17% by mass ZnO) and 8.67 g of the aqueous sol of dialyzed ZnO Evonik prepared in the previous step (14.5% by weight in ZnO). The reaction medium is milky white, very homogeneous without formation of above.

Third example: agglomerates having 90% ZnO Nyacol + 10% ZnO Evonik, by mass.

0.92 g of PVA (Fluka: 4-88) is added to 25 g of DI water. The mixture is stirred at room temperature until complete dissolution of the PVA. The PVA solution is added at room temperature to a mixture of 33.3 g of the aqueous dialyzed ZnO Nyacol sol prepared in the preceding step (17% by mass ZnO) and 4.34 g of the aqueous sol of dialyzed ZnO Evonik prepared in the previous step (14.5% by weight in ZnO). The reaction medium is milky white, very homogeneous, without formation of precipitate. The reaction medium is then added dropwise in liquid nitrogen (DEWAR 5 I), the diameter of the drops is about 5 mm. The agglomerates obtained after quenching in liquid nitrogen are then filtered on a plastic Buchner. They are weighed and freeze-dried for 48 hours. Lyophilization usually lasts 48 hours. After 36 hours, the lyophilization is stopped and the agglomerates are weighed. They are then left to freeze dry for 12 hours, then they are reweighed. We consider that the lyophilization is complete if the mass variation between 36 hours and 48 hours does not exceed 0.5 g per 100 g of material involved. The agglomerates are then conditioned under argon and stored at room temperature.

Claims

1. Nuclear reactor comprising:

a core having nuclear fuel assemblies;

a circuit (20) for cooling the core in which a cooling fluid circulates;

a device (50) provided for the injection of nanoparticles into the cooling fluid;

characterized in that the nanoparticles comprise first nanoparticles (82) of a first type having a first form factor of less than two, and second nanoparticles (84) of a second type different from the first type having a second form factor greater than two, the nanoparticles comprising between 10% and 90% by weight of the first nanoparticles (82) and between 90% and 10% by weight of the second nanoparticles (84).

2. Reactor according to claim 1, characterized in that the device (50) provided for the injection of nanoparticles comprises a storage (52) of said nanoparticles in solid form, and a body (54) for injecting the nanoparticles in solid form. from the storage (52) directly into the coolant.

3. Reactor according to any one of the preceding claims, characterized in that the nanoparticles, before injection, are in the form of agglomerates (80), each agglomerate (80) comprising first nanoparticles (82) and second nanoparticles ( 84).

4. Reactor according to claim 3, characterized in that the agglomerates (80) have predominantly sizes between 150 nm and 400 nm.

5. Reactor according to any one of claims 3 or 4, characterized in that the agglomerates (80) have a general zig-zag shape.

6. Reactor according to any one of the preceding claims, characterized in that the first nanoparticles (82) have a form factor of between 1 and 1.5.

7. Reactor according to any one of the preceding claims, characterized in that the first nanoparticles (82) are in a mineral oxide, typically selected from Al ₂ 0 ₃ , ZnO, Ce0 ₂ or Fe ₂ 0 ₃ .

8. Reactor according to any one of the preceding claims, characterized in that the second nanoparticles (84) have a form factor of between 2 and 5.

9. Reactor according to any one of the preceding claims, characterized in that the second nanoparticles (84) are in a mineral oxide, typically selected from Al ₂ 0 ₃ , ZnO, Ce0 ₂ or Fe ₂ 0 ₃ .

10. Reactor according to any one of the preceding claims, characterized in that the nanoparticles have predominantly sizes between 50 nm and 250 nm, before agglomeration.