DE3513019A1 - CORE REACTOR - Google Patents

Description

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Nuclear reactor

The invention relates to a nuclear reactor according to the preamble of claim 1.

Liquid metal cooled fast breeder reactors (LMR), like other reactors, generate heat by fissioning nuclear material in fuel assemblies, which are arranged within a reactor core, which in turn is in a reactor vessel or reactor pressure vessel. In commercial nuclear reactors, the resulting heat is used for generation used by electricity. Such nuclear reactors typically have one or two primary circuits provided with heat exchangers and a corresponding number of secondary circuits with heat exchangers, to which conventional steam turbines and electric generators are connected. A typical energy conversion process in commercial nuclear reactors therefore requires heat transfer from the reactor core to one primary cooling system, then to a secondary cooling system and finally, in steam, from the electricity is produced. In the case of nuclear reactors with liquid cooling, for example a liquid metal-cooled breeder reactor, a reactor coolant, such as liquid sodium, is pumped through the primary cooling system. A typical primary cooling system includes a reactor core, a heat exchanger and a circulation pump. With systems according to the so-called "pool" construction (tank construction)

are located

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the reactor core, the heat exchanger and the circulation pump are located in a large bath of cooling liquid, the is enclosed by a single housing, while in the so-called "loop" construction (circuit construction) the The heat exchanger and the circulation pump are removed from the vessel with the reactor core and usually in separate ones Containers are housed. In general, several heat exchangers and circulation pumps belong to the reactor core. the Heat generated in the reactor core is removed by the reactor coolant flowing into the reactor vessel and flows through the reactor core. The heated coolant then flows through the heat exchangers that use the heat delivered to connected secondary flow systems will. The cooled coolant exits the heat exchangers and flows to a circulating pump that generates the Pumps coolant back into the reactor vessel, thus closing the flow cycle.

The alkali metals in particular have excellent heat transfer properties and extremely low vapor pressure temperatures, as they are of particular interest in power generation. Sodium is particularly attractive since it has a relatively low melting point and a high heat transfer coefficient. It is coming continues to frequently exist, is commercially available in sufficient purity and is relatively cheap. It's not special corrosive provided a low oxygen concentration is maintained. Its core properties are excellent for fast reactors. Collects in liquid metal-cooled fast breeder reactors the sodium used in the primary circuit takes the heat generated in the reactor core and transfers it in the heat exchanger on a secondary circuit, from where the heat is transported to the steam generators.

However

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However, there is an activation problem with sodium because

22nd

Na is formed by absorption of a neutron and is a high-energy gamma emitter with a half-life of 15 hours. The security system therefore requires expensive biological shielding. In addition, sodium reacts violently with water and is therefore severe Problems with the construction of steam generators for the heat transfer from sodium to water.

Reactor safety is therefore a primary design goal i Due to the above-mentioned characteristics of the Liquid metal coolant, namely sodium, the design must take precautions against the unlikely event meet that a loss of coolant occurs around the reactor core. Such a loss of coolant could occur if the reactor vessel or one of the main lines for the coolant breaks. For this The reason will be a protective container around the reactor and protective devices around the lines that are used to maintain the required level of coolant in the reactor core when a break occurs. In addition, the concrete walls of the security building are made of steel lined to avoid contact between the sodium and the concrete structures if a leak occurs.

Finally, the security building is provided with a massive dome, which is made of a steel shell and thick Concrete walls are made to absorb excess pressure and form a radioactive shield. The required Planning effort, labor and time in construction and what is necessary for adequate maintenance and safety Complexity leads to considerable capital costs of LMR reactors, so that their construction to this day unattractive stayed.

the

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The present invention therefore has the object of specifying a nuclear reactor of the type mentioned above, which reduces the capital costs with constant or improved safety and thus reactor plants with liquid-cooled reactors economically competitive power.

This object is achieved by the invention characterized in claim 1; Refinements of the invention * -. 10 are characterized in the subclaims.

The construction proposed here eliminates the need for a large steel-clad security building To create concrete, which is common in conventional liquid metal cooled reactors, by Adequate precautions are taken against leaks and loss of reactor coolant, and thus against the the resulting high pressure and contamination. The improved construction leads to a reduction of the construction volume in seismic category I by almost half and in non-seismic construction volumes by more than a quarter compared to conventional designs

of liquid metal-cooled reactors. The usage of fewer and simpler systems, smaller buildings and the possibility of a maximum of elements in the Establishing a factory results in lower costs for the reactor plant in terms of equipment, construction materials and labor costs. Additional cost reductions result from the use of foundations with simple straight walls and the elimination of steel cladding.

Another important benefit of this new design is the low cost of security. The security in the reactor plant is achieved through the use of natural processes to ensure a high level of reliability

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and through passive, inherently very safe facilities that provide an additional margin of safety for the reactor plant. The main passive safety features of the improved Reactor plant design includes a large volume of coolant under low pressure, the one Loss of coolant and inadequate heat dissipation are excluded, and safe shutdown also then possible heat dissipation. In addition, there is a special feature in the improved design of the reactor plant Auxiliary cooling system provided for the reactor, the dissipates heat directly from the reactor vessel to the atmosphere through the natural circulation of sodium and air.

In the preferred embodiment, the contains according to the invention Nuclear reactor a system by which heat is released directly from the reactor vessel to the atmosphere The natural circulation of coolant within the reactor vessel and of air around it the exterior of the containment is exploited. The improved structure also includes a concrete envelope for the security container, which also carries the lid. The envelope defines a chamber in the atmospheric air circulates to cool the containment.

In an alternative embodiment, the nuclear reactor further includes circulating pumps and heat exchangers that are attached outside the reactor vessel and the containment, as well as devices with which the pumps and the heat exchangers through the lid and the top of the reactor vessel with the large liquid path are connected. The pumps and the heat exchangers

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exchangers are preferably housed in auxiliary tanks, the end of which is tightly connected to the cover.

Embodiments of the invention will now be explained with reference to drawings. Show it:

Fig. 1 is a schematic representation of the structure of a Reactor system with a conventional liquid metal-cooled fast breeder reactor; The figure

shows the security building with an outer cylindrical steel-clad, made of reinforced concrete existing dome shape arranged around the reactor vessel and an inner one cylindrical, steel-lined and made

Reinforced concrete cladding that surrounds the containment and reactor containment.

2 shows the preferred embodiment in a schematic representation of the present invention with a

improved construction of a reactor system with a liquid metal-cooled reactor.

Fig. 3 in a schematic representation of another embodiment of the present invention with a

improved construction of a reactor system with a liquid metal-cooled reactor.

For a better understanding of the present invention, a brief description of the structure of reactor plants appears according to the state of the art and its disadvantages. Fig. 1 shows in a schematic representation the construction of a conventional reactor system with a typical liquid metal-cooled fast breeder reactor,

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which generally bears the reference number 10. The reactor plant 10 is of the type that is detailed in EPRI Report Number NP-1016-SY, Project 620-26.27, dated March 1979 and entitled "Large Pool LMFBR Design, Executive Summary ". Since the reactor plant is known to be an extraordinarily complex one Structure, only the main components of the prior art reactor plant have been simplified in FIG. 1 Way shown for the proposed here improved structure of the reactor plant of Are interested.

The reactor system 10 according to the prior art is designed according to the so-called "pool" design, in which im essentially a hemispherical reactor vessel 12 contains a large coolant bath (pool), for example from liquid sodium, in which a reactor core 14, a heat exchanger 16 and a circulation pump 18 are housed. The reactor vessel 12 is open at its upper end and is supported by a transversely extending cover 20 held, in turn with its outer retaining ring 22 on a cylindrical side wall 24 made of reinforced concrete rests, which extends from a concrete foundation 26 upwards. On the foundation 26 are still external cylindrical vertical walls 28, 30 and intermediate walls 32, which over numerous horizontal floors 34 with the Sidewall 24 similar to honeycombs are connected to define a plurality of cells 36 in which the various equipment belonging to the reactor are housed.

The reactor system 10 further includes a safety tank or container 38 surrounding the reactor container 12, The sodium-filled reactor vessel 12 is within

of

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of the safety tank 38 suspended so that the container 12 and tank 38 are separated from one another and independent of one another are hung. The container 12 is at its top open end straight to the bottom of the cover 20 connected, for example by a completely continuous bimetallic weld. The lid 20 thus forms a seal for the reactor vessel 12 in order to protect the coolant of the reactor, the cover gas, keep fuel rods and other radioactive materials under lock and key. The safety tank 38 is against it an open tank and has an upper flange 39 with which it rests on a lower annular ledge 42, which is formed in the upper part of the cylindrical side wall 24; the cylindrical side wall 24 forms thereby a reactor interior 40 in which the safety tank 38 is suspended. The flange 39 of the tank is screwed to the support ledge 42 so that vertical lateral loads are withstood. The safety tank 38 serves as a collecting basin for the sodium contained in the primary part of the reactor, which is extracted from the reactor vessel 12 can escape if errors occur. The tank also serves to isolate the reactor core 14 from the side walls 24 and the bottom 2 6 of the reactor interior 40. The space between the reactor vessel 12 and the safety tank 38 is filled with nitrogen gas.

While the reactor vessel 12 is fastened directly to the cover 20, there is between the safety tank 38 and the lid 20 no connection at all. As can be seen from Fig. 1, the upper flange 38 is outside the circumference of the cover 20 and arranged under the outer ring carrier 22, with which the cover 20 on a rests on the upper annular support ledge 44, which is also formed in the upper part of the cylindrical side wall 24

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forms is. So although the reactor vessel 12 and the lid 20 are a first safety barrier between the contents of the reactor vessel 12 and the outside atmosphere, the safety tank 38 actually does not provide any second real safety barrier between the reactor vessel 12 and the outside atmosphere. All sodium, that enters tank 38 from reactor vessel 12 could eventually come into contact with the compound get between the concrete side wall 24 and the outer support ring 22 of the lid 20 or the ledge 39 of the tank 38 and step out.

Since the safety regulations for nuclear reactors require a double safety barrier around the reactor, a concrete security building 46 is provided in the conventional reactor plant 10, in which all of the above-mentioned parts of the reactor system 10 are housed and an outer steel lining 48 contains, which surrounds all parts of the reactor plant. In Fig. 1, the thickness of the cross section is for better illustration of the liner 48 is shown in an exaggerated manner. It should also be noted that in the upper dome 50 of the security building 46 the lining 48 at a distance from the inner wall of the concrete structure of the Building 46 is attached (this is not shown in Fig. 1). In addition, there is 24 on the concrete side walls and an inner steel lining 52 is provided on the concrete floor 26 of the reactor interior. In the representation lies the liner 52 is in direct contact with the interior surfaces of the walls 24,26, in fact however, there is a small gap between the liner and the walls. The distance between the liner 48 and the dome 50 and between the liner 52 and

the

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the walls 24, 26 serve to make heat transfer from the interior of the dome 50 to the concrete structure of the building 46 and from the interior of the reactor interior 40 to the concrete walls 24, 26 more difficult.
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Fig. 2 shows the preferred embodiment of the here proposed improved structure of a nuclear reactor plant, which generally bears the reference numeral 54. In this preferred embodiment of the reactor plant 54 the nuclear reactor itself contains essentially the same basic components as those in the reactor plant 10 can be found according to the prior art, which is shown in Fig. 1: a reactor core 56, a or more circulating pumps 58 and one or more heat exchangers 60. Also similar to reactor systems According to the prior art, the reactor system 54 includes a reactor vessel 62 for the large bath 64 liquid coolant under low pressure, for example liquid sodium, in which the reactor core is also located 5 6 is housed. In the preferred embodiment, the circulating pump 58 and the heat exchanger 60 are located also in the coolant bath 64. The reactor system 54 according to the invention contains a safety container 66 with the associated suspension, which differs significantly from the previous one for the safety tank.

The realization that the type of installation of the safety tank is the main cause of the complex and expensive safety structures led to a different solution: the boundary of the security area became as close as possible approximated to the nuclear reactor and as far as possible passive natural processes were used to a to achieve high reliability and higher security. In the present invention, the security container delivers 66 in addition to the first safety lock,

the

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represented by the reactor vessel 62 between the coolant 64 and the outside atmosphere, a second Safety barrier between the reactor vessel 62 and the outside atmosphere. The outer containment 66 surrounds the entire inner reactor vessel 62 at a certain mutual distance. About every exit to render the liquid coolant from the reactor vessel 62 in the containment 66 harmless, the space between the two containers is filled with a non-reactive gas, for example nitrogen.

The reactor vessel 62 and the containment vessel 66 are both at their open upper ends 68 and 70 by a lower plate 72 of a cover 73 of the improved Reactor installation 54 supported and sealed.

The top plate 72 has an annular notch 74 into which the upper ends 68,70 of the containers 62,66 fit and connected to plate 72 in a suitable manner, for example by welding. To this Thus, the top plate 72 completes the first and second security barriers formed by the containers 62, 66, by closing and sealing their upper ends. The tightly closed containment 66 thereby ensures that the sodium level in the reactor vessel 62, even if a leak occurs therein cannot fall below the minimum safe level required in reactor vessel 62.

In the improved reactor assembly 54, the lid 73 further includes two separate compartments 76, 78 which pass through a wall 80 are sealed against each other. The lower compartment 76 contains a non-reactive gas such as Nitrogen, which improves the effectiveness of the seal, provided by the cover plate 72 for the containers

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ter 62, 66 is formed. The lower compartment 66 also contains the upper portions of the pump 58 and heat exchanger 60 that extend into the upper compartment 78.
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The double safety lock that is now available, through the inner reactor vessel 62 and the outer Protective container 66 is formed together with the lower plate 72 and the compartment 76 of the lid 72 which holds the container carries, a reactor interior or a reactor chamber 82 can now be used to cool the protective container 66 will; this reactor chamber 82 is formed by a concrete casing 83 which consists of the side walls 84 and the foundation 86 of the reactor plant 54. As shown in Fig. 2, the envelope 83 in its Sidewall 84 has upper and lower openings 88, 90. A fan 92 is connected to the lower opening 88, with the cool ambient air of the outside atmosphere being blown into the chamber 82 while at the top opening 90 a vent 94 is connected in order to remove the warm air from the chamber 82. As an alternative, however, can also a free air circulation through natural thermal Circulation can be provided so that no fan is then necessary. In this way, atmospheric air can be passed through the chamber 82 to cool the containment 66. The side wall 84 of the concrete envelope 83 is also used with its upper end to hold the cover 72.

The preferred embodiment of the improved reactor plant in Fig. 2 is referred to as a "pool" type, since the reactor core 56, the circulation pump 58 and the Heat exchangers 60 are all housed within the large coolant bath 64 in the reactor vessel 62. One

other

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Another embodiment of the improved reactor system is shown in FIG. 3 and indicated generally at 96. This type belongs to the so-called "loop" design, in which the circulation pump 98 and the heat exchanger 100 are arranged outside of the reactor vessel 102 and the containment vessel 104. Corresponding lines 106 and 108 connect the pump 98 and the heat exchanger 100 to the large coolant bath 110 in the reactor vessel 102 through the lid 112 and the top of the container

102. Similar to lid 73, lid 112 includes upper and lower compartments 114, 116 that are separated from one another by a Wall 118 are sealed. The connecting lines 106, 108 run through the lower compartment 114 of the lid 112. As in the previous case, the lower compartment 114 contains a non-reactive gas. In addition, the pump is 98 and the heat exchanger are each housed in their own containers 120, 122, which are supported by a lower plate 124 of the Lid 112 are supported and sealed. A chamber 132 is delimited by a cylindrical concrete envelope 126, which consists of the foundation 130 and the cylindrical side wall 128, at the upper end of the cover 112 rests. Similar to the chamber 82 in the embodiment described above, the chamber 13 receives 2 cold ones atmospheric air blown with a fan 136 through a lower opening 134 in the wall. The air circulates in the chamber, absorbing heat from the safety container 104 and the auxiliary container 120, 122 and exits through an upper opening 138 in the wall. The hot air is through a pipe 140, which with the top port 138 is passed to a suitable blow-off point.

the

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Figures 2 and 3 clearly show that the proposed improved structure of a nuclear reactor plant obviates a significant part of the concrete and steel lining structure, and therefore also the complexity and the cost of liquid metal-cooled reactor systems compared to known ones Plants considerably reduced. Instead of the expensive security building made of concrete, a Steel structure to be constructed at a lower cost can be used to accommodate the improved reactor facility.

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Claims (10)

10 PATENT CLAIMS Nuclear reactor with a reactor core (56) in a coolant bath (64) of low pressure, for example liquid Sodium, within a reactor vessel (62) having a top end (68) and a first safety barrier forms between the coolant and the external atmosphere, characterized in that a safety container (66) is provided which surrounds the reactor vessel (62) and has an open top end (70), and that a lid (78) is provided, the upper open end (68) of the reactor vessel and the upper open end (70) of the containment seals tightly, so that the security container has a second security barrier between the Coolant and the external atmosphere. 2. Nuclear reactor according to claim 1, characterized in that the containment (66) is at a distance from the Has reactor container (62) which is filled with a non-reactive gas. 3. Nuclear reactor according to claim 1 or 2, characterized in that the cover (73) upper and lower compartments (78, 76), which are sealed from one another, and that the lower compartment (76) with a non-reactive gas is filled. 4. Nuclear reactor - 2 - WS425P-2925 4. Nuclear reactor according to claim 3, characterized in that that the lower compartment (76) contains equipment for operating the reactor. 5. Nuclear reactor according to one of claims 1 to 4, characterized in that a system for circulating air around the exterior of the containment (66) is provided. 6. Nuclear reactor according to one of claims 1 to 5, characterized in that circulating pumps (58) and heat exchangers (60) are provided, which are arranged in the coolant bath (64) within the reactor container (62). 7. Nuclear reactor according to one of claims 1 to 5, characterized in that at least one circulating pump (98) and a heat exchanger (100) is arranged outside the reactor vessel (102) and the containment vessel (104), and that devices (106, 108) are provided with which the pump (98) and the heat exchanger (100) with the Coolant bath (110) connected by the lid (112) and the upper end of the reactor vessel (102). 8. Nuclear reactor according to claim 7, characterized in that the upper and lower compartments (116, 114) of the Cover (112) are sealed against each other and that the devices for connecting the pump (98) and the Run the heat exchanger (100) with the coolant bath (110) through the lower compartment (114) of the cover (112). 30th 9. Nuclear reactor according to claim 7 or 8, characterized in that additional containers (120, 122) for receiving - 3 - WS425P-2925 would take the pump (98) and the heat exchanger (100) provided are, and that the additional containers (120, 122) are sealed by the lid (112). 10. Nuclear reactor according to one of claims 1 to 9,
characterized in that the security container
(66, 104) is surrounded by a concrete envelope (83, 126) which carries the lid (73, 112), and that the envelope defines a chamber (82, 132) in which atmospheric air is circulated around the containment (66 , 104) to cool.