FR2702301A1 - Arrangement for the protection of a nuclear reactor in the event of a core meltdown. - Google Patents

Abstract

Arrangement for protecting a nuclear reactor (1) in the event of core meltdown, comprising a collecting device (3) installed below the resistant casing (2) of the reactor, and a cooling system (4) for the corium collection. The collecting device (3) is a structure made from shell elements made of cast iron and / or steel in a crucible which form a flow system (5) and a collecting system (6) for the effluent corium. The shell elements comprise cooling channels connected to a cooling system (7) by thermosyphon (12, 13, 14). The thermosyphon cooling system (12, 13, 14) forms a circuit. The mass of cast iron and / or steel in the crucible is calculated in such a way that it is capable of absorbing the heat of fusion of the effluent corium for at least the period of time necessary before the cooling system by thermosiphon (12, 13, 14) provides sufficient heat dissipation through its thermosyphon effect.

Description

The invention relates to an arrangement for the

  tection of a nuclear reactor in the event of core melting, comprising a collecting device installed below the resistant casing of the reactor and intended to collect the corium leaks, and a cooling system for the collected corium The term corium designates the molten material which flows during a melting of the core, i.e.

  a mixture of uranium, zircaloy steel and other elements.

  In the well known arrangement which constitutes the

  starting point of the invention (DE-PS 2 035 089), the provision

  sitive collector is an open collecting basin with a

  flat bottom, side walls and cooling pipes

  recessed part of the cooling system

  The collecting basin is made for example of steel,

  but it may also include fusible lead for di-

  lute the corium The conformation and the arrangement are chosen in such a way that, as soon as the corium comes into contact with

  the bottom of the pool, the heat is transferred to the return water

  cooling pipes cooling

  cooling evaporates and the steam is evacuated

  point, it does not use a thermosiphon effect.

  Rather, it is evaporative cooling with

  steam ejection The cooling system

  therefore takes on the one hand a cooling water tank with connection to the cooling pipes and, on the other hand, a steam separator, a connection pipe being provided between the steam separator and the cooling water tank The surface of the collecting basin

  must be large enough so that the corium which re-

  pand forms only a thin layer which solidifies quickly-

  in contact with the cooled bottom of the collecting basin.

  The collecting basin has dimensions such that it

  thus solidifies all of the effluent corium.

  An implementation of the thin film technology described involves the implementation of well-known measures, also from a spatial aspect. This also applies

  in case the cooling pipes are fitted with ele

  elements which increase the active surface for heat transfer It is not planned to build the system from

prefabricated elements.

  The object of the invention is to create an arrangement of the aforementioned type and intended for the application described above which is assembled from prefabricated elements.

  To this end, the invention relates to an agency-

  for the protection of a nuclear reactor in the event of core meltdown, comprising a collecting device arranged

  below the resistant reactor vessel and intended to re-

  to receive, in the event of core melting, the corium flowing, and a cooling system for the collected corium, realizing the combination of the following characteristics: a) The collecting device is a structure made from shell elements in cast iron and / or steel in the crucible which form a flow system and a collecting system for the effluent corium,

  b) the shell elements include return channels

  cooling connected to a thermosyphon cooling system, c) the thermosyphon cooling system forms a circuit,

  the mass of cast iron and / or steel in the crucible being cal-

  abutment in such a way that it is able to absorb heat

  their corium fusion effluent for at least the lapse

  of time that is required before the cooling system

  In the context of the invention, the term shell is used in the sense of the foundry technique In the sense of the technique of thermosiphon ensuring sufficient heat dissipation by thermosyphon effect

  foundry, a shell is a metal mold, the most

  wind made of a special alloy for ingot molds, for casting molten metal materials, and shell casting designates a corresponding casting process It is essential that when pouring the material in the molten state, the material of shell does not melt This one and the thickness of the shell wall are chosen such

  way that the heat of fusion is absorbed without the co-

  keel is destroyed by fusion phenomena According to

  the invention, corium is the metal in the molten state.

  prefabricated shell parts are fitted into the

  sitive collector and assembled in shells or co-

  already completed keels are assembled in a co-

  bowling The term shell also includes casting tubs The arrangement has the effect that the contents of the shells, that is to say the corium and respectively the corium

  solidified are at suitable distances from the agen-

  cement considered in its total volume so as to prevent any hypercritical state The shell elements are

  made of suitable materials as they are commonly used

  used for foundry shells The collecting device can correspond to a system of foundry shells The invention takes advantage of the fact that the shells

  used today in foundries can receive without pro-

  pale for example melting slag at a temperature

  from 1600 to 18000 C and respectively from industrial products

  chemical sorting at a temperature of around 22000 C without destroying the shell structure, for example as a result of uncontrolled melting processes The volume or the

  mass of the shell material are large enough

  On the basis of these preconditions, it is

  It is essential for the invention that the mass of cast iron and / or steel in the crucible is sufficient to be able to absorb the heat of fusion of the effluent corium at least during the

  time required before the cooling system

  thermosiphon can dissipate an amount of

  sufficient heat through a thermo-effect

  siphon This is obtained by the fact that the heat

  dual produced due to the presence of radionuclides can be dissipated over a long period, in the order of magnitude of about 0.1% of the thermal power of the atomic power station, until the start of suppression

  from the nuclear power plant or until the heat

  sidual produced at a later time due to the

  thermal conductivity of the arrangement can be dissipated

  in the environment Regarding the layout

  according to the invention, the cooling channels are generally

  are actually filled with water and the whole system is somewhat at rest at the time of the incident As soon as the

  hot corium reaches the shell system, the fluid

  the carrier heats up, and taking into account the different density

  rent or, in other words, the resulting rising force, the heat transfer fluid rises in the groups of the thermosyphon cooling system located at

  higher levels The energy produced is ceded to the envi-

  ron for example via heat exchangers The thermosyphon cooling system can operate with water or with air In the context of the invention, the term system designates an ordered entity to perform the function planned of the whole We mean by

  thermosyphon effect the fact that the cooling system

  The thermosyphon operation works by means of thermal rising forces The fact that, in accordance with the invention, the thermosyphon cooling system forms a closed circuit does not exclude the possibility of refilling the cooling water if leaks cannot be avoided It goes without saying that the collecting device is designed to receive the

all of the effluent corium.

  In detail, the invention offers several possibilities.

  Tees of realization and configuration It is thus, that a part of the shell elements can be assembled in a flow dome of conical shape, and this with an axis of the dome oriented coaxially to the axis of the resistant box of the reactor. Likewise, the dome can be cast in one

  piece In addition, the shell elements can also

  also be made in the form of containers and / or as-

  appear in containers and form the volume (s) col-

  collector system reader (s) In accordance with an embodiment of the invention to which preference has been given, the shell elements are produced, where appropriate, in the form of plates of cast iron and / or steel with integrated cooling channels and / or pipes, arranged for example as bottom plates of the collecting system A particular advantage is the

  possibility of using co-

  Foundry keels and / or ordinary casting tubs.

  As already mentioned, the cooling system

  thermosyphon can work with water or

  with air According to the invention, the cooling system

  thermosyphon constitutes a cooling water circuit

  closed dissement with outside air cooling tower

  equipped with a suitable heat exchanger.

  The following description, with reference to the

  sins annexed by way of nonlimiting examples, will make it possible to understand clearly how the invention can be implemented

convenient.

  FIG. 1 represents the diagram of a nuclear reactor with the arrangement for protection in the event of core melting; Figure 2 shows, on a larger scale, a detail of the object of Fig 1; Figure 3 shows a sectional view along line A-A of the object of Fig 2; FIG. 4 represents a sectional view along line B- B of the object of FIG. 2, and FIG. 5 represents, in accordance with FIG. 1,

  a diagram of another nuclear reactor according to the invention.

  A comparative examination of Figs 1 to 4 shows

  the details of an arrangement according to the invention for the pro-

  tection of a nuclear reactor in the event of core meltdown.

  Fig 1 shows the nuclear reactor 1 with the resistant casing 2 of the reactor Below the resistant casing 2 of the reactor is installed a collecting device 3 for the corium flowing in the event of melting of the core In addition, a cooling system 4 is provided for corium

collection.

  It emerges from a comparative examination of FIGS 2 to 4 that the collecting device 3 constitutes a structure produced from shell elements which in turn are made of cast iron and / or steel in the crucible They form a system 5 and a collector system

  6 for effluent corium The shell elements include

  tent cooling channels 7 which are connected to a cooling system by tnez ^ mosiphon 12, 13, 14 Le

  thermosyphon cooling system forms a cir-

  cooked. The mass of cast iron and / or steel in the crucible of the whole arrangement is calculated in such a way that it is capable of absorbing the heat of fusion of the effluent co-rium at least during the lapse of time required before the thermosyphon cooling system 12, 13, 14 ensures sufficient heat dissipation through its thermosyphon effect It goes without saying

  that, moreover, sufficiently large distances are realized

  in the entire volume of the arrangement to prevent

  any hypercritical state of the effluent or spent corium.

  In the example of embodiment and according to the mode of

  realization of the invention to which preference has been given

  dée, part of the shell elements is assembled in a flow dome 8 of conical shape, the axis of the dome being

  oriented coaxially to the axis of the resistant box 2 of the reac-

  In addition, the shell elements are shaped

  in containers and / or assembled in containers, so as to form

  sea of the collecting volumes 9 of the collecting system 6 From

  more, in the embodiment, elements of co-

  keels are made in the form of cast iron and / or steel plates 15 with cooling channels 10 and / or integrated cooling pipes, and arranged as bottom plates 11 of the collecting system 6 In

  principle, it is also possible to use as an-

  shell parts foundry shells and / or basins

  ordinary casting quets which are then installed and

  arranged in such a way that in the region of the volumes col-

  drives 9 shown in the figures they are flooded and

  filled with molten corium.

  In the embodiment, the system of re-

  thermosyphon cooling 12, 13, 14 forms a closed cooling water circuit with external air cooling tower 13 in which the heat transfer

  between the cooling water and the air is effected by the

  through a heat exchanger.

  The embodiment according to FIG. 5 is easily understood with the references indicated and ex-

  The shell elements here consist of pouring tubs 16 which are arranged one next to the other and equipped with distribution elements 17 for the corium.

Claims (4)

  1 Arrangement for the protection of a reactor   nuclear (1) in the event of core meltdown, comprising a dis-   positive collector (3) installed below the reflector box   sistant (2) from the reactor and intended to collect the corium   flowing in case of core melting, and a system of re-   cooling (4) for the collected corium, which achieves the combination of the following characteristics: a) the collecting device (3) is a structure made from shell elements made of cast iron and / or steel in the crucible which form a flow system   (5) and a collecting system (6) for the corium ef- fluent,   b) the shell elements include return channels   cooling (7) connected to a cooling system   thermosyphon (12, 13, 14), c) the thermosyphon cooling system (12, 13, 14) forms a circuit,   the mass of cast iron and / or steel in the crucible being cal-   abutment in such a way that it is able to absorb heat   their corium fusion effluent for at least the lapse   of time that is required before the cooling system   thermosyphonization (12, 13, 14) ensures dissipation   sufficient heat from its thermosyphon effect.   2 Arrangement according to claim 1, wherein shell elements are assembled in a dome   flow (8) conical.   3 Arrangement according to one of claims 1   or 2, in which shell elements are shaped into containers and / or assembled into containers and form   manifold volumes (9) of the collector system.   4 Arrangement according to one of claims 1 to   3, in which shell elements are made in the form of plates of cast iron and / or steel with   cooling channels (10) and / or cooling pipes   integrated divider, and arranged as bottom plates (11) of the collector system.   Arrangement according to one of claims 1 to   4, in which ordinary foundry shells and / or pouring buckets are used as co-   bowling. 5 6 Arrangement according to one of claims 1 to   4, in which the thermosiphonic cooling system (12, 13, 14) forms a cooling water circuit   closed with outside air cooling tower.