FR2463886A1 - PROCESS FOR DISPERSING LOCAL GAS CONCENTRATIONS IN OVERLAY LAYER ATMOSPHERES - Google Patents

Abstract

THE PRESENT INVENTION CONCERNS A PROCESS FOR DISPERSING LOCAL CONCENTRATIONS OF GAS IN STACKED-LAYER ATMOSPHERES IN CLOSED OR SUBSTANTIALLY CLOSED SPACES, SUCH AS, FOR EXAMPLE, CONVEYOR CASTLES IN REACTORS. PROCESS CHARACTERIZED BY THE FACT THAT A DISTURBANCE OF THE BALANCE IN THE STRATIFIED ATMOSPHERE IS PRODUCED BY A LOCAL CHANGE OF DENSITY IN A REGION OF AN ATMOSPHERIC LAYER, THEREFORE THAT THE ATMOSPHERE IS SUBJECT LOCALLY TO A DUE ACCELERATION TO CHANGE IN DENSITY, DIRECTED VERTICALLY, AND PRODUCING CONVECTION.

Description

The present invention relates to a method for dispersing

  local concentrations of gas in atmospheres

  superimposed layers in closed spaces or

  normally closed, such as transport casks in reactors. In both free atmospheres and in

  atmospheres in enclosed spaces can occur

  to make provisions by relatively stable thermal layers and /

  or provisions by layer of the mixture. the formation of

  atmospheric effects result from differences in the density of cer-

  some components or mixtures at different temperatures

  and can be further favored depending on the construction of the building.

  These differences are offset only slowly by

  transferred, the speed of the compensation process decreases

  with the attenuation of differences in concentration.-In the case of subdivided buildings, this method of compensation

  can be slowed down by locally diminished sections.

  It is known that the formation of superimposed atmospheres can be prevented or that the removal of a layered arrangement can be achieved when at least one mixture in the atmosphere is produced in certain regions. In this way, the formation of local concentrations of gas is prevented. To achieve the proper mixing, use is made, for example, of fans, blowers, air circulators or similar devices, which always require

  a motorization and that require a lot of space.

  Of particular importance is the prevention of

  local gas centrations, respectively the dissipation of local concentrations of gas., in the case of an accident by loss of the coolant in the transport cask of a reactor. If such an accident occurs, molecular hydrogen and oxygen may occur by radiolysis in the cooling fluid. For safety requirements, it is necessary to suppress local concentrations of oxygen

released.

  After a loss of coolant accident, a stratified thermal atmosphere occurs in, for example,

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  a pressurized water reactor, in which an inferior layer

  relatively cold atmosphere is superimposed

  atmospheric layer significantly warmer.

  In order to disperse a local hydrogen concentration, the hitherto known measurements envisage the use of circulation bellows and / or of recombiners. A mixture of different atmospheric layers must be obtained

  bellows, the local concentrations of

  the dispersing hydrogen. The recombiners oxidize free hydrogen, for example, by catalytic combustion with oxygen and thus reduce the hydrogen content of the hydrogen.

  the atmosphere that is driving them.

  Both measurements are technically complicated

  expensive because the devices must be equipped with

  specific to this type of accident, depend on a food

  appropriate energy and can not be arranged in any way. In addition, it is not yet clear where in the castle transport it would be most advantageous to dispose of them. This concerns

  especially the local position of the vacuum opening

  ration and return. If it is located in the area

  superior of the castle-of transport, as in some

  existing plants, it must be ensured that, for example, the hydrogen released by the rupture of the pipe which is in

  low, arrives well at the opening of spiration.

  As a further disadvantage is the fact that it can not be ruled out that these devices lose their effect in the event of a technical malfunction or if they themselves act as an unwanted ignition source for

  the atmosphere containing hydrogen in the castle of trans-

  Harbor. If these devices are located outside the transport castle, this is important with regard to safety considerations, as each penetration of the transport castle represents an increased risk of failure of the transport castle, especially when the penetrations and the isolation valves must have significant dimensions

  in the case of bellows or recombiners placed in the

  because of the required gas flow.

  In the case of an arrangement of the apparatus in

  of the transport castle, which is not possible in all cases, it must be taken into account that the transport castle can not be used after an accident.

  loss of coolant due to fis-

  released, or only under special security measures and for a short period of time, so that repairs can not be accomplished or

only with difficulty.

  A further disadvantage of these known measurements is the fact that existing reactors can not be equipped or with difficulty with these devices. The object of the invention is to provide a method for dispersing gas concentrations in layered atmospheres. superimposed, which is safe and easy to apply, as safe as possible in the event of an accident or breakdown, and

  costly, which can be applied to existing reactors.

  * The process according to the invention is characterized in that

  disturbance of equilibrium is produced in the atmosphere.

  phère stratified by a local change in density in a

  region of an atmospheric layer, with the result that the

  mosphere is locally subject to acceleration due to density change, directed vertically, and producing a convection. According to the method relating to the invention, it is possible, in a simple and safe manner, to dissipate local concentrations of gas, since a disturbance is produced in

  the stratified atmosphere, which undermines the balance of this

  at least locally, so that a volume of gas is subject to upward or downward acceleration,

  which generates a convection current.

  If a first atmospheric layer with a first

  Specific density is superimposed by a second layer

  mospheric with a second specific gravity, the first

  density being lower than the second specific density

  specific, disturbance of the equilibrium can be obtained

  either in the first atmospheric layer or in the second

  atmospheric layer x, simultaneously in both

atmospheric layers.

  Subsequently, the atmospheric layer with density

  lower specific is indicated as the atmospheric layer.

  light and that with the higher density

  as the heavy atmospheric layer.

  If we now introduce into the region of the atmos-

  light gas a heavy gas, so that a change in density of

  the light atmosphere ensues such that the heavy atmosphere

  come at least locally heavier, it manifests in this localized region an acceleration directed downwards,

  so that a downward flow is born. This disturbance

  As a result of the downward direction of the downward flow, a current flows upwards into another part of the atmosphere, so that a convection occurs in the total atmosphere. As a result, a mixture of the gas of the first atmospheric layer occurs with the gas of the

second atmospheric layer.

  The birth of a convection current can be ac-

  tive in this case by the fact that a light gas arrives at

  in the heavy atmosphere essentially simultaneously with the introduction of heavy gas into the

  place that is horizontally displaced from the place of in-

  troduction of the light atmosphere. The specific density of the heavy atmosphere is diminished by the introduction of a. gas

  light, since the new specific density results from

  Aunt is smaller than that of the light atmosphere,

  in this region, there is a rapid acceleration of

  upwards, which results in a

Ride up.

  If a heavy atmosphere superimposes a light atmosphere

  manages, a convection current can then be produced by introducing

  releasing into the heavy atmosphere a gas of such specific density that at least a specific gravity occurs locally in the region of the heavy atmosphere such that either the boundary layer between the two atmospheric layers is broken and gas the atmospheric layer, or that first of all under the conservation of the layered arrangement of the atmospheres, the total atmosphere is rotated, with the result that the region

  in which the heavy gas is introduced down.

  In this case also, the birth of a convection current can be activated by the fact that a light gas is introduced in another region of the light atmosphere, so that there, because of the thrust of this light gas , layer

  heavy atmospheric is pushed upwards.

  According to this invention, density changes in the atmospheric layers, which are necessary to produce an imbalance, may be caused by driving, or

  by drawing a quantity of heat instead of the introduc-

  gas. A smaller density is obtained in a

  region by heating, and a higher density by cooling

ment.

  Depending on which gases are composed of

  atmospheric gases, different gases may be introduced

  successively. If a convection current has already taken

  this stream may, for example, be maintained as an intro-

  Giving a gas continuously or at intervals. The

  gas must have a density such that it. be subject in the atmosphere

  total phere at an acceleration such that it is not opposed to the direction of the convection current, because otherwise the current

  convection is slowed or even removed.

  Inert gases are particularly suitable for carrying out the process of the invention. An advantage is, in this case, that no chemical reaction occurs between such a gas and other gases in the atmosphere. In addition, .the instruments

  or devices in space, in which the

  mosphere is locked up, not attacked or damaged by

  chemical reactions of an inert gas.

  If the process relating to this invention is provided, for example, for the transport cask of a reactor, wherein

  a cooling system can generate hydro-

  molecular gene that comes out of the coolant pipe

  In the transport cask, if a rupture occurs, the gas can advantageously be introduced directly into the coolant pipe. The advantage is that the gas can be brought immediately to the place where the hydro-

gene comes out.

  It is then assumed that the process according to the invention is to be applied to a reactor. The introduction of a gas into the

  region of an atmospheric layer can be practiced without

  ficulty from the outside of a transport castle, because only

  openings and ducts of a small section are required

  in the wall of the transport castle. Since no

  In this case, the process according to the invention is very necessary. In particular, no element is necessary, which can act, if necessary, as a source of ignition for hydrogen, as may be the case, for example, engines for the bellows circulation. As a further advantage of this process according to the invention is added the fact that

  it can also be placed in reactors already

tives.

  But the process is also safe and reliable if the

  necessary density is obtained in the atmosphere layers.

  by adding or drawing heat. In one

  such case, it is sufficient to provide heat exchangers.

  These heat exchangers can be fed from outside the transport castle with a medium that is at the desired temperature. The methods according to the invention can also, if desired, be used with recombiners disposed inside or outside the reactor. In this case, it is produced by means of the processes according to the invention, a transport of atmospheres containing hydrogen from the place of exit,

  that is, for example, from the breaking point of the con-

  primary coolant withdrawal to the recombiners.

  These methods can be applied at the same time or successively. The process by which a gas is introduced to change (the specific gravity of an atmospheric layer will be described by way of example with reference to a loss of cooling fluid accident in the transport cask of a

  reactor, with reference to the figure in which is shown

  a pressurized water reactor schematically in section. A reactor transport vessel is indicated by

  reference 13 in the figure. The interior of the castle of

  port is divided locally by dividing walls, delimiting

  so spaces 2 to 100 Each of the spaces is in communi-

  nication with at least one neighboring space through the communication openings. In spaces 3, 5, 8 and 4, 7, 10 are placed

  DE steam generators, which are in communication with the

  primary coolant 14 with a pressurized cellar reactor RDB, which is arranged in the space 9. By reference 1 is indicated the place in which a

  rupture occurred in the primary fluid line of

froidissement.

  Gas introduction pipes 11 and 12 are

  views, which open inside the castle 13 of the reactor.

  In each of spaces 8 and 10 ends a pipe 11 for introducing gas. The introduction pipes 12 are arranged in the upper zone of the reactor castle 13 and

  serve for the introduction of gas into space 2.

  Due to the experiences of the transport cask, it is known that in a long time field, that is to say after hours or even days, after the accident due to loss of coolant is arrived, a thermal arrangement by atmospheric layers in the castle can be expected. The atmosphere then presents in the upper zone of the transport castle a temperature much higher than the atmosphere located in the lower zone of the castle.

  transport. We are therefore dealing with the case of a thermal inversion.

  It is also conceivable that it occurs in exceptional cases.

  frames a warmer layer between the lower and upper atmospheric layers. This warmer layer would have the effect of a thermal boundary layer0

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  After an atmospheric layer arrangement has been formed, the atmospheres of each space, interconnected by the communication apertures, show no noticeable pressure difference. Due to the lower temperature of the existing atmospheric layer in the lower zone of the transport cask, it has a specific density greater than the warmer atmospheric layer. This means that, according to the laws of physics, the lowest temperature atmosphere would be subject to an opposite "isolation acceleration" if it tried to mount against the inverse layered arrangement due to temperature. thermal insulation can be overcome if the specific gravity of the deep atmospheric layer is

  smaller than that of the upper atmospheric layer.

  Such a state could be achieved by sufficient enrichment

  of hydrogen introduced by the accident case because of a

  loss of coolant. Under the conditions to

  in relation to the different temperatures of the cou-

  Atmospheric conditions should result in a concentration of hydrogen in the lower layer, which should be avoided for safety reasons. The limit in respect of the safety requirements is reached at 4% volumetric, that is to say by

  the lower limit of inflammation or explosion.

  According to the invention, in the present example, the density of the lower atmospheric layer is at least locally reduced insofar as the thermal insulation effect can be overcome so that the hydrogen is distributed in a larger volume. before the hydrogen concentration

  in the lower region of the transport castle or the

  The lower atmospheric air has reached a large undesired value.

  This takes place in the case of this example according to the

  by introducing a light gas, preferably inert, such as, for example, helium, into the lower spaces of the

  transport castle, spaces 8 and / or 10. By this means, the

  the lower atmospheric layer is reduced, that is

  that is to say that this atmosphere receives in comparison with the total system an increasing thrust by the rise resulting from the concentration, which finally can overcome the acceleration

  thermal insulation and thus prepare a convection corres-

  ponding. The convection thus produced would take the form of a cylinder or roll which preferably passes through the

pages 3, 5, 8, 9, 10, 7, 4 and 2.

  As long as a stratified atmosphere is present

  the lower atmospheric layer filling, for example, the spaces 5 to 10 and the upper layer the spaces 2 to 4 of the transport castle, a convection through the spaces 4, 3 and 2 is excluded without taking additional measure for a

  long time, because the thermal layering is stable.

  In the lower atmospheric layer itself, however, a convection current can be introduced through the spaces 7, 6, 5, 8, 9, 10. But by this convection current would not arrive

  that a mixture within the lower atmospheric layer

  in which the hydrogen is released into the space 100. In the lower atmospheric layer, therefore, hydrogen concentrations can be established, of which

  the value exceeds the accepted safety value of 4% volum-

  cudgel. Instead of the introduction of a light inert gas such as, for example, helium, it is also possible to take into consideration

  the introduction of water vapor. It would be possible by using

  the introduction of an inert gas in addition to heating, to suppress the temperature inversion produced in one place, or at least to reduce it, so that the difference in density present, locally due to hydrogen, water vapor and / or inert gas, would result in a corresponding convection formation

  of the current, where a convection cylinder would be formed

  to spaces 3, 5, 8, 9, 10, 7, 4 and 2.

  The technical implementation of the method according to the invention is not related to any remarkable difficulty. It is only essential that means be provided by which the desired gas can be conducted to the atmosphere within the transport cask in prescribed locations. Such means can be

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  legconduits 11 and 12, which are connected to a gas source

  which is outside the reactor transport castle.

  Such a gas source may be constituted by gas bottles, in which the gas is normally located, under a large pressure in the liquid state. storage of such stores

  gas bubbles is no problem because, especially

  if it is an inert gas such as helium, no risk is to be feared. The necessary control means such as valves, valves, etc. may be provided outside the transport castle, so that no safety measures

  particular technique is to be considered.

  It is also possible to envisage adding an inert gas such as helium by means of cooling, for example, in the cooler for the residual heat dissipation, or in the vicinity of the pumps for the residual cooling,

  etc., because in the event of an accident of loss of coolant

  the gas will be carried by the coolant to the point where the break occurred in the

cooling fluid.

  The timing and duration of a single or repeated introduction

  gas may be determined in any case by

  existing system for the control and monitoring of the

  temperature and hydrogen concentration.

  It is also conceivable to dispose of the gas source itself, that is to say, for example, helium cylinders, inside the reactor transport cask, measures to be taken, however, to avoid damage to the gas cylinders and their associated valves and ducts, in the event of a loss of fluid accident

  cooling. The advantage lies in this case in that

  a break in the wall of the transport castle is not necessary.

  sary. In many cases, however, pipes are already in existence for test purposes (for example, for H12 measurements), which penetrate the transport cask and

  can be used for the introduction of a gas.

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Claims (20)

- R E V E N D I C A T I 0 N S -   A method for dispersing local concentrations of gas in layered atmospheres in closed or substantially closed spaces, such as reactor transport casks, characterized by the fact that   disturbance of the equilibrium in the atmosphere is   stratified by a local change in density in a region of an atmospheric layer, causing the atmosphere to be locally subject to vertically directed acceleration due to density change, and producing a convection.   2. Method according to claim 1, characterized by   the fact that the change in density is produced by the   troduction of a gas in this region.   3. Method according to claim 1, characterized in that the local-density change is produced by a change in the temperature of the atmosphere in this region.   4. Process according to at least one of the claims   1 to 3, characterized in that the local change of density is produced simultaneously or successively   in two regions at horizontal distances.   Method according to claim 2, characterized in that the region in which a local change of   density is produced lies in a first atmospheric layer   phérique with a first density, which is superimposed on a second atmospheric layer with a higher density and a gas with a density is introduced in this region,   which is larger than the density of the second atmospheric layer pheric.   6. Method according to claim 2, characterized in that the region in which a local change of   density is produced lies in a second-layer atmosphere   phérique with a second density, which is superimposed by a first atmospheric layer with a lower density, and that a gas is introduced into this region with a higher density.   small than that of the first atmospheric layer.   7. Method according to claim 2, characterized in that the region in which a local change of   density is produced lies in a first atmospheric layer   phérique with a first density, which is superimposed on a second atmospheric layer with a lower density, and that a gas is introduced into this region with a density   larger than the density of the first atmospheric layer.   8. Method according to claim 2, characterized in that the region in which a local change of   density is produced lies in a second layer atmospheric   phérique with a second density, which is superimposed by a first atmospheric layer with a higher density, and that a gas is introduced into this region with a higher density   small as the density of the second atmospheric layer.   9. Process according to any one of the claims   2 or 5 to 8, characterized in that the gas is a mixture gas.   10. Process according to any one of the claims   2 or 5 to 8, characterized in that different gases are introduced simultaneously or successively in at least one of the atmospheric layers.   11. Process according to any one of the claims   2 or 5 to 10, characterized in that the introduced gas contains an inert gas.-   12. Process according to claim 11, characterized by   the fact that lelélium is used as an inert gas.   13. Process according to any one of the claims   2 or 5 to 10, characterized in that steam is used of water as gas to introduce.   14. Process according to any one of the claims   2 or 5 to 13, characterized in that in a reactor transport cask, the gas to be introduced is introduced into   the coolant line of a cooling system dissement.   15. Process according to any one of the claims   2 or 5-to 13, characterized in that the gas is introduced through lines for the test portions in the castle of 13 2463886 reactor.   Process according to any one of the claims   2 or 5 to 12, characterized in that the temperature of a gas introduced into an atmospheric layer is greater than the temperature of this atmospheric layer.   17. Method according to any one of the claims   2 or 5 to 12, characterized in that the temperature of the gas introduced into an atmospheric layer is lower than   the temperature of this atmospheric layer.   18. Process according to claim 3, characterized by   the fact that the region in which a local change of den-   sity is produced is in a first atmospheric layer.   that with a first density that is superimposed on a second atmospheric layer with a higher density and that the   heat is drawn from this region.   19. The method of claim 3, characterized by   the fact that the region in which a local change of den-   sity is produced is in a second atmospheric layer   only with a second density, which is superimposed   first atmospheric layer with a lower density, and that   heat is added to this area.   20. Process according to claim 3, characterized by   the fact that the region in which a local change of den-   sity is produced is in a first atmospheric layer   with a first density, which superposes a second atmospheric layer with a smaller density, and that   heat is drawn from this region.   21. The method of claim 3, characterized by   the fact that the region in which a local change of den-   sity is produced lies in a second atmospheric layer with a second density, which is superimposed by a first atmospheric layer with a greater density, and that of the   heat is added in this region.