Abstract:
The invention relates to a guide tube especially for an instrumentation lance extending into a reactor pressure vessel. The guide tube includes a lower tube section and an upper tube section that extends into the interior of the reactor pressure vessel. In order to prevent radioactively contaminated particles from reaching the lower tube section disposed outside the reactor pressure vessel from forming a source of radiation, a separator is arranged in the upper tube section. The separator has a separation chamber in which the particles are deposited and are removed from the water.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a continuation of copending International Application No. PCT/EP02/02166, filed Feb. 28, 2002, which designated the United States and was not published in English. 

   BACKGROUND OF THE INVENTION 
   Field of the Invention 
   The invention relates to a guide tube which extends into a pressure vessel, in particular into a pressure vessel in a nuclear power station, and in which a so-called instrumentation lance is guided. The invention also relates to a method for preventing an accumulation of particles, in particular, radioactively loaded particles in the guide tube outside the pressure vessel. 
   The guide tube is often passed into the pressure vessel through its base, so that it includes an upper tube part, which is arranged in the pressure vessel, and a lower tube part, which projects out of the pressure vessel. The lower tube part is closed at the end by a closure flange. The guide tube has a flow connection to the interior of the pressure vessel and is also filled with water, in the same way as the pressure vessel. The pressure vessel is, in particular, a reactor pressure vessel or else a steam generator for a nuclear power station, in which radioactively loaded water or steam is located. The instrumentation lance normally has measured instrumentation for measuring the pressure, the temperature, the neutron flux, the filling level, etc. in the pressure vessel. 
   Temperature fluctuations result in the water being forced into the interior of the pressure vessel out of the guide tube when it is heated. Conversely, when the temperature decreases, water is sucked out of the pressure vessel into the guide tube. The temperature changes are caused, for example, by different operating states of the reactor pressure vessel. Large temperature differences occur in particular when starting and shutting down the nuclear power station, during which, for example, the water that is located in the reactor pressure vessel is heated from 20° to 300° C. 
   When water enters the guide tube from the pressure vessel, radioactively loaded contamination particles, inter alia, are also introduced into the guide tube, and are deposited at the lower end of the guide tube, which is closed by the closure flange. There, they form a highly radioactively emitting source outside the pressure vessel and represent a significant danger source for the workers during maintenance work. 
   SUMMARY OF THE INVENTION 
   It is accordingly an object of the invention to provide a guide tube for an instrumentation lance extending into a pressure vessel, a reactor pressure vessel for a nuclear power station, and a method for preventing the accumulation of particles outside of a pressure vessel in a guide tube for an instrumentation lance extending into a pressure vessel, which overcomes the above-mentioned disadvantages of the prior art apparatus and methods of this general type. 
   In particular, it is an object of the invention to prevent the accumulation of particles in the guide tube outside the pressure vessel. 
   With the foregoing and other objects in view there is provided, in accordance with the invention, a guide tube for guiding an instrumentation lance into an interior of a pressure vessel. The guide tube includes: a lower tube part; an upper tube part for configuration in the interior of the pressure vessel; and a separator for particles. The separator is configured in the upper tube part. The guide tube enables the instrumentation lance to extend into the pressure vessel. This embodiment is based on the idea that, when a temperature fluctuation occurs, although it is possible for water to enter the guide tube from the pressure vessel which, in particular, is in the form of a reactor pressure vessel, the water can, however, be separated in the guide tube from particles, in particular, the radioactively loaded particles, and the particles can be kept back in the upper tube part. The separator is thus used to separate the water from the loaded particles, which accumulate in the separator. Since the upper tube part is located in the interior of the pressure vessel, they do not form a radiation source acting outside the pressure vessel. This safely prevents any load on the workers during maintenance work. 
   The separator advantageously has a separation chamber with a chamber base, and the separation chamber has a first flow connection to the lower tube part. This first flow connection in this case has an outlet opening that is arranged in the separation chamber, and at a distance from the chamber base. 
   The chamber base in this case advantageously acts as a settling base, on which the particles which are introduced into the guide tube are deposited as a sediment. The outlet opening, which is arranged above the chamber base, of the flow connection allows water to pass from the upper tube part into the lower tube part without the particles, which have been deposited as a sediment on the chamber base, being carried with it. The arrangement of the chamber base with the flow connection thus on the one hand allows the particles to settle in the upper tube part while, at the same time, it allows unloaded water to be exchanged without any problems between the upper tube part and the lower tube part. 
   The separation chamber is expediently in the form of a closed chamber, and for this purpose has a chamber cover. A second flow connection is additionally provided between the separation chamber and the interior of the pressure vessel. The arrangement of the chamber cover and the boundary of the separation chamber that is connected to it prevents particles from entering the outlet opening from the first flow connection. 
   As an alternative to this, it is possible for the separation chamber to be open at the top, and for the entry of particles into the outlet opening from the first flow connection to be prevented by suitable measures. One such suitable measure is, advantageously, for the first flow connection in the separation chamber to be in the form of an upside down siphon. Furthermore, the siphon is preferably of such a size that any particles which nevertheless enter the outlet opening cannot pass through the siphon curve, which is located further above this point, and thus cannot enter the lower tube part. 
   In one preferred development, an inlet opening for water entering the separation chamber from the pressure vessel is arranged in the lower area element of the separation chamber and, in particular, in the vicinity of the chamber base. The loaded water thus flows into the separation chamber in the vicinity of the chamber base, so that this prevents particles from entering the outlet opening from the first flow connection, and thus from entering the lower tube part. For this purpose, provision is preferably also made for the separation chamber to be subdivided into two chamber elements which are connected to one another for flow purposes, with the inlet opening and the outlet opening being arranged in different chamber elements. 
   The arrangement of the inlet opening in the vicinity of the chamber base furthermore also has another advantage for the opposite flow situation, that is to say when water is forced out of the guide tube into the reactor pressure vessel. This is because particles are in this case passed out of the separation chamber back into the pressure vessel via the inlet opening, which now acts as an opening for water emerging from the separation chamber. This results in automatic self-cleaning of the separation chamber. 
   In one particularly expedient and simple embodiment, the two flow connections are in the form of simple, and in particular straight tubes. The inlet opening of the second flow connection is arranged underneath the outlet opening from the first flow connection. 
   In order to ensure that the water that enters the separation chamber enters and emerges only via the two flow connections, the chamber base and the chamber cover are each sealed with respect to the tube inner wall of the upper tube part. In consequence, a part of the tube inner wall is at the same time advantageously used as a boundary for the separation chamber. All that is therefore required to form the separation chamber is to arrange a chamber base and a chamber cover in the upper tube part. As an alternative to this, either just the chamber cover or the chamber base is sealed with respect to the tube inner wall of the upper tube part, and the separation chamber has its own side walls, which are at a distance from the tube inner wall. This makes it possible, for example, to insert the separation chamber into the guide tube from above, like an inserted part, and to be installed with the chamber cover or the chamber base on a projection on the tube inner wall, forming a seal. 
   According to one preferred development, the separator is arranged in the interior of the instrumentation lance. The separator is thus arranged in a cavity in the instrumentation lance. Since the physical space between the instrumentation lance and the tube inner wall of the guide tube is often confined, this refinement allows particularly simple assembly. In order to prevent loaded particles from entering the lower tube part, the separator represents the only flow connection between the upper tube part and the lower tube part. To this end, the instrumentation lance is preferably surrounded by a sealing ring, which is arranged between the instrumentation lance and the tube inner wall of the guide tube. 
   With the foregoing and other objects in view there is provided, in accordance with the invention, a method for preventing an accumulation of particles outside of a pressure vessel in a guide tube. The method includes steps of: providing a separator in an upper tube part of the guide tube; configuring the upper tube part of the guide tube within the pressure vessel; guiding an instrumentation lance into the pressure vessel with the guide tube; and using the separator to prevent particles from traveling from the upper tube part of the guide tube to other parts of the tube guide. 
   In accordance with an added mode of the invention, the method includes: providing the separator with a separation chamber having an outlet opening configured above an inlet opening; and configuring the separation chamber for operating such that, when water loaded with particles enters the inlet opening of the separation chamber, unloaded water emerges from the outlet opening of the separation chamber into a lower tube part of the guide tube. 
   In accordance with an additional mode of the invention, the method includes providing the separator with a separation chamber operating such that, when unloaded water flows out of a lower tube part of the guide tube into the separation chamber of the separator, water loaded with particles flows out of the separation chamber via a second flow connection into the pressure vessel. 
   Other features which are considered as characteristic for the invention are set forth in the appended claims. 
   Although the invention is illustrated and described herein as embodied in a guide tube for an instrumentation lance which extends into a pressure vessel, and a method for preventing the accumulation of particles in a guide tube such as this outside the pressure vessel, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
   The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic illustration of a configuration of a guide tube with a built-in separator in a lower area of a reactor pressure vessel; 
       FIG. 2  is an enlarged illustration of the separator shown in  FIG. 1 ; 
       FIG. 3  is a schematic illustration of an alternate embodiment of the separator with an open separation chamber and a first flow connection designed like a siphon; 
       FIG. 4  is a schematic illustration of a further embodiment of a separator with a separation chamber that is subdivided by a separating wall into two chamber elements; 
       FIG. 5  is a schematic illustration of a separator with a separation chamber that has side walls that are at a distance from the tube inner wall of the guide tube, and an outlet communicating with the lower tube part; 
       FIG. 6  is a schematic illustration of a separator of the type illustrated in  FIG. 5 , with the flow connection to the lower tube part being formed by a tube; and 
       FIG. 7  is a schematic illustration of a separator in an instrumentation lance being passed through the guide tube. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Parts having the same effect are provided with the same reference symbols throughout the figures. 
   Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown a guide tube  2  being passed from underneath into a reactor pressure vessel  6 . The guide tube  2  runs through the base  4  of the reactor pressure vessel  6  into the interior  8  of the reactor pressure vessel  6 . The guide tube  2  has an upper tube part  10 , which extends into the interior  8 , as well as a lower tube part  12 , which is arranged outside the reactor pressure vessel  6 . The guide tube  2  is closed at the end on the lower tube part  12  by a closure flange  14 . An instrumentation lance  16  is passed through the guide tube  2 , and extends into a reactor core  18  which is arranged in the reactor pressure vessel  6 . 
   During operation, the reactor pressure vessel  6  and the guide tube  2  are filled with water. Temperature fluctuations result in water being exchanged between the guide tube  2  and the reactor pressure vessel  6 . Both the upper tube part  10  and the lower tube part  12  typically have a length of about 5 meters. The guide tube  2  contains a total of about 10 liters of water, and the exchange of water resulting from temperature changes is at most 15–20% of this amount of water. When the water in the guide tube  2  cools down and its volume in consequence decreases, water is sucked into the guide tube  2  out of the reactor pressure vessel  6 . Conversely, when the temperature of the water in the guide tube  2  rises, water is forced out of the guide tube  2  into the reactor pressure vessel  6 . 
   A separator  20 , in which radioactively loaded particles  22  are kept back, is arranged in the upper tube part  10 . The separator  20  prevents the loaded particles  22  from entering the lower tube part  12  from the interior  8 . This prevents the particles  22  from accumulating on the closure flange  14 , and from forming a radiation source outside the reactor pressure vessel  6  at the closure flange  14 . The configuration of the separator  20  is in this case based on the idea of allowing water that is loaded with particles  22  to enter the guide tube  2 , since providing a seal on the guide tube  2 , for example, a dirt cap, does not reliably prevent particles  22  from entering the guide tube  2 . The particles  22  and the water are separated in the separator  20 , with the water from which the particles  22  have been separated entering the lower tube part  12  as unloaded water. For this purpose, there is a flow connection from the lower tube part  12  to the separator  20 , which allows the pressures to be equalized in a simple manner. 
   A particularly simple, but extremely effective embodiment of the separator  20 , is shown in an enlarged form in  FIG. 2 . According to this figure, the separator  20  has a separation chamber  24 , which is closed at the top by a chamber cover  26  and at the bottom by a chamber base  28 . The side boundary is formed by the tube inner walls  30  of the guide tube  2 . The chamber cover  26  and the chamber base  28  are each sealed with respect to the tube inner wall  30  via a seal  32 . This seal  32  is, in particular, in the form of a ring seal which runs in a groove in the chamber cover  26  and in the chamber base  28 . 
   The instrumentation lance  16  is guided centrally in the guide tube  2 , and passes through both the chamber cover  26  and the chamber base  28 . 
   The separator  20  also has a first flow connection  34 , which is in the form of a straight tube and allows water to be exchanged between the separation chamber  24  and the lower tube part  12 . At the end, the first flow connection  34  has an outlet opening  36  in the separation chamber  24 . A second flow connection  38  is also arranged alongside it, is likewise in the form of a straight tube and connects the separation chamber  24  to the interior  8  of the reactor pressure vessel  6 . The second flow connection  38  has an inlet opening  40  arranged in the separation chamber  20 . 
   The two flow connections  34 ,  38 , which are in the form of tubes, respectively pass through the chamber cover  26  and the chamber base  28 . The two flow connections  34 ,  38  are in this case arranged such that the inlet opening  40  is arranged underneath the outlet opening  36 . This safely ensures that water which is loaded with particles  22  and which is introduced into the separation chamber  24  via the second flow connection  38  does not pass via the first flow connection  34  into the lower tube part  12 . This arrangement also ensures that loaded water in the area of the chamber base  28  enters the separation chamber  24  from the inlet opening  40 . The particles  22  which are carried with the water are deposited on the chamber base  28 . The water in the upper area of the separation chamber  24  is free of contamination. The outlet opening  36  is arranged in this upper area. In consequence, only unloaded water leaves via this outlet opening  36 . If the temperature-dependent flow conditions are reversed, then water is forced out of the lower tube part  12  into the separation chamber  24 , and from there into the reactor pressure vessel  6 . Thus, in this case, water flows via the outlet opening  36  into the separation chamber  24 , and via the inlet opening  40  into the reactor pressure vessel  6 . The arrangement of the inlet opening  40  in the lower area of the separation chamber  24  automatically results in loaded water being forced back into the interior  8 . This prevents the separation chamber  24  from gradually being filled up with particles  22 . 
     FIGS. 3 and 4  show alternate embodiments of the separator  20 , illustrating only those elements that are relevant to the flows that take place and, for example, with the instrumentation lance  16  not being illustrated. 
   As is shown in  FIG. 3 , the separation chamber  24  is in the form of a settling chamber, open at the top, which has only the chamber base  28 . In consequence, there is no need for a second flow connection  38 . The first flow connection  34  has an upside down siphon  42  in the interior of the separation chamber  24 . Its siphon curve  44  is thus arranged above the outlet opening  36 . This configuration prevents deposited particles  22  from falling into the outlet opening  36  from above, and thus from entering the lower tube part  12 . In order to prevent particles  22  from entering the outlet opening  36 , this outlet opening  36  is also at a distance from the chamber base  28 . Furthermore, the length L of the tube element  45  between the outlet opening  36  and the start of the siphon curve  44  is preferably of a suitable size. To be precise, this size is such that the maximum amount of temperature-dependent water that can be expected to be exchanged between the reactor pressure vessel  6  and the guide tube  2  corresponds to the majority or all of the volume that is enclosed by the tube element  45 . This prevents the particles  22  from being passed through the siphon curve  44 , even if loaded water enters the outlet opening  36 . 
   According to the further alternative that is illustrated in  FIG. 4 , the separation chamber  24  is separated by a separating wall  46  into two chamber elements  24 A and  24 B. The separating wall extends from the chamber cover  26 , which is provided with a hole that forms the second flow connection  38 , into the lower area of the separation chamber  24 . The first flow connection  34  is once again in the form of a straight tube, which extends into the second chamber element  24 B. Its outlet opening  36  is arranged in the upper area, in the vicinity of the chamber cover  26 . The separation chamber  24  once again acts as a settling chamber, with the particles  22  being deposited on the chamber base  28 . This reliably prevents particles  22  from directly entering the outlet opening  36 , via the hole, through the separating wall  46 . 
   According to the exemplary embodiments shown in  FIGS. 5 and 6 , the separation chamber  24  has a side wall  50  which is designed to have a cross section in the form of a circular ring and is at a distance from the tube inner wall  30 . The seal with respect to the tube inner wall  30  is provided only via the chamber cover  26 . In particular, the separation chamber  24  is in the form of an autonomous unit. 
   A hole is incorporated into the side wall  50 , in the vicinity of the chamber cover  26 , as an outlet opening  36  for connection to the lower tube part  12 . The water can enter the intermediate space between the side wall  50  and the tube inner wall  30  from the separation chamber  24  via this hole. The second flow connection  38  to the upper tube part  10  is formed by a straight tube, whose inlet opening  40  is arranged in the area of the chamber base  28 . 
   In contrast to the separation chamber  24  shown in  FIG. 5 , the separation chamber  24  shown in  FIG. 6  has a first flow connection  34 , which is in the form of a tube, to the lower tube part  12 . No hole is provided in the side wall  50 . This embodiment corresponds to the embodiment illustrated in  FIG. 2 , with the measure that the separation chamber shown in FIG.  6  has a side wall  50  and, in particular, is in the form of an autonomous unit. In the embodiment shown in  FIG. 6 , there is no need for any flow space between the side wall  50  and the tube inner wall  30 , as a result of the first flow connection  34  that is formed by the tube. 
     FIG. 7  shows one particularly advantageous embodiment, in which the separator  20  is integrated in the interior of the instrumentation lance  16 . The instrumentation lance  16  is normally in the form of a cylindrical hollow body. The chamber cover  26  and the chamber base  28  are connected directly to the inner wall  52  of the tubular instrumentation lance  16 , and, in particular, are welded to it. The second flow connection is once again in the form of a straight tube, and connects the separation chamber  24  to an upper cavity  54  in the instrumentation lance. The separation chamber  24  has a flow connection via this upper cavity  54  to the interior  8  of the reactor pressure vessel  6 . By way of example, a flow opening to the reactor pressure vessel  6  is incorporated in the instrumentation lance  16  for this purpose, or the instrumentation lance has a flow opening at its upper end (neither of which is illustrated). 
   In order to prevent loaded particles from entering the lower tube part  12  through the intermediate space between the tube inner wall  30  of the guide tube  2  and the instrumentation lance  16 , the instrumentation lance  16  is sealed by a sealing ring  56  with respect to the tube inner wall  30 . The only flow connection between the lower tube part  12  and the reactor pressure vessel  6  is the separation chamber  24 . In this case, the separation chamber  24  has a hole in the tube wall of the instrumentation lance, which acts as an outlet opening  36  and allows a flow connection to be formed to the lower tube part  12 . A further hole  58  is incorporated in the tube wall of the instrumentation lance  16  underneath the separation chamber  24 , so that a lower cavity  60  in the instrumentation lance  16  has a flow connection to the lower tube part  12 . 
   The variant which is illustrated in  FIG. 7  and which has the separator  20  integrated in the instrumentation lance  16  is particularly simple to assemble. In general, the installation space formed between the instrumentation lance  16  and the tube inner wall  30  is confined, and in general arranging tubes in the intermediate space between the tube inner wall  30  and the instrumentation lance  16  involves effort since the spatial conditions there are usually confined.