DE102020117227A1 - Process for wet decontamination of radioactively contaminated workpieces with process water treatment - Google Patents

Abstract

The procedure described here using a vacuum belt filter 100 and a coalescence filter 200 allows the secondary waste-free treatment of the process water 10 from a high-pressure treatment for decoating potentially radioactively contaminated elements, so that the process water can be used again for a high-pressure treatment.

Description

The present invention relates to a method for wet decontamination of radioactively contaminated workpieces with a process water treatment.

In nuclear facilities such as nuclear power plants, surfaces can regularly be radioactively contaminated because radioactive substances accumulate on them. If such contaminations have to be removed, for example in the context of the dismantling of a nuclear facility, various methods are used, including wet decontamination. Here, the surfaces of workpieces to be cleaned are cleaned with liquid decontamination agents by bringing the surface into contact with the liquid decontamination agent, for example in the form of an immersion bath or by applying the liquid decontamination agent to the surface under pressure. Liquid water-based decontamination agents are regularly used here. The liquid decontamination agent can consist entirely of water, but other substances can also be added to the water that are tailored to the contaminating substances and / or the surface, for example soap or complexing agents that form complexes with certain radioactive substances or compounds that for example fail.

The aim of wet decontamination is at least to reduce the contamination of the workpiece so that the liquid decontamination agent (the process water) has a radioactive contamination after the wet decontamination, so that a treatment of the process water is necessary in order to be able to use the purified process water again as a liquid decontamination agent or to submit it to a delivery path for delivery.

Furthermore, many elements in nuclear facilities are coated, for example with a decontamination paint in accordance with DIN 25415, in order to avoid contamination of the element and / or to make it easy to remove during operation. In the course of time, many elements in nuclear facilities can be coated several times. This is carried out in particular to close holes, cracks or the like in areas below the new coating, which can represent both an older coating and the surface of the element itself, since in the event of radioactive contamination in these regularly contaminated particles or Build up substances. When a nuclear facility is dismantled, the coatings must be removed from many elements. Since these coatings are predominantly, if at all, only slightly radioactively contaminated, different processes are used here than with wet decontamination. In particular, water-based process media, preferably process water, can be used to decoat the elements. This process water is usually much less contaminated with radioactive contamination than the liquid decontamination agent after wet decontamination. The liquid decontamination agent after the wet decontamination is usually subjected to a very complex processing, which includes an evaporation of the decontamination agent to isolate radioactively contaminated particles.

In order to remove the corresponding radioactive contamination from the process water of a stripping process, it is known to pass the process water through a filter mixed with activated carbon, so that the radioactive contamination is bound in the filter. The corresponding filter then usually has to be disposed of.

Proceeding from this, the present invention is based on the object of at least partially overcoming the disadvantages known from the prior art.

This object is achieved with the features of the independent claims. Further advantageous embodiments of the invention are specified in the dependent claims. The features listed individually in the dependently formulated claims can be combined with one another in a technologically meaningful manner and can define further embodiments of the invention. In addition, the features specified in the claims are specified and explained in more detail in the description, with further preferred embodiments of the invention being presented.

1. a) einer Unterdruckfiltrierung, bei der ein poröser Filtergurt mit einer Unterseite über eine Filterkammer geführt wird, die mit einem Unterdruck relativ zum Druck oberhalb des Filtergurtes beaufschlagt wird, wobei Prozesswasser so geführt wird, dass es mit einer der Unterseite gegenüberliegenden Oberseite des Filtergurtes in Kontakt kommt, so dass Prozesswasser durch den anliegenden Unterdruck von der Oberseite durch den Filtergurt zur Unterseite des Filtergurtes geführt wird, wobei zumindest ein Teil von im Prozesswasser enthaltenen Feststoffen als Filterkuchen auf dem Filtergurt verbleibt, der in einen Sammelbehälter überführt wird, wobei das von den Feststoffen zumindest teilweise befreite Prozesswasser als Filtrat abgeführt wird; und
2. b) einem Abtrennen von Kohlenwasserstoffen, bei dem das Prozesswasser einer Koaleszenzabscheidung zur Abtrennung von Kohlenwasserstoffen unterzogen wird.

The method according to the invention for stripping coated elements of a nuclear facility comprises a high-pressure treatment with a process water, in which the process water is subjected to at least a two-stage treatment to form pure water:

1. a) vacuum filtration, in which a porous filter belt with an underside is guided over a filter chamber which is subjected to a negative pressure relative to the pressure above the filter belt, with process water being guided in such a way that it comes into contact with an upper side of the filter belt opposite the underside comes, so that process water is guided by the applied negative pressure from the top through the filter belt to the underside of the filter belt, with at least some of the solids contained in the process water as The filter cake remains on the filter belt, which is transferred to a collecting container, with the process water, at least partially freed from the solids, being discharged as filtrate; and
2. b) a separation of hydrocarbons, in which the process water is subjected to a coalescence separation for the separation of hydrocarbons.

The term decoating is understood to mean the removal of one or more coatings that have been applied to the surface of the coated element. The coating comprises in particular a lacquer and / or is based on polymers. A high pressure treatment is understood to mean the application of process water to the surface of the coated element, which is discharged onto the surface under a high pressure, in particular a pressure of 500 bar to 2500 bar. The process water is preferably tempered to a temperature of up to 60 ° C. Deionate, i.e. demineralized water, is preferably used as the process water. Deionized water is understood here to mean in particular water with an electrical conductivity of 3 μS / cm [microsiemens per centimeter] or less, in particular 0.1 μS / cm or less. The temperature control up to 60 ° C takes place in particular taking into account the heating of the process water during the relaxation of the mentioned high pressure to ambient pressure. In particular, before the expansion, the process water is cooled to a temperature below the ambient temperature, in particular to 10 ° C. and less.

The high pressure treatment removes at least part of the coating in the form of particles. Since the coated element is or was part of a nuclear facility, radioactive contamination cannot be ruled out. The process water therefore contains particles that can possibly be radioactively contaminated.

In the context of the present invention, the process water is treated. Before treatment, the process water comprises water, possibly solids, that is to say substances that are solid and therefore not dissolved in the water, and possibly liquids that are not soluble in the water, such as hydrocarbons such as oils. The solids are optionally in the form of suspended matter, floating matter and / or debris. Suspended substances are solids contained in the process water that do not go into solution and are kept in suspension due to their small size and density similar to water. Floats are solids contained in the process water that do not go into solution and float on the surface of the process water. Debris is a solid matter that, due to its density, sinks to the bottom in the process water.

Both the solids and the dissolved chemical compounds and the liquids that are not soluble in the process water can contain radioisotopes. During the treatment of the process water, the radioisotope concentration is reduced so that the pure water can be released into a discharge path, for example in a wastewater treatment system for later discharge into a body of water, for example into a river, or can be used again as process water for stripping, if necessary with the addition of fresh water or deionized water. For this purpose, the pure water should fall below certain limit values, in particular with regard to the particle load, the radiological activity, the electrical conductivity and / or the particle size distribution of the particles in the process water or pure water.

The high-pressure treatment of an element itself preferably includes the application of process water to a surface of the element, which is discharged under a pressure of in particular 500 bar to 2,500 bar and directed onto the surface. This can be done both by manual guidance of a corresponding high-pressure lance and by a corresponding manipulator that automatically guides a high-pressure lance. The process water is in particular deionized water. The process water can preferably be tempered, the temperature of the process water preferably being selected as a function of the substances to be removed. A temperature range from 8 ° C. to 60 ° C. is preferred.

The vacuum filtration according to step a) is also referred to as vacuum belt filtration. A filter belt made of a plastic, in particular an elastomer, is preferably used as the filter belt. In particular, a multi-part filter belt can also be used in which a movable carrying belt is provided with a porous filter element, for example a porous filter cloth. In particular, the vacuum filtration can at least partially separate solids from the process water.

The coalescence separation in step b) is based on a demixing phenomenon in which dispersed liquid droplets, for example hydrocarbon droplets, combine to form larger droplets and in particular to form a colloidal phase that can be removed from the process water. As a result, liquids with a lower density than water such as, in particular, hydrocarbons such as oil, gasoline, alcohols, aromatics and / or certain other organic Solvent separated and removed from the process water.

Steps a) and b) can be carried out in any order.

The method according to the invention allows a stripping of potentially radioactively contaminated coated elements in a treatment of the process water, which allows an at least partially re-use of the process water for high pressure treatment, and / or an introduction into bodies of water without incurring secondary waste. In particular, steps a) and b) allow the process water to be treated without the accumulation of filter media that have to be disposed of due to being loaded with radioisotopes.

The filter belt is preferably moved in a circumferential manner in step a). This enables simple process management in step a). Preferably, the filter cake can simply be separated from the filter belt while the filter belt is circulating, for example by a mechanical separating element such as a blade or the like, and transferred to the collecting container. This enables a secondary filter-free treatment of the process water. There are therefore no secondary filter media that also have to be decontaminated or stored depending on the radiological and chemical contamination.

1. A) das Prozesswasser,
2. B) das Filtrat und
3. C) das Reinwasser

einer Bestrahlung mit einer UV-Strahlung unterzogen.At least one of the following liquids is preferred:

1. A) the process water,
2. B) the filtrate and
3. C) the pure water

subjected to exposure to UV radiation.

UV radiation is understood to mean ultraviolet electromagnetic radiation. UV radiation is understood to mean, in particular, electromagnetic radiation with a wavelength of 100 nm [nanometers] to 400 nm.

By irradiating with UV radiation, a reduction in the number of germs in the liquid is achieved. If the liquid has biological contamination, the corresponding germs, in particular bacteria and viruses, are inactivated by the UV radiation, so that the biological contamination can also be reduced below predeterminable limit values. A vapor lamp, for example at least one mercury vapor lamp and / or at least one LED (light-emitting diode) with corresponding radiation characteristics, is preferably used as the radiation source.

1. A) das Prozesswasser,
2. B) das Filtrat und
3. C) das Reinwasser

mindestens einer der folgenden Messungen unterzogen:

1. i) Messung der radiologischen Aktivität;
2. ii) Messung der elektrischen Leitfähigkeit;
3. iii) Messung der Partikelfracht und
4. iv) Messung der Partikelgrößenverteilung.

At least one of the following liquids is preferred:

1. A) the process water,
2. B) the filtrate and
3. C) the pure water

subjected to at least one of the following measurements:

1. i) measurement of radiological activity;
2. ii) measurement of electrical conductivity;
3. iii) measurement of the particle load and
4. iv) Measurement of the particle size distribution.

The particle load is understood to mean the mass of the particles contained in the respective liquid. The particle size distribution is understood to mean the frequency distribution of a size of the particles.

The measured values obtained in i), ii), iii) and / or iv) can preferably be used to regulate the method, in particular with regard to the sequence of steps a) and b).

The process parameters of at least one of steps a) and b) are preferably changed as a function of the results of at least one of the measurements carried out. In particular, the speed at which the filter belt is moved and / or the negative pressure in the filter chamber can be changed based on the result of at least one of the measurements carried out.

The pure water is preferably used to carry out a high-pressure treatment. In this way, the pure water can at least partially be used in a cycle.

Particles which settle out are preferably taken up in a collecting container in step b). In the coalescence separator, the process water flows at comparatively low flow speeds, which allow suspended matter to settle. In order to avoid an uncontrolled accumulation of particles here, the collecting container is used to collect such particles. The collecting container is preferably designed in the shape of a funnel.

Particles present in the collecting container are preferably removed therefrom by a backwashing process. This enables the particles to be removed easily and in a controlled manner.

As a precaution, it should be noted that the numerals used here (“first”, “second”, ...) primarily (only) to distinguish between several similar ones Objects, sizes or processes are used, that is to say, in particular, no dependency and / or sequence of these objects, sizes or processes with respect to one another is mandatory. Should a dependency and / or sequence be necessary, this is explicitly stated here or it is obvious to a person skilled in the art when studying the specifically described embodiment.

• 1 ein Beispiel einer Vorrichtung zur Aufbereitung von Prozesswasser;
• 2 und 3 ein Beispiel eines Unterdruckbandfilters in verschiedenen Ansichten;
• 4 und 5 weitere Elemente des Beispiels einer Vorrichtung nach 1.

The invention and the technical environment are explained in more detail below with reference to the figures. It should be pointed out that the invention is not intended to be restricted by the exemplary embodiments shown. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and to combine them with other components and findings from the present description and / or figures. In particular, it should be pointed out that the figures and in particular the size relationships shown are only schematic. The same reference symbols denote the same objects, so that explanations from other figures can be used in addition, if necessary. Show it:

• 1 an example of a device for treating process water;
• 2 and 3 an example of a vacuum band filter in different views;
• 4th and 5 further elements of the example of a device according to 1 .

1 shows very schematically the process sequence of the process described here for treating a process water 10 a stripping of a potentially radioactively contaminated coated element of a nuclear facility in a corresponding device 1 . The coated element can represent, for example, a pipe, a floor or wall element or the like. Here the process water 10 as waste water from a stripping (not shown) initially a vacuum belt filter 100 fed, in particular in connection with the 2 and 3 is described in more detail. The resulting filter cake 106 becomes a collecting container 108 supplied, collected there and then later stored for final or temporary storage. The resulting filtrate 113 becomes a coalescence separator 200 fed, in particular in connection with the 4th and 5 is described in more detail. The one in the coalescence separator 200 collected deposited hydrocarbons 208 are in a collection tank 205 collected in order to then be sent to an interim or final storage facility. The resulting filtrate 209 is via a pure water tank 300 a filter unit 400 fed. The pure water produced there 404 becomes a pump template 600 fed. From the pump template 600 the process water is taken for the operation of the stripping.

The one during backwashing in the filter unit 400 resulting filter residue 405 is again the vacuum belt filter 100 fed. Furthermore, depending on the operating status, alluvial water 406 from the filter unit 400 into the pure water tank 300 backwashed. The filter unit 400 will be used in the following in connection with the 4th and 5 described in more detail.

2 and 3 show an example of a vacuum belt filter 100 , also known as vacuum belt filter, in different views. 2 shows the functional principle of the vacuum belt filter 100 , while 3 a perspective view of the vacuum belt filter 100 indicates.

The process water 10 is thereby via a process water supply 101 in a process water task 102 led through which the process water 10 on a filter belt 103 is applied. The filter belt 103 is porous and runs around two rollers 104 emotional. The process water 10 including the load of solids contained therein comes into contact with the filter belt 103 . The filter belt 103 has an upper side 105 and one of the top 105 opposite bottom 116 on. The filter belt 103 becomes with the bottom 116 through a filter chamber 109 out, in which a negative pressure is generated, which the process water 10 from the top 105 through the filter belt 103 drifts, with the process water 10 is guided so that it is upside down 105 of the filter belt 103 comes in contact, so that the process water 10 due to the negative pressure from the top 105 through the filter belt 103 to the bottom 116 of the filter belt 103 is performed, at least a part of in the process water 10 contained solids as filter cake 106 on the filter belt 103 remains. The filter cake 106 is through the filter belt 103 up to a filter cake separator 107 promoted by the filter cake 106 into a collecting container 108 is promoted. The filter cake separator 107 is designed, for example, as a scraper, alternatively or additionally as at least one rotating brush.

The negative pressure in the filter chamber 109 is done by a compressor 110 generated via a filtrate reservoir 111 with the filter chamber 109 connected is. The compressor 110 is with a gas space 112 of the filtrate reservoir 111 connected, which in turn with the filter chamber 109 connected is. The filtrate 113 , i.e. the process water freed from at least part of the cargo 10 , collects in the filtrate reservoir 111 and can from there via a filtrate drain line 114 from the filtrate reservoir 111 removed. The compressor also has 110 Via a filter (not shown), in particular a HEPA filter, particularly preferably a HEPA filter of specification H14, on the suction side of the compressor 110 , with which preferably (but not shown here) the air spaces of the vacuum belt filter 100 , the coalescence separator 200 and the pure water tank 300 are connected to prevent the breakthrough of radiologically contaminated aerosols.

The vacuum belt filter 100 also has fasteners 115 on, are attached to the radiation shielding elements (not shown) for shielding ionizing radiation, in particular gamma radiation. The radiation shielding elements include, in particular, lead.

Furthermore, the vacuum belt filter 100 a filter residue task 110 on. About the filter residue task 110 can filter residue 405 from the filter unit 400 on an area of the filter cake 106 are applied, which is no longer with the process water 10 is in contact. The filter cake is in this area 106 Completely built up in one cross-sectional direction, so that an efficient filtration of the solids in the filter residues 405 he follows.

4th and 5 show further details of the device 1 out 1 . 4th shows a sectional view and 5 a perspective view. The device 1 further comprises a coalescence separator 200 , a pure water tank 300 , a filter system 400 and a UV system 500 which are described below with reference to both figures.

The filtrate from the vacuum belt filter 100 is via a coalescence separator inlet 201 in the coalescence separator 200 brought in. The coalescence separator 200 is used to remove liquids with a density that is less than the density of water from the process water. These are in particular hydrocarbons such as alcohols and / or oils. The coalescence separator 200 includes a plurality of inclined plates 202 . For the sake of clarity, there is only a single inclined plate 202 shown, however, are a plurality of inclined plates 202 formed, which are oriented at an angle to the vertical and which each run parallel to each other. Any inclined plate 202 is corrugated, in particular corrugated or ribbed, the inclined plates 202 are aligned so that the direction of extent of the corrugations, in particular the corrugations or ribs, extend from bottom to top at an angle to the vertical.

Through the coalescence separator 201 the process water to be cleaned is entered in such a way that it is between the inclined plates 202 flows upwards. The inclined plates 202 are designed as lamellar plates with a cyclic profile. Drops of liquids with a density smaller than the density of water collect on the underside of the lamellas. The drops combine with other drops to form larger drops, which float up due to the lower density of the drops compared to water and collect in the upper area 203 of the coalescence separator 200 . Via extraction points 204 the collected liquid can be removed and placed in a collection tank 205 be convicted. The pure water of the coalescence separator 200 is via a coalescence separator outlet 206 into the pure water tank 300 convicted. Also the coalescence separator 200 has fasteners 207 on, are attached to the radiation shielding elements (not shown) for shielding ionizing radiation, in particular gamma radiation. The coalescence separator 201 further comprises a collecting container 210 , which is funnel-shaped. The coalescence separation is based on relatively low flow velocities, which enable the droplets to coalign. At the same time, however, it is also possible that part of the remaining particle load settles and uncontrolled particle deposits in the coalescence separator 201 comes. To prevent this from happening, the sump is 210 formed in which corresponding particles collect. Via a backwash line 211 the particles in the collecting container 210 removed by backwashing and filtration, for example in the vacuum belt filter 100 or the filter system 400 are fed.

The filter system 400 includes a first filter 401 and a second filter 402 . In the first filter 401 a filter medium flows through from the inside to the outside, whereby a filter cake builds up inside. In the first filter 401 the pressure loss across the filter medium and the inside of the first filter is monitored 401 is cleaned when the pressure loss exceeds a predeterminable limit value. This is preferably done mechanically, the removed filter cake is rinsed out with process water and stored as filter residue 405 to the vacuum belt filter 100 transferred and there via the filter residue task 117 on the filter cake 116 abandoned (cf. 2 ). The first filter 401 is also known as a so-called lensing filter.

The second filter 402 is an analysis filter with which the functionality and efficiency of the first filter 401 can be analyzed. This is where the second filter is used 402 downstream of the first filter 401 formed so that the second filter 402 from through the first filter 401 Purified pure water is flowed through. The second filter 402 is designed in particular as a so-called absolute filter. This is understood to mean a filter that has a precisely defined separation limit. If, for example, an absolute filter with a separation limit of 1 µm [micrometer] is used, only particles with a diameter of less than 1 µm can pass through it. The separation limit of the second filter is preferred 402 chosen so that it matches the filter behavior of the first filter 401 This corresponds to the fact that this is particles of a diameter smaller than the cut-off limit of the second filter in normal operation 402 safely filters out, so that if particles in the second filter 402 be filtered out from a malfunction of the first filter 401 can be assumed. The second filter 402 is used as a so-called police filter. Unless particles in the second filter 402 can be found from a malfunction of the upstream of the second filter 402 lying elements of the device are assumed.

If necessary, it can be done in the UV system 500 exposure to UV radiation to inactivate germs. The filtrate or pure water that the filter system 400 leaves is via a feed line 403 into the pure water tank 300 convicted. From this the water can be used again to carry out a stripping process or to backwash the first filter 401 can be removed.

The procedure described here is carried out using a vacuum belt filter 100 and a coalescing filter 200 allows the secondary waste-free treatment of the process water 10 so that it can be used again as process water for stripping or can be released into a body of water via a delivery path.

The device described here 1 as well as the corresponding process management allows the safe separation of particles up to a particle size of 1 micrometer and the safe separation of oils, fats and the like from the process water, so that the corresponding pure water is again used by a suitable pump under pressure for a high-pressure treatment of a coated element can be promoted. The resulting filter residues are free of secondary filters, so that the resulting amount of filter residue can be reduced compared to approaches that are assumed to be known.

List of reference symbols

1

Device for the treatment of a process water of a wet decontamination

10

Process water

100

Vacuum belt filter

101

Process water supply

102

Process water task

103

Filter belt

104

role

105

Top

106

Filter cake

107

Filter cake separator

108

Collection container

109

Filter chamber

110

compressor

111

Filtrate reservoir

112

Gas compartment

113

Filtrate

114

Filtrate drain line

115

Fastener

116

bottom

117

Filter residue task

200

Coalescence separator

201

Coalescence separator inlet

202

Inclined plate

203

upper area

204

Tapping point

205

Collection tank

206

Coalescence separator outlet

207

Fastener

208

collected hydrocarbons

209

Filtrate

210

Collection container

211

Backwash line

300

Pure water tank

400

Filter system

401

first filter

402

second filter

403

Supply line

404

Pure water

405

Filter residue

406

Alluvial water

500

UV system

600

Pump template

Claims (9)

Process for stripping coated elements of a nuclear facility, comprising a high-pressure treatment with a process water, in which the process water is subjected to at least a two-stage treatment to a pure water: a) a negative pressure filtration, in which a porous filter belt with an underside is guided over a filter chamber that has a negative pressure relative to the pressure above of the filter belt is acted upon, process water being guided in such a way that it comes into contact with an upper side of the filter belt opposite the underside, so that process water is guided by the applied negative pressure from the upper side through the filter belt to the underside of the filter belt, with at least a part of solids contained in the process water remain as filter cake on the filter belt, which is transferred to a collecting container, the process water at least partially freed from the solids being discharged as filtrate; and b) a separation of hydrocarbons, in which the process water is subjected to a coalescence separation for the separation of hydrocarbons. Procedure according to Claim 1 , in which the filter belt is moved around in step a). Method according to one of the preceding claims, in which at least one of the following liquids: A) the process water, B) the filtrate and C) the pure water is exposed to UV radiation. Method according to one of the preceding claims, in which at least one of the following liquids: A) the process water, B) the filtrate and C) the pure water is subjected to at least one of the following measurements: i) measurement of radiological activity; ii) measurement of electrical conductivity; iii) measurement of the particle load and iv) Measurement of the particle size distribution. Procedure according to Claim 4 , in which the pure water is used as process water for high-pressure treatment if the result of the measurements carried out is below a specifiable limit value in each case. Procedure according to Claim 4 or 5 , in which the process parameters of at least one of steps a) and / or b) are changed as a function of the results of at least one of the measurements carried out. Method according to one of the preceding claims, in which the pure water is used to carry out a high-pressure treatment for stripping. Method according to one of the preceding claims, in which in step b) particles which settle out are taken up in a collecting container (210). Procedure according to Claim 8 , in which the particles present in the collecting container (210) are removed therefrom by a backwashing process.

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