EP4154279B1 - Process for liquid decontamination of radioactively contaminated objects with process-water retreatment - Google Patents

Description

The subject of the present invention is a method for wet decontamination of radioactively contaminated workpieces using process water treatment.

In nuclear facilities such as nuclear power plants, surfaces can regularly be radioactively contaminated, with radioactive substances accumulating on them. If such contamination needs to be removed, for example as part 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 decontaminants by bringing the surface into contact with the liquid decontaminant, for example in the form of an immersion bath or by applying the liquid decontaminant to the surface under pressure. Water-based liquid decontamination agents are regularly used. 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 for example, failures.

The aim of wet decontamination is at least to reduce the contamination of the workpiece, so that the liquid decontamination agent after wet decontamination (the process water) has radioactive contamination, so that the process water must be treated in order to contain the cleaned process to supply the delivery path for delivery,

From the US 3,962,078 is a known process for freeing radioactive process water from radioactive particles through negative pressure filtration and coalescence separation.

Furthermore, many elements in nuclear facilities are coated, for example with a decont paint according to DIN 25415, in order to avoid contamination of the element and/or to make it easily removable during operation. Over time, many elements in nuclear facilities can be coated multiple times. This is carried out in particular in order 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, contaminated particles or accumulate substances. When dismantling a nuclear facility, the coatings of many elements have to be removed. Since these coatings are predominantly, if at all, only slightly radioactively contaminated, different processes are used here than for wet decontamination. In particular, water-based process media, preferably process water, can be used to strip the elements. This process water is usually significantly less contaminated with radioactive contamination than the liquid decontamination agent after wet decontamination. The liquid decontaminant after wet decontamination is usually subjected to a very complex preparation, which includes evaporation of the decontaminant to isolate radioactively contaminated particles.

In order to remove the corresponding radioactive contamination from the process water during decoating, it is known to pass the process water through a filter containing activated carbon so that the radioactive contamination is bound in the filter. Then the corresponding filter usually has to be subjected to final storage.

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

This task is solved 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 dependent claims can be combined with one another in a technologically sensible 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 includes a high-pressure treatment with a process water, in which the process water is subjected to at least a two-stage treatment to produce pure water:

1. a) 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 remaining as filter cake on the filter belt, which is transferred to a collecting container, whereby the process water, at least partially freed from the solids, is discharged as filtrate; and
2. b) a separation of hydrocarbons, in which the process water is subjected to coalescence separation to separate hydrocarbons.

The term decoating means the removal of one or more coatings that are applied to the surface of the coated element. The coating in particular comprises a lacquer and/or is polymer-based. High-pressure treatment means the application of process water to the surface of the coated element, which is discharged onto the surface under 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 preferred as process water. Here, deionate is understood 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 when the pressure is relaxed from the high pressure mentioned 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 may possibly be radioactively contaminated.

As part of the present invention, the process water is treated. Before treatment, the process water includes water, possibly solids, i.e. substances that are solid and therefore not dissolved in water, and possibly liquids that are not soluble in water, such as hydrocarbons such as oils. The solids may be present as suspended matter, floating matter and/or bedload. Suspended solids are solids contained in the process water that do not dissolve and are kept in suspension because of their small size and density similar to water. Floating solids are solids contained in the process water that do not dissolve and float on the surface of the process water. Bedloads are solids that sink down in the process water due to their density.

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 delivery path, for example into a wastewater treatment for later discharge into a body of water, for example into a river, or can be used again as process water for decoating, if necessary with the addition of fresh water or deionized water. For this purpose, the pure water should fall below certain limit values, especially 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 either by manually guiding a corresponding high-pressure lance or by using a corresponding manipulator, which automatically guides a high-pressure lance. The process water is in particular deionized water. The process water can preferably be tempered, with the temperature of the process water preferably being selected depending on the substances to be removed. A temperature range of 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 deposition in step b) is based on a segregation phenomenon in which dispersed liquid drops, for example hydrocarbon drops, combine to form larger drops and in particular to form a colloid phase that can be removed from the process water. This allows liquids with a lower density than water, in particular hydrocarbons such as oil, gasoline, alcohols, aromatics and/or certain other organic solvents, to be 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 decoating of potentially radioactively contaminated coated elements during treatment of the process water, which enables at least partial reuse of the process water for high-pressure treatment and/or discharge into bodies of water, without generating secondary waste. In particular, steps a) and b) allow the process water to be treated without producing filter media that have to be disposed of due to being loaded with radioisotopes.

In step a), the filter belt is preferably moved in a rotating manner. 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 rotating, for example by a mechanical separating element such as a blade or the like, and transferred to the collecting container. This enables the process water to be treated without secondary filters. This means that no secondary filter media is created, which also needs to be decontaminated or stored in accordance with 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 irradiation with UV radiation.

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

Exposure to UV radiation reduces the number of germs in the liquid. 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 predetermined limit values. The radiation source is preferably a vapor lamp, such as at least one mercury vapor lamp and/or at least one LED (light-emitting diode) with corresponding radiation characteristics is used.

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 particle load and
4. iv) Measurement of 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 process, in particular with regard to the order of steps a) and b).

The process parameters of at least one of steps a) and b) are preferably changed depending on 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. This means that the pure water can at least partially be used in a circuit.

In step b), settling particles are preferably collected in a collecting container. In coalescence separation, the process water flows at comparatively low flow velocities, which allows suspended solids to settle. In order to avoid an uncontrolled accumulation of particles, the collection container is used to collect such particles. The collecting container is preferably funnel-shaped.

Particles present in the collecting container are preferably removed from it by a backwashing process. This enables easy and controlled removal of the particles.

As a precaution, it should be noted that the number words used here ("first", "second", ...) primarily serve (only) to distinguish between several similar objects, sizes or processes, i.e. in particular no dependency and/or order of these objects, sizes or prescribe processes to each other. If a dependency and/or sequence is required, this is explicitly stated here or it will be obvious to the person skilled in the art when studying the specifically described embodiment.

Fig. 1

ein Beispiel einer Vorrichtung zur Aufbereitung von Prozesswasser;

Fig. 2 und 3

ein Beispiel eines Unterdruckbandfilters in verschiedenen Ansichten;

Fig. 4 und 5

weitere Elemente des Beispiels einer Vorrichtung nach Fig. 1.

The invention and the technical environment are explained in more detail below using the figures. It should be noted that the invention is not intended to be limited 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 noted that the figures and in particular the proportions shown are only schematic. The same reference numbers designate the same objects, so that explanations from other figures can be used in addition if necessary. Show it:

Fig. 1

an example of a device for treating process water;

Figs. 2 and 3

an example of a vacuum band filter in different views;

Figs. 4 and 5

further elements of the example of a device Fig. 1 .

Fig. 1 shows very schematically the process sequence of the method described here for the treatment of a process water 10 of a decoating of a potentially radioactively contaminated coated element of a nuclear facility in a corresponding device 1. The coated element can, for example, represent a pipe, a floor or wall element or the like. Here, the process water 10 is first fed as wastewater from a decoating (not shown) to a vacuum belt filter 100, which is particularly in connection with the Figures 2 and 3 is described in more detail. The resulting filter cake 106 is fed to a collecting container 108, collected there and then later stored or stored temporarily. The resulting filtrate 113 is fed to a coalescence separator 200, which is used in particular in connection with the Figures 4 and 5 is described in more detail. The separated hydrocarbons 208 collected in the coalescence separator 200 are collected in a collection tank 205 in order to then be sent to intermediate or final storage. The resulting filtrate 209 is fed to a filter unit 400 via a pure water tank 300. The pure water created there 404 is fed to a pump template 600. The process water is taken from the pump receiver 600 for the decoating operation.

The filter residue 405 resulting from backwashing in the filter unit 400 is fed again to the vacuum belt filter 100. Furthermore, depending on the operating state, precoat water 406 is backwashed from the filter unit 400 into the pure water tank 300. The filter unit 400 will be discussed below in connection with Figures 4 and 5 described in more detail.

Figs. 2 and 3 show an example of a vacuum belt filter 100, also referred to as a vacuum belt filter, in various views. Fig. 2 shows the operating principle of the vacuum belt filter 100, while Fig. 3 a perspective view of the vacuum belt filter 100 shows.

The process water 10 is fed via a process water supply 101 into a process water feed 102, through which the process water 10 is applied to a filter belt 103. The filter belt 103 is porous and is moved around two rollers 104. The process water 10, including the load of solids contained therein, thus comes into contact with the filter belt 103. The filter belt 103 has an upper side 105 and an underside 116 opposite the upper side 105. The filter belt 103 is guided with the bottom 116 over a filter chamber 109, in which a negative pressure is generated, which drives the process water 10 from the top 105 through the filter belt 103, the process water 10 being guided so that it is with the top 105 of the Filter belt 103 comes into contact, so that the process water 10 is guided by the applied negative pressure from the top 105 through the filter belt 103 to the underside 116 of the filter belt 103, with at least some of the solids contained in the process water 10 remaining as filter cake 106 on the filter belt 103 . The filter cake 106 is passed through the filter belt 103 to a filter cake separator 107 promoted, through which the filter cake 106 is transported into a collecting container 108. 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 generated via a compressor 110, which is connected to the filter chamber 109 via a filtrate reservoir 111. The compressor 110 is connected to a gas space 112 of the filtrate reservoir 111, which in turn is connected to the filter chamber 109. The filtrate 113, i.e. the process water 10 freed from at least part of the load, collects in the filtrate reservoir 111 and can be removed from there from the filtrate reservoir 111 via a filtrate drain line 114. Furthermore, the compressor 110 has a filter, not shown, in particular a HEPA filter, particularly preferably a HEPA filter of the H14 specification, on the suction side of the compressor 110, with which preferably (but not shown here) the air spaces of the vacuum belt filter 100, of Coalescence separator 200 and the pure water tank 300 are connected to prevent the breakthrough of radiologically contaminated aerosols.

The vacuum band filter 100 also has fastening elements 115, via which radiation shielding elements, not shown, are fastened for shielding from ionizing radiation, in particular gamma radiation. The radiation shielding elements include in particular lead.

Furthermore, the vacuum belt filter 100 has a filter residue task 110. Via the filter residue task 110, the filter residues 405 from the filter unit 400 can be applied to an area of the filter cake 106 that is no longer in contact with the process water 10. In this area is the filter cake 106 is completely built up in a cross-sectional direction, so that the solids in the filter residues 405 are filtered off efficiently.

Figs. 4 and 5 show further details of the device 1 Fig. 1 . Fig. 4 shows a sectional view and Fig. 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 introduced into the coalescence separator 200 via a coalescence separator inlet 201. The coalescing 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 comprises a plurality of inclined plates 202. For the sake of clarity, only a single inclined plate 202 is shown, but a plurality of inclined plates 202 are formed, which are aligned at an angle to the vertical and which each run parallel to one another. Each inclined plate 202 is corrugated, in particular corrugated or ribbed, with the inclined plates 202 being aligned so that the direction of extension of the corrugations, in particular the corrugations or ribs, extend from bottom to top at an angle to the vertical.

The process water to be cleaned is introduced through the coalescence separator 201 in such a way that it flows upwards between the inclined plates 202. The inclined plates 202 are designed as lamella plates with a cyclic profile. Drops of liquids with a density less than the density of water collect on the underside of each slat. The drops combine with other drops to form larger drops, which float the lower density of the drops compared to water and collect in the upper area 203 of the coalescence separator 200. The collected liquid can be removed via removal points 204 and transferred to a collection tank 205. The pure water from the coalescence separator 200 is transferred to the pure water tank 300 via a coalescence separator outlet 206. The coalescence separator 200 also has fastening elements 207, via which radiation shielding elements, not shown, are fastened for shielding from ionizing radiation, in particular gamma radiation. The coalescence separator 201 further comprises a collecting container 210, which is funnel-shaped. Coalescing separation is based on relatively low flow velocities, which enable the drops to coalesce. At the same time, however, it is also possible that part of the remaining particle load settles and uncontrolled particle deposits occur in the coalescence separator 201. To prevent this, the collecting container 210 is designed in which the corresponding particles collect. The particles in the collecting container 210 can be removed by backwashing via a backwash line 211 and fed to filtration, for example in the vacuum belt filter 100 or the filter system 400.

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, with a filter cake building up inside. In the first filter 401, the pressure loss across the filter medium is monitored and the interior of the first filter 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 transferred as filter residue 405 to the vacuum belt filter 100 and there applied to the filter cake 116 via the filter residue feeder 117 (cf. Fig. 2 ). The first filter 401 is also referred to 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. For this purpose, the second filter 402 is formed downstream of the first filter 401, so that the pure water purified by the first filter 401 flows through the second filter 402. The second filter 402 is designed in particular as a so-called absolute filter. This refers to a filter that has a precisely defined separation limit. For example, if an absolute filter with a cutoff limit of 1 µm [micrometers] is used, only particles with a diameter of less than 1 µm can pass through it. Preferably, the separation limit of the second filter 402 is chosen so that it corresponds to the filter behavior of the first filter 401, so that in normal operation it reliably filters out particles with a diameter smaller than the separation limit of the second filter 402, so that when particles in the second Filter 402 are filtered out, a malfunction of the first filter 401 can be assumed. The second filter 402 is used as a so-called police filter. If particles are found in the second filter 402, it can be assumed that the elements of the device located upstream of the second filter 402 are malfunctioning.

If necessary, the UV system 500 can be irradiated with UV radiation to inactivate germs. The filtrate or pure water that leaves the filter system 400 is transferred to the pure water tank 300 via a supply line 403. The water can be removed from this again to carry out decoating or to backwash the first filter 401.

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

The device 1 described here as well as the corresponding procedure 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 supplied again under pressure by a corresponding pump 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 residues can be reduced compared to approaches assumed to be known.

Reference symbol list

1

Device for preparing process water for wet decontamination

10

Process water

100

Vacuum belt filter

101

Process water supply line

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 room

113

Filtrate

114

Filtrate drain line

115

fastener

116

bottom

117

Filter residue task

200

coalescing separator

201

Coalescence separator inlet

202

slanted plate

203

upper area

204

Collection point

205

collection tank

206

Coalescing separator output

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

precoat water

500

UV system

600

Pump template

Claims (9)

1. Method for decoating coated elements of a nuclear plant, comprising a high-pressure treatment with a process water, in the course of which the process water (10) for preparation is subjected to at least a two-stage preparation to form a clean water (404), comprising the following steps:

   a) a negative-pressure filtering, in the course of which a porous filter belt (103) with a lower side is passed via a filter chamber to which a negative pressure relative to the pressure above the filter belt is applied, wherein process water is conducted such that it comes into contact with an upper side of the filter belt that is opposite the lower side, such that process water (10) is conducted through the filter belt (103) from the upper side to the lower side of the filter belt owing to the prevailing negative pressure, wherein at least some solids present in the process water remain on the filter belt as a filter cake (106), which is transferred to a collection container (108), wherein the process water at least partially freed of the solids is discharged as filtrate; and

   b) a separating out of hydrocarbons, in the course of which the process water (10) is subjected to coalescence separation (200) for separating out hydrocarbons.
2. Method according to Claim 1, in which, in step a), the filter belt is moved in circulating fashion.
3. Method according to either of the preceding claims, in which at least one of the following liquids:

   A) the process water (10),

   B) the filtrate (113) and

   C) the clean water (404)

   is subjected to irradiation with UV radiation.
4. Method according to one of the preceding claims, in which at least one of the following liquids:

   A) the process water (10),

   B) the filtrate (113) and

   C) the clean water (404)

   is subjected to at least one of the following measurements:

   i) measurement of the radiological activity;

   ii) measurement of the electrical conductivity;

   iii) measurement of the particulate load and

   iv) measurement of the particle size distribution.
5. Method according to Claim 4, in which the clean water is used as process water for the high-pressure treatment if the result of the measurements taken is below a respective predefinable threshold value.
6. Method according to Claim 4 or 5, in which the process parameters of at least one of the steps a) and/or b) are changed depending on the results of at least one of the measurements taken.
7. Method according to one of the preceding claims, in which the clean water is used to carry out a high-pressure decoating treatment.
8. Method according to one of the preceding claims, in which, in step b), particles that settle are received in a collection container (210).
9. Method according to Claim 8, in which particles present in the collection container (210) are removed from it by a backflushing operation.

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