Grinding blast

Abstract

To provide a blast cleaning method.SOLUTION: A blast cleaning method is provided, comprising subjecting a work surface to a blast stream, the work surface being a metal contaminated with one or more radioactive moieties and the blast stream comprising water and one or more types of resin particles.SELECTED DRAWING: None

Description

Background Art

[0001] It is often desirable to decontaminate metal surfaces contaminated with radioactive isotopes. For example, when a nuclear reactor is partially or completely decommissioned, it is desirable to remove radioactivity from metal components. In particular, steel materials exposed to neutron radiation become contaminated with cobalt-60, and much of this contamination is located near the surface of the steel. The decontamination methods known heretofore include various techniques, each of which has significant drawbacks such as the following: chemical or electrochemical methods that remove layers from the work surface, which produce an undesirable large amount of secondary waste; mechanical methods that involve cleaning or applying a removable coating, which involve an undesirable large amount of intensive manual labor. Although several decontamination techniques have been proposed, methods including, for example, microorganisms, microwaves, lasers, supercritical fluids, exothermic powders, or electrical heating of the work surface are not widely used. Some decontamination methods involve either water blasting or dry blasting using a mixture of abrasive materials such as zeolite and air. Blasting with only water generates a large amount of contaminated water, causing serious waste problems. All dry blasting processes are known to cause problems with airborne dust.

[0002] Japanese Patent Laid-Open No. 05-87983 describes a method of removing radioactive substances from a surface by spraying a mixture of zeolite and air onto the surface. It is desirable to provide a decontamination method that avoids the problem of dust generated by dry blasting and also reduces the contamination of water used in the decontamination process.

Summary of the Invention

Means for Solving the Problems

[0003] The following is an explanation of the present invention.

[0004] A first aspect of the present invention is a blasting cleaning method including bringing a working surface into contact with a blasting stream, wherein the working surface is a metal contaminated with one or more radioactive portions, and the blasting stream includes water and one or more resin particles.

DETAILED DESCRIPTION OF THE INVENTION

[0005] The following is a detailed description of the present invention.

[0006] As used herein, unless clearly indicated otherwise by context, the following terms have the designated definitions.

[0007] As used herein, "resin" is synonymous with "polymer", which is a relatively large molecule composed of reaction products of smaller chemical repeating units. The polymer may have a structure that is linear, branched, star-shaped, loop-shaped, hyperbranched, cross-linked, or a combination thereof; the polymer may have a single type of repeating unit ("homopolymer") or may have two or more types of repeating units ("copolymer"). Copolymers may have various types of repeating units arranged randomly, in an orderly manner, in blocks, in other arrangements, or in any mixture or combination thereof.

[0008] Molecules that can react with each other to form the repeating units of a polymer are recognized herein as "monomers". The repeating units thus formed are recognized herein as the "polymerization units" of the monomer.

[0009] Vinyl monomers have the structure

CHEMICAL FORMULA

[0010] Some vinyl monomers have one or more polymerizable carbon-carbon double bonds incorporated into one or more of R 1 , R 2 , R 3 and R 4 Such vinyl monomers are recognized herein as polyfunctional vinyl monomers. A vinyl monomer having exactly one polymerizable carbon-carbon double bond is recognized herein as a monofunctional vinyl monomer.

[0011] Styrene-based monomers have each of R 1 and R 2 being hydrogen, R 3 being hydrogen or alkyl, and -R 4 having the structure

Chemical formula

[0012] An acrylic monomer is a vinyl monomer in which each R 1 and R 2 are hydrogen, R 3 is either hydrogen or methyl, and -R 4 has the following structure:

Chemical formula

[0013] A resin having 90% by weight or more of polymerized units of a vinyl monomer is a vinyl resin. A resin having 80% by weight or more of polymerized units of a styrene monomer is a styrene resin. A resin having 55% by weight or more of polymerized units of an acrylic monomer is an acrylic resin. When the resin contains 0.5% by weight or more of polymerized units of a polyfunctional vinyl monomer, the resin is considered to be crosslinked in this specification. In a typical sample of a crosslinked resin, if 20% by weight or less of the resin dissolves in any solvent, the crosslinked resin is considered to be "fully" crosslinked in this specification.

[0014] In this specification, "beads" are solid particles at 25°C. Spherical beads are characterized by their diameter. Non-spherical beads are considered to have the same diameter as a virtual sphere of the same volume as the actual beads. An aggregate of beads is characterized by the volume average diameter. Beads containing 80% by weight or more of a resin are resin beads. The resin beads may be macroporous beads or gel beads.

[0015] Macroporous resin beads have a porous structure with an average pore diameter of 20 nm or more. The pore diameter is measured using the Brunauer-Emmett-Teller (BET) method using nitrogen gas.

[0016] In gel resin beads, the pores are the free volume between atoms in the intertwined, and in some cases crosslinked, polymer chains of the polymer beads. The pores of gel-type polymer beads are less than 20 nm. In some cases, the pores in the gel-type resin are too small to be detected by using the BET method.

[0017] As used herein, "ultrafiltration" (UF) refers to a process in which water containing impurities is pushed out by a pressure gradient through a membrane having permanent pores. The UF membrane is semipermeable and blocks (i.e., retains) the passage of particles 50 nm or larger in diameter. Water, dissolved substances, and smaller particles pass through the UF membrane through the pores. The transmembrane pressure is typically 10 to 100 kilopascals (kPa) (1.45 to 14.5 psig).

[0018] As used herein, "reverse osmosis" (RO) refers to a process in which, similar to ultrafiltration, water containing impurities is pushed out by a pressure gradient through a membrane. The RO membrane is semipermeable but does not have permanent pores. The RO membrane blocks the passage of all particles. Water passes through the RO membrane by diffusion through the membrane material. RO is typically very effective at retaining almost all solutes, including monovalent ions.

[0019] As used herein, "ion exchange" is a process in which water containing dissolved ions passes through a fixed bed of ion exchange resin particles. The ions dissolved in the water are exchanged with ions of the same charge present within the ion exchange resin particles (i.e., cation exchange with other cations and anion exchange with other anions). For example, dissolved cobalt cations present in water can be exchanged with sodium ions present in the ion exchange resin, and then the water, after passing through the fixed bed of ion exchange resin particles, will have dissolved sodium ions instead of some or all of the original dissolved cobalt ions.

[0020] Steel is any of various alloys of iron and carbon. Other elements such as manganese, nickel, chromium, molybdenum, boron, titanium, vanadium, tungsten, cobalt, and niobium may also be present in the steel. Iron is always 50 wt% or more of the composition of the steel.

[0021] Ratios are described in this specification as follows. For example, if a ratio is said to be 3:1 or more, the ratio can be 3:1 or 5:1 or 100:1, but cannot be 2:1. A general way of expressing this concept is as follows: When a ratio is said to be X:1 or more in this specification, it means that the ratio is Y:1 where Y is equal to or more than X. Similarly, for example, if a ratio is said to be 15:1 or less, the ratio can be 15:1 or 10:1 or 0.1:1, but cannot be 20:1. Generally speaking: When a ratio is said to be W:1 or less in this specification, it means that the ratio is Z:1 where Z is equal to or less than W.

[0022] The present invention includes the use of a blast stream containing both water and one or more resin particles. Preferably, the resin particles form a slurry in which the resin particles are distributed throughout a continuous medium containing water. Preferably, the blast stream has a pH of 6 or less; more preferably 5 or less; more preferably 4 or less; more preferably 3 or less. Preferably, the blast stream has a pH of 0 or more; more preferably 1 or more.

[0023] Preferably, the amount of the resin particles is 2% by weight or more; more preferably 5% by weight or more; more preferably 8% by weight or more based on the total weight of water and the resin particles. Preferably, the amount of the resin particles is 45% by weight or less; more preferably 35% by weight or less based on the total weight of water and the resin particles.

[0024] Preferably, the resin particles have a volume average diameter of 100 μm or more; more preferably 200 μm or more; more preferably 400 μm or more. Preferably, the resin particles have a volume average diameter of 2000 μm or less; more preferably 1000 μm or less.

[0025] A preferred resin is a vinyl resin; an acrylic resin and a styrene resin are more preferred; a styrene resin is more preferred. Preferably, the amount of polymerized units of styrene monomer is 90% by weight or more; more preferably 95% by weight or more based on the weight of the resin.

[0026] Preferably, the resin is crosslinked; more preferably, the resin is fully crosslinked. Preferably, the amount of polymerized units of the polyfunctional vinyl monomer in the resin is 2% by weight or more based on the weight of the resin; more preferably, 4% by weight or more. Preferably, the amount of polymerized units of the polyfunctional vinyl monomer in the resin is 15% by weight or less based on the weight of the resin; more preferably, 10% by weight or less.

[0027] The resin may or may not contain covalently bonded functional groups. A functional group is any chemical group containing an atom other than hydrogen or carbon, except that the ester bond in an ester of acrylic acid or methacrylic acid is not regarded as a functional group. The functional group may be in a neutral form or an ionic form.

[0028] Preferably, the resin contains a covalently bonded functional group selected from a sulfonic acid group, a carboxyl group, a secondary amine group (including a secondary amine group in which one or more carbon atoms bonded to the nitrogen atom are part of an alkyl group substituted with a phosphonic acid group), a tertiary amine group, and a quaternary ammonium group (including a quaternary amine group in which one or more carbon atoms bonded to the nitrogen atom are part of a hydroxyalkyl group). More preferably, the resin contains a covalently bonded functional group selected from a sulfonic acid group, a carboxyl group, a secondary amine group in which each carbon atom bonded to nitrogen (excluding carbon atoms that are part of the polymer chain of the resin) is part of an unsubstituted alkyl group, a tertiary amine group in which each carbon atom bonded to nitrogen (excluding carbon atoms that are part of the polymer chain of the resin) is part of an unsubstituted alkyl group, and a secondary amine group in which one or more carbon atoms bonded to the nitrogen atom are part of an alkyl group substituted with a phosphonic acid group.

[0029] Mixtures of suitable and preferred resins are also suitable and preferred.

[0030] The blasting cleaning process includes bringing the blasting stream into contact with the working surface. Preferably, the blasting stream is emitted at the working surface. The blasting stream may be emitted in any way. For example, a mixture of water and resin particles may be mixed with a stream of compressed air to form a mixed stream, and then the mixed stream may be directed towards the working surface. In another example, a mixture of water and resin particles may be emitted by a pump.

[0031] When air is mixed with the slurry, the preferred air-to-slurry ratio is 0.05:1 or more; more preferably 0.10:1 or more. When air is mixed with the slurry, the preferred air-to-slurry ratio is 0.5:1 or less; more preferably 0.3:1 or less.

[0032] Preferably, the blasting stream, whether it contains compressed air or not, is extruded through a nozzle to generate a stream directed towards the working surface. Preferably, the pressure of the blasting stream inside the nozzle is 1 megapascal (MPa) (145 psi) or more; more preferably 2 MPa (290 psi) or more; more preferably 3 MPa (435 psi) or more. Preferably, the pressure of the blasting stream inside the nozzle is 7 MPa (1015 psi) or less.

[0033] Preferably, the blasting stream has a temperature of 0 °C or more; more preferably 10 °C or more; more preferably 15 °C or more; more preferably 18 °C or more. Preferably, the blasting stream has a temperature of 35 °C or less; more preferably 30 °C or less.

[0034] The working surface is the surface of an article. Preferably, the article is made of steel. Preferably, the article contains one or more radioisotopes; more preferably, the article contains one or more radioisotopes of chromium, nickel, or cobalt; more preferably, the article contains cobalt-60 ( 60 also represented as Co). Preferred articles are parts of a current or past nuclear power plant that have been exposed to neutron radiation.

[0035] After the working surface comes into contact with the blast stream, the blast stream is referred to herein as "spent". The term "spent blast stream" as used herein refers to the blast stream and materials removed from the working surface by the blasting process. The materials removed from the working surface are preferably recovered from the spent blast stream.

[0036] Preferably, the spent blast stream undergoes a separation process, such as filtration and / or other processes, to separate water from resin particles, other solid materials, and dissolved contaminants. The water thus separated from various contaminants is considered to be pure enough for use in industrial processes, such as serving as the water used in the blast stream of the present invention.

[0037] It is also expected that after water removal, the waste solids (including other solid substances such as resin particles and compounds dissolved in the water of the blast stream) will contain radioactive waste removed from the working surface, and that the waste solids will then be sufficiently concentrated to be disposable in a reasonable manner.

[0038] One advantage of the present invention is thought to be that when a radioactive working surface is cleaned, the removed radioactive substances tend to adhere to solid particles (i.e., resin particles) in the blast stream rather than remaining in the water to a much greater extent than with conventional known methods. Therefore, the radioactive waste is mainly concentrated in solid form, and it is expected that the problem of disposal of water contaminated with radioactivity will be reduced.

Examples

[0039] The following are examples of the present invention.

[0040] The operation of bringing a metal surface containing radioactive cobalt into contact with a blast stream was reproduced by using the following model system. Stirring paddles were fabricated from a high-cobalt alloy, and the paddles were rotated in a slurry of water and resin beads. Rectangular specimens of the same alloy were also placed as baffles in the stirred slurry. The ability of the process to remove cobalt from the metal and the preferential tendency for cobalt to be located in the resin beads rather than in the water were measured.

[0041] The water used in these examples was MILLI-Q TM water from Millipore Corporation. This water was of high purity and had a resistivity of 10 megaohm*cm at 25°C.

[0042] The metal samples were HAYNES TM 188 alloy from Haynes International, which had the following composition:

[0043]

Table 1

[0044] After adjusting the solution to pH 2.1 with HCl, a stirred flask test was conducted using approximately 1500 g of a 10 wt% aqueous slurry of various particle types. Mechanical stirring was set at 500 rpm using a HAYNES® 188 alloy (UNS R30188) stirring paddle. Additionally, a baffle containing HAYNES® 188 alloy specimens was placed in each flask. After 24 hours, at 25°C, a fixed portion of the test water and particles ("test resin") was removed and the metal content was measured using inductively coupled plasma mass spectrometry (ICP-MS). Also, a control resin (not used in any of the tests) was examined by ICP-MS.

[0045] ICP-MS was performed as follows. The elemental concentrations (ng / g) of three sample preparations of each resin (both the test resin and the control resin) were determined by ICP mass spectrometry and fitting to a calibration curve after MW digestion. Each resin of approximately 0.25 g was digested in nitric acid using a Milestone MW. The final samples were prepared by diluting the total weight to 20 g with water (80-fold sample dilution) and filtering through a 0.2 mM filter. The calibration matrix for these samples consisted of HCl. The parameters of the ICP procedure were as follows:

[0046]

Table 2

[0047] The following table shows the concentrations (nanograms of a specific element per gram of water or resin, ng / g) of specific isotopes of the target elements found in the test water, control resin, and test resin.

[0048] The particle types examined were sand and five types of ion exchange resins as follows. All five ion exchange resins are fully cross-linked. All are manufactured as styrene / divinylbenzene copolymers, which are then bonded to functional groups shown by reacting with various reagents. All are products of the Dow Chemical Company. The resins were either gel resins or macroporous (MP) resins. "nt" means no test. "<LOD" means below the detection level.

[0049]

Table 3

[0050] The results were as follows:

[0051]

Table 4

[0052]

Table 5

[0053]

Table 6

[0054] Except for SBA resin, the elements Co, Cr, Ni, and to some extent W, are found in larger amounts in the test resin than in the test water or the control resin. Therefore, the resin was able to remove and retain these elements. For example, when using any of the IRC, WBA, SAC1, or SAC2 resins, the test resin incorporated a significant amount of cobalt-59 from the alloy, and the amount of cobalt-59 remaining in the water was relatively small. These resins are also thought to be effective in removing and retaining cobalt-60 removed from steel during the blasting process. The aspects of the present invention are listed below. (Aspect 1) A blasting cleaning method including bringing a working surface into contact with a blasting stream, wherein the working surface is a metal contaminated with one or more radioactive portions, and the blasting stream contains water and one or more resin particles. (Aspect 2) The method according to Aspect 1, wherein the metal is steel. (Aspect 3) The method according to Aspect 1, wherein the radioactive portion contains one or more radioisotopes of cobalt, nickel, or chromium. (Aspect 4) The radioactive portion is 60 The method according to Aspect 1, including Co. (Aspect 5) The method according to Aspect 1, wherein the resin particles contain a styrene resin. (Aspect 6) The resin particles are ion exchange resin particles having covalently bonded sulfonic acid groups; ion exchange resin particles having covalently bonded carboxylic acid groups; ion exchange resin particles having covalently bonded secondary amine groups; ion exchange resin particles having covalently bonded tertiary amine groups; ion exchange resin particles having covalently bonded quaternary ammonium groups; and mixtures thereof; The method according to Aspect 1, including particles of one or more ion exchange resins selected from the group consisting of. (Aspect 7) The method according to Aspect 1, wherein the pH of the blasting stream is 4 or less. (Aspect 8) The method according to Aspect 1, wherein the blasting stream has a temperature of 15°C to 35°C.

Claims

1. A blasting cleaning method comprising bringing a working surface into contact with a blasting stream, wherein the working surface is a metal contaminated with one or more radioactive parts, the blasting stream contains water and one or more resin particles, the resin particles include an ion exchange resin having a covalently bonded sulfonic acid group; an ion exchange resin having a covalently bonded carboxylic acid group; an ion exchange resin having a covalently bonded secondary amine group; an ion exchange resin having a covalently bonded tertiary amine group; an ion exchange resin having a covalently bonded quaternary ammonium group; and mixtures thereof; include particles of one or more ion exchange resins selected from the group consisting of, and removing at least a part of the radioactive part from the working surface and attaching it to the particles of the ion exchange resin, a method characterized by.

2. The method according to claim 1, wherein the metal is steel.

3. The method according to claim 1, wherein the radioactive part contains one or more radioisotopes of cobalt, nickel, or chromium.

4. wherein the radioactive moiety is ６０ The method according to claim 1, wherein the radioactive moiety contains Co.

5. The method according to claim 1, wherein the resin particles contain a styrene resin.

6. The method according to claim 1, wherein the pH of the blasting stream is 4 or less.

7. The method according to claim 1, wherein the blasting stream has a temperature of 15°C to 35°C.

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