Systems and methods for treating fluids containing radioactive materials

Abstract

A process and system are provided for treating a fluid including water, radioactive particles, dissolved ions, and a neutron absorber. The fluid is received from a cutting zone that recovers the radioactive components. The process includes receiving the fluid into a crystallization unit, the fluid including water, radioactive particles, and the neutron absorber dissolved therein, cooling the fluid below the freezing point of the fluid to form first crystals including water, forming second crystals that are denser than the first crystals and include the neutron absorber, and separating the first crystals from the second crystals, the radioactive particles, and the dissolved ions.

Description

Cross-reference and priority claim to related applications

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 123,321, filed December 9, 2020, the entire contents of which are incorporated herein by reference. [Technical Field]

[0002] Aspects of the present disclosure relate to the field of fluid processing, and in particular, in some embodiments, aspects of the present disclosure relate to systems and methods for processing fluids containing radioactive materials. [Background technology]

[0003] The failure or decommissioning of a nuclear reactor, which means that fuel is trapped within the reactor, presents many technical challenges. In many cases, the fuel reaches high temperatures under decay heat and melts, destroying the casing, support structures, and any containment structures that hold the fuel. After cooling, the result is a mixture of solidified nuclear fuel, fission products, fuel rod casings, moderator rods, steel plates, and concrete, which may be recovered and / or segmented for storage. Summary of the Invention [Problem to be solved by the invention]

[0004] During decommissioning, reactor cooling is achieved by adding water to the fuel melt. The spent cooling water is then removed from the reactor, treated, and recycled to the reactor. This water is contaminated with radioactive species, but its low activity means it can be used for conventional treatment processes. Aspects of this application relate to the situation when attempting to cut the melt into salvageable pieces. The cutting process is carried out underwater, and as a by-product of cutting, the cooling water is contaminated with highly radioactive particles. Highly radioactive particles may not be compatible with conventional treatment processes for the following reasons: High levels of radiation can cause degradation of the materials of construction, in the case of polymers Filters and strainers can become clogged with particles - Excess ion exchange material leads to deterioration Complex systems can quickly become contaminated

[0005] Furthermore, freeze crystallization can sometimes significantly reduce energy consumption compared to vacuum distillation techniques.

[0006] In some embodiments, cooling water can be recycled to minimize waste and overcome storage limitations.

[0007] In some embodiments, aspects of the present application can circulate cooling water that is clear enough that the remote cutting operation can be observed underwater.

[0008] According to one aspect, a system for treating a fluid received from a nuclear reactor cutting zone, the fluid containing radioactive particles, is provided, the system including at least one heat exchanger for cooling the fluid containing radioactive particles, at least one pump configured to pump the fluid through the at least one heat exchanger at a rate greater than a precipitation threshold, a crystallization unit configured to cool the fluid initially cooled by the at least one heat exchanger to a temperature below the freezing point of the fluid, at least one scraper for removing formed ice crystals from the fluid in the crystallization unit, a scrubbing system configured to reduce small particles entrained by the ice crystals with surface water, and a melter configured to melt the scrubbed ice crystals into a fluid returning to the reactor cutting zone.

[0009] Embodiments may include combinations of the above features.

[0010] According to another aspect, a system for treating fluid received from a nuclear reactor cutting zone, the fluid including water, radioactive particles, dissolved ions, and neutron absorbers, is provided. The system includes at least one heat exchanger that cools a fluid containing radioactive particles; at least one pump configured to pump the fluid through the at least one heat exchanger at a rate greater than a precipitation threshold; a crystallization unit configured to cool the fluid initially cooled by the at least one heat exchanger to a temperature below the freezing point of the fluid to form first crystals comprising water and second crystals comprising a neutron absorber, the crystallization unit including a mechanical device for removing the first crystals from the crystallization unit and an outlet for discharging the second crystals, the radioactive particles, and dissolved ions; at least one scraper for removing at least one of the first ice crystals and the second ice crystals formed from the fluid in the crystallization unit; a washing system configured to reduce small particles entrained by the first ice crystals using surface water; and a melter configured to melt the washed ice crystals into a purified fluid that is returned to the reactor cutting zone.

[0011] In one embodiment, the system includes a fluid treatment system configured to treat the melted ice crystals before they are returned to the reactor cutting zone.

[0012] In one embodiment, the system comprises a settling tank configured to receive and separate a bottom product from the crystallization unit, and a supernatant treatment system configured to treat a supernatant from the settling tank.

[0013] In one embodiment, the system comprises one or more shielding elements configured to provide shielding for one or more aspects of the system.

[0014] In one embodiment, the system includes a second stage crystallization unit configured to receive the cooled fluid, the second crystals, the radioactive particles, and the dissolved ions from the crystallization unit, the second stage crystallization unit including a heat exchanger for reducing the temperature of the cooled fluid, the second crystals, the radioactive particles, and the dissolved ions below a saturation point of the neutron absorber to precipitate third crystals comprising water and fourth crystals comprising the neutron absorber, and the second stage crystallization unit includes a second mechanical device for removing the third crystals and a second outlet for discharging the cooled fluid, the second crystals, the fourth crystals, the radioactive particles, and the dissolved ions.

[0015] In one embodiment, the system includes a separator that separates the cooled fluid, second crystals, fourth crystals, radioactive particles, and dissolved ions discharged from the second outlet of the second-stage crystallization unit into a crystal-rich slurry and a liquid concentrate, wherein the crystal-rich slurry comprises the second crystals and the fourth crystals, and the liquid concentrate comprises the cooled fluid, radioactive particles, and dissolved ions.

[0016] Embodiments may include combinations of the above features.

[0017] According to another aspect, there is provided a process for treating a fluid received from a cutting zone to recover radioactive components, the fluid comprising water, radioactive particles, dissolved ions, and a neutron absorber, the process comprising: receiving the fluid into a crystallization unit, the fluid comprising water, radioactive particles, and a neutron absorber dissolved therein; cooling the fluid below the freezing point of the fluid to form first crystals comprising water and second crystals comprising the neutron absorber, the second crystals being denser than the first crystals; and separating the first crystals from the second crystals, radioactive particles, and dissolved ions.

[0018] In one embodiment, the neutron absorber is boric acid.

[0019] In one embodiment, the hardening rate of the radioactive particles is 0.5 to 2 mh -1 is.

[0020] In one embodiment, the process includes removing solid suspended particles from the fluid before the fluid is received in the crystallization unit.

[0021] In one embodiment, the process includes pre-cooling the fluid to a temperature above the freezing point of the fluid before the fluid is received in the crystallization unit.

[0022] In one embodiment, the process includes mechanically discarding at least one of the first crystals and the second crystals from a cooling surface of the crystallization unit.

[0023] In one embodiment, the process includes mechanically removing the first crystals from the crystallization unit.

[0024] In one embodiment, the process includes washing the first crystal to clean the surface of the first crystal and reduce the amount of entrained radioactive particles and fluid on the surface of the first crystal.

[0025] In one embodiment, the process includes melting the first crystals to form purified water and recycling the purified water to the cutting zone.

[0026] In one embodiment, the process includes maintaining fluid through a crystallization unit at a velocity greater than the precipitation threshold using at least one pump.

[0027] In one embodiment, the process includes removing the second crystals, the radioactive particles, and the dissolved ions from the bottom of the crystallization unit, and separating the second crystals from the radioactive particles in a separator using at least one of gravity settling, sedimentation, or enhanced settling. In one embodiment, the enhanced settling is hydrocycloning or centrifugation.

[0028] In one embodiment, the process includes providing shielding against radioactive particles for at least one aspect of the process.

[0029] Embodiments may include combinations of the above features.

[0030] According to another aspect, a method for treating a fluid containing radioactive particles received from a reactor cutting zone is provided, the method including: cooling the fluid containing radioactive particles in at least one heat exchanger; maintaining the fluid through the at least one heat exchanger with at least one pump at a rate greater than a precipitation threshold; cooling the fluid in a crystallization unit to a temperature below the freezing point of the fluid; removing formed ice crystals from the fluid in the crystallization unit; washing the ice crystals with surface water to reduce small particles entrained on the ice crystals; and melting the washed ice crystals in a fluid returned to the reactor cutting zone.

[0031] Embodiments may include combinations of the above features.

[0032] Further details of these and other aspects of the subject matter of the present application will become apparent from the detailed description and drawings included below. [Brief explanation of the drawings]

[0033] In the drawings, embodiments are shown by way of example, and it is to be expressly understood that the present description and the figures are for illustrative purposes only and are intended to aid understanding. [Figure 1] FIG. 1 is a schematic diagram illustrating aspects of an exemplary processing system. [Figure 2] FIG. 1 is a schematic diagram illustrating aspects of an exemplary processing system. [Figure 3] 1 is a schematic diagram illustrating an exemplary process for treating a fluid containing water, radioactive particles, dissolved ions, and a neutron absorber. DETAILED DESCRIPTION OF THE INVENTION

[0034] Decommissioning of nuclear facilities containing very high levels of radioactivity often requires the underwater ablation of radioactive materials. In one example, material recovery can be performed from a reactor's uranium core, supporting steel work, fuel cladding, fission products, and surrounding concrete. The mixture of recovered materials varies in composition and density, necessitating the segmentation and removal of sections of the reactor, e.g., the reactor core, by methods such as laser ablation. The radioactive ablation process can be performed underwater for cooling purposes and to prevent the spread of contaminated dust. As a byproduct of the ablation, the cooling water becomes contaminated with highly radioactive particles and dissolved radioactive species. Contaminated cooling water is also referred to herein as "liquor." High levels of radioactivity are incompatible with conventional water treatment technologies, such as ion exchange or semipermeable membrane separation, because the energy from radioactive decay breaks the covalent bond between the two constituent molecules. For waste minimization purposes and due to storage limitations, the cooling water can be reused whenever practical.

[0035] Coolant water is fed into the (reactor) cutting zone and accumulates there to form a pool of cooling water. After passing through the cutting zone, the cooling water may be contaminated with solid particles including zircaloy, uranium oxide, strontium, cesium, steel, stainless steel, concrete, and / or other materials present in the reactor. In this specification, the fluid is referred to as "liquor." The particle size of the solids in the liquor depends on the cutting technique and is typically less than 5 mm.

[0036] The cooling water may include a neutron absorber to prevent radioactive materials from achieving criticality in the cutting zone. In one example, the neutron absorber may be boric acid. The neutron absorber may be dissolved in the cooling water and circulated through the cutting zone, where it then forms part of the liquid. As described herein, the neutron absorber may be recovered from the liquid and reused or stored in accordance with the systems and methods described herein.

[0037] In this disclosure, terms such as "maximize," "minimize," and "optimize" may be used, but it should be understood that such terms are used to refer to improvements, adjustments, and refinements that may not be strictly limited to a maximum, minimum, or optimum.

[0038] The terms "connected" or "coupled" can include both direct coupling (where the two elements coupled together are in contact with each other) and indirect coupling (where at least one additional element is located between the two elements).

[0039] As used herein, the term "substantially" may be applied to modify any quantitative expression. A quantitative expression may be permissibly varied without ultimately changing the basic function to which the expression relates. For example, a drive shaft disclosed herein having a circular cross section may be permissibly varied within the scope of the present invention, provided that its rotational drive capability is not substantially altered.

[0040] As used herein, the term "cutting zone" or "cutting operation" refers to a volume underwater where radioactive material resides and can be cut for recovery. The cut is performed underwater and in the presence of neutron absorbers to regulate temperature and mitigate criticality of the radioactive material.

[0041] As used herein, the term "melter" refers to a heated vessel in which the crystals described herein are melted.

[0042] Aspects of various embodiments are described with reference to the drawings.

[0043] Referring to FIG. 1 , which illustrates an exemplary system 100 according to the present disclosure, highly radioactive liquid 101 is pumped from a cutting zone 103 by a pump 102 suitable for solids processing (e.g., an open-impeller metal centrifugal pump). In some embodiments, pump 102 is configured to pump fluid 101 at a sufficiently high velocity to maintain suspension. The appropriate velocity depends on the cutting technique. In some embodiments, this velocity is greater than 1.5 m / s.

[0044] The first stage of the process is pre-cooling with one or more heat exchangers 104. In some embodiments, two heat exchangers are configured to operate in series. In some embodiments, three or more heat exchangers can be used.

[0045] In some embodiments, the heat exchanger 104 is a commercially available metal shell and tube construction designed to prevent the accumulation of radioactive particles. The heat exchanger is cooled via a commercially available refrigeration plant with a medium selected to optimize the cooling / melting cycle energy.

[0046] In some embodiments with multiple exchangers 104, the first stage heat exchanger is cooled with chilled water, and the second stage may be cooled with a water / glycol mixture or by direct evaporation of the refrigerant. The temperature of the liquid is brought close to its freezing point. Shielding may be provided to protect the operator and to maintain the liquid velocity to prevent precipitation.

[0047] The cooled liquid 101 is introduced into the crystallization unit 105, where the liquid is cooled below its freezing point. The process of freezing the nuclei and forming ice crystals can occur on the internal cooling surfaces 106 of the crystallization unit 105. The internal cooling surfaces 106 are mechanically scraped to prevent ice buildup. Mechanical means, such as electrically driven mechanical scrapers, are used to remove ice deposits from the cooled internal surfaces. Crystallization can also occur in the bulk liquid within the crystallization unit 105. During the crystallization process, most of the particulate materials mentioned above (e.g., uranium oxide chips, steel scraps, concrete dust, etc.) are excluded from the ice crystals due to their physical and chemical properties. Ice crystals formed from water are less dense than the liquid and therefore rise under natural buoyancy. The ice crystals may contain traces of dissolved salts and particulates. A cooling system 123 can provide chilled fluid to cool the crystallization unit 105, and more specifically, the internal cooling surfaces 106.

[0048] A portion of the solid particles entrained in the liquid (e.g., particles greater than about 100 microns in size) will settle rapidly to the bottom of the crystallization unit 105. A portion of the particles (e.g., particles less than 100 microns) will gradually settle into the liquid and be drawn out the bottom of the crystallization unit along with the settled particles.

[0049] The system 100 may be made from radiation-resistant materials. Radiation shielding is used as needed to protect operators and radiation-sensitive equipment.

[0050] In use, ice crystals 107 formed from water produced in crystallization unit 105 rise to the top of the unit and are continually removed by buoyancy or mechanical means until they reach scrubbing system 108, which is configured to reduce entrainment of particulates on the surface of the ice crystals using a scrubbing fluid 109, such as water. Spent purified water 110 is returned to the steam supply 111.

[0051] The washed ice crystals 112 are transferred to the melter 113 where they are melted. In some embodiments, the melter 113 is configured to use heat rejected from the initial cooling stage, conserving electrical energy. The melter 113 is a vessel with a recycled water stream. The melted ice crystals are the processed product and are returned to the reactor as clear, cold cooling water. A cooling system 123 can circulate warmed, cooled fluid from the crystallization unit 105 to the melter 113 to melt the washed ice crystals 112 and recycle them to the crystallization unit 105. In some embodiments, the melted ice crystals 114 are treated in a treatment process 115, such as Spinionic™, filtration, ion exchange, and / or another suitable treatment process to purify the melted ice crystal stream for recycle to the cutting zone 103 in a purified water stream 116.

[0052] The bottom product 117 from the crystallization unit 105 is a mixture of settled solids, finely suspended solids, and chilled liquid. This mixture is fed to a settling tank 118. The solids 119 can be separated from the water by settling in the settling tank 118 and, depending on the type of bottom product 117, by chemical dosing. In some embodiments, the supernatant 120 from the settling tank 118 can be treated by processes such as ALPS™ 121 and Spinionic™ 122. The bottom product of solids 119 from the settling tank 118 is suitable for sludge treatment and / or final disposal.

[0053] In some embodiments, the system 100 is capable of treating water containing highly radioactive particulate contaminants, including fuel and fission products.

[0054] In some embodiments, at least some aspects of system 100 can separate particulate contamination without the use of physical barriers (filters / membranes). In some embodiments, the system can be resistant to high levels of radiation because it does not use polymeric materials used in the reverse osmosis or ultrafiltration stages of conventional processing pathways. In some embodiments, each component of system 100, including crystallization unit 105, does not contain polymeric materials.

[0055] In some embodiments, the present system can use significantly less energy than other barrier-less technologies, such as vacuum distillation.

[0056] FIG. 2 illustrates a system 200 for processing a fluid containing water, radioactive particles, dissolved ions, and neutron absorbers. Similar to the fluid 101 in the embodiment shown in FIG. 1, the fluid 201 may be contaminated water containing radioactive particles received from a cutting operation for the recovery of radioactive components. The composition of the fluid 201 depends on the cutting target but may include derivatives of zircaloy, uranium oxide, strontium, cesium, steel, stainless steel, concrete, and other materials present in nuclear reactors. The fluid 201, sometimes referred to as a liquor, is highly radioactive. The particle size of solids in the liquor depends on the cutting technique and is typically less than 5 mm, but may range from 1 to 20 microns. The liquor is transported from the cutting zone by a pump suitable for handling solids (e.g., an open-impeller metal centrifuge) at a rate sufficient to maintain suspension. The velocity of the fluid 201 depends on the cutting technique. In one example, the velocity of the fluid 201 is greater than 2 m / s.

[0057] Fluid 201 may undergo an optional initial separation in separator 202. Separator 202 may be configured to remove solid suspended particles entrained during fluid 201, i.e., liquid, transport from the cutting zone. The technical specifications of separator 202 are selected based on the characteristics of the solids in fluid 201. Separator 202 may be configured to remove 99% of particles in fluid 201 larger than 10 μm before entering the freeze crystallization process in crystallization unit 205. In one example, separator 202 is a gravity settling, sedimentation, or enhanced settling separation, e.g., hydrocyclone. Solid slurry 221 is generated from separator 202 forming the first product and is suitable for disposal via an appropriate disposal route (e.g., encapsulation). In one example, separator 201 is configured to separate water from radioactive particles based on the density of the solids in fluid 201. In one embodiment, separator 202 is a settling tank or a gravity-assisted separation unit, such as a hydrocyclone.

[0058] The clarified fluid 203 can be sent to a first-stage crystallization unit 205 to form floating ice crystals on the surface of the fluid within the first-stage crystallization unit 205, forming crystals containing a neutron absorber that settle within the first-stage crystallization unit 205. Optionally, the clarified fluid 206 can be pre-cooled by at least one heat exchanger 204, which can be arranged in series, before entering the first-stage crystallization unit 205. The heat exchanger 204 can be a commercially available metal shell-and-tube structure and can be specifically configured to prevent the accumulation of radioactive particles and avoid potential criticality. The heat exchanger 204 can be cooled via a commercially available refrigeration plant with a medium selected to optimize the cooling / melting cycle energy. In one example, the heat exchanger 204 can comprise two heat exchangers, i.e., a first-stage and a second-stage heat exchanger connected in series. In this embodiment, the first stage heat exchanger is cooled with chilled water, and the second stage may be cooled with a water / glycol mixture or by direct evaporation of the refrigerant. The liquid may be brought close to its freezing point. Further in this embodiment, the first stage heat exchanger may cool the clarified fluid 203 to about -2°C to about -5°C, and the second stage heat exchanger may cool the clarified fluid 203 to about -12°C to about -20°C. Shielding may be provided around the heat exchanger 204 and other components of the system 200 to protect operators from radiation, maintain liquid velocity, and prevent solids buildup.

[0059] The clarified fluid 203, i.e., the liquid, is introduced into the first-stage crystallization unit 205, where the liquid is cooled below its freezing point. The process of freezing the nuclei and forming crystals can be carried out on the internal cooled metal surface of the crystallizer, which is mechanically scraped by an electrically driven mechanical scraper to prevent the accumulation of crystals (e.g., boric acid crystals and / or ice crystals). The metal cooled surface of the crystallization unit 205 can be electropolished stainless steel. The crystallization unit 205 can have a cooling jacket cooled by the same fluid as defined for the second-stage heat exchanger 204 in the example above. Crystallization can also occur in the bulk liquid within the crystallization unit 205. Due to physical and chemical characteristics during the crystal growth process, the grown crystals can be pure, and impurities such as ionic species (e.g., strontium) and particulates (e.g., metal dust smaller than 10 μm) are not incorporated into the crystal lattice. A density difference exists within the crystallization unit 205 between the (HO) ice crystals and other crystals formed (e.g., neutron absorber crystals, e.g., boric acid). The less dense ice crystals rise to the top of the crystallization unit 205, while the denser crystals (e.g., neutron absorber crystals) settle to the bottom of the crystallizer along with the free particles and proceed to the next stage. Thus, the neutron absorber according to the present disclosure can have a crystal density greater than that of the ice crystals. Solid particles (concrete, steel plates, uranium) in the crystallization unit 205 settle as a function of the density, shape, size, and viscosity of the liquid. In one example, the settling rate of the solid particles is between 0.5 and 2 mh. -1The ice crystals may rise to the top of the crystallization unit 205 by buoyancy and continue to be removed by mechanical means, such as a mechanical member configured to remove the crystals from the liquid surface, via the first ice crystal steam 207 until they reach the first washing system 208. The first washing system 208 is configured to wash the surface of the ice crystals to reduce entrainment of liquid and particulates on the surface of the crystals. The first washing system 208 may wash the ice crystals using water, such as water sprayed onto the surface of the ice crystals. The purified water 210 is returned to the first stage crystallizer 205 as a recycle stream. The washed ice crystals from the first washing system 208 are transferred to the melter 213, where they are melted. In one example, the melter 213 is a melter with an electric heating element. In another example, the washed ice crystals are melted using heat rejected from the initial cooling stage, i.e., a heated vessel, to conserve electrical energy. The molten purified water 240 from the melter 213 can be recycled to the first washing system 208 , the second washing system 228 as washing fluid 209 , 229 or pumped to the cutting zone 241 .

[0060] The bottom product 217 from the crystallization unit 205 is a mixture of neutron absorber crystals (e.g., boric acid), finely suspended solids, dissolved salts, and a chilled liquid. The bottom product 217 is separated in a separator 218 to produce a first crystal-rich slurry 219 and a liquid 220 that also contains finely suspended solids and dissolved salts. The separator 218 is configured to separate the first crystal-rich slurry 219 by a method dependent on the concentration and density of the components. Examples of separation methods include gravity settling, sedimentation, or enhanced settling (e.g., hydrocyclone or centrifugation). The first crystal-rich slurry 219 contains the neutron absorber and is a product suitable for reuse in the process, where the neutron absorber can be stored and / or reused to mitigate criticality in the cutting zone. The liquid stream 220, containing all dissolved material and remaining particles, is fed to a second crystallizer 225, which utilizes a similar operating method as the first-stage crystallizer 205. The crystallizer unit 225 reduces the temperature of the liquid stream 220 below the saturation point of the neutron absorber (e.g., boric acid), resulting in the precipitation of more neutron absorber crystals. Furthermore, the crystallization unit 225 also crystallizes water in the liquid stream 220, resulting in a higher concentration of liquid and particles, as the resulting ice crystals are removed in a second ice crystal stream 227. The ice crystals rise to the top of the crystallization unit 225 by buoyancy and may continue to be removed by mechanical means until they reach a second wash system 228. The bottom product 237 of the second crystallization unit 225 may be a mixture of finely suspended solids, cold liquid, and dense crystals containing the neutron absorber (e.g., boric acid). The bottom product 237 may be sent to a separator 238 for separation into a second crystal-rich slurry 239 and a liquid concentrate 240 containing residual particles and dissolved salts. The liquid concentrate 240 may be the final waste stream and may contain remaining suspended particles and dissolved salts. Similar to the first crystal-rich slurry 219, the second crystal-rich slurry 239 contains a neutron absorber (e.g., boric acid), which can be reused in the cutting zone to mitigate criticality. The systems and methods described herein allow for the removal of the neutron absorber from the solution without the use of additives such as pH adjusters for separation.

[0061] The second ice crystal stream 227 may be sent to a second scrubbing system 228. The second scrubbing system 227 may scrub the surfaces of the ice crystals with a scrubbing fluid 229 to reduce entrainment of liquid and particulates on the wet surfaces of the ice crystals. The clarified water 230 is returned to the second stage crystallization unit 225 as a recycle stream.

[0062] The exemplary systems 100, 200 described herein may not include polymeric materials. Polymeric materials are used in the reverse osmosis, ultrafiltration, or ion exchange stages of conventional treatment systems, which may include the use of polymeric materials in the reverse osmosis, ultrafiltration, or ion exchange stages of conventional treatment systems. 5 ("Application of Membrane Technology for Liquid Radioactive Waste Treatment", Technical Report No. 431, IAEA, p. 23, Section 4.1.5). Systems according to the present disclosure can withstand high levels of radiation due to the elimination of polymeric materials.

[0063] FIG. 3 shows a schematic diagram illustrating a process for treating a fluid containing water, radioactive particles, dissolved ions, and a neutron absorber. Reusing the water and neutron absorber recovered from the process minimizes the amount of new material, i.e., water and neutron absorber, used in the cutting zone. In one example, the cutting zone may be a nuclear reactor containing damaged, decommissioned, or decommissioned equipment. The process includes, at 302, receiving a fluid from the cutting zone. The fluid may be received in a crystallization unit having a cooling surface configured to remove heat from the fluid. The cooling surface may be scraped by mechanical means, e.g., a scraping member, to remove crystals on the cooling surface. In one embodiment, the fluid is pre-cooled to a temperature above the freezing point of the fluid, e.g., about −2° C., before being received in the crystallization unit. In one embodiment, solid suspended particles are removed from the fluid before it is received in the crystallization unit.

[0064] In 304, the fluid is cooled below its freezing point. As the fluid cools below its freezing point, the water and neutron absorber in the fluid crystallize. In one embodiment, the fluid is cooled to about 2°C to -6°C. In another embodiment, the fluid is cooled to about -12°C to -20°C. First crystals containing water are formed, and second crystals containing the neutron absorber are formed. In one embodiment, the neutron absorber is boric acid. Crystallization can occur in the bulk liquid of the fluid or on the cooling surface of a crystallization unit. Due to the physical and chemical properties of the crystal growth process, the grown crystals may be pure, with no impurities, such as ionic species (e.g., strontium) and particulates (e.g., metal dust smaller than 10 μm), incorporated into the crystal lattice. The density difference between the first and second crystals, i.e., ice crystals and neutron absorber crystals (e.g., boric acid), causes the less dense ice crystals to rise to the top of the fluid, while the denser second crystals (i.e., neutron absorber crystals) sink to the bottom of the fluid along with the free particles, moving on to the next stage. Solid particles in the fluid (e.g., concrete, steel plates, uranium) settle depending on the density, shape, size, and viscosity of the liquid. Dissolved ions also remain in the fluid. In one embodiment, solid particles in the fluid remain in the fluid for 0.5-2 mhr. -1 Since the first and / or second crystals may be formed on the cooling surface of the crystallization unit, in one embodiment, the first and / or second crystals may be mechanically discarded from the cooling surface of the crystallization unit.

[0065] The first crystals are separated from the second crystals, radioactive particles, and dissolved ions at 306. In one example, the first crystals may be separated from the second crystals by mechanical means, such as a mechanical member or conveyor that skims the crystals from the surface of the fluid.

[0066] In one embodiment, after the first crystals are separated from the second crystals, radioactive particles, and dissolved ions, the first crystals are washed to purify the surface of the first crystals and reduce the amount of entrained fluid and radioactive particles on the surface of the first crystals. The first crystals can also be melted to form purified water that can be recirculated to the cutting zone.

[0067] In one embodiment, the second crystals, radioactive particles, and dissolved ions are separated from the bottom of the crystallization unit, and the second crystals are separated from the radioactive particles in a separator using at least one of gravity settling, sedimentation, or enhanced sedimentation separation. In one example, enhanced gravity separation is hydrocycloning or centrifugation.

[0068] In accordance with the systems and processes described herein, precipitation of solids, including radioactive materials, can be mitigated by maintaining a fluid velocity above the precipitation threshold in some of the systems and / or processes described herein. As an example, the processes described herein may require the use of at least one pump to maintain a fluid velocity greater than the precipitation threshold through a crystallization unit.

[0069] Shielding may be placed in the systems and processes described herein to provide protection against radioactive particles of at least one embodiment of the systems and processes described herein, and the shielding may provide radiation protection to individuals in close proximity to the systems and processes described herein.

[0070] Although the embodiments have been described in detail, it is to be understood that various changes, substitutions, and alterations can be made therein without departing from the scope of the present disclosure. Moreover, the scope of the present disclosure is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification.

[0071] Those skilled in the art will readily appreciate that the corresponding embodiments described herein may utilize any now existing or later developed disclosures, processes, machines, manufacture, compositions of matter, means, methods, or steps which perform substantially the same function or achieve substantially the same results, and therefore, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

[0072] It will be understood that the above-described and illustrated embodiments are intended to be examples only.

Claims

1. 1. A process for treating a fluid received from a cutting zone to recover radioactive components, the fluid including water, radioactive particles, dissolved ions, and neutron absorbers, comprising: receiving a fluid into a crystallization unit, the fluid comprising the water, the radioactive particles, and the neutron absorber dissolved therein; cooling the fluid below its freezing point to form first crystals comprising the water and second crystals having a higher density than the first crystals, the second crystals comprising the neutron absorber; separating the first crystals from the second crystals, the radioactive particles, and the dissolved ions; The process includes:

2. The process of claim 1 , wherein the neutron absorber is boric acid.

3. The settling velocity of solid particles in the fluid is 0.5 to 2 mhr －１ and the solid particles comprise the radioactive particles.

4. 4. The process of any one of claims 1 to 3, comprising removing solid suspended particles from the fluid before it is received in the crystallization unit.

5. 5. The process of any one of claims 1 to 4, comprising pre-cooling the fluid to a temperature above the freezing point of the fluid before it is received in the crystallization unit.

6. 6. The process of any one of claims 1 to 5, comprising mechanically discarding at least one of the first crystals and the second crystals from a cooling surface of the crystallization unit.

7. 7. The process of any one of claims 1 to 6, comprising mechanically removing the first crystals from the crystallization unit.

8. 8. The process of claim 7, comprising washing the first crystal to clean a surface of the first crystal and reduce the amount of the radioactive particles and the fluid entrained on the surface of the first crystal.

9. 9. The process of claim 7 or 8, comprising melting the first crystals to form purified water and recycling the purified water to the cutting zone.

10. 10. The process of any one of claims 1 to 9, comprising using at least one pump to maintain the fluid through the crystallization unit at a velocity greater than a precipitation threshold.

11. 11. The process of any one of claims 1 to 10, comprising removing the second crystals, the radioactive particles, and the dissolved ions from a bottom of the crystallization unit; and separating the second crystals from the radioactive particles and the dissolved ions in a separator using at least one of gravity settling, sedimentation, or enhanced sedimentation separation.

12. 12. The process of claim 11, wherein the enhanced sedimentation is hydrocycloning or centrifugation.

13. The process of any one of claims 1 to 12, comprising in at least one aspect of the process providing shielding against the radioactive particles.

14. 1. A system for treating a fluid received from a nuclear reactor cutting zone, the fluid including water, radioactive particles, dissolved ions, and neutron absorbers, comprising: at least one heat exchanger for cooling the fluid containing the radioactive particles; at least one pump configured to pump the fluid through the at least one heat exchanger at a rate greater than a precipitation threshold; a crystallization unit configured to cool the fluid initially cooled by the at least one heat exchanger to a temperature below the freezing point of the fluid to form first crystals comprising the water and second crystals comprising the neutron absorber, the crystallization unit comprising: a mechanical device for removing the first crystals from the crystallization unit; and an outlet for discharging the cooled fluid, the second crystals, radioactive particles, and the dissolved ions; at least one scraper for removing at least one of the first crystals and the second crystals formed from the fluid in the crystallization unit; a washing system configured to reduce small particles entrained on the first crystals with surface water; a melter configured to melt the washed crystals; A system comprising:

15. a fluid treatment system configured to treat the molten crystals before they are returned to the reactor cutting zone. The system of claim 14.

16. a settling tank for receiving a bottom product from the crystallization unit and separating the bottom product; a supernatant processing system configured to process the supernatant from the settling tank; The system of claim 14 comprising:

17. The system of claim 14 , comprising one or more shielding elements configured to provide shielding for one or more aspects of the system.

18. a second stage crystallization unit configured to receive the cooled fluid, the second crystals, the radioactive particles, and the dissolved ions from the crystallization unit; the second-stage crystallization unit comprises a heat exchanger for lowering the temperature of the cooled fluid, the second crystals, the radioactive particles, and the dissolved ions below a saturation point of the neutron absorber to precipitate third crystals comprising water and fourth crystals comprising the neutron absorber; 15. The system of claim 14, wherein the second stage crystallization unit comprises a second mechanical device that removes the third crystals and a second outlet that discharges cooled fluid, the second crystals, the fourth crystals, radioactive particles, and the dissolved ions.

19. 20. The system of claim 18, further comprising a separator that separates the cooled fluid, the second crystals, the fourth crystals, the radioactive particles, and the dissolved ions discharged from the second outlet into a crystal-rich slurry and a liquid concentrate, wherein the crystal-rich slurry includes the second crystals and the fourth crystals, and the liquid concentrate includes the cooled fluid, the radioactive particles, and the dissolved ions.

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