RU2339718C2 - Method for receiving actinium-227 and thorium-228 from treated by neutrons in reactor radium-226 - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention concerns manufacturing of radionuclides for industry, science, nuclear medicine, especially radioimmunotherapy. Particularly it concerns method of receiving actinium -227 and thorium -228 from treated by neutrons in reactor radium-226. Method includes irradiation of target containing of metallic capsule in which there is located reaction vessel, containing radium-226 in the form of compound. Then it is implemented unsealing of target's metallic capsule, dissolving of received radium. From solution it is separated by means of precipitation, and then it is implemented regeneration, preparation to new irradiation and extraction of actinium-227 and thorium-228 from solution. At that irradiation, dissolving, radium separation, its regeneration and preparation to new irradiation are implemented in the form of its united chemical form - radium bromide, in the same reaction vessel made of platinum. Method provides reusing of the same platinum vessel for receiving of actinium-227 and thorium-228 from one portion of radium by recycling of irradiation and extraction in the same vessel. Separation of metallic capsule by means of dissolving provides saving of mechanical integrity of platinum reaction vessel for each new irradiation cycle and extraction.

EFFECT: increasing of radiationally-environmental safety of process, excluding operations of increased radiation hazard.

2 cl, 2 ex

Description

The invention relates to the production of radionuclides for industry, science, medicine and especially nuclear medicine, the problems of which require the use and organization of obtaining radionuclides in significant quantities and a wider range of radiation properties. The scale of the spread of cancer requires new approaches in the treatment of these diseases - radioimmunotherapy, and new radionuclides for their implementation. Alphon emitters are recognized as such radionuclides, the cytotoxic effect of which is 2-3 orders of magnitude higher than the effect of beta emitters. Of these, Tb-149, At-211, Pb-212 (Bi-212), Ra-223, Ra-224, Ac-225, Bi-213 are recognized as the most promising (in terms of biological effect and radiotherapeutic effectiveness) [McDevitt MR. Sgouros G., Firr RD at. al. "Eur, J. Nucl. Med. "1998. v.25. No. 9, p.1341-1351]. Three of them are the decay products of Ac-227 (Ra-223) and Th-228 (Ra-224, Pb-212 (Bi-212). The process of their separation from irradiated fuel is most satisfactory in obtaining them in sufficient quantities at a relatively low cost thermal neutrons in the Ra-226 reactor according to the multi-neutron capture reaction

Other sources of Ac-227 and Th-228 are laborious enough to produce them in the required quantities: Ac-227 — from previously obtained and aged Pa-231 preparations [Henrecsen G., Alstad J., Larsen R. “Radiochim. Acta "(2001) 89, 661-666]; Ac-227 from Uranium Processing Waste and Concentrates [Bray at al. U.S. Patent 5809394, September 15, 1998. Bray at al. U.S. Patent 5885465, 09/23/1999]; Th-288 - from the aged preparations of U-232 obtained by neutron irradiation of Pa-231 [Deliken O. "Health Phys" (1978) v. 35 (Juli), p.21-14] or from old thorium salts through preliminary isolation of Ra-228 [Sani A.R. "J. Radioanal chem. ", 1970, v. 4, p. 127]. The production of these isotopes from other nuclear reactions is not justified because of the small yield.

The process of separation of large quantities of Ac-227 and Th-228 from irradiated Ra-226 is characterized by specific features of this system: high specific energy release, due to the formation of two more radioactive families (Ac-227 (4n + 3) and Th-228 (4n)) manifested in the radiation destruction of technological reagents, the radiolysis of solutions, the violation of technological regimes, the release of large quantities of radioactive gases (Rn-22, Tn-220, An-219) and in an increased level of radiation hazard. Therefore, the urgent problem of any large-scale process of separation of Ac-227 and Th-228 from irradiated Ra-226 is the removal (separation) of primarily Ra-226 and other radium isotopes from the process in order to reduce the radiation effect on the process.

When receiving small quantities of Ac-227 and Th-228 for research programs, these problems do not arise.

Known gas-phase processes to some extent solve these problems, since they are less susceptible to radiation and can be carried out in hermetically sealed volumes (devices):

fractional sublimation of halides at temperatures of 800-900 ° C and a discharge of ~ 10 ^-6 mm Hg [French patent, No. 1518786, cl. C22 B, 05.17.1968]. However, engineering, technical and technological solutions for the implementation of such processes have not received the necessary development for use in applied, large-scale radiochemical processes.

Closest to the claimed is the Belgian process of large-scale production of Ac-227 from irradiated Ra-226 for an isotope thermoelectric generator based on it [LHBaetsle, P. Dejonghe, ACDemild, A.De. Troyer, A.Droissart, M.Poskin " Fourth United Nation International Conference on the Peaceful uses of Atomic Energy "Geneva, 1971, A / Conf. 49 / P / 287. Belgium, May, 1971].

This process includes the following main stages and operations, which reflect the features of its technological implementation:

- Preparation of the target for irradiation, the target consists of a capsule made of stainless steel, in which an aluminum matrix (Al matrix) with holes for filling them with calcined and ground radium carbonate powder (RaCO ₃ ) and sealing it is inserted into tight contact with the capsule walls in them up to a certain density (~ 1.9 g / cm), the capsule is sealed (prototype terminology, Fig. 2);

- Irradiation of the target in the reactor is carried out in the form of carbonate (RaCO ₃ );

- Opening an irradiated target. It is carried out by cutting the outer capsule;

- Separation of radium (from Ac and Th):

- Dissolution of irradiated RaCO _{3 is} carried out directly in the capsule in the channels of the Al matrix in diluted nitric acid (HNO ₃ ) (with the addition of acetic acid to quench foaming). At this stage, the corrosion products of the capsule and Al matrix enter the process.

- A solution of radium nitrate Ra (NO ₃ ) _{2 is} transferred from the capsule to a vessel of tantalum for precipitation and separation of radium. The separation of radium is carried out in the form of radium nitrate by precipitation with concentrated nitric acid (80% HNO ₃ ) in a tantalum vessel. After washing the precipitate, the solution is sent to the separation and separation of Ac-227 and Th-228, and the precipitate of radium nitrate is sent to regeneration in the carbonate form. The corrosion products of the capsule and Al matrix are distributed between the precipitate Ra (NO ₃ ) ₂ and the solution containing Ac-227 and Th-228.

- Radium regeneration (preparation for new exposure); since the form of irradiation of radium is radium carbonate, and the form of its separation is radium nitrate in the prototype, a series of operations are carried out to convert radium nitrate to carbonate (RaCO ₃ ). The precipitate Ra (NO ₃ ) ₂ in the tantalum vessel after separation of the filtrate is dissolved in water and transferred to another vessel to precipitate RaCO ₃ .

- The precipitation of RaCO _{3 is} carried out by adding an excess of NH ₄ OH to the aqueous solution of Ra (NO ₃ ) ₂ while continuously passing gaseous CO ₂ through the ammonia solution to form a precipitate of RaCO ₃ . The precipitation and separation of radium in the form of RaCO ₃ is not complete. The reason for this is the high radiation loads (radiolysis, due to the presence of all radium isotopes Ra-226, Ra-224, Ra-223 with decay products that violate the deposition mode) and the presence of corrosion products of the capsule and Al matrix Al, Fe, Cr, Ni, Mn and others, forming in the ammonia medium hydrolyzed and colloidal forms, capturing part of the radium.

- In order to avoid losses of radium at this stage in the prototype an additional stage of fixing losses in the form of radium chromate RaCrO ₄ , which is deposited in the filtrate after separation of the precipitate RaCO ₃ .

- Preparing RaCO ₃ for a new exposure:

- The precipitate RaCO ₃ in the tantalum vessel is dried and calcined;

- The calcined and sintered precipitate RaCO _{3 is} crushed;

- Powder of ground RaCO ₃ fill the channels of a new Al-matrix of a new target and use it in them for new exposure.

- The separation and isolation of Ac-227 and Th-228 is carried out by a known ion-exchange method on Dawex AG 1 × 8 anion exchange resin in 5 M HNO ₃ .

- Purification of Ac-227 is carried out in a known manner in the form of oxalate [Z.K. Karalova, B.F. Myasoedov, "Actinium", M., 1982].

The method selected as a prototype, its features and structure (scheme) of the separation process were determined by two initial positions: the difference in the chemical forms of radiation of radium (in the form of carbonate, RaCO ₃ and its separation from Ac-227 and Th-228 (in the form of radium nitrate , Ra (NO ₃ ) ₂ ), as well as a target device for irradiating radium carbonate.

The first of these requires the inclusion of radium regeneration operations in the process to prepare it in the form of carbonate for new irradiation. This is expressed in the organization of a separate stage with the appropriate infrastructure and hardware. This stage, due to high radiation exposures due to the presence of all radium isotopes and their decay products, as well as the appearance of target corrosion products (upon dissolution of irradiated RaCO ₃ ), is accompanied by technological violations of the operation mode and technological losses of radium, which in turn requires the introduction of a process scheme one more independent stage - fixing radium losses in the form of RaCrO ₄ chromate (and also with its infrastructure).

In addition, the regeneration process proposed in the prototype under the conditions of its implementation is accompanied by radiation-hazardous operations such as sparging of CO ₂ gas through an ammonia solution of radium to form carbonate, which is accompanied by the powerful release of all radioactive gases (Rn-222, Tn-220, An-219 ) and the formation of aerosols with all isotopes of radium (Ra-226, Ra-224, Ra-223) and their decay products. The target device for irradiating the carbonate used in the prototype necessitates the stage of dissolving the irradiated radium carbonate directly in the capsule (after cutting it) in the channels of the Al matrix and the appearance of corrosion products of the capsule and matrix in the technological process. The latter are, as already indicated, one of the causes (along with radiolysis) of the violation of the technological regime of the radium regeneration stage, due to the formation of hydrolyzed and colloidal forms of corrosion products that are difficult to separate and radium losses with them. And the introduction of a separate stage of fixing losses of radium in the form of RaCrO ₄ , and at the stage of separation of Ac-227 and Th-228, the refusal to use radiation-resistant inorganic ion exchangers (Zr and Ti phosphates) due to their loss of ion exchange capacity on corrosion products (see prototype, page 7).

The use of the target in its device, as proposed in the prototype, is inevitably accompanied by the application at the stage of preparation of the target for irradiation of radiation-hazardous dust-forming operations: grinding the sintered during calcination of RaCO ₃ , transferring it from the vessel for calcination to the Al matrix and filling it with powder of channels Al-matrices and its seals. In addition, the design solution, which is implemented in the target proposed in the prototype, allows only a single use of each target with the obligatory passage each time of all stages of the technological process of preparing radium for new exposure.

The objective of the present invention is:

- reduction of the multi-stage process;

- increase the technological reliability of the process (the exclusion of operations unreliable in their implementation in conditions of high radiation exposure to radiation and capable of causing a violation of technological conditions);

- simplification and reduction of the complexity of operations;

- increase the radiation safety of the process: the exclusion or reduction in the number of radiation-hazardous operations (the formation of aerosols, dust-forming, bubbling).

To obtain such technical results, which are determined by the tasks, in the presented invention, which retains all the functional stages and operations with radium common with the prototype, it is proposed, unlike the prototype, the use of a single chemical form of radium - radium bromide (RaBr ₂ ) - on all stages and operations with it: dissolution, separation (precipitation), regeneration, preparation for new irradiation and irradiation itself, and all these operations are proposed to be carried out in the same reaction vessel, manufactured made of platinum, as a thermally and corrosion-resistant material, inert to activation by neutron irradiation in a reactor, and which, before irradiation, is placed for sealing in a metal capsule, for example, from aluminum.

Using a single chemical form - radium bromide - allows you to carry out the following of the tasks:

- The combination of the stages of separation of radium (in the form of nitrate) and its regeneration (in the form of carbonate) in one chemical process of separation of radium (in the form of bromide) excludes the regeneration process as a separate, independent stage (stage) of the technological process; precipitated RaBr ₂ , after separation of the mother liquor containing Ac-227 and Th-228, is a form ready for new irradiation.

- The exclusion of the stage of regeneration in its form, as it is carried out in the prototype, avoids the operations of fixing the loss of radium in the form of RaCrO ₄ as a separate stage of the process.

- The exclusion of the regeneration stage in the form presented in the prototype allows to increase the process reliability of the process - to avoid operations as precipitating radium carbonate in ammonia in the presence of corrosion products and the formation of difficult to separate forms of corrosion products under conditions of high radiation exposure (radiolysis, decomposition of reagents) .

- To improve the radiation environment and radiation safety of the process by eliminating such radiation-hazardous operations as sparging of CO ₂ gas through an ammonia solution of radium, accompanied by a strong release of radioactive gases (Rn-222, Tn-220, An-219) and the formation of aerosols with all isotopes radium (Ra-226, Ra-224, Ra-223) and their decay products.

- The combination of the stages of separation of radium and its regeneration simplifies the process, reduces its complexity in its implementation and equipment.

Carrying out all of these operations, including irradiation, in the same reaction platinum vessel allows, in development to the results indicated earlier, to carry out other of the tasks:

- the combination of operations for preparing radium for irradiation (calcination, grinding) and irradiation in one platinum vessel avoids such a time-consuming stage as filling the calcined radium powder with narrow channels of the Al matrix (5 mm in diameter) and compacting them to a certain density.

- The combination of dissolution of irradiated radium, separation (precipitation) and regeneration, carried out, according to the prototype, in three different reaction vessels (dissolution in a capsule, deposition in a tantalum vessel, regeneration in a third vessel) in the same platinum vessel significantly simplify the process, avoid operations to transfer solutions from the capsule to the tantalum vessel, and from it to the vessel for regeneration, thereby reducing the complexity of the process and simplify it in the technological equipment and implementation.

- The use of this difference allows to exclude the ingress of mechanical impurities and corrosion products (when opening the capsule and dissolving the irradiated radium in it) in the process and to avoid disruption of its technological mode.

- To improve the radiation environment and radiation safety of the process - to avoid radiation-hazardous dust-forming operations such as grinding calcined radium in the regeneration vessel, transferring the powder to the Al-matrix, filling its channels and compaction in them, which also simplifies the whole process .

The use of a platinum vessel for such a multifunctional purpose allows carrying out the technological process of separating Ac-227 and Th-228 multiple times in the same platinum vessel with the same portion (load) of radium in the alternation and repetition of irradiation and isolation cycles, which distinguishes the claimed the method of the prototype, in which for each new exposure requires the preparation (equipment) of a new Al-matrix.

To achieve this result, in the proposed invention for sealing a platinum vessel, in contrast to the prototype, a metal capsule is used, for example, of aluminum, in which a platinum vessel is placed. This allows you to open the aluminum capsule by dissolution without violating the integrity of the platinum vessel, thereby ensuring its multiple use with one portion of radium.

The proposed method is carried out in the following sequence:

1. Irradiation of the target with radiation by neutrons in the reactor (the target is RaBr ₂ in a platinum vessel in an aluminum capsule sealed by welding).

2. The target is opened by dissolving the aluminum capsule.

3. The separation of radium.

3.1. Dissolution of irradiated RaBr ₂ in a platinum vessel in 0.1 M HBr in a minimum volume.

3.2. Precipitation of RaBr _{2 with} concentrated HBr.

3.3. The separation of the mother liquor.

4. Preparation of RaBr ₂ for new exposure.

4.1. Drying and calcining the RaBr ₂ precipitate in a platinum vessel.

4.2. Sealing a platinum vessel with calcined RaBr ₂ in a new aluminum capsule.

5. The separation of Ac-227 and Th-228 is carried out by extraction of Th-228 with tributyl phosphate or trioctylamine in a known manner.

6. The purification of Ac-227 is carried out by its precipitation in the form of oxalate. [Z.K. Karalova, B.F. Myasoedov, "Actinius", M., 1982].

EXAMPLE 1

The target was to be processed (a platinum vessel in an aluminum capsule) containing 150 mg of Ra-226 (for metal) in the form of radium bromide, 137 mCi Ac-227 and 130 mCi Th-228.

The opening of the aluminum capsule was carried out by its dissolution in a solution of the composition (NaNO ₃ + NaOH). Dissolution of irradiated RaBr ₂ was carried out in a 0.1 M HBr platinum vessel (in a minimum volume to create a saturated solution).

Radium is separated in the same platinum vessel by precipitation in the form of bromide (RaBr ₂ ) concentrated HBr. The mother liquor containing Ac-227 and Th-228 is separated from the precipitate, the precipitate is washed with concentrated HBr. The combined mother liquor is evaporated to convert it to the nitrate form. The wet residue is dissolved in 6 M HNO ₃ . The separation of Ac-227 and Th-228 is carried out with 40% tributyl phosphate (TBP) in benzene from an aqueous solution of 6 M in HNO ₃ . The aqueous phase containing Ac-227 is washed with benzene. Reextraction of Th-228 from the organic phase is carried out with 0.1 M HNO ₃ . The re-extract is washed with benzene. The yield of Ac-227 is 92%, Th-228 is 81%.

EXAMPLE 2

The target (a platinum vessel in an aluminum capsule) containing 1990 mg of Ra (for metal) in the form of RaBr ₂ (radium bromide) 1880 mCi Ac-227 and 1760 mCi Th-228 was subject to processing.

The opening of the aluminum capsule is carried out by its dissolution in a solution of the composition (NaOH + NaNO ₃ ). The dissolution of irradiated radium bromide is carried out in a platinum vessel in a minimum volume of 0.1 M HBr. Radium is separated in the same platinum vessel by its precipitation in the form of concentrated HBr bromide. The precipitate is separated, washed with concentrated HBr, the washing solutions are combined with the main mother liquor.

The combined mother liquor containing Ac-227 and Th-228 is evaporated to convert it to the nitrate form. The wet residue is dissolved in 3 M HNO ₃ .

The separation of Ac-227 and Th-228 is carried out by extraction with a 0.4 M solution of trioctylamine (TOA) in dibutyl ether (DBE) from an aqueous solution of 3M HNO ₃ . The extract containing Th-228 is washed with 3M HNO ₃ and Th-228 is re-extracted with 0.1 M HNO ₃ , the re-extract is washed with RHEED. The raffinate containing Ac-227 is washed with RHEED.

Radium bromide (after precipitation) in the same platinum vessel is dried, calcined at a temperature of ~ 300 ° C, closed with a stopper and sealed in a new aluminum capsule for new irradiation.

Claims (2)

1. A method of producing actinium-227 and thorium-228 from radium-226 irradiated with neutrons in a reactor, comprising irradiating a target consisting of a metal capsule into which a reaction vessel containing radium-226 in the form of a compound is placed, opening the target metal capsule, dissolving the irradiated radium, its separation by precipitation, regeneration, preparation for a new exposure and the separation of actinium-227 and thorium-228 from a solution, characterized in that the irradiation, dissolution, separation of radium, its regeneration and preparation for a new exposure is carried out in the form its single chemical form - radium bromide, in the same reaction vessel made of platinum. 2. The method according to claim 1, characterized in that the opening of the metal capsule in which the platinum vessel is placed is carried out by dissolution.