Optimization of Isotope Separation
Experimental Investigations S-2 Laboratory Mass-Separator Operating Characteristics Aimed at Optimization of Coefficient of Separated Materials Utilization
Tech Area / Field
- FIR-ISO/Isotopes/Fission Reactors
- PHY-PFA/Particles, Fields and Accelerator Physics/Physics
3 Approved without Funding
VNIIEF, Russia, N. Novgorod reg., Sarov
- Institut Laue-Langevin, France, Grenoble\nGSI, Germany, Darmstadt\nBattelle Energy Alliance LLC (BEA) / Idaho National Laboratory, USA, ID, Idaho Falls\nUniversity of Oslo / Department of Chemistry, Norway, Oslo\nInternational Atomic Energy Agency, Austria, Vienna\nUS Department of Energy / New Brunswick Laboratory, USA, IL, Argonne
Project summaryMore than 35 years ago separation of isotopes was performed in VNIIEF using S-2 mass-separator in order to use them in solving scientific and applied tasks. As differentiated from other similar laboratory mass-separators used at the Institutes of Nuclear Physics (St.Petersburg) and Russia Scientific Center “Kurchatov Institute” (Moscow) the S-2 mass- separator is shielded against radiation. This provides the possibility of carrying out the works not only with stable, but with radioactive materials, and allows production of highly enriched isotopes in g- and even in mg-amounts sufficient to realize experiments using modern highly sensitive methods of registration.
Today this is the only mass-separator all over the world making it possible to carry out such works with radioactive isotopes. The efficiency of S-2 laboratory mass-separator application and the isotopes produced on it within the above-mentioned years has been demonstrated by the works of VNIIEF and other Russian Institutes (IPPE, Radium Institute by V.G.Khlopin, RSC KI, NIIAR). Consequently, there has been successfully realized a Program of Measuring Nuclear Physics Constants for the needs of Nuclear Power Engineering and, in the recent years, for studying the transmutation possibility of a set of long-lived isotopes to solve the problem of nuclear materials disposal. By the time of this program completion there became more acute another sphere of applying the method of isotopes electromagnetic separation - fundamental investigations in physics, medicine, industrial technologies etc.
In spite of the fact that inadequacy of large-scale production of fissile material isotopes was experimentally proved, nevertheless, the electromagnetic method of isotopes separation demonstrated unique potentialities in producing highly enriched (> 99.99%) isotopes widely used in a set of applied trends, namely, in nuclear medicine. Practical experience in using mass-separators demonstrated that the enrichment repetition factor of particular isotope depends highly on structural and electromagnetic characteristics of the installation and its operation modes, especially on type and temperature of ion source, on the place of this isotope in pleyade of the element, on mass number. In the course of separation there act several groups of isotopic pollution factors reducing the achieved in reality enrichment repetition factor, they are: availability of neutral vapors of separated material in the separation chamber, focusing imperfection, scattering and recharging of ions, their spread by energy, breakdowns in ion sources etc.
The possibility of getting high isotopic purity is as well related to the installation output. The lower is the capacity, the higher is, in principle, the isotopic purity of the final product. As differentiated from KI mass-separator at rubidium isotopes separation on Sidonie installation, France, Orsay Research Center, the enrichment level for rubidium-85 and rubidium-87 achieved at rubidium isotopes separation was 99,996% and 99,987%, correspondingly. Moreover, it should be taken into account that as compared to Kurchatov Institute where the source current was equal to 50-100mA, the French experts used the source current equal to ~3mA.
In connection with the fact that the original material in the ion source should be evaporated and the pressure of 10-2-10-3mm mercury column should be created, one has to increase the operating temperature of this assembly what is quite difficult - chiefly in limiting the permissible source operating current to fractions of milli-ampere.
Though the application of chloride compounds of separated materials many of which have the required vapor pressure at 700-1000oC allows separation of a wide group of elements, it is limited by useful ion current from the source because the volume charge creates all ions in the accelerated gap - both useful and impurity ones. As a rule, the number of impurity ions are several times higher and they considerably increase load to a high-voltage rectifier what leads to requirements of its operation higher stability, at least up to 0.2% per work day at the output current of 0.5-1A.
The acuteness of applying highly enriched stable and radioactive isotopes as original material for medical methods of different diseases diagnostics and curing, in industry and agricultural engineering, in nuclear physics researches required creation of a wide spectrum of ion-optical systems for ion sources, namely, those steadily operating under increased temperatures of heaters 1500-2200oС.
For a set of ion source systems and mass-separators used today quite achievable is the coefficient of material utilization equal to 35-40%. In RSC KI the highest value is 63%. Within the last four years there have been achieved in RFNC-VNIIEF the results opening prospects in perfecting and stabilizing operating characteristics of mass-separator and radiochemical techniques used at production of high-purity isotopes with unique characteristics for enrichment. As applied to one of elements – plutonium – these works were successfully carried out within the frames of ISTC Project No1318 funded by the USA and Norway.
It should be mentioned that though the obtained by today operating parameters of S-2 mass-separator assure production of high-purity isotopic specimens, a considerable mass of start material that is quite expensive as a rule, is lost in connection with low yield of singly charged ions at applying trichlorides in the ion source of S-2 mass-separator. In connection with abrupt reduction of regenerated material amount, the carrying out of consequent series of its regeneration increases multifold the labor output ratio of the works performed and leads to essential growth of the final product cost; it also increases radiation load to personnel responsible for S-2 maintenance.
Such characteristics as 85-90%- regeneration coefficient of material scattered in the installation for its further involvement in the separation process and ~100-% coefficient of accumulated in the collector isotopes isolation, should be considered both maximum possible and, correspondingly, those achieved. However, as in the accepted and used today process of electromagnetic separation of isotopes the operating substance loaded to the ion source of S-2 mass-separator is presented by trichlorides of separated elements, the coefficient of material utilization in the ion source cannot be high in principle; on the average it does not exceed 5%.
The cited facts and results prove the acuteness of realizing 2-3-fold increase of the coefficient of material utilization in the ion source of S-2 mass-separator. The improvement of this characteristic opens for S-2 mass-separator new prospects in getting highly enriched isotopes:
- production of the required amount of final product at essential reduction of the necessary mass of original material;
- carrying out of works in electromagnetic separation as applied to utilization of radioactive specimens of high specific activity;
- reduction of time needed to realize electromagnetic separation and, consequently, labor output ratio;
- corresponding decrease of the produced unit cost.
For quantitative determination of possible indexes the experimental investigations on S-2 mass-separator are required. The key point in perfecting the method of electromagnetic separation of isotopes and mass-separator technical (engineering) characteristics is the application of high-temperature ion source using original product in the form of metal as working substance. This increases ionization characteristics of the source and leads to the increase of isotopic ions yield.
The given paper seems to be science and technology development and continuation of the fulfilled developments and the subject of a new ISTC Project that immediately uses science, research and equipment base created as a result of carrying out the works on ISTC Project No1318.
Some particular experience in using metal form of original material was accumulated during trial experiments realized in the mid-seventies that were unfortunately not continued later on.
The scope of works of the advanced Project includes:
- development of techniques of getting separated substances in metal form at low initial amounts;
- selection and investigation of design characteristics of high temperature version of the ion source permitting the use of original material in metal form and applicable in the existing installation;
- enhancement of the installation power supply blocks and (schemes) of ion beam stabilization;
- development of algorithm of the procedure operations as well as development of elements ensuring quick adjustment of ion beam and optimal introduction of ions to the isotope collector boxes;
- development of monitoring techniques aimed at isotope mixture separation for different elements in order to select optimal methods of electromagnetic separation procedure.
Highly qualified specialists of the laboratory of electromagnetic separation of isotopes and radiochemistry possessing large experience in carrying out research works in this direction and in getting high-purity isotopes so that they are applied in promising scientific and applied tasks will be involved in the works on the Project.
The realization of new engineering solutions will make it possible to considerably increase the output of the produced isotopes at essentially lower expenditure of original materials and, thus, to reduce the cost of the unit of output. This will assist in a wider utilization of highly enriched stable and radioactive isotopes by scientific laboratories in fundamental and applied researches, especially in medicine. At the same time the increase of mass-separator operating characteristics, namely, of the coefficient of original material utilization in the source will make it possible to apply electromagnetic enrichment to a group of little distributed elements, such as berkelium, californium, einsteinium available in minimal amounts. This is of undoubted interest for the development of fundamental physics and for the experiments in synthesis of far transactinides.
The advanced Project is a good example of realizing conversion initiatives in special programs of RosAtom aimed at using highly enriched isotopes, for example, in medicine; in solving complex tasks of studying radioactive elements migration in environment and reliability of special-purpose repositories of Power Engineering radioactive wastes; in solving the problems of control over nuclear materials non-proliferation; in revealing undeclared nuclear activity as well as in fundamental researches, for example, under new transactinide elements synthesis.
The works on the Project will provide reorientation of RosAtom specialists who were earlier involved in weapon activities to the sphere of researches in unclassified conversion directions.
The scope of activities on the Project equal to 30 months and its cost equal to $270 000 were estimated basing on minimal expenses for its realization at maximum use of non-financial contribution and equipment of FSUE RFNC-VNIIEF.
Our business contacts with a set of leading foreign laboratories makes us hope for the fact that the world-famous scientists will be the Project collaborators and their participation in the Project will assist in optimization and scheduling of experiments as well as in critical analysis of trends where the works are scheduled to be performed.