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On-line Control of Iodine-129

#0663


Iodine -129 and Nitrogen Oxides Monitoring at a Radiochemical Plant and in Air

Tech Area / Field

  • ENV-MIN/Monitoring and Instrumentation/Environment

Status
3 Approved without Funding

Registration date
28.05.1996

Leading Institute
MIFI, Russia, Moscow

Supporting institutes

  • Khlopin Radium Institute, Russia, St Petersburg

Collaborators

  • Institut für Umwelttechnologien GmbH, Germany, Berlin\nBritish Nuclear Fuels Ltd (BNFL), UK, Chesire, Risley Warrington\nMediSyn Technologies Limited, Ireland, Wicklow

Project summary

The objective of this project is to carry out comprehensive study in the field of laser fluorescence spectroscopy of iodine isotopes and nitrogen dioxide and to develop high sensitive laser system for on-line monitoring of these substances in process gas inside the items of radiochemical plant equipment as well as iodine-129 in gas effluence of such a plant.

Safe operation of radiochemical plants processing high radioactive burned up nuclear fuel rods is one of the main today's environmental problems. It is significant that safety improvement is close connected with the problem of processing efficiency gain, and both problems need in sensitive and reliable instrumentation to detect radioactive and-highly toxic substances. Nitrogen oxides and iodine radioisotopes arise by burned up nuclear fuel dissolution in nitric acid. Among these hazardous gaseous products it is essential to note iodine-129. This long-lived isotope has decay period of 16 million years, and so, iodine-129 is the more harmful to the health than short-lived iodine-131 that is notorious in connection with Three Mile Island and Chernobyl accidents. But no effective high-sensitive instrumentation for on-line monitoring of the iodine-129 is available, though the related investigations are proceeded extensively in the US, Great Britain, France and Russia.

The participants of the project have advanced a technique for high-sensitive continuous monitoring of iodine-129 and nitrogen oxides based on combination of fluorescence and absorption methods of laser spectroscopy with the use of a He-Ne laser.

Now we are able to detect iodine-129 at a concentration as small as 3 ґ 1011 cm-3 (molecules per cm3) in process gases produced when burned up nuclear fuel is dissolved in nitric acid. Such detection limit is superior to results obtained by other authors (Soviet - French Workshop "Methods and Techniques to Control Processing of Burned up Fuel of Atomic Electric Power Stations", Chlopin’s Radium Institute, Leningrad, 1993), but it must be at least an order of magnitude better for safe and effective operation of a radiochemical plant. Detection limit of about 1010 cm-3 is need to detect iodine-129 reliably both in process gas and in emission gas flow after purification apparatus, and 109 cm-3 to provide iodine-129 environmental monitoring in an area close to a radiochemical plant.

To achieve so high a sensitivity more detail study of iodine isotopes and nitrogen oxides fluorescence must be carried out including measurements of cross-sections of fluorescence self-quenching and quenching by various buffer gases (He, Ne, Ar, Kr, Xe, O2, N2, CO2, H2O, NO, NO2 and air), cross-sections of collision induced energy transfer in iodine isotope - buffer gas system; investigation of optimum pressure, temperature and exciting radiation frequency to maximize fluorescence intensity of iodine isotopes; development of a technique to detect iodine-129 in the presence of nitrogen dioxide and the most abundant natural isotope iodine-127. Results of these investigations will be critical to fulfill the project successively; more over we expect that the results being of independent importance will make a contribution to fundamental spectroscopy.

We are planning to use results of these investigations in development of computer controlled laser system for continuous monitoring iodine-129 and nitrogen oxides in process gas and iodine-129 in gas emission flow of a radiochemical plant.

The laser system being the subject of the project has a number of practical advantages over known detection techniques:


- iodine-129 detection limit as low as 1010 molecules per cm3,
- performance of continuous on-line monitoring;
- simultaneous detection iodine-129 and nitrogen oxides;
- possibility to detect iodine-129 in mixtures with natural isotope iodine-127;
- feasibility to use electrical output signal to control the radiochemical processing of burned up nuclear fuel;
- long exploitation period, low power requirement, reliability, simplicity in operation and moderate cost.

We suppose that the laser system application will improve environmental safety of radiochemical industry and gain efficiency of burned up nuclear fuel processing.

Commercial significance of the project lies in the fact that the prototype of the laser system to be developed may be used to detect iodine isotopes and nitrogen oxides both in laboratories and at radiochemical plants. Participating institutions and collaborators will have an opportunity to produce such laser systems.

Potential Role of Foreign Collaborators

In the framework of the project the participation of foreign collaborating institutions BNFL (Great Britain), I.U.T. (Germany), is planned in the form of information and data exchange, as well as consultations, joint seminars and workshops to discuss results of investigations on the subject of the project.


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