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Radiation Resistant Optical Fibers

#1472


Research and Development of Radiation-Hardened Optical Fibers Intended for Use in the Civil Nuclear Industry

Tech Area / Field

  • FIR-INS/Nuclear Instrumentation/Fission Reactors
  • ENV-MIN/Monitoring and Instrumentation/Environment

Status
8 Project completed

Registration date
10.03.1999

Completion date
12.05.2005

Senior Project Manager
Lapidus O V

Leading Institute
TRINITI, Russia, Moscow reg., Troitsk

Supporting institutes

  • Institute of General Physics named after A.M. Prokhorov RAS / Fiber Optical Research Center, Russia, Moscow

Collaborators

  • Heraeus Quarzglas GmbH & Co. KG, Germany, Hanau\nEURATOM-Ciemat, Spain, Madrid\nFraunhofer-INT, Germany, Euskirchen\nDepartment of the Navy / Naval Research Laboratory, USA, DC, Washington\nSCK-CEN, Belgium, Mol\nCEA / Saclay (Essonne), France, Gif-sur-Yvette Cedex

Project summary

The aim of this project is to develop radiation-hardened large-core silica optical fibers, to optimize their design and fabrication technology, and to work out radiation-hardening techniques applicable already after the fiber drawing. Radiation-hardened fibers of this type are intended for plasma diagnostics in fusion reactors. In addition, the optimized preform technology and radiation-hardening techniques to be developed will allow improvement of fiberscopes intended for visual inspection of inaccessible parts of nuclear and thermonuclear installations.

Nuclear radiation produces point defects (color centers) in the fiberglass network, which cause absorption of the light signal propagating in the fiber (the so-called induced absorption effect). Another unwanted radiation-induced effect is radioluminescence producing a spurious light background in the fiber. Radiation hardening of fibers means reduction of the magnitude of the above effects. The participants of this project have demonstrated in their previous works that it is possible to significantly lower the induced absorption by optimizing the fiber technology and by applying certain radiation-hardening techniques to as-drawn fibers. Therefore, the research program of this project is based on the participants' previous achievements in this field.

The work under this project will include fabrication of fiber preforms using plasma outside deposition process (POD) and substrate silica rods made from KU and KS-4V silicas, drawing of polymer- and metal-coated fibers, hardening of the fibers against radiation via H2-loading and pre-irradiation, and investigation of the induced absorption and radioluminescence in the fibers in g-radiation fields and mixed g-neutron radiation fields at doses of up to 10 MGy. Thermal and optical bleaching of radiation-induced color centers will also be applied as 'in-situ' radiation-hardening techniques. The design and technology of preforms and fibers will be optimized via feedback with testing fibers under radiation.

The project is expected to yield the following results. The optimal regimes of hardening fibers against radiation via H2-loading and pre-irradiation will be determined. A technique for H2-loading of metal-coated fibers will be developed. The optimal core material of radiation-hardened fibers will be established. Based on the investigation of the radial distribution of radiation-induced color centers and luminescent centers over the fiber cross-section, the optimal core diameter and numerical aperture will be determined. The efficiency of 'in-situ' hardening of fibers via thermal and optical bleaching of radiation-induced color centers will be evaluated. The latter hardening techniques can be applied immediately in the process of reactor operation, or during shut-downs. The optimal parameters of laser radiation (wavelength, intensity, etc.) will be found for optical bleaching. An interesting way of performing thermal bleaching is to heat the fiber by passing an electric current through the metal coating. The efficiency of this thermal bleaching technique will be evaluated.

The research program concludes with demonstration of the optimized radiation-hardened fibers and optimized radiation-hardening techniques in radiation fields representative of the International Thermonuclear Experimental Reactor.

Duration of the project is three years.


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