Electron accelerator applications for radiation processing

Full text: Department of Nuclear Sciences and Applications (NS) - contributes to the worldwide nuclear sciences and technology development. Through NS, jointly with institutes and laboratories worldwide, the IAEA supports R and D on critical problems facing developing countries. Work targets food, health, water, environment and high tech areas where nuclear and radiation technologies can make a difference. The results and recommendations from the programme elaborated at NAPC lead to organization and execution of the following meetings on the most important issues regarding radiation technology applications, mostly based on accelerator technology: - Technical Meeting (TM) on 'Emerging Applications of Radiation Processing', April, 2003, Vienna, Austria (TECDOC-1386) - Consultants Meeting (CT) on 'Advances in Radiation Processing of Polymers', September 2003, Notre Dame, Indiana, U.S.A. (TECDOC-1420) - Consultants Meeting (CT) on 'Status of Industrial Scale Radiation Treatment of Wastewater', October 2003, Daejon, Republic of Korea (TECDOC-1407) - Consultants Meeting (CT) on 'Radiation Processing of Polysaccharides', November 2003, Takasaki, Japan (TECDOC-1422) - Consultants Meeting (CT) on 'Emerging Applications of Radiation in Nanotechnology', March 2004, Bologna, Italy (TECDOC-1438) - Consultants Meeting (CT) on 'Radiation Processing of Gaseous and Liquid Effluents', September 2004, Sofia, Bulgaria. The total number of accelerators installed all over the world exceeds 13,000, among them the number of units applied for radiation processing being close to 1,200. Direct, transformer accelerators, single resonant cavity accelerators and microwave source powered linear accelerators have been found to be the most suitable for radiation processing. The industrial accelerators' development is still in progress, not only due to new areas of application but also because of demands of lower cost and more compact size machines. Some new countries elaborated their own programmes concerning accelerator family developments. The low energy accelerators' capability has not been explored fully up to now. New environmental applications demand development of high power, reliable accelerators. The most powerful radiation processing facility, applying accelerators over 1 MW total power has been constructed for power plant emitted flue gases purification. However, these new challenges for accelerator manufactures demonstrated that further progress in accelerator technology is needed and possible. Application of X-rays for radiation processing based on X-ray tubes is quite popular in the case of blood irradiation. The concept of e-/X conversion is known for years, a lot of R and D was performed in the field and some units were installed. However, a breakthrough in technology is expected after implementation of the high power units, which are already being tested. Commercial irradiators are being offered on the market. The recent developments in the field of radiation technology and application of electron accelerators are presented in the paper delivered as a plenary lecture at IMRP, Chicago, 2003. Besides, there are some well-established technologies like: - Sterilization; - Food irradiation (mostly spices and herbs); - Polymer cross-linking (cables, thermo shrinkable materials, tires, composites etc). There are also new and emerging applications: - Environment protection; - Natural polymers processing; - Homeland security; - Nanotechnology. These and other applications require new modeling and dose distribution calculation methods. The progress in the field of instrumental and modeling methods may allow to achieve better control of Sterility of Assurance Level (SAL) which can allow to apply, if regulated, optimum dose leading to higher throughput. Sometimes it is good to recall basics concerning the dose rate calculations that explain why in the on-line systems almost exclusively electron accelerators are applied. The continuous flow of material irradiators was proposed by different authors, were applied in the industrial scale for flue gas and wastewater irradiation. Another application is sludge hygenization. However, low energy accelerators were applied for on-line surface sterilization as well. The flow mixed reactor has been applied for natural latex vulcanization as well. This is a new approach from the point of view of radiation process engineering. It is well known that chemical or material engineering mostly apply high temperature and/or high pressure processes for material synthesis/modification and quite often a catalyst is required to speed up the reaction. Radiation is the unique source of energy, which can initiate chemical reactions at any temperature, including ambient, under any pressure, in any phase (gas, liquid or solid), without the use of catalysts. However, the temperature rise factor should be considered when material is processed with the high dose. The new application of radiation is homeland security. This subject was reviewed during the NATO workshop held in Budapest, Hungary in March 2004. Environmental application possible reduction of Persistent Organic Pollutants (POPs) by electron beam or combined processes is being studied. Final success depends on clear demonstration of toxicity reduction and economical feasibility e.g. by the hybrid processes applications. However, if process developed, it can be implemented to destruct dioxins in off-gases emitted from municipal waste incinerator. The natural polymer radiation treated products and nanotechnology are other emerging applications. (author)