Рассмотрены возможности увеличения наработки 99 Mo с помощью модер низации урансодержащих мишеней и размещения бериллиевых блоков в активной зоне реактора ВВР ц. Обнаружено, что существует резерв уве личения наработки изотопа медицинского назначения 99 Mo для производ ства радиофармпрепаратов.Ключевые слова: реактор ВВР ц, наработка 99 Mo, блоки бериллиевого замедли теля.

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UDC 546.77.02.99 and R. V. Fomin 2The results of computational studies of the possibility of using beryllium refl ectors to improve the neutronphysical characteristics of the VVR-Ts reactor, which is used at the Karpov Research Institute of Physical Chemistry to produce radionuclides, are presented. The calculations showed that in principle beryllium can be used by substituting it for some number of standard fuel assemblies. This made it possible to decrease the number of fuel assemblies from 70 in the standard core to 59 in a modifi ed core and increase the run time to 14 days. The calculations also indicate that the neutron fl ux density in the experimental channels can be increased signifi cantly, which is important for increasing the production of radionuclides. The˛thermophysical aspects of the modifi ed core are not studied.The VVR-Ts swimming-pool reactor was built at an affi liate of the Karpov Research Institute of Physical Chemistry (NIFKhI) in 1964. The fuel is 235 U with enrichment 36% and water the coolant. The maximum power output is 15 MW. The˛reactor is used for the production of medical isotopes [1]. The possibility of modernizing the core of such reactors is now being studied. Initially, beryllium was used as a moderator in some reactors, while water is used as moderator and coolant in others. Beryllium is known to be the most effective moderator, and for this reason it can be supposed that used as a refl ector it could improve the neutron-physical characteristics. Such computational studies were performed in 2008 at the National Nuclear Center of the Republic of Kazakhstan for a 6-MW VVR-K reactor (VVR-Ts analog) with fi ve and three fuel elements per fuel assembly; the fuel assembly with fi ve fuel elements is similar to a VVR-Ts fuel assembly. The modifi cation of the VVR-Ts fuel assembly with three fuel elements presupposes an internal, hexahedral, free cavity (span size 32.7 mm) intended for holding control rods as well as different experimental setups.The results of analogous computational studies for VVR-Ts are presented in the present article. A particularity of the computational studies performed to improve the neutron-physical characteristics of VVR-Ts is the substitution of beryllium blocks for some fuel assemblies with similar outer geometric dimensions in the standard core. This approach was used for calculations of a similar VVR-K reactor in Kazakhstan [2].Let us examine the load of a standard core with 70 fuel assemblies, giving criticality with the following positions of the control rods: AZ-1, AZ-2, AZ-3, RR-1 -top position; AR inserted to 50% (200 mm), RR-2 -to 380 mm, RR-3 -bottom position (Fig. 1). The criticality for the same positions of the control rods is preserved with 59 fuel assemblies in the core and rearrangement of the remaining ones (Fig. 2). The confi guration of the new core is presented in Fig. 2.

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