IFMIF/EVEDA BEAM DUMP SHIELDING: OPTIMIZED DESIGN OF THE FRONT PART M. García, F. Ogando, D. López, P. Sauvan, A. Mayoral, J. Sanz, Departamento de Ingeniería Energética, UNED, Madrid, Spain B. Brañas, J. M. Arroyo, Laboratorio Nacional de Fusión, CIEMAT, Madrid, Spain Abstract The Beam Dump of the IFMIF/EVEDA accelerator prototype needs to fulfil radioprotection requirements. In order to protect workers and public against radiation arising from the Beam Dump, a shielding for this device has been designed. This radiation is generated due to the stopping of the 125 mA and 9 MeV deuteron beam on the copper cone Beam Stop. The activation of the Beam Dump materials give rise to a residual dose around it but also produce a dose field in the area devoted to the accelerator components maintenance. The purpose of this paper is to present a first design of the front part of the Beam Dump shielding that helps to allow the manual maintenance in the accelerator area. INTRODUCTION: DEFINITION OF THE PROBLEM The IFMIF-EVEDA accelerator prototype will be a 9 MeV, 125 mA CW deuteron accelerator [1], identical to the low energy section of one of the IFMIF [2] accelerators, which will be tested in Japan to verify the validity of the design before launching the IFMIF construction. As no target is foreseen for the accelerated deuterons, a Beam Dump (BD) is located at the end of the accelerator to stop the beam. A specific shielding for the BD has been designed demonstrating its capability to fulfil the radioprotection requirements during beam-on and on beam-off phases [3,4]. Figure 1 shows the already defined shielding, where the beam is coming from the left side of the figure. Figure1: Shielding of the Beam Dump. In the design of the BD two of the key radioprotection requirements to be fulfilled are: i) dose values outside the accelerator vault during accelerator operation must be below the limits for workers and ii) inside the accelerator vault manual maintenance must be allowed during beam- off phases. This paper is focused in the design of the front part of the BD shielding whose main objective is to reduce doses during beam shutdown to fulfil requirement ii). Figure 2 shows the location of the BD at the end of the accelerator line. The beam line is bent 20⁰ before the BD to protect the accelerator components from the radiations coming from the BD on beam-on phase. Figure 2: General layout of the accelerator vault. Location of the front BD shielding to be designed is showed. Radiation Sources to Take Into Account The radiations to be shielded during beam-off phase are coming to the BD activated components. The main activated materials are: i) the copper-cone Beam Stop; which is mainly activated by the deuteron beam and ii) the external iron layer of the BD shielding, activated by the secondary neutron source generated by the deuteron- copper interaction. It was shown previously [3,4] that outside the BD cell contribution ii) was negligible. A preliminary analysis showed that residual radiation in the accelerator area due to the BD activation is mainly that coming across the vacuum line of the accelerator due to deuteron activation of the copper cone. METHODOLOGY The Monte Carlo codes MCNPX and PHITS, widely used in radioprotection accelerator studies, were initially considered as candidates for this kind of IFMIF/EVEDA applications. These codes use built-in analytical models to deal with deuteron nuclear interactions. In some of the first EVEDA radioprotection studies aimed to the BD design, the applicability of MCNPX to predict neutron production with sufficient accuracy in the particular situation of 9 MeV deuterons impinging on the copper Proceedings of IPAC2011, San Sebastián, Spain TUPS045 07 Accelerator Technology T20 Targetry 1635 Copyright c ○ 2011 by IPAC’11/EPS-AG — cc Creative Commons Attribution 3.0 (CC BY 3.0)