The energy release and temperature field in the ultracold neutron source of the WWR-M reactor at the Petersburg Nuclear
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ING DESIGN OF NUCLEAR PHYSICS EQUIPMENT
The Energy Release and Temperature Field in the Ultracold Neutron Source of the WWR-M Reactor at the Petersburg Nuclear Physics Institute A. P. Serebrov*, B. V. Kislitsin, M. S. Onegin, V. A. Lyamkin, D. V. Prudnikov, V. A. Ilatovskiy, S. P. Orlov, G. A. Kirsanov, A. K. Fomin, and D. V. Filchenkova Petersburg Nuclear Physics Institute, National Research Center Kurchatov Institute, Gatchina, Leningradskaya oblast, 188300 Russia *e-mail: [email protected] Received September 9, 2015
Abstract―Results of calculations of energy releases and temperature fields in the ultracold neutron source under design at the WWR-M reactor are presented. It is shown that, with the reactor power of 18 MW, the power of energy release in the 40-L volume of the source with superfluid helium will amount to 28.5 W, while 356 W will be released in a liquid-deuterium premoderator. The lead shield between the reactor core and the source reduces the radiative heat release by an order of magnitude. A thermal power of 22 kW is released in it, which is removed by passage of water. The distribution of temperatures in all components of the vacuum structure is presented, and the temperature does not exceed 100°C at full reactor power. The calculations performed make it possible to go to design of the source. Keywords: ultracold neutron source, superfluid helium, low temperatures, heat and mass transfer DOI: 10.1134/S1063778816090118
INTRODUCTION On the basis of the operating WWR-M research reactor, it is proposed to create a highly intense source of ultracold neutrons (UCNs) for scientific studies in the field of fundamental physics [1]. A program of studying fundamental interactions is planned for the new UCN source. It includes a search for the electric dipole moment of a neutron and a precision measurement of the neutron lifetime. Both tasks have a fundamental importance for particle physics and cosmology [2]. At the WWR-M reactor of the Petersburg Nuclear Physics Institute (PNPI), there are very suitable conditions for creating a UCN source on the basis of superfluid helium as a converter. There is a thermal column of the reactor―a channel of large diameter (1 m), adjoining the reactor core. Such a diameter of the channel provides the arrangement of the powerful lead shield from γ radiation of the reactor core, the graphite moderator at room temperature, the liquiddeuterium premoderator at a temperature of 20 K for producing cold neutrons, and, finally, the UCN source proper based on superfluid helium at a temperature of 1.2 K. Ultracold neutrons are “produced” in superfluid helium from cold neutrons with a wavelength of 9 Å or with energy of 12 K, which is just equal to the phonon energy; i.e., a cold neutron excites a phonon and this neutron almost stops, becoming
ultracold. The cold neutrons penetrate through the wall of the trap, while the UCNs are reflected; therefore, the effect of UCN accumulation up to the density determined by the time of storage in the trap with helium is feasible. The ultracold
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