New advanced high-flux NEPTUNE neutron source

Leader: M.V. Bulavin

JINR has a deep tradition in the field of neutron scattering research on condensed matter and a long history of producing world-class neutron sources of first rank for such research. In accordance with the scientific policy developed by the Scientific Council of the Institute, there is a very clear plan not only to keep on working in this area, but also in the future, to maintain a leading position by producing a new advanced neutron source that should become one of the highest flux sources in the world.

Taking into account the current trend in the development of European neutron facilities, only five sources will be available after 2030, including three currently operating ones: ISIS (Didcot, UK), SINQ (PSI, Willigen, Switzerland), FRM II (TU Munich, FRG) and two new sources - ESS (Lund, Sweden) and the PIK stationary reactor (PNPI NRC KI, Gatchina, Russia) that are scheduled to start operating in 2023-2024.

The analysis of the special "European Strategy Working Group on Physical Sciences and Engineering" (ESFRI) shows that the increasing interest in neutron research in the world runs parallel to the reduction in the number of high-flux neutron sources. Against this background, development of a new neutron source at JINR will largely compensate for the loss of "beam time" and, at the same time, will attract the users that currently implement their experiments on European sources with low and average intensity.

JINR has proposed to construct a new advanced source of neutrons of the 4th generation on its site. From several proposed concepts, a pulsed fast reactor with a power of 12–15 MW has been chosen as the main one, with a core based on neptunium nitride (the Neptune reactor) (Fig.1). In combination with an advanced complex of bispectral moderators, sample environment systems and spectrometers, such a source should become one of the best sources in the world and open up unprecedented opportunities in the field of research in condensed matter physics, fundamental physics, chemistry, biology, geology and new materials for scientists from JINR Member States and all over the world.

Fig.1. Schematic of the Neptune 4th generation pulsed reactor: 1 - reactor core, 2 - reactivity modulator void sector, 3 - titanium hydride reactivity modulator sector, 4 - moderator, 5 - beryllium reflector.

The main advantage of Neptune compared to ESS that is considered as the highest flux neutron source in the world, is a significantly shorter neutron pulse with almost the same average neutron flux density and higher peak density. This means that Neptune will not be inferior to ESS in low resolution experiments and will significantly outperform it in high resolution experiments.

Currently, the Neptune reactor is at the stage of development and creation of a conceptual design within the framework of the Theme No. 04-4-1140-2020/2022 of FLNP.

Together with N.A. Dollezhal Research and Development Institute of Power Engineering (NIKIET) and A.A. Bochvar High-Technology Scientific Research Institute of Inorganic Materials (VNIINM), two options for the layout of the core of the new reactor have been developed, a technical assignment for production of fuel rods of a new source has been prepared. The FLNP staff has carried out a number of detailed calculations in support of the idea of ​​changing the fuel composition of the peripheral fuel rods of the reactor in order to radically improve the parameters of the facility related to operation stability, reliability and safety. The results of these studies have formed the basis for the design changes made by NIKIET specialists. At present, the necessary personnel changes have been made in the Laboratory and work has been completed on the formation of a new structural unit where the project will be developed and a new neutron source will be created.

A rough estimate of the cost of the Neptune project today is about 440 million euros. More precise figures are expected by the end of 2022 after the completion of the conceptual design stage. The start of operation of the new reactor is scheduled no later than 2040.