We present the concept of an ultracold neutron (UCN) source with a superfluid He-4 (SF ⁴He) converter located in the thermal column of the WWR-K research reactor at the Institute of Nuclear Physics (INP) in Almaty, Kazakhstan. The conceptual design is based on the proposal of accumulating UCNs in the source and effectively transporting them to experimental setups. We propose to improve the UCN density in the source by separating the heat and UCN transport from the production volume and decreasing the temperature of the SF ⁴He converter to below about 1 K. To obtain operation temperatures below 1 K, we plan to use a He-3 pumping cryogenic system and minimize the thermal load on the UCN accumulation trap walls. Additional gain in the total number of accumulated UCNs can be achieved through the use of a material with a high critical velocity for the walls of the accumulation trap. The implementation of such a design critically depends on the availability of materials with specific UCN and cryogenic properties. This paper describes the conceptual design of the source, discusses its implementation methods and material requirements, and plans for material testing studies.

WWR-K (Water-Water Reactor - Kazakhstan) was restarted after a major modernization related to its conversion to low enriched uranium (LEU) fuel and has been operating on LEU fuel since September 2016. The reactor, built in 1967, has been significantly modernized to meet modern safety requirements. This important neutron source in Kazakhstan serves various purposes, such as basic and applied research in physics, chemistry, biology, materials science, as well as for radiation treatment of materials and production of radioisotopes. It is also used for training. Instrumentation projects are planned to be launched on the basis of the WWR-K reactor to install a basic set of experimental stations. Significant efforts will be made to develop an ultracold neutron (UCN) source, which will expand research capabilities. For this purpose, it is proposed to use the niche of thermal column, a large diameter horizontal channel that allows irradiation of objects up to 1000 mm in size. In addition, the niche of thermal column has four radial channels that can be used to extract cold (10−6–10−3 eV) and very cold (10−7–10−6 eV) neutrons. The paper presents calculations of spatial and energy distributions of neutron and gamma fields for the current and for the additional moderator configuration of the niche of thermal column of the WWR-K reactor. It is shown that the configuration with additional moderator does not lead to an increase in the slow neutron fields (<1 eV), and the existing moderator thickness is optimal.

We measured the temperature dependence of the probability of small heating and total losses of UCNs on the PFPE Fomblin Y surface with various molecular mass [equation](2800, 3300, 6500 amu) in the...

This article presents the development of ultracold neutron (UCN) research in Kazakhstan and outlines a concept for a new high-intensity UCN source at the WWR-K research reactor of the Institute of Nuclear Physics (INP, Almaty). A brief overview of the emergence of UCN physics and the formation of the INP scientific school is given in the context of early work at WWR-type research reactors equipped with thermal columns, where the first UCN sources were realized. The results of experiments performed at the WWR-K reactor are summarized, including configurations of UCN production and transport systems, key measurements, and limitations of the existing infrastructure. Based on an analysis of the neutronic characteristics of the WWR-K thermal column, a concept for a modernized UCN source is developed. The proposed approach includes the installation of a dedicated cryogenic module in the thermal column, optimization of the neutron spectrum and spatial distribution, and efficient extraction of UCNs to experimental stations. It is shown that the combination of reactor parameters, thermal column design, and proposed engineering solutions provides favorable conditions for the creation of an internationally competitive high-intensity UCN source and for the implementation of a long-term program of fundamental and applied research in Kazakhstan.

This paper presents a preliminary safety assessment of the liquid deuterium premoderator container developed for the AlSUN ultra-cold neutron source, integrated into the thermal column of the WWR-K reactor. Analytical calculations, implemented using Python-based iterative schemes, were conducted to evaluate the container’s response under three categories of hypothetical accident scenarios: (1) power control and cooling failures, (2) breaches in the vacuum insulation, and (3) combustion-related incidents - liquid deuterium deflagration and detonation. Key thermodynamic parameters—including temperature and pressure evolution—were tracked in each scenario to characterize the transient system behavior. The resulting profiles were then used to estimate mechanical stresses on the container walls, considering the thermomechanical properties of the materials used in its construction. Special attention was given to the structural integrity of Aluminum Alloy 5056, assessing its performance under extreme thermal and mechanical loads. These findings lay a foundation for material selection and design optimizations, serving as a basis for future, more comprehensive studies employing advanced simulation tools.