Abstract: Embodiments of the disclosure may include a reactor vessel with a lower chamber, a core, a hot chamber, an upper chamber, and heat exchangers. In some embodiments, the hot chamber may be located above the core and may include a substantially cylindrical body. In some embodiments, the hot chamber body may include an inner shell and an additional shell installed with a gap on the outside and being concentric with the inner shell of the hot chamber, forming at least one cooling channel. In some embodiments, the connecting pipe may include an inner shell and an additional shell installed with a gap on the outside, being concentric with the inner shell of the connecting pipe and forming at least one cooling channel of the connecting pipe, where the cooling channel of the hot chamber and the connecting pipe are in communication with the outlet of the heat exchangers.