Abstract: A hollow toroidal assembly, for example a heat and radiation blanket for a nuclear fusion reactor, has an improved modular structure. The toroidal assembly is formed by a number of annular modules of at least two types, each module being subdivided into submodules. The modules are conically converging at the outer or inner circumferential side so that they are tightly mounted in an alternating configuration. When providing a blanket for a nuclear fusion reactor the toroidal assembly surrounds the toroidal plasma reaction cavity and provides efficient cooling or heat exchange through the modules. The toroidal assembly advantageously provides a convenient subdivision of the blanket surrounding a plasma cavity into a sufficient number of separate modules.