The fuel element of the HTR-module, a prerequisite of an inherently safe reactor

Abstract

To retain fission products after postulated accidents, power reactors usually rely on active safety systems inside the primary circuit, such as e.g. redundant shut down systems and multiple redundant decay heat removal systems. The HTR-Module is employing a different approach which relies entirely on the ability of the coated particle to retain all key radio-nuclides as long as a certain maximum fuel element temperature is not exceeded. Consequently, the reactor is designed such that for any postulated accident this maximum fuel element temperature is not reached even without relying on any active safety systems inside the primary circuit, since the decay heat can be removed to an outside heat sink solely by passive means. The paper discusses the experimental results of fission product release from spherical fuel elements for various temperatures. From the tests as well as from statistical considerations it can be concluded that any hazardous radiation dose to the environment can be excluded if the maximum fuel element temperature in the HTR-Module stays below 1600°C.