The HTR module pressure vessel unit, design criteria and safety philosophy

Abstract A modular-helium-cooled high temperature reactor system for the cogeneration of electricity and process heat has been developed by Siemens—Interatom. Design, manufacture and operation of the pressure vessel unit will conform to German nuclear codes and standards for LWR's, some deviations or peculiarities for their application to HTR's are unavoidable. These are for instance: • - The main steam nozzle, through which the steam line at 530°C penetrates the steam generator pressure vessel with a nominal design temperature of 350°C. • - The pressure test concept in which the preservice pressure test will be performed in complete accordance with the codes and standards at 1.3 times the design pressure of 70 bar using water. Afterwards, the presence of graphite structures, ceramic insulation and, of course, the pebble bed core has to be considered. Pneumatic pressure tests are performed at 1.1 times design pressure accompanied by more detailed ultrasonic examinations. • - The position of operational material irradiation surveillance specimens has to be chosen carefully. Design postulates concerning the incrase of ΔRT NDT will pe confirmed in a separate program. In general, the requirements of the assured safety concept, aimed to rule out catastrophic failure of the pressure vessel unit during lifetime are fulfilled.