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discovered 02_2012

COLLABORATIONS// The HZDR Research Magazine WWW.Hzdr.DE 42 43 For the safe operation of nuclear power plants there is a staggered safety concept with a whole range of measures intended to limit the impacts on the plant should technical components fail. One scenario of a potential failure in a pressurized water reactor is the loss-of-coolant accident. This type of accident can occur when a cooling-water pipe in the primary circuit (for example between the reactor pressure vessel and the steam generator) breaks. The chain reaction in the reactor is then interrupted immediately while neutron absorbers (control rods) automatically cave into the reactor core. Subsequently various emergency core cooling systems are switched on to remove the decay heat in the reactor core as well as to replace the coolant that is leaking out of the cooling circuit due to the failure. The additional emergency cooling water is fed from different storage vessels into the main pipes of the primary circuit that is under pressure. These main pipes connect the reactor pressure vessel with the steam generator (the hot legs, where the heated water flows away from the reactor) and the main coolant pump (cold legs, where the colder water flows towards the reactor). Under operating conditions, pressures and temperatures in those pipes with diameters of nearly one meter are 155 bar and up to 325 degrees Celsius, respectively. In case of a loss-of-coolant accident, steam will be produced in the thermal-hydraulic circuit due to water inventory decrease and the pressure drop and, consequently, during emergency core cooling cold water meets steam and hot water in the pipes. PRESSURIZED WATER REACTOR: Sectional view of containment structure showing the primary circuit with the reactor pressure vessel, steam generator, and main coolant pump highlighted in orange, light blue, and yellow, respectively. Image credit: (Information on the peaceful use of nuclear energy) // Together with international partners, Rossendorf researchers investigate the physical phenomena behind the emergency cooling of reactor cores. _TEXT . Uwe Hampel & Matthias Beyer Translation . Sarah Gwillym-Margianto Endurance test for reactor walls