comprises two first non reversal valves 18 to prevent the first cooling fluid 15 to flow in reverse direction into the first pumps 16 also the condenser 6 belongs to the pab 101 in the condenser 6 the first cooling fluid 15 and the steam 4 a are thermally coupled during the power mode during the standby mode only sealing steam 9 a is thermally coupled with the first cooling fluid 15 in both cases the first cooling fluid 15 cools down the steam 4 a 9 a the pab 101 also comprises a pab pipe system 19 which is thematically split or named according to the thermal condition of the first cooling fluid 15 during power mode into a pab cold part 20 and a pab hot part 21 the pab cold part 20 connects the condenser 6 with the cold water outlets 17 of the cooling tower 14 while the pab hot part 21 connects the condenser 6 with a first hot water inlet 23 a of the cooling tower 14 at the end of the pab hot part 21 a first flow control valve 22 is installed it is open during the power mode at the cold water outlet 17 a bypass valve 24 is installed in parallel to the first pumps 16 it is closed during power mode third bold arrows 25 indicate the circulation of the water 15 through the pab 101 during the power.