Print View Posted on: 18 October 2024
Dukovany NPP is equipped by a digital Control and Protection system of Reactor.On January 11, 2024 Unit 3 of Dukovany NPP was a few days before refuelling outage, on stable operation on Power and Temperature effect with actual power 97 % Nnom, operation was in accordance with manuals. Routine testing of PPR Tester was planned.At 08:35 after connecting of the PPR Tester into division 3 of the reactor protection system a faulty connection was signalled and the test did not start. The personnel reconnected the PPR Tester and after that Error A1 was signalled.At the same time, the data in the safety network SN 3 become invalid. Subsequently all process units connected to this network (= whole division 3 of reactor protection system, including information subsystem) became invalid and stopped work. Investigation of event revealed, due to human errors and inner fault of the PPR tester a test data was transmitted into division 3 of the Reactor protection system. Due to architecture of the Reactor protection system, into Safety networks of division 1 and 2 of the Protection system also testing data was transmitted. It caused Divisions 1 and 2 also were blocked.The Tester was disconnected and testing was cancelled. The MCR stuff did not knew how complex problem was, they assumed safety functions were not affected.Investigation of event revealed, internal error of PPR Tester occurred 3 days before during maintenance of the PPR tester.08:38 the MCR stuff started shut down of Unit 3 fluently according to General rules of OLC.09:41 2 divisions of Reactor Protection system were restored, so Unit 3 entered into state defined in OLC and Unit 3 wasstabilised on 81 % Nnom.10:02 all 3 divisions of Reactor protection system were Restored, OLC were fully fulfilled.During the event manual control of reactor including manual trip, Post accident monitoring system and directly displayed data were available.