Generation Aino Ahonen CABABILITY OF APROS IN THE ANALYSES OF DIESEL LOADING SEQUENCES E. Raiko, H.Kontio, K.Porkholm, presented by A. Ahonen Fortum Nuclear Services Ltd, Espoo, Finland

Generation Aino Ahonen Contents of the presentation Loviisa NPP APROS simulation software Analysis of diesel loading sequences

Generation Aino Ahonen Loviisa NPP Two VVER 440-type pressurised-water reactors. Commissioned in 1977 and 1980 After power upgrade the total electric power of the plant is now 1020 MW Load factors 88.6% and 93.3% in 2006 Modernization and upgrading project finalised in year 2000 Operation licensing extension project in years I&C renewal project in years

Generation Aino Ahonen Advanced Process Simulator (APROS) The thermal hydraulic library contains 3-, 5- and 6-equation models for the calculation of one- dimensional two-phase flow The component library includes an extensive set of ready-made process component models for the simulation of different kind of processes The development was initiated 1986 in co-operation by Fortum Nuclear Services Ltd and VTT Technical Research Centre of Finland

Generation Aino Ahonen Loviisa Modernization and Power upgrading project A modernization and power upgrading program of Loviisa VVER- 440 reactors was carried out in As a result of this program, the power levels of the reactors were upgraded by 9.1 %, from 1375 MWth to 1500 MWth The safety analyses included in the FSAR were renewed, and APROS was the main tool in this analysis work

Generation Aino Ahonen Events which were analyzed using APROS code –LBLOCA –SBLOCA –ATWS –PRISE –reactor coolant pump trips –reactor coolant pump seizure –main feed water pumps trip –feed water line break –loss of on and off-site AC power –overpressure protection analysis –decrease of feed water temperature –inadvertent closure of main steam line isolation valve –inadvertent opening of one steam generator safety valve –uncontrolled withdrawal of a control rod group during power operation Fig. 1. LBLOCA hot rod cladding temperatures (BOC)

Generation Aino Ahonen Loviisa operating license extension project The current operating license is valid until the end of 2007 so an application for a new operating license for 20 years was submitted 1 November 2006 For the application FSAR analyses were updated and again APROS was the main tool in the analysis work Because of improved capabilities containment simulation the containment pressure behavior in LSLBLOCA and MSLB analyses were calculated now with APROS as well

Generation Aino Ahonen Loviisa I&C Renewal Project The Loviisa I&C renewal project was started in 2005 and is scheduled to be completed in The I&C system modernization will cover all automation and control systems of the power plant

Generation Aino Ahonen Simulators in the I&C Renewal project Development simulator Testing simulator Training simulator Engineering simulator

Generation Aino Ahonen Development simulator The HMI of the development simulator has been implemented on a process computer platform identical to the existing Loviisa process computer system The processes and I&C are simulated with APROS application model of Loviisa

Generation Aino Ahonen Testing Simulator Based on the Apros model of the development simulator I&C systems to be renewed are replaced by real and virtual I&C systems including HMI New simulation-aided testing environment has been developed to support the testing

Generation Aino Ahonen Training Simulator

Generation Aino Ahonen Engineering Simulator Engineering simulator is APROS based application model of Loviisa NPP different from development simulator, testing simulator and training simulator applications because of the higher fidelity of the model versus minor requirement of real time calculation

Generation Aino Ahonen Analyses of diesel loading sequences (1/6) In Loviisa NPP there are four emergency diesels to feed safety related equipment in case of loss of power supply In addition one of the diesels can be replaced with connection to a hydro power plant during maintenance In the second phase of Loviisa I&C renewal project changes will be made to logics and to the total number of the diesel back-up pumps and fans and also the time delays of the steps of the diesel loading sequences will be changed

Generation Aino Ahonen Analyses of diesel loading sequences (2/6) In the loss of the electricity an automation system will connect a diesel generator in 15 s to the redundant 6 kV voltage grid. After that the diesel loading sequence will start to reconnect the back- up devices to the electricity network, each component group according to the pre-designed time steps If the start command of the device (pump or fan) will come only after the blackout the starting time of the device can be different compared to the normal diesel loading sequence step time and the individual device may start e.g. during the next sequence step -> so it is possible that the temporary diesel generator load and current through the transformers can be much higher than the load and current values in the normal designed sequence step

Generation Aino Ahonen Analyses of diesel loading sequences (3/6)

Generation Aino Ahonen Analyses of diesel loading sequences (4/6) As an example an analysis of a LOCA including loss of on and off site power is discussed -> aim of the analyses was to find out the maximum momentary diesel generator load and transformer current values in different accident situations In the simulated accident the high pressure safety injection pump, low pressure safety injection pump, emergency feed water pump and secondary side make-up water pump were started at the unexpected sequence step In this case the maximum momentary diesel generator load value in one redundancy was about 3120 kW and the maximum momentary current value trough the transformer from 6 kV network to 400 V network was about 4070 A

Generation Aino Ahonen Analyses of diesel loading sequences (5/6)

Generation Aino Ahonen Analyses of diesel loading sequences (6/6)

Generation Aino Ahonen Conclusions APROS has been used extensively in the engineering, safety analysis and training simulator applications The capability of APROS to simulate the whole power plant including reactor, processes, automation and electrical systems makes it very suitable for the best-estimate analyses of nuclear power plants APROS is used today as the main safety analysis code at Loviisa Nuclear Power Plant After the Loviisa I&C renewal project APROS will also be the simulation environment of Loviisa full scope training simulator