The paper describes an operation of the reactor control and protection system of VVER-1000 in case of the steam generator (SG) feedwater failure. As the initiating event, the last main feedwater pump (MFWP) tripping under current reactor power no more then 25 % is assumed. Further feeding of steam generators is provided by two or one auxiliary feedwater pumps (AFWP). According to the VVER-1000 design requirements, the last MFWP tripping under reactor power more than 25 % shall be accompanied by the reactor scram signal. If the reactor power is less than 25 %, the reactor should be transferred to the reduced power level of 5 % by operation the power limitation controller (ROM). The results of the MFWP tripping transient analyses under power 25 % or less are presented. It is shown that in some cases the ROM does not provide a transition of the reactor to the required power level. AFWP capacity is insufficient to maintain the required levels in the steam generators that results in tripping of main circulation pumps (MCP) then, respectively, reactor scram initiation. The reasons for the distinctions of analyzed transients from the required design progression are examined and some procedures to prevent reactor scram are proposed.
Keywords: VVER, reactor scram, main feedwater pump, auxiliary feedwater pump, steam generator level.
1. Complex (consolidated) program to improve the safety of NPPs of Ukraine (K(c)PB) (approved by the Cabinet of Ministers of Ukraine № 1270, December 7, 2011). (Rus)
2. EliseevV.V., Pivovarov G.Yu., Nabatov A.S. Neutron flux monitoring system NFMS-IF: features, and safety assessment // Yadernaya i radiatsionnaya bezopasnost'. - 2007. - № 1. - P. 33 - 49. (Rus)
3. Arhangelskaya A.I. Economic policy in terms of reforming the market of electric energy and capacity and the investment program of OAO "Rosenergoatom" // Collection of Reports. 7th ISTC "Safety efficiency and safety of nuclear power. - Moskva, 2010. - P. 22 - 25. (Rus)
4. Report on the state examination nuclear safety alerts № 03-56-10 to change the number 1 to the typical TRBE B.0.03.179 RG-09. SSTC, 2010. (Ukr)
5. Technical Report "Modernization design operation AUU on VVER-1000. SAR development to modernize the operation of AUU". "FIZAR". L.t.d., 2008. (Rus)
6. Bykov M.A., Alechin G.V., Petkevich I.G. Analysis of the statements of the neutron flux monitoring system with operation accelerated unit unloading for reactor units with VVER-1000 (The 6th Intern. Scientific and Technical Conf. "Safety Assurance on NPP with WWER."-6-29.05.2009. OKB “GIDROPRESS”, Podolsk, Russia). (Rus)
7. Technical reference. The analysis of the neutron-physical characteristics and reliability Fuel block number 2 Khmelnitsky NPP in transition mode after tripping accelerated preventative protection. - Moskva: Kurchatov Institute, 2008. (Rus)
8. Borysenko V.I., Kadenko I.M., Samoilenko D.V. WWER-1000 accelerated unit uploading activation transient features // Nuclear Physics and Power Engineering. - 2009 . - Vol. 10, № 2. – P. 157 - 164. (Ukr)
9. Technical Report "On the safety and stability of NPPs with VVER-1000 under dynamic conditions with opera-tion of AUU."- ОАО «VNIIAES», 2008. (Rus)
10. Borysenko V.I., Kadenko I.M., Samoilenko D.V. Study of accelerated unit unloading mode initiated by turbine feed pump trip with tvsa fuel assemblies operation in WWER-1000 // Collection of Reports of the 4th IC Current Problems in Nuclear Physics and Atomic Energy (NPAE-Kyiv2012) 3 - 7 Sept. 2012.
11. Limits and conditions of safe operation. 43-923.203.254.OB.16.RED.2.F. SAR. T.16, Ch.16. - NAEC "Energoatom", 2004. (Rus) 12. Validation of coupled neutron kinetic/thermalhydraulic codes against transients measured in VVER reactors. Final Technical Report. Reference: FZR/SRR195/FIN2.1 / European commission. Phare programme / Safety related research project SRR 1/95.
13. Borysenko V.I. About features of the formation of signal emergency protection in reactivity accidents in VVER-1000 // Problemy bezpeky atomnyh electrostantsiy i Chornobylya (Problems of nuclear power plants' safety and of Chornobyl). - 2012. - Iss. 19. - P. 20 - 28. (Rus)
14. Borysenko V.I. That is necessary to determine: period or reactivity of reactor? // Problemy bezpeky atomnyh electrostantsiy i Chornobylya (Problems of nuclear power plants' safety and of Chornobyl). - 2010. - Iss. 13. - P. 8 - 18. (Rus)
15. Technological rules of safe operation of power unit № 4 Rivne NPP. 4-P-PAЭС. (Rus)
16. Borysenko V.I., Krushynsky A.G., Mukoyd V.P. et al. Reactor unit VVER-440 primary to secondary leakage ac-cident analysis fot RELAP5 code validation under collobaration of Ukrainian and Bulgarian specialist // Prob-lemy bezpeky atomnyh electrostantsiy i Chornobylya (Problems of nuclear power plants' safety and of Chorno-byl). - 2008. - Iss. 10. - P. 12 - 19. (Rus)
17. Borysenko V.I, Goranchuk V.V. Determination of conservative parameters of model of reactor for research of transient of VVER-1000 // Problemy bezpeky atomnyh electrostantsiy i Chornobylya (Problems of nuclear power plants' safety and of Chornobyl). - 2013. - Iss. 20. - P. 28 - 36. (Rus)
18. Rules nuclear reactors safety of nuclear power plants with pressurized water reactors. NP 306.2.145-2008. (Ukr)
19. Khmelnitsky NPP. Unit number 2. Final Safety Analysis Report. T.4. Chapter 4. Reactor. Part 3. Neutronic calculations. 49 923.202.254.OБ.04.03.РЕД.1.Ф. 2005. (Rus)
20. Thermohydraulic calculation "Termination of feed water in SG (off two TFP). Zaporizhzhya NPP. 320-Пр-287. OKB "Gydropress". - Podolsk, 1995. - P. 44. (Rus)
21. Industry technical decision to implement the reactor scram signal in case the last MFWP tripping. # OTP-M.1234.03 -190.12. - NAEC "Energoatom", 2011. (Rus)