Assuring reactor’s subcriticality following beyond design accident by simultaneous cool down and depressurization
The article presents the results of analysis of emergency transient, when reactor is maintained in subcritical conditions by autonomous passive safety systems, providing for residual heat removal along with primary depressurisation. The method presents analytical modelling of beyond design accident with complete long-term blackout caused by loss of all in-house safety power sources of a NPP. The research has been performed on a model of WWER-1000/V-320 using RELAP5 Сode. Specific feature of the model under study is availability of two passive safety systems: Passive Residual Heat Removal System from primary circuit (PRHRS-R) and Passive Cooldown System of Pressurizer (РСS-PRZ). Heat exchangers based on evaporative condensing devices of closed type – two-phase thermosyphons are used as the heat exchange equipment that conducts heat transfer from the primary circuit to the intermediate circuit in these passive systems. Such heat exchange equipment provides high efficiency, reliability and safety of emergency heat sink. In a beyond design accident conditions the two systems provide for transition and maintaining the reactor in final safe conditions. The main objective of the research is to analyse the possibility of maintaining subcriticality during long term simultaneous operation of the above mentioned passive systems. The analytical modelling shows that parallel operation of the RHRS-R and РСS-PRZ provides for reliable and effective heat removal along with primary depressurisation down to 2 MPa. Despite that the residual pressure allows injection of only 50% of the design inventory of ECCS Hydro Accumulators (ECCS-HA), the boron concentration reaches the level when primary subcritiality along all stages of the accident is guaranteed. In addition, the operation of the above mentioned systems provides for safe cooldown rate, avoiding challenges to primary pressure boundary (Pressurised Thermal Shock). The result achieved takes into account release of positive reactivity due to Reactor de-poisoning. Highest level of reactivity reached –2.79 $.
- Kinase S., Takahashi T., Saito K. Long-term predictions of ambient dose equivalent rates after the Fukushima Daiichi Nuclear Power Plant accident. Journal of Nuclear Science and Technology. 2017, v. 54(8), pp. 819-829.
- Spasskov V.P., Dragunov YU.G., Ryzhov S.B., Podshibyakin A.K., Volkov G.A., Abagyan YU.G., Abramov V.I., Levin E.I., Damrin E.M., Lubyanko V.N., Fil’ N.S., Zajcev S.I., Alekhin G.V., Krasnov S.N., Shumskij A.M., Denisov V.P. Calculated substantiation of thermal hydraulic characteristics of reactor and WWER reactor plant. Moscow. Akademkniga Publ., 2004, 340 p. (in Russian).
- Sviridenko I.I. Passive residual heat removal system. Ukraine Patent of invention No. UA 81419. Bul. No. 1, published 01.10.2008 (in Ukrainian).
- Sviridenko I.I. Method of passive shut-down cooling of pressurizer. Zbіrnik naukovih prac’ SNUYAEtaP. 2008, v. 4(28), pp. 56-62 (in Russian).
- Gershuni O.N., Nishchik O.P., Pis’mennij E.N. Evaporative condensing heat transfer systems for nuclear power technologies. Kiev. Alterpres Publ., 2007, 236 p. (in Ukrainian).
- Fu W., Li X., Wu X., Zhang Z. Investigation of a long term passive cooling system using two-phase thermosyphon loops for the nuclear reactor spent fuel pool. Annals of Nuclear Energy. 2015, v. 85, pp. 346-356.
- Sviridenko I.I., Klevcov S.V. WWER-1000 Safety Improvement Using Autonomous Thermosyphon Type PRHRS R for Emergence Heat Removal. Energeticheskie ustanovki i tekhnologii. 2015, v. 1, iss. 1, pp. 28-33 (in Russian).
- Sviridenko I.I., Prokhodtsev A.Y. Autonomous Thermosiphon PHRS Reliability Assessment on the Basis of Systematic Analysis. Zbіrnik naukovih prac’ SNUYAEtaP. 2011, v. 1(37), pp. 48-55 (in Russian).
- Sviridenko Igor I., Shevelyov Dmitriy V., Polyakov Oleksiy V., Timofeev Vyacheslav A., Sviridenko Natalya N. Passive Residual Heat Removal System for WWER with the Thermosiphon Heatexchange Equipment. International Journal of Energy for a Clean Environment. 2015, v. 16. iss. 1-4, pp. 209-223.
- Sviridenko Igor I. Actuation algorithm of the autonomous passive residual heat removal thermosiphon system for WWER reactors. International Journal of Energy for a Clean Environment. 2017, v. 18, iss. 4, pp. 349-363.
- Final report on safety analysis. Chapter 15. Analysis of design basis accidents. NSGP Database. Part 2. The main components of RF. Rivne NPP-4. 2011, 214 p. (in Russian).
- Sviridenko I.I. Heat exchangers based on low temperature heat pipes for autonomous emergency WWER cooldown systems. Applied Thermal Engineering. 2008, v. 28(4), pp. 327-334.
- Sviridenko I.I., Sukhov A.K., Shevielov D.V., Polyakov A.V. Thermosiphon Based Heat Exchanger of WWER 1000 Primary Circuit Passive Residual Heat Removal system. Zbіrnik naukovih prac’ SNUYAEtaP. 2013, v. 1(45), pp. 54-67. (in Russian).
- Sviridenko I.I. The method of multi-barrier protection of nuclear power plants as the development of the principle of «protection in depth». Sbornik nauchnyh trudov SNIYAEHiP. 2004, v. 12, pp. 171-182 (in Russian).
- Sviridenko I.I. Optimization of reactor thermosiphones cooldown system commissioning process. Optimizaciya proizvodstvennyh processov: Sbornik nauchnyh trudov SevNTU. 2004, v. 7, pp. 89-96 (in Russian).
- Sviridenko I.I. Features of Emergency Process at Small Not Compensated Leak WWER-1000 with Use Independent PRHR System. Zbіrnik naukovih prac’ SNUYAEtaP. 2007, v. 3(23), pp. 100-108 (in Russian).
- Safety analysis report. Analysis of beyond design basis accidents. Analysis of scenarios of beyond design basis accidents. Zaporizhzhya NPP-5. Package 1. 2007, 781 p. (in Russian).
- Instruction on elimination of accidents and emergency situations at the reactor facility of the Zaporizhzhya NPP-5. 2017, 444 p. (in Russian).
- Klyuchnikov A.A., Skalozubov, V.I. Komarov Yu.A., Kolisnichenko M.I., Kovtanyuk P.I., Pavlov Yu.A. Analysis of PORV Failure to Close at RIVNE-3 on 22.09.2009. Problemi bezpeki atomnih elektrostancіj і Chornobilya: naukovo tekhnіchnij zbіrnik. 2011, v. 15, pp. 51-59. (in Russian).
- Sviridenko I.I. Emergency Coolant System’s Passive Part Influence on Stability of the Independent Thermosyphon Passive Residual Heat Removal System. Vіsnik SevNTU. Ser. Mekhanіka, energetika, ekologіya: Zbіrnik naukovih prac’. 2010, v. 106, pp. 132-136 (in Russian).