Abstract
In Loviisa NPP, there are two limiting thermal margins called the enthalpy rise margin and the linear heat rate margin that are monitored during normal operation. Engineering safety factors are applied in determination of both of these factors. The factors take into account the effect of various manufacturing tolerances, impact of the irradiation and simulation uncertainties on the local heat rate and on the enthalpy of the coolant. The engineering factors were re-evaluated during 2015 and the factors were approved by the Finnish radiation and nuclear safety authority in 2016. The re-evaluation was performed by considering all of the identified phenomena that affect the local heat rate or the enthalpy of the coolant. This paper summarizes the work that was performed during the re-evaluation of the engineering safety factors and presents the results for each uncertainty component. The new engineering safety factors are 1.115 for the linear heat rate and 1.100 for the enthalpy rise margin when the old factors were 1.12 and 1.16, respectively. The new factors improve the fuel economy by about 1%.
Kurzfassung
Im KKW Loviisa gibt es zwei limitierende thermische Sicherheitsabstände, den des Anstiegs der Enthalpie und den der linearen Stableistung. Beide werden während des Betriebs überwacht. Bei der Ermittlung dieser beiden Sicherheitsabstände werden Sicherheitsfaktoren berücksichtigt. Diese Faktoren berücksichtigen die Wirkung verschiedener Fertigungstoleranzen, Auswirkungen der Bestrahlung und der Simulationsunsicherheit auf die lokale Stableistung und auf die Enthalpie des Kühlmittels. Im Jahr 2015 wurden diese Sicherheitsfaktoren neu bewertet und im Jahr 2016 von der Aufsichtsbehörde genehmigt. Die Neubewertung wurde unter Berücksichtigung aller identifizierten Phänomene, die die lokale Stableistung oder die Enthalpie des Kühlmittels beeinflussen, durchgeführt. Dieser Beitrag beschreibt die Arbeitsschritte der Neubewertung und stellt die Ergebnisse für jeden Einflussparameter vor. Die neuen Engineering-Sicherheitsfaktoren betragen 1.115 (vorher 1,12) für die lineare Stableistung und 1.100 (vorher 1,16) für den Anstieg der Enthalpie. Durch die neuen Faktoren verringert sich der Brennstoffverbrauch um etwa 1%.
References
1 Lahtinen, T.; Saarinen, S.; Antila, M.: Effect of HEXBU-3D feedback and boundary condition models on the calculated reactor core characteristics of Loviisa NPP. Fortum Nuclear Services Ltd, Proceedings of the 18th Symposium of AER on VVER Reactor Physics and Reactor Safety, Eger, Hungary, 2008Search in Google Scholar
2 Kuusisto, J.; Antila, M.; Siltanen, P.; Anttila, M.: Comparison of ELSI-1440 calculations with measured pinwise power distribution in the Armenian-1 experimental core. IVO International Ltd and VTT Energy, Proceedings of the 4th Symposium of AER on VVER Reactor Physics and Reactor Safety, Sozopol, Bulgaria, 1994Search in Google Scholar
3 Antila, M.; Kuusisto, J.: Recent improvements in on-line core supervision at Loviisa NPP. Fortum Engineering Ltd, Workshop Proceedings of Core Monitoring for Commercial Reactors: Improvements in Systems and Methods, Stockholm, Sweden, October, 1999 10.1787/9789264181526-enSearch in Google Scholar
4 Rhodes, J.; Smith, K.; Edenius, M.: CASMO-4E, Extended Capability CASMO-4, User's Manual. Studsvik Scandpower, SPP-01/401 Rev. 2, December, 2004Search in Google Scholar
5 Serpent website, http://montecarlo.vtt.fi/. Accessed: January 19, 2017Search in Google Scholar
6 ANSYS Fluent website, http://www.ansys.com/Products/Fluids/ANSYS-Fluent. Accessed: January 19, 2017Search in Google Scholar
7 Knott, D.; Forssén, B. H.; Edenius, M.: CASMO-4, a fuel assembly burnup program, Methodology. Studsvik of America Inc. and Studsvik Core Analysis AB, STUDSVIK/SOA-95/2 Rev. 0, September, 1995Search in Google Scholar
8 Serpent 1.1.7 cross section library based on ENDF/B-VII, http://montecarlo.vtt.fi/download/sss_ace_endfb7u.pdf. Accessed: January 19, 2017Search in Google Scholar
9 Serpent 1.1.0 thermal scattering libraries based on JEF-2.2, JEFF3.1, ENDF/B-VI.8 and ENDF/B-VII, http://montecarlo.vtt.fi/download/SSS_THERMAL.pdf. Accessed: January 19, 2017Search in Google Scholar
10 Ekström, K.; Toppila, T.: CFD analyses of the rod bowing effect on the subchannel outlet temperature distribution. KERNTECHNIK82 (2017) 455Search in Google Scholar
11 Lahtinen, T.; Kuopanportti, J.; Lehtinen, I.: Evaluation of rod and assembly bowing effect on rod-wise fission powers using Serpent and CASMO-4E. Fortum Power and Heat Ltd, Proceedings of the 25th Symposium of AER on VVER Reactor Physics and Reactor Safety, Balatongyörök, Hungary, 2015Search in Google Scholar
12 Lehtinen, I.: Poolside inspections of spent nuclear fuel at Loviisa NPP. Fortum Power and Heat Ltd, Proceedings of the 26th Symposium of AER on VVER Reactor Physics and Reactor Safety, Helsinki, Finland, 2016Search in Google Scholar
13 Lehtinen, I.: Poolside inspections at Loviisa NPP. Fortum Power and Heat Ltd, 11th International conference on WWER fuel performance, modelling and experimental support, Proceedings. Report Number INIS-BG-2493, INIS Volume 47, INIS Issue 31, Reference Number 47082445, Varna, Bulgaria, 2015Search in Google Scholar
14 Brandt, T.; Lahtinen, T.; Toppila, T.: CFD study on coolant mixing inside VVER-440 fuel rod bundle. Fortum Nuclear Services Ltd, Proceedings of the 19th Symposium of AER on VVER Reactor Physics and Reactor Safety, Varna, Bulgaria, 200910.1115/ICONE17-75316Search in Google Scholar
15 Toppila, T.; Kuopanportti, J.; Rämä, T.: Assessment of CFD model for Loviisa NPP coolant mixing studies using data of steam safety valve tests. Fortum Power and Heat Ltd, Proceedings of CFD for Nuclear Reactor Safety applications (CFD4NRS-4), Zurich, Switzerland, 2014Search in Google Scholar
16 Saarinen, S.; Kuopanportti, J.; Lahtinen, T.; Arjoranta, J.: Recent improvements and operating experience of Loviisa NPP fuel management. Fortum Power and Heat Ltd, Proceedings of the 26th Symposium of AER on VVER Reactor Physics and Reactor Safety, Helsinki, Finland, 2016Search in Google Scholar
© 2017, Carl Hanser Verlag, München
