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      A neutronics feasibility study on utilization of a thinned cladding fuel design at Loviisa NPP Translated title: Studie zur Auswirkung eines dünneren Hüllrohrdesigns auf die Neutronenkinetik im Brennstoff für das KKW Loviisa


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          Recently, an initiative has been made to improve the fuel economy of VVER-440 reactors by implementing a modification on the geometry of the current fuel assembly design. The proposed modification involves reduction of the fuel rod outer diameter from 0.91 cm to 0.89 cm by using 0.01 cm thinner cladding tubes than earlier. The design improvement would shift the neutronics of an under-moderated system slightly towards optimum moderation and, therefore, increase the reactivity of the assembly. In this paper, a neutronics feasibility study on utilization of the proposed new fuel design at Loviisa NPP is carried out. The study involves a comprehensive comparison of two individual equilibrium fuel cycles: one applying current TVEL 2 nd generation fuel design and another one where the new fuel design is used. In addition to equilibrium cycle characteristics, also cycle economics as well as back-end effects are considered. The study concludes that the proposed fuel design modification enables to improve the fuel economy of Loviisa NPP.


          Vor kurzem wurde eine Initiative zur Verbesserung des Brennstoffverbrauchs von VVER-440-Reaktoren eine Änderung der Geometrie des aktuellen Brennelementdesigns gestartet. Die vorgeschlagene Modifikation beinhaltet die Reduzierung des Brennstabaußendurchmessers von 0,91 cm auf 0,89 cm durch Verwendung von 0,01 cm dünneren Hüllrohren als bisher. Die Designverbesserung würde die Neutronik eines untermoderierten Systems leicht in Richtung optimaler Moderation verschieben und damit die Reaktivität der Baugruppe erhöhen. In diesem Beitrag wird eine Machbarkeitsstudie zur Nutzung des vorgeschlagenen neuen Brennstoffdesigns im Kernkraftwerk Loviisa durchgeführt. Die Studie beinhaltet einen umfassenden Vergleich zweier individueller Gleichgewichts-Brennstoffkreisläufe: eines mit dem aktuellen TVEL-Design der zweiten Generation und eines mit dem neuen Design. Neben den Gleichgewichtszykluseigenschaften werden auch die Zyklusökonomie sowie Backend-Effekte berücksichtigt. Die Studie kommt zu dem Schluss, dass die vorgeschlagene Designänderung eine Verbesserung des Brennstoffverbrauchs des Kernkraftwerks Loviisa ermöglicht.

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          Effect of spacer grid mixing vanes on coolant outlet temperature distribution

          In Loviisa VVER-440-type NPP the coolant outlet temperature of the hot subchannel is constantly monitored during the operation. According to the authority requirement the maximum subchannel outlet temperature must not exceed the saturation temperature. Coolant temperature distribution inside the fuel assembly is affected by the efficiency of the coolant mixing. In order to enhance the coolant mixing the fuel manufacturer is introducing the additional mixing vanes on the fuel bundle spacer grids. In the paper the effect of the different mixing vane modifications is studied with computational fluid dynamics (CFD) simulation. Goal of the modelling is to find vane modifications with which sufficient mixing is reached with acceptable increase in the spacer grid pressure loss. The results of the studies are discussed in the paper.
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            Development of fuel cycles with new fuel with 8.9 mm external diameter for VVER-440: Preliminary assessment of operating efficiency

            Since the introduction of VVERs-440, their fuel assemblies are subject to ongoing improvements. Until now, the basic structural parameters of fuel, such as rod diameter of 9.1 mm, have never changed. This paper focuses on computational estimates of basic neutronic parameters of the fuel cycle that involves assemblies consisting of fuel rods with diameter reduced to 8.9 mm.
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              Development of fuel cycles with new fuel with 8.9 mm external diameter for VVER-440: Preliminary assessment of operating efficiency


                Author and article information

                Carl Hanser Verlag
                27 August 2018
                : 83
                : 4
                : 314-318
                1 Fortum Power and Heat Ltd., P.O. Box 100, 00048 Fortum, Finland
                Author notes
                © 2018, Carl Hanser Verlag, München
                : 30 January 2018
                Page count
                References: 7, Pages: 5
                Self URI (journal page): https://www.hanser-elibrary.com/loi/kt
                Technical Contributions/Fachbeiträge

                Materials technology,Materials for energy,Nuclear physics
                Materials technology, Materials for energy, Nuclear physics


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