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1	Kvantifiering av osäkerheter i lyftkraftsmodellen / Quantification of uncertainties in the lift force model Holmkvist, Carolin January 2014 (has links) With today´s power uprates in BWR reactors the bundle lift force has become aproblem. The lift force is calculated using a best estimate approach and the resultfrom the calculation should pass the existing lift force margin. Lift force margin isdefined so that the lift force may not exceed 80 % of the fuel weight. The margin issupposed to cover all the uncertainties that exist in the lift force calculations.However, no uncertainty analysis has been conducted to quantify the uncertainties. In this report the uncertainties in the lift force model have been quantified. Each inputparameter to the lift force model which has been assumed to have an uncertainty isassigned a probability distribution. Through the Monte Carlo method and Wilk´smethod an uncertainty propagation has been performed at different points in thereactor´s power flow map. By using these two methods, uncertainty in input datahave been translated into uncertainty in output data. This study has investigated fuelfrom different companies. From the Monte Carlo and Wilk´s method the lift force hasbeen calculated at various probabilities. By using these results, a lift force margin hasbeen calculated for each fuel type and at various probabilities. The results from the uncertainty propagation shows that the current lift force margincorresponds to approximately 95 % probability that lift doesn´t occur for all fueltypes. By using the uncertainty propagation, a new way of calculation the lift forcemargin has been developed. kärnkraft osäkerhetsanalys lyftkrafter bränslepatron bränsleknippe
2	Förbättrade effektmarginaler med radiell anrikningsfördelning för PWR-bränsle / Improved peaking factors with radial enrichment distribution för PWR fuel assembly Åkerman, Mattias January 2016 (has links) In recent years, the enthalpy raise hot channel factor limit has decreased significantly due to the power upgrade of Ringhals 4 and the use of shielding fuel assemblies. The shielding fuel assemblies task are to reduce the neutron leakage to the reactor vessel and in that way extend the reactor lifetime. This is achieved by replacing a few fuel rods with steel rods. Experiences from the last fuel cycles show that the core design procedure has been hampered because of this and that it’s hard to stay under the design limit. A way to overcome this problem and to improve the fuel economy is to introduce the use of radial enrichment distribution in the fuel assembly. This master thesis shows, through a case study of three fuel cycles at Ringhals 4, that the internal peaking factor can be improved by roughly 2–3 % and that the maximum enthalpy raise hot channel factor can be improved by about 2.0–2.5 % if the fuel assemblies contain three different levels of enrichments instead of currently one. This can be achieved without any noticeable decrease in cycle length. / Genom en fallstudie av tre driftcykler för Ringhals 4 visar den här rapporten att max FΔH under cykeln kan sänkas med 2,0–2,5 % om bränsleknippena radiellt anrikningsoptimeras med minst tre delanrikningar. Totalt under cykeln kan FΔH sänkas med upp till 4 %. Om radiell anrikningsoptimering införs för Vattenfalls PWR:er skulle arbetet med att designa härdarna förenklas och utrymme ges för att ladda reaktorerna på ett mer ekonomiskt sätt. Ringhals 4 PWR fuel rod fuel assembly shielding fuel assembly reactor core reactor cycle burnable absorber peaking factor internal peaking factor enthalpy raise hot channel factor radial enrichment distribution enrichment optimization CASMO SIMULATE XIMAGE Ringhals 4 PWR bränslestav bränsleknippe skärmande knippen reaktorhärd reaktorcykel brännbar absorbator intern effektformfaktor radiell effektformfaktor effektmarginal radiell anrikningsfördelning anrikningsoptimering bränsledesign härddesign CASMO SIMULATE XIMAGE

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Kvantifiering av osäkerheter i lyftkraftsmodellen / Quantification of uncertainties in the lift force model

Förbättrade effektmarginaler med radiell anrikningsfördelning för PWR-bränsle / Improved peaking factors with radial enrichment distribution för PWR fuel assembly