Odziv jedrskega reaktorja v načinu sledenja bremenu

Mihelčič, Anže (author), Snoj, Luka (mentor), Žerovnik, Gašper (co-mentor)

Jedrski reaktorji bodo, zaradi povečevanja deleža nestalnih obnovljivih virov energije, kot sta veter in Sonce, primorani v obratovanje s prilagajanjem moči potrebam omrežja. V magistrskem delu je predstavljena analiza odziva jedrskega reaktorja v takem načinu obratovanja. Zaradi relativno hitrih sprememb moči se vzbudijo različni prehodni pojavi in povratni vplivi na reaktivnost, ki v reaktorju učinkujejo na različno dolgih časovnih skalah. Najhitrejši so temperaturni povratni učinki, ki se pojavijo zaradi sprememb temperature goriva in hladila ter delujejo v časovni skali do nekaj minut. Srednjeročne učinke predstavljata nastanek in razpad enih izmed bolj pomembnih fisijskih produktov glede vpliva na reaktivnost – $^{135}$Xe in $^{149}$Sm, ki delujeta v časovni skali do nekaj deset ur. Najpočasnejši pa so učinki zaradi zgorevanja goriva na skali tednov oziroma mesecev. Za analizo je uporabljen difuzijski približek z eno energijsko grupo nevtronske transportne enačbe. Najprej kot enotočkovni model, kjer je predstavljena časovna stabilnost sistema pri različnih lastnostih sistema. Nato je za sredico razdeljeno v aksialni smeri na dve enaki polovici uporabljen še dvotočkovni model, ki vpelje grobo prostorsko ločljivost in s tem tudi možnost oscilacij koncentracije $^{135}$Xe v sredici. Za testiranje prilagodljivosti reaktorja sta vpeljana dva scenarija časovne odvisnosti zahtevane proizvodnje. Prvi je kvazi-realni, ki predpostavlja proizvodnjo električne energije s pomočjo sončne in vetrne energije. Drugi je testni scenarij, s katerim se preveri zmožnost sledenja zahtevam EU in energetskemu dovoljenju za jedrsko elektrarno Krško 2 (JEK2). Za sledenje predstavljenega kvazi-realnega scenarija bremena s $500\,\mathrm{MW}$ reaktorjem in uporabo enotočkovnega modela je potrebno okoli od $-100\,\mathrm{pcm}$ do $200\,\mathrm{pcm}$ reaktivnosti, ki jo je potrebno spreminjati s hitrostjo do približno $1\,\mathrm{pcm\, s^{-1}}$. Z uporabo dvotočkovnega modela pa je potrebno v vsaki polovici uporabiti približno do $-260\,\mathrm{pcm}$ reaktivnosti s hitrostjo do $0.2\,\mathrm{pcm\, s^{-1}}$.

• Language: Slovenian
• Keywords: jedrska elektrarna, sledenje bremenu, enogrupna difuzijska enačba, stabilnost, obnovljivi viri energije
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: FMF - Faculty of Mathematics and Physics
• Year: 2023
• PID: 20.500.12556/RUL-146750
• COBISS.SI-ID: 155947523
• Publication date in RUL: 10.06.2023

Secondary language

• Language: English
• Title: Nuclear reactor response in the load-following mode

Abstract

This master thesis investigates the nuclear reactor response analysis of its ability to operate in the load-following operation mode. Due to the increase of intermittent renewable sources usage, the need for operation in the load-following mode is also increasing. Due to relatively fast changes in power, different transient effects and feedback effects on reactivity appear in the reactor core on different time scales. The fastest response is temperature feedback effects due to changes in fuel and coolant temperature. Their typical time scales are up to a few minutes. Midterm effects are caused by the formation and decay of the two fission products with the largest impact on reactivity – $^{135}$Xe and $^{149}$Sm. They have an effect on the reactor core on the time scale of a few tens of hours. The slowest effects are due to burnup, which occurs over the scale of weeks and months. For analysis, the one-group diffusion approximation of the neutron transport equation was used. First is a one-point kinetic model with an analysis of time stability at different physical parameters of the reactor core. Followed by the division of the reactor core into two equal halves in the axial direction using a two-point kinetic model. Using a two-point model results in rough spatial resolution and the possibility of the occurrence of spatial effects, such as oscillations of $^{135}$Xe concentrations. For testing of the reactor's capacity, two load-following scenarios are introduced. The first is quasi-realistic and includes the electric production from intermittent solar and wind power. The second is a test scenario with which the capability of following the requirements of the EU and energy permit for the nuclear power plant Krško 2 (JEK2) is tested. To follow the presented quasi-realistic load-following scenario with a $500\,\mathrm{MW}$ reactor, using a one-point model, reactivity varying from $-100\,\mathrm{pcm}$ to $200\,\mathrm{pcm}$ is required, which has to be varied at a rate of up to approximately $1\,\mathrm{pcm\,s^{-1}}$. Using a two-point model, about $-260\,\mathrm{pcm}$ of reactivity in each half is needed at a rate of up to $0.2\,\mathrm{pcm\,s^{-1}}$.

• Keywords: nuclear power plant, load-following, one-group diffusion equation, stability, renewable sources of energy