Operating of Nuclear Power Plants in Load-Following Mode

V prvem poglavju smo analizirali probleme, ki se pojavljajo v elektroenergetskem sistemu, zaradi katerih bi bilo ugodno, da bi imele jedrske elektrarne boljše manevrske sposobnosti, kot je to večinoma praksa sedaj, tj. zmožnost sledenja bremenu in da bi v primeru nezgod bile sposobne hitro spremeniti svojo proizvodnjo električne energije. V drugem poglavju se naloga navezuje na fizikalne probleme, ki se pojavijo, če želimo jedrski elektrarni spreminjati količino proizvedene električne energije, to je Dopplerjev učinek, vpliv zastrupitve s ksenonom, vpliv moderatorja, vpliv spreminjanja reaktivnosti med trajanjem gorivnega cikla itd. Diplomsko delo v tretjem poglavju obravnava osnove dveh najbolj pogostih osnovnih tipov reaktorjev: to sta tlačnovodni in vrelovodni jedrski reaktor, ki spadata v kategorijo lahkovodnih reaktorjev. Sprva je opisano splošno delovanje, prednosti in slabosti, načini sledenja bremenu ter tehnične in varnostne lastnosti. Sledi obravnava zahtev EUR, ki jih morajo jedrske elektrarne izpolnjevati za obratovanje v načinu sledenja. Najpomembnejše so: spreminjanje moči reaktorja od 2 do 5 % za nadzor omrežne frekvence s hitrostjo 1 % Pn na sekundo, sledenje bremenu v izrednih razmerah od 50 % Pn do 100 % Pn, s povečanjem moči s hitrostjo po 5 % Pn na minuto in zmanjšanjem moči s hitrostjo 20 % Pn na minuto. Več režimov obratovanja je podanih v poglavju Zahteve sledenja bremenu v tabeli 1. Kasneje smo se osredotočili na jedrsko elektrarno EU-APWR, ki sodi v tretjo generacijo tlačnovodnih jedrskih reaktorjev. V nadaljnjem poglavju analiziramo manevrske sposobnosti različnih jedrskih elektrarn z jedrskimi reaktorji iz generacij 2, 3 in 3+. V generacijo 2 štejemo francoske jedrske elektrarne PWR-900, PWR-1300 in N4v generacijo 3 ABWR in APR-1400, v 3+ pa AP1000 ter EPR. Na koncu smo se osredotočili na ekonomičnost sledenja bremenu in vpliv tega na gorivo. Izkaže se, da so stroški proizvodnje električne energije precej odvisni od faktorja obremenitve, ki diktira, s kolikšno močjo obratujejo elektrarne. Uporabili smo 5 % oz. 10 % diskontno stopnjo. Cena proizvedene električne energije je tudi hkrati konstantna in se ne spreminja v obratovalni dobi elektrarne, vsa proizvedena energija se v trenutku proda po podani ceni. V primeru, da jedrska elektrarna obratuje s polno močjo, so stroški proizvedene električne energije v primerjavi z drugimi tipi elektrarn nizki. Če bi bil povprečni faktor obremenitve za jedrske elektrarne pod določeno mejo (približno 65 % pri 5-odstotni diskontni stopnji), bi se njihov konkurenčni položaj zmanjšal. Trenutno je povprečni faktor obremenitve dovolj visok, obrestna mera pa je dovolj majhna, da bi se verjetno lahko štelo, da vpliv sledenja bremenu na stroške proizvedene električne energije ne vpliva bistveno na konkurenčnost jedrske energije na reguliranih trgih. Prav tako sledenje bremenu nima velikega vpliva npr. na gorivo, lahko pa se pojavijo stroški zaradi dodatnega vzdrževanja obratovalnih komponent, kot so ventili. V Franciji, kjer je visok delež jedrskih elektrarn in pogosto uporabljajo režim sledenja bremenu, je vpliv tega na faktor obremenitve le 1,2 %.In the first chapter, which deals with problems occurring in the electricity network, it would be essential for nuclear power plants to have strong maneuvering capabilities that they could use in their energy production. In the first chapter, I mentioned the problems that arise in the electricity network, which would make it convenient for nuclear power plants to have strong maneuverability, the ability to load follow, and in case of incidents that the power plants are able to quickly change their electricity production. In the second chapter, the task relates to the physical problems that arise where the nuclear power plant wants to change the amount of electricity produced, such as the Doppler effect, the xenon effect, the effect of the moderator, the influence of the fuel cycle, etc. In the third chapter, the thesis deals with the basics of two of the most common basic types of reactors, namely, the pressurized-water and boiling-water nuclear reactors belonging to the category of light-water reactors. Initially i went to describe the general operation, advantages and disadvantages, methods of load tracking, and technical and safety features of those reactors. The next chapter lists the requirements of EUR, which most nuclear power plants have to fulfill for operation in the load following mode. Here are some of the several requirements: Changing the reactor power from 2 to 5% for monitoring the network frequency at a rate of 1% Pn per second, monitoring the load in an emergency from 50% Pn to 100% Pn with power increase at a rate of 5% Pn per minute and reducing power at a speed of 20% Pn per minute. Several operating modes are still given in the chapter in Table 1. Later, I focused on the EU-APWR nuclear power plant coming from the third generation of pressurized-water nuclear reactors, where I mentioned the key components of the power plant, such as the nuclear island, the evaporator, the primary system, the fuel, the control elements, the reactor vessel, the pressure vessel, etc. In the next section I have listed the maneuvering capabilities of different nuclear power plants with nuclear reactors from the generations 2, 3 and 3+. From generation 2 I listed in table 6 French nuclear power plants PWR-900, PWR-1300 and N4. In the third generation, I quoted ABWR and APR-1400. From the last generation I\u27ve mentioned AP1000 and EPR. In the last chapter, I focused on the cost-effectiveness of the load tracking and the impact of this on fuel. At first I started defining the LCOE (Levelised cost of generating electricity). Where it is observed that it is quite dependent on the load factor, which dictates the power of the power plants. In the equation, the discount rate "r" is constant and does not change during the operation of the power plant. I used a 5% and 10% discount rate. The price of the produced electricity is also constant and does not change in the operating period of the power plant, and all the energy produced is immediately sold at a given price. In case the nuclear power plant operates at full power, the costs of electricity produced are low compared to other types of power plants. If the average load factor for nuclear power plants were below a certain limit (approximately 65% at a 5% discount rate), their competitive position would be reduced. At present, the average load factor is sufficiently high and the interest rate is small enough so that it is likely that the impact of the load following on the costs of produced electricity does not significantly affect the competitiveness of nuclear energy on regulated markets. The impact of load following does not have a major impact on fuel, but costs may arise due to maintenance of operating components, such as valves. In France, where there is a high share of nuclear power plants and the load following regime is regularly used, the impact of this on the load factor is only 1.2%