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Various stand-alone hybrid power systems are widely used to fulfil the electric loads for remote, rural villages. Although there are many investigations based on various aspects of renewable hybrids energy microgrids, the discussions about the application of biomass combustion power plants are rare. Also, detailed investigations of the system steady and transient stability analysis, and the power curtailment control optimization of wind turbines in these stand-alone hybrid systems are seldom found. This paper focuses on wind/biomass/diesel/battery stand-alone microgrids and discusses the system operation, energy management and dispatch issues detailed. The renewable and controllable biomass power is localized to follow the load fluctuations over a long timescale to decrease the power production from diesel and the peak-load shifting demands of the battery banks. An optimization strategy of the wind power curtailment control is also proposed to effectively decrease the frequency and amplitude of the pitch actor and, to some extent, improve the power generation through the combination of the active turbine speed control and pitch regulation. Then a parallel double-mode optimal operation strategy with a “fault detector” is presented to realize economic optimization dispatch under the normal mode and emergency power control for large disturbance scenarios. Finally, case studies of a microgrid on a remote Canadian aboriginal community are conducted to demonstrate the performance of the proposed methods.

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 N4 v 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've 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%.

In the last three decades, core design and operational requirements of German PWRs have evolved significantly in order to optimize plant operation and to react to changed market conditions. In the first phase, steady state operation was optimized to limit plant operation costs or increase availability and power output. The second phase of the evolution was triggered by the necessity of flexible plant operation in order to compensate fluctuating power generation by wind and solar power and by optimization of phase out cores. The changes of core design and operation parameters had among the direct, expected impacts on safety analyses and reactor physics also several indirect and unexpected ones. Examples for expected impacts are changes of reactivity coefficients or boron worth compared to safety analysis assumptions or changes of possible initial conditions of incidents. Unexpected impacts showed for example on rod bow, cladding corrosions or neutron noise. The tasks of TÜV NORD EnSys as technical expert organization is to identify all these impacts of core design and operational parameter evolution, evaluate whether these impacts compromise plant safety, evaluate models and correlations regarding unexpected effects, assess if intended countermeasures are effective and acceptable and evaluate whether the set and ranges of plant parameters used for core limitation and protection are still valid. The paper gives an overview over selected experiences and tasks performed by the Reactor Physics and Criticality Safety Group of TÜV NORD EnSys for the evolution of core designs and operational requirements in German PWRs.

International audience; The increase of the intermittent renewable energies Contribution is a major challenge in the context of the French energy transition, with renewable energies forecasted to be around 30% of the total production by 2030, thus increasing the manageability required of nuclear power plants. This works aims at optimizing load-follow operations on French 1300MW pressurized water reactors, according to values of interests (volume of boron effluents and axial stability) by changing the operating parameters of the rods. A simulator oriented reactor model is designed, coupling a 0D secondary model and a core model with a model including 3D neutronics, multi1D thermal-hydraulics and fuel thermal effects. A simplified controller imitating the current “G mode” operator is presented. Finally, a study of the fitness landscape of the optimization problems shows the potential of this model and these parameters for the optimization process.