Nuclear Engineering - Introduction to nuclear engineering a+b

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POLITECNICO DI MILANO Scuola di Ingegneria Industriale e dell'lnformazione "INTRODUCTION TO NUCLEAR ENGINEERING" COURSE Pag. I WRITTEN EXAMINATION — 2024/01/23 O PART A O PART B Surname: Name: CODE: PLEASE USE CLEAR WRITING (PART-A) EXERCISE #1. A utility operates two nuclear power stations: one is hosting a large reactor (API 000) while the other one is hosting 4 SMR units (BWRX-300). Assuming the data reported in the Table, what is the power station offering the cheapest cost of electricity (€/MWhe)? Parameter Power plant output, net (MWe) Power plant efficiency, net Load factor Fuel cycle length (months) Num. tycle lengths per fuel assembly enrichment, wt% 'Cm e, num. of fuel assemblies assembly type /•Jum. oi equivalent fuel rods per assembly Active length of fuel rods (mm) Fuel pellet diameter (rnrn) IJ02 theoreticai density (g/cm 3) Fuel pellet density, % of theoretical Economy of scale law: exponent cost (€/y) Capital cost interest rate (%/y) molar mass O (g/mol) molar mass 235 1--1 (g/mol) molar mass (g/mol) BWRX-300 290 32% 95% 24 3 3.40% 240 10 x 10 87 3800 8,19 10,96 0.62 25 000 000 4% 15.9994 235,0439 238.0508 Fuel costs Natural uranium (€/kgHM) Conversion (€/kgHM) Enrichment (€/SWU) Enrichment work (SWU/kgHM) Depleted U storage (€/kgHM) Fabrication (€/kgHM) Interim storage (€/kgHM) Disposal spent fuel (€/kgHM) Power plant output, net (MWe) Power plant efficiency, net Load factor Burnup (MWt d/tHM) Fuel cost (€/kgHM) O&M cost (€/y) Capital cost interest rate (Wy) Specific construction capital cost (€/kWe) Both NPPs operational lifetime (y) BWRX-300 80 10 160 4,1 200 470 1117 33% 2400 70000000 6% 5000 60 (optional) #2. To balance the delta cost of electricity between the two nuclear power stations, the utility wants to use 50% of the nominal electrical power produced by the most expensive power plant to produce hydrogen via electrolysers. According to the following data, is that a sound strategy? H2 production H2 ton produced 1 MWhe consumed 36 MWht consumed 9 new power plant efficiency, net 29% H2 value €/ton 3000 POLITECNICO DI MILANO Scuola di Ingegneria Industriale e dell'lnformazione "INTRODUCTION TO NUCLEAR ENGINEERING" COURSE WRITTEN EXAMINATION — 2024/01 /23 (PART-A) OUESTION Pag. 3 l) About safety: explain in brief (bullet point list) why a nuclear power plant is different from any other power station (fossil fired or renewable) and what are the corresponding safety systems. 2) Are those critical features the same for ALL nuclear reactor technologies? POLITECNICO DI MILANO Scuola di Ingcgncria Industrialc c dcll'lnformazione "INTRODUCTION TO NUCLEAR ENGINEERING" COURSE WRIITEN EXAMINATION — 2024/01/23 (PART-B) EXERCISE Analysis of Decay Heat Removal during a Severe Accident Pag. 4 Extreme events in which the reactor core melts partially or completely, are designated by nuclear engineers as 'severe accidents'. Consider a severe accident during which the core has completely melted, thus falling to the bottom of the pressure vessel. The situation is illustrated in Figure 1. The molten mixture of fuel (U02), fission products, clad (Zr), control rod material (BC) and core-supporting structures (steel) is known in severe accident analysis as 'corium'. In the situation considered here, the corium melt fills the bottom of the vessel up to the junction of the hemispherical lower head with the cylindrical beltline region. There is water above the corium and water outside the vessel. The fuel decay heat is removed by boiling above the corium, and by conduction through the vessel wall (with boiling outside the vessel being the heat sink for this heat removal mechanism). The whole system is at atmospheric pressure. Vessel 4.8 m Water Curium inelt Water 22 cm Figure 1. The lower head of the reactor vessel during a severe accident with complete melting of the core. At normal operating conditions the thermal power of the reactor is 3400 M Wth. Three hours after the reactor shutdovm, the corium melt is at 2000 0 C, the temperature on the outer surface of the vessel is 120 0 C and the temperature of the water above the corium is 100 0C. At this time is the corium heating up, cooling down or staying at steady temperature? (Hint: assume that the temperature distribution within the corium melt is uniform) Heat transfer correlation — Film Boiling (FB) heat transfer correlation (by Berenson): hEB — +0.75/1 rad 0.25 = 0.425 —pg)p e h' h sat g(p, —pg) hfg= (hg- hf) (w= wall, sat= saturation, f=fluid (liquid), g = gas (vapour), c= convection, rad= radiation) Pro erties o materials POLITECNICO DI MILANO Scuola di Ingcgncria Industrialc e dcll'lnformazione "INTRODUCTION TO NUCLEAR ENGINEERING" COURSE Pag. 5 WRITTEN EXAMINATION — 2024/01/23 Corium — Density: 8000 kg/m3, Specific Heat: 530 J/kg oc, Emissivity: 0.5 Vessel steel — Density: 7500 kg/m 3 , Thermal Conductivity: 30 W/m oc Decay pou'er.• W = x 0.066 x t-02 (where t in seconds) Stefan-Boltzmann constant: W/(m 2 K4) Saturated water data at atmos heric ressure sat = mo oc or 373 K Parameter Value Parameter 960k /m 3 0.6k /m 3 hf 419 kJ/k kf hg 2675 kJ/k kg 4.2 kJ/ k oc Cp.g 2.1 kJ/k oc Value 2.8.10 4 Pas 1.2.10 -5 Pas 0.68 W/ m oc 0.02 W/ m oc 0.06 N/m (Hint: before starting calculations. set-up the solving system/solving procedure) POLITECNICO DI MILANO Scuola di Ingegneria Industriale e dell'lnformazione "INTRODUCTION TO NUCLEAR ENGINEERING" COURSE WRITTEN EXAMINATION — 2024/01/23 (PART-B) OUESTION Pag. 6 Explain in brief the key steps and motivations of the technological evolution of the Gas Cooled Reactors.