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During a severe accident in a light water reactor nuclear power plant, hydrogen may be generated, and its combustion could threaten the integrity of the nuclear power plant containment, which could lead to release of radioactive material into the environment. The study of hydrogen distribution in the containment is important to predict the occurrence of regions with flammable mixture, in order to effectively install hydrogen mitigation systems. A theoretical model to describe the homogenization of the layered atmosphere due to the vertical injection in an enclosure was developed. In linear two-equation eddy viscosity turbulence models, constant values of turbulent Schmidt and Prandtl numbers are usually used. It was shown that constant values fail to reproduce some phenomena observed in experiments. For the purposes of this work, firstly, a local Froude number is introduced, which can be directly used in computational fluid dynamics calculations. Secondly, a model that prescribes turbulent Schmidt and Prandtl numbers dynamically, which uses local Froude number and vertical velocity, is proposed. Non-essential parts of the experimental facilities, which do not contribute much to the mixing process, were identified according to experimental results. Accordingly, axisymmetric two-dimensional and three-dimensional numerical models of cylindrical vessels were developed, and the effects of numerical domain reduction were studied. Since OpenFOAM is a multipurpose computational fluid dynamics code, it was first adapted to simulate the considered cases. An additional term accounting for enthalpy diffusion due to compositional changes was implemented into the energy equation, and a term describing the molecular diffusion had to be added to the convection-diffusion equation for mean mass fraction. The developed physical model for simulation of mixing in nonhomogeneous atmosphere in large enclosures was verified and validated on fourteen different experiments performed in three experimental facilities. The comparison with experimental results showed that the selected modelling approach is able to correctly predict the helium distribution and temperature values. Furthermore, with the proposed model the successful modelling of breaking-up of atmosphere stratification, induced by vertical injection, was extended to isothermal conditions with high mass inflow. Med težko nesrečo v lahkovodnem jedrskem reaktorju lahko pride do nastanka vodika, njegovo zgorevanje pa lahko ogrozi celovitost zadrževalnega hrama jedrske elektrarne, kar bi lahko vodilo v izpust radioaktivnih snovi v okolje. Študija porazdelitve vodika v zadrževalnem hramu je pomembna za napovedovanje območij z vnetljivo mešanico. Razvit je bil teoretični model za opis homogenizacije razslojene atmosfere zaradi navpičnega vbrizgavanja v eksperimentalni napravi zadrževalnega hrama. V turbulentnih modelih, ki temeljijo na modeliranju vrtinčne viskoznosti se običajno uporabljajo konstantne vrednosti turbulentnega Schmidtovega in Prandtlovega števila. Pokazano je, da konstantne vrednosti teh števil ne morejo pravilno reproducirati nekaterih fizikalnih pojavov opaženih v eksperimentih. Za namene tega dela je najprej definirano lokalno Froudovo število, ki se lahko neposredno uporablja v programih za računsko dinamiko tekočin. Poleg tega je predlagan model za dinamično predpisovanje turbulentnega Schmidtovega in Prandtlovega števila, ki uporablja lokalno Froudovo število in navpično hitrost. Nepomembni deli eksperimentalnih naprav, ki ne prispevajo veliko k procesu mešanja, so bili identificirani s pomočjo eksperimentalnih rezultatov in rezultatov simulacij. V skladu z ugotovitvami so bili razviti poenostavljeni osno simetrični dvodimenzionalni in tridimenzionalni numerični modeli cilindričnih posod ter proučeni učinki redukcije numerične domene. Ker je OpenFOAM večnamenski program za računsko dinamiko tekočin, je bil najprej prilagojen za modeliranje obravnavanih primerov. V energijsko enačbo je bilo potrebno implementirati dodatni izraz, ki upošteva difuzijo entalpije zaradi sprememb sestave, konvekcijsko-difuzijski enačbi za masni delež plina pa je bilo potrebno dodati člen, ki popisuje molekularno difuzijo. Razviti fizikalni model za simulacijo mešanja v nehomogeni atmosferi je bil preverjen na štirinajstih eksperimentih izvedenih v treh različnih eksperimentalnih napravah. Primerjava z eksperimentalnimi rezultati je pokazala, da razviti fizikalni model pravilno napove porazdelitev helija in temperaturo znotraj zaprte posode. S predlaganim modelom za dinamično predpisovanje turbulentnih števil je bilo uspešno modeliranje erozije razslojene atmosfere z navpičnim vpihovanjem razširjeno na izotermne pogoje z visokimi hitrostmi vpihovanja, pri katerih pride do nastanka Kelvin-Helmholtzeve nestabilnosti.

During a hypothetical severe accident in a light water nuclear power plant, the molten reactor core may come in contact with the coolant water. One of the consequences can be a vapour explosion. Typically in nuclear safety, the vapour explosions are mostly analysed in the melt jet-coolant pool geometry. In the stratified melt-coolant configuration, which was less analysed, a layer of melt lies below a layer of coolant. The stratified melt-coolant configuration was believed to be incapable of producing a strong energetic interaction between the melt and coolant.. This belief was based on the conclusions from the past theoretical and some experimental research, where the lack of the interfacial instabilities and consequently the lack of an explosive premixture was determined. In the recent fuel-coolant interaction experiments performed in the stratified configuration at the SES and PULiMS facilities (KTH, Sweden), a premixed layer formation of ejected melt drops in water was clearly visible and was followed by strong spontaneous vapour explosions. The purpose of our research was to improve the knowledge, understanding and modelling of the fuel-coolant interaction phenomena in the stratified configuration. Firstly, the phenomenon of the vapour explosion is presented. An overview of the experimental work is given. The SES and PULiMS experiments (KTH, Sweden) and other experiments of vapour explosion and premixed layer formation in stratified configuration as well as some other relevant experiments are presented. Existing modelling approaches for mixing in case of the vapour explosions in the stratified configuration are reviewed. Possible mechanisms for the premixed layer formation are discussed and assessed according to their relevance to the reviewed experiments. Based on the visual observations and some available mechanisms from the literature, models for the premixed layer formation are presented. Due to the uncertainties and the lack of detailed information, two different approaches are followed in the modelling. Both approaches are based on the bubble collapse mechanism, where coolant micro-jet is formed. The first modelling approach describes the melt drops ejection due to the coolant micro-jet penetration in the melt and its vaporization. The second modelling approach describes the melt drops ejection due to the pressure perturbation, when the coolant micro-jet hits the melt surface. Both models and experimental observations are discussed and joined into the third model, which describes the considered phenomena the best. The developed model is implemented into the MC3D code (IRSN, France) and validated against the experimental results. To enable the implementation of the proposed model into the Eulerian fuel-coolant interaction codes, a description of melt drops with a two-melt-drop-group approach is introduced. The behaviour of the implemented model is verified with numerical and physical tests. The implementation of the model into the fuel-coolant interaction code enables the simulation of the observed fuel-coolant interaction in the stratified configuration. The presented analyses demonstrate the model capability to describe the premixed layer formation in a qualitative agreement with the available experimental data. The indirect comparison of the simulated premixed layer with the SES S1 and PULiMS E6 experiments via the strength of vapour explosion shows underestimation in simulations’ explosion strength. This underestimation is further discussed and other possible contributions, e.g. contribution from the melt jet break-up and mixing during the explosion are highlighted. Hipotetična težka nesreča v jedrski elektrarni lahko vodi do poškodb sredice, vključno s taljenjem sredice. Če staljena reaktorska sredica pride v stik z vodo lahko pride do parne eksplozije. V reaktorskih varnostnih analizah se parne eksplozije večinoma analizira v geometriji izliva curka taline v bazen hladila. V razslojenih razmerah, ki so bile deležne manj pozornosti, pa leži plast taline pod plastjo hladila. Za razslojene razmere taline in hladila se je predpostavljalo, da ne morejo privesti do močnih interakcij med talino in hladilom. Ta hipoteza je bila osnovana na teoretičnih in eksperimentalnih študijah, kjer niso opazili površinskih nestabilnosti in posledično eksplozivne mešanice taline in hladila. V pred kratkim opravljenih eksperimentih interakcije taline s hladilom v razslojenih razmerah na eksperimentalnih napravah SES in PULiMS (KTH, Švedska) je bil jasno opažen nastanek mešalne plasti kapljic taline v vodi, kateremu je sledila močna spontana parna eksplozija. Namen našega raziskovalnega dela je doprinos k znanju, razumevanju in modeliranju interakcije taline s hladilom v razslojenih razmerah. Najprej je predstavljen pojav parne eksplozije. Opravljen je pregled eksperimentalnega dela. Predstavljena sta pred eksperimenta PULiMS in SES (KTH, Švedska) ter nekateri ostali eksperimenti, povezani s parnimi eksplozijami in mešalno plastjo v razslojenih razmerah. Opravljen je pregled modeliranja mešanja pri parnih eksplozijah v razslojenih razmerah. Obravnavani so možni mehanizmi za nastanek mešalne plasti in ocenjeni glede na njihovo relevantnost za posamezne eksperimente. Na podlagi opazovanj in nekaterih razpoložljivih mehanizmov iz literature so predstavljeni modeli za nastanek mešalne plasti. Zaradi negotovosti in pomanjkanja podrobnih informacij pri modeliranju uporabimo dva različna pristopa. Oba pristopa slonita na mehanizmu kolapsa mehurčkov, kjer nastanejo mikrocurki hladila. Prvi pristop k modeliranju predpostavlja izmet kapljic taline zaradi vdora mikrocurkov hladila v talino ter njihovega uparjanja, drug pristop k modeliranju pa izmet kapljic taline zaradi tlačne motnje ob udarcu mikrocurka hladila ob talino. Oba modela ter rezultati eksperimentov so obravnavani in združeni v tretji model, ki najbolje opisuje obravnavane pojave. Razviti model je vključen v računalniški program MC3D (IRSN, Francija) in validiran na eksperimentalnih rezultatih. Za vključitev predlaganega modela v računalniški program Eulerjeve narave za interakcijo taline s hladilom se vpelje dvogrupni pristop za popis kapljic taline. Pravilno obnašanje modela je verificirano z numeričnimi in fizikalnimi testi. Vključitev modela v računalniški program za interakcijo taline s hladilom nam omogoča simulacijo opažene interakcije taline s hladilom v razslojenih razmerah. Predstavljena analiza pokaže zmožnost modela za popis nastanka mešalne plasti v kvalitativnem ujemanju z razpoložljivimi rezultati eksperimentov. Posredna primerjava simulirane mešalne plasti v eksperimentalnih testih SES S1 in PULiMS E6 preko moči parne eksplozije pa nakaže podcenitev moči eksplozije v simulacijah. Razprava zajema opažene razlike in osvetli nekatere možne dodatne prispevke, kot sta prispevka zaradi razpada curka taline in mešanje med samo eksplozijo.

Thermal fatigue is a structural damage mechanism which has been among the causes of reactor coolant leakages in nuclear power plants. A well-recognized source of thermal fatigue in the safety related nuclear piping is the turbulent mixing of fluids at different temperatures. The thermal fatigue assessment of components requires an interdisciplinary approach. This involves the evaluation of the fatigue driving loads from the fluid temperatures, heat transfer to the pipe and stress amplitudes within the pipe wall. The fatigue analyses are then needed to predict the fatigue life using the estimated driving loads and experimental fatigue resistance data. It is clear that the accuracy of fatigue life estimates strongly depends on the accuracy of the estimated fatigue driving loads, especially fluid temperature histories. These can be obtained from complex and extremely time-consuming experiments or computational fluid dynamic (CFD) simulations of turbulently mixing fluids. These could only offer spatially incomplete temperature histories, which are typically limited to minutes or hours at the best, and reported in compact terms of the first two statistical moments combined with power spectral densities. Extrapolation of compact and comparatively short fluid temperature histories to the expected fatigue life time of months or years is inherently uncertain and lacks deeper understanding and proper treatment in the open literature. The major goal of the dissertation is therefore to contribute to the prediction and understanding of the uncertainties involved in the assessment of the safe life of pipes exposed to thermal fatigue due to the turbulently mixing fluids. To this end, the dissertation explores a range of simplified and complex state-of-the-art numerical methods, including one-dimensional (1D) approximations with one- and multi-frequency (spectral) approaches and turbulent three-dimensional (3D) CFD models with and without conjugate heat transfer. An improved spectral loading approach for the generation of synthetic fluid temperatures at affordable computational costs is proposed. Synthetic fields of temperatures acting near the surface of pipes during turbulent fluid mixing are employed in 3D structural analyses of pipes to verify the persistence of nearly equi-biaxial stress states in the pipe surface away from geometrical, structural and material discontinuities. Then, the improved spectral approach is employed to generate a wide variety of fluid temperature histories resulting in a set of estimated fatigue lives. These are further analyzed to quantify the magnitudes of inherent uncertainties. Linear 1D heat diffusion and thermal stress estimates are used together with fatigue assessment codified rules in the uncertainty analysis. Toplotno utrujanje je pojav, ki povzroča strukturne poškodbe materialov in je eden od vzrokov za nastanek puščanja reaktorskega hladila v jedrskih elektrarnah. Dobro poznan vir toplotnega utrujanja v ceveh, ki so pomembne za jedrsko varnost, je turbulentno mešanje tekočin različnih temperatur. Ocenjevanje toplotnega utrujanja komponent zahteva interdisciplinarno obravnavo. Ta vključuje oceno obremenitev - temperaturnih polj tekočine, ki povzročajo utrujanje, oceno prenosa toplote med tekočino in cevjo ter oceno mehanskih napetosti v stenah cevi. Na podlagi ocenjenih obremenitev in izmerjenih krivulj odpornosti materiala na utrujanje nato z analizami utrujanja napovemo življenjsko dobo komponent. Jasno je, da je natančnost ocene življenjske dobe utrujanja močno odvisna od natančnosti ocene obremenitev, predvsem časovnega poteka temperaturnih polj. Le-ta lahko pridobimo s pomočjo kompleksnih in časovno zelo zahtevnih eksperimentov ali simulacij turbulentnega mešanja tekočin s pomočjo računske dinamike tekočin (CFD). Na ta način dobljena temperaturna polja so ali prostorsko nezvezna ali pa so časovno omejena tipično na nekaj minut oz. kvečjemu ur. Poleg tega so dostopni podatki običajno predstavljeni le v kompaktni obliki, npr. s prvima dvema statističnima momentoma in gostoto spektralne moči. Ekstrapolacija kompaktnih in relativno kratkih časovnih temperaturnih polj glede na pričakovano življenjsko dobo komponent, ki je reda velikosti nekaj mesecev oz. let, je inherentno obremenjena z negotovostjo, njena poglobljena obravnava v dostopni literaturi pa je pomanjkljiva. Zato je glavni cilj disertacije prispevati k napovedim in razumevanju negotovosti pri ocenjevanju varne življenjske dobe cevi, ki so izpostavljene toplotnemu utrujanju zaradi turbulentnega mešanja tekočin. V disertaciji v ta namen raziščemo nabor najsodobnejših poenostavljenih in kompleksnih numeričnih metod, med katere sodijo enodimenzionalni (1D) približni modeli, ki jih rešujemo z eno- ali več-frekvenčnim (spektralnim) pristopom, ter turbulentni tridimenzionalni (3D) modeli CFD, ki upoštevajo vezan oz. nevezan prenos toplote. Predlagamo izboljšan, računsko nezahteven spektralni pristop za generacijo sintetičnih temperaturnih polj tekočine. Sintetična temperaturna polja, ki delujejo tik ob površini cevi, uporabimo v 3D termo-mehanskih analizah, s katerimi preverjamo obstojnost približno izo-dvoosnega napetostnega stanja na površini cevi daleč stran od geometrijskih, strukturnih in materialnih nezveznosti. V nadaljevanju z izboljšanim spektralnim pristopom izračunamo širok nabor temperaturnih signalov tekočine, s katerimi ocenimo pripadajoče življenjske dobe utrujanja. Z analizo teh rezultatov nato kvantificiramo inherentne negotovosti ocen. Pri analizi negotovosti poleg linearnega 1D modela difuzije toplote in termičnih napetosti uporabimo standardizirana pravila za ocenjevanje utrujanja.

Hydrogen may be produced in a light water reactor nuclear power plant containment during a postulated severe accident. Ensuing hydrogen combustion, which is essentially inevitable, could inflict irreparable damage to the containment itself, resulting in a failure of the final protection barrier for the fission products release to the environment. Since the actual containment volumes surpass the volumes of even the largest available experimental facilities capable of conducting hydrogen combustion experiments for a few orders of magnitude, the computer-aided modelling presents itself as a formidable and accessible tool in this regard. Thus, use and development of reliable computational fluid dynamics modelling approaches for large-scale geometries is imperative for providing relatively cost-effective hydrogen combustion risk assessment. The present dissertation focuses on further theoretical investigation of hydrogen combustion, specifically hydrogen deflagration in large enclosures. This investigation is carried out through the development and validation of hydrogen combustion models and addresses some of the challenges on the way for the computer-aided modelling to become readily available for use in the real-scale containment dimensions. Specifically, it tackles the difficulties of available combustion models in producing the reliable predictions of the large-scale hydrogen deflagration experiments. The validation of combustion models was performed against the results obtained in two large-scale experimental facilities, i.e. THAI and HYKA-A2 experimental vessels. Firstly, a new combustion model was introduced, i.e. the extended eddy break-up (EEBU) model, which was developed from the existing less elaborate eddy break-up (EBU) model, with the additional treatment of the flame phenomenology also in the quasi-laminar combustion regime. This model retains beneficial characteristics of the EBU model, i.e. superior computational efficiency, while at the same time providing improved predictions for hydrogen deflagrations in the considered large-scale experiments. Furthermore, a novel approach was recommended undertaking a focused treatment of the laminar flame speed with the weighted laminar flame speed concept. This approach effectively balances the turbulent reaction rate with the buoyancy effects of the surrounding flow. It was applied to already existing extended turbulent flame speed closure (ETFC) model as well as to the newly introduced EEBU model. When properly executed, it proved to be extremely effective in improving the predictions of both models regarding the flame behavior in the considered large-scale hydrogen deflagration experiments. V primeru težke nesreče v lahkovodni jedrski elektrarni lahko pride do nastajanja vodika. Nadaljnje zgorevanje vodika, ki je v bistvu neizogibno, lahko povzroči nepopravljivo škodo na samem zadrževalnem sistemu, kar bi pomenilo odpoved končne zaščitne ograde za izpustitev radioaktivnih fisijskih produktov v okolje. Ker dejanske geometrije zadrževanja več sto krat presegajo geometrije celo največjih razpoložljivih eksperimentalnih objektov, v katerih se lahko izvaja poskuse zgorevanja vodika, se v tem pogledu računalniško podprto modeliranje ponuja kot izjemno uporabno in dostopno orodje. Zato je uporaba in razvoj zanesljivih modelov za modeliranje dinamike tekočin za obsežne geometrije nujna za zagotavljanje relativno stroškovno učinkovite ocene zgorevanja vodika. Disertacija se osredotoča na nadaljnje teoretične raziskave zgorevanja vodika, zlasti deflagracije vodika v velikih zaprtih prostorih jedrskih elektrarn. Ta raziskava se izvaja z razvojem in validacijo modelov zgorevanja vodika in naslavlja nekatere izzive na poti do računalniško podprtega modeliranja, ki bi bilo na voljo za uporabo v realnih dimenzijah zadrževalnih hramov. Konkretno se spopada s težavami razpoložljivih modelov zgorevanja pri kreiranju zanesljivih napovedi obsežnih eksperimentov deflagracije vodika. Validacija modelov izgorevanja je bila izvedena v primerjavi z rezultati pridobljenimi v dveh obsežnih eksperimentalnih objektih, tj. eksperimentalnih posodah THAI in HYKA-A2. Najprej je formuliran in predstavljen nov, t.i. razširjen model razpada vrtincev (ang. »extended eddy break-up model« - EEBU), ki smo ga razvili z nadgradnjo obstoječega modela razpada vrtincev (ang. »eddy break-up model« - EBU), z dodatno obravnavo fenomenologije plamena tudi v kvazi-laminarnem režimu zgorevanja. Novo formirani EEBU model ohranja koristne značilnosti modela EBU, tj. boljšo računsko učinkovitost, hkrati pa zagotavlja boljše napovedi deflagracije vodika v obravnavanih eksperimentih. Poleg tega je bil predstavljen tudi nov pristop, ki je usmerjen v obravnavo hitrosti laminarnega plamena s konceptom utežene hitrosti laminarnega širjenja plamena. Uveden pristop učinkovito uravnava turbulentno hitrost reakcije z vzgonskimi učinki okoliškega pretoka. Uporabljen je bil za že obstoječi razširjen model zgorevanja temelječ na turbulentni hitrosti plamena (ang. »extended turbulent flame speed closure model« - ETFC), kot tudi za novo predstavljen model EEBU. Ko je ta pristop ustrezno izveden, se izkaže za izjemno učinkovitega pri izboljšanju napovedi omenjenih modelov v zvezi z obnašanjem plamena v obravnavanih obsežnih eksperimentih deflagracije vodika.

Po nesreči v Fukušimi leta 2011 se ljudje mnogo pogosteje sprašujemo o vplivih ionizirajočega sevanja na ljudi in okolje. Ta katastrofa je odmevala po vseh svetovnih medijih. Kot posledica razprav o prihodnosti in varnosti jedrske energije so bile sprejete nekatere spremembe na tem področju. Evropska komisija je dobila nalogo od Sveta EU, da pregleda obstoječe ukrepe za zagotavljanje varnosti na jedrskem področju in predlaga izboljšave. To se je tudi zgodilo leta 2014 z popravljeno direktivo o jedrski varnosti. Odmevala je tudi odločitev Nemčije, da opusti jedrski program do leta 2022. V javnosti bolj odmevajo nesreče, ki se zgodijo v jedrskih elektrarnah, vendar pa tudi dogodki, ki se lahko zgodijo v jedrskih objektih, kjer so shranjeni jedrski odpadki lahko povzročijo veliko škode. Problematika povezana v zvezi z jedrskimi odpadki, se na prvi pogled ne zdi tako pomembna kot posledice, ki jih povzroči nesreča v jedrski elektrarni, vendar pa menimo da bo v prihodnjih letih o njih vse več razprav. Ocenjujemo, da je trenutno varnostno stanje odlagališč z jedrskimi odpadki v Sloveniji zadovoljivo. Pregled stanja odlagališč v državah, kjer jedrska energija predstavlja pomemben delež pridobljene energije kot so Združene države Amerike, Nemčija ter Francija nam pove, da je skupna problematika naštetih držav vključno z Slovenijo dolgoročno zagotoviti odlagališče visoko radioaktivnih odpadkov. Opozoriti je pomembno tudi na ranljivosti oziroma potencialne primere nevarnosti, ki pretijo objektom v zvezi z jedrsko energijo. In teh je veliko. Najbolj verjetni so človeški in naravni dejavniki ter teroristična dejanja. Kot primer pri posledicah nesreč in prav tako pri vzrokih, ki lahko privedejo do katastrofalnih razsežnosti sta primera nesreč v Fukušimi ter Černobilu. Pomemben je tudi nadzor nad subjekti, ki se ukvarjajo z jedrsko energijo. Pristojni organi v Republiki Sloveniji so Uprava RS za jedrsko varnost, Uprava RS za varstvo pred sevanji ter agencija za radioaktivne odpadke. Ti subjekti tudi načrtujejo smernice in način razvoja jedrskih subjektov v prihodnosti. Pristojna za nadzor na mednarodni ravni je mednarodna Agencija za atomsko energijo. Vsi ti subjekti nadzora delujejo po ustrezni zakonodaji, po direktivi EU imenovani Direktiva Sveta 2011/70/ EUROATOM ter po nacionalni zakonodaji med katerimi sta najpomembnejša Zakon o varstvu pred ionizirajočimi sevanji in jedrski varnosti ter Pravilnik o ravnanju z radioaktivnimi odpadki in izrabljenim gorivom. After the Fukushima accident in 2011, people more often ask themselves about the effects of ionizing radiation on humans and the environment. This catastrophe was spread by all the world's media. As a result of discussions about the future and security of nuclear energy some changes have been made in this area. The European Commission was given the task by the EU Council to review existing measures to ensure safety in the nuclear field and to propose improvements. This is exactly what happened in 2014 with the revised directive of nuclear safety. Also big news was Germany's decision to abandon nuclear program by 2022. The public has more interest in accidents that occur in nuclear power plants but events that can occur in nuclear storage facilities can also cause a lot of damage. Issues related to the nuclear waste, at first glance, does not seem as important as the effects caused by the accident at the nuclear power plant, but we believe that in the coming years there will be a lot of discussion on this theme. We believe that the current security status of nuclear waste dumps in Slovenia is secure. In countries, where nuclear power plays a significant role, such as United States, Germany and France tell us that the common problem of these countries including Slovenia is providing a long-term repository of highly radioactive waste. It is also important to alert in the possible vulnerability and potential threats facing the nuclear storage facilities. And there are many. Most likely are the human factor, natural influences and terrorist acts. What are the consequences and also the causes that can lead to nuclear accident of catastrophic proportions are examples in Fukushima and Chernobyl. Also very important is the control over the subjects involved in nuclear energy. The competent authorities of the Republic of Slovenia is the nuclear safety administration, administration for radiation protection and radioactive waste management agency. These subjects are also responsible for planning guidance and the the development of nuclear operators in the future. Responsible for monitoring at the international level is the international atomic energy agency. All of these entities operate under the supervision of the relevant legislation, according to EU Directive appointed by Council Directive 2011/70/ EURATOM and the national legislation of which the most important are the law on radiation protection and nuclear safety act and also regulations on the management of radioactive waste and spent fuel.

V svetu hitro razvijajočih se tehnologij in vse zahtevnejših poslovnih procesov postaja znanje najdragocenejša poslovna prvina, ki lahko bistveno vpliva na konkurenčnost podjetja. Vse hitrejši tehnološki razvoj zahteva čedalje večje prilagajanje ljudi, da lažje obvladujejo področje svojega dela. Zahteva se tudi prilagajanje podjetij, da zaposlenim olajšajo dostop do znanja in jih spodbudijo tudi k samostojnejšemu iskanju ustreznih virov in s tem pridobivanju znanja v skladu z lastnimi poklicnimi in osebnostnimi interesi. Poslanstvo zaposlenih je uspešno vključevanje v izvajanje delovnih nalog ob pomoči managerjev, da imajo zaposleni potrebno znanje — ali pa si ga pridobijo — in spretnosti za opravljanje dela danes ali v prihodnosti. Pomembno je, da zaposleni ustvarjalno sodelujejo v procesu usposabljanja in da vsak človek najde svoj cilj v zadovoljevanju potreb, s tem pa vpliva na večjo produktivnost, kakovost opravljenih storitev, ugled in uspeh. Star pregovor, ki pravi: »Kolikor znaš, toliko veljaš!«, je še danes pomembno vodilo zaposlenih. Šolanje zaposlenih v Nuklearni elektrarni Krško (NEK) je ena od pomembnih dejavnosti za dosego zastavljenih ciljev, dvig varnostne kulture, učinkovitost in varno obratovanje. Jedrska varnost je naša največja prioriteta, varnostni vidiki dela so prednostni na vseh nivojih v NEK-u. Dobri kadri, ki so rezultat tega usposabljanja, so jamstvo za varno in zanesljivo obratovanje elektrarne sedaj in v prihodnosti. In the world of quickly developing technologies and more and more demanding business processes, knowledge is becoming the most valuable business element, which can vitally influence the competitive position of an enterprise. Quicker and quicker technological development demands bigger and bigger adaptations of people to enable them easier mastering of their work field. Adaptation of enterprises is also demanded in order to give the employees access to knowledge and stimulates them to search suitable sources more independently, and by this in gaining knowledge in accordance with their professional and personal interests. The mission of the employees is a successful incorporation in realization of work tasks with the assistance of managers, so the employees have or gain necessary knowledge and skills to attend their duties in the present or in the future. It is important that employees creatively cooperate in the qualification process and that every person finds his own aim in satisfying his needs and with that he affects higher productivity, quality of the attended duties, reputation and success. Old proverb, that says: »As much as you know, that much you are worth!« is still a rule for all the people. Training of Nuclear Power Plant Krško (NEK) personnel is one of the important functions in achieving the set goals, improvement of safety, effectiveness and safe operation. Nuclear safety is our biggest priority, safety aspects are priority on every level of operation in NEK. High level of professional workers is the guarantee for safety operation of the power plant today and in the future.