Nuclear reactors with improved safety concepts are currently being studied within the nuclear engineering community, with a focus on passive safety features. One of these reactor concepts is the Very High Temperature gas-cooled Reactor (VHTR) of which the Reactor Cavity Cooling Systems (RCCS) is seen as an integral and crucial part of the passive safety concept. Considerable validation and development of the necessary software tools is required to perform analysis and designs of these future reactor concepts. The primary objective of this study is to establish a methodology for the creation of an integrated system level process model of a typical air-cooled RCCS in Flownex®, and to illustrate its applicability by simulating different scenarios that illustrate the operational characteristics of such a system. For this purpose, the existing RCCS conceptual design that is being studied by the KAERI was used as the case study. As a start, selected case studies were performed to verify that the Flownex® models were set up correctly to perform natural circulation flows, both in steady and transient conditions, and with radiation, convection and conduction taking part. These are the major typical physical phenomena in the RCCS. The models were compared with EES (Engineering Equation Solver) models of the same geometries and specifications. There was a good agreement between Flownex® and EES model results. After this verification, a simulation model of the integrated RCCS system was developed. The Flownex® models were applied to model selected possible operational scenarios. The major observations from the results are that: - The RCCS carries with it enough heat to the ambient such that the concrete wall temperature is maintained below the benchmark value of 65°C for the different boundary conditions imposed. - The RCCS maintains its functionality even with three quarters of the risers blocked or in the event that there is a break in one of the chimney pipes. / MIng (Nuclear Engineering), North-West University, Potchefstroom Campus, 2015

Nuclear reactors with improved safety concepts are currently being studied within the nuclear engineering community, with a focus on passive safety features. One of these reactor concepts is the Very High Temperature gas-cooled Reactor (VHTR) of which the Reactor Cavity Cooling Systems (RCCS) is seen as an integral and crucial part of the passive safety concept. Considerable validation and development of the necessary software tools is required to perform analysis and designs of these future reactor concepts. The primary objective of this study is to establish a methodology for the creation of an integrated system level process model of a typical air-cooled RCCS in Flownex®, and to illustrate its applicability by simulating different scenarios that illustrate the operational characteristics of such a system. For this purpose, the existing RCCS conceptual design that is being studied by the KAERI was used as the case study. As a start, selected case studies were performed to verify that the Flownex® models were set up correctly to perform natural circulation flows, both in steady and transient conditions, and with radiation, convection and conduction taking part. These are the major typical physical phenomena in the RCCS. The models were compared with EES (Engineering Equation Solver) models of the same geometries and specifications. There was a good agreement between Flownex® and EES model results. After this verification, a simulation model of the integrated RCCS system was developed. The Flownex® models were applied to model selected possible operational scenarios. The major observations from the results are that: - The RCCS carries with it enough heat to the ambient such that the concrete wall temperature is maintained below the benchmark value of 65°C for the different boundary conditions imposed. - The RCCS maintains its functionality even with three quarters of the risers blocked or in the event that there is a break in one of the chimney pipes. / MIng (Nuclear Engineering), North-West University, Potchefstroom Campus, 2015

Orbital rendezvous enables spacecraft to perform missions to service satellites, remove space debris, resupply space stations, and return samples from other planets. These missions are often considered high risk due to concerns that the two spacecraft will collide if the maneuvering capability of one spacecraft is compromised by a fault.<br>In this thesis, a passive safety analysis is used to evaluate the probability that a fault that compromises maneuvering capability results in a collision. For a rendezvous<br>mission, the chosen approach trajectory, state estimation technique, and probability of collision calculation each impact the total collision probability of the mission. This<br>thesis presents a modular framework for evaluating the comparing the probability of collision of rendezvous mission design concepts.<br>Trade studies were performed using a baseline set of approach trajectories, and a Kalman Filter for relative state estimation and state estimate uncertainty. The state covariance matrix following each state update was used to predict the resulting probability of collision if a fault were to occur at that time. These trade studies emphasize that the biggest indicator of rendezvous mission risk is the time spent on a nominal intercept trajectory.

This research contributes to the existing body of knowledge relating to crash compatibility (the minimisation of injury risk faced by all participants involved in a collision in traffic). The research focuses on the topic of structural interaction in collisions involving passenger vehicles, a phenomenon describing the efficiency of energy dissipation within existing deformation-zones of a passenger vehicle during a collision. A new definition for structural interaction was developed and several metrics to evaluate structural interaction and compatibility in car-to-car collisions were proposed, based on the commonly known Equivalent Energy Speed (EES) metric. The new EES metrics describe equivalent closing velocities for a given collision based on the energy dissipated within the front-ends (EESFF) and the entire structure (EESVV) of both vehicles involved in a head-on collision. These metrics form the basis of the new knowledge generated by this research. Additionally, a new method was developed to measure the amount of energy dissipated through structural deformation in a collision, based on accelerometer readings. This method was applied to several experimental and simulationbased car-to-car collisions and the validity of the method was proven. Based on the energy dissipation which occurred in the car-to-car collisions analysed, the degree of compatibility reached and the level of structural interaction which occurred in each collision was evaluated by applying the newly developed EESFF and EESVV metrics. Thie research also investigates the assessment of vehicles' structures in a standardized procedure with a view to improving structural interaction in the real-world. Several fixed barrier crash tests have been proposed in different configurations and with different assessment criteria. All assessments aim to evaluate the geometrical characteristics of the front-ends of passenger vehicles. A set of factors required from a compatilibility assessment focused on assessing vehicle geometry were identified. The proposed compatibility assessment procedures were evaluated based on their ability to predict the potential for structural interaction offered by passenger vehicles.

The thesis describes the problems of a complex system for analysis of road accidents, specifically the methodology for solving the collision between vehicle and motorcycle. There are statistics described motorcycle accidents, motorcycle safety features, the basic types of collision positions between vehicles and motorcycles, design methodology for solving with traffic accidents between vehicles and motorcycles. The work is performed a set of different measurements used to supplement and refine the input data for the analysis of road accidents involving motorcycles. The work contains data obtained from measurements.

<p dir="ltr">Nuclear mobile microreactors will serve as a unique, transportable power source, especially for remote communities. Because mobile microreactors are meant to remain operable after initial startup, keeping the microreactor cool during transport is a safety concern that must be taken into consideration. Due to the compact nature of shipping containers, there is no significant room for the installation of active cooling mechanisms. The thermal limitations imposed by current regulatory guidelines lead to a reactor shipment external maximum temperature of 85◦C. Transporting heat from the microreactor's exterior walls to its surrounding air within the shipping container under natural convection will serve as the greatest source of resistance to the decay heat removal. In the event of mechanical failure or local regulations restricting forced cooling systems within the shipping container, natural convection will be the primary method for transferring heat. Before mobile microreactors can reach commercial status, research must be conducted on ensuring continued passive safety. </p><p><br></p><p dir="ltr">During the unavailability of helium circulation, the internal reactor core is designed to cool by block-to-block conduction and radiation, and the reactor vessel surface is cooled by the ambient air. This scenario is anticipated during the transport of the micro-high temperature gas-cooled reactor (HTGR) in a shipping container. The conduction and radiation between the prismatic micro-HTGR blocks in the core can be influenced by variances in the thermal contacts. This work investigated the conduction within a simulated horizontal micro-HTGR core. An experimental setup was used to validate a numerical model for conduction radiation cooldown with postulated thermal contact conductances (TCC). The experimental setup consisted of a hexagonal assembly with scaled prismatic blocks placed within a high-temperature vacuum environment. The gaps between the blocks were well controlled and monitored. The experimental setup was designed in such a way that the temperature variation in the axial direction was minimal, such that the experiment could be observed as a 2D (r,θ) heat transfer problem. The experimental scenario was computationally modelled with a finite element analysis (FEA) program. Once validated, the computational model was used to investigate the impact of gap conductance on overall decay heat removal. Using a conservative estimate for gap conductance value (100 W/m2 − K) between the prismatic blocks, there is a negligible increase in temperature observed during decay heat generation with constant natural convection coefficients. </p><p><br></p><p dir="ltr">However, the internal temperature profile may change drastically depending on the exterior conditions of the microreactor. A second model for the worst case scenario of exterior cooling being limited to natural convection flows was validated against existing benchmark experimental data on natural convection in closed cavities. The investigations have been performed for several configurations, including different reactor sizes, power levels, and scenarios with or without shielding around the reactor pressure vessel (RPV). This conservative safety analysis restricts the power level of the reactor to be equal to 1 MWe. A more realistic analysis with intermittent shutdown of shipping container air circulation demonstrates that a 4 MWe reactor will reach 85◦C Code of Federal Regulations (CFR) limitations after one hour while a 5 MWe reactor reaches the limit after 34 minutes. </p><p><br></p><p dir="ltr">Finally, both models were combined into a conjugate heat transfer model to examine whether thermal contact conductance (TCC) values would affect the external temperature profile as well as the maximum temperature reached by the core to ensure material limitations would be maintained. Studies have been conducted on a micro-HTGR design that originates from the fuel block design of the MHTGR-350 with changes to the overall power level, TCC values, and outer shipping container wall temperatures. Changes to TCC values do not significantly change microreactor exterior temperatures. In addition, the internal temperatures under all examined conditions remained under 875◦C. </p>

Baigiamajame magistro darbe tiriamos lengvojo automobilio kėbulo elementų stiprumo charakteristikos. Išanalizuoti literatūros šaltiniai, automobilių kėbulų konstrukcijos, dinaminis modeliavimas, kompiuterinė technika, naudojama saugumo elementų tobulinimui. Sija, daugiausiai kinetinės energijos sugeriantis automobilio elementas, projektuota priekinio susidūrimo atvejui. Atlikus teorinius skaičiavimus, rezultatai palyginti su modeliavimo. Pateikta išsami išilginės priekinės sijos tobulinimo metodika, modeliavimo rezultatų analizė ir apibendrinimas. Sumodeliavus priekinę išilginę siją, jos geometrinius parametrus, pateikiamos baigiamojo darbo išvados, literatūros šaltiniai. Darbą sudaro 9 dalys: įvadas, mokslinės literatūros apžvalga, automobilių kėbulų konstrukciniai ypatumai saugumui užtikrinti, dinaminiai automobilio modeliavimo bandymai, kompiuterinė technika, naudojama tobulinant saugumo komponentus, priekinės išilginės sijos konstrukcijos modeliavimas, taikant skaitinį metodą, išvados ir pasiūlymai, literatūros sąrašas, priedai. / The stiffness behaviour of the passenger vehicle body elements is investigated in the Master thesis. The analyzed literature, automotive body design, dynamic simulations, computer equipment used for safety development is investigated too. This beam absorbs majority of kinetic energy, it is designed for the frontal impact. Theoretical calculations are compared with simulation results. The deep development methodology of the beam are described, the analysis of the simulation results and discussion are described also. The thesis conclusion, literature is presented after the simulation of the front longitudinal beam geometrical specifications. The thesis is divided to 9 sections: an introduction, review of a scientific literature, automotive body design safety features, dynamic simulation tests of a vehicle, a computer equipment, used for the development of safety components, design simulation of the front longitudinal beam by numerical method, conclusion and suggestions, literature, appendix.

[pt] Esta dissertação tem como hipótese que as deficiências de projeto do cinto e do habitáculo traseiros dos automóveis de passeio, do ponto de vista ergonômico, causam desconforto e constrangimento no uso ordinário do cinto de segurança, provocando seu uso errado, sua rejeição, e sujeitando os passageiros, em caso de acidentes, a lesões e à morte. Sobre a importância do uso do cinto, especialmente o do banco traseiro, se explica o conceito e a magnitude das forças envolvidas na proteção dos ocupantes de um veículo. Se mostra que a história da legislação do cinto está muito relacionada com a evolução do produto, exceto no Brasil. Faz-se uma análise do ergodesign dos componentes do cinto, seus complementos e suplementos, em particular do ergodesign destes no habitáculo traseiro dos carros mais vendidos. As entrevistas com vítimas de acidentes no banco traseiro, com taxistas e com o bombeiro aposentado serviram de apoio para a confirmação da hipótese. O registro, em vídeo, do comportamento real dos passageiros, em conjunto com as respostas dos questionários aplicados aos mesmos, também ratificaram boa parte dos problemas ergonômicos detectados nesse estudo, cujas principais causas são: ausência de dispositivo emergencial de soltura, ausência do dispositivo retrator, ausência do dispositivo pré- tensionador, falta de mais pontos de ancoragem (fixação) do cinto, e presença do ocupante central. Conclui-se que, para reduzir lesões e mortes dos usuários de automóvel, nos corriqueiros acidentes, é urgente estender as boas soluções de alguns carros a todos os demais e reformular a respectiva legislação. / [en] This study is developed based on the hypothesis that the deficiencies of project of the package for the automobile s rear passengers, as well as of the rear seat safety-belt itself, from the ergonomic point of view, cause discomfort and constrain people to its usual use. Therefore, its rejection or misuse have been subjecting the passengers to injuries and even to death, in case of accidents. Concerning the importance of the safety-belt s use, especially at the rear seat, the concept and the magnitude of all forces involved toward the protection of the occupants of a vehicle are explained. The legislation history of safety belts is very related with the evolution of the product, except in Brazil. An analysis is done about the ergodesign of the safety-belt s components, its complements and supplements; and particularly its ergodesign in the rear passengers package of the best selling automobiles in the market. Interviews with taxi-drivers, a pensioner fireman and victims of accidents who were at rear seat, became to support the confirmation of the hypothesis. The video recording of the real behaviour of passengers, in addition to the answers of a questionnaire applied to each one of them, had also ratified part of the ergonomic problems detected in this study, which main causes are: absence of emergency release device, absence of the retrator device, absence of the pretensioner device, lacks of more points of anchorage for the belt and the presence of a central occupant in the rear seat of a vehicle. Therefore, we conclude that to reduce injuries and deaths of the automobile users, in current accidents, it is urgent to extend the good solutions for the safety belt of some cars to all of them and to remodel its respective legislation.

This thesis is devoted to the investigation of passivesafety and inherent features of subcritical nucleartransmutation systems - accelerator-driven systems. The generalobjective of this research has been to improve the safetyperformance and avoid elevated coolant temperatures inworst-case scenarios like unprotected loss-of-ow accidents,loss-of-heat-sink accidents, and a combination of both theseaccident initiators. The specific topics covered are emergencydecay heat removal by reactor vessel auxiliary cooling systems,beam shut-off by a melt-rupture disc, safety aspects fromlocating heat-exchangers in the riser of a pool-type reactorsystem, and reduction of pressure resistance in the primarycircuit by employing bypass routes. The initial part of the research was focused on reactorvessel auxiliary cooling systems. It was shown that an 80 MWthPb/Bi-cooled accelerator-driven system of 8 m height and 6 mdiameter vessel can be well cooled in the case of loss-of-owaccidents in which the accelerator proton beam is not switchedoff. After a loss-of-heat-sink accident the proton beam has tobe interrupted within 40 minutes in order to avoid fast creepof the vessel. If a melt-rupture disc is included in the wallof the beam pipe, which breaks at 150 K above the normal coreoutlet temperature, the grace period until the beam has to beshut off is increased to 6 hours. For the same vessel geometry,but an operating power of 250 MWth the structural materials canstill avoid fast creep in case the proton beam is shut offimmediately. If beam shut-off is delayed, additional coolingmethods are needed to increase the heat removal. Investigationswere made on the filling of the gap between the guard and thereactor vessel with liquid metal coolant and using water spraycooling on the guard vessel surface. The second part of the thesis presents examinationsregarding an accelerator-driven system also cooled with Pb/Bibut with heat-exchangers located in the risers of the reactorvessel. For a pool type design, this approach has advantages inthe case of heat-exchanger tube failures, particularly if wateris used as the secondary uid. This is because a leakage ofwater from the secondary circuit into the Pb/Bi-cooled primarycircuit leads to upward sweeping of steam bubbles, which wouldcollect in the gas plenum. In the case of heatexchangers in thedowncomer steam bubbles may be dragged into the ADS core andadd reactivity. Bypass routes are employed to increase the owspeed in loss-of-ow events for this design. It is shown thatthe 200 MWth accelerator-driven system with heat-exchangers inthe riser copes reasonably well with both a loss-of-ow accidentwith the beam on and an unprotected loss-of-heat-sink accident.For a total-loss-of-power (station blackout) and an immediatebeam-stop the core outlet temperature peaks at 680 K. After acombined loss-of-ow and loss-of-heat-sink accident the beamshould be shut off within 4 minutes to avoid exceeding the ASMElevel D of 977 K, and within 8 minutes to avoid fast creep.Assuming the same core inlet temperature, both the reactordesign with heat-exchanger in the risers and the downcomershave similar temperature evolutions after a total-loss-ofpoweraccident. A large accelerator-driven system of 800 MWth with a 17 mtall vessel may eventually become a standard size. For thishigher power ADS, the location of the heat-exchangers hasgreater impact on the natural convection capability. This isdue to that larger heatexchangers have more inuence on thedistance between the thermal centers during a lossof- owaccident. The design with heat-exchangers in the downcomers,the long-term vessel temperature peaks at 996 K during aloss-of-ow accident with the beam on. This does not pose athreat of creep rupture for the vessel. However, the locationof the heat-exchangers in the downcomers will probably requiresecondary coolant other than water, like for example oil (fortemperatures not higher than 673 K) or Pb/Bi coolant.

<p>This thesis is devoted to the investigation of passivesafety and inherent features of subcritical nucleartransmutation systems - accelerator-driven systems. The generalobjective of this research has been to improve the safetyperformance and avoid elevated coolant temperatures inworst-case scenarios like unprotected loss-of-ow accidents,loss-of-heat-sink accidents, and a combination of both theseaccident initiators. The specific topics covered are emergencydecay heat removal by reactor vessel auxiliary cooling systems,beam shut-off by a melt-rupture disc, safety aspects fromlocating heat-exchangers in the riser of a pool-type reactorsystem, and reduction of pressure resistance in the primarycircuit by employing bypass routes.</p><p>The initial part of the research was focused on reactorvessel auxiliary cooling systems. It was shown that an 80 MWthPb/Bi-cooled accelerator-driven system of 8 m height and 6 mdiameter vessel can be well cooled in the case of loss-of-owaccidents in which the accelerator proton beam is not switchedoff. After a loss-of-heat-sink accident the proton beam has tobe interrupted within 40 minutes in order to avoid fast creepof the vessel. If a melt-rupture disc is included in the wallof the beam pipe, which breaks at 150 K above the normal coreoutlet temperature, the grace period until the beam has to beshut off is increased to 6 hours. For the same vessel geometry,but an operating power of 250 MWth the structural materials canstill avoid fast creep in case the proton beam is shut offimmediately. If beam shut-off is delayed, additional coolingmethods are needed to increase the heat removal. Investigationswere made on the filling of the gap between the guard and thereactor vessel with liquid metal coolant and using water spraycooling on the guard vessel surface.</p><p>The second part of the thesis presents examinationsregarding an accelerator-driven system also cooled with Pb/Bibut with heat-exchangers located in the risers of the reactorvessel. For a pool type design, this approach has advantages inthe case of heat-exchanger tube failures, particularly if wateris used as the secondary uid. This is because a leakage ofwater from the secondary circuit into the Pb/Bi-cooled primarycircuit leads to upward sweeping of steam bubbles, which wouldcollect in the gas plenum. In the case of heatexchangers in thedowncomer steam bubbles may be dragged into the ADS core andadd reactivity. Bypass routes are employed to increase the owspeed in loss-of-ow events for this design. It is shown thatthe 200 MWth accelerator-driven system with heat-exchangers inthe riser copes reasonably well with both a loss-of-ow accidentwith the beam on and an unprotected loss-of-heat-sink accident.For a total-loss-of-power (station blackout) and an immediatebeam-stop the core outlet temperature peaks at 680 K. After acombined loss-of-ow and loss-of-heat-sink accident the beamshould be shut off within 4 minutes to avoid exceeding the ASMElevel D of 977 K, and within 8 minutes to avoid fast creep.Assuming the same core inlet temperature, both the reactordesign with heat-exchanger in the risers and the downcomershave similar temperature evolutions after a total-loss-ofpoweraccident.</p><p>A large accelerator-driven system of 800 MWth with a 17 mtall vessel may eventually become a standard size. For thishigher power ADS, the location of the heat-exchangers hasgreater impact on the natural convection capability. This isdue to that larger heatexchangers have more inuence on thedistance between the thermal centers during a lossof- owaccident. The design with heat-exchangers in the downcomers,the long-term vessel temperature peaks at 996 K during aloss-of-ow accident with the beam on. This does not pose athreat of creep rupture for the vessel. However, the locationof the heat-exchangers in the downcomers will probably requiresecondary coolant other than water, like for example oil (fortemperatures not higher than 673 K) or Pb/Bi coolant.</p>