Thesis (M.A.)--Monterey Institute of International Studies, 2002. / Translation of: Avariĭnye i perekhodnye prot︠s︡essy v bystrykh reaktorakh.

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The failure of graphite moderator bricks in an Advanced Gas cooled Reactor (AGR) is potentially a serious problem. This thesis describes the generation of self stress in the moderator brick during irradiation and the derivation of a simple analytical model to predict the magnitude of this stress. The magnitude of the self stress in the brick is affected by the variations in the material properties of the graphite used for the brick and this is also examined, developing a statistical approach to the analysis. Property variations between bricks are considered but no allowance has been made for material property variations within a brick. Finally, the thesis compares the self stress in one of the critical peak rated moderator bricks to the strength of the irradiated oxidised material on a statistical basis and predicts the failure probability of a brick due to self stress to be extremely low at 25.5 full power years (FPY). However, the failure probability rises steeply and for the peak rated bricks at 29 FPY it approaches 100%.

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The improvement of the indicated thermal efficiency of an argon power cycle (replacing nitrogen with argon in the combustion reaction) is investigated in a CFR engine at high compression ratios in homogeneous charge compression ignition (HCCI) mode. The study combines the two effects that can increase the thermodynamic efficiency as predicted by the ideal Otto cycle: high specific heat ratio (provided by argon), and high compression ratios. However, since argon has relatively low heat capacity (at constant volume), it results in high in-cylinder temperatures, which in turn, leads to the occurrence of knock. Knock limits the feasible range of compression ratios and further increasing the compression ratio can cause serious damage to the engine due to the high pressure rise rate caused by advancing the combustion phasing. The technique proposed in this study in order to avoid intense knock of an argon cycle at high compression ratios is to cool the intake charge to subzero temperatures which leads to lower in-cylinder temperatures and hence, less possibility of having knock. The main variable in this study was the intake temperature which was investigated at 40.0 °C and -6.0 °C which corresponded to low and high compression ratios, respectively. Emission analysis shows that the low in-cylinder temperature of the cooled case led to less complete combustion, and so, lower combustion efficiency. Since nitrogen is replaced with argon, NOx was only formed in negligible amounts due to some nitrogen traces in the used gasses cylinders. Furthermore, the cooled charge required more work to be done in the gas exchange process due to the decrease in the intake pressure caused by cooling the intake which deteriorated the gas exchange efficiency. The heat losses factor was found to be the main parameter that dictated the improvement of the thermodynamic efficiency and it was found that the indicated thermal efficiency was deteriorated for the cooled case as a result of all the aforementioned factors. Although the values of the thermodynamic efficiency at high compression ratios did not meet the expectations based on the ideal Otto cycle due to the assumptions of the ideal cycle, the obtained values, in general, are relatively high.

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Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 132-137). Also available on the World Wide Web.