Browsing by Author "Guerfi, Reda"

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Laskentaparametrien epätarkkuuden vaikutus säteilyannosten laskennassa
(2010) Guerfi, Reda
School of Science | Master's thesis
Because of the existence of radioactive nuclei in the process of nuclear power production, there are various environmental risks related to the process. Therefore, the objective of the nuclear industry is to conduct all operations of the nuclear power plants as safely as possible. National surveillance and international cooperation play a key role in fulfilling this purpose. In Finland, nuclear power production is supervised by the Radiation and Nuclear Safety Authority of Finland (STUK). Regulatory Guides on nuclear safety (YVL guides) published by STUK set tight standards to actions of licences. To fulfil the safety requirements it is important to be able to assess the radiation doses of the people living in the vicinity of a nuclear power plant, both during normal operation and in the case of possible accidents. In order to calculate the doses, a computerized dose assessment program is required. When assessing radiation doses, there are several uncertainties which stem from different sources. These uncertainties may contribute to the results calculated with the computer model. International Commission on Radiological Protection (ICRP) has drawn up a set of guides, which help to recognize the uncertainties of the dose calculation. This can be done by using a deterministic approach and setting the values of critical parameters conservatively. This may, however, result to a notable increase of costs. Instead of conservative assessments, stochastic methods by using Best Estimate (BE) values can be used to identify an appropriate range for each critical parameter. Finally, a Monte Carlo method is used to assess the range of variation for the results. This thesis has been completed at Fortum Nuclear Services Ltd (FNS). In FNS a computerized program TUULET is used to calculate the radiation doses. The general methods to assess the radiation doses and the implementation of TUULET program are described in the thesis. The main focus has been to verify the parameter values of TUULET. Based on literature, a probability distribution and a range of variation are proposed for the most important parameters. Finally, an uncertainty analysis environment created for TUULET is presented. The Monte Carlo -based environment enables to estimate the range of variation for the results at a fixed confidence level. The results indicate that the individual doses at a fixed calculation point in the vicinity of the power plant and with a given combination of parameter range do not vary remarkably. In this study, the minimum value of the individual dose around Loviisa NPP is not more than approximately 57 % lower than the BE value. On the other hand, maximum value is not more than about 75 % larger than the BE value. The collective dose is at most 29 % lower or 43% larger than the BE value of the collective dose, respectively. When calculating the distribution of individual doses at a fixed distance from the power plant, the unforeseen habits of individuals are a significantly greater source of uncertainty than the inaccuracies related to the parameter values.
Säteilyannosten arviointimalli ja päästövanan gammalaskennan verifiointi
(2008) Guerfi, Reda
Informaatio- ja luonnontieteiden tiedekunta | Bachelor's thesis