Helium in CERMET fuel - binding energies and diffusion

This thesis presents a first principle approach to model helium diffusionand retention in molybdenum. Results from electron structure calculations within the framework of density functional theory are used to assess parameters in a rate theory model. The model is used to reproduce experimental desorption spectra, which, to a large degree of accuracy, coincide with experimental data in temperature regions relevant for nuclear fuel applications. The models indicate that produced helium will diffuse out into the fuel pin during operation. However, some helium will be trapped in molybdenum vacancies. The amount of trapped helium will largely depend on the fuel operational temperature. Data presented in the thesis is a first step towards a self consistent dataset of first principle data on helium diffusion in CERMET fuel, one candidate fuel suggested for transmutation of nuclear waste. To realise the use of CERMET fuel, modelling of fuel performance is essential, and to accomplish this, the understanding of helium diffusion and retention in molybdenum is one important aspect.

Heliumfyllda bubblor i fasta material : Kärnbildning, tillväxt och svällning

When nuclear fuel, fabricated for the purpose of transmuting spent fuel is irradiated, significant amounts of He is produced from alpha particles mainly emitted when 242Cm decays into 238Pu. From irradiation experiments it is known that the presence of He in the solids alters the swelling behaviour of the material. The thesis presents the theoretical background from which nucleation models of He bubbles can be formulated. Such models are presented for He in metals, and the case of He in Mo is studied as an example. MgO, which together with Mo is suggested as a matrix material in transmutation fuel is also studied and the stability of He containing bubbles in this material is discussed. By calculating parameters for a rate theory model derived from atomistic modelling, it is shown that He can stabilise vacancy clusters and cause cluster growth at temperatures and irradiation doses where nucleation and growth would not otherwise occur. At the initial stages of nucleation He can stabilise small bubbles while larger bubbles are unstable. This results in an incubation time of swelling, which implies that He does not always cause increased swelling, but can at certain irradiation conditions slow down the growth of large vacancy clusters and thereby delay swell\-ing beyond the time of the irradiation. When comparing the behaviour of bubble nucleation in Mo and MgO, it is found that He has a significant impact even at very low concentrations in Mo. In contrast, the concentration of He has to be considerably higher in MgO to affect the swelling behaviour. For an inert matrix fuel, designed for transmutation purposes, this implies that the Mo matrix will have a tendency to swell considerably at rather high temperatures due to He stabilised vacancy clusters. If operated at lower temperatures, the swelling could instead be reduced due to the incubation time. In a MgO matrix, the swelling behaviour will instead depend largely on the production rate of He. For a low production rate, the material will have a swelling behaviour similar to the one seen when He is not present in the material. A high production rate implies that He will remain in vacancy clusters, thereby stabilising the clusters and enhancing the growth and swelling

Taxation on Labour Incomes : The Effect of Changes in Marginal Taxation on Labour Supply in Sweden

In this study I investigate how changes in marginal taxation on labour income affect labour supply in Sweden in the time period 1991-2006. Unlike previous research which has used data on the individual level, this study uses aggregated data on the municipality level and another methodological approach. The results indicate that labour supply is reduced as marginal taxation is increased, but the reduction is modest and varies between those in the public and the private sector. The reduction in labour supply is in line with conclusions from previous research, but in contrast to previous studies it is found that labour income increases as marginal taxation increases

Helium in CERMET fuel - binding energies and diffusion

This thesis presents a first principle approach to model helium diffusionand retention in molybdenum. Results from electron structure calculations within the framework of density functional theory are used to assess parameters in a rate theory model. The model is used to reproduce experimental desorption spectra, which, to a large degree of accuracy, coincide with experimental data in temperature regions relevant for nuclear fuel applications. The models indicate that produced helium will diffuse out into the fuel pin during operation. However, some helium will be trapped in molybdenum vacancies. The amount of trapped helium will largely depend on the fuel operational temperature. Data presented in the thesis is a first step towards a self consistent dataset of first principle data on helium diffusion in CERMET fuel, one candidate fuel suggested for transmutation of nuclear waste. To realise the use of CERMET fuel, modelling of fuel performance is essential, and to accomplish this, the understanding of helium diffusion and retention in molybdenum is one important aspect.

The Swedish Air Passenger Tax : The impact on passenger numbers

In this essay I have estimated what impact the Swedish air passenger tax that was introduced in Sweden on April 1st in 2018 has had on passenger numbers in Sweden. The tax was introduced to lower demand for air travel within the public and thus, decrease the aviation industry´s greenhouse gas emissions as aviation contributes through these emissions to a large extent to climate change and is expected to have an even greater impact in the future as the number of air travels are expected to grow continuously. Besides that the emissions from aviation have this large negative impact on the climate, a large part of these emissions are not included in any pricing system or market. Therefore, aviation is a source of negative externalities and the Swedish air passenger tax is an instrument implemented to correct for these negative externalities. Previous studies that have evaluated similar taxes and their effects have reached different conclusions. I have used the difference-in-difference method to estimate any effect from the introduced aviation tax in Sweden. Denmark is used as the control group to compare the development in Sweden with. I found that the tax has had a decreasing effect on passenger numbers in Sweden. It is discussed however if this estimated decrease in passenger numbers might be biased and thus overstated. It is also discussed if this decrease might be due to other reasons than the air passenger tax itself

Heliumfyllda bubblor i fasta material : Kärnbildning, tillväxt och svällning

When nuclear fuel, fabricated for the purpose of transmuting spent fuel is irradiated, significant amounts of He is produced from alpha particles mainly emitted when 242Cm decays into 238Pu. From irradiation experiments it is known that the presence of He in the solids alters the swelling behaviour of the material. The thesis presents the theoretical background from which nucleation models of He bubbles can be formulated. Such models are presented for He in metals, and the case of He in Mo is studied as an example. MgO, which together with Mo is suggested as a matrix material in transmutation fuel is also studied and the stability of He containing bubbles in this material is discussed. By calculating parameters for a rate theory model derived from atomistic modelling, it is shown that He can stabilise vacancy clusters and cause cluster growth at temperatures and irradiation doses where nucleation and growth would not otherwise occur. At the initial stages of nucleation He can stabilise small bubbles while larger bubbles are unstable. This results in an incubation time of swelling, which implies that He does not always cause increased swelling, but can at certain irradiation conditions slow down the growth of large vacancy clusters and thereby delay swell\-ing beyond the time of the irradiation. When comparing the behaviour of bubble nucleation in Mo and MgO, it is found that He has a significant impact even at very low concentrations in Mo. In contrast, the concentration of He has to be considerably higher in MgO to affect the swelling behaviour. For an inert matrix fuel, designed for transmutation purposes, this implies that the Mo matrix will have a tendency to swell considerably at rather high temperatures due to He stabilised vacancy clusters. If operated at lower temperatures, the swelling could instead be reduced due to the incubation time. In a MgO matrix, the swelling behaviour will instead depend largely on the production rate of He. For a low production rate, the material will have a swelling behaviour similar to the one seen when He is not present in the material. A high production rate implies that He will remain in vacancy clusters, thereby stabilising the clusters and enhancing the growth and swelling

Taxation on Labour Incomes : The Effect of Changes in Marginal Taxation on Labour Supply in Sweden

In this study I investigate how changes in marginal taxation on labour income affect labour supply in Sweden in the time period 1991-2006. Unlike previous research which has used data on the individual level, this study uses aggregated data on the municipality level and another methodological approach. The results indicate that labour supply is reduced as marginal taxation is increased, but the reduction is modest and varies between those in the public and the private sector. The reduction in labour supply is in line with conclusions from previous research, but in contrast to previous studies it is found that labour income increases as marginal taxation increases