Abstract
Original language  English 

Qualification  Doctor Degree 
Awarding Institution 

Supervisors/Advisors 

Award date  8 May 2015 
Place of Publication  Espoo 
Publisher  
Print ISBNs  9789513882426 
Electronic ISBNs  9789513882433 
Publication status  Published  2015 
MoE publication type  G5 Doctoral dissertation (article) 
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Keywords
 Monte Carlo
 neutron tracking
 temperature
 Dopplerbroadening
 DBRC
 Target Motion Sampling
 TMS
 temperature majorant cross section
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Development of a stochastic temperature treatment technique for Monte Carlo neutron tracking : Dissertation. / Viitanen, Tuomas.
Espoo : VTT Technical Research Centre of Finland, 2015. 185 p.Research output: Thesis › Dissertation › Collection of Articles
TY  THES
T1  Development of a stochastic temperature treatment technique for Monte Carlo neutron tracking
T2  Dissertation
AU  Viitanen, Tuomas
PY  2015
Y1  2015
N2  Thermal motion of nuclides has a significant effect on the reaction probabilities and scattering kinematics of neutrons. Since also the nuclides in nuclear reactor materials are in constant thermal motion, the temperatureinduced effects need to be taken into account in all neutron transport calculations. This task is notably complicated by the fact that the temperature distributions within operating power reactors are always nonuniform. With conventional transport methods, accurate modeling of temperature distributions within a reactor is cumbersome. The temperature distributions that are in reality continuous in space need to be approximated with regions of uniform temperature. More importantly, pregenerated temperaturedependent data on reaction probabilities must be stored in the computer memory at each temperature appearing in the system, which restricts the feasible level of detail in the modeling of temperature distributions. This thesis covers the previous development of a temperature treatment technique for modeling the effects of thermal motion onthefly during Monte Carlo neutron transport calculation. Thus, the Target Motion Sampling (TMS) temperature treatment technique is capable of modeling arbitrary temperature distributions such that the memory footprint of the interaction data is unaffected by the resolution of the temperature discretization. As a very convenient additional feature the TMS technique also provides for modeling of continuous temperature distributions asis, making the discretization of temperature distributions unnecessary altogether. The basic idea of the TMS technique is introduced, and the results are shown to be in accordance with reference solutions calculated with conventional neutron transport methods. The TMS method is developed further by optimizing its implementation, and the performance is compared against conventional neutron transport methods in different reactor systems. The results show that the TMS method significantly facilitates the modeling of complex temperature distributions in nuclear reactors without compromising the accuracy of the calculations. The method also proves to be wellfeasible in terms of performance, especially as long as the number of temperaturedependent nuclides remains relatively small.
AB  Thermal motion of nuclides has a significant effect on the reaction probabilities and scattering kinematics of neutrons. Since also the nuclides in nuclear reactor materials are in constant thermal motion, the temperatureinduced effects need to be taken into account in all neutron transport calculations. This task is notably complicated by the fact that the temperature distributions within operating power reactors are always nonuniform. With conventional transport methods, accurate modeling of temperature distributions within a reactor is cumbersome. The temperature distributions that are in reality continuous in space need to be approximated with regions of uniform temperature. More importantly, pregenerated temperaturedependent data on reaction probabilities must be stored in the computer memory at each temperature appearing in the system, which restricts the feasible level of detail in the modeling of temperature distributions. This thesis covers the previous development of a temperature treatment technique for modeling the effects of thermal motion onthefly during Monte Carlo neutron transport calculation. Thus, the Target Motion Sampling (TMS) temperature treatment technique is capable of modeling arbitrary temperature distributions such that the memory footprint of the interaction data is unaffected by the resolution of the temperature discretization. As a very convenient additional feature the TMS technique also provides for modeling of continuous temperature distributions asis, making the discretization of temperature distributions unnecessary altogether. The basic idea of the TMS technique is introduced, and the results are shown to be in accordance with reference solutions calculated with conventional neutron transport methods. The TMS method is developed further by optimizing its implementation, and the performance is compared against conventional neutron transport methods in different reactor systems. The results show that the TMS method significantly facilitates the modeling of complex temperature distributions in nuclear reactors without compromising the accuracy of the calculations. The method also proves to be wellfeasible in terms of performance, especially as long as the number of temperaturedependent nuclides remains relatively small.
KW  Monte Carlo
KW  neutron tracking
KW  temperature
KW  Dopplerbroadening
KW  DBRC
KW  Target Motion Sampling
KW  TMS
KW  temperature majorant cross section
M3  Dissertation
SN  9789513882426
T3  VTT Science
PB  VTT Technical Research Centre of Finland
CY  Espoo
ER 