Abstract
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.
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) 
Keywords
 Monte Carlo
 neutron tracking
 temperature
 Dopplerbroadening
 DBRC
 Target Motion Sampling
 TMS
 temperature majorant cross section
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Viitanen, T. (2015). Development of a stochastic temperature treatment technique for Monte Carlo neutron tracking: Dissertation. VTT Technical Research Centre of Finland. http://www.vtt.fi/inf/pdf/science/2015/S84.pdf