### Abstract

This article discusses the optimization of the target
motion sampling (TMS) temperature treatment method,
previously implemented in the Monte Carlo reactor physics
code Serpent 2. The TMS method was introduced in [1] and
first practical results were presented at the PHYSOR 2012
conference [2]. The method is a stochastic method for
taking the effect of thermal motion into account
on-the-fly in a Monte Carlo neutron transport
calculation. It is based on sampling the target
velocities at collision sites and then utilizing the 0 K
cross sections at target-at-rest frame for reaction
sampling. The fact that the total cross section becomes a
distributed quantity is handled using rejection sampling
techniques. The original implementation of the TMS
requires 2.0 times more CPU time in a PWR pin-cell case
than a conventional Monte Carlo calculation relying on
pre-broadened effective cross sections. In a HTGR case
examined in this paper the overhead factor is as high as
3.6. By first changing from a multi-group to a
continuous-energy implementation and then fine-tuning a
parameter affecting the conservativity of the majorant
cross section, it is possible to decrease the overhead
factors to 1.4 and 2.3, respectively. Preliminary
calculations are also made using a new and yet incomplete
optimization method in which the temperature of the basis
cross section is increased above 0 K. It seems that with
the new approach it may be possible to decrease the
factors even as low as 1.06 and 1.33, respectively, but
its functionality has not yet been proven. Therefore,
these performance measures should be considered
preliminary.

Original language | English |
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Title of host publication | Proceedings |

Subtitle of host publication | International Conference on Mathematics and Computational Methods Applied to Nuclear Science & Engineering, M&C 2013 |

Pages | 950-961 |

Publication status | Published - 2013 |

MoE publication type | Not Eligible |

Event | International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering, M&C 2013 - Sun Valley, ID, United States Duration: 5 May 2013 → 9 May 2013 |

### Conference

Conference | International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering, M&C 2013 |
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Abbreviated title | M&C 2013 |

Country | United States |

City | Sun Valley, ID |

Period | 5/05/13 → 9/05/13 |

### Keywords

- doppler
- Monte Carlo
- neutron tracking
- on-the-fly
- tempereature

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## Cite this

Viitanen, T., & Leppänen, J. (2013). Optimizing the implementation of the target motion sampling temperature treatment technique: How fast can it get? In

*Proceedings: International Conference on Mathematics and Computational Methods Applied to Nuclear Science & Engineering, M&C 2013*(pp. 950-961)