Nuclear Science and Techniques

《核技术》(英文版) ISSN 1001-8042 CN 31-1559/TL     2019 Impact factor 1.556

Nuclear Science and Techniques ›› 2017, Vol. 28 ›› Issue (6): 76 doi: 10.1007/s41365-017-0234-7

• NUCLEAR ENERGY SCIENCE AND ENGINEERING • Previous Articles     Next Articles

Impact of photoneutrons on reactivity measurements for TMSR-SF1

Rui-Min Ji1,2, Ming-Hai Li1, Yang Zou1, Gui-Min Liu1   

  1. 1 Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Jiading Campus, Shanghai 201800, China
    2 University of Chinese Academy of Sciences, Beijing 100049, China
  • Supported by:

    Supported by the ‘‘Strategic Priority Research Program’’ of the Chinese Academy of Sciences (No. XDA02010000) and the Frontier Science Key Program of the Chinese Academy of Sciences (No. QYZDY-SSW-JSC016).

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Rui-Min Ji, Ming-Hai Li, Yang Zou, Gui-Min Liu. Impact of photoneutrons on reactivity measurements for TMSR-SF1.Nuclear Science and Techniques, 2017, 28(6): 76     doi: 10.1007/s41365-017-0234-7


The solid-fueled thorium molten salt reactor (TMSR-SF1) is a 10 MWth test reactor design to be deployed in 5–10 years by the TMSR group. Its design combines coated particle fuel and molten FLiBe coolant for great intrinsic safety features and economic advantages. Due to a large amount of beryllium in the coolant salt,
photoneutrons are produced by (c, n) reaction, hence the increasing fraction of effective delayed neutrons in the core by the photoneutrons originating from the long-lived fission products. Some of the delayed photoneutron groups are of long lifetime, so a direct effect is resulted in the transient process and reactivity measurement. To study the impact of photoneutrons for TMSR-SF1, the effective photoneutron fraction is estimated using k-ratio method and performed by the Monte Carlo code (MCNP5) with ENDF/B-VII cross sections. Based on the coupled neutron–photon point kinetics equations, influence of the photoneutrons
is analyzed. The results show that the impact of photoneutrons is not negligible in reactivity measurement. Without considering photoneutrons in on-line reactivity
measurement based on inverse point kinetics can result in overestimation of the positive reactivity and underestimation of the negative reactivity. The photoneutrons also lead to more waiting time for the doubling time measurement. Since the photoneutron precursors take extremely long time to achieve equilibrium, a ‘‘steady’’ power operation may not directly imply a ‘‘real’’ criticality.

Key words: TMSR-SF1, Delayed photoneutrons, Coupled neutron–photon point kinetics, Reactivity measurement