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Journal Articles

A New convention for the epithermal neutron spectrum for improving accuracy of resonance integrals

Harada, Hideo; Takayama, Naoki; Komeda, Masao

Journal of Physics Communications (Internet), 4(8), p.085004_1 - 085004_17, 2020/08

A new convention of epithermal neutron spectrum is formulated for improving accuracy of resonance integrals. The new type function is proposed as an approximating function of epithermal neutron spectrum based on calculations by the state-of-art Monte Carlo code MVP-3. Bias effects on determination of resonance integrals due to utilizing approximating functions of the traditional types and the new type are compared. The other bias effect is also investigated, which is caused by neglecting position dependence of a neutron spectrum inside an irradiation capsule. For demonstrating the bias effects due to these assumptions on neutron spectrum quantitatively in a practical case, the thermal neutron-capture cross section and resonance integral of $$^{135}$$Cs measured at a research reactor JRR-3 are re-evaluated. A superior property of the proposed new convention is discussed. The experimental method is proposed to determine the new shape factor $$beta$$ introduced in the convention by a combinational use of triple flux monitors ($$^{197}$$Au, $$^{59}$$Co and $$^{94}$$Zr), and its analytical methodology is formulated.

Oral presentation

Development of the ocean forecast system in the Japan Sea (JADE), 4; Assimilation of tide data

Takayama, Katsumi*; Hirose, Naoki*; Kawamura, Hideyuki; Shimizu, Daisuke*; Watanabe, Tatsuro*

no journal, , 

An ocean general circulation model in the Japan Sea has been being developed to reproduce and forecast movement of pollutants at JAEA. It was demonstrated that an assimilation of sea level variation at tide stations along the Japanese coast is effective to reproduce oceanic condition in the nearshore region. In this study, an effect of assimilation of satellite altimeter data, CTD data and tide data is quantitatively surveyed. As a result, it was demonstrated that this assimilation scheme improves the oceanic condition.

Oral presentation

Time-dependent Monte Carlo simulation for transit time measurement of bubbly water flow with neutron noise technique

Takayama, Naoki; Nagaya, Yasunobu; Yamamoto, Toshihiro*

no journal, , 

We have been studying a technique of computer simulation in order to contribute the development of estimation method of "bubbly water flow speed", hereafter referred to as the flow speed, using the neutron noise analysis method. We estimated the flow speed based on the neutron time series data obtained by time-dependent Monte Carlo simulation for the system where positions of bubbles in the bubbly water change with time. We will show the result of the flow speed evaluated by using cross correlation function (CCF) and cross power spectral density(CPSD) in this presentation.

Oral presentation

The Evaluation of sample position effect on activation by reactor neutrons

Takayama, Naoki; Harada, Hideo; Komeda, Masao

no journal, , 

As a basic research to accurately perform the activation experiment by the neutrons in the nuclear reactor, the irradiation position dependence of the neutron flux in the HR-1 irradiation hole of JRR-3 was calculated using MVP-3. Based on the calculation results, the influence of the deviation of the position of the metal foil for monitoring the neutron flux and the irradiated sample on the activation amount was evaluated. As a result, a significant effect was confirmed, and findings were obtained to enhance the method of deriving activation amounts and neutron cross sections.

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