First demonstration of a single-end readout position-sensitive optical fiber radiation sensor inside the Fukushima Daiichi Nuclear Power Station based on wavelength-resolving analysis

Terasaka, Yuta; Sato, Yuki; Uritani, Akira*

Nuclear Instruments and Methods in Physics Research A, 1062, p.169227_1 - 169227_6, 2024/05

https://doi.org/10.1016/j.nima.2024.169227

Measurement methods for the radioactive source distribution inside reactor buildings using a one-dimensional optical fiber radiation sensor (Contract research); FY2021 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Nagoya University*

JAEA-Review 2022-033, 80 Pages, 2022/12

JAEA-Review-2022-033.pdf:4.08MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2021. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station (1F), Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2019, this report summarizes the research results of the "Measurement methods for the radioactive source distribution inside reactor buildings using a one-dimensional optical fiber radiation sensor" conducted from FY2019 to FY2021. Since the final year of this proposal was FY2021, the results for three fiscal years were summarized. The present study aims to develop an optical fiber type radiation sensor that can measure the radiation distribution one-dimensionally along the fiber under a high radiation field for the decommissioning of 1F. Based on the conventional time-of-flight method, we found several promising sensor candidates for the radiation distribution measurement under high dose rate and many scattered gamma-rays.

Measurement methods for the radioactive source distribution inside reactor buildings using a one-dimensional optical fiber radiation sensor (Contract research); FY2020 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Nagoya University*

JAEA-Review 2021-033, 55 Pages, 2021/12

JAEA-Review-2021-033.pdf:2.9MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2020. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2019, this report summarizes the research results of the "Measurement methods for the radioactive source distribution inside reactor buildings using a one-dimensional optical fiber radiation sensor" conducted in FY2020. We are developing a one-dimensional optical fiber radiation sensor that can estimate the radioactive source distribution "along lines" instead of "at points". To improve the conventional time-of-flight optical fiber radiation sensor for the application under high dose rate environment, basic evaluation tests were conducted using various optical fibers with different diameters and materials.

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

https://doi.org/10.1088/2399-6528/aba735

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 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 introduced in the convention by a combinational use of triple flux monitors (Au, Co and Zr), and its analytical methodology is formulated.

Calculation of gamma and neutron emission characteristics emitted from fuel debris of Fukushima Daiichi Nuclear Power Station

Riyana, E. S.; Okumura, Keisuke; Terashima, Kenichi

Journal of Nuclear Science and Technology, 56(9-10), p.922 - 931, 2019/09

https://doi.org/10.1080/00223131.2019.1621781

Continuous energy Monte Carlo criticality calculation of random media under power law spectrum

Ueki, Taro

Proceedings of International Conference on Mathematics and Computational Methods applied to Nuclear Science and Engineering (M&C 2019) (CD-ROM), p.151 - 160, 2019/00

A dynamical system under extreme physical disorder has the tendency of evolving toward the equilibrium state characterized by an inverse power law spectrum. In this paper, the author proposes a practically implementable modeling of random media under such a spectrum using a randomized form of the Weierstrass function. The proposed modeling is demonstrated by the continuous energy Monte Carlo particle transport with delta tracking for the criticality calculation of a randomized version of the Topsy spherical core in International Criticality Safety Benchmark Evaluation Project.

A Power spectrum approach to tally convergence in Monte Carlo criticality calculation

Ueki, Taro

Journal of Nuclear Science and Technology, 54(12), p.1310 - 1320, 2017/12

AA2017-0413.pdf:1.05MB

https://doi.org/10.1080/00223131.2017.1365022

In Monte Carlo criticality calculation, confidence interval estimation is based on the central limit theorem (CLT) for a series of tallies. A fundamental assertion resulting from CLT is the convergence in distribution (CID) of the interpolated standardized time series (ISTS) of tallies. In this work, the spectral analysis of ISTS has been conducted in order to assess the convergence of tallies in terms of CID. Numerical results indicate that the power spectrum of ISTS is equal to the theoretically predicted power spectrum of Brownian motion for effective neutron multiplication factor; on the other hand, the power spectrum of ISTS for local power fluctuates wildly while maintaining the spectral form of fractional Brownian motion. The latter result is the evidence of a case where a series of tallies is away from CID, while the spectral form supports normality assumption on the sample mean.

Spectrum-dose conversion operator of NaI(Tl) and CsI(Tl) scintillation detectors for air dose rate measurement in contaminated environments

Tsuda, Shuichi; Saito, Kimiaki

Journal of Environmental Radioactivity, 166(Part 3), p.419 - 426, 2017/01

https://doi.org/10.1016/j.jenvrad.2016.02.008

Air dose rate monitoring in the environment has been performed since the Fukushima Dai-ichi Nuclear Power Plant accident happened. In the measurement, NaI(Tl) and CsI(Tl) scintillation detectors are used, which are usually used in nuclear power plants and calibrated in a uniform irradiation condition in a radiation calibration field. In general, however, the detector responses are dependent on incident direction and in reality, the incident direction of the photons is not uniform in the environment. In this study, to evaluate the dependence of dose on the photon incident direction, the spectrum - dose conversion operator (G(E) function) for air kerma in a semi-infinite radiation field were obtained using the PHITS code for commonly used NaI(Tl) and CsI(Tl) scintillation detectors. The results indicate that the commonly used scintillation detectors overestimate the doses by a maximum of 40% for mono-energetic photons but under the real environment, one could obtain the dose in the semi-infinite radiation field within 20%.

Desorption of cluster ions from frozen gases following high-density electronic excitation

Baba, Yuji; Sekiguchi, Tetsuhiro; Shimoyama, Iwao

Surface Science, 593(1-3), p.324 - 330, 2005/11

https://doi.org/10.1016/j.susc.2005.06.078

no abstracts in English

Design of a single moderator-type neutron spectrometer with enhanced energy resolution in energy range from a few to 100 keV

Tanimura, Yoshihiko; Saegusa, Jun; Yoshizawa, Michio; Yoshida, Makoto

Nuclear Instruments and Methods in Physics Research A, 547(2-3), p.592 - 600, 2005/08

https://doi.org/10.1016/j.nima.2005.03.162

The moderator structure of a neutron spectrometer was optimized with a Monte Carlo code of MCNP-4B. The spectrometer consists of a cylindrical moderator and a position-sensitive thermal neutron detector. It can obtain an energy spectrum from thermal neutron distribution along the cylindrical axis of the moderator. The structure of the moderator was improved by putting a low hydrogen density material in the front of a high hydrogen density one and inserting a neutron absorber which eliminated thermal neutrons diffusing in the moderator. These improvements make energy resolution of the spectrometer better especially for the low energy neutrons from a few tens to 100 keV. The designed spectrometer can be applied to the measurement of energy spectrum over a neutron energy range from a few keV to 20 MeV.