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JAEA Reports

Critical mass evaluation of minor actinides in aqueous solution; Data for criticality safety assessment of separation process

Morita, Yasuji; Fukushima, Masahiro; Kashima, Takao*; Tsubata, Yasuhiro

JAEA-Data/Code 2020-013, 38 Pages, 2020/09

JAEA-Data-Code-2020-013.pdf:1.94MB

Critical Masses of Cm, Am and the mixture were calculated in metal-water mixtures with water reflector as a basic data for criticality safety assessment of minor actinide separation process. In the mixture of Cm-244 and Cm-245, higher ratio of Cm-245 gives smaller critical mass, but the amount of Cm-245 in the critical mass can be obtained by concentration of Cm-245 in the Cm mixture without depending on the Cm-245 ratio. Critical mass of Cm isotope mixture with 30% Cm-245 was smaller than that of Pu isotope mixture in the practical reprocessing (71% Pu-239 + 17% Pu-240 + 12% Pu-241). When Cm is separated from other element including Am and the solution is concentrated, measure for the critical accident has to be taken. Critical mass of Am-242m is smaller than that of Cm-245, but the ratio of Am-242m in the Am contained in practical spent fuel is small enough, about several percent, and therefore the critical accident by Am does not have to be considered. That by the mixture of Am and Cm does not either.

Journal Articles

Systematic measurements and analyses for lead void reactivity worth in a plutonium core and two uranium cores with different enrichments

Fukushima, Masahiro; Goda, J.*; Oizumi, Akito; Bounds, J.*; Cutler, T.*; Grove, T.*; Hayes, D.*; Hutchinson, J.*; McKenzie, G.*; McSpaden, A.*; et al.

Nuclear Science and Engineering, 194(2), p.138 - 153, 2020/02

 Times Cited Count:0 Percentile:100(Nuclear Science & Technology)

To validate lead (Pb) nuclear cross sections, a series of integral experiments to measure lead void reactivity worth was conducted systematically in three fast spectra with different fuel compositions on the Comet critical assembly of the National Criticality Experiments Research Center. Previous experiments in a high-enriched uranium (HEU)/Pb and a low-enriched uranium (LEU)/Pb systems had been performed in 2016 and 2017, respectively. A follow-on experiment in a plutonium (Pu)/Pb system has been completed. The Pu/Pb system was constructed using lead plates and weapons grade plutonium plates that had been used in the Zero Power Physics Reactor (ZPPR) of Argonne National Laboratory until the 1990s. Furthermore, the HEU/Pb system was re-examined on the Comet critical assembly installed newly with a device that can guarantee the gap reproducibility with a higher accuracy and precision, and then the experimental data was re evaluated. Using the lead void reactivity worth measured in these three cores with different fuel compositions, the latest nuclear data libraries, JENDL 4.0 and ENDF/B VIII.0, were tested with the Monte Carlo calculation code MCNP version 6.1. As a result, the calculations by ENDF/B-VIII.0 were confirmed to agree with lead void reactivity worth measured in all the cores. It was furthermore found that the calculations by JENDL 4.0 overestimate by more than 20% for the Pu/Pb core while being in good agreements for the HEU/Pb and LEU/Pb cores.

Journal Articles

Recent activities in the field of reactor physics

Fukushima, Masahiro; Tojo, Masayuki*

Journal of Nuclear Science and Technology, 56(12), p.1061 - 1062, 2019/12

 Times Cited Count:0 Percentile:100(Nuclear Science & Technology)

Reactor Physics that treat the essentials of how fission nuclear reactors work fundamentally has important roles on safe operations and design studies of various types of nuclear reactors. From the latest activities in the field of reactor physics, this report summarizes some outstanding researches and developments published in scientific journals including the Journal of Nuclear Science and Technology.

Journal Articles

Sample worth measurements with systematically changed mixing ratios of lead and bismuth in A-core of KUCA for ADS

Fukushima, Masahiro; Oizumi, Akito; Yamanaka, Masao*; Pyeon, C. H.*

KURNS Progress Report 2018, P. 143, 2019/08

For the design study of ADS, integral experimental data of nuclear characteristics of LBE is necessary to validate cross sections of lead (Pb) and bismuth (Bi). In present study, sample worth measurements were carried out with systematically changed mixing ratios of lead and bismuth, which would be complementary to the previous data of Pb and Bi samples individually measured in FY 2013 and FY 2017, respectively.

Journal Articles

Count-loss effect in determination of prompt neutron decay constant by neutron correlation methods that employ two sets of neutron counting systems

Kitamura, Yasunori*; Fukushima, Masahiro; Kitamura, Yasunori*

Annals of Nuclear Energy, 125, p.328 - 341, 2019/01

 Times Cited Count:0 Percentile:100(Nuclear Science & Technology)

It has been taken for granted that the neutron correlation methods that employ two sets of neutron counting systems, e.g., the covariance-to-mean and the cross-correlation methods, are free from the count-loss effect for determination of the neutron decay constant. It was however found in the present study that these methods overestimate the neutron decay constant under high counting rate conditions. New formulae of these methods were hence obtained on the basis of a rigorous theoretical approach for treating the count-loss process. It is expected that the present formulae work better than conventional ones for determination of the neutron decay constant.

Journal Articles

Measurement of MA reaction rates using spallation neutron source

Oizumi, Akito; Fukushima, Masahiro; Tsujimoto, Kazufumi; Yamanaka, Masao*; Sano, Tadafumi*; Pyeon, C. H.*

KURRI Progress Report 2017, P. 50, 2018/08

In the nuclear transmutation system such as ADS, the nuclear data validation of MA is required to reduce the uncertainty caused by the nuclear data of MA. This study aims to measure the reaction rates of Neptunium-237 ($$^{237}$$Np) and Americium-241 ($$^{241}$$Am) using the nuclear spallation neutron source in the KUCA for 3 hours. The observed distributions of pulse-height of $$^{237}$$Np and $$^{241}$$Am fission reactions were significantly different from the ones generally observed in critical and pulsed neutron source (PNS) experiments because of the influence of the $$gamma$$-ray generated by the nuclear spallation reaction. On the other hand, the capture reaction rate of $$^{237}$$Np was measured in this experiment. The capture reaction rate of the critical experiment which was available to be measured the fission reaction rate of $$^{237}$$Np and $$^{241}$$Am was almost 8 times larger than that of this experiment. Consequently, reducing the influence of the $$gamma$$ generated by the nuclear spallation reaction and extending the duration of the irradiation to 24 or more hours would be necessary for detecting signals of fission reactions under the spallation neutron source.

Journal Articles

Lead void reactivity worth in two critical assembly cores with differing uranium enrichments

Fukushima, Masahiro; Goda, J.*; Bounds, J.*; Cutler, T.*; Grove, T.*; Hutchinson, J.*; James, M.*; McKenzie, G.*; Sanchez, R.*; Oizumi, Akito; et al.

Nuclear Science and Engineering, 189, p.93 - 99, 2018/01

 Times Cited Count:3 Percentile:35.66(Nuclear Science & Technology)

To validate lead (Pb) nuclear cross sections, a series of integral experiments to measure lead void reactivity worths was conducted in a high-enriched uranium (HEU)/Pb system and a low enriched uranium (LEU)/Pb system using the Comet Critical Assembly at NCERC. The critical experiments were designed to provide complementary data sets having different sensitivities to scattering cross sections of lead. The larger amount of the $$^{238}$$U present in the LEU/Pb core increases the neutron importance above 1 MeV compared with the HEU/Pb core. Since removal of lead from the core shifts the neutron spectrum to the higher energy region, positive lead void reactivity worths were observed in the LEU/Pb core while negative values were observed in the HEU/Pb core. Experimental analyses for the lead void reactivity worths were performed with the Monte Carlo calculation code MCNP6.1 together with nuclear data libraries, JENDL 4.0 and ENDF/B VII.1. The calculation values were found to overestimate the experimental ones for the HEU/Pb core while being consistent for the LEU/Pb core.

Journal Articles

Analyses with latest major nuclear data libraries of the fission rate ratios for several TRU nuclides in the FCA-IX experiments

Fukushima, Masahiro; Tsujimoto, Kazufumi; Okajima, Shigeaki

Journal of Nuclear Science and Technology, 54(7), p.795 - 805, 2017/07

 Times Cited Count:4 Percentile:37.05(Nuclear Science & Technology)

A series of integral experiments was conducted in FCA assemblies with systematically changed neutron spectra covering from the intermediate to fast ones. The experiments provide systematic data of central fission rates for TRU nuclides containing minor actinides, $$^{237}$$Np, $$^{238}$$Pu, $$^{239}$$Pu, $$^{242}$$Pu, $$^{241}$$Am, $$^{243}$$Am, and $$^{244}$$Cm. Latest major nuclear data libraries, JENDL-4.0, ENDF/B-VII.1, and JEFF-3.2, were tested using benchmark models regarding the fission rate ratios relative to $$^{239}$$Pu. For all the libraries, the benchmark tests by a Monte Carlo calculation code show obvious overestimations particularly for the fission rate ratios of $$^{244}$$Cm to $$^{239}$$Pu. Additionally, a large discrepancy about by 20% between the libraries is revealed for the fission rate ratio of $$^{238}$$Pu to $$^{239}$$Pu measured in the intermediate neutron spectrum. The cause of discrepancy is furthermore clarified by sensitivity analyses.

Journal Articles

A Simple and practical correction technique for reactivity worth of short-sized samples measured by critical-water-level method

Kitamura, Yasunori*; Fukushima, Masahiro

Nuclear Science and Engineering, 186(2), p.168 - 179, 2017/05

 Times Cited Count:1 Percentile:78.69(Nuclear Science & Technology)

An inconsistency between the reactivity worth of short-size samples measured by the critical-water-level (CWL) method and that conventionally analysed for validating the nuclear data and the nuclear calculation methods has been known. The present study investigated this inconsistency in terms of a simple theoretical framework and proposed a simple and practical technique for correcting the measured sample reactivity worth without making supplementary experiments. A series of Monte Carlo calculations that simulated typical sample reactivity worth measurement by the CWL method showed that this inconsistency is effectively reduced by the present correction technique.

Journal Articles

Benchmark tests of newly-evaluated data of $$^{235}$$U for CIELO project using integral experiments of uranium-fueled FCA assemblies

Fukushima, Masahiro; Kitamura, Yasunori*; Yokoyama, Kenji; Iwamoto, Osamu; Nagaya, Yasunobu; Leal, L. C.*

Proceedings of International Conference on the Physics of Reactors; Unifying Theory and Experiments in the 21st Century (PHYSOR 2016) (USB Flash Drive), p.605 - 619, 2016/05

A nuclear data of $$^{235}$$U has been recently evaluated for the CIELO (Collaborative International Evaluated Library Organization) project. We tested the newly-evaluated data of $$^{235}$$U using integral experiments of the Fast Critical Assembly (FCA) performed at JAEA. We selected two integral data of uranium-fueled FCA assemblies; one is the sodium-void reactivity worth of FCA XXVII-1 assembly and the other is the criticalities of the seven assemblies of FCA IX. The benchmark tests support the evaluation done in the resonance regions. However, the $$^{235}$$U capture cross section above the unresolved resonance range needs further investigation.

Journal Articles

Fission rate ratios of FCA-IX assemblies as integral experiment for assessment of TRU's fission cross sections

Fukushima, Masahiro; Tsujimoto, Kazufumi; Okajima, Shigeaki

EPJ Web of Conferences (Internet), 111, p.07002_1 - 07002_5, 2016/03

 Times Cited Count:2 Percentile:10.88

In the IX-th series at FCA, central fission rate ratios for TRU such as $$^{237}$$Np, $$^{238}$$Pu, $$^{242}$$Pu, $$^{241}$$Am, $$^{243}$$Am, $$^{244}$$Cm and $$^{239}$$Pu were measured in the seven uranium-fueled assemblies with systematically changed neutron spectra. The FCA-IX assemblies were constructed with simplicity both in geometry and composition. Taking their advantage, benchmark models with respect to central fission rate ratios had been recently established for the assessment of the TRU's fission cross sections. By virtue of these FCA-IX assemblies where the simple combinations of uranium fuel and diluent in their core regions were systematically varied, the neutron spectra of these benchmark models cover those of various reactor types, from fast to epithermal reactors. As an application of these benchmark models, JENDL-4.0 was utilized by a Monte Carlo calculation code. Several results show obvious discrepancies between calculation and experimental values. The benchmark models would be well suited for the assessment and improvement of the nuclear data for TRU's fission cross sections.

Journal Articles

Benchmark models for criticalities of FCA-IX assemblies with systematically changed neutron spectra

Fukushima, Masahiro; Kitamura, Yasunori; Kugo, Teruhiko; Okajima, Shigeaki

Journal of Nuclear Science and Technology, 53(3), p.406 - 424, 2016/03

 Times Cited Count:8 Percentile:24.13(Nuclear Science & Technology)

Journal Articles

Count-loss effect in subcriticality measurement by pulsed neutron source method, 2; Proposal for utilization of neutron detection system operated in current mode

Kitamura, Yasunori; Fukushima, Masahiro

Journal of Nuclear Science and Technology, 52(6), p.801 - 810, 2015/06

 Times Cited Count:7 Percentile:31.87(Nuclear Science & Technology)

JAEA Reports

Effect of experiments using Transmutation Physics Experimental Facility on the reduction of uncertainties in reactor physics parameters of an accelerator-driven system

Iwamoto, Hiroki; Nishihara, Kenji; Katano, Ryota*; Fukushima, Masahiro; Tsujimoto, Kazufumi

JAEA-Research 2014-033, 82 Pages, 2015/03

JAEA-Research-2014-033.pdf:6.53MB

The effect of experiments using Transmutation Physics Experimental Facility (TEF-P) is analysed from the viewpoint of the reduction of uncertainties in reactor physics parameters (criticality and coolant void reactivity) of an accelerator-driven system (ADS). The analysis is conducted by the nuclear-data adjustment method using JENDL-4.0 on the assumption that ve types of reactor physics experiments (a total of 44 experiments) are performed in TEF-P: (1) criticality experiment, (2) lead void reactivity experiment, (3) reaction rate ratio experiment, (4) sample reactivity experiment, and (5) fuel replacement reactivity experiment. As the result, 1.0% of uncertainty in criticality is found to be reduced to approximately 0.4%, and effective experiments for the reduction of uncertainty in criticality and coolant void reactivity are shown to be fuel replacement reactivity experiments and lead void reactivity experiments, respectively. Although these effects depend largely on the composition and amount of minor-actinide (MA) fuels, it is found that a combination of different types of experiments and database of existing experiments is effective in reducing the uncertainties.

JAEA Reports

Establishment of benchmark problems for TRU fission rate ratios of FCA-IX assemblies

Fukushima, Masahiro; Oizumi, Akito; Iwamoto, Hiroki; Kitamura, Yasunori

JAEA-Data/Code 2014-030, 50 Pages, 2015/03

JAEA-Data-Code-2014-030.pdf:10.34MB

In the IX-th experimental series in 1980's at the fast critical assembly (FCA) facility, central fission rate ratios for TRU such as $$^{237}$$Np, $$^{238}$$Pu, $$^{242}$$Pu, $$^{241}$$Am, $$^{243}$$Am and $$^{244}$$Cm to $$^{239}$$Pu were measured in the seven uranium-fueled assemblies with systematically changed neutron spectra. In the present report, benchmark problems with respect to central fission rate ratios were established for the assessment of the TRU's fission cross sections. We reported the sample calculation results on the benchmark problems by using JENDL-4.0.

Journal Articles

Void reactivity evaluation by modified conversion ratio measurements in LWR critical experiments

Yoshioka, Kenichi*; Kikuchi, Tsukasa*; Gunji, Satoshi*; Kumanomido, Hironori*; Mitsuhashi, Ishi*; Umano, Takuya*; Yamaoka, Mitsuaki*; Okajima, Shigeaki; Fukushima, Masahiro; Nagaya, Yasunobu; et al.

Journal of Nuclear Science and Technology, 52(2), p.282 - 293, 2015/02

 Times Cited Count:0 Percentile:100(Nuclear Science & Technology)

We have developed a void reactivity evaluation method by using modified conversion ratio measurements in a light water reactor (LWR) critical lattice. Assembly-wise void reactivity is evaluated from the "finite neutron multiplication factor", $$k^ast$$, deduced from the modified conversion ratio of each fuel rod. The distributions of modified conversion ratio and $$k^ast$$ on a reduced-moderation LWR lattice, for which the improvement of negative void reactivity is a serious issue, were measured. Measured values were analyzed with a continuous-energy Monte Carlo method. The measurements and analyses agreed within the measurement uncertainty. The developed method is useful for validating the nuclear design methodology concerning void reactivity.

Journal Articles

Count-loss effect in subcriticality measurement by pulsed neutron source method, 1; Investigation on count-loss effect in determination of neutron decay constant

Kitamura, Yasunori; Fukushima, Masahiro

Journal of Nuclear Science and Technology, 51(6), p.752 - 765, 2014/06

AA2013-0401.pdf:0.67MB

 Times Cited Count:7 Percentile:38.25(Nuclear Science & Technology)

Journal Articles

Correction of count-loss effect in neutron correlation methods that employ single neutron counting system for subcriticality measurement

Kitamura, Yasunori; Fukushima, Masahiro

Journal of Nuclear Science and Technology, 51(6), p.766 - 782, 2014/06

 Times Cited Count:6 Percentile:44.15(Nuclear Science & Technology)

Journal Articles

Benchmark calculations for reflector effect in fast cores by using the latest evaluated nuclear data libraries

Fukushima, Masahiro; Ishikawa, Makoto; Numata, Kazuyuki*; Jin, Tomoyuki*; Kugo, Teruhiko

Nuclear Data Sheets, 118, p.405 - 409, 2014/04

 Times Cited Count:0 Percentile:100(Physics, Nuclear)

Journal Articles

Intra-pellet neutron flux distribution measurements in LWR critical lattices

Yoshioka, Kenichi*; Kikuchi, Tsukasa*; Gunji, Satoshi*; Kumanomido, Hironori*; Mitsuhashi, Ishi*; Umano, Takuya*; Yamaoka, Mitsuaki*; Okajima, Shigeaki; Fukushima, Masahiro; Nagaya, Yasunobu; et al.

Journal of Nuclear Science and Technology, 50(6), p.606 - 614, 2013/06

 Times Cited Count:1 Percentile:86.44(Nuclear Science & Technology)

We have developed an intra-pellet neutron flux and conversion ratio distribution measurement method. A foil activation method with special foils was used for the neutron flux distribution measurement. A $$gamma$$-ray spectrum analysis method with special collimators was used for the conversion ratio distribution measurement. Using the developed methods, intra-pellet neutron flux distributions and conversion ratio distributions were measured in critical experiments on a reduced-moderation LWR. Measured values were analyzed with a deterministic method and a Monte Carlo method. The neutron flux distribution measurements and analyses agreed within the range of 1% to 2%. The conversion ratio distribution measurements and analyses were consistent with each other. We found that the measurement methods are useful for the validation of neutron behavior in a fuel pellet, which is known as micro reactor physics.

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