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Journal Articles

Investigation of uncertainty caused by random arrangement of coated fuel particles in HTTR criticality calculations

Ho, H. Q.; Honda, Yuki; Goto, Minoru; Takada, Shoji

Annals of Nuclear Energy, 112, p.42 - 47, 2018/02

 Times Cited Count:1 Percentile:100(Nuclear Science & Technology)

Journal Articles

Impact of perturbed fission source on the effective multiplication factor in Monte Carlo perturbation calculations

Nagaya, Yasunobu; Mori, Takamasa

Journal of Nuclear Science and Technology, 42(5), p.428 - 441, 2005/05

 Times Cited Count:41 Percentile:5.42(Nuclear Science & Technology)

A new method to estimate a change in the effective multiplication factor due to the perturbed fission source distribution has been proposed for Monte Carlo perturbation calculations with the correlated sampling and differential operator sampling techniques. The method has been implemented into the MVP code for verification. Simple benchmark problems have been set up for fast and thermal systems and the applicability of the method has been verified with the problems. In consequence, it has been confirmed that the method is very effective to estimate the change. It has been also shown that there are some cases where the perturbed source effect is significant and the change in reactivity cannot be estimated accurately without taking the effect into account. Even in such cases, the new method can estimate the perturbed source effect and the estimation of the change in reactivity has been remarkably improved.

Journal Articles

Examination for neutron dose assessment method from induced sodium-24 in human body in criticality accidents

Takahashi, Fumiaki; Endo, Akira; Yamaguchi, Yasuhiro

Journal of Nuclear Science and Technology, 42(4), p.378 - 383, 2005/04

 Times Cited Count:2 Percentile:79.22(Nuclear Science & Technology)

Experiments were made to verify a dose assessment method from activated sodium in body in criticality accidents. A phantom containing sodium chloride solution was irradiated in the Transient Experiment Critical Facility to simulate activation of sodium. Monte Carlo calculations were performed to obtain quantitative relation between the activity of induced Na-24 and neutron dose in the phantom. In the previous work, conversion coefficients from specific activity of induced Na-24 to neutron dose had been analyzed with the MCNP-4B code concerning neutron spectra at some hypothesized configurations. One of the prepared coefficients was applied to evaluate neutron dose from the measured activity. The estimated dose agreed with the dose analyzed by the Monte Carlo calculation in the present study within an acceptable uncertainty, which is indicated by the IAEA. In addition, the dose calculated with the prepared coefficient was close to the result measured with dosimeters. These results suggest that the prepared coefficients can be applied to dose assessments from induced Na-24 in body.

Journal Articles

Classification of criticality calculations with correlation coefficient method and its application to OECD/NEA burnup credit benchmarks phase III-A and II-A

Okuno, Hiroshi

Journal of Nuclear Science and Technology, 40(7), p.544 - 551, 2003/07

 Percentile:100(Nuclear Science & Technology)

A method for classifying benchmark results of criticality calculations according to similarity was proposed in this paper. After formulation of the method utilizing correlation coefficients, it was applied to burnup credit criticality benchmarks Phase III-A and II-A, which were conducted by the Expert Group on Burnup Credit Criticality Safety under auspices of the OECD/NEA. Phase III-A benchmark was a series of criticality calculations for irradiated BWR fuel assemblies, whereas Phase II-A benchmark was a suite of criticality calculations for irradiated PWR fuel pins. These benchmark problems and their results were summarized. The correlation coefficients were calculated and sets of benchmark results were classified according to the criterion that the correlation coefficients were no less than 0.15 for Phase III-A and 0.10 for Phase II-A benchmarks. When a couple of results were in a same group, one result was found predictable from the other. An example was shown for each of the Benchmarks. The evaluated nuclear data seemed the main factor of errors.

Journal Articles

Dose assessment from activated sodium within a body in criticality accidents

Takahashi, Fumiaki; Endo, Akira; Yamaguchi, Yasuhiro

Radiation Protection Dosimetry, 106(3), p.197 - 206, 2003/00

 Times Cited Count:3 Percentile:71.44(Environmental Sciences)

Some data were derived using recent sophisticated methods to convert rapidly specific activity of induced sodium-24 to average dose over a whole body in criticality accidents. Monte Carlo calculations using the MCNP-4B code were performed to study energy spectra of neutrons and gamma rays for some criticality systems with fissile uranium. Absorbed dose to human body and activation of sodium were also analysed against external radiation by simulations using a phantom. It was found that neutron dose assessment from induced $$^{24}$$Na would be important to give an initial guidance of a treatment. The condition of neutron exposure, however, did not influence the quantitative relation dose by gamma rays induced within a body and activity of $$^{24}$$Na. Analyses were made to clarify the dependence of conversion from $$^{24}$$Na specific activity to dose on the orientation and the size of human body. This study suggested that the size of uranium solution and material around the fuel should be informed to properly estimate dose against external photons from neutron dose.

Journal Articles

Burnup importance function introduced to give an insight into the end effect

Okuno, Hiroshi; Sakai, Tomohiro*

Nuclear Technology, 140(3), p.255 - 265, 2002/12

 Percentile:100(Nuclear Science & Technology)

In order to facilitate discussions based on quantitative analysis about the end effect, which is often talked about in connection to burnup credit in criticality safety evaluation of spent fuel, we introduced in this paper a burnup importance function. This function shows the burnup effect on the reactivity as a function of the fuel position; an explicit expression of this function was derived according to the perturbation theory. The burnup importance function was applied to the Phase IIA benchmark model that was adopted by the OECD/NEA Expert Group on Burnup Credit Criticality Safety. The function clearly displayed that burnup importance of the end regions increases (1) as burnup, (2) as cooling time, (3) in consideration of burnup profile, and (4) in consideration of fission products.

Journal Articles

Burnup importance function and its application to OECD/NEA/BUC phase II-A and II-C models

Okuno, Hiroshi; Tonoike, Kotaro; Sakai, Tomohiro*

Proceedings of International Conference on the New Frontiers of Nuclear Technology; Reactor Physics, Safety and High-Performance Computing (PHYSOR 2002) (CD-ROM), 8 Pages, 2002/10

As the burnup proceeds, reactivity of fuel assemblies for light water reactors decreases by depletion of fissile nuclides, especially in the axially central region. In order to describe the importance of the end regions to the reactivity change, a burnup importance function was introduced as a weighting function to a local burnup variation contributed to a reactivity decrease. The function was applied to the OECD/NEA/BUC Phase II-A model and a simplified Phase II-C model. The application to Phase II-A model clearly showed that burnup importance of the end regions increases as burnup and/or cooling time increases. Comparison of the burnup importance function for different initial enrichments was examined. The application result to the simplified Phase II-C model showed that the burnup importance function was helpful to find the most reactive fuel burnup distribution under the conditions that the average fuel burnup was kept constant and the variations in the fuel burnup were within the maximum and minimum measured values.

Journal Articles

New acceleration method of source convergence for loosely coupled multi unit system by using matrix K calculation

Kuroishi, Takeshi; Nomura, Yasushi

Proceedings of International Conference on the New Frontiers of Nuclear Technology; Reactor Physics, Safety and High-Performance Computing (PHYSOR 2002) (CD-ROM), 10 Pages, 2002/10

To accelerate the slow convergence of the fission source distribution, the matrix k calculation has been developed and incorporated in the ordinary Monte Carlo method. The acceleration can be performed by the fission source correction using the eigenvector of the fission matrix, if the coupling coefficients are approximately evaluated in the middle of Monte Carlo calculation. In this paper, we propose two effective applications of the matrix k, that is, the acceleration repetition method and the source generation method. The former simply repeats the matrix k calculation, and the result for the irradiated fuel pin cell shows enough effective to accelerate the fission source on the criticality estimation. However, in some cases of the loosely coupled multi unit system, the repetition of matrix k more than twice could not be carried out to get into convergence because of many units of low source level. The latter is newly devised here to apply to such cases. The checkerboard fuel storage rack is one of the typical cases, and the calculated results show the effectiveness of this method.

Journal Articles

Core calculation of the JMTR using MCNP

Nagao, Yoshiharu

JAERI-Conf 2000-018, p.156 - 167, 2001/01

no abstracts in English

Journal Articles

External doses in the environment from the Tokai-mura criticality accident

Endo, Akira; Yamaguchi, Yasuhiro; Sakamoto, Yukio; Yoshizawa, Michio; Tsuda, Shuichi

Radiation Protection Dosimetry, 93(3), p.207 - 214, 2001/00

 Times Cited Count:6 Percentile:51.48(Environmental Sciences)

no abstracts in English

Journal Articles

Start up core physics tests of High Temperature Engineering Test Reactor (HTTR), 2; First criticality by an annular form fuel loading and its criticality prediction method

Fujimoto, Nozomu; Nakano, Masaaki*; Takeuchi, Mitsuo; Fujisaki, Shingo; Yamashita, Kiyonobu

Nippon Genshiryoku Gakkai-Shi, 42(5), p.458 - 464, 2000/05

 Times Cited Count:6 Percentile:53.22(Nuclear Science & Technology)

no abstracts in English

JAEA Reports

Analysis of the HTTR's benchmark problems and comparison between the HTTR and the FZJ code systems

Fujimoto, Nozomu; U.Ohlig*; H.Brockmann*; Yamashita, Kiyonobu

JAERI-Tech 98-060, 56 Pages, 1999/01

JAERI-Tech-98-060.pdf:2.25MB

no abstracts in English

JAEA Reports

Preliminary analyses for HTTR's start-up physics tests by HTTR nuclear characteristics evaluation code system

Fujimoto, Nozomu; Nojiri, Naoki; Nakano, Masaaki*; Takeuchi, Mitsuo; Fujisaki, Shingo; Yamashita, Kiyonobu

JAERI-Tech 98-021, 66 Pages, 1998/06

JAERI-Tech-98-021.pdf:2.63MB

no abstracts in English

Journal Articles

A Method to calculate sensitivity coefficients of reactivity to errors in estimating amounts of nuclides found in irradiated fuel

; Suyama, Kenya; *

Journal of Nuclear Science and Technology, 35(3), p.240 - 242, 1998/03

 Times Cited Count:1 Percentile:83.28(Nuclear Science & Technology)

no abstracts in English

JAEA Reports

OECD/NEA burnup credit criticality benchmark; Result of phase IIA

; Okuno, Hiroshi

JAERI-Research 96-003, 170 Pages, 1996/02

JAERI-Research-96-003.pdf:5.24MB

no abstracts in English

JAEA Reports

Calculational study on reactivity effect of pipe intersections

Okuno, Hiroshi; Naito, Yoshitaka; *

JAERI-Tech 95-025, 21 Pages, 1995/03

JAERI-Tech-95-025.pdf:0.6MB

no abstracts in English

JAEA Reports

OECD/NEA burnup credit criticality benchmark; Result of phase-1A

JAERI-M 94-003, 145 Pages, 1994/01

JAERI-M-94-003.pdf:3.82MB

no abstracts in English

JAEA Reports

Reactor physics activities in Japan; July, 1992 $$sim$$ July, 1993

Research Committee on Reactor Physics

JAERI-M 93-254, 36 Pages, 1994/01

JAERI-M-93-254.pdf:1.27MB

no abstracts in English

JAEA Reports

A Differential albedo for a Monte Carlo criticality program KENO IV

Komuro, Yuichi; *; *

JAERI-M 93-246, 19 Pages, 1994/01

JAERI-M-93-246.pdf:0.68MB

no abstracts in English

JAEA Reports

Reactor physics activities in Japan; June 1991 $$sim$$ July 1992

Research Committee on Reactor Physics

JAERI-M 92-209, 43 Pages, 1993/01

JAERI-M-92-209.pdf:1.43MB

no abstracts in English

38 (Records 1-20 displayed on this page)