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

https://doi.org/10.1080/00223131.2014.937781

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", , deduced from the modified conversion ratio of each fuel rod. The distributions of modified conversion ratio and 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.

Development of Monju Easy-to-Introduce System for Total Evaluation of Reactor Core

Kitano, Akihiro; Teruyama, Hidehiko; Nishi, Hiroshi; Yamaoka, Mitsuaki*; Moriki, Yasuyuki*; Nakagawa, Masatoshi*

Saikuru Kiko Giho, (15), p.1 - 16, 2002/06

https://rdreview.jaea.go.jp/gihou/pdf2/n15-01.pdf

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Core study on Pu-burning fast reactors loaded with minor actinides/FPs and research on material characteristics of fuels and targets for Pu/FP burning

Yamaoka, Mitsuaki*; Fujita, Reiko*

PNC TJ9164 97-002, 105 Pages, 1997/03

PNC-TJ9164-97-002.pdf:2.34MB

As a study on technology utilization of advanced fast reactors, a core study on burning technology of actinides and FPs by fast reactors is carried out together with a research on material characteristics of fuels and targets for Pu/FP Burning. In the core study, a Pu-burning fast reactor corc was studied which can also burn minor actinides and FPs based upon the 600MWe Pu-burning fast reactor core with high Pu enrichment (40%). The criteria of core design were no significant change of core specification and small sodium void reactivity, and so on. In the core, minor actinides and FPs are loaded in the following way. (a)Core region ; loading of Pu/Np (Oxide fuel, Pu enrichment of 40%) (b)Outside of core region ; the first layer loading of Am/Cm/rate earths mixed with ZrH the second laycr loading of Tc-99 mixed with ZrH. The operation cycle length is 5 months and the averagc discharge burnup is about 80GWd/t. The burning capability of Pu, minor actinides and FPs is as follows ; (1)Pu burning rate ; 390kg/Year(74kg/TWhe) (2)Burning rate of minor actinides; 4.2%/Year(43kg/Year) (3)Burning rate of Tc-99; 3.7%/Year(6.5kg/Year) The sodium void reactivity is very small. (0.1% k/kk'=40cent) It is much smaller than that of the conventional fast reactors. This is the advantage of the core concept. The recent progress of material investigation of Pu, minor actinides and FP burning fuels was summaried. Also, basic characteristics of targets for FP burning was summalized, and the compatibility of the targets with ZrH is evaluated.

Module preparation for "MAGI Code System Renewal (III)

*; Yamaoka, Mitsuaki*

PNC TJ9164 98-011, 299 Pages, 1997/02

PNC-TJ9164-98-011.pdf:7.79MB

"MAGI" system renewal has been continued for improving the prediction accuracy for neutronic and thermal characteristics along with the core-upgrading to the MK-III core. Preparation of several modules was finished before the present work for neutron diffusion calculation of nomal/adjoint flux, gamma-source, and power distribution, as well as burnup calculation. The modules to calculate the gamma flux distribution based on diffusion theory and reactor kinetics parameters such as effective delayed neutron fraction and prompt neutron life time were made. Test calculation for each module was carried out to confirm the validity of calculation results. As for future works, it is required to make several modules for the evaluation of thermal characteristics, and preparation of effective cross section, in addition to the I/O interfaces and system control modules, for the further renewals of "MAGI" system.

Study on advanced fast reactor; Analysis of burning Characteristics of long-lived FPs

Yamaoka, Mitsuaki*; Kawashima, Masatoshi*

PNC TJ9164 96-007, 106 Pages, 1996/12

PNC-TJ9164-96-007.pdf:1.96MB

Some of fission products (FPs) in spent fuels have very long half lives as transuranic nuclides. Fast reactors have a potential to transmute these FPs into short-lived ones because of high neutron flux. As neutron capture cross sections of FPs increase in low energy region, one of the effective means to transmute them is to irradiate them using target assemblies that contain pins loaded with neutron moderating material such as ZrH as well as FP loading Pins. In the work carried out in 1994, a study was performed on transmutation of long-lived FPs, assuming that FP target assemblies are loaded in the core region of fast reactors. As a result, it was found that neutron moderation tends to improve transmutation rate whereas it causes to significant power spike in the adjacent core fuel. So as to suppress the power spike, FPs' loading at the outer periphery of the core was suggested. In the present study, an analysis was carried out to transmute FPs in fast reactors, assuming that target assemblies containing ZrH pins and Tc pins are loaded at the outer periphery of the core. The analysis was mainly performed using the continuous energy Monte Carlo code that is effective for rigorous trestment of rcsonance absorption of Tc99 in the target assembly with large heterogeneity. The results are shown below. (1)To increase absorption rate of Tc99, the neutron spectrum where absorption in the resonance region is more than in the thermal region is advantageous. This is because the spectrum helps to suppress absorption by structural material. Therefore, the appropriate loading mass of moderator depends upon the moderating power. (2)The target assembly selected from the survey indudes 19 ZrH pins with large diameter and 36 Tc pins with small diameter. The transmutation rate of Tc99 is about 4-5%/year and the mass is about 15-20kg/year. (3)The effect of loading target assembly upon main core characteristics were analyzed. It was found that the ...

Study on charactelistics of transmutation of long-lived FPs

Yamaoka, Mitsuaki*; *

PNC TJ9164 95-011, 115 Pages, 1995/03

PNC-TJ9164-95-011.pdf:2.42MB

Some of fission products (FPs) in spent fuels have very long half lives as transuranic nuclides. Fast reactors have a potential to transmute these FPs into short-lived ones because of high neutron flux. As neutron capture cross sections of FPs increase in low energy region, one of the effective means to transmute them is to irradiate them using target assemblies that contain pins loaded with neutron moderating material such as ZrHx as well as FP loading Pins. A study has been performed on transmutation of long-lived FPs, Tc99 and I129 in fast reactors usig target assemblies. The Monte Carlo method (MC method) with continuous-energy cross section was mainly employed to analyze rigorously resonance absorption of FPs in target assemblies with large heterogeneity. Specications of target assemblies were investigated with a aim to transmute FPs effectively. The target assemblies were assumed to be located in the core region. Also, comparison of calculation methods was carried out, where results from deterministic methods (diffusion and transport calculations) were compared with those from the MC method. Further, the effect of heterogeneity upon resonance absorption was analyzed. The results are as follows: (1)As the number of FP pins increases with total number of FP pins and ZrHx pins kept constant, transmutation rate decreases monotonously, whereas amount of transmutation decreases after it shows its peak value. The transmutation rate is about 1-2%/year at the case with maximum transmutation amount. (2)Heterogeneity effect upon transmutation rate is very large ; the rate for heterogeneous geometry is 30% smaller than that for homogeneous geometly with the same average composition. This is caused by heterogeneity effect upon resonance absorption. (3)Amount of transmutation vary by about 20-30% with arrangement variation of FP pins. Dispersing FP pins increases transmutation rate. (4)The difference between absorption rates from the MC method and the ...

Progress report of the design study on a large scale reactor

; Hayashi, Hideyuki; ; Yamaoka, Mitsuaki; ; ;

PNC TN9410 93-162, 494 Pages, 1993/07

PNC-TN9410-93-162.pdf:24.65MB

A design study on a large scale fast reactor was performed based on the results of the study on 600 MWe class "reactor vessel head access concept" plant in FY19901991. The objective of this study is to confirm quantitatively the applicability of "reactor vessel head access concept" to larger scale fast reactor plant as well as to establish the basic design such as core design, reactor structure, heat transport system, of 1300 MWe class "reactor vessel head access concept" plant and to evaluate its feasibility. In the former half period of FY1992, studies were performed aiming at evaluation of precision of core design, integrity of the structure and safety reflecting the final equipment design, feasibility of the concept of spent fuel storage, etc. While in the latter half period, added were the subjects on key technologies and plant concepts which enhance economy, safety, and social acceptance in order to ascertain the direction of a design study in the future and to contribute the realization of a commecial fast reactor.

Study on TRU transmutation by LMFBRs (II); Study on super long life core for TRU transmutation and influence of uncertainties of TRU cross sections

Yamaoka, Mitsuaki;

PNC TN9410 92-371, 94 Pages, 1992/12

PNC-TN9410-92-371.pdf:1.95MB

TRU nuclides (Np, Am, and Cm) contained in the high level waste have extremely long-term radioactivity. They would be managed much more easily if transmuted in a short period. The present study deals with TRU transmutation by Fast Breeder Reactors (FBRs). The results are summarized below. (1)Study on a 300MWe Super Long Life Core for TRU Transmutation An FBR core loaded with TRU has a large potentiality of extending operation cycle length. Making use of the potentiality, a super long life FBR core loaded with TRU was studied aiming at continuous operation without refueling during plant life and efficient reduction of TRU nuclides. Core parameters were optimized with the electric power of 300MWe and analyses of nuclear and thermal characteristics were carried out. As a result, the burnup reactivity change of the optimized core for 34 years is very small (2.5% k/kk'). The power swing is also small, which resulted in satisfaction of the thermal design criteria. The amount of TRU transmuted during lifetime is about 5300Kg, which is equal to that 6 LWRs of 1000MWe produce during their lifetime. The Doppler coefficient (absolute value) is rather small because of TRU loading. Further study is needed on core kinetics from the view point of core safety and control. (2)Study on influence of uncertainties of TRU cross sections There are large uncertainties in TRU cross sections because of lack of experimental data. The influences of the uncertainties upon nuclear characteristics were evaluated for the super long life core and a large FBR core loaded with TRU of 5%. Sensitivity analysis on cross sections was carried out and uncertainties of nuclear characteristics were roughly evaluated. Based on the results, the TRU cross sections with large influences were identified.

Progress report of the design study on a 600MWe class plant; Evaluation of construction cost and summary of drawings

; Hayashi, Hideyuki; ; ; ; Yamaoka, Mitsuaki;

PNC TN9410 92-353, 120 Pages, 1992/11

PNC-TN9410-92-353.pdf:3.2MB

A design study on a large scale fast reactor was performed at OEC about 600MWe class plant which might be the lowest power scale as a commercial one. Results of the design study till the end of JFY1991 were summarized in a previous progress report of the design study on a large scale reactor (PNC ZN9410 92-137). In this report, the evaluation results of the construction cost of the 600MWe class plant are described and also the drawings of their various parts are summaried.

PNC's Analyses of Passive Safety Test Phase IIB in the Fast Flux Test Facility

Yamaguchi, Akira; ; Shimakawa, Yoshio; Yamaoka, Mitsuaki; Tsukimori, Kazuyuki; Aizawa, Kiyoto

International Conference on Design and Safety of Advanced Nuclear Power Plants (ANP '92), 3, p.30.4.1 - 30.4.9, 1992/10

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