Operational Experiences of Fast Neutron Source Reactor “YAYOI” as Pulsed Fast Reactor

University of Tokyo research reactor “YAYOI” is intended to be operated as a dynamic fast neutron source reactor as well as a stationary one. It is equipped with reactivity adding devices with both slow and quick action, and a LINAC PNS (Pulsed Neutron Source) to be operated with the devices mentioned above. The unique idea of fly-through type pulse reactivity addition into the core lends itself to minimizing thermal shock problems pertaining to fast burst reactors thereby increasing safety of a single shot type burst reactor.

Operational experiences of YAYOI obtained during the dynamic testing of super critical state are described here with some explanation of design aspects of YAYOI as a fast pulsed reactor.

Throughout present experiments, the super prompt critical state reactivity of about up to 29 cents was realized for YAYOI core, and it was confirmed that the sizes of pulse power were well controllable with this reactivity pulser (R-P) mode pulse operation.     

Radiation Field for Fission Neutron Enhanced Boron Neutron Capture Therapy Employing Fast Neutron Source Reactor “YAYOI”

Boron Neutron Capture Therapy (BNCT) of a localized tumor needs a sufficient thermal neutron flux at the tumor. A surgical operation including ennucleation of the main part of tumor is required for the case of thermal neutron beam from a thermal reactor because of the rapid decrease of the neutron flux in the tissue. Intermediate neutrons with little fast neutron component are only produced by a specifically designed reactor which awaits to be build.

In the present paper, a positive use of fast neutron beams in addition to BNCT is proposed for treatment of some kind of localized tumors employing a fission fast neutrons from a fast neutron source reactor “YAYOI” of University of Tokyo which is licenced as such. Dose distributions in a water phantom located at a proposed position for two collimator cases were measured and its availability was confirmed as a possible port for therapy.     

Evaluation of Activation Cross Sections for (n,2n) Reactions on Some Nuclei

The evaluations of activation cross sections of (n,2n) reaction for ~(58)Ni, ~(87)Rb, ~(89)Y, ~(90)Zr, ~(140)Ce and ~(169)Tm were performed in order to update the previous evaluated data. The cross sections are recommended based on the recent experimental data, especially the new measured results in CIAE. The present evaluated data are compared with other evaluated data.     

Cross Sections of 14 MeV Neutron Induced Reactions on Wolfram Isotopes

Introduction The importance of nuclear data for fusion power reactor design has been acknowledged, in particular for safety, environment reasons and economics. The 14 MeV neutron activation cross sections are the key nuclear data for environmental impact, material recycling, waste handling. Due to the large number of materials and traces of alloy elements and contamination, there are requirements for a complete database covering large number of nuclides. Problems still exist for some reactions, for example, for ~(182)W(n,n′α)~(178m2)Hf reaction only one measurement was published,     

Progress on the Evaluation of Total Cross Section for Some Fission Product Nuclides

The total cross section for some fission product nuclides or their substitutes, ~(139)La, ~(133)Cs, ~(103)Rh, ~(120)Sn, ~(127)I, ~(140)ce, ~(nat)Sb, ~(nat)Cd, ~(nat)Ag, ~(nat)Ce, ~(nat)pd, ~(nat)La, ~(nat)Te, ~(nat)Xe and ~(nat)Ba, have been evaluated on the basis of the experimental data. The experimental data were collected from EXFOR library and recent pub     

Evaluation of Neutron Induced Helium Production and Activation Cross Sections for Some Nuclei

The activation characters of chosen fusion materials are important in determining proper reactor technologies. In order to meet these requirements for fusion design studies, not only all activation cross sections for the fusion materials themselves have to be know, but also those for all possible impurities require to be considered if they lead to long-lived activities.     

Evaluation of Cross Sections of Photonuclear Reactions for ~(180,182,183,184,186)W below 30 MeV

Introduction The photoneutron cross sections of wolfram's isotopes up to 10 MeV are very important from the view point of reactor engineering field in the context of radiation induced material damage, radiation safety, reactor incore dosimetry, etc. Meanwhile, the photonuclear reactions are usually used for performing activation analysis of     

Calculations of Double Differential Deuteron Emission Cross Sections at 62 MeV Proton Induced Reactions

In this study, double differential deuteron emission cross sections for ²⁷Al, ^54,56Fe, ¹⁹⁷Au, ²⁰⁸Pb and ²⁰⁹Bi target nuclei have been calculated by the TALYS code at 62 MeV proton energy. The use of TALYS involved calculations by the pre-equilibrium exciton model and the Hauser–Feshbach model. The calculated double differential cross sections have been compared with the experimental data taken from the literature.     

Cross Sections Calculations of (d, t) Nuclear Reactions up to 50 MeV

In nuclear fusion reactions two light atomic nuclei fuse together to form a heavier nucleus. Fusion power is the power generated by nuclear fusion processes. In contrast with fission power, the fusion reaction processes does not produce radioactive nuclides. The fusion will not produce CO₂ or SO₂. So the fusion energy will not contribute to environmental problems such as particulate pollution and excessive CO₂ in the atmosphere. Fusion powered electricity generation was initially believed to be readily achievable, as fission power had been. However, the extreme requirements for continuous reactions and plasma containment led to projections being extended by several decades. In 2010, more than 60 years after the first attempts, commercial power production is still believed to be unlikely before 2050. Although there have been significant research and development studies on the inertial and magnetic fusion reactor technology, there is still a long way to go to penetrate commercial fusion reactors to the energy market. In the fusion reactor, tritium self-sufficiency must be maintained for a commercial power plant. Therefore, for self-sustaining (D–T) fusion driver tritium breeding ratio should be greater than 1.05. Working out the systematics of (d, t) nuclear reaction cross sections is of great importance for the definition of the excitation function character for the given reaction taking place on various nuclei at different energies. Since the experimental data of charged particle induced reactions are scarce, self-consistent calculation and analyses using nuclear theoretical models are very important. In this study, (d, t) cross sections for target nuclei ¹⁹F, ⁵⁰Cr, ⁵⁴Fe, ⁵⁸Ni, ⁷⁵As, ⁸⁹Y, ⁹⁰Zr, ¹⁰⁷Ag, ¹²⁷I, ¹⁹⁷Au and ²³⁸U have been investigated up to 50 MeV deuteron energy. The excitation functions for (d, t) reactions have been calculated by pre-equilibrium reaction mechanism. Calculation results have been also compared with the available measurements in literature.     

Conceptual Design of a Modular Island Core Fast Breeder Reactor “RAPID-M”

A metal fueled modular island core sodium cooled fast breeder reactor concept RAPID-M to improve reactor performance and proliferation resistance and to accommodate various power requirements has been demonstrated. The essential feature of the RAPID-M concept is that the reactor core consists of integrated fuel assemblies (IFAs) instead of conventional fuel subassemblies. The RAPID concept enables quick and simplified refueling by replacing IFAs in which all the core and blanket fuel elements are comprised. In this paper, the 600 MWe RAPID-M design consists of 7 IFAs is presented. Significant reactor mass savings and the improvement of inherent safety features are discussed. Plant dynamics analyses using the multi-point reactor kinetics equations to accommodate the modular core configuration demonstrated a favorable transient response in case of unprotected transient over power (UTOP).     

Calculations of Various Cross Sections for n ~(63,65)Cu Reactions in Energy Region up to 70 MeV

A set of neutron optical potential parameters for ~(63, 65)Cu in energy region of 2～80 MeV was obtained with available experimental data. Various cross sections of n ~(63, 65)Cu reactions are calculated and predicted in the energy range up to 70 MeV.     

Core Restraint Analysis for 75 MW Power Ascension Tests of Experimental Fast Reactor “JOYO”

In the “JOYO” initial power ascension tests to 75 MW, unexpected large negative power coefficients were observed during ascension to new power levels beyond 50 MW, which results in approximately a 40¢ permanent loss in reactivity.

This anomaly was studied from the viewpoint of radial dimensional change in the core using a three-dimensional structural analysis code along with a whole-core thermal-hydraulic analysis code. Conclusions drawn from the study can be summarized as follows:

(1) The absolute value of the power coefficient increases sharply beyond the 50 MW power level due to the outward leaning and thermal bowing of core elements, but the calculated increase in the coefficient is less than 20% of the observed value.

(2) At most, an 80 permanent loss in reactivity is caused by this outward leaning, which is 20% of the observed value.

(3) These results confirm that the radial dimensional change can not be the main cause for the power coefficient anomaly.     

Verification Experiment of Threshold Detector 107Ag(n,n′)107mAg on “YAYOI” Standard Neutron Field

The validity of the ¹⁰⁷Ag(n, n′)^107mAg reaction for reactor neutron dosimetry has been examined through an irradiation experiment using the standard neutron field in the “YAYOI”, a fast neutron source reactor. The test foil used was 99.0% ¹⁰⁷Ag enriched silver, which was irradiated along with five reference foils already well evaluated. The reaction rate of 107Ag was determined by K X-ray counting with a high-purity Ge detector. The cross section for the ¹⁰⁷Ag(n, n′) ^107mAg reaction was compiled from the excitation cross section data of ¹⁰⁷Ag published in ENDF/B-IV, in combination with the decay scheme of ^107mAg listed in the “Table of Isotopes“. Using the neutron spectrum which had previously been precisely measured, it was found that the compiled activity of ^107mAg was underestimated by 12.8±5%. This error is attributed to significant underestimation involved in the cross section of the ¹⁰⁷Ag(n, n′)^107mAg reaction.     

Analysis and Prediction of the Cross Sections of d ~6Li and d ~7Be Reactions for Energy up to 30 MeV

A set of deuteron optical potential parameters is obtained based on the relevant experimental data, and various nuclear data of d ~6Li reaction at incident energies spanning 0.1～30 MeV were calculated with the Distorted Wave Born Approximation, preequilibrium nuclear reaction and Hauser-Feshbach (HF) theory.The cross sections of d ~7Be reaction were predicted. The results show that the experimental measure- ment for d ~7Be reaction is feasible at HI-13 tandem accelerator.     

Evaluation of Cross Sections for ~(197)Au(n,3n) and ~(197)Au(n,4n) Reactions from Threshold to 50 MeV

The measured data of cross sections for ~(197)Au(n,3n) and ~(197)Au(n,4n) reactions were collected and analysed. The theoretical calculations of above mentioned reactions were carried out to predict the data in higher energy region. The sets of cross sections for ~(197)Au(n,3n) and ~(197)Au(n,4n) reactions from threshold to 50 MeV were recommended on the basis of the experimental and calculated data.     

Investigation of Neutron-Production Cross Sections of the Structural Fusion Material 181Ta for (α,xn) Reactions up to 150 MeV Energy

In this study, the theoretical neutron-production cross-sections produced by (α,xn) reactions (x = 3, 4, 5, 6, 7) for structural fusion material ¹⁸¹Ta in alpha-induced reactions have been investigated up to 150 MeV alpha incident energy. Also, neutron-emission spectra of ¹⁸¹Ta(α,xn) reactions have been investigated for incident alpha energies at 26.8 and 45.2 MeV. Reaction cross-sections as a function of alpha energy and neutron-emission spectra have been calculated theoretically using ALICE/ASH and TALYS 1.2 computer codes. The calculated results have been compared with the each other and experimental data existing in EXFOR database. The obtained results have been discussed and compared with the available experimental data and found agreement with each other.     

Evaluation of Cross Sections for Neutron Monitor Reactions ~(169)Tm(n,xn)~(168, 167, 166, 165)Tm from Threshold to 100 MeV

The cross sections for ~(169)Tm(n,xn)~(168,167,166,165)Tm reactions in intermediate energy region are useful for neutron field monitor, safety design consideration and material damage research for fusion material irradiation test and the radioactivities induced in components of accelerator. The evaluation of activation cross sections of (n,2n) reaction for ~(169)Tm has been performed below 20 MeV. In our evaluation, the identification and correction have been made to the differences and discrepancies among the existing activation cross sections from different laboratories to obtain more accurate da     

Evaluation of Cross Sections for Neutron Monitor Reactions ~(90)Zr(n,x)~(89,88)Zr,~(88,87,86)Y from Threshold to 100 MeV

The cross sections for ~(90)Zr(n,x)~(89,88)Zr and ~(90)Zr(n,x)~(88,87,86)Y reactions in intermediate energy region are useful in neutron field monitor, safety and material damage research. Below 20 MeV, the evaluated cross sections for (90)Zr(n,2n)~(89)Zr reaction are recommended based on the recent experimental data, including the new measured results in CIAE(Above 20 MeV). The measured cross sections are still insufficient to do evaluation. So the evaluation for ~(90)Zr(n,x)~(89,88)Zr and (90)Zr(n,x)~(88,87,86)Y reactions from threshold to 100 MeV are based on experimental and calculated data.     

Prediction of the Cross Sections of p ~(11)C and d ~(11)C Reactions for Energy up to 25 MeV

~(11)C (half time is 20.3 min) is a proton-rich radioactive nucleus. The cross sections of p ~(11)C and d ~(11)C reactions were predicted in energy region up to 25 MeV. From the calculated results one can see some features of nuclear reactions of proton-rich radioactive nuclei. The calculated results also show that the experimental measurement to ~(11)C d reaction is more feasible than to ~(11)C p reaction at HI-13 tandem accelerator.     

Evaluation of Neutron Monitor Cross Sections for ~(63, 65, Nat)Cu(n,x)~(56～58, 60)Co Reactions from Threshold to 70 MeV

The cross sections for monitor reactions ~(63, 65, Nat)Cu(n,x)~(56～58, 60)Co were analysed and evaluated based on measured data and theoretically calculated results from threshold up to 70 MeV. The recommended data could reproduce the experimental data very well. In higher energy region, the data were provided by theoretical calculation with adjusted model parameters based on measured data.