A. Kumar

Phase III experimental results of JAERI/USDOE collaborative program on fusion neutronics

Abstract A pseudo-line D–T neutron source has been developed with new experimental techniques. This line source was applied in sophisticated neutronics experiments for an annular blanket arrangement simulating the tokamak geometry, as a new series in the JAERI/USDOE collaborative experimental program on fusion neutronics. The source characteristics of the present line source and the measurements for an annular assembly are described. The discussion on the experimental results focuses on the tritium production rate measured in an annular blanket and comparisons were made with the previous point source experiment, and also between the annular blankets with and without an armor reflector of graphite.

Measurement and Analysis of Nuclear Heat Depositions in Structural Materials Induced by D-T Neutrons

AbstractNuclear heat deposition rates in ten different materials, Li2CO3, Graphite, Ti, Ni, Zr, Nb, Mo, Sn, Pb and W, subjected in D-T neutrons have been measured by a microcalorimetric technique in the frame work of JAERI/USDOE collaborative program on fusion neutronics. A great improvement in accuracy of experimental data was achieved by introducing a high sensitivity voltmeter and applying constant current on the thermal sensors. The measured heating rates were compared with calculations to verify the adequacy of the currently available data base relevant to the nuclear heating process. In general, calculations with data of JENDL-3 and ENDL-85 libraries gave excellent agreements with experiments for all materials except Zr. The calculation with the MBCCS suffered large discrepancy from measurement.

Measurements of the Source Term for Annular Blanket Experiment with a Line Source: Phase IIIA of JAERI/USDOE Collaborative Program on Fusion Neutronics

AbstractA pseudo line DT neutron source has been realized by moving an experimental assembly with respect to a point DT source in the Phase-III experiment of JAERI/USDOE collaborative program on fusion blanket neutronics. In order to examine characteristics of the pseudo-line source made by two types of operational modes, source term experiments were carried out. Neutron flux distribution above 10 MeV was measured by NE213 scintillator with stepwise source mode. The reaction rate distributions were also measured by activation foil technique with continuous source mode. The measured distributions were almost flat over central 1 m region of the simulated line source and agreed relatively with a simple calculation assuming the ideal line source. From these experimental results it was concluded that both modes worked successfully to obtain the pseudo-line source and could simulate well neutron flux distribution emitted from a finite length line source with small influence of reaction kinematics and target str...

Direct nuclear heating measurements in fusion neutron environment and analysis

Abstract Experimental measurement of nuclear heating rates has been carried out in a simulated D-T fusion neutron environment from 1989 through 1990 under the USDOE/JAERI collaborative program at the Fusion Neutronics Source Facility. The microcalorimetric technique has been employed for online measurements. Small probes of materials have been irradiated in close vicinity of a rotating target. A typical probe contains a core measuring 2 cm in diameter by 2 cm in length. Probes of leading candidates, for different applications, have been investigated: molybdenum, tungsten, titanium, graphite (plasma facing components), copper (magnet coils), iron, stainless steel 304, nickel (structural material components) and aluminum. The measured temperature-change rates range from 30 μK/s (iron) to 330 μK/s (graphite). The corresponding nuclear heating rates range from ∼ 35 μ W/g (tungsten) to ∼ 225 μ W/g (graphite). These measurements have been analyzed using three dimensional Monte Carlo code MCNP and various heating number/kerma factor libraries. The ratio of computed to measured heating rates shows large deviation from 1 for all the materials. In addition, there is a large spread for different libraries; for example, this ratio varies from 1.03 to 1.81 for aluminum. Also, there have been three experiments with each having a host medium of iron, graphite or copper, that measures 85 mm in diameter by 100 mm in length. Small single probes of the host medium graphite and tungsten are placed inside to measure the spatial profile of heat deposition. Analysis of the measurements shows that the ration of computed to measured rates varies widely, e.g., in iron host, it goes from 0.5 to 1.1. Further effort is to be invested to locate the sources of this discrepancy.

(Deuterium-Deuterium)-Driven Experimental Hybrid Blankets and Their Neutronic Analyses

The impressive progress made so far toward the achievement of the physics goal of ignited fusion fuel of deuterium-tritium (D-T) is stirring the scientific community to look back and work for the earliest possible introduction of advanced fusion fuel based reactors with the ultimate objective of very clean, safe, and limitless fusion power. As the introduction of advanced fuel fusion drivers is expected to be in phases due to energetics considerations, it is quite instructive to examine the neutronic aspects of deuterium-deuterium (D-D) neutron driven hybrid blankets. The neutronics investigations of some compact hybrid blankets that could be tested experimentally are presented. The blanket designs are selected to conform to a rather small experimental chamber of the LOTUS fusionfission hybrid facility. The parallelepiped-shaped blankets are driven by a (D-D) neutron source from one side. The fertile fuel is either ThO/sub 2/, natural UO/sub 2/, or LOTUS UO/sub 2/. The tritium breeders are chosen from lithium, LiAlO/sub 2/, or Li/sub 2/O. The relative performances of different fertile fuels and tritium breeders are compared. The performance characteristics of ThO/sub 2/ blankets driven by (D-T) and (D-D) neutrons are compared. The improvement in performance characteristics obtained by the introduction of actinides as multipliersmorexa0» with ThO/sub 2/ hybrid blankets is also investigated.«xa0less

Measurements and Analyses of Decay Radioactivity Induced in Simulated Deuterium-Tritium Neutron Environments for Fusion Reactor Structural Materials

To meet urgent requirements for data validation, an experimental analysis has been carried out for isotopic radioactivity induced by deuterium-tritium neutron irradiation in structural materials. The primary objective is to examine the adequacy of the activation cross sections implemented in the current activation calculation codes considered for use in fusion reactor nuclear design. Four activation cross-section libraries, namely, JENDL, LIB90, REAC * 63, and REAC * 175 were investigated in this current analysis. The isotopic induced radioactivity calculations using these four libraries are compared with experimental values obtained in the Japan Atomic Energy Research Institute/U.S. Department of Energy collaborative program on fusion blanket neutronics. The nine materials studied are aluminum, silicon, titanium, vanadium, chromium, MnCu alloy, iron, nickel, niobium, and Type 316 stainless steel. The adequacy of the cross sections is investigated through the calculation to experiment analysis. As a result, most of the discrepancies in the calculations from experiments can be explained by inadequate activation cross sections. In addition, uncertainties due to neutron energy groups and neutron transport calculation are considered. The JENDL library gives the best agreement t with experiments, followed by REAC * 175, LIB90, and REAC * 63, in this order. Clear suggestions for a future direction to improve the overall calculation accuracy are developed based on the current experimental analysis.

Characterization of TFTR shielding penetrations of ITER relevance in D-T neutron field

Abstract D-T phase of TFTR began with trace tritium discharges in mid-November 1993. The availability of high D-T fusion neutron yields at TFTR has provided a unique opportunity to characterize tokamak fusion reactor shielding-penetration geometries of relevance to ITER. It was undertaken to characterize neutron energy spectra near three different kinds of penetrations on walls of TFTR test cell. Thirteen foils each were irradiated on seven locations. The saturation activities have been obtained and are discussed with a view to characterizing the neutron energy spectra. Also, unfolded spectra have been utilized to estimate dose equivalents for the same locations. These types of measurements are potentially useful for validating calculational methods and meeting fusion reactor licensing requirements.

Integral experiment of induced radioactivity in D-T fusion neutron environment and validation of activation cross section library

Abstract Under ITER/EDA R&D Task T-218, an integral experiment on the induced radioactivity was conducted at the Fusion Neutronics Source (FNS) facility in JAERI. The objective was to provide experimental data for validating the inventory calculation codes and relevant activation cross section libraries to be used in the ITER nuclear design. Sample materials investigated were Al, Mg, Ti, V, Mn, Fe, Ni, SS-316LN, Cu, Zn, Nb, Mo, Ag, In, Sn, Hf, Ta, W and Pb. The corresponding neutron spectra at two locations were calculated by MCNP4A with JENDL-Fusion File based nuclear data library by modeling the experimental assembly precisely. The calculations with currently updated activation cross sections, JENDL-ACT96, FENDL-A1 and FENDL-A2, were carried out to compare the results with the experiment. The results for the comparison between the measurement and calculation of radioactivity are discussed in terms of the adequacy of calculation as far as the D-T neutron dominated neutron field is concerned.

Fusion Integral Experiments and Analysis and the Determination of Design Safety Factors — II: Application to the Prediction Uncertainty of Tritium Production Rate from the U.S. DOE/JAERI Collaborative Program on Fusion Blanket Neutronics

Many fusion integral experiments were performed during the last decade within a well-established collaboration between the United States and Japan on fusion breeder neutronics. These experiments started in 1983 and aimed at verifying the prediction accuracy of key neutronics parameters based on the state-of-the-art neutron transport codes and basic nuclear databases. The tritium production rate (TPR) has the prime focus among other reactions. The experimental and calculational data sets of local TPR in each experiment were interpolated to give an estimate of the prediction uncertainty, u i , and the standard deviation, σ i of the line-integrated TPR, a quantity that is closely related to the total breeding ratio (TBR) in the test assembly. A novel methodology developed during the collaboration was applied to arrive at estimates to design safety factors that fusion blanket designers can use to ensure that the achievable TBR in a blanket does not fall below a minimum required value. Associated with each safety factor is a confidence level, designers may choose to have, that calculated TPR will not exceed the actual measured value. Higher confidence levels require larger safety factors. Tabular and graphical forms for these factors are given, as derived independently for TPR from Li-6 (T 6 ), Li-7 (T 7 ), and natural lithium (T n ). Furthermore, distinction was made between safety factors based on the technique applied, discrete ordinates methods, and Monte Carlo methods in the U.S. calculations, JAERIs calculations, and in both calculations considered simultaneously. The derived factors are applicable to TPR in Li 2 O breeding material ; nevertheless, the results can be used as initial guidance to assist in resolving the tritium self-sufficiency issue in other breeding media.

Decay Radioactivity Induced in Plasma-Facing Materials by Deuterium-Tritium Neutrons

Deuterium-tritium (D-T) neutron-induced radioactivity constitutes one of the foremost issues in fusion reactor design. Designers have been using radioactivity codes and associated nuclear data libraries for nucleonic designs offusion reactors. However, in the past, there was hardly any experimental validation of these codes/libraries. An elaborate, experimental program was initiated in 1988 under a U.S. Department of Energy/Japan Atomic Energy Research Institute collaborative program to validate the radioactivity codes/libraries. Measurements of decay gamma spectra from irradiated, high-purity samples of Al, Si, Ti, V, Cr, Mn-Cu alloy, Fe, Co, Ni, Cu, SS316/AISI316, Zn, Zr, Nb, Mo, In, Sn, Ta, W, and Pb, among others, have been carried out under D-T neutron fluences ranging from 1.6 x 10 10 to 6.1 x 10 13 n/cm 2 and cooling times ranging from ∼10 min to ∼3 weeks. As many as 14 neutron energy spectra were covered for a number of materials. The analyses of the isotopic activities of the irradiated materials using the activation cross-section libraries of four leading radioactivity codes, i.e., ACT4/THIDA-2, REAC-3, DKR-ICF, and RACC, have shown large discrepancies among the calculations on one hand and between the calculations and the measurements, on the other. Vanadium, Co, Ni, Zn, Zr, Mo, In, Sn, and W each count the largest number of discrepant isotopic activities. It is strongly recommended to continue additional radioactivity experiments under additional neutron energy spectra and large neutron fluence on one hand and to improve activation cross sections related to the problematic isotopic activities on the other. A unique activation cross-section library and associated radioactivity code are also recommended for the best results. In addition to providing detailed results of the status of predictability of individual isotopic activities using the ACT4, REAC-3, DKR-ICF, and RACC activation cross-section libraries, safety factors cum quality factors characterizing each library are presented and discussed. The related issues of confidence level and associated uncertainty are also highlighted. These considerations are of direct practical importance to reactor designers.