The Nuclear Analysis of an Annular Li₂O Blanket System Surrounding an Artificially Simulated 14-MeV Line Source and Comparison of Calculations to Measurements

Abstract

Experimental simulation to a line source has been realized at the Japan Atomic Energy Research Institute (JAERI) Fusion Neutronics Source within the U.S. Department of Energy/JAERI collaborative program on fusion neutronics. This simulation, achieved by cyclic movement of an annular Li₂O test assembly relative to a stationary point source, was a step forward in better simulation of the energy and angular distributions of the incident neutron source found in tokamak plasmas. Thus, compared with other experiments previously performed with a stationary point source, the uncertainties (that are system dependent) in calculating important neutronics parameters, such as tritium production rate (TPR), will be more representative of those anticipated in a fusion reactor. The rectangular annular assembly used is 1.3 × 1.3 m and 2.04 m long with a square cavity of 0.42 × 0.42 m cross section where the simulated line source (2 m long) is located axially at the center. To characterize the incident neutron source, flux mapping with foil activation measurements was performed in the axial direction (Z = −100 cm to Z = 100 cm) at the front surface of the assembly in the cavity with the annular blanket in place, and comparison was made to the bare line-source case (without annular blanket). Three phases of experiments were performed. In Phase-IIIA, a 1.5-cm-thick stainless steel first wall was used. An additional 2.45-cm-thick carbon layer was added in Phase-IIIB, and a large opening (42.55 × 37.6 cm) was made at one side at the center of the annular assembly in Phase-IIIC. Calculations were performed independently by the United States and JAERI for many measured items that included TPR from ⁶Li(T₆), ⁷Li(T₇), in-system spectrum measurements, and various activation measurements. In this paper, the calculated-to-measured values for the aforementioned measured items are given, as obtained separately by the United States and JAERI. In addition, the mean value of the prediction uncertainties of the local and line-integrated TPR and the associated standard deviations are given based on the calculational and experimental results obtained in all the experiments.