Akio Yamaji

Shielding Design to Obtain Compact Marine Reactor

The marine reactors equipped in previously constructed nuclear ships are in need of the secondary shield which is installed outside the containment vessel. Most of the weight and volume of the reactor plants are occupied by this secondary shield. An advanced marine reactor called MRX (Marine Reactor X) has been designed to obtain a more compact and lightweight marine reactor with enhanced safety. The MRX is a new type of marine reactor which is an integral PWR (The steam generator is installed in the pressure vessel.) with adopting a water- filled containment vessel and a new shielding design method of no installation of the secondary shield. As a result, MRX is considerably lighter in weight and more compact in size as compared with the reactors equipped in previously constructed nuclear ships. For instance, the plant weight and volume of the containment vessel of MRX are about 50% and 70% of those of the Nuclear Ship MUTSU, in spite of the power of MRX is 2.8 times as large as the MUTSUs reactor. The s...

Shielding Design for Steam Generator of Advanced Marine Reactor MRX

Compactness and light weight are of importance for a reactor plant used for ship propulsion. An advanced marine reactor, MRX, which has been designed by Japan Atomic Energy Research Institute, has accomplished a passively safe, compact and light weight design by adoption of an integral PWR and a water filled containment vessel. Dose equivalent rates in all areas inside and outside a ship are required to be reduced below design criteria without any bulk shield outside the containment vessel. In this paper, a shielding design for installation of the steam generator in the vicinity of the reactor core to achieve a compact plant by reducing fast neutrons in the steam generator and to enable the engine room, where pipes of the secondary loop are installed, to be classified as surveillance area, not controlled area, is described. The main purpose to classify the engine room as the surveillance area is the improvement of working efficiency of crew. To accomplish the design goal, a relatively thick core barrel and a shield for the steam generator are introduced.

Characteristics of Discrete Sn Calculation for Angular Distribution and Scalar Flux of Neutrons Penetrating through Media

The significant discrepancies often observed between the discrete Sn calculations and the measurements of the angular flux spectrum of neutrons at an angle of 0° have been studied for the benefit of analyses of time-of-flight measurements. Examination of the uncollided angular flux and scalar flux distribution yielded information on the relation between the accuracies obtainable in the calculations and the order of quadrature set used therein. Predictions on the angular flux in graphite resulting from the use of S 16, S 32 and S 48 quadratures, and on the scalar flux in water from the S 16 quadrature were compared with the results of measurements and of PALLAS transport calculations. It was found as a result that the. S 48 quadrature is most suitable for analyzing the 0° angular flux spectrum of the time-of-flight measurements, and that the S 16 quadrature is sufficient for scalar neutron flux calculations for reactor shields. The spurious fluctuations observed in the ANISN angular distributions are not d...