Hirofumi Takeda

Quantitative prediction of natural circulation in an LMFR with a similarity law and a water test

This paper is devoted to logical derivation of a similarity law for single-phase natural circulation expected in a liquid metal fast reactor (LMFR). Though the way of the derivation is principally conventional, this paper shows that explicit definition of a representative velocity and a representative temperature difference, as used in previous studies, is generally inappropriate in formulating a similitude law. The paper also presents formulae which allow to directly convert water test results into actual plant values. Using the conversion formulae, it is demonstrated that data acquired in a small scale water experiment can be converted and the results are comparable with results of actual LMFR computation. The accuracy of the experimental prediction is discussed.

Experimental and computational simulation for natural circulation in an LMFBR

This study has been conducted to establish a simulation method for the natural circulation phenomena in the reactor vessel of an LMFBR. The principal results obtained in the present study are as follows: 1. (1) Two dimensionless numbers, the Gr′ number and the Bo′ number, are derived and found the most influential on the natural circulation. 2. (2) A large velocity fluctuation is observed even in the steady state as if a mean velocity field does not exist in natural circulation. 3. (3) A higher order numerical scheme seems to be appropriate to simulate natural circulation.

Image processing system for velocity measurements in natural convection flows

Abstract An image processing system based on a particle-tracking method has been developed to measure quantitatively at one time the two-dimensional velocity components arising in natural convection flows. The analysis of the image data proceeds automatically, due in part to the video recording system utilized in our method. The image processing system was applied to the natural convection flows in a 1/10 scale basic reactor model. The velocity vectors and the vorticities were obtained under transient and steady states in different experimental cases, enabling us to examine in detail the transition of the flow patterns and other aspects under different experimental conditions. The uncertainty of this system was evaluated for use in our experiments and it was confirmed that the margin of error is acceptable.

An application of a higher order finite difference method to a natural convection experiment in the hot plenum of an LMFBR

Abstract A two dimensional thermal-hydraulic analysis of a natural circulation experiment has been performed to evaluate the effectiveness of a higher order finite difference method for solving the Navier-Stokes and the energy equations. In the method, the convection terms appearing in each equation are solved by the Method of Characteristics using the third order Lagrange type polynomial as the interpolation function, and an iterative procedure is applied to solve the time derivative terms of each equation stably with second order accuracy. The analytical results have been compared with an experiment in which the temperature and the velocity distributions in the plenum region were measured with their fluctuations, and it was shown that the higher order finite difference method could simulate natural convection phenomena involving fluctuations well.

Transport and storage of spent nuclear fuel

This chapter introduces the amount of spent fuel generation and storage in the world and the characteristics of spent fuel. An overview of the historical development of spent fuel storage technologies is provided and some examples of the storage casks are introduced. Current topics on transport and storage of spent fuel are described, including issues of long-term storage, long-term containment of metal gaskets for metal casks, interactions between transport and storage on containment, stress corrosion cracking of canisters, and a holistic approach to assure transport and storage safety of metal casks.

Development of Salt Particle Collection Device to Prevent SCC of Canisters

A natural cooling system is economical for removing the decay heat from casks at interim storage facilities of spent nuclear fuel. At storage facilities of concrete casks built near the seashore, the air including the sea salt particles comes into the concrete casks and may cause Stress Corrosion Cracking (SCC) to the canister made of welded stainless steel plates. In order to prevent SCC on the canister, it is necessary to keep the density of salt on the surface of the canister smaller than the threshold which causes SCC. In this study, the authors propose a salt particle collection device with a low flow resistance which doesn’t block the air inlet of the storage building. The salt particle collection device is installed at the inlet and composed of a duct with multiple trays where the water is filled. When the air including sea salt particles comes through the duct, it collides with the surface of the water in the trays, and the part of sea salt particles in the air dissolves in the water. Therefore, the salt carried into the building by the air is reduced. The salt water in the trays is discharged out of the building by overflowing. The device has the following characteristics. a) Because of the low flow resistance, the device doesn’t block the inflow of the air which needs for removing the heat from casks. b) Rainwater may be usable for the water used in the device. c) Because of the simple structure, the maintenance is easy. The authors conducted the experiments using the device in the laboratory and outdoors near the seashore. The obtained results are as follows: (1)The pressure loss of the device is 1/7 of that of a filter used in a forced cooling system and the efficiency of salt particle collection is approximately 24%. (2)The efficiency of salt particle collection in the outdoor tests is larger than that in the laboratory tests. By further experimental study, the authors will develop the device with lower pressure loss and higher efficiency of salt particle collection.Copyright