Minoru Miki

BWR Plants with Low Shutdown Radiation Level: Design and Construction of Plants and Current Experience with Occupational Exposure of Plants

Occupational exposure during BWR refueling and annual maintenance periods is determined by radioactive corrosion products, such as 60Co and 58Codeposited on major components and piping of the primary cooling system. The authors have investigated behavior of radioactive corrosion products, e.g. generation, activation and deposition processes, in the primary cooling system, and then ex- pressed the findings as mathematical equations. These provide corrosion product simulation models to predict the amounts of radioactive corrosion products depositing on components and piping. The effects of corrosion product reduction procedures on shutdown dose rate were evaluated using the model. The procedures were incorporated into the Japanese Improvement and Standardization Program. Improvements of operational procedures to control water chemistry, such as Ni/Fe ratio, as well as application of hardware improvements resulted in an extremely low occupational exposure of less than 90 man-rem/yr for currently constructed ...

Conceptual Design and Thermal-Hydraulic Characteristics of Natural Circulation Boiling Water Reactors

A natural circulation boiling water reactor (BWR) with a rated capacity of 600 MW(electric) has been conceptually designed for small- and medium-sized light water reactors. The components and syste...

Water Quality Control at Primary Cooling System of Crud Concentration Suppressed Boiling Water Reactor, (II): Evaluation of Cobalt-58 Behavior in Iron Crud Suppressed BWR

A possible accumulation mechanism of Ni and radioactive 58Co ions in the reactor water of a low iron crud concentration plant was modeled based on a direct deposition of Ni ion on fuel cladding surfaces as a form of NiO, followed by the solid phase reaction between NiO and iron crud (α-Fe2O3) to produce NiFe2O4. The calculated results agreed satisfactorily with measurements in the first Japanese standard BWR, Fukushima 2-2 (1,100 MWe). These calculations showed that controlling the Fe/Ni corrosion products ratio in the feed water to a value larger than 2 was effective to suppress 58Co activity in the reactor water as well as Ni ion concentration.

Iron Oxide Deposition on Heated Surfaces in Pressurized Boiling Water

The deposition of suspended iron oxide in water at a 10-atm pressure during nucleate boilings on a Zircaloy heated surface has been studied. The effects of pressure on the deposition rate during the initial period have been investigated. The previously proposed iron oxide deposition model, based on the microlayer evaporation and dryout phenomena that occur in the nucleate boiling bubble at atmospheric pressure, is extended to high-pressure nucleate boiling conditions. The model is shown to be applicable for high-pressure studies.

Conceptual design and safety characteristics of a natural-circulation boiling water reactor

The Hitachi simplified boiling water reactor (BWR) is a natural-circulation BWR with a rated capacity of 600 MW (electric). It has been designed for the classes of small- and medium-sized light water reactors. The power density is ∼70% of that in current BWRs because of natural circulation, and the reactor pressure vessel is larger. The components and systems have been simplified by eliminating pumped recirculation systems and pumped emergency core cooling systems. Consequently, the volume of the reactor building is ∼50% that of current BWRs, with the same rated capacity. The construction period is also shorter. In addition, the lower power density allows continuous operation for a 23-month period. The safety characteristics of this BWR are investigated during transient and accident conditions, and the high standards of its simple safety systems are shown