Method for improving water chemical environment of soluble-boron-free coolant of nuclear power plant

Abstract

The invention provides a method for improving the water chemical environment of a soluble-boron-free coolant of a nuclear power plant. The method comprises that at the startup stage of a nuclear powerplant unit, after the temperature of the water chemical environment of the coolant in a primary circuit is gradually increased to a preset medium-temperature threshold, a lithium hydroxide solution is injected into the primary circuit through a RCS charging pipeline until the lithium ion concentration in the coolant achieves a predetermined value, wherein the coolant does not contain boron ions before and after being injected into the lithium hydroxide solution; and after the nuclear power plant unit operates to reach a full-power operation stage, the pH value of the coolant is periodically detected, the lithium hydroxide solution is continuously injected into the primary circuit through the RCS charging pipeline if the detected pH value is lower than 7.2 until the lithium ion concentration is maintained at the predetermined value, and the pH value is maintained at 7.2. According to the present invention, with the method, by eliminating the preparation of soluble boron and the coordination strategy thereof, the water chemical environment of the coolant is easily stabilized, the cost is saved, the control strategy is simplified, and the corrosion is retarded.

Description

technical field [0001] The invention relates to the technical field of nuclear safety, in particular to a method for improving the water chemical environment of a nuclear power plant based on a soluble boron-free coolant. Background technique [0002] The initial pH value of the water chemical environment of the coolant in the primary circuit of the nuclear power plant is 6.9, and the target pH value is 7.2. However, existing nuclear power plants use natural boron to control the reactivity of the core, which will lead to a high concentration of boron ions in the water chemical environment of the coolant in the primary circuit of the nuclear power plant at the beginning of the fuel life. Concentration increased to 3.5mg / kg. According to the general idea of ​​improving the chemical control strategy, the concentration of lithium ions should be kept constant at this time, and the fuel consumption of the random group will decrease the concentration of boron ions. When the pH val...

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Problems solved by technology

[0004] However, the method for adjusting the pH value of the water chemical environment of the coolant in the primary circuit of the nuclear power plant has the following disadvantages: (1) The operation process is complicated, and because the pH value of the fuel at the beginning of its life is maintained at 6.9, boron ions are present in this environment. Acidity will cause corrosion risks to the structural materials of the primary circuit of the nuclear power plant; (2) In order to control the concentration of boron ions in the water chemical environment of the coolant in the primary circuit of the nuclear power plant, it is necessary to establish a system to control the preparation, storage, addition, recovery and filtration of soluble boron in the primary circuit. Equipment and systems, not only the process flow and equipment configuration are very complicated, occupying space, but also increase the use of chemical additives, difficulty in operation, and input costs

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