JP3109917B2 - Decay heat removal system for nuclear reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a decay heat removal system for a nuclear reactor, for example, a modular HTGR plant.

[0002]

2. Description of the Related Art In reactors mentioned above, in addition to the main cooling system, as a safety measure for the reactor, the decay heat generated from the reactor core is continuously output even after shutdown due to abnormality or failure of the main cooling system. It is equipped with a decay heat removal system that removes heat.
On the other hand, as the decay heat removal system, a cooling panel is arranged around the reactor pressure vessel, and the decay heat of the reactor received in the form of radiant heat is led to a radiator, and then cooled by cooling air or the like. In addition to the method in which heat is dissipated to the heat sink outside the system, a heat pipe (sealed pipe) is inserted between the surrounding area of the reactor pressure vessel and the heat sink (air ventilation duct or cooling water pool, etc.) outside the system. A heat pipe filled with a small amount of pure working fluid (eg, water) is placed inside the reactor, and the decay heat of the reactor received at the evaporator of the heat pipe is converted into latent heat by the heat pipe evaporation / condensation cycle to the condenser. Japanese Patent Application Laid-Open No. 4-72597 has already proposed a decay heat removal system using a heat pipe in which heat is transferred to a heat sink outside the system through a condenser.

[0003]

However, in the proposed decay heat removal system for a nuclear reactor, the following problems remain in terms of functions. That is, as shown in the principle diagram of FIG. 2, in a normal heat pipe in which only a small amount of hydraulic fluid is sealed in a sealed pipe with a wick, the heat transfer capacity is determined by the temperature difference between the evaporating section and the condensing section, and the evaporating section. The heat conductance of the heat pipe is almost constant irrespective of the magnitude of the heat input, which is determined by the thermal resistance to the heat flow through the condenser, the heat transfer coefficient, and the like.

Accordingly, in the proposed decay heat removal system for a nuclear reactor employing the above heat pipe, the heat pipe operates even during normal operation of the nuclear reactor, and a part of the heat generated in the nuclear reactor is removed by the heat pipe. The heat is wasted to the heat sink outside the system through the process, and as a result, the thermal efficiency during the normal operation of the reactor plant is reduced.

The present invention has been made in view of the above points, and an object of the present invention is to solve the above-mentioned problems in a heat pipe type decay heat removing system, and to suppress the heat radiating ability of a heat pipe during normal operation of a nuclear reactor. It has an excellent function to minimize the heat loss of the reactor plant and maximize the heat dissipation capacity of the heat pipe to efficiently remove the decay heat when the heat input increases due to an accident. A new reactor decay heat removal system is provided.

[0006]

In order to achieve the above object, in the decay heat removal system of the present invention, a variable conductance heat pipe having a non-condensable gas sealed with a working fluid is used as a heat pipe. Shall be. Further, as an embodiment of the decay heat removal system, a variable conductance heat pipe, a vapor diffusion passage of the working fluid between the evaporator and the condenser disposed on the upper side thereof,
Separate thermosyphon with a condensate reflux path and an appropriate amount of non-condensable gas sealed with the working fluid inside, and a non-condensable gas reservoir downstream of the condensing section There is a configuration in which a gas reservoir is provided.

[0007]

The above-mentioned variable conductance heat pipe is a type in which an appropriate amount of non-condensable gas is positively sealed together with the working fluid in the heat pipe as shown in the principle diagram of FIG.
When heat input is given to the evaporating part of the heat pipe, the working fluid vapor and the non-condensable gas sealed in the heat pipe are separated on the condensing part side, and a boundary surface is created between them, and the heat input is small. In some cases, the non-condensable gas blocks a portion of the condensing portion to form a local condensation-insensitive portion, limiting the effective heat transfer area acting as a condensing portion to the remaining condensing active portion. That is, the heat conductance of the heat pipe is kept low. On the other hand, when the amount of heat input to the evaporating section increases, the vapor pressure of the working fluid increases and compresses the non-condensable gas, so that the boundary surface moves to the end side (right corner in the drawing) of the condensing section. As a result, the heat transfer area of the condensing section is increased, whereby the heat conductance is increased, and the self-control works so as to increase the heat transfer capacity of the heat pipe.

Therefore, by disposing such a variable conductance heat pipe between the peripheral region of the reactor vessel and the heat sink, during normal operation of the reactor having a relatively low heat input, the above-described variable conductance heat pipe is used. Due to the self-control characteristic, the heat loss wasted to the outside of the system through the heat pipe can be kept low, and the heat loss of the reactor plant can be minimized. On the other hand, when a large amount of heat is applied to the heat pipe as a heat load due to the occurrence of the accident, the heat conductance switches automatically to increase due to the self-control characteristic of the variable conductance heat pipe. The heat dissipation capacity of the reactor increases, and the decay heat can be efficiently radiated out of the system to safely protect the reactor.

On the other hand, according to the configuration in which the variable conductance heat pipe is configured as a separate thermosiphon and a reservoir for a non-condensable gas is additionally provided downstream of the condenser, a steam wick is not provided. The condensed liquid can be returned from the condenser to the evaporator by natural flow, simplifying the structure of the heat pipe, and in the operating state where the heat input to the evaporator is large, the vapor of the working fluid compresses the non-condensable gas. And the entire area of the condenser is effectively involved in the heat dissipation function as a condensation active part, which increases the heat dissipation capacity of the heat pipe to the maximum and causes the collapse of the reactor in the event of an accident. Heat can be efficiently radiated to a heat sink outside the system.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. Example 1 In FIG. 1, 1 is a reactor core, 2 is a reactor pressure vessel,
Reference numeral 3 denotes a reactor building, 3a denotes a furnace room in which the reactor is housed, 4 denotes a chimney-type air ventilation duct as a heat sink provided outside the reactor chamber, and a surrounding area of the reactor pressure vessel 2 and an air ventilation duct 4
And a number of variable conductance heat pipes 5 (only one heat pipe is shown in the figure).

Here, the variable conductance heat pipe 5 is one in which an appropriate amount of non-condensable gas is positively sealed together with the working fluid in the heat pipe as described above. An evaporator 5a disposed opposite to the inner peripheral area of the furnace chamber 3a, and a condenser 5 positioned above the evaporator 5a and disposed in the air ventilation duct 4.
b, a gas reservoir 5c for the non-condensable gas described later connected to the downstream side of the condenser 5b, and a vapor diffusion passage 5d for the working fluid, which is connected between the evaporator 5a and the condenser 5b.
Further, it is configured as a separated thermosiphon comprising a condensed liquid recirculation passage 5e, and a heat insulating partition wall 5f separating the vapor diffusion passage 5d and the condensed liquid recirculation passage 5e. In addition, 5
g indicates a working fluid (for example, water) contained in the evaporator 5a, and 5g indicates a non-condensable gas.

With this configuration, the decay heat generated in the reactor core 1 is radiated to the surroundings from the reactor pressure vessel 2 as radiant heat, and is received by the evaporating section 5a of the variable conductance heat pipe 5. As a result, the working fluid 5g evaporates, and the vapor diffuses through the vapor diffusion passage 5d and moves to the condenser 5b as indicated by an arrow, from which the air flows through the air ventilation duct 4 through the heat transfer surface of the condenser 5b. After condensing by releasing heat
The evaporating / condensing cycle is repeated so that the evaporating / condensing flow returns to the evaporating section 5a by flowing down the reflux path 5e by its own weight. As a result, the decay heat of the reactor is radiated and removed to the heat sink outside the system through the condenser 5b of the heat pipe.

By the way, during normal operation of the nuclear reactor in which the heat input into the evaporating section 5a is relatively small, since the vapor pressure of the working fluid 5g in the heat pipe 5 is also small, the non-condensable gas 5h sealed in the heat pipe 5 As shown in FIG. 4, a part of the heat transfer surface of the condenser 5 b exits from the gas reservoir 5 c and partially blocks the heat transfer surface, thereby suppressing the effective heat dissipation capacity of the condenser 5 b. As a result, the amount of heat released to the outside of the system through the heat pipe 5 can be minimized. That is,
Heat loss during normal operation is negligible.

On the other hand, when the decay heat of the reactor increases due to the occurrence of an accident, the amount of heat input to the heat pipe 5 increases and the vapor pressure of the working fluid in the heat pipe increases, so that the non-condensable gas 5 h Is compressed by the vapor pressure, most of which is removed from the condenser 5b and pushed into the gas reservoir 5c. As a result, the effective heat transfer area of the condenser 5b is increased to increase the effective heat dissipation capacity, and the decay heat of the reactor is efficiently radiated to the heat sink outside the system.

[0015]

As described above, according to the decay heat removal system for a nuclear reactor according to the present invention, a variable conductance heat pipe is used as a heat pipe for decay heat removal, so that the heat input is relatively low. During normal operation of the reactor, the self-control characteristic of the variable conductance heat pipe minimizes the amount of heat radiated out of the system through the heat pipe, minimizing waste heat loss in the reactor plant, and When a large amount of heat is applied to the heat pipe as a thermal load, the heat conductance is automatically increased due to the self-control characteristics of the heat pipe, and the decay heat of the reactor is efficiently radiated out of the system to make the reactor safe. A decay heat removal system for the reactor that can provide effective heat dissipation characteristics in accordance with the normal operation / accident conditions of the reactor It can be provided.

Further, according to the configuration in which the variable conductance heat pipe is formed as a separate type thermosiphon and an additional reservoir of a non-condensable gas is provided downstream of the condenser, the condensation of the steam without the wick is achieved. The liquid can be returned from the condenser to the evaporator by gravity flow to simplify the structure, and in the operating state where the heat input to the evaporator is large, the non-condensable gas is pushed into the gas reservoir and the heat pipe It has excellent effects such as automatic switching of heat dissipation characteristics so that the heat dissipation capacity is maximized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a decay heat removal system corresponding to a first embodiment of the present invention.

FIG. 2 is a principle diagram of a normal heat pipe in a conventional decay heat removal system.

FIG. 3 is a principle diagram of a variable conductance heat pipe.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reactor core 2 Reactor pressure vessel 3 Reactor building 4 Atmospheric ventilation duct 5 Variable conductance heat pipe 5a Evaporator 5b Condenser 5c Gas reservoir 5e Vapor diffusion passage 5f Condensate flow passage 5g Working fluid 5h Non-condensable gas

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kazutaka Ohashi 1-1-1, Tanabe-Shinda, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fuji Electric Co., Ltd. (56) References JP-A-4-72597 (JP, A) 1992 (30th) Spring Annual Meeting Abstracts p. 423 “M33 Basic Study on Static Reactor Decay Heat Removal Method: (Part 3) Examination of Possibility of Decay Heat Removal System by Separate Thermosyphon” (58) Fields investigated (Int. Cl. ⁷⁾ , DB name) G21C 15/18 G21C 15/257 JICST file (JOIS)

Claims (4)

(57) [Claims] 1. A heat pipe is disposed between a peripheral region of a reactor vessel and an external heat sink, and decay heat of the reactor received by an evaporating portion of the heat pipe is transferred to a heat sink through a condensing portion of the heat pipe. A decay heat removal system for a nuclear reactor in which heat is dissipated, wherein a variable conductance heat pipe in which a non-condensable gas is sealed together with a working fluid in the pipe is used as the heat pipe. 2. The decay heat removal system according to claim 1, wherein the variable conductance heat pipe is provided between the evaporator and the condenser disposed above the evaporator, and a vapor diffusion passage for the working fluid.
A decay heat removal system for a nuclear reactor, wherein the decay heat removal system is configured as a separated thermosiphon that is connected by a condensate reflux passage and that contains an appropriate amount of non-condensable gas together with a working fluid therein. 3. A decay heat removal system for a nuclear reactor according to claim 2, wherein a gas reservoir functioning as a non-condensable gas reservoir is connected to the downstream side of the condensing section. 4. The decay heat removal system according to claim 2, wherein the condenser and the gas reservoir of the heat pipe are provided in a cooling air ventilation duct provided outside the reactor chamber. .