KR20220118653A - Passive Ex-vessel Water Flooding System - Google Patents

Abstract

The present invention relates to a passive guard vessel flooding system. More specifically, the passive guard vessel flooding system includes: a nuclear reactor vessel including nuclear fuel and lead-bismuth coolant; at least one lower pipe provided in a lower part of the nuclear reactor vessel, and receiving a flood from the outside due to a pressure difference with the outside; at least one upper pipe provided in an upper part of the nuclear reactor vessel, and discharging the flood as steam due to heat delivered from an outer wall of the nuclear reactor vessel; and a guard vessel housing the nuclear reactor vessel at a predetermined distance from the outer wall of the nuclear reactor vessel such that the flood introduced from the lower pipe can flow toward the upper pipe. Therefore, the present invention is capable of cooling an extremely heated nuclear reactor vessel.

Description

Passive Ex-vessel Water Flooding System

The present invention relates to a passive type guard vessel filling system, and more particularly, to a passive type guard vessel filling system capable of safely removing heat from a nuclear reactor by having a passive safety system applicable to a marine environment.

A nuclear reactor refers to a device that can be used for various purposes, such as generating heat by artificially controlling the chain fission reaction of fissile materials, or producing radioactive isotopes and plutonium. When a nuclear fission reaction occurs in a nuclear reactor, the released energy generates a lot of heat and the temperature of the core increases. If it is not cooled properly, there is a risk of damage to the reactor.

Currently, various studies on the development of various small modular reactors based on light water reactors are underway around the world. Small modular reactors are generally referred to as reactors with an electrical output of 300 MWe or less.

In the case of an existing light water reactor, an accident of loss of coolant may occur, and an additional device is required to remove the decay heat generated after the reactor is shut down. If the coolant loss accident occurs, since the nuclear fuel is exposed to the air, if the core cooling function is not restored within a short time, it will lead to a serious accident in which the core is melted.

Therefore, in the case of a light-water reactor-based small modular reactor, as in a large-scale LWR, various safety systems such as a residual heat removal system and a safety injection system are required to prepare for decay heat removal and coolant loss accidents after the reactor is shut down.

Related Document 1 relates to a small modular nuclear reactor core having multiple fissile layers and a nuclear reactor having the same. Because it does not have a passive safety system applicable to the marine environment, there is an unavoidable limit of additional power consumption to operate the safety system.

KR 10-1633493

The present invention is intended to solve the above problems, and it is possible to cool the extremely heated reactor vessel passively or for a long time without a separate power supply device and a pump. An object of the present invention is to obtain a passive-type guard vessel filling system having an inlet lower pipe and an upper pipe in which the filling water is discharged as steam by the heat transferred from the outer wall of the reactor vessel.

In addition, it is an object of the present invention to solidify at room temperature in the reactor vessel so that the radiation material does not move more than a predetermined distance even when the reactor vessel is melted, and thus can prevent the occurrence of an exposure accident in which people are exposed to the radiation material. It is to provide a passive guard vessel filling system comprising a lead-bismuth coolant.

In order to achieve the above object, the passive guard vessel filling system of the present invention is a reactor vessel containing nuclear fuel and a lead-bismuth coolant, at least one is provided in the lower part of the reactor vessel, At least one introduced lower pipe, one or more is provided on the upper part of the reactor vessel, and the upper pipe through which the supplemental water is discharged as steam by the heat transferred from the outer wall of the reactor container, and the upper pipe and the supplemental water introduced from the lower pipe in the direction of the upper pipe Provided is a guard vessel accommodating the reactor vessel at a predetermined distance from the outer wall of the reactor vessel so as to be movable.

As described above, according to the present invention, a lower pipe through which supplemental water is introduced from the outside due to a pressure difference with the outside and an upper pipe through which supplemental water is discharged as steam by heat transferred from the outer wall of the reactor vessel are provided, and an offshore plant, By applying to structures including ships and submarines, there is an effect that it is possible to cool the extremely heated reactor vessel passively or in the long term without a separate power supply device and a pump.

In addition, the present invention is provided with a lead-bismuth coolant that solidifies at room temperature in the reactor vessel, so that even if the reactor vessel is melted, the radiation material does not move more than a predetermined distance, and thus people are exposed to the radiation material. It has the effect of preventing it from happening.

1 is a configuration diagram of a passive-type guard vessel filling system according to an embodiment of the present invention.
2 is a graph showing the critical heat flux phenomenon.
3 is a graph comparing the performance of a passive type guard vessel filling system and a previously verified pressurized water reactor according to an embodiment of the present invention.

The terms used in this specification have been selected as currently widely used general terms as possible while considering the functions in the present invention, which may vary depending on the intention or precedent of a person skilled in the art, the emergence of new technology, and the like. In addition, in a specific case, there is a term arbitrarily selected by the applicant, and in this case, the meaning will be described in detail in the description of the corresponding invention. Therefore, the term used in the present invention should be defined based on the meaning of the term and the overall content of the present invention, rather than the name of a simple term.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. does not

Hereinafter, an embodiment according to the present invention will be described in detail with reference to the accompanying drawings. 1 is a block diagram of a passive-type guard vessel filling system according to an embodiment of the present invention.

Referring to FIG. 1 , the passive guard vessel filling system 100 of the present invention includes a reactor vessel 110 , a lower pipe 120 , an upper pipe 130 , and a guard vessel 140 .

More specifically, the reactor vessel 110 contains nuclear fuel and a lead-bismuth coolant.

Nuclear fuel is a material used as a fuel to produce energy through nuclear fission, and uranium isotopes uranium-235, uranium-238, and plutonium-239 may be included. These materials can be formed in one of oxide, metallic and liquid forms.

In addition, the lead-bismuth coolant may be solidified so that the radiating material does not leak out. The reactor vessel 110 may include a lead-bismuth coolant. Among many types of coolant, using the lead-bismuth coolant in liquid form has a melting point of 123 degrees, so the internal temperature of the reactor vessel 110 is It is liquid in liquid form at about 300 degrees Celsius, but when exposed to room temperature around 20 degrees, it solidifies by itself and has the effect of not leaking radiation.

Next, at least one of the lower pipes 120 is provided at the lower portion of the reactor vessel 110 , and supplemental water is introduced from the outside due to a pressure difference with the outside. At this time, the basic state of the lower pipe 120 is a closed state so as not to be filled through the lower pipe 120 . The lower pipe 120 is not limited to a specific size, shape, or number.

The passive guard vessel filling system 100 may most preferably be used as a power source for offshore plants, ships and submarines, and thus the use environment may be below the surface of the sea or river. That is, when the lower pipe 120 is opened, supplemental water may be passively introduced by the pressure difference with the outside. In this case, the added water may be seawater or river water. Therefore, even in a situation in which the power supply is cut off, the vessel is overturned, or the vessel is collapsing sideways because the added water is automatically introduced into the lower pipe 120 provided in the lower part of the reactor vessel 110 without a separate power supply device and a pump. It has the effect of enabling reliable core cooling and removal of residual heat.

Next, one or more upper pipes 130 are provided on the upper portion of the reactor vessel 110 , and the added water is discharged as steam by the heat transferred from the outer wall of the reactor vessel 110 . The basic state of the upper pipe 130 is a closed state so that the steam is not discharged through the upper pipe 130 . The upper pipe 130 is not limited to a specific size, shape, and number.

In addition, the upper pipe 130 may be installed in structures including offshore plants, ships and submarines so that only the steam can be discharged without passively flowing in due to a pressure difference with the outside. . This is to maximize heat transfer efficiency.

And when the upper pipe 130 is opened, the added water may absorb heat transferred from the outer wall of the reactor vessel 110 and then phase change into the vapor. In addition, since hot steam generally rises from the bottom, the steam passively absorbing heat may be discharged to the outside even if a separate power supply device and a pump are not provided.

Next, the guard vessel 140 is spaced a predetermined distance from the outer wall of the reactor vessel 110 so that the appended water introduced from the lower pipe 120 can move in the direction of the upper pipe 130 , and the reactor vessel (110) is accepted.

That is, the guard vessel 140 is not limited to a specific size and shape, and the outer wall of the reactor vessel 110 is sufficient to ensure a flow rate of the added water capable of cooling the extremely heated reactor vessel in the event of an accident. may be spaced at a predetermined distance from

Meanwhile, the present invention may further include a control unit 150 for controlling the opening and closing of at least one of the upper pipe 130 and the lower pipe 120 .

Here, the control unit 150 determines whether an accident has occurred according to the temperature of the reactor vessel 110, and opens the upper pipe 130 and the lower pipe 120 that were closed at the time of the accident. do.

That is, the control unit 150 can quickly determine whether the temperature of the outer wall of the reactor vessel 110 is above a preset temperature due to a loss of coolant accident in which the reactor vessel 110 is melted and nuclear fuel is exposed or a cooling system failure accident, etc. and an accident may have occurred.

Most preferably, the control unit 150 simultaneously opens the upper pipe 130 and the lower pipe 120 that were closed when an accident occurs.

According to the present invention, by applying to structures including offshore plants, ships, and submarines, there is an effect that it is possible to cool the extremely heated reactor vessel passively or in the long term without a separate power supply device and a pump.

In addition, since a lead-bismuth coolant that solidifies at room temperature is provided in the reactor vessel 110 , the radiation material does not move beyond a predetermined distance even when the reactor vessel 110 is melted, thereby exposing people to the radiation material It has the effect of preventing accidents from occurring.

Example 1

Experimental conditions and methods

There are two major factors that threaten the soundness of the reactor vessel 110 . One is a factor related to melting and ablation of the reactor vessel 110 . If the temperature of the inner wall of the reactor vessel 110 is high and continuously melts, the thickness of the reactor vessel 110 may decrease, which may lead to loss of soundness. This means that the guard vessel 140 filling strategy fails due to high temperature, and the temperature of the reactor vessel 110, specifically, the inner wall of the reactor vessel 110 in contact with the contents melts expected to be the highest. It presents the need for temperature analysis.

The second factor is the inability to remove residual heat due to loss of cooling capacity and loss of integrity due to melting of the reactor vessel 110 . Coolability at the outer wall of the reactor vessel 110 may be limited by a phenomenon called Critical Heat Flux (CHF).

2 is a graph showing a critical heat flux (CHF) phenomenon. Referring to FIG. 2 , when the heat flux (CHF) at the boiling surface increases above a certain level, the heating surface is overturned by air bubbles, which is the vapor covering the heating surface in efficient nuclear boiling accompanied by a phase change of the working fluid on the heating surface. It is transitioned to inefficient membrane boiling, which transfers heat to the surrounding working fluid through conduction and radiation of the membrane. Here, the boiling surface is the outer wall of the reactor vessel 110 in which the charged water is phase-changed into the vapor.

This transition from nucleate boiling to membrane boiling causes a large decrease in the heat transfer capacity, which can be expressed as a decrease in the heat transfer coefficient. When considering Newton's cooling law, which is the following [Equation 1], in general, when q is, that is, when the output acts as a variable, when the heat transfer coefficient h decreases, the area A is the same, so ΔT corresponding to the temperature difference is will increase Therefore, after the critical heat flux (CHF) phenomenon, the temperature of the heating surface greatly increases up to several thousand degrees, which is expressed as a loss of cooling ability. Through this, we need to analyze the boiling heat transfer phenomenon in the outer wall of the reactor vessel by focusing on the heat flux.

That is, in order to prove the reliability of the present invention, it is necessary to analyze the temperature of the inner wall of the reactor vessel 110 related to the soundness of the reactor vessel 110 and the heat flux of the outer wall of the reactor vessel 110 related to the limit of the cooling capacity. The analysis was also conducted focusing on these two variables.

To evaluate the cooling potential of the guard vessel filling system, an internal MATLAB code using the one-dimensional lumped capacity method (LCM) was utilized.

First, various physical properties or constants are input, and a dimensionless number related to the heat transfer coefficient is calculated by estimating the initial value. Based on this, the bulk heat transfer coefficient is calculated and then the temperature is calculated. Thereafter, dimensionless numbers are again calculated using the calculated temperature, and this process is repeated until the calculated temperature value falls below the convergence criterion.

After the overall temperature is calculated and the calorific balance of the entire system is calculated, calculations are performed for each detailed layer, the light metal layer in which the internal structure of the reactor vessel is melted, the oxide layer in which the nuclear fuel is melted, and the lead-bismuth coolant layer). will do

In the calculation of each layer, a correlation formula was prepared to take into account the vertical heat flux and temperature deviation. The following [Equation 2] is an equation for calculating the thermal balance of the overall system, and [Equation 3] is an equation for calculating the thermal balance in the light metal layer.

The heat balance in the lead-bismuth coolant layer was calculated by approximating it with heat transfer fins, since natural convection hardly occurs in the case of top heating and bottom and side cooling considering its structure.

The heat transfer between the inner wall and the outer wall of the reactor vessel 110 was calculated by the following [Equation 4].

Boiling heat transfer at the outer wall was simulated using the general Rosenow correlation equation in [Equation 5] below.

Experiment result

3 is a graph comparing the performance of the passive-type guard vessel filling system 100 and the verified pressurized light water reactor according to an embodiment of the present invention. Prior to the performance analysis, the results of the verified pressurized water reactor were derived to show the correctness of the methodology, and this was displayed as a black graph (Reference). The results according to an embodiment of the present invention are displayed as a red graph (Benchmark).

As can be seen in FIG. 3 , it can be confirmed that the verified pressurized water reactor and the result value of an embodiment of the present invention show similar result values. Therefore, the reliability of the passive guard vessel filling system according to an embodiment of the present invention was proved.

As described above, although the embodiments have been described with reference to the limited embodiments and drawings, various modifications and variations are possible by those skilled in the art from the above description. For example, the described techniques are performed in a different order than the described method, and/or the described components of the system, structure, apparatus, circuit, etc. are combined or combined in a different form than the described method, or other components Or substituted or substituted by equivalents may achieve an appropriate result.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

100.. Passive guard vessel filling system
110.. Reactor Vessel
120.. Bottom piping
130.. Top piping
140.. Guard Vessel
150.. Controls

Claims (3)

a reactor vessel containing nuclear fuel and lead-bismuth coolant;
a lower pipe provided at least one lower part of the reactor vessel and through which supplemental water is introduced from the outside by a pressure difference with the outside;
an upper pipe provided at least one upper portion of the reactor vessel, and through which the added water is discharged as steam by the heat transferred from the outer wall of the reactor vessel; and
and a guard vessel accommodating the reactor vessel at a predetermined distance from the outer wall of the reactor vessel so that the filling water introduced from the lower pipe can move in the direction of the upper pipe. The method of claim 1,
Further comprising; a control unit for controlling the opening and closing of at least one of the upper pipe and the lower pipe;
The control unit is
A passive type guard vessel filling system, characterized in that determining whether an accident has occurred according to the temperature of the reactor vessel, and opening the closed upper pipe and lower pipe when the accident occurs. The method of claim 1,
The lead-bismuth coolant comprises:
A passive-type guard vessel filling system, characterized in that it is solidified so that the radiation material does not leak out.

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