Patent Publication Number: US-2021174978-A1

Title: Dismantling and decontamination system and method of biodegradable concrete of pwr type nuclear power plant

Description:
TECHNICAL FIELD 
     The present disclosure relates to a dismantling and decontamination system and method of biodegradable concrete of a nuclear power plant. More particularly, the present invention relates to a dismantling and decontamination system and method of biodegradable concrete of a PWR type of nuclear power plant. 
     BACKGROUND ART 
     As fossil energy is depleted worldwide, nuclear power generation is being used as a major energy source. In such nuclear power generation, a generally-used pressurized water reactor (PWR) nuclear power plant consists of a primary system circulating in a nuclear reactor, a secondary system circulating in a steam generator, and a tertiary system circulating in a condenser. Specifically, in the primary system, a pressure is applied to a coolant contained in a reactor to maintain 150 atm and 300° C., and in the secondary system, the coolant boils water on the side of the steam generator while passing through the steam generator to generate steam to turn a turbine. In the tertiary system, the steam generated for turning the turbine passes through a condenser, becomes water again, and is sent to the steam generator. 
     The nuclear reactor of such a PWR type of nuclear power plant includes an external pressure vessel, and a nuclear reactor vessel composed of a core barrel that is formed with a smaller diameter than that of the pressure vessel and installed at the center of the pressure vessel. Inside the core barrel, the core into which a nuclear fuel rod is loaded is positioned, and a precipitation unit, which is a space of a ring shape due to the difference in diameter, is formed between the core barrel and the pressure vessel. In addition, a plurality of low temperature tubes that are connected to the pressure vessel and become circulation passages of cooling water, and a high temperature tube (hot leg) connected to the core barrel so that the cooling water heated while inflowing through the low temperature tubes and passing through the precipitation unit and the core flows toward the steam generator, are included. 
     In this PWR type of nuclear power plant, biodegradable concrete is installed as a reinforced concrete structure to protect against radiation exposure of workers by supporting the nuclear reactor and shielding neutrons. 
     The biodegradable concrete forms a large cylindrical reinforced concrete structure by stacking a plurality of layers and is highly radioactive by irradiation of neutrons, so if workers work in close proximity thereto, there is a risk of radiation exposure. Particularly, since the inner wall of the biodegradable concrete is severely contaminated with a radioactive material, when dismantling a pressurized light water reactor (PWR) type of nuclear power plant that has expired and is permanently stopped, a decontamination process of the inner wall of the biodegradable concrete is required. 
     However, for the decontamination process, if a worker forms a separate through-hole for inserting the decontamination device into the biodegradable concrete, there is a concern of radioactive exposure and movement of radioactive dust. 
     DISCLOSURE 
     Technical Problem 
     The present exemplary embodiment relates to a dismantling and decontamination system and method of biodegradable concrete of a nuclear power plant that may shorten the dismantling process time and a worker exposure. 
     Technical Solution 
     A dismantling and decontamination system of biodegradable concrete of a nuclear power plant according to an exemplary embodiment includes: a dismantling device for dismantling an in-core instrument installed under biodegradable concrete to form a lower penetrated part of the biodegradable concrete; a decontamination device inserted inside the biodegradable concrete for decontaminating radioactive waste of the inner wall of the biodegradable concrete; a waste receiving device movable through the lower penetrated part of the biodegradable concrete; and a blocking device for blocking the upper opening of the biodegradable concrete to block an outflow of the radioactive dust. 
     A dust collecting device connected to the dust blocking device and collecting the radioactive dust may be further included. 
     The waste receiving device may include: a receiving unit receiving radioactive waste; a receiving unit size adjusting unit for adjusting the size of the receiving unit; and a moving unit for moving the receiving unit. 
     In the lower penetrated part, the size of the receiving unit may be smaller than the diameter of the lower penetrated part, and in the biodegradable concrete, the size of the receiving unit may be smaller than the interior diameter of the biodegradable concrete. 
     The lower penetrated part of the biodegradable concrete may be connected to the interior of the biodegradable concrete. 
     The decontamination device may include an inner wall hammer or a scabbler. 
     The dust blocking device may include a tent or a shield. 
     A decontamination and dismantling method of biodegradable concrete of a nuclear power plant according to an exemplary embodiment includes: dismantling an in-core instrument installed under the biodegradable concrete by using a dismantling device to form a lower penetrated part of the biodegradable concrete; inserting a decontamination device inside the biodegradable concrete to decontaminate radioactive waste of the inner wall of the biodegradable concrete; and inserting the waste receiving device through the lower penetrated part of the biodegradable concrete inside the biodegradable concrete. 
     Blocking the upper opening of the biodegradable concrete by using a dust blocking device to block outflow of the radioactive dust may be further included. 
     Collecting the radioactive dust by using a dust collecting device connected to the dust blocking device may be further included. 
     The lower penetrated part of the biodegradable concrete may be connected to the interior of the biodegradable concrete. 
     Dismantling a nuclear reactor installed inside the biodegradable concrete before decontaminating the radioactive waste of the inner wall of the biodegradable concrete may be further included. 
     Advantageous Effects 
     According to an exemplary embodiment, during the decontamination and dismantling process of the biodegradable concrete of the nuclear power plant, the dismantling process time may be shortened by frequently inputting and drawing out the radioactive waste by using the lower penetrated part of the biodegradable concrete where the dismantled in-core instrument was disposed without taking out the radioactive waste to the upper opening of the biodegradable concrete, thereby efficiently carrying out the decontamination and dismantling process of the biodegradable concrete inner wall. 
     In addition, since the decontamination process of the biodegradable concrete inner wall is performed using the lower penetrated part of the biodegradable concrete, the exposure of workers to the radioactive dust may be reduced by maintaining the sealing of the upper part of the biodegradable concrete. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a dismantling and decontamination system of biodegradable concrete of a nuclear power plant according to an exemplary embodiment. 
         FIG. 2  is a top plan view showing a state in which a size of a receiving unit of a waste receiving device of  FIG. 1  is changed inside biodegradable concrete. 
         FIG. 3  is a flowchart of a decontamination and dismantling method of biodegradable concrete of a nuclear power plant according to an exemplary embodiment. 
         FIG. 4  is a view showing a step before dismantling biodegradable concrete of a nuclear power plant according to an exemplary embodiment. 
     
    
    
     MODE FOR INVENTION 
     The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. 
     In order to clearly explain the present invention, portions that are not directly related to the present invention are omitted, and the same reference numerals are attached to the same or similar constituent elements through the entire specification. 
     In addition, the size and thickness of each configuration shown in the drawings are arbitrarily shown for better understanding and ease of description, but the present invention is not limited thereto. 
     In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. In the drawings, for better understanding and ease of description, the thicknesses of some layers and areas are exaggerated. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. 
     In addition, unless explicitly described to the contrary, the word “comprise”, and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. Further, in the specification, the word “on” means positioning on or below the object portion, but does not essentially mean positioning on the upper side of the object portion based on a gravity direction. 
       FIG. 1  is a schematic diagram of a dismantling and decontamination system of biodegradable concrete of a nuclear power plant according to an exemplary embodiment. 
     As shown in  FIG. 1 , a dismantling and decontamination system of biodegradable concrete of a nuclear power plant according to an exemplary embodiment includes a dismantling device  5  dismantling an in-core instrument (ICI)  300  installed under biodegradable concrete  200 , a decontamination device  10  decontaminating radioactive waste  1  of the inner wall of the biodegradable concrete  200 , a waste receiving device  20  receiving the radioactive waste  1  decontaminated by the decontamination device  10 , a dust blocking device  30  blocking radioactive dust  3  generated during the decontamination of the radioactive waste  1 , and a dust collecting device  40  collecting the radioactive dust  3 . 
     The dismantling device  5  forms a lower penetrated part  210  under the biodegradable concrete  200  by dismantling the in-core instrument  300  installed from the lower part of the biodegradable concrete  200  to the inside of a nuclear reactor  100 . The lower penetrated part  210  of the biodegradable concrete  200  is the space where the in-core instrument (ICI)  300  of the biodegradable concrete  200  was positioned. The in-core instrument  300  is a device to measure an output distribution and combustibility of a nuclear fuel inside the nuclear reactor and to measure an outlet temperature of the core of the nuclear reactor  100  by detecting neutrons generated during the nuclear fission reaction process of the nuclear reactor  100 . 
     The decontamination device  10  is put into the inside of the biodegradable concrete  200 . The decontamination device  10  may include an inner wall hammer or a scabbler. The inner wall hammer hits the inner wall of the biodegradable concrete  200  to remove the radioactive waste  1  from the inner wall of the biodegradable concrete  200 . Further, the scabbler scrapes the inner wall of the biodegradable concrete  200  to remove the radioactive waste  1  from the inner wall of the biodegradable concrete  200 . In the present exemplary embodiment, the inner wall hammer or the scabbler has been described as an example of the decontamination device, but it is not limited thereto, and various devices are possible as long as it is a device for removing the radioactive waste  1  from the inner wall of the biodegradable concrete  200 . 
     The waste receiving device  20  may include a receiving unit  21  for receiving the radioactive waste  1 , a receiving unit size adjusting unit  22  for adjusting the size of the receiving unit  21  and a moving unit  23  for moving the receiving unit  21 . 
     As shown in  FIG. 2 , the size of the receiving unit  21  is adjustable. When passing through the lower penetrated part  210 , the size of the receiving unit  21  may be smaller than the diameter of the lower penetrated part  210  so that the receiving unit  21  may easily pass through the lower penetrated part  210 . Further, when being disposed inside the biodegradable concrete  200 , the size of the receiving unit  21  is expanded so that the receiving unit  21  may receive most of the radioactive waste  1  and may be smaller than the interior diameter of the biodegradable concrete  200 . 
     This waste receiving device  20  is movable through the lower penetrated part  210  of the biodegradable concrete  200 . The lower penetrated part  210  of the biodegradable concrete  200  may be connected to the interior of the biodegradable concrete  200  where the decontamination device  10  is positioned. 
     Thus, the waste receiving device  20  may be disposed under the decontamination device  10 . Therefore, the waste receiving device  20  may easily accommodate the radioactive waste  1  separated from the inner wall of the biodegradable concrete  200  by the decontamination device  10 . 
     As described above, when the decontamination process of the biodegradable concrete  200  of the nuclear power plant is in progress, the waste receiving device  20  may be easily inserted and taken out from time to time by using the lower penetrated part  210  of the biodegradable concrete  200  without the need to take out the radioactive waste  1  of the inner wall of the biodegradable concrete  200  to an upper opening  220 . Therefore, it is possible to shorten the decontamination process time of the inner wall of the biodegradable concrete  200 . 
     The dust blocking device  30  may block the upper opening  220  of the biodegradable concrete  200  to block the outflow of the radioactive dust  3 . The dust blocking device  30  may include a tent or a shield. In the present exemplary embodiment, the tent or shield has been described as an example of the dust blocking device  30 , but it is not limited thereto, and various devices for blocking the radioactive dust are possible. In addition, the dust blocking device  30  may further include a blocking adjusting unit for blocking or opening the upper opening  220  of the biodegradable concrete  200 . 
     In this way, when the decontamination and dismantling process of the inner wall of the biodegradable concrete  200  is performed using the lower penetrated part  210  of the biodegradable concrete  200 , the upper opening  220  of the biodegradable concrete  200  is kept sealed by using the dust blocking device  30 , thereby reducing worker exposure to the radioactive dust  3  and preventing the spread of the radioactive dust. 
     The dust collecting device  40  is connected to the dust blocking device  30  and is disposed outside the biodegradable concrete  200 . It is possible to secure a view inside the work part through the dust collecting device  40  using an exhaust fan. 
     Meanwhile, the decontamination and dismantling method of the biodegradable concrete of the nuclear power plant according to an exemplary embodiment of the present invention is described in detail below with reference to drawings. 
       FIG. 2  is a top plan view showing a state in which a size of a receiving unit of a waste receiving device of  FIG. 1  is changed inside biodegradable concrete, and  FIG. 3  is a flowchart of a decontamination and dismantling method of biodegradable concrete of a nuclear power plant according to an exemplary embodiment. 
     As shown in  FIG. 3  and  FIG. 4 , in the decontamination and dismantling method of the biodegradable concrete of the nuclear power plant according to an exemplary embodiment of the present invention, the in-core instrument  300  installed under the biodegradable concrete  200  is dismantled by using the dismantling device  5  to form the lower penetrated part  210  under the biodegradable concrete  200  (S 10 ). Since the in-core instrument  300  is connected to the nuclear reactor  100  through a plurality of cables, etc., the cables may be separated from the nuclear reactor  100  to physically separate the in-core instrument  300  from the nuclear reactor  100 . 
     At this time, the nuclear reactor  100  disposed inside the biodegradable concrete  200  is also dismantled by using a nuclear reactor dismantling device  6 . 
     Next, as shown in  FIG. 1  and  FIG. 3 , the decontamination device  10  is inserted inside the biodegradable concrete  200  to decontaminate the radioactive waste  1  of the inner wall of the biodegradable concrete  200  (S 20 ). Further, the waste receiving device  20  is inserted into the interior of the biodegradable concrete  200  through the lower penetrated part  210  of the biodegradable concrete  200  (S 30 ). At this time, the lower penetrated part  210  of the biodegradable concrete  200  may be connected to the interior of the biodegradable concrete  200 . Thus, the waste receiving device  20  may be disposed under the decontamination device  10 . Therefore, the waste receiving device  20  may easily accommodate the radioactive waste  1  of the inner wall of the biodegradable concrete  200  generated by the decontamination device  10 . 
     In addition, as shown in  FIG. 1 , the upper opening  220  of the biodegradable concrete  200  is blocked using the dust blocking device  30  to block the outflow of the radioactive dust  3 . At this time, the radioactive dust  3  may be collected using the dust collecting device  40  connected to the dust blocking device  30 . 
     As described above, when the decontamination process of biodegradable concrete  200  of the nuclear power plant is in progress, since the waste receiving device  20  may be easily input and taken out from time to time by using the lower penetrated part  210  of the biodegradable concrete  200  without the need to carry out the radioactive waste  1  of the inner wall of the biodegradable concrete  200  to the upper opening  220  of the biodegradable concrete  200 , the decontamination and dismantling process time of the inner wall of the biodegradable concrete  200  may be shortened. 
     While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.