Patent Description:
In general, among nuclear facilities used for nuclear power generation, a pressurized light water reactor type of nuclear power plant includes a reactor pressure vessel and a cavity in which the reactor pressure vessel is positioned, and includes biological shield concrete surrounding the reactor pressure vessel.

It is known from <CIT> to dismantle a nuclear facility that includes a nuclear reactor pressure vessel and a plurality of pipes directly connected to the nuclear reactor pressure vessel by cutting the pipes through the side penetration holes.

In decommissioning of a nuclear facility, it is necessary to expand a space above the cavity to secure a working space in order to easily separate the reactor pressure vessel from the biological shield concrete.

An exemplary embodiment provides a method for decommissioning a nuclear facility, which can easily cut pipes that are directly connected with a nuclear pressure vessel and surrounded by a biological shield concrete.

One aspect of the present invention provides a method for decommissioning a nuclear facility that includes a nuclear reactor pressure vessel, a plurality of pipes that are directly connected to the nuclear reactor pressure vessel, biological shield concrete that surrounds the plurality of pipes and the nuclear pressure vessel and includes a plurality of upper penetration holes that overlap the plurality of pipes, and a plurality of sandboxes that cover the plurality of upper penetration holes. The method includes: exposing the plurality of pipes through the plurality of upper penetration holes by removing the plurality of sandboxes; and cutting the plurality of pipes through the plurality of upper penetration holes.

The exposing the plurality of upper penetration holes may be carried out by removing a sealant that seals between the plurality of sandboxes and the upper portion of the biological shield concrete, and separating the plurality of sandboxes from the plurality of upper penetration holes.

The plurality of upper penetration holes may completely expose the plurality of pipes in a width direction.

The cutting the plurality of pipes may be carried out by cutting the plurality of pipes in the width direction by using a wire saw or a circular saw.

The method for decommissioning the nuclear facility may further include separating the nuclear pressure vessel from the biological shield concrete.

The nuclear reactor pressure vessel may be a pressurized water reactor.

According to the exemplary embodiment, a method for decommissioning a nuclear facility that can easily cut pipes that are directly connected to a nuclear pressure vessel and surrounded by a biological shield concrete can be provided.

Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawing so that a person of ordinary skill in the art to which the present invention belongs can easily implement it.

The present invention may be implemented in various different forms and is not limited to an exemplary embodiment described herein.

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.

Hereinafter, referring to <FIG>, a decommissioning method of a nuclear facility according to an exemplary embodiment will be described.

Hereinafter, a pressurized water reactor (PWR) type of nuclear power plant will be described as an example of a nuclear facility, but this is not restrictive, and the nuclear facility may be a boiling water reactor (BWR) type of nuclear power plant.

The PWR-type nuclear power plant uses light water as a coolant and a moderator, and uses uranium <NUM> concentrated to about <NUM> % to <NUM> % as nuclear fuel.

The PWR-type nuclear power plant may be divided into a facility related to the nuclear reactor system that sends heat generated by nuclear fission within the reactor to a steam generator for heat exchange, and a facility related to a turbine and a generator system which turns the turbine with the steam generated from the steam generator and condenses the steam to water through a condenser and then the water is circulated back to the steam generator.

In general, a coolant (light water), which is a heat transfer medium of a nuclear reactor system, is heated to about <NUM> in a nuclear reactor and pressurized to about <NUM> atmospheres so that it does not boil.

A device that forms the system includes a pressurizer that adjusts pressure to maintain constant enthalpy, and a coolant pump that circulates the coolant between the reactor and the steam generator.

The system in which the steam generated from the steam generator rotates the turbine and generates power from the generator connected to the turbine shaft may be the same as the principle of a general thermal power plant.

<FIG> is a flowchart of a decommission method of a nuclear facility according to an exemplary embodiment.

<FIG> are provided for description of the decommission method of the nuclear facility according to the exemplary embodiment.

First, referring to <FIG>, a plurality of pipes <NUM> are exposed through a plurality of upper penetration holes <NUM> by removing a plurality of sandboxes <NUM> (S100).

Specifically, referring to <FIG>, a nuclear facility <NUM> includes a nuclear reactor pressure vessel <NUM>, a plurality of pipes <NUM> that are directly connected with the nuclear reactor pressure vessel <NUM>, steam generators <NUM> that are connected with the nuclear reactor pressure vessel <NUM> through the pipes <NUM>, biological shield concrete <NUM> that support the nuclear reactor pressure vessel <NUM> while surrounding the nuclear reactor pressure vessel <NUM> and the pipes <NUM>, and a plurality of sandboxes <NUM>.

The nuclear reactor pressure vessel <NUM> may be a pressurized light-water reactor, but this is not restrictive.

For example, the nuclear reactor pressure vessel <NUM> may be a boiling water reactor.

The nuclear facility <NUM> may be formed in various shapes when it includes the nuclear reactor pressure vessel <NUM>, the pipes <NUM>, the biological shield concrete <NUM>, and the sandboxes <NUM>.

The biological shield concrete <NUM> includes a cavity where the nuclear reactor pressure vessel <NUM> is located, and a plurality of upper penetration holes <NUM> that expose the pipes <NUM> by overlapping the pipes <NUM>.

The upper penetration holes <NUM> of the biological shield concrete <NUM> may correspond to welding portions between the pipes <NUM> and nozzles of the nuclear reactor pressure vessel <NUM>, but this is not restrictive.

The sandboxes <NUM> cover the upper penetration holes <NUM>.

The sandboxes <NUM> may have a box shape filled with sand, but is not limited thereto.

An upper flange to be supported on an upper portion of the biological shield concrete <NUM> of the sandboxes <NUM> may be included, and the upper flange may be supported on the upper portion of the biological shield concrete <NUM>.

The sandboxes <NUM> are supported on the upper portion of the biological shield concrete <NUM>, and sealants may be provided between the sandboxes <NUM> and the upper portions of the biological shield concrete <NUM>.

The sandbox <NUM> may be a structure for easily checking the integrity of the pipe <NUM> that is directly connected to the nuclear reactor pressure vessel <NUM>.

For example, when the operation of the nuclear facility <NUM> is stopped, the sandboxes <NUM> are separated from the upper penetration holes <NUM> of the biological shield concrete <NUM>, and the integrity of the pipes <NUM> exposed by the upper penetration holes <NUM> can be checked.

The above described nuclear reactor pressure vessel <NUM>, the pipes <NUM>, the steam generator <NUM>, the biological shield concrete <NUM>, and the sandboxes <NUM> may be disposed in a containment vessel.

<FIG> shows the upper portion of the biological shield concrete of the nuclear facility.

Referring to <FIG>, the pipes <NUM> connected to the nuclear reactor pressure vessel <NUM> that is disposed in the cavity <NUM> of the biological shield concrete <NUM> include a first pipe <NUM>, a second pipe <NUM>, a third pipe <NUM>, and a fourth pipe <NUM>.

The first pipe <NUM> and the second pipe <NUM> are connected with one steam generator, and the third pipe <NUM> and the fourth pipe <NUM> are connected with another steam generator.

Hot water may pass through the first pipe <NUM> and the third pipe <NUM>, and cold water may pass through the second pipe <NUM> and the fourth pipe <NUM>, but this is not restrictive.

The upper penetration holes <NUM> of the biological shield concrete <NUM> are separated from each other in the upper portion of the biological shield concrete <NUM>.

The upper penetration hole <NUM> has a quadrangular shape on a plane.

The upper penetration holes <NUM> includes a first upper penetration hole <NUM>, a second upper penetration hole <NUM>, a third upper penetration hole <NUM>, and a fourth upper penetration hole <NUM>.

The first upper penetration hole <NUM> exposes the first pipe <NUM> by overlapping the first pipe <NUM>.

The second upper penetration hole <NUM> exposes the second pipe <NUM> by overlapping the second pipe <NUM>.

The third upper penetration hole <NUM> exposes the third pipe <NUM> by overlapping the third pipe <NUM>.

The fourth upper penetration hole <NUM> exposes the fourth pipe <NUM> by overlapping the fourth pipe <NUM>.

The upper penetration holes <NUM> completely expose the pipes <NUM> in the width direction of each pipe.

Specifically, the first upper penetration hole <NUM>, the second upper penetration hole <NUM>, the third upper penetration hole <NUM>, and the fourth upper penetration hole <NUM> respectively completely expose the first pipe <NUM>, the second pipe <NUM>, the third pipe <NUM>, and the fourth pipe <NUM> respectively in width directions of the respective pipes.

The sandboxes <NUM> are separated from each other in the upper portion of the biological shield concrete <NUM>.

The sandbox <NUM> has a quadrangular shape on a plane.

The sandboxes <NUM> include a first sandbox <NUM>, a second sandbox <NUM>, a third sandbox <NUM>, and a fourth sandbox <NUM>.

The first sandbox <NUM> is disposed inside the first upper penetration hole <NUM> and covers the first upper penetration hole <NUM>.

The second sandbox <NUM> is disposed inside the second upper penetration hole <NUM> and covers the second upper penetration hole <NUM>.

The third sandbox <NUM> is disposed inside the third upper penetration hole <NUM> and covers the third upper penetration hole <NUM>.

The fourth sandbox <NUM> is disposed inside the fourth upper penetration hole <NUM> and overs the fourth upper penetration hole <NUM>.

Each of the first sandbox <NUM>, the second sandbox <NUM>, the third sandbox <NUM>, and the fourth sandbox <NUM> may be a structure for determining integrity of each of the first pipe <NUM>, the second pipe <NUM>, the third pipe <NUM>, and the fourth pipe <NUM>.

For example, when the operation of the nuclear facility <NUM> is stopped, the first sandbox <NUM>, the second sandbox <NUM>, the third sandbox <NUM>, and the fourth sandbox <NUM> are respectively separated from the first upper penetration hole <NUM>, the second upper penetration hole <NUM>, the third upper penetration hole <NUM>, and the fourth upper penetration hole <NUM> of the biological shield concrete <NUM>, and integrity of each of the first pipe <NUM>, the second pipe <NUM>, the third pipe <NUM>, and the fourth pipe <NUM>, which are respectively exposed by the first upper penetration hole <NUM>, the second upper penetration hole <NUM>, the third upper penetration hole <NUM>, and the fourth upper penetration hole <NUM>, can be determined.

First, for decommissioning of the nuclear facility <NUM>, the plurality of sandboxes <NUM>, which are the first sandbox <NUM>, the second sandbox <NUM>, the third sandbox <NUM>, and the fourth sandbox <NUM> are respectively separated from the plurality of upper penetration holes <NUM>, which are the first upper penetration hole <NUM>, the second upper penetration hole <NUM>, the third upper penetration hole <NUM>, and the fourth upper penetration hole <NUM>.

In this case, the sealant provided between the sandboxes <NUM> and the biological shield concrete <NUM> is removed.

Thus, the plurality of upper penetration holes <NUM>, which are the first upper penetration hole <NUM>, the second upper penetration hole <NUM>, the third upper penetration hole <NUM>, and the fourth upper penetration hole <NUM>, are exposed, and the first pipe <NUM>, the second pipe <NUM>, the third pipe <NUM>, and the fourth pipe <NUM> are respectively exposed through the first upper penetration hole <NUM>, the second upper penetration hole <NUM>, third upper penetration hole <NUM>, and fourth upper penetration hole <NUM>.

The first pipe <NUM>, the second pipe <NUM>, the third pipe <NUM>, and the fourth pipe <NUM> are completely exposed in width directions of the respective pipes through the first upper penetration hole <NUM>, the second upper penetration hole <NUM>, the third upper penetration hole <NUM>, and the fourth upper penetration hole <NUM>.

Next, referring to <FIG>, the plurality of pipes <NUM> exposed through the plurality of upper penetration holes <NUM> are cut (S200).

Specifically, the pipes <NUM> completely exposed in the width direction through the upper penetration holes <NUM> are cut along virtual cut lines CL extending in the width direction of the pipes <NUM>.

The first pipe <NUM> exposed through the first upper penetration holes 4201is cut along a cut ling CL extending in a width direction of the first pipe <NUM>, the second pipe <NUM> exposed through the second upper penetration hole <NUM> is cut along a cut ling CL extending in a width direction of the second pipe <NUM>, the third pipe <NUM> exposed through the third upper penetration hole <NUM> is cut along a cut line CL extending in a width direction of the third pipe <NUM>, and the fourth pipe <NUM> exposed through the fourth upper penetration hole <NUM> is cut along a cut line CL extending in a width direction of the fourth pipe <NUM>.

The pipes <NUM> may be cut using a wire saw, but the present invention is not limited thereto, and the pipes <NUM> may be cut using other cutting means such as a circular saw.

Since the pipes <NUM> are completely exposed through the upper penetration holes <NUM> in the width direction, the pipes <NUM> can be easily cut through the upper penetration holes <NUM> by using a cutting means.

Next, referring to <FIG>, the nuclear reactor pressure vessel <NUM> is separated from the biological shield concrete <NUM> (S300).

Specifically, the nuclear reactor pressure vessel <NUM> of which the pipes connected thereto are cut is separated from the biological shield concrete <NUM> through the enlarged upper space of the cavity <NUM> of the biological shield concrete <NUM>.

In addition, since pipes connected with the reactor pressure vessel <NUM> are in the cut state through the upper penetration holes <NUM>, the reactor pressure vessel <NUM> can be easily separated from the biological shield concrete <NUM> without interference between the biological shield concrete <NUM> and the pipes.

In addition, since pipes connected with the reactor pressure vessel <NUM> and a steam generator are in the cut state through the upper penetration holes <NUM>, the steam generator can be easily separated from the biological shield concrete <NUM> without interference between the biological shield concrete <NUM> and the pipes.

As described, in the method for decommissioning the nuclear facility according to the exemplary embodiment, when the pipes <NUM> that are directly connected to the reactor pressure vessel <NUM> are cut, the pipes <NUM> are completely exposed in the width direction through the upper penetration holes <NUM> by separating the sandboxes <NUM> for determining integrity of the pipes <NUM> from the upper penetration holes <NUM> of the biological shield concrete <NUM>, which are provided for determining integrity of the pipes <NUM>, from the upper penetration holes <NUM> of the biological shield concrete <NUM> without forming separate holes in the biological shield concrete <NUM> such that a work space for cutting the pipes <NUM> can be assured, thereby easily cutting the pipes <NUM> connected with the nuclear reactor pressure vessel <NUM>.

In addition, in the method for decommissioning the nuclear facility according to the exemplary embodiment, the pipes <NUM> disposed inside the biological shield concrete <NUM> are cut through the upper penetration holes <NUM> that are exposed by separating the sandboxes <NUM>, and the nuclear reactor pressure vessel <NUM> and the steam generator are separated from the biological shield concrete <NUM> such that the decommission process time can be shortened by using the sandboxes <NUM> without performing separate work for decommissioning of the biological shield concrete <NUM>.

That is, a method for decommissioning the nuclear facility that can reduce time for decommissioning the nuclear facility and cost for decommission by easily cutting the pipes <NUM> that are directly connected to the nuclear pressure vessel <NUM> and surrounded by the biological shield concrete <NUM> is provided.

Claim 1:
A method for decommissioning a nuclear facility (<NUM>) that includes a nuclear reactor pressure vessel (<NUM>), a plurality of pipes (<NUM>) that are directly connected to the nuclear reactor pressure vessel (<NUM>), biological shield concrete (<NUM>) that surrounds the plurality of pipes (<NUM>) and the nuclear pressure vessel (<NUM>) and includes a plurality of upper penetration holes (<NUM>) that are separated from each other in the upper portion of the biological shield concrete (<NUM>) and overlap the plurality of pipes (<NUM>), and a plurality of sandboxes (<NUM>) that cover the plurality of upper penetration holes (<NUM>), wherein the upper penetration holes (<NUM>) serve to check the integrity of the pipes (<NUM>) when exposed, the method comprising:
exposing the plurality of pipes (<NUM>) through the plurality of upper penetration holes (<NUM>) by removing the plurality of sandboxes (<NUM>); and
cutting the plurality of pipes (<NUM>) through the plurality of upper penetration holes (<NUM>).