WO2003063177A1

WO2003063177A1 - Direct vessel injection system for emergency core cooling water using vertical injection pipe, sparger, internal spiral threaded injection pipe, and inclined injection pipe

Info

Publication number: WO2003063177A1
Application number: PCT/KR2003/000161
Authority: WO
Inventors: Kune-Yull Suh; Sang-Hyuk Yoon
Original assignee: Philosophia, Inc.
Priority date: 2002-01-24
Filing date: 2003-01-24
Publication date: 2003-07-31
Also published as: KR100572046B1; KR20030064634A

Abstract

The present invention pertains to a system for injecting emergency core cooling water in which the emergency cooling water injected through a safety injection pipe can flow into the reactor downcomer in a vertical direction by attaching a vertical pipe to the safety injection pipe horizontal with a reactor vessel, or installing a sparger; a system for injecting the emergency core cooling water in which the safety injection pipe is installed at the upper head of a reactor vessel to maximize the momentum of the injected water in a vertical direction; a system for injecting the emergency core cooling water to maximize the efficiency that the emergency cooling water can flow into a reactor downcomer in that spiral threads are provided at the inlet of a vertical pipe for injecting the water and thereby the water injected is rotated with less steam resistance; and a system for emergency core cooling water in which a safety injection pipe is installed at a predetermined angle to a reactor vessel wall, so that the injected cooling water can flow in at a predetermined angle to a reactor downcomer, in a pressurized water reactor, a boiling water reactor, or an advanced reactor by the direct vessel injection (DVI) by which the emergency cooling water is injected through the safety injection pipe installed separately from a cold leg.

Description

DIRECT VESSEL INJECTION SYSTEM FOR EMERGENCY CORE COOLING WATER USING VERTICAL INJECTION PIPE, SPARGER, INTERNAL SPIRAL THREADED INJECTION PIPE, AND INCLINED

INJECTION PIPE

Technical Field

The present invention relates to a direct vessel injection (DVI) system of a nuclear reactor for injecting emergency core cooling water using a vertical injection pipe, a sparger, spiral threads at the inner surface of an injection pipe, an inclined pipe, and a safety injection pipe installed at the upper head of the reactor, and more particularly to a system for injecting the emergency core cooling water into the reactor vessel downcomer utilizing a horizontal safety injection pipe with a vertically downward elbowed tip, a sparger, an injection pipe spirally threaded on the inner surface, an injection pipe connected vertically at the upper head of a nuclear reactor, rather than on the side thereof, for the purpose of enhancing the emergency core coolant penetration capability into the core, or an injection pipe installed at an angle to the reactor vessel wall to allow for the cooling water to flow into the downcomer at a predetermined angle, in a pressurized water reactor (PWR), a boiling water reactor (BWR) or an advanced reactor using a DVI system for which the emergency core cooling water is injected through the safety injection pipe installed separately from a cold leg or a hot leg.

Background Art

Nuclear reactors resort on reactions within the atomic nuclei to produce energy. In a PWR that uses light water as the coolant that acts as a medium for transporting the thermal energy generated by the nuclear reaction within nuclear fuel, the pressure inside the reactor is maintained high enough to prevent the coolant from boiling in the reactor vessel, while in a BWR the coolant is allowed to boil in the reactor vessel to produce steam directly. When designing a nuclear power plant with such a PWR or BWR, hypothetical accidents which may hardly take place in actuality are considered for the safety analysis thereof. One of these hypothetical accidents is the so-called loss-of-coolant accident (LOCA), in which the pressure boundary of the reactor coolant system is breached, causing the coolant to flow out of the system.

When such a LOCA occurs in a reactor, fuel rods which are usually submerged in the coolant during normal operation are uncovered, which in turn suddenly increases the temperature on the fuel rod surfaces. Therefore, to cope with accidents like LOCA that may result in overheating and potential melting of the fuel rods in the nuclear reactor, the so-called Engineered Safety Features (ESFs) are installed that allow the emergency core cooling water to be injected at high pressure from a tank or a pump into the reactor vessel when the coolant in the reactor is depleted, whose feature is commonly called the Emergency Core Cooling System (ECCS).

The cold leg injection (CLI) or DVI is applied for injecting emergency cooling water into the core of the nuclear reactor utilizing a safety injection system for the reactor. Conventionally, the safety injection trains are used for injecting the emergency cooling water through a cold leg by connecting the safety injection nozzles to each of the cold legs. When designing the conventional CLI system, the safety injection system consists of two safety injection trains, onto each of which a high-pressure safety injection (HPSI) pump and a low-pressure safety injection (LPSI) pump are arranged, so that the emergency core cooling water can be injected through the remaining unbroken cold legs even if one of the cold legs is broken or one of the two safety injection trains fails. According to the Probabilistic Safety Assessment (PSA) for a nuclear power plant, it has been found that when the safety injection system is designed as a mechanical four-safety injection train system, the safety in a nuclear power plant is significantly improved as compared with a two-safety injection train system. If the safety injection system is designed as a four-safety injection train system and if the cold leg injection is applied, the number of HPSI and LPSI pumps required is four, respectively, in order to supply the sufficient amount of coolant required for the emergency core cooling. On the contrary, if the DVI is adopted in this case, it is possible to design the system with pumps of a smaller capacity than the conventional safety injection capacity for an accident in which the cold legs are broken. In case the safety injection nozzles are connected to the cold legs as in the conventional ECCS, when the cold legs are broken, the emergency cooling water that must flow into the reactor core through the safety injection nozzles may flow out of the break prior to reaching the downcomer. That is, since the emergency cooling water flowing in through the safety injection nozzles is mixed with the coolant that flows backward through the cold legs due to a pressure differential between the reactor core and the break and thus flows out through the break in the cold legs together with the coolant, the emergency cooling water cannot flood the core.

Recently, in view of such aforementioned problems, as shown in Fig. 3, a method has been proposed to connect the safety injection pipes directly to a nuclear reactor vessel to allow for the emergency core cooling water to flow directly into the reactor vessel, so that the emergency cooling water does not flow out of the primary system through the break in the cold legs. Therefore, the emergency cooling water has a higher potential to submerge the core. To summarize, the safety injection pipes are connected directly to the reactor vessel to allow for the emergency core cooling water to be injected directly into the vessel in the DVI method.

In the System 80+™, a U.S. advanced type PWR, the ECCS is designed with the DVI utilizing a four-safety injection train system. The U.S. Electric Power Research Institute (EPRI) recommended designing the safety injection in an emergency core cooling system with direct injection into a downcomer in the reactor vessel, rather than the conventional CLI in the Advanced Light Water Reactor Utility Requirements Document (ALWR URD). In conformity with the recommendation, the DVI was employed for injecting the emergency core cooling water when designing the APR1400 (Advanced Power Reactor 1400MWe) in Korea.

However, it was found that the emergency cooling water may bypass through the break even in the aforementioned DVI system. Namely, if the safety injection pipes are situated higher than the cold legs, a considerable amount of the emergency cooling water injected through the safety injection pipes may bypass through the break in the cold legs together with the coolant which flows backward into the cold leg, while flowing down along the internal wall of the reactor vessel when the cold leg, which is an inlet pipe for the coolant, is broken. If the safety injection pipes are positioned lower than the cold leg, however, the emergency cooling water at a low temperature injected through the safety injection pipes suddenly strikes onto the reactor vessel at a high temperature and high pressure, causing a pressurized thermal shock (PTS) so that the reactor vessel 1 may be damaged. In particular, when the safety injection pipes are broken, even more coolant may flow out through the safety injection pipes than the case in which the direct vessel injection nozzle 6 is attached to the cold leg nozzle 2.

To overcome the aforementioned problems, the U.S. Patent No. 5135708, titled

"Method of Injection to or near Core Inlet", discloses a method to install a cylindrical or tubular safety injection channel from the safety injection pipe above the cold leg to the bottom of the core support inside the vessel to maximize the effect of the safety injection.

By the above method, it is possible to supply the emergency cooling water directly to the bottom of the downcomer when a cold leg is broken. However, when the safety injection pipes outside the reactor vessel are broken, the coolant in the reactor continues to flow out by the siphon effect until the reactor core gets fully uncovered, which results in a serious situation in which the amount of the coolant for preventing the core from melting lacks.

The Korean Patent publication No. 10-0319068, titled "Safety Injection Train in Reactor for Blocking Siphon Effect and Contact with Steam Flow", discloses a direct injection nozzle positioned at a higher location than a cold leg of the nuclear reactor and connected to the reactor with a gap, wherein the direct injection nozzle has a safety injection pipe to allow for the emergency cooling water from the injection nozzle to bypass the reactor inlet nozzle and to be injected into the lower plenum of the reactor vessel, so as to minimize the amount of emergency cooling water flowing out through the cold leg, to block the siphon effect by which the coolant continues to flow out through the safety injection pipe and to prevent contact with steam flow, which happens when the cold leg that is an inlet pipe of coolant is broken.

The above Korean patent discloses that such a nozzle blocks the siphon effect through the gap, but it is difficult to block the siphon effect due to the safety injection pipe for injecting the emergency core cooling water at a lower location than the cold leg in the reactor vessel, and a PTS may also occur because the safety injection pipe injects the cooling water at a location overly adjacent to the core.

Disclosure of Invention It is an object of the present invention to efficiently prevent the siphon effect and PTS, using a direct vessel injection system for injecting emergency core cooling water through a vertical pipe, a sparger, a threaded pipe, and an inclined injection pipe.

It is another object of the present invention to increase the amount of the emergency cooling water that flows into the lower plenum without bypassing due to the steam injected from a cold leg by increasing the downward momentum of the cooling water through direct vertical injection, thus solving the problem that the emergency core cooling water could not flow into the reactor core because a considerable amount of cooling water flows out through a break when injecting the emergency core cooling water. More particularly, it is an object of the direct vessel vertical injection according to the present invention to allow for the emergency cooling water to more efficiently and stably flow into a lower plenum through a downcomer than the conventional horizontal injection so as to keep the temperature of fuel rods under a predetermined value in a nuclear reactor, which employs direct injection of the emergency core cooling water when a LOCA occurs in a nuclear steam supply system (NSSS). Since the cooling water injected horizontally into a reactor vessel flows into the reactor vessel in the circumferential direction in the usual DVI, a considerable amount of the cooling water cannot flow into the lower plenum but is directed to bypass through a break by means of vertically rising steam from the lower portion of the downcomer. It is another object of the DVVI (Direct Vessel Vertical Injection) to significantly increase the vertical momentum of the emergency cooling water and to reduce the risk of uncovering fuel rods due to bypass of the emergency cooling water by preventing impingement where the emergency cooling water strikes on the inner wall of the downcomer and spreads in the circumferential direction. It is still another object of the present invention to contribute significantly to securing the safety of a nuclear reactor when the present invention is applied to a DVI system employed in the APR1400.

Further objects and application of the present invention will be apparent to those skilled in the art from the following detailed description of the invention.

Hereinafter, a DVI system for injecting the emergency core cooling water using vertical pipes, spargers, internal spirally threaded injection pipes, and inclined injection pipes according to the invention, and a DVI system in which such pipes for injecting the emergency core cooling water are installed at the upper head of a reactor vessel will be described in detail with reference to the accompanying drawings.

In a PWR, a BWR or an advanced reactor with safety injection of a DVI system for injecting the emergency core cooling water using a vertical pipe, a sparger, an internal spirally threaded injection pipe, and an inclined injection pipe according to the present invention and of a DVI system in which such pipes for injecting the emergency core cooling water are installed at the upper head of a reactor vessel, the reactor comprises an emergency core cooling water injection system. This system allows for the cooling water entering through the safety injection pipe to flow into the core in a vertical direction by attaching a vertical pipe to the safety injection pipe horizontal with a reactor vessel or installing a sparger, or allows the injected cooling water to flow into the core with less steam resistance by providing spiral threads in the injection pipe, and an emergency core cooling water system in which the safety injection pipe is installed at an angle to the wall of the reactor vessel to allow for the cooling water to flow into the core at a predetermined angle or to maximize the vertical momentum of the injected water by installing the safety injection pipe at the upper head of the reactor, for efficient injection of the emergency cooling water.

Brief Description of the Drawings

These and other features, aspects, and advantages of the present invention will become apparent to those skilled in the art through the following description of exemplary embodiments, illustrated in the appended drawings. In the drawings:

Fig. 1 is a schematic view of an embodiment of a direct vessel vertical injection (DWI) of a nuclear reactor according to the present invention; Fig. 2 is a sectional view of a DVVI for APR1400;

Fig. 3 is a schematic diagram of an embodiment of cold leg injection (CLI) and DVI;

Fig. 4 is a schematic view of an embodiment of a DVVI using a protection disk, where Fig. 4a shows the protection disk installed in the reactor downcomer, and Fig. 4b is a partially enlarged three-dimensional view illustrating the conical disk as an embodiment of the protection disk;

Fig. 5 shows DVVI using a sparger according to an embodiment of the invention, where Fig.5(a) is a bottom perspective view of the sparger installed in the nuclear reactor, Fig.5(b) is a top perspective view of the sparger installed in the reactor and Fig. 5(c) is a schematic sectional view of the sparger;

Fig. 6(a) is a sectional view of an embodiment of an inclined DVI, and Fig. 6(b) is a sectional view of an embodiment of a horizontal DVI to compare against the inclined DVI in Fig. 6(a); Fig. 7 is a perspective view illustrating the spirally threaded injection pipe for injecting the emergency cooling water;

Fig. 8 is a top view showing an emergency core cooling water injection pipe (DVI pipe) according to one embodiment of the invention installed at the upper head of a nuclear reactor; Figs. 9(a) and 9(b) are perspective views of a downcomer using the CFX code for a multidimensional flow analysis of (a) horizontal injection and (b) vertical injection for the direct vessel injection according to one embodiment of the invention;

Fig. 10 compares the downward velocity distributions between (a) the horizontal injection and (b) the vertical injection predicted by the CFX multidimensional flow analysis code according to the downcomer models illustrated in Figs. 9(a) and 9(b), respectively;

Fig. 11 shows distributions of the iso-velocities by the horizontal injection and the vertical injection through the multidimensional flow test;

Fig. 12 shows a schematic diagram for the arrangement of downcomer nozzles used for the multidimensional flow analysis; Fig. 13 compares the velocity distributions depending on the height from a safety injection pipe by DVI and DVVI when the emergency core cooling water is injected through each nozzle of Fig. 12; and

Fig.14 compares the velocity distributions by (a) the horizontal injection and (b) the vertical injection integrated from the graphs of Fig. 13.

Best Mode for Carrying out the Invention

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Fig. 1 shows a system for injecting the emergency core cooling water, in which a vertical pipe 6 is attached to a safety injection pipe 4 horizontal with a reactor vessel to allow for the cooling water injected through the safety injection pipe 4 to flow into the reactor downcomer in a vertical direction, in a PWR, a BWR or an advanced reactor 1 with direct injection of the emergency core cooling water in which the emergency cooling water is injected through the safety injection pipe 4 installed separately from a cold leg 2.

The safety injection pipe 4 is located above the cold leg 2. The location is selected so as to prevent the cooling water from flowing out through the safety injection pipe when the safety injection pipe is broken in case where the safety injection pipe 4 is located lower than the cold leg 2, as aforementioned in the prior art. The reactor vessel of the present system employs the same structure as the conventional horizontal DVI system outside the reactor but has a further structure for vertical injection unlike the structure for the horizontal injection inside the reactor. Such a vertical pipe 6 has almost the same diameter as that of the safety injection pipe 4 and the lower end of the vertical pipe 6 is located above the upper end of the cold leg 2.

Since the vertical pipe 6 has almost the same diameter as that of the safety injection pipe 4, the horizontal momentum of the injected emergency cooling water gets transformed to the vertical momentum without loss at the vertical pipe 6, so that the emergency cooling water can easily penetrate the downcomer. If the diameter of the vertical pipe 6 is smaller than that of the safety injection pipe 4 or the width of the downcomer, the cooling water may flow out by the siphon effect through the vertical pipe 6. To prevent such outflow, the diameter of the vertical pipe 6 is designed to take almost the same value as that of the safety injection pipe 4. The length of the vertical pipe 6 may vary within the range that the lower end of the vertical pipe 6 does not extend lower than the top of the cold leg 2. If the lower end of the vertical pipe 6 is located lower than the top of the cold leg 2, the cooling water flows into the reactor at a location overly proximate to the core, thereby possibly causing a pressurized thermal shock (PTS). When the safety injection pipe 4 is broken, the cooling water flows out through the safety injection pipe 4 that must supply the cooling water, until the level of the cooling water in the reactor vessel recedes below the lower portion of the vertical pipe 6, and even the cooling water which flows in through the cold leg 2 may also flow out through the safety injection pipe. Since more cooling water thereby flows out, the cooling water is depleted to the extent proper cooling of the heated reactor core is jeopardized.

Fig. 2 is a schematic view for vertical injection of the emergency cooling water into the APR1400 vessel, which is an example of a nuclear reactor according to the invention that illustrates the shape and dimensions of the entire reactor to show the installation height of a safety injection pipe to which a vertical pipe is attached.

Fig. 3 is a schematic diagram of an embodiment for illustrating the cold leg injection and the direct vessel injection, and shows a safety injection pipe 4 for the direct injection and the safety injection trains 3 connected to cold leg 2 according to the prior art. As seen in Fig. 3, in case where the safety injection trains 3 are connected to the cold legs, the emergency cooling water cannot reach the reactor vessel and flows out through a break when a cold leg is broken. On the contrary, the direct vessel injection does not have such a risk. Fig. 4 shows a schematic diagram of an embodiment for a direct vessel vertical injection (DVVI), using a protection disk. More specifically, Fig. 4(a) shows a diagram of a nuclear reactor in which the protection disk is installed, and Fig. 4(b) shows a partially enlarged diagram illustrating the attached conical disk that is an embodiment of the protection disk. As shown in Fig. 4(a), the protection disk 7 is attached to the inlet of the vertical pipe 6 to minimize steam resistance and maximize the inflow of cooling water into the reactor core. The disk 7 is installed at the inlet of the vertical pipe 6 to minimize resistance by upcoming steam and maximize penetration of the emergency cooling water into the core, since a considerable amount of steam may be generated from the overheated core which is not being properly cooled, and the steam in turn acts against injection of the emergency core cooling water into the core when a LOCA occurs. Fig. 4(b) shows an embodiment of such a conical protection disk which is fixed at the inlet of the vertical pipe 6 using three supporting bars. Use of such a conical disk minimizes resistance by the upcoming steam to the flow of the injected cooling water into a downcomer.

Figs. 5(a) through 5(c) show diagrams illustrating the vertical injection using a sparger 10 according to one embodiment of the invention. Fig. 5(a) is a bottom perspective view of the sparger 10 installed in the reactor. Fig. 5(b) is a top perspective of the sparger 10 installed in the reactor. Fig. 5(c) shows schematically the cross section of the sparger 10.

Figs. 5(a) and 5(b) show an embodiment according to the invention to combine the direct injection from the upper head of the reactor with the injection using the sparger 10. A toroidal pipe installed at the location where the emergency core cooling water is injected serves for the water to be uniformly sprinkled in a downcomer.

Fig. 5(c) discloses a system for injecting the emergency core cooling water by installing a sparger 10 on the safety injection pipe horizontal with a reactor vessel to allow for the cooling water injected through the safety injection pipe to flow into the downcomer in a vertical direction, in a PWR, a BWR, or an advanced reactor with safety injection of a DVI system for injecting the emergency core cooling water through a safety injection pipe installed separately from a cold leg.

Figs. 6(a) and 6(b) show sectional views of an embodiment according to the invention for the inclined injection of cooling water. The present invention, as shown in Fig. 6(a), discloses a system for injecting the emergency core cooling water in which a safety injection pipe 4 is installed at an angle to the reactor vessel wall so that the injected cooling water may flow into a core at a predetermined angle, in a PWR, a BWR, or an advanced reactor with direct vessel injection for injecting the emergency core cooling water through a safety injection pipe 4 installed separately from a cold leg 2. The angle θ may vary within the range from 0° to 90°. As the angle θ increases, more efficient inflow of the cooling water into the core is achieved. However, the structure of a nuclear reactor is complicated, which renders adding such a safety injection pipe with greater angles difficult enough. In such a case, it is also possible to apply the present invention by installing a horizontal structure outside the reactor vessel and then inclining the safety injection pipe within the downcomer through which the emergency cooling water actually flows at an angle onto the inner wall of the reactor downcomer.

Fig. 6(b) shows a sectional view of an embodiment for the horizontal injection of cooling water in a conventional manner in comparison to the inclined injection in Fig. 6(a). As seen from the flow of the emergency cooling water on the diagram, when the emergency cooling water is injected horizontally, the water spreads circumferentially before reaching the core at the lower part of the reactor and thus the temperature of the fuel rods in the core rises. Therefore, it is noted that in terms of achieving adequate cooling of the core by the emergency cooling water, the inclined injection according to the invention is preferred to the conventional horizontal injection. Fig. 7 shows a three-dimensional diagram illustrating spirally threaded injection pipe for supplying the emergency cooling water. The spiral threads grooved on the inner surface of the emergency cooling water injection pipe causes the injecting water to be rotated, achieving efficient inflow of water into the core with greater penetrability, as in the case of a rotated bullet fired from a fire arm. Fig. 8 is a top view illustrating a direct injection pipe for injecting the emergency core cooling water according to an embodiment of the invention installed at the upper head of a nuclear reactor.

It is possible to maximize the vertical momentum of cooling water by installing an injection pipe for the emergency cooling water at the upper head of the reactor vessel, rather than on the side of the vessel as in the prior art. As shown in Fig. 8, the injection pipe installed at the upper head according to an embodiment of the invention is made by attaching a vertical pipe to the horizontal direct injection pipe. The direct injection pipe installed at the upper head of the reactor is highly effective in that it can be combined with the structures according to the invention, such as a vertical pipe, a sparger, an inclined injection pipe and internal spirally threaded injection pipe.

Hereinafter, results of simulation will be presented to demonstrate the effect of the vertical injection according to the invention in comparison with the conventional horizontal injection.

A simulation was carried out to compare the conventional horizontal injection in the direct vessel injection (DVI) of the emergency core cooling water through a safety injection pipe, instead of a cold leg, against the direct vessel vertical injection (DVVI) for injecting the cooling water through a safety injection pipe having a vertical pipe attached thereto. Results of the multidimensional flow simulation are presented for the horizontal injection and the vertical injection. Such simplistic code analysis, which partly depends on models not necessarily supported by experimental results, nonetheless provides enough information about how the multidimensional flow actually develops in a downcomer. The CFX code used in the analysis of the multidimensional flow is a well-known commercial computational fluid dynamics tool, and the analysis was carried out by means of simple virtual replicas of a downcomer as shown in Fig. 9. The analysis was performed for a turbulent flow in a three-dimensional, orthogonal coordinate system. For this analysis the assumption of incompressible fluid was applied and the gravity effect was taken into account. Only the single-phase liquid flow was considered. The system pressure was set equal to the atmospheric pressure, the system temperature to 350K, the temperature of the emergency cooling water to 288K and the individual injection velocity to 12m/s. The vector distribution of the emergency cooling water for two types of (a) horizontal injection and (b) vertical injection of Fig. 9 is shown in Fig. 10. It is seen that the downward velocity distribution is more pronounced in the vertical injection.

Fig. 11 shows the contours of the iso-velocities in a flow field on the assumption that the initial injection velocity of the emergency cooling water is 12m/s, wherein (a) shows the iso-velocity contour for flow velocity of 2.5m/s in the horizontal injection;

(b) shows the iso-velocity contour for flow velocity of 2.5m/s in the vertical injection;

(c) shows the iso-velocity contour for flow velocity of 5m/s in the horizontal injection;

(d) shows the iso-velocity contour for flow velocity of 5m/s in the vertical injection; (e) shows the iso-velocity contour for flow velocity of lOm/s in the horizontal injection; and (f) shows the iso-velocity contour for flow velocity of lOm/s in the vertical injection. The difference between the vertical injection and the horizontal injection becomes more apparent when the iso-velocity contours for (a), (c), (e) and (b), (d), (f) are examined. That is, in the vertical injection, a high downward velocity contour extends more broadly than in the horizontal injection. In particular, as seen from (c) and (d), the contour in which the emergency cooling water in the flow field is at 5m/s is shown to be broader in the vertical injection, which signifies that the vertical injection is a secure method to maximize downward penetration of the emergency cooling water so that it can reach a core.

Results of the analysis for the vertical and horizontal injection of the emergency cooling water can be evaluated for their comparative integral performance only when performance of individual injection pipes are examined and compared.

Fig. 12 shows a schematic diagram of an arrangement of downcomer nozzles used in the analysis and the break in a cold leg. Fig. 13 shows velocity distributions depending on heights from each DVI line (DVI 1, 2, 3 and 4). Fig. 13(a) illustrates velocity distributions in the horizontal injection (DVI 1) and the vertical injection (DVVI 1) for the injection line 1. Fig. 13(b) shows velocity distributions depending on heights in the horizontal injection (DVI 2) and the vertical injection (DVVI 2) for the injection line 2. Fig. 13(c) shows velocity distributions depending on heights in the horizontal injection (DVI 3) and the vertical injection (DVVI 3) for the injection line 3. Fig. 13(d) shows velocity distributions depending on heights in the horizontal injection (DVI 4) and the vertical injection (DVVI 4) for the injection line 4. The highest velocity is indicated at the injection point of the emergency cooling water by the DVI, and a break in the cold leg is located at about 5.5m in height. Fig. 14 presents velocity distributions in each of the injection lines for the vertical and horizontal injections, respectively. Fig. 14(a) shows velocity distributions in each line in the horizontal injection, and Fig. 14(b) shows velocity distributions in each line in the vertical injection. For the horizontal injection in Fig. 14(a), it is shown that the emergency cooling water reaches a core with a large velocity difference at the break amongst the injection pipes, whereas for the vertical injection in Fig. 14(b), the cooling water reaches the core without a significant velocity difference at the break amongst the injection pipes.

As such, comparison of results between the vertical and horizontal injections demonstrate advantage of the vertical injection over the horizontal injection in terms of performance and safety in that the emergency cooling water by the vertical injection reaches the reactor core more efficiently than by the horizontal injection.

As aforementioned, a system for injecting the emergency core cooling water directly into a reactor vessel using a vertical pipe, a sparger, an internal spirally threaded injection pipe, and an inclined injection pipe of the invention, and a direct injection system where such injection pipes are installed at the upper head of a reactor vessel employ passive injection for which the gravity is used when injecting the emergency core cooling water into the core. Therefore, according to the invention, it is possible to prevent degradation of performance in the direct vessel injection system due to thermal hydraulic phenomena such as impingement, breakup and bypass that take place in a downcomer of the reactor vessel after injecting the emergency core cooling water, and to allow for the emergency core cooling water to flow more efficiently and stably into the lower plenum than by the convention horizontal injection. The invention can contribute significantly to improving economics as well as enhancing safety in a system of a nuclear power plant. It is undesirable from the economics point of view to design a large-capacity ESF that would not be used at all in most cases during the life time of a nuclear power plant. Since it is possible to ensure safety even by injecting relatively a small amount of the emergency core cooling water according to the invention, it is possible to reduce the size of an arrangement that occupies larger areas than required, when designing the arrangement, so that the initial construction cost can be reduced.

Also, the invention can be applied to the Generation IV Nuclear Energy System currently under development through international collaboration amongst ten countries. The present invention has been described in detail. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

Claims

1. An emergency core cooling water injection system in a pressurized water reactor, a boiling water reactor or an advanced reactor with direct vessel injection (DVI) by which the emergency cooling water is injected through a safety injection pipe installed separately from a cold leg, wherein the emergency core cooling water injected through the safety injection line flows into a reactor downcomer in a vertical direction by attaching a vertical pipe to the safety injection pipe horizontal with a reactor vessel.

2. The system as claimed in claim 1, wherein the vertical pipe has approximately the same diameter as that of the safety injection pipe and the lower end of the vertical pipe is located above the top of the cold leg.

3. The system as claimed in claim 1, wherein a protection disk is attached at the inlet of the vertical pipe to minimize steam resistance and to maximize penetration of the emergency cooling water into the reactor downcomer.

4. The system as claimed in claim 3, wherein the protection disk is a conical disk which is installed at and spaced apart from the inlet of the vertical pipe and whose central part is convex.

5. The system as claimed in claim 1, wherein spiral threads are provided on the inner surface of the vertical pipe so that the injected emergency cooling water can be rotated.

6. A system for injecting emergency core cooling water in a pressurized water reactor, a boiling water reactor, or an advanced reactor with safety injection of the DVI by which the emergency cooling water is injected through a safety injection line installed separately from a cold leg, wherein the emergency cooling water injected through the safety injection pipe flows into a reactor downcomer in a vertical direction through a toroidal sparger with a plurality of holes formed on the lower circumferential surface.

7. A system for injecting emergency core cooling water in a pressurized water, boiling water or advanced reactor with safety injection of DVI by which emergency cooling water is injected through a safety injection pipe installed separately from a cold leg, wherein the safety injection pipe is installed at an angle to a reactor vessel wall so that the emergency cooling water can flow into a reactor core at a predetermined angle.

8. A system as claimed in any of claims 1 through 7, wherein the safety injection pipe is installed at the upper head of the reactor vessel.