JP2012251894A - Reactor core molten material retainer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reactor core molten material retainer for mitigating a degree of thermal damages that can be generated in a reactor container and suppressing soundness decline of the reactor container more than before.SOLUTION: A first reactor core molten material retainer 30A is positioned below a reactor pressure vessel 1, is formed in a pedestal area surrounded by a cylindrical pedestal sidewall 5 supporting the reactor pressure vessel 1 and a pedestal floor 9, and includes a heat resistance material 8 for retaining a core molten material in the pedestal area and a cooling flow path provided between the heat resistant material 8 and the pedestal floor 9 for supplying a coolant. The cooling flow path includes a water supply header 7 to which the coolant is supplied, a riser flow path 32 formed in a circumferential direction along an inner peripheral surface of the pedestal sidewall 5, and cooling channels 31 that are a plurality of parallel flow paths whose one end is connected with the water supply header 7 and other end is connected with the riser flow path 32.

Description

  The present invention relates to a core melt holding device.

  FIG. 10 is a vertical sectional view of a reactor containment vessel 2 equipped with a conventional core melt holding device (core catcher) 4.

  In a water-cooled nuclear reactor, when cooling water is lost due to the stoppage of water supply to the reactor pressure vessel 1 or the breakage of piping connected to the reactor pressure vessel 1, the reactor water level drops and the core is exposed. Cooling may be insufficient. Assuming such a case, the reactor is automatically shut down in response to a water level lowering signal, and the core is submerged and cooled by injecting coolant using an emergency core cooling system (ECCS), and a core melting accident is performed. It is designed to prevent it.

  However, although the probability is very low, it is possible to assume a situation in which the emergency core cooling device does not operate and water injection devices for other cores cannot be used. In such a case, the core is exposed due to a decrease in the reactor water level, and sufficient cooling is not performed, and the fuel rod temperature rises due to decay heat that continues to occur after the reactor shuts down, eventually leading to core melting. It is possible.

  When the core melts, the high-temperature core melt (corium) melts into the lower part of the reactor pressure vessel 1 supported by the pedestal side wall 5 in the reactor containment vessel 2, and further, the reactor pressure vessel lower head 3 is melted and penetrated to fall on the floor in the reactor containment vessel 2. Corium that has fallen to the floor heats the concrete stretched on the floor of the containment vessel 2, reacts with the concrete when the contact surface reaches a high temperature, and generates a large amount of noncondensable gases such as carbon dioxide and hydrogen. Melt and erode concrete.

  The generated non-condensable gas increases the pressure inside the containment vessel 2 and may cause damage to the containment vessel 2, and the containment vessel structure may be damaged by melting and erosion of concrete. There is a possibility of reducing the strength. As a result, if the reaction between corium and concrete continues, the reactor containment vessel 2 is damaged, and there is a risk that radioactive materials in the reactor containment vessel 2 are released to the outside environment.

  In order to suppress this reaction between corium and concrete, the corium is cooled and the temperature of the contact surface with the concrete at the bottom of the corium is cooled below the erosion temperature (under 1500K for general concrete), or It is necessary to avoid direct contact. For this reason, various countermeasures have been proposed in case the core melt falls. A typical one is called a core melt holding device 4, which is a facility that receives the dropped core melt with a heat-resistant material and cools the core melt in combination with water injection means.

  Even if cooling water is poured onto the top surface of the core melt that has fallen on the floor of the reactor containment vessel 2, if the heat removal amount at the bottom of the core melt is small, the temperature at the bottom of the core melt remains high due to decay heat The concrete erosion of the floor of the containment vessel 2 cannot be stopped. In view of such circumstances, for example, as described in Non-Patent Documents 1 and 2, an apparatus for removing heat from the bottom surface by introducing cooling water to a cooling water flow path provided below the corium deposition floor surface And methods have been proposed.

Rick Wawiak, “Management of Severe Accentent Phenomena in the ESBWR Design,” Regulation Information Conference 2006, Severe Accident Research. 7, 2006 M.M. Jahn and H.M. H. Reineke, “Free convection heat transfer with internal heat sources calculations and measurements,” Proc. 5th Int. Heat Transfer Conf. , Tokyo Japan, Paper NC 2.8, pp. 74-78, 1974

  11 is a top view of the conventional core melt holding device 4, FIG. 12 is a cross-sectional view of the conventional core melt holding device 4 taken along the line III-III (FIG. 11), and FIG. 13 is a conventional core melt holding device 4. It is the arrow line view seen from the direction of arrow B (FIG. 11).

  The core melt holding device 4 is installed in a pedestal region surrounded by the pedestal side wall 5 and the pedestal floor 9. The cooling channel 6 and the feed water header 7 are installed on the base member 10 at the top of the pedestal floor 9. The base member 10 is a member that constitutes the core melt holding device 4 and is a member that supports the cooling channel 6 and the water supply header 7.

  The core melt holding device 4 supplies a coolant such as cooling water to a cooling channel 6 and a water supply header 7 as cooling channels disposed in the device, and cools the heat-resistant material 8 holding corium. The coolant is supplied to a water supply header 7 of a horizontal straight pipe that passes through the center of a substantially circle that appears when viewed from above, and cooling channels 6 that are inclined to the water supply header 7 are arranged in parallel. The cooling channel 6 is constituted by, for example, a pipe such as a circular pipe, and one end is connected to the water supply header 7 at a right angle, the other end is bent vertically upward along the pedestal side wall 5, and opens upward. Be placed. On the upper surface of the cooling channel 6, a heat-resistant material 8 for protecting the cooling channel 6 from the heat of the core melt (corium) is laid.

  As shown in FIGS. 11 and 12, while the cooling channel 6 is arranged without any gap immediately below the heat-resistant material 8 with which the corium contacts, as shown in FIG. There is a region (region near the center in the left-right direction) where the cooling channel 6 is not partially disposed.

  FIG. 14 is a diagram showing a heat flux distribution from corium deposited in the hemispherical shell of the conventional core melt holding device 4 to the hemispherical shell surface. The right semicircle shows a cross section of the hemispherical shell of the core melt holding device 4, and φ (0 ≦ φ ≦ 90) degrees (deg) is a straight line drawn downward from the center o of the semicircle. The angle of circumference.

  In general, in a natural convection heat transfer system with internal heat generation, the heat flux tends to be higher at a higher spatial position (as φ shown in FIG. 14 is closer to 90 degrees). In other words, the heat flux is predicted to be higher on the corium side surface than on the corium lower surface.

  However, in the conventional core melt holding device 4, there is a region where the cooling channel 6 does not exist on the surface corresponding to the corium side surface, and heat removal from the portion may be insufficient. When the heat removal of corium is insufficient, the heat-resistant material 8 is melted and corroded by corium, and when the heat-resistant material 8 progresses, the pedestal sidewall 5 may be damaged. As a result, the reactor containment vessel 2 Soundness may be reduced and damage may occur.

  Further, it is known that the flow stability of the boiling two-phase flow in the flow path having parallel channels in which the cooling channels 6 are arranged in parallel depends on the flow path pressure loss change with respect to the flow rate change.

  FIG. 15 is a graph showing the relationship between flow rate and pressure loss in a system in which non-uniform flow rate distribution occurs.

  In a system in which the pressure loss increases as the flow rate increases, the flow distribution to the multichannel flow path is stable. However, in a system in which the pressure loss decreases as the flow rate increases, flow rate fluctuations occur, and the flow rate distribution in the parallel channel flow paths becomes unstable and non-uniform. That is, as in a region x shown in FIG. 15, a region where the pressure loss decreases as the flow rate increases is a non-uniform flow rate generation region where the flow distribution becomes unstable and non-uniform.

  In the core melt holding device 4 having the parallel flow path, when the flow rate becomes unstable and non-uniform, the cooling channel 6 with the reduced flow rate does not sufficiently remove the heat from the corium, and the pedestal is heated with the heat from the corium. The side wall 5 may be damaged. As a result, the soundness of the reactor containment vessel 2 may not be sufficiently maintained.

  The present invention has been made in view of the above-described problems, and eliminates a region that is not cooled (non-cooled region) on the corium side surface, and mitigates flow channel instability in parallel channels. An object of the present invention is to provide a core melt holding device that alleviates the degree of thermal damage that can occur in a vessel and suppresses the deterioration of the soundness of a containment vessel.

  In order to solve the above-described problems, a core melt holding device according to an embodiment of the present invention is positioned below a reactor pressure vessel and surrounded by a cylindrical pedestal side wall and a pedestal bed that support the reactor pressure vessel. In the core melting and holding apparatus formed in the pedestal region, a heat-resistant material that holds the core melt in the pedestal region, a cooling channel that is provided between the heat-resistant material and the pedestal bed, and supplies a coolant, The cooling flow path includes a feed header to which a coolant is supplied, an intermediate header formed in a circumferential direction along an inner peripheral surface of the pedestal side wall, one end connected to the feed header, and the other. It has a plurality of parallel flow paths whose ends are connected to the intermediate header.

  According to the present invention, the degree of thermal damage that can occur in a reactor containment vessel can be mitigated as compared with the prior art, and a decrease in soundness of the reactor containment vessel can be suppressed.

1 is a top view of a core melt holding device according to a first embodiment of the present invention. Sectional drawing in the II line | wire (FIG. 1) of the core melt holding | maintenance apparatus which concerns on the 1st Embodiment of this invention. Schematic of the 1/4 sector (FIG. 1) of the core melt holding | maintenance apparatus which concerns on the 1st Embodiment of this invention. The schematic diagram of the core melt maintenance device (1/4 sector) concerning a 2nd embodiment of the present invention. The top view of the core melt holding | maintenance apparatus which concerns on the 3rd Embodiment of this invention. The schematic diagram of the core melt maintenance device (1/4 sector) concerning a 3rd embodiment of the present invention. The schematic diagram of the core melt maintenance device (1/4 sector) concerning a 4th embodiment of the present invention. The top view of the core melt holding | maintenance apparatus which concerns on the 5th Embodiment of this invention. Sectional drawing in the II-II line (FIG. 8) of the core melt holding | maintenance apparatus which concerns on the 5th Embodiment of this invention. The elevation sectional view of the reactor containment vessel provided with the conventional core melt maintenance device (core catcher). The top view of the conventional core melt holding | maintenance apparatus. Sectional drawing in the III-III line (FIG. 11) of the conventional core melt holding | maintenance apparatus. The arrow view seen from the direction of arrow B (Drawing 11) of the conventional core melt maintenance device. The figure which shows the heat flux distribution from the corium deposited in the hemispherical shell of the conventional core melt holding | maintenance apparatus to the said hemispherical shell surface. A graph showing the relationship between flow rate and pressure loss in a system where non-uniform flow distribution occurs.

  Hereinafter, a core melt holding device according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[First Embodiment]
FIG. 1 is a top view of a first core melt holding device 30A, which is an example of a core melt holding device according to the first embodiment of the present invention, and FIG. A sectional view taken along line I (FIG. 1), and FIG. 3 is a schematic view of a quarter sector (symbol A surrounded by a broken line shown in FIG. 1) of the first core melt holding device 30A. Note that substantially the same components as those of the conventional apparatus shown in the drawing (FIGS. 10-15) referred to in the description of the background art are denoted by the same reference numerals, and the description thereof is omitted.

  The first core melt holding device 30A is different from the conventional core melt holding device 4 in that the inclined straight pipe portion of the tubular cooling channel 31 is in contact with the inner peripheral side of the pedestal side wall 5 (inclined The riser flow that is a flow path in which the riser portion raised upward along the wall surface of the pedestal side wall 5 at the end of the pipe portion is communicated between the cooling channels 31 and is made to make a round along the inner circumference of the pedestal side wall 5 It differs in that it is configured as a path 32.

  That is, the first core melt holding device 30A is formed in a pedestal region surrounded by the substantially cylindrical pedestal side wall 5 that supports the reactor pressure vessel and the pedestal floor 9 below the reactor pressure vessel. The heat-resistant material 8 that holds the core melt in the pedestal region, and a cooling channel that is provided between the heat-resistant material 8 and the pedestal floor 9 and that supplies the coolant. The water supply header 7 to which the coolant is supplied, the riser flow path 32 as an intermediate header formed in the circumferential direction along the inner peripheral surface of the pedestal side wall 5, the water supply header 7 and one end are connected, and the other end Has a cooling channel 31 constituting a plurality of parallel flow paths connected to the riser flow path 32.

  The cooling channel 31 and the water supply header 7 are installed on the base member 10 above the pedestal floor 9. The base member 10 is a member that constitutes the first core melt holding device 30 </ b> A, and is a member that supports the cooling channel 31 and the water supply header 7.

  For example, as shown in FIG. 1, the cooling channel 31 is arranged in parallel with a water supply header 7 formed of a substantially horizontal straight pipe passing through the central portion of a corium holding surface formed in a substantially circular shape. Each cooling channel 31 is disposed with an inclination in a direction rising from the water supply header 7 toward the pedestal side wall 5 as shown in FIG. 1, for example.

  The riser flow path 32 is a flow path that makes a round along the inner periphery of the pedestal side wall 5 at the end of the inclined straight pipe portion of the cooling channel 31. For example, as shown in FIG. It is formed to appear in an annular shape. The riser flow path 32 has a predetermined height along the pedestal side wall 5 so as to form a riser portion that rises at the outer peripheral end of the holding surface that holds the core melt (corium). Composed.

  In the first core melt holding device 30 </ b> A, coolant such as cooling water flowing through the feed water header 7 is guided to the cooling channel 31, and is further present uniformly over the entire circumference along the inner circumference of the pedestal side wall 5. It is guided to the annular riser channel 32. The riser flow path 32 is substantially annular along the inner periphery of the pedestal side wall 5 when viewed from above, and forms a riser portion having a desired height substantially perpendicular to the outer periphery of the corium holding surface. The riser flow path 32 cooled by the coolant being guided cools the corium dropped on the corium holding surface from the side surface.

  Further, in the first core melt holding device 30 </ b> A, the parallel channel section of the cooling channel 31 has a length corresponding to the height of the riser flow path 32 with respect to the cooling channel 6 of the conventional core melt holding device 4. Shorten by minutes. This is because the behavior of the system in which the pressure loss decreases as the flow rate increases depends on the fluid property value, heat transfer amount, heat transfer surface length, and flow path shape, and generally the longer parallel channel section becomes unstable. This solves the problem that it is easy, and fluctuations in the flow rate of parallel channels are suppressed more than in the past.

  In the first core melt holding device 30A configured as described above, since the riser flow path 32 exists uniformly on the outer periphery of the corium holding surface, no matter where the corium falls on the corium holding surface, Preheating from the side can be performed without unevenness.

  Further, the first core melt holding device 30A has a riser flow path having a flow path area larger than that of the cooling channel 31 at the end of the inclined straight pipe portion located on the downstream side of the cooling channel 31 where the two-phase pressure loss increases. By providing 32, the flow rate can be reduced and the pressure loss can be reduced, so that the natural circulation of the coolant can be promoted.

  Further, since the lower end portion of the riser flow path 32, that is, the end of the inclined straight pipe portion of the cooling channel 31, becomes the pressure boundary of the parallel channel, the section of the parallel channel is higher than the conventional core melt holding device 4. The length corresponding to the height of the flow path 32 is shortened, and the flow rate fluctuation of the parallel channel can be suppressed as compared with the conventional case.

  According to the first core melt holding device 30A, the corium falling on the corium holding surface can be uniformly and sufficiently cooled, and the heat-resistant material 8 can be melted when heat removal from the corium is insufficient. Erosion can be avoided, the degree of thermal damage that can occur in the reactor containment vessel can be mitigated, and deterioration in the integrity of the reactor containment vessel can be suppressed.

[Second Embodiment]
FIG. 4 is a schematic diagram of (1/4 sector) of the second core melt holding device 30B which is an example of the core melt holding device according to the second embodiment of the present invention.

  The second core melt holding device 30B is different from the first core melt holding device 30A in that ribs 33 are further provided in the riser flow path 32, but the other points are substantially different. do not do. Therefore, in the description of the second embodiment, the difference from the first core melt holding device 30A will be mainly described, and the same components as those in the first core melt holding device 30A will be denoted by the same reference numerals. The description is omitted.

  The second core melt holding device 30 </ b> B is provided with ribs 33 in the riser flow path 32 as deformation preventing members that prevent the riser flow path 32 from being deformed when a physical external force such as thermal stress is applied. The rib 33 provided in the riser flow path 32 suppresses the deformation amount of the riser flow path 32 even when thermal stress is applied to the riser flow path 32 by absorbing the heat of corium.

  Further, the rib 33 reinforces the strength of the riser flow path 32 while forming one flow path in which the riser flow path 32 connected to the end of the inclined straight pipe portion of the cooling channel 31 is communicated. At the upper part (the part above the lower end connected to the end of the inclined straight pipe part of the cooling channel 31).

  In the second core melt holding device 30B configured as described above, when the rib 33 provided in the riser flow path 32 reinforces the strength of the riser flow path 32, thermal stress is applied to the riser flow path 32. However, the deformation amount of the riser flow path 32 is suppressed. Moreover, since the lower end of the riser flow path 32 is connected also by the rib 33 provided in the riser flow path 32 in the 2nd core melt holding | maintenance apparatus 30B, the said part becomes a pressure boundary.

  According to the second core melt holding device 30B, by providing the rib 33 on the upper side of the riser flow channel 32, the riser flow channel 32 is reinforced, and thus the same as the first core melt holding device 30A. In addition to the effects, the riser flow path 32 is more difficult to deform than the first core melt holding device 30A, and therefore an increase in local pressure loss due to the deformation of the riser flow path 32 can be prevented. .

  Further, according to the second core melt holding device 30 </ b> B, the lower side of the riser flow path 32 is divided by the rib 33 at the lower end of the riser flow path 32 connected to the end of the inclined straight pipe portion of the cooling channel 31. Since each cooling channel 31 forms a single flow path, the end of the inclined straight pipe portion of the cooling channel 31 is the pressure boundary of the parallel channel, as in the first core melt holding device 30A. Therefore, the flow rate fluctuation of the parallel channels can be suppressed more than before.

[Third Embodiment]
FIG. 5 is a top view of a third core melt holding device 30C, which is an example of a core melt holding device according to the third embodiment of the present invention. FIG. 6 is a diagram (1) of the third core melt holding device 30C. / 4 sector).

  The third core melt holding device 30C is different from the first core melt holding device 30A in that an intermediate channel 34 as a tubular body formed in a tubular shape instead of the riser channel 32, and a tubular body However, the other risers are not substantially different. Therefore, in the description of the third embodiment, the difference from the first core melt holding device 30A will be mainly described, and the same components as those in the first core melt holding device 30A will be denoted by the same reference numerals. The description is omitted.

  The third core melt holding device 30C has a substantially horizontal straight line passing through the central part of the corium holding surface formed in a substantially circular shape provided with a heat-resistant material 8 for protecting the cooling channel 31 from the heat of the core melt (corium). A cooling channel 31 having an inclination in the feed header 7 formed of a pipe is arranged in parallel, and an intermediate flow path 34 that goes around the inner circumference of the pedestal side wall 5 at the end of the inclined straight pipe portion of the cooling channel 31; An individual riser flow path 35 is provided, which is a riser portion that rises substantially vertically from the intermediate flow path 34 and guides the coolant guided to the intermediate flow path 34 further upward.

  That is, the third core melt holding device 30C is configured so that the riser flow path 32 of the first core melt holding apparatus 30A is substantially separated from the intermediate flow path 34 that appears in a substantially annular shape in the top view. It is composed of individual riser channels 35 that are vertically raised. The individual riser flow path 35 is formed, for example, as an aggregate of pipes having one end opened in the intermediate flow path 34 and the other end opened upward.

  Here, in the third core melt holding device 30C, the number of pipes n (n is a natural number of 1 or more) constituting the individual riser flow path 35 is the number m of parallel channels (m is 1 or more) constituting the cooling channel 31. It is not always necessary to correspond to the natural number). That is, the number n of pipes constituting the individual riser flow path 35 may be the same as or different from the number m of parallel channels constituting the cooling channel 31.

  In the third core melt holding device 30C configured as described above, the intermediate flow path 34 that communicates each cooling channel 31 is provided at a position that is the end of the inclined straight pipe portion of the cooling channel 31, thereby providing an intermediate flow. The passage 34 becomes the pressure boundary of the parallel channel similarly to the lower side of the riser passage 32 of the second core melt holding device 30B. Further, in the third core melt holding device 30C, the individual riser flow path 35 is reinforced by providing the individual riser flow path 35 connected to the intermediate flow path 34. It plays the same role as the upper side of the riser flow path 32 of the core melt holding device 30B.

  That is, in the third core melt holding device 30C, the lower side of the riser channel 32 of the second core melt holding device 30B is the intermediate channel 34, and the upper side of the riser channel 32 where the ribs 33 are provided. The individual riser channel 35 is configured in place of the individual riser channel 35, and acts in the same manner as the second core melt holding device 30B in which the riser channel 32 is reinforced in the first core melt holding device 30A.

  According to the third core melt holding device 30C, in addition to the same effects as the first core melt holding device 30A, the individual riser flow path 35 corresponding to the upper side of the riser flow path 32 is, for example, Since individual flow paths such as individual pipes are formed, it is less likely to deform than the riser flow path 32 of the first core melt holding device 30A, and local pressure loss increases due to deformation of the riser flow path 32. Can be prevented.

  Further, according to the third core melt holding device 30C, the intermediate flow path 34 corresponding to the lower side of the riser flow path 32 forms one flow path that connects the individual cooling channels 31. Similarly to the core melt holding device 30A, the end of the inclined straight pipe portion of the cooling channel 31 becomes the pressure boundary of the parallel channel, and the flow fluctuation of the parallel channel can be suppressed as compared with the conventional case.

[Fourth Embodiment]
FIG. 7 is a schematic view of a fourth core melt holding device 30D (1/4 sector) which is an example of the core melt holding device according to the fourth embodiment of the present invention.

  The fourth core melt holding device 30D is further provided with a partition wall 36 that divides the intermediate flow path 34 serving as an intermediate header into a plurality of parts in the circumferential direction with respect to the third core melt holding device 30C. Although it is different, other points are not substantially different. Therefore, in the description of the fourth embodiment, the description will focus on the differences from the third core melt holding device 30C, and the same components as those in the third core melt holding device 30C will be denoted by the same reference numerals. The description is omitted.

  Similar to the third core melt holding device 30C, the fourth core melt holding device 30D includes an intermediate flow path 34 and an individual riser flow path 35. Moreover, the intermediate flow path 34 which comprises an intermediate header is provided with the partition wall 36 which divides | segments the area | region of the intermediate flow path 34 into plurality with respect to the circumferential direction.

  In the fourth core melt holding device 30D configured as described above, in addition to the same operation as the third core melt holding device 30C, the steam concentrated at the position where the longest cooling channel 31 is connected is relaxed. (Dispersed).

  More specifically, as shown in FIG. 13 referred to when the conventional core melt holding device 4 is described, the position where the intermediate flow path 34 is formed in the fourth core melt holding device 30D, and The height of the end position of the cooling channel 31 (parallel channel) becomes lower as the length of the cooling channel 31, that is, the distance from the water supply header 7 becomes shorter (the cooling channel 6 located near the center shown in FIG. 13). ), The longer it is, the higher it is (the cooling channel 6 located near the left and right ends shown in FIG. 13). This also applies to the fourth core melt holding device 30D.

  The steam generated by the vaporization of the coolant moves to a higher position due to its nature. Therefore, the cooling channel 31 having a termination at a higher position, that is, the cooling channel having the longest distance from the water supply header 7. There is a tendency to concentrate on 31. This tendency is observed in the other core melt holding devices 30A, 30B, 30C, and 30E including the riser flow path 32 and the intermediate flow path 34 as intermediate headers not provided with the partition wall 36.

  On the other hand, in the fourth core melt holding device 30D, the intermediate flow path 34 is partitioned by the partition wall 36, and the steam does not move beyond the partition wall 36. Therefore, the fourth core melt holding apparatus 30D is guided to the individual riser flow path 35. The steam concentration is suppressed from being concentrated locally, and in a dispersed state, the vapor is guided to the individual riser flow path 35 and exhausted.

  The space | interval which provides the partition wall 36 in the intermediate flow path 34 can be set on the basis of the flow volume etc. of the coolant which flows through the water supply header 7, for example. The flow rate of the coolant flowing through the feed water header 7 decreases as the position is closer to the center of the substantial circle that appears when the fourth core melt holding device 30D is viewed from above. Therefore, at a position near the center of the approximate circle where the coolant flow rate is relatively small, the section of the intermediate flow path 34 connected at the end of the cooling channel 31 connected to the water supply header 7 is made large, In addition, at a position near the outer periphery of the substantially circle where the flow rate of the coolant increases, a section of the intermediate flow path 34 connected at the end of the cooling channel 31 connected to the water supply header 7 is made small.

  As described above, the size of the section in the circumferential direction of the intermediate flow path 34 is set based on the flow rate of the coolant flowing through the water supply header 7, so that each intermediate flow path 34 is divided by the partition wall 36. In the section, the flow rate of each coolant, that is, the amount of steam can be distributed in a well-balanced manner, and the steam can be guided to the individual riser flow path 35 connected in each section in a balanced manner and exhausted.

  In addition to this, as a reference for setting the interval at which the partition wall 36 is provided in the intermediate flow path 34, for example, the number of the cooling channels 31 and the center of a substantially circle that appears when the fourth core melt holding device 30D is viewed from above. References such as corners can be set as appropriate.

  According to the fourth core melt holding device 30D, in addition to the effect exhibited by the third core melt holding device 30C, the intermediate flow path 34 is partitioned by the partition wall 36 that restricts the movement of the steam. It is possible to suppress local concentration of the steam guided from the flow path 34 to the individual riser flow path 35 and guide the vapor to the individual riser flow path 35 in a dispersed state so as to be discharged out of the apparatus.

  Moreover, according to the 4th core melt holding | maintenance apparatus 30D, since it can suppress that the vapor | steam guide | induced to the individual riser flow path 35 concentrates locally, the individual riser which may arise by local concentration of steam | vapor A local decrease in cooling capacity of the flow path 35 can be eliminated.

  In addition, it is a part with a long pipe | tube length especially among the parallel flow paths from which a pipe | tube length differs as shown in FIG. 11 that a some parallel flow path is connected. In a riser connected to a parallel flow path having a short pipe length, only one parallel flow path may be connected to the divided riser flow path.

  The fourth core melt holding device 30D shown in FIG. 7 is configured by providing a partition wall 36 in the intermediate flow path 34 serving as an intermediate header with respect to the third core melt holding device 30C. However, the target for providing the partition wall 36 is not necessarily limited to the intermediate header of the third core melt holding device 30C, and may be the intermediate header of the other core melt holding devices 30A, 30B, 30E.

  That is, in the first core melt holding device 30A and the fifth core melt holding device 30E, the riser flow that becomes the intermediate header in the riser flow path 32 that becomes the intermediate header and the riser flow that becomes the intermediate header in the second core melt holding device 30B A fourth core melt holding device 30 </ b> D may be configured by providing a partition wall 36 on the lower side of the path 32. In addition, when applying to the 2nd core melt holding | maintenance apparatus 30B, you may comprise the rib 33 and the partition wall 36 integrally.

[Fifth Embodiment]
FIG. 8 is a top view of a fifth core melt holding device 30E, which is an example of a core melt holding device according to the fifth embodiment of the present invention, and FIG. 9 is a sectional view of II- 5 of the fifth core melt holding device 30E. It is sectional drawing in the II line (FIG. 8).

  The fifth core melt holding device 30E is configured such that a part of the cooling channels 31 communicates with the adjacent cooling channels 31 in the inclined straight pipe portion with respect to the first core melt holding device 30A. However, the other points are not substantially different. Therefore, in the description of the fifth embodiment, the same components as those in the first core melt holding device 30A are denoted by the same reference numerals and description thereof is omitted.

  As with the first core melt holding device 30A, the fifth core melt holding device 30E is a substantially horizontal straight pipe that passes through the center of the corium holding surface formed in a substantially circular shape with the heat-resistant material 8 laid. A cooling channel 31 with an inclination is formed in parallel to the formed feed header 7, and a riser flow path 32 that goes around the inner periphery of the pedestal side wall 5 is provided at the end of the inclined straight pipe portion of the cooling channel 31.

  Further, the fifth core melt holding device 30E includes a cooling channel 31 having a parallel flow path having a relatively long flow path length in the cooling channel 31, that is, a cooling channel located near the center of the corium holding surface. 31 is provided with a communication hole 37 to allow adjacent cooling channels 31 to communicate with each other. From the viewpoint of effectively dispersing the pressure boundary position of the cooling channel 31, the communication hole 37 is preferably near the midpoint with respect to the total length of the parallel flow paths.

  In the fifth core melt holding device 30E, by providing the communication hole 37 with the adjacent cooling channel 31 near the middle of the cooling channel 31 having a long parallel flow path section, the coolant guided to the cooling channel 31 communicates. It becomes possible to pass through the hole 37, and the communication hole 37 can be further set as a pressure boundary of the parallel flow path. That is, in the fifth core melt holding device 30E, the cooling channel 31 communicated by the communication hole 37 acts in the same manner as when the flow path length of the parallel flow path section is shortened, and the flow rate fluctuation of the cooling channel 31 is stabilized. It can be made.

  According to the fifth core melt holding device 30E, in the cooling channel 31 in which the flow lengths of the parallel flow paths are relatively long, the end of the inclined straight pipe portion of the cooling channel 31, that is, the lower end of the riser flow path 32 Since the pressure boundary is set not only in the pressure boundary located in the portion but also in the middle of the inclined straight pipe portion of the cooling channel 31, the flow rate fluctuation in the cooling channel 31 is more stable than the first core melt holding device 30A. It can be made.

  Note that the fifth core melt holding device 30E shown in FIG. 9 is an example in which the communication hole 37 is provided in the cooling channel 31 of the first core melt holding device 30A. Instead of the device 30A, a communication hole 37 may be provided in the cooling channel 31 of the other core melt holding devices 30B, 30C, 30D.

  As described above, according to the core melt holding device according to the embodiment of the present invention, since the riser flow path 32 exists uniformly on the outer periphery of the corium holding surface, no matter where the corium falls on the corium holding surface, the corium is dropped. The preheating from the side can be performed evenly. Further, by providing a riser flow path 32 having a flow path area larger than that of the cooling channel 31 at the end of the inclined straight pipe portion located on the downstream side of the cooling channel 31 where the two-phase pressure loss increases, the flow velocity is reduced, Since pressure loss can be reduced, natural circulation of the coolant can be promoted.

  Furthermore, according to the core melt holding device according to the embodiment of the present invention, the lower end portion of the riser flow path 32 (the end of the inclined straight pipe portion of the cooling channel 31) becomes the pressure boundary of the parallel channel, so that the conventional core Compared to the melt holding device 4, the section of the parallel channel is shortened by a length corresponding to the height of the riser flow path 32, and the flow rate fluctuation of the parallel channel can be suppressed as compared with the related art.

  Therefore, according to the core melt holding device according to the embodiment of the present invention, the corium falling on the corium holding surface can be sufficiently cooled, and the heat-resistant material that can be caused when the heat removal of the corium is insufficient. Thus, the degree of thermal damage that can occur in the reactor containment vessel can be mitigated and the deterioration of the integrity of the reactor containment vessel can be suppressed.

  It should be noted that the present invention is not limited to the above-described embodiment as it is, and can be implemented in various forms other than the above-described examples in the implementation stage, and various modifications can be made without departing from the spirit of the invention. Can be omitted, added, replaced, or changed. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

1 Reactor pressure vessel 2 Reactor containment vessel 3 Reactor pressure vessel lower head 4 (Conventional) Core melt holding device (core catcher)
5 Pedestal side wall 6 Cooling channel 7 Water supply header 8 Heat-resistant material 9 Pedestal floor 10 Base member 30 (30A, 30B, 30C, 30D, 30E) Core melt holding device 31 Cooling channel 32 Riser flow path (intermediate header)
33 Rib (deformation prevention member)
34 Intermediate channel (intermediate header)
35 Individual riser flow path 36 Partition wall 37 Communication hole

Claims (8)

In the core melting and holding apparatus, which is located below the reactor pressure vessel and formed in a pedestal region surrounded by a cylindrical pedestal side wall and a pedestal bed that supports the reactor pressure vessel,
A heat-resistant material that holds the core melt in the pedestal region,
A cooling channel provided between the heat-resistant material and the pedestal floor and supplying a coolant;
The cooling flow path includes a water supply header to which a coolant is supplied, an intermediate header formed in a circumferential direction along an inner peripheral surface of the pedestal side wall, the water supply header and one end connected, and the other end connected to the intermediate A core melt holding device having a plurality of parallel flow paths connected to a header. The core melt holding device according to claim 1, wherein the intermediate header has a plurality of sections divided in a circumferential direction of a circle appearing when projected from above. The plurality of divided sections of the intermediate header are at least the other end of the parallel flow path where one end is connected to the first point that is closer to the center of the circle among the two points on the water supply header. The first section, which is a partial section of the intermediate header connected at, and the second section, which is a point far from the center of the circle, and the middle connected at the other end of the parallel flow path to which one end is connected 3. A core melt holding device according to claim 1, wherein the first section is configured to be larger than the second section. apparatus. 4. The flow path according to claim 1, wherein at least a part of the parallel flow path is a flow path provided with a communication hole communicating with another parallel flow path adjacent in the middle of the flow path. The core melt holding device according to item. The communication hole includes a communication hole that communicates at least a parallel flow path having the longest flow path length of the parallel flow path and any one of the parallel flow paths adjacent to the parallel flow path. Item 5. The core melt holding device according to Item 4. The core melt holding device according to any one of claims 1 to 5, wherein the intermediate header is a flow path having a predetermined length with an upper opening. The core melt holding device according to claim 6, wherein the intermediate header is provided with a deformation preventing member at a position above a connection portion connected to the parallel flow path. The intermediate header includes an intermediate flow path of a tubular body formed in a circumferential direction along the inner wall of the pedestal, and a tubular body having one end connected to the intermediate flow path and the other end opened upward. The core melt holding device according to claim 1, comprising a plurality of individual riser channels disposed along the channel.

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