Reactor measurement-pipe maintenance clamp apparatus

A reactor measurement-pipe maintenance clamp apparatus includes a first clamp mechanism and a second clamp mechanism. The first clamp mechanism includes clamps to fix the measurement pipe between the clamps, first clamp operation bolts that are allowed to be turned by remote control from above a reactor core, and wedge mechanisms to convert the turning of the clamp operation bolts to displacement of the clamps in a radial direction of the diffuser to generate clamping forces for securing the measurement pipe. The second clamp mechanism includes a support clamp to hold the support, a second clamp operation bolt that is allowed to be turned by remote control from above the reactor core, and a wedge mechanism to convert the turning of the second clamp operation bolt to displacement of the support clamp in a tangential direction of the diffuser to generate clamping force for fixing the support.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from PCT Application PCT/JP2013-000300, filed Jan. 23, 2013, the entire contents of which are incorporated herein by reference.

FIELD

An embodiment of the present invention relates to a reactor measurement-pipe maintenance clamp apparatus and particularly to a reactor measurement-pipe maintenance clamp apparatus for fixing robustly a measurement pipe that measures a flow rate of a jet pump system.

BACKGROUND

FIG. 6is a diagram of a boiling water reactor. To increase power density, the boiling water reactor employs a jet pump system that combines a recirculation pump, provided outside a reactor pressure vessel1, and jet pumps11, provided inside the reactor pressure vessel1.

The reactor pressure vessel1accommodates a coolant2and a reactor core3. The reactor core3is made up of a plurality of fuel assemblies and a plurality of control rods, and is surrounded by a core shroud10. The coolant2flows through the reactor core3upward. While flowing through the reactor core3, the coolant2is heated due to heat produced by nuclear reaction in the reactor core3, generating two-phase flow of water and steam. The two-phase flow of the coolant2flows into a steam separator4, provided above the reactor core3, to be separated into water and steam.

The resulting steam is introduced into a steam dryer5, provided above the steam separator4, to turn to dry steam. The dry steam is transferred through a main steam line6, connected to the reactor pressure vessel1, to a steam turbine to be used for power generation. The resulting water flows down a downcomer7, provided between the reactor core3and the reactor pressure vessel1, into a space below the reactor core3.

The control rods are inserted into or withdrawn from the reactor core3through control rod guide tubes8, which are provided below the reactor core3. A plurality of control rod drive mechanisms9are provided below the control rod guide tubes8to control the insertion and withdrawal of the control rods.

A plurality of jet pumps11are provided in the downcomer7at circumferentially equal spacings. The recirculation pump, not shown, is provided outside the reactor pressure vessel1. The recirculation pump, the jet pumps11, and a recirculation line routed between the recirculation pump and the jet pumps11constitute a recirculation system. The recirculation pump supplies driving water to the jet pumps11, so that the jet pumps11operate to provide forced circulation of the coolant2into the reactor core3.

FIG. 7is a diagram of an arrangement of one of the jet pumps11inFIG. 6.

InFIG. 7, reference numeral12refers to a riser pipe of the jet pump11. The riser pipe12is attached on the reactor pressure vessel1. The riser pipe12is connected to a recirculation inlet nozzle13of the recirculation pump. The coolant2is supplied through the recirculation inlet nozzle13to the riser pipe12to be introduced into the reactor.

An upper portion of the riser pipe12is connected by a transition piece14to a pair of elbows15A and15B. The elbows15A and15B are connected through mixing nozzles16A and16B to inlet throats17A and17B, respectively. The inlet throats17A and17B are connected to diffusers18A and18B, respectively.

As the coolant2is jetted by the mixing nozzles16A and16B into the inlet throats17A and17B, the letting involves surrounding water, allowing the jets of the coolant2and the involved water to be mixed in the inlet throats17A and17B. The diffusers18A and18B then allow hydrostatic head to be restored.

To control power of a nuclear power plant with the reactor including the coolant recirculation system using the jet pumps11as described above, it is important to measure flow rates in the et pumps11during normal operation. For this purpose, flow rate measurement pipes19are provided on the diffusers18A and18B as illustrated inFIG. 7to measure a static pressure difference between upper and lower portions of each of the diffusers18during the operation. The measurement is compared to a calibration value, which is a measurement taken before the operation of the plant, to calculate a flow rate of the jet pumps11. The measurement pipes19, which are welded to static pressure holes located at the upper and lower portions of the diffusers18A and18B, are supported by connecting members24fixed to the diffusers18A and18B.

As illustrated inFIGS. 8A and 8B, the measurement pipes19are arranged in an annular space29between the reactor pressure vessel1and the shroud10. The measurement pipes19are routed in the annular space29in a complex manner to be connected through a jet pump measurement nozzle27to a pipe arrangement outside the reactor. Two such jet pump measurement nozzles27are symmetrically positioned in the reactor pressure vessel1.

Because of flows of the coolant2fed from the recirculation pump, the jet pumps11as described above are used under more severe conditions than other devices. This results in significant load acting on components of the jet pumps11. The measurement pipes19, in particular, are affected by fluid oscillation around the diffusers10and other factors directly or via the connecting members24, leading to a significant stress acting in the measurement pipes19. The measurement pipes19thus may be susceptible to cracks and ruptures.

To reduce stress caused in the measurement pipes19due to the fluid oscillation and the like, various improvements have been traditionally made for the fixing of the measurement pipes19.

In the event of a crack or a rupture caused in any of the measurement pipes19or its welded portion to a corresponding one of the connecting members24in the jet pump system in the reactor, it is necessary to conduct repair work from above the reactor core, which is located in a control area for radiation, in a remote manner. Additionally, this repair work involves underwater work.

It is desirable that the measurement pipes19, when repaired, is fixed to a corresponding one of the diffusers18A and18B robustly so that stress to be applied to the welded portion to the connecting members24due to the fluid oscillation is reduced as much as possible. It is, however, extremely difficult to access the measurement pipes19, which is located in the extremely narrow space, to fix it robustly from above the reactor core remotely.

As a solution to the issues described above, a reactor measurement-pipe maintenance clamp apparatus is provided which is capable of facilitating fixing a measurement pipes, routed in an extremely narrow space, robustly to the diffuser by remote control from above the reactor core and reducing stress in a welded portion of the measurement pipe to a support.

DETAILED DESCRIPTION

A reactor measurement-pipe maintenance clamp apparatus according to an embodiment is which fix a measurement pipe routed horizontally along a diffuser of a jet pump provided in a reactor pressure vessel of a boiling water reactor, the measurement pipe being welded on a connecting member at a side of the diffuser, the clamp apparatus including:

a body frame having a vertical block and a horizontal block, the vertical block being attached to an outer surface of the diffuser, the horizontal block being perpendicular to the vertical block;

a first clamp mechanism including a plurality of clamps which fix the measurement pipe between the clamps, a plurality of clamp operation bolts provided vertically in the horizontal block of the body frame in such a manner that the clamp operation bolts are allowed to be turned by remote control from above a reactor core, and a plurality of wedge mechanisms which convert the turning of the plurality of clamp operation bolts to displacement of the plurality of clamps in a radial direction of the diffuser to generate clamping forces for fixing the measurement pipe; and

a second clamp mechanism including a support clamp which hold the connecting member, a support clamp operation bolt provided vertically in the horizontal block of the body frame in such a manner that the support clamp operation bolt is allowed to be turned by remote control from above the reactor core, and a wedge mechanism which convert the turning of the support clamp operation bolt to displacement of the support clamp in a tangential direction of the diffuser to generate a clamping force for fixing the connecting member.

The reactor measurement-pipe maintenance clamp apparatus according to the embodiment will now be described with reference to the drawings.

FIG. 5is a diagram of a measurement pipe19fixed to a side of a diffuser18in a jet pump system in a reactor, with the measurement pipe19not clamped by the clamp apparatus. A connecting members24is fixed to the side of the diffuser18. The measurement pipe19is welded on the connecting members24and held horizontally.

FIG. 1is a diagram of the measurement pipe19clamped by the clamp apparatus.FIG. 2is a side view of the clamp apparatus observed from arrow direction A inFIG. 1;FIG. 3is a side view of the clamp apparatus observed from arrow direction B inFIG. 1; andFIG. 4is a side view of the clamp apparatus observed from arrow direction C inFIG. 1.

The clamp apparatus includes a substantially L-shaped body frame30. The body frame30, which is arranged in a narrow space between an outer surface of the diffuser18and the measurement pipe19, has a vertical block31to be attached to the outer surface of the diffuser18and a horizontal block32extending horizontally from the top end of the vertical block31. The vertical block31includes at its back a contact surface having a curvature identical with that of the outer surface of the diffuser18.

The clamp apparatus according to this embodiment includes a first clamp mechanism using four clamps33,34,35, and36to grip the measurement pipe19and a second clamp mechanism holding the connecting member24on opposite sides of the connecting member24. Reference numerals37,38,39, and40refer to washer-faced bolts, which are clamp operation bolts to operate the clamp mechanisms. The washer-faced bolts37,38,39, and40each have at their heads a plurality of grooves in an axial direction.

An arrangement of the first clamp mechanism will now be described. InFIG. 1, a first slider41is mounted on a lower surface of the horizontal block32of the body frame30. A guide portion43is formed also in the lower surface of the horizontal block32, and the first slider41is mounted slidably along the guide portion43in a radial direction of the diffuser18. The two clamps33and34, which are to grip the measurement pipe19on one side, are retained vertically at a predetermined spacing under the first slider41.

As illustrated inFIGS. 1 and 4, a second slider44and a third slider45are also mounted on the lower surface of the horizontal block32of the body frame30slidably along a guide portion, not shown. The clamp35is supported vertically under the second slider44, and the clamp36is supported vertically under the third slider45. The clamps35and33face each other to grip the measurement pipe19on opposite sides of the measurement pipe19, and so do the clamps36and34.

The first washer-faced bolt37is mounted vertically through a washer46on an upper surface of the horizontal block32of the body frame30. The first washer-faced bolt37is coupled to a wedge mechanism that converts the turning of the first washer-faced bolt37to the horizontal displacement of the cleans33and34. As illustrated inFIG. 3, a first wedge block48is screwed onto the threaded shaft of the first washer-faced bolt37, so that the turning of the first washer-faced bolt37displaces the first wedge block48up and down. The first wedge block48has a slanted wedge surface in contact with a slanted surface formed at a rear end of the first slider41. This arrangement yields a wedging action to push out the first slider41as the first washer-faced bolt37is turned to displace the first wedge block48upward, so that the clamps33and34, which are integrated with the first slider41, are pressed against the measurement pipe19.

As illustrated inFIGS. 1 and 2, the second washer-faced bolt38is mounted vertically through a washer46on the upper surface of the vertical block31of the body frame30. A second wedge block50having a wedge surface is screwed onto the threaded shaft of the second washer-faced bolt38. The wedge surface of the second wedge block50is in contact with a slanted surface formed at the back of the second slider44.

The third washer-faced bolt39is also mounted vertically through a washer46on the upper surface of the vertical block31of the body frame30. The third washer-faced bolt39is coupled to a wedge mechanism similar to that for the second washer-faced bolt38. A third wedge block (not shown) screwed onto the threaded shaft of the third washer-faced bolt39has a wedge surface in contact with a slanted surface of the third slider45.

Thus, as the second washer-faced bolt30and the third washer-faced bolt39are turned, the wedging action of the second wedge block50and the third wedge block, not shown, causes the clamp35, which is integrated with the second slider44, and the clamp36, which is integrated with the third slider45, to be pressed against the measurement pipe19.

The second clamp mechanism will now be described. With reference toFIGS. 3 and 4, the fourth washer-faced bolt40, which is mounted vertically through a washer46on the horizontal block32of the body frame30at a longitudinal end of the horizontal block32, is to operate the second clamp mechanism. A fourth wedge block52is screwed onto the threaded shaft of the fourth washer-faced bolt40. A clamp plate54is provided at the vertical block31of the body frame30movably in parallel with a tangential direction of the diffuser18and in a horizontal direction. In this embodiment, a guide groove55to guide the clamp plate54is formed in the vertical block31as illustrated inFIG. 4. The clamp plate54is fitted slidably in the guide groove55.

The fourth wedge block52has a wedge surface that slides in contact with a slanted surface formed at a rear end of the clamp plate54. As the fourth washer-faced bolt40is turned to raise the fourth wedge block52, the clamp plate54is pushed out in the horizontal direction toward the connecting member24that supports the measurement pipe19. A fixing clamp56is fixed on the body frame30at a position of the body frame30where the connecting member24is held between the body frame30and the clamp plate54. The body frame30is fixed to the diffuser18in a manner such that the fixing clamp56is in contact with the connecting member24. The clamp plate54has an end surface, which is in contact with the connecting member24and desirably has one or more projection for engagement with the connecting member24.

An operation and effect of the reactor measurement-pipe maintenance clamp apparatus according to the embodiment, which has the structure as described above, will now be described.

With reference toFIG. 5, the measurement pipe19, when it has been repaired, is welded onto the connecting member24to be fixed to the side of the diffuser18. The clamp apparatus is then suspended by a wire through an eyebolt60, as illustrated inFIG. 1, from above the reactor core to allow the vertical block31to be welded onto the side of the diffuser18. With the vertical block31welded, the clamps33and34are placed opposite to the clamps35and36with the measurement pipe19therebetween. The connecting member24that supports the measurement pipe19is placed between the clamp33and the clamp34and between the clamp35and the clamp36.

A clamp operation to enable the clamps33and34and the clamps35and36to grip the measurement pipe19will now be described.

A nut of a bolt tightening tool, which is not shown and suspended from above the reactor core, is fitted onto each of the heads of the second washer-faced bolt38and the third washer-faced bolt39, which are among the four washer-faced bolts37,38,39, and40located on upper surface of the body frame30. The bolt tightening tool is used to torque and turn the second washer-faced bolt38and the third washer-faced bolt39to thereby raise the second wedge block50and the third wedge block, not shown. Through the wedging action, the clamp35, which is integrated with the second slider44, and the clamp36, which is integrated with the third slider45, are pushed out until the clamps35and36come into contact with the measurement pipe19.

The nut of the undepicted bolt tightening tool, which is suspended from above the reactor core, is then fitted onto the head of the fourth washer-faced bolt40. The fourth washer-faced bolt40is turned to raise the fourth wedge block52. This pushes out the clamp plate54toward the connecting member24of the measurement pipe19to fix the connecting member24between the clamp plate54and the fixing clamp56.

The nut of the undepicted bolt tightening tool, suspended from above the reactor core, is then fitted onto the head of the first washer-faced bolt37to turn the first washer-faced bolt37. As the first washer-faced bolt37is turned, the first wedge block48is raised upward. Through the wedging action, the first slider41is pushed out to press the clamps33and34, which are integrated with the first slider41, against the measurement pipe19and thereby fix the measurement pipe19between the clamps33and34and the clamps35and36.

The washer-faced bolts37,38,39, and40are, then, each tightened to a specified torque. As a result, the washers46prevent the washer-faced bolts37,38,39, and40from turning.

The measurement pipe19, routed in a narrow space between the core shroud and the diffuser18of the jet pump11, can be fixed to the side of the diffuser18by underwater remote control from above the reactor core with reliability and efficiency in the manner described above. Additionally, this allows the measurement pipe19and the connecting member24that supports the measurement pipe19to be fixed together to the diffuser18robustly, resulting in reduced stress caused to a welded portion between the measurement pipe19and the connecting member24due to fluid oscillation. Because of this, the maintenance of the measurement pipe19and its welded portion can be maintained for a prolonged period without a crack or the like.

Additionally, the clamp operation, which is performed above the reactor core in the control area for radiation, involves merely tightening the washer-faced bolts37,38,39, and40by remote control, provides easy access, and requires merely a simple operation. This can reduce operation time and thereby reduce the radiation exposure levels of operators significantly.