JPH0151793B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for repairing a pressure tube nuclear reactor,
More specifically, it relates to a method that can be repaired with relatively simple work and restart reactor operation within a short period of time in the event that a problem occurs in the pressure pipe that interferes with the operation of the reactor. be.

In a pressure tube reactor, each fuel assembly is housed individually in a pressure tube, the pressure tube is surrounded by a moderator that slows down neutrons into thermal neutrons, and cooling water is allowed to flow inside the pressure tube. A nuclear reactor with a structure that extracts thermal energy from fuel, such as ATR in Japan, CANDU in Canada, and SGHWR in the UK.
There is.

The pressure pipes and related equipment in a pressure tube reactor are particularly important components, so various considerations (in terms of shape, material, etc.) have been taken in their design to prevent them from being damaged. Although it is highly reliable, it is also necessary to thoroughly consider how to deal with failures such as cracks, deformation, and damage in pressure pipes.

The present invention was born from such studies and was completed by devoting much creativity to the invention, and will be described in detail below.

In a pressure tube reactor, pressure tube extensions are connected above and below to the pressure tube main body by a rolled joint method or the like, and in the present invention, these are collectively referred to as pressure tubes.

If a problem occurs in the pressure pipe that may impede the operation of the reactor, such as hydrogen delayed cracking, cracking due to fatigue, damage during fuel extraction, etc.
Conventionally, methods have been considered to replace the faulty pressure pipe, or to leave the faulty pressure pipe as is and shut off (plug) the coolant flow path to resume operation.

However, when replacing pressure pipes, this replacement work must be done under high radiation conditions.
Moreover, the work becomes difficult because the number of man-hours involved in welding work increases. In addition, when simply plugging a pressure pipe, although the plugging process itself is easy, it has the disadvantage that it is not possible to pull out the pressure pipe where a fault has occurred, making it difficult to investigate the cause of the fault. .

The purpose of the present invention is to eliminate the various drawbacks of the conventionally considered methods as described above, and to make it possible to resume operation of the nuclear reactor within a relatively short period of time in the event of a failure in the pressure pipe, and to eliminate the need for repair work. It is an object of the present invention to provide a method for repairing a pressure tube type nuclear reactor which reduces the amount of damage caused and allows the cause of a pressure tube failure to be directly investigated.

In summary, the present invention provides a system for, when a fault occurs in a pressure pipe that impedes the operation of a nuclear reactor, plugging the inlet pipe and outlet pipe connected to the faulty pressure pipe and pulling out the pressure pipe. This is a method for repairing a pressure tube reactor configured to insert a radiation shielding plug tube instead.

Hereinafter, one embodiment of the present invention will be described in more detail based on the drawings. FIG. 1 is an explanatory view showing the reactor structure upon completion of repair work, and FIG. 2 is an inserted view of the radiation shielding plug pipe used in the present invention.

The pressure tube type nuclear reactor body is composed of a briquette-like calandria tank 1, a pressure tube 2, a fuel assembly, an iron water shield 3, and the like. calandria tank 1
is filled with heavy water as a moderator, and the pressure tubes 2 are inserted into calandria tubes 4 arranged in a square grid. The nuclear fuel assembly is located in the pressure tube 2 and is cooled by light water coolant flowing through the inlet tube 5 at the bottom of the core, which boils in the reactor and becomes a two-phase flow of steam and water. Pass through the cooling system outlet pipe 6,
Steam and water are separated in the steam drum 7, and the steam is sent to the turbine system, the water is sent to the water drum 10 via the downcomer pipe 8 by the recirculation pump 9, and is sent into the furnace again from the inlet pipe 5.

Now, let's assume that a problem occurs in the pressure pipe 2 that interferes with the operation of the nuclear reactor. If the reactor is in operation, immediately stop the reactor operation. The steps for the repair work are as follows. First, the nuclear fuel assembly is pulled out from the pressure pipe 2 and removed. Then, appropriate locations 12a and 12b of the inlet pipe 5 near the water drum 10 and the outlet pipe 6 near the steam drum 7 connected to the pressure pipe causing the trouble are cut, and the water drum 10 of the cut location 12a is cut off.
A plug 1 is attached by welding or the like to the end of the inlet pipe 5 on the side and the end of the outlet pipe 6 on the steam drum 7 side at the cut point 12b.
Install 1. The above-mentioned cutting points 12a and 12b are
In the case of an ATR (advanced converter reactor), it is preferable to use a vertical pipe near the steam drum 7 and water drum 10 from the viewpoint of a location with low radiation exposure and good workability. This pressure tube is then disconnected from the inlet tube 5 and outlet tube 6 connected to it at positions 13 and 14, respectively. Similarly, in the case of ATR, the pressure pipes are separated at the upper pressure pipe upper rising pipe vertical portion 14 and the lower pressure pipe lower extension portion 13. Note that there is no particular need to plug the ends of the inlet pipe 5 and the outlet pipe 6 at the separation positions 13 and 14.

After doing this, pull out and remove the faulty pressure pipe, and replace it with the radiation shielding plug pipe 1.
Insert 5.

As shown in FIG. 2, the radiation shielding plug pipe 15 is made to be continuous at the upper end using a double pipe 16 or two parallel pipes, and the lower end is communicated with the outside so that the coolant is not injected into the radiation shielding plug pipe 15. It has a structure including a reciprocating flow path and shielding plugs 17 located at both ends of the reciprocating flow path.
When the radiation shielding plug pipe 15 is inserted, these shielding plugs 17 are in a positional relationship such that they fit into the iron/water shield 3, and in such a state, the radiation shielding plug pipe 15 is inserted into the support flange 18, etc. Therefore, it is fixed to the iron-water sleeve 19 that supported the pressure pipe.

A shielding cooling device for cooling the plug pipe is connected to the radiation shielding plug pipe 15 as necessary. This cooling device includes a coolant supply circulation device 2
0, a heat exchanger 21, a valve 22, etc., and is configured so that the coolant can flow through the reciprocating flow path within the radiation shielding plug pipe 15. Such cooling is required when the radiation shielding plug tube 15 generates heat due to neutrons and gamma rays from the core and reaches a high temperature, and when the temperature rise is small (approximately 300 degrees Celsius or less). does not require cooling.

In this way, the radiation shielding plug pipe 15 is inserted and installed in place of the faulty pressure pipe, the shielding cooling system is operated as necessary, the reactor is started in this state, and the reactor is operated at the allowable output. They will resume operation.

Since the present invention is a method for repairing a pressure tube type nuclear reactor configured as described above, it is difficult to replace the pressure tubes, which was conventionally considered, and required pipe connection work by welding under high radiation. It does not involve any work, and can be done relatively easily and in a short time, whether it is plugging the inlet/outlet pipe or cutting the pipe, reducing the amount of radiation exposure for workers and improving safety. This has the effect of allowing the restart of nuclear reactor operation within a short period of time. Further, according to the present invention, since the pressure pipe is pulled out, the cause of the failure can be thoroughly investigated, which can be of great use in preventing future accidents. Furthermore, if there are several pressure pipes that have failed, the method of the present invention is used, in which the representative pressure pipe is pulled out in order to investigate the cause, and a radiation shielding plug pipe is inserted in that part. It is possible to employ a method such as plugging the pressure pipe without pulling it out and operating it, and the effects of the present invention are even more remarkable, and other excellent effects can be achieved.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the nuclear reactor structure when the repair work is completed by the method of the present invention, and FIG. 2 is an explanatory diagram of the insertion state of the radiation shielding plug pipe used therein. 2...Pressure pipe, 5...Inlet pipe, 6...Outlet pipe,
11... Welding plug, 12... Piping cut point, 13,
14... Pressure pipe separation position, 15... Radiation shielding plug pipe, 16... Double pipe, 17... Shielding plug.

[Claims]

1. A metal clad tube including stacked nuclear fuel pellets and a ceramic wafer inserted between adjacent mutually facing concave end faces of at least a majority of the stacked nuclear fuel pellets,
and each of the wafers has a diameter substantially the same as a nuclear fuel pellet, and each of the wafers contains less than the amount of uranium present in natural uranium dioxide.
A nuclear fuel rod consisting of a sintered body of a mixture of uranium dioxide and gadolinium oxide containing 235.