JP2803730B2 - Neutron irradiation monitoring device and method for reactor vessel, and method for supporting radiation sensor device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates generally to methods and apparatus for monitoring a nuclear reactor, and more particularly to such methods and apparatus utilizing parameters that can be monitored from outside the reactor core.

As is well known, a typical pressurized water reactor typically includes a reaction zone, commonly referred to as a "core," in which nuclear fission reactions occur continuously to generate heat. The core has a plurality of fuel assemblies arranged in a predetermined geometric pattern determined by the physics of nuclear reaction, and a plurality of elongated fuel rods made of fissile material are arranged in the fuel assemblies. . Neutrons that bombard fission material promote the fission reaction, which releases new neutrons and maintains a continuous fission process. The heat generated in the core is carried away by the cooling medium circulating between the fuel assemblies and supplied to the heat exchanger, which generates steam for power generation.

In addition, the cooling medium contains a neutron absorbing component at a controlled variable concentration in order to adjust the reactivity and to adjust the heat generated in the core as needed. In addition, the fuel assemblies are interspersed with control rods that are axially movable in the core to control the reactivity of the core and thus its power.

The power, that is, the power distribution of the core, is determined in particular by the neutron flux portion. The radial power distribution of the core is fairly predictable due to the predetermined arrangement of fuel assemblies and the positioning of the control rods that are radially symmetrically arranged throughout the core, but the axial power distribution is atomic. It can vary greatly during furnace operation. In addition, changing the fuel management plan during the life of a nuclear power plant can result in significant changes in both the size and distribution of neutron flux, and thus neutron fluence, throughout the reactor vessel zonal area. obtain. Therefore, it is desirable to monitor the axial power distribution in the core of a nuclear power plant.

In a normal nuclear power plant, the monitoring of the axial power distribution is generally performed using not only the out-of-core instrumentation system but also the in-core instrumentation system. The in-core instrumentation system consists of a movable miniature splitter box designed to provide information about the neutron flux distribution at a given location in the core, a fuel assembly exit thermocouple, and, in some cases, a fixed miniature splitter. Such an in-core instrumentation system, consisting of a box, is an accurate means of indicating the relative power distribution of the core, but does not provide the reactor with automatic protection.

On the other hand, the out-of-core instrumentation system is located symmetrically with respect to the core and in four vertical instrumentation wells outside the reactor vessel. It typically comprises an uncorrected long ion chamber or output area detector. The power range detector is calibrated for the corresponding in-core instrumentation system and is used to automatically protect the reactor against adverse power peaking. Additional information can also be obtained by using an auxiliary passive neutron dosimeter located in the annular reactor cavity between the reactor vessel wall and the primary biological shield.

Conventional means of using such auxiliary passive neutron dosimeters have typically suspended the neutron dosimeter with stainless steel, nickel or iron wires in various cases within the reactor cavity. However, in most nuclear power plants, accurate placement or positioning of the dosimeter has been difficult, since the interior of the reactor cavity is often narrow and inaccessible. In addition, dosimeter movement due to various causes, such as mechanical vibrations, intense ventilation airflow through the dosimeter, and expansion or contraction of the reactor vessel during heat-up (heating) and cool-down (cooling), Complicating the accuracy and reproducibility of dosimeter positioning during the life of a nuclear power plant. Accordingly, it can be readily appreciated that there is a need for a method and apparatus for accurately and reproducibly positioning a passive neutron dosimeter in a reactor cavity.

Another problem with conventional means, such as those described above, for deploying auxiliary passive neutron dosimeters is that they often interfere with refueling operations. During a typical refueling operation (i.e., during a fuel assembly change after the fuel in the reactor fuel assembly is depleted), the reactor vessel head assembly may be used to withdraw the spent fuel assembly. Must be removed. However, additional shielding must be provided due to potentially dangerous radiation levels that may be incurred during refueling. Accordingly, the reactor cavity is sealed to fill the space above the reactor vessel.

Such sealing of the reactor vessel is performed using one of the following two methods. The first method is to simply clamp heavy steel plates with gaskets on each side of the reactor cavity onto the reactor cavity. Second
The method uses an inflatable bladder that functions to further seal the reactor cavity at the top of the reactor cavity, in addition to using the steel sheet of the first method. Thus, obviously, any reactor cavity dosimetry device used in a nuclear power plant must prevent the possibility of perforation of the inflated bladder.

In addition to the access problems caused by changes in the shape of the reactor cavity, the installation of a reactor cavity dosimeter is further problematic due to the need to wear protective clothing for the personnel who change dosimeters. In order to work around a shut down reactor, as usual, workers must wear a number of protective clothing and gas masks covering the entire face. Such protective clothing not only severely impairs the agility of the wearer, but also causes the wearer to become fatigued by heat when used for a long time. Therefore, when designing a reactor cavity dosimeter, it is desirable to provide one that can be deployed quickly and remotely.

A recent method of deploying a reactor cavity dosimeter is disclosed in Japanese Patent Application No. 63-76656 filed by the present applicant. However, the apparatus and method disclosed therein relies on remotely positioning and retrieving an auxiliary passive neutron dosimeter from a reactor sump located below the reactor vessel. Reactor cavity dosimetry when high levels of activity are present in the sump, in deep water, or when there is no permanently installed scaffolding in the sump, if such conditions exist. It is concluded that the device is desirably located and recovered from the top of the reactor vessel.

SUMMARY OF THE INVENTION Accordingly, it is a general object of the present invention to provide a method and apparatus for monitoring neutron irradiation on a reactor vessel. More specifically, an object of the present invention is to provide a reactor cavity dosimetry device that can accurately and reproducibly position or position a dosimeter at a plurality of predetermined locations within a reactor cavity. To provide.

It is another object of the present invention to provide a reactor cavity dosimetry apparatus which does not hinder a refueling operation of a reactor and a method of using the same.

Yet another object of the present invention is to provide a reactor cavity dosimeter that allows a dosimeter to be quickly located from a remote location to minimize exposure of operating personnel to high radiation levels. And a method of using the same.

It is a further object of the present invention to provide a reactor cavity dosimetry device deployed from the top of a reactor cavity and a method of using the same.

Briefly, these and other objects of the invention are achieved by a reactor cavity dosimetry device having the access support stand and a method of deploying the device. A support stand having a substantially rectangular frame assembly formed by a pair of cross members and a pair of frame tubes suitably holds the dosimeter as part of a continuous loop. The continuous loops are first routed through a U-tube located below the support stand and connected to each other by a chain support plug. A chain support plug is adapted to be inserted into a hole formed in the upper cross member to fix the position of the dosimeter axially with respect to the core of the nuclear power plant in which the device is deployed. . Each frame tube is provided with a pivotable arm assembly having a spring-biased slider. After insertion into the reactor cavity, the arm assembly is pivoted away from the plane of the frame assembly and is positioned and secured in a plane perpendicular to the reactor cavity. In this way, the support stand is held in a substantially upright position by the spring bias of the arm assembly.

The above objects, other objects, advantages and novel features of the present invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION The accompanying drawings will be described below. In the drawings, the same or corresponding portions are denoted by the same reference numerals. FIG. 1 shows the reactor vessel 14
A nuclear power plant 10 having a pressurized water reactor (PWR) 12 housed therein is schematically illustrated. As is well known, the reactor vessel 14 forms a pressurized vessel for the reactor core 16 when sealed by the head assembly 1.

The core 16 is mainly composed of a plurality of clad nuclear fuel elements 20 arranged in a fuel assembly to generate a considerable amount of heat by a normal fission process, and includes a partial length control rod and a full length control rod 22. The specific amount of heat that is controlled to be generated by the core 16 depends primarily on the position of the aforementioned control rod 22 with respect to the fuel element 20.

Heat generated by the core 16 is carried by the coolant stream flowing in through the inlet means 24 and flowing out of the outlet means 26. These means 24, 26 respectively penetrate the cylindrical body wall 28 of the reactor vessel 14, are formed integrally with the body wall 28,
Also known as "nozzles". Generally, the coolant stream exiting the outlet means 26 is conveyed to one or more steam generators 30, where the coolant and the water used to make the steam (known as the "secondary coolant"). A heat exchange relationship is formed. The steam generated in this manner is finally used as a turbine generator (not shown) for generating electricity.
Is commonly used to drive

As described above, the recirculation primary closed loop or the steam generation loop includes the coolant piping that connects the reactor vessel 14 and the steam generator 30. Obviously, the reactor vessel 14 shown in FIG. 1 has three such loops, but the number of such loops differs for each nuclear power plant, and usually two, three or four loops are used. Should be understood.

Also, as shown in FIG. 1, the PWR 12 is surrounded by a primary biological shield 32 made of common concrete,
Minimize the release of dangerous radioactivity from organisms released by R12. To monitor the core 16, extra-core neutron detectors 34 (not shown, but in addition to various forms of in-core instrumentation) are symmetrically disposed about the core within the biological shield 32. The entire plant 10 is typically surrounded by a containment vessel 36, and a reactor sump 38 is formed below the core 16. For other details regarding the purpose of in-pile instrumentation and out-of-pile instrumentation, as well as details regarding normal operation of the PWR 12, see the applicant's Japanese Patent Application No. 63-76656.

Although much information can be obtained by in-core instrumentation and extra-core instrumentation as described above, an auxiliary passive neutron dosimeter is installed in the annular portion formed between the reactor vessel 14 and the biological shield 32. By doing so, you can obtain other information. This annular portion is hereinafter referred to as an atomic cavity 40,
It is shown in the figure.

A conventional method of installing an auxiliary neutron dosimeter in the reactor cavity 40 is to suspend the dosimeter from the accessible portion of the reactor vessel 14 with a length of stainless steel, nickel or iron wire. It was typical. Such a method
Not only is the positioning of the dosimeter relative to the "strip" region of the reactor vessel 14 axially inaccurate, but also the fuel element
Problems also occurred during the replacement of 20 (ie, during the refueling operation). As is well known, an inflatable bladder 42 is often used to seal the top space between the reactor vessel 14 and the biological shield 32. The bag-shaped member 42 is used for a fuel changing operation, is installed prior to the fuel changing operation, and is removed when the fuel changing operation is completed. The bag-like member 42 fills a space (also referred to as a “refueling cavity”) 44 (refer to FIG. 1) in the living body shield 32 and above the reactor vessel 14 with water. The radioactivity associated with removing the fuel element 20 from the container 14 is to be minimized.

Therefore, it is very clear that the conventional method of suspending the dosimeter from the wire has a risk that a hole is easily formed in the bag-shaped member 42, and that the bag-shaped member 42 is To prevent proper sealing of the top space between them. Still other problems are due to strong ventilation airflow within the reactor cavity 40, mechanical vibrations during operation of the PWR 12, and expansion and contraction of the reactor vessel 14 during heat up and cool down of the plant 10. It concerns inaccuracies in positioning the dosimeter due to the movement of the auxiliary passive neutron dosimeter.

In an attempt to solve these problems, the present inventor has disclosed a device and method for accurately and reproducibly positioning an auxiliary neutron dosimeter in a reactor cavity 40 of a PWR 12. It is disclosed in the specification of Sho 63-76656. The apparatus includes neutron dose indicating means for indicating a neutron dose accumulated during a fuel cycle of the reactor, and positioning means for remotely positioning the indicating means at a plurality of predetermined locations in a reactor cavity. It is mainly composed. The neutron dose indicating means is a continuous loop (see Fig. 3)
And a plurality of dosimeters arranged along a beaded chain adapted to form a dosimeter. According to a first embodiment of the invention, the positioning means comprises a U-tube fixed to the shell wall of the reactor vessel. A continuous loop is led through the U-tube and the dosimeter is located remotely from the reactor sump. According to another embodiment of the invention, the locating means comprises a collapsible support stand mounted in the reactor cavity, from which a bar having at least one U-tube is suspended, U
The tubing is also used to guide a continuous loop when located remotely from the reactor sump.

However, a major problem with the reactor cavity dosimetry apparatus and method according to Japanese Patent Application No. 63-76656 is that the deployment of the apparatus in a nuclear power plant with limited access or access to the reactor sump. Is difficult. Such access is limited because (1) the radioactivity level in the reactor sump is high, (2) the water in the reactor sump is deep, (3) there is no permanent scaffold in the reactor sump. For at least one of the three reasons: Accordingly, in each of the embodiments disclosed in the specification of Japanese Patent Application No. 63-76656, since it is necessary to access the reactor sump for positioning and recovery of the dosimeter, it is disclosed in the above specification. It will be apparent that a reactor cavity dosimetry apparatus and method that is more easily accessible than the apparatus and method is desired in a nuclear power plant having the aforementioned limitations.

Thus, according to one of the important features of the present invention, access for positioning and retrieving the dosimeter is provided in the reactor vessel.
Enabled from 14 tops. Referring to FIG. 2, the core
An upper access support stand 46 mounted within the reactor cavity 40 for accurately and reproducibly positioning the dosimetry means (not shown in FIG. 2) at a predetermined position axially relative to 16. It is shown.

As best shown in FIGS. 3-7, the upper access support stand 46 includes a frame assembly 48, a pair of pivoting arms having a spring-loaded slider 52 and a radial clamping bolt 54. Assembly (frame assembly holding means) 50
And a continuous chain loop or a continuous loop 56 having a chain support plug 58. Still referring to FIG. 3, it can be seen that the continuous loop 56 is comprised of a transport or delivery chain 126, a locating or placement chain 128, and a dosimetry chain 140. Would.

Each pivot arm assembly 50 is adapted to be rotated from a mounting position in the same plane as the frame assembly 48 to a fixed position that is deployed at right angles across the reactor cavity 40. As shown in FIG. 2, in such a deployed position, the sliders 52 of both pivot arm assemblies 50 are mounted on the reactor vessel 14 to hold the upper access support stand 46 in the proper orientation. It is pressed against the insulating layer 60 by a spring biasing force. If necessary, radial clamping bolts 54 are installed and adjusted to account for process variations between the insulating layer 60 and the outer wall 62 of the reactor cavity 40 as measured by field measurements.

As can be seen from FIG. 3, the frame assembly 48 consists primarily of a pair of frame tubes 64 attached by welding or the like to a pair of cross members or cross members 66. Referring to a typical sized reactor cavity 40, the frame tube 64 has an outer diameter of about 12.7 mm (1/2 in.) And a wall thickness of about 1.
Made of 65mm (0.065in.) 304 type stainless steel tube,
The cross member 66 is about 38.1 mm x 38.1 mm (3/2 in. X 3/2 in.) Made of 304 type stainless steel with a wall thickness of about 3.18 mm (1/8 in.).
Consists of angle iron. Therefore, the dimensions of the fully assembled upper access support stand 46 are approximately 304 mm × 304 mm (12i
n. × 12 in.).

Next, the details of the pivot arm assembly 50 will be described with reference to FIG. In FIG. 4, only one of the pivot arm assemblies 50 is shown, but each pivot arm assembly 50 is connected to a frame sleeve 70 slidably connected to a respective frame tube 64. It should be understood that it has 68. A pair of radially opposed grooves
A 72 is formed at the top of the frame sleeve 70 for engaging a spring pin 74 attached to the top of each frame tube 64. Because it is formed in this way,
Coil spring 76 and washer 78 compatible with frame sleeve 70
And the spring pin 74 and the groove 72
When engaged, the pivot arm assembly 50 is secured in a position transverse to the reactor cavity 40 at right angles.

Further, a pivot arm tube 80 is attached to each connection block 68, and the pivot arm tube 80 has a spring pin 82 that is mounted so as to penetrate in parallel with the frame sleeve 70. The slider 52 is slidably connected to the pivot arm tube 80. Each slider 52 is spring biased by a coil spring 84 provided therein to be biased outwardly from a respective pivot arm tube 80. Also, each slider 52
The slider 52 is formed with a pair of T-shaped slots 86 which are slidably engaged with the spring pins 82 to form a bayonet joint between the slider pin 52 and the corresponding pivot arm tube 80. Combine. With this configuration, the slider 52 is guided along the long axis portion of the slot 86 and the corresponding connection block 68
By sliding inward toward
Can be fixed in compression against the force of the spring 84. When the intersection of the long axis of the slot 86 and the short axis of the slot 86 is reached, the slide 52 is rotated about its corresponding pivot arm tube 80 and the short axis of the slot 86 is reached. A spring pin 82 is pushed into the portion, thereby securing the slider 52 in place.

Referring again to FIG. 3 in conjunction with FIGS. 4-6, a plurality of predetermined locations within the reactor cavity 40 are remote from the plane where the head assembly 18 joins the shell wall 28 of the reactor vessel 14. Means for accurately and reproducibly positioning the reactor cavity dosimeter (see FIG. 7) at the location will be described.

The reactor cavity dosimeter shown in FIG. 7 which constitutes indicating means for indicating the neutron dose accumulated by the reactor vessel 14 during the refueling cycle (the period from refueling to the next refueling) In all respects as disclosed in the specification of Japanese Patent Application No. 63-76656. Accordingly, the dosimeter mainly consists of a plurality of neutron or radiation sensor devices 88 (see FIG. 7) housed in a holder 134, which are connected to each other by a beaded chain 90 of a predetermined length, From the location to a predetermined location within the reactor cavity 40 by a U-tube 92. However, a detailed description of the components of such a dosimeter may not be necessary for a complete understanding of the present invention. Therefore, this dosimeter is described in Japanese Patent Application No. 63-7665.
See No. 6 specification.

An upper access support stand for repeatedly positioning the neutron dose indicating means at a plurality of predetermined locations within the reactor cavity 40 remotely from the plane where the head assembly 18 joins the shell wall 28 of the reactor vessel 14 46 cross members 66
Hole 94 adapted to hold chain support plug 58
And a slit 96. Chain support plug 58
Supports one end of a continuous loop 56 having a sensor device 88 and a beaded chain 90, and a slit 96 captures the other end.

As shown in an enlarged manner in FIG.
Is mainly composed of a T-shaped rear member or a back member 98 on which a pair of pins 100 are formed. The end connector 102 attached to the rosary chain 128 is adapted to be mounted on the pins 100 so as to hang straight from the chain support plug 58. In this manner, each end of the chain 128 constituting the continuous loop 56 is connected to the chain support plug 5 by the end connector 102.
8, and the end connector 102 is suitably retained by a cover member 104 which is attached to the back member 98 by any suitable known means, such as screws 106. The sensor device 88 shown in FIG. 7 is suspended by an arrangement chain 128 hanging down from the lower part of the chain support plug 58 (see FIG. 6), while it is suspended from the upper part of the chain support plug 58 (see FIG. 6). The other end of the connecting loop 56 starting from the extending delivery chain 126 passes through a slit 96,
96 as appropriate. The length of the placement chain 128 is based on field measurements on the upper surface of the upper cross member 66.

As can be understood from FIGS. 3 to 5, the slit 96 is
Formed in the upper part of the upper cross member 66 and having a triangular outer part, the outer part is the plate 1 on which the spring plunger (continuous loop holding means) 110 is mounted.
It becomes narrow near 08. According to a preferred embodiment of the present invention, the spring plunger 110 is a full-stroke manual tension spring plunger that allows the plunger portion 112 to be fully retracted into the body portion 116 and then to be secured in a fully retracted position. Be composed. By simply turning the handle portion 114 as shown in FIG. 4, the fixing of the plunger portion 112 is released, and the plunger portion 112 can extend from the main body portion 116. One suitable spring plunger of this type is the Reid Tool Supply Company.
Company).

The spring plunger 110 fits into the hole 10 formed in the plate 108.
8 and attached to the plate 108 by known means such as nuts 120. With this arrangement, and as particularly shown in FIGS. 3 and 5, the plunger portion 112 of the spring plunger 110, when extended, accurately repeats the other end of the continuous loop 56. The delivery chain 126 fixed in the slit 96 is held. Here, as shown in FIG.
Note that the width of 96 and the thickness of the upper cross member 66 very close to the slit 96 are formed to be approximately equal to the dimensions of the wire between the individual balls in the distribution chain 126. It is. It has been found that such a configuration allows a simple but sufficient capture of the delivery chain 126 in the slit 96 during remote positioning of the reactor cavity dosimeter.

The U-shaped tube 92 shown in FIG. 3 is appropriately attached to the support plate 122 by a pair of brackets 124,
22 is attached to insulating layer 60 surrounding reactor vessel 14 by any suitable means, such as a # 14 x 7/8 in. Stainless steel tapping screw (not shown). U-tube 92, support plate
One such combination of 122 and bracket 124 is provided, one at each of a plurality of predetermined locations azimuthally positioned about and below the reactor vessel 14. U-shaped tube 92
Are positioned upwardly toward the upper access support stand 46, as shown in FIG.

If the guiding means consisting of the U-tube 92, the support plate 122 and the bracket 124 were arranged as described above, the reactor cavity dosimeter would be axially accurate and reproducible relative to the core 16. Is positioned. The appropriate length of bead chain (the portion previously described as "delivery chain" 126) is threaded through each of the U-tubes 92, the free ends of which are withdrawn to the refueling cavity 44.

From the refueling cavity 44, at the level of the plane defined by the joint between the head assembly 18 and the shell wall 28 of the reactor vessel 14, one of the free ends of the delivery chain 126 is connected to a chain support plug 58. Connected to the top of Then, the sensor device
A dosimeter chain 140 (see FIG. 7) consisting of 88 and a holder 134, an interlocking bead chain 90, and an upper and lower stop element 130 are connected at one end to a deployment chain 128. The other end of the arranging chain 128 is passed through the hole 94 of the upper cross member 66 of the upper access support stand 46 and is connected to the lower portion of the chain support plug 58. The dosimetry chain 140 is likewise connected to the other free end of the delivery chain 126, completing a continuous loop 56 through each of the U-tubes 92. If necessary, the continuous loop 56 is circulated through the U-tube 92 to ensure free movement. Further, each dosimetry chain 140 may include a recognition plate 132 mounted near one of the stop elements 130.

The operation will be described. When installing the reactor cavity dosimeter, the operator first compresses the spring-loaded slider 52 of each pivot arm assembly 50, and appropriately fixes the slider 52 with a bayonet joint (FIG. 3). reference). Thereafter, each pivot arm assembly 50 is depressed and rotated to the plane of the frame assembly 48. Next, the upper access support stand 46 (with the continuous loop 56 in place as described above) is inserted into the reactor cavity 40 and the shelf 150 formed in the primary biological shield 32 (see FIG. 2). ).

Once the upper access support stand 46 has been positioned by the operator in this manner, each pivot arm assembly 50 is rotated out of the plane of the frame assembly 48 and the frame sleeve
Engage the groove 70 of 70 with the corresponding pin 74 of the frame tube 64,
This secures the pivot arm assembly 50 in a position transverse to the reactor cavity 40 at right angles.

The operator then rotates the pivot arm slider 52 to release from each bayonet joint, thereby causing the slider 52
Is pressed against the insulating layer 60 by a spring urging force. The difference in the radial gap between the primary biological shield 32 and the insulating layer 60 measured in the field is eliminated by appropriately adjusting the tightening bolts 54 in advance. That is, with the springs 84 slightly compressed, the tightening bolts 54 are threaded or loosened into the corresponding connection blocks 68 as required to hold the upper access support stand 46 in a substantially upright position. They make adjustments.

Thereafter, the dosimeter chain 128 is connected to the reactor cavity 40
The chain is fixed in place by lowering it and holding a part of the chain by the slit 96 and holding it by the plunger portion 112. As can be seen from the specification of Japanese Patent Application No. 63-76656, the reactor cavity dosimeter may include only the length of the bead chain 90 centered on the intermediate plane of the core 16 in the axial direction. Is a solid state track detector (SSTR) housed in an aluminum capsule axially centered at a predetermined location (eg, upper and lower reactor vessel strip circumferential welds) with respect to the reactor core 16
And a radiation monitor (RM).

Subsequently, when replacing the reactor cavity dosimeter,
The plunger portion 112 is pulled by operating the plunger 110, the delivery chain 126 is detached from the slit 96, and the dosimetry chain 140 is connected to the refueling cavity floor 160 (FIG. 2).
Chain loop so that it can be lowered to the height of
Cycle through 56. The part between the stop elements 130 is removed and replaced with a new sensor device 88, holder 134 and chain 90. Next, the reverse procedure is performed, and the chain is manually lowered until the chain support plug 58 is again placed on the upper surface of the upper cross member 66. In this manner, the dosimeter is axially moved with respect to the core 16 and the reactor vessel 14. Reposition accurately. Then, the delivery chain side of the loop 56 is gently pulled up, the chain is engaged in the slit 96, and the plunger 110 is released to function as a retainer or a keeper that crosses the slit 96, thereby dropping the chain from the slit 96. To prevent After this, the extra chain is moved to the upper access support stand 46, as shown in FIG.
Hang on.

The method of the present invention for monitoring the irradiation of neutrons on the reactor vessel 14 comprises forming a plurality of sensor devices 88,
From the plane defined by the joint between the insulating layer 60 attached to the torso wall 28 of 14 and the head assembly 18, the sensor device
It consists mainly of the step of remotely positioning 88. Thus, the sensor device 88 is positioned at a predetermined position in the reactor cavity 40, and is exposed to neutrons by operating the nuclear power plant 10. If the fuel element 20 of the PWR 12 is depleted, the operation of the plant 10 is shut down and the sensor device 88 is remotely retrieved to the plane, thereby minimizing refueling operations. Then, in order to better evaluate the long-term effects of neutron irradiation on the material properties of the reactor vessel 14, the new sensor apparatus 88 is accurately positioned at a predetermined height with respect to the reactor vessel 14. Reposition.

Obviously, various modifications are possible from the above description.
Therefore, it is to be understood that the invention may be practiced otherwise than as specifically described without departing from its scope.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a typical nuclear power plant, and FIG.
The figure shows a side view of the upper access support stand used with the device according to the invention, an enlarged view of the enclosing part 2 of FIG. 1, and FIG. 3 is a perspective view of the upper access support stand shown in FIG. 4 is an exploded perspective view of an upper portion of the upper access support stand shown in FIG. 3, FIG. 5 is an enlarged view of a slit shown in FIG. 3, and FIG. 6 is a chain support shown in FIG. FIG. 7 is a schematic exploded view of a sensor device used with the device according to the present invention. In the figure, 10: Nuclear power plant 12 ... Pressurized water reactor, 14 ... Reactor vessel 16 ... Core, 18 ... Head assembly 28 ... Body wall, 32 ... Primary biological shield 40 ... Reactor cavity 46 ... Upper access support stand (positioning means) 48 ... Frame assembly 50 ... Pivoting arm assembly (Frame assembly holding means) 52 ... Slider (Fixing means) 56 ... Continuous loop ( Positioning means) 58 Chain support plug 88 Sensor device (neutron dose indicating means) 94 Hole

Claims (3)

(57) [Claims] 1. A reactor vessel having a body wall and a head assembly, and a plurality of neutron generating reactors housed in the reactor vessel, wherein the fuel is exhausted and replaced periodically. A nuclear power plant comprising: a reactor core having a group of fuel elements; and a primary biological shield that substantially surrounds the reactor vessel and forms a reactor cavity between the shell wall. A support stand that is adapted to be removably mounted within; a plurality of axially different locations preset relative to the core within the reactor cavity suspended between two long chains. Neutron dose indicating means for indicating a neutron dose accumulated during a refueling cycle; and a neutron dose indicating means disposed on the support stand for indicating each of the chains; Neutron irradiation monitoring at a plurality of preset positions, and positioning means for repeatedly positioning the neutron dose indicating means remotely from the position of the surface where the head assembly is joined to the trunk wall. apparatus. 2. A reactor vessel having a body wall and a head assembly, and a plurality of neutron-generating reactors housed within the reactor vessel, the fuel being exhausted and replaced periodically. A nuclear power plant having a core having a group of fuel elements of the following type and a primary biological shield substantially surrounding the reactor vessel and forming a reactor cavity therewith: B) forming between two long chains suspended from a support stand of a plurality of neutron sensor devices adapted to indicate the neutron dose accumulated during a refueling cycle; Locating the neutron sensor device at a plurality of predetermined locations in a tee remotely from the location of the surface where the head assembly joins the torso wall; and (c) operating the nuclear power plant during a refueling cycle. Irradiating the remotely located neutron sensor device, and (d) causing the irradiated neutron sensor device to illuminate the surface when the nuclear power plant stops operating after the end of the refueling cycle. (E) placing a plurality of similar neutron sensor devices at the plurality of predetermined locations, and monitoring the neutron irradiation of the reactor vessel. 3. A nuclear power plant, comprising a reactor cavity having a body wall and a head assembly and having a reactor vessel accommodating a reactor core, the reactor water having a reactor vessel having a predetermined height. A method for supporting a radiation sensor device positioned at: a) a substantially rectangular frame assembly having a cross member with holes; and a pivotable for holding said frame assembly in a substantially upright position. And a support stand having fixing means for fixing the frame assembly holding means itself at a pivotal position across the reactor cavity. (B) providing a chain for suspending the radiation sensor device; (c) providing a substantially U-shaped U-tube at a predetermined height below the support stand, (D) feeding one end of the chain through the U-tube, (e) attaching the other end of the chain to the radiation sensor device, (f) Forming a continuous loop with the chain and the radiation sensor device; (g) attaching a chain support plug to the continuous loop at a point separated from the radiation sensor device by a predetermined distance corresponding to the predetermined height; (H) providing a continuous loop holding means for holding the continuous loop with respect to the support stand; (i) the continuous loop in the U-tube until the point where the chain support plug rests on the cross member. And (j) engaging the continuous loop holding means. A method for supporting a radiation sensor device.