JPH0445799B2 - - Google Patents

Description

Detailed Description of the Invention The present invention emits ultrasonic waves from an ultrasonic transmitter/receiver (hereinafter referred to as a transducer) located near the upper end of the core of a sodium-cooled fast reactor, and is installed opposite the transducer. This is a reflector-based ultrasonic fluoroscope that can quickly detect obstacles (anomalies in the reactor core, especially abnormalities in the loading status of core components) using the waves reflected from the reflector. By making the mounting structure of the reflector mounted on the reactor so that it can slide, deformation due to the difference in thermal expansion caused by the temperature difference between the reactor inner cylinder and the reflector during reactor scram does not become a restraining load on the reflector. , relates to an ultrasonic fluoroscopy device characterized by reducing thermal stress and increasing structural reliability.

In general, in a sodium-cooled fast reactor, before refueling, the control rod drive mechanism and control rods installed at the top of the reactor vessel containing the reactor core are separated and inserted into the reactor core to reduce the reactor output (hereinafter referred to as reactor scram)
After this, a rotating plug integrated with the upper core structure (hereinafter referred to as UCS) is rotated to exchange fuel. By the way, if the control rods are not reliably separated and inserted into the reactor core during fuel exchange, or
If a core component is floating and interfering with the UCS, rotating the rotating plug may cause catastrophic damage to the core. Therefore, a transducer and a reflector are installed at a position where the gap between the core components and the UCS can be seen, and monitoring is performed using ultrasonic waves emitted from the transducer. To perform this monitoring, the transducer is
A superstructure that can perform an elevation movement parallel to the bottom surface of the UCS, a horizontal movement that covers the entire top of the core components, and a vertical movement that covers the entire gap between the top of the core components and the bottom surface of the UCS. A sonic fluoroscopy system is used to detect whether the control rods have been separated and inserted into the reactor core, and whether there is any interference with the UCS due to floating core components.

Incidentally, the reactor scram operation is performed to ensure the safety of the reactor even in the event of an abnormality such as an earthquake. After this reactor scram operation, there is no heat generated from the fuel, and the reflector, UCS, etc. are at a low temperature of approximately 400℃.
There is a time when the reactor inner cylinder reaches a high temperature of about 500℃ (Na temperature at the outlet during reactor operation). At this time, high stress is generated on the reflector due to the combination of stress due to the sudden drop in surface temperature, stress due to the difference in thermal deformation due to the temperature difference with the reactor inner cylinder, and stress due to the earthquake. Therefore, there are the following problems.

(1) Since reactor scram operations are scheduled a considerable number of times during the reactor's life, repeated high stresses will shorten the life determined by thermal fatigue.
Furthermore, distortion of the reflecting surface may increase, which may reduce reflection accuracy.

(2) Not only the reflector, but also the inner cylinder side of the reactor, is subject to extremely severe conditions when considering the stress due to the temperature difference between the inner and outer surfaces, seismic load, etc., as well as the restraining load of the reflector, which may affect the structural integrity. This poses a problem in terms of guarantee.

The present invention has been made to address the above problems, and provides a highly reliable ultrasonic fluoroscopy device by reducing thermal stress caused by the temperature difference between the inner cylinder and the reflector plate during reactor scram. With the goal.

The present invention will be described below with reference to the drawings of one embodiment.

FIG. 1 is a longitudinal sectional view of a nuclear reactor vessel equipped with an ultrasonic fluoroscope according to the present invention. A reactor vessel 12 is provided that houses a reactor core 10 in which core components are constructed, a core barrel 11 that supports the reactor core 10, and the like. A shield plug 13 is provided above the reactor vessel 12 to form a cover gas space at a coolant liquid level 14 within the reactor vessel 12 . In the coolant inside the reactor vessel 12, an inner cylinder 15 is provided outside the core barrel 11 to surround the core barrel 11.

A UCS 16 is provided on the lower surface of the shield plug 13 with a gap above the core components. Further, a drive unit 17 for driving a transducer is provided on the shield plug 13, and is connected to the core 10 in the reactor vessel 12 during normal operation.
A transducer 18 is provided to be located in the gap of the UCS 16, and this transducer 1
8 is connected to the drive section 17 by a holding tube 19 provided through the shield plug 13. These drive section 17, holding tube 19, and transducer 18 constitute a transducer drive device. A reflector plate 20 is attached within the inner cylinder 15 at a position facing the transducer 13 . The attachment of the reflection plate 20 to the inner cylinder 15 is shown in FIGS. 2 to 5. Figures 2 to 5
In the embodiment shown in the figure, a mounting seat 15a for mounting a reflector 20 is provided on the inner surface of the cylinder 15, and a necessary number of reflectors 20 are provided to cover the top of the reactor core in the circumferential direction.

Further, the reflection plate 20 is attached with two bolts via a disc-shaped liner.

Figure 3 shows the fixed side, where the fixed side liner 23 and the reflector 20 are tightened with the fixed side bolts 21 without any gaps, and the fixed side liner 23, the reflector 20, and the fixed side bolts 21 are all made of the same material (for example, stainless steel).
is used.

Figure 4 shows the slide side, slide side liner 2
4, and a reflector plate 20 having circumferentially elongated bolt holes.
The slide-side bolts 22 are tightened with a certain gap, and the slide-side liner 24 and the slide-side bolts 22 are made of a material different from the reflector 20 (for example, Inconel material) or surface hardened (Stellite, etc.).
The material used is coated with Kolmonoy (Kolmonoy, etc.).

Fixed side bolt 21 and sliding side bolt 22
The pin 25 passes through the mounting seat 15a and is prevented from rotating.

The functions and operations of the ultrasonic fluoroscope described above will be described below.

A transducer drive device including a transducer drive section 17, a holding tube 19, a transducer 18, etc. is installed in the reactor vessel 12 by penetrating the shield plug 13. The reflector plate 20 is installed in the furnace at the time when the inner cylinder 15 is installed.
The control rods are separated and inserted into the core 10 by transmitting ultrasonic waves toward the reflector 20 through the gap between the lower surface of the UCS 16 and the upper surface of the core 10 and receiving the reflected waves from the reflector 20. UCS due to levitation of core components.
The presence or absence of interference with 16 is detected. Here, if there is a temperature difference between the reflector 20 and the inner cylinder 15 during reactor scram, and a difference in thermal expansion occurs, in the example shown in FIG. However, since the slide-side bolts 22 are tightened with a certain gap to the reflector 20, the slide-side bolts 22 slide between the heads of the slide-side bolts 22 and the slide-side liner 24, and the difference in thermal expansion occurs. absorb.

When sliding, the slide side liner 24 and the slide side bolt 22 are attached to the reflector 20.
Since they are made of different materials, there is no need to worry about galling or abrasion. In addition, the fixed side of the reflector plate 20 is tightened with fixed side bolts 21 without any gaps, and the sliding side has almost no gaps except for the circumferential elongated holes, so it has sufficient positioning and movement prevention functions. have.

In addition, it is very simple in structure and easy to manufacture because the fixed side and sliding side are the same except for the thickness of the liner.

Therefore, even when reactor equipment equipped with this ultrasonic fluoroscopy device undergoes reactor scram operation due to a fuel change, an earthquake, or other reasons, deformation due to the difference in thermal expansion between the reflector and the inner cylinder will not be affected by the restraining load. This reduces thermal stress. As a result, the reflector and inner cylinder perform their normal functions without abnormalities, reflect the ultrasonic waves emitted from the transducer normally, and promptly detect obstacles near the upper end of the core (control Confirmation of rod separation and complete insertion into the core, confirmation of interference between the UCS and core components, etc.)
After confirming that there are no abnormalities, rotate the rotary plug and replace the fuel.

As explained above, the ultrasonic fluoroscope of the present invention has the following features:
By using a reflector mounting structure that prevents the difference in thermal expansion between the inner cylinder and the reflector during reactor scram from becoming a restraining load, thermal stress can be reduced and reflections can be achieved even under seismic loads and severe thermal loads. Abnormalities within the reactor can be normally detected without disturbing the structural integrity of the plate, which has the following effects.

Deformation of both the reflector and the inner cylinder is reduced, the accuracy of the reflecting surface of the reflector is maintained, and the safety of fuel exchange is improved due to improved detection of abnormalities within the reactor. (Damage of the reactor core due to false detection is a fatal accident for the reactor.) Additionally, the structural reliability of the inner cylinder is improved, increasing the reliability of the reactor.

The lifespan against thermal fatigue is improved, and the structural integrity against loads such as during thermal transients and earthquakes is improved, and damage can be prevented. Therefore, it is essential to install ultrasonic fluoroscopy equipment in nuclear reactors designed for long life.

Furthermore, abnormality inspection inside the reactor using ultrasonic fluoroscopy equipment is especially necessary when the reactor is subjected to large earthquakes or thermal transient conditions, and it is necessary to confirm abnormalities in the core. The ability to perform the above inspection using a nuclear reactor is extremely effective in ensuring the safety of a nuclear reactor. This will also lead to improved reactor availability. (The ultrasound fluoroscope was damaged,
If a malfunction occurs, not only will it be impossible to replace the fuel, but repairing the device itself is extremely difficult work. )

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a nuclear reactor vessel according to an embodiment in which an ultrasonic fluoroscope according to the present invention is attached, FIG. 2 is an enlarged view of the reflection plate mounting structure of FIG.
The figure is a vertical cross-sectional view of the fixed side, FIG. 4 is a vertical cross-sectional view of the slide side, and FIG. 5 is an enlarged view of the reflector. 10... Core, 11... Core barrel, 12...
Reactor vessel, 13...Shiyahei plug, 14...
Coolant liquid level, 15...Inner cylinder, 15a...Mounting seat,
16... UCS (upper core mechanism), 17... Drive section,
18...Transducer, 19...Holding tube, 2
0...Reflector plate, 21...Fixed side bolt, 22...
Slide side bolt, 23...Fixed side liner, 2
4...Slide side liner, 25...pin.

Claims (1)

[Claims] 1. An ultrasonic transceiver that transmits ultrasonic signals across the upper part of the reactor core from a position near the upper end of the reactor core housed in the reactor vessel of a liquid metal cooled fast reactor, and this ultrasonic transceiver can be rotated. a reflector plate provided on the inner cylinder near the upper end of the core and opposite the ultrasonic transmitter/receiver, and means for attaching the reflector plate to the inner cylinder; The plate is provided with a round hole and a horizontally oblong circular hole on the fixed side and the sliding side, respectively, and the reflecting plate is inserted into the inner cylinder through the holes, restricting vertical movement while allowing horizontal sliding. An ultrasonic fluoroscopy device characterized in that it is attached.