JPS6342759B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a refueling machine used for exchanging nuclear fuel in a nuclear reactor.

In general, in a nuclear reactor, it is necessary to understand the nuclear state inside the reactor, such as the reactivity at the end of criticality, for safety reasons such as preventing incorrect loading of nuclear fuel into the reactor core during fuel exchange or near criticality. Therefore, the neutron flux inside the reactor vessel is being measured.

However, in liquid metal-cooled nuclear reactors such as sodium-cooled fast reactors, the temperature of the sodium coolant is 500°C or higher during reactor operation, and the reactor vessel must be completely sealed, so neutron The neutron detector is installed in the reactor vessel close to the core due to the difficulty of taking the detector measurement line outside the reactor vessel and the fact that the sodium coolant is chemically very active. It was extremely difficult to do so.

For this reason, in conventional fast breeder reactors, for example, the first
As shown in the figure, a neutron detector 2 is installed outside the reactor vessel 1.
The neutron flux inside the reactor vessel 1 is detected by arranging the neutron flux.

However, in such a conventional method, because the distance between the core 3 and the neutron detector 2 is large, the number of neutrons detected by the neutron detector 2 is very small, and therefore the number of neutrons detected by the neutron detector 2 is very small. Since the number of neutrons counted is small, the reliability of neutron flux detection is low, and even if a plurality of neutron detectors 2 are arranged along the circumferential direction outside the reactor vessel 1, the number of neutrons that are counted in the reactor core 3 is low. The drawback was that changes in neutron flux due to loading or withdrawal from the core 3 could not be detected. Additionally, for detectors installed inside the reactor vessel, the neutron flux level, gamma ray level, and temperature conditions range widely during reactor shutdown and power operation, and various restrictions are imposed on the detector usage conditions and operating methods. was.

On the other hand, as shown in FIG. 1, a fast breeder reactor generally has a reactor vessel 1 with a hemispherical bottom and a rotating plug 4 that shields the opening of the reactor vessel 1. The drilled through hole is equipped with a fuel exchanger 5 for exchanging the nuclear fuel in the reactor core 3.

The tip of this fuel exchanger 5 is used when exchanging fuel.
It accurately approaches a predetermined position of the core 3 while maintaining a predetermined positional relationship.

In addition, the fuel exchanger 5 is used only when exchanging fuel.
Since the furnace vessel 1 is inserted into the furnace vessel 1, the thermal influence on the insertion portion inside the furnace vessel 1 is relatively small compared to that during operation.

Therefore, it is thought that if a neutron detector is installed at the tip of this fuel exchanger 5, the above-mentioned conventional drawbacks can be overcome even when the neutron flux level is very low at the time of reactor shutdown. .

The present invention has been made with attention to this point, and is a fuel exchanger used for exchanging nuclear fuel in a nuclear reactor, characterized in that a neutron detector is attached to the lower end of the fuel exchanger. This is what we are trying to provide.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to an embodiment shown in the drawings. Note that parts common to those in FIG. 1 are indicated by the same reference numerals.

The fuel exchanger shown in FIG. 2 includes a nuclear fuel gripping section 6 that grips nuclear fuel, a connecting section 7 following this nuclear fuel gripping section 6, and a driving section 8 following this connecting section 7 for driving the fuel gripping section 6. The main portion is composed of the following, and the lower end of the connecting portion 7 is equipped with a neutron detector 9 using a fusion counter, for example.

From this neutron detector 9, for example,
A measurement line 10 consisting of an MI cable is led to a measurement device 11 through a connection section 7 and a drive section 8.

The fuel exchanger configured as described above is used by mounting the driving part 8 on a through hole formed in the rotary plug 4, and inserting the connecting part 7 following this into the through hole.

In the refueling machine configured as described above, the neutron detector 9 is located near the fuel gripping part 6 that grips the nuclear fuel during nuclear fuel exchange, so the neutron detector 9 is brought very close to the reactor core. This makes it possible to detect a much larger amount of neutrons than in the past.

In addition, the neutron detector 9 approaches the position closest to the fuel to be replaced and is most strongly affected by the fuel, so the core of the reactor core 3 during fuel replacement or when loading fuel near criticality. This makes it possible to accurately grasp the current state.

Furthermore, since the fuel exchanger is placed outside the reactor vessel 1 during operation of the nuclear reactor, the neutron detector 9 and the measurement line 10 are not thermally or chemically affected by the high temperature coolant during operation.

As described above, according to the refueling machine of the present invention, changes in neutron flux during refueling can be easily and accurately detected, so erroneous loading or unloading of fuel into the reactor core can be promptly prevented. be able to.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of a reactor vessel of a fast breeder reactor, and FIG. 2 is a schematic view showing an embodiment of a fuel exchanger of the present invention. 1... Reactor vessel, 2, 9... Neutron detector, 3...
... Core, 4 ... Rotating plug, 5 ... Fuel exchange machine,
6... Nuclear fuel holding part, 7... Connection part, 8... Drive part, 10... Measuring line, 11... Measuring device.

Claims (1)

[Scope of Claims] 1. A fuel exchange machine used for exchanging nuclear fuel in a nuclear reactor, characterized in that a neutron detector is attached to the lower end of the fuel exchange machine. 2. The fuel exchanger according to claim 1, wherein the nuclear reactor is a liquid metal cooled nuclear reactor.