Method for judging state of fuel element based on temperature sensing

Abstract

The invention belongs to the technical field of reactor fuel damage detection, and particularly relates to a method for judging the state of a fuel element based on temperature sensing. Comprising the following steps that 1, the temperature in an air gap between a fuel cladding and a pellet is monitored, and air gap temperature change rate reference values under different crevasse sizes of the cladding are determined; 2, the state of the fuel element is judged; and step 3, after judging that the fuel element is damaged, estimating the crevasse size of the fuel cladding. The method has the beneficial effects that the state of the fuel element is judged based on temperature sensing, the accuracy of state judgment of the fuel element can be improved, the state of the fuel element can be reflected in real time, the state judgment process of the fuel element is shortened, state monitoring is independently carried out on each fuel element, and damaged fuel can be accurately positioned; and subsequent maintenance treatment is facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of reactor fuel damage detection, and in particular relates to a method for judging the state of a fuel element based on temperature sensing. Background Art

[0002] Fuel elements are the core components and power sources of the reactor, and are also the first safety barrier for radioactive fission products. Once a fuel element is damaged, the radioactive material in the element will leak into the reactor coolant, which will significantly increase the radioactivity level of the reactor coolant and pose a radiation safety risk to the normal operation and shutdown of the reactor for maintenance. Therefore, timely and accurate monitoring of whether fuel elements are damaged is crucial to the safety of reactor operation.

[0003] Currently, the methods for monitoring nuclear fuel cladding damage during shutdown and unloading are relatively flexible. The online damage monitoring methods are mainly based on the detection of fission products or decay products released by damaged components. There are certain uncertainties and it is impossible to quickly and accurately locate the damaged area. Summary of the invention

[0004] The purpose of the present invention is to provide a method for judging the state of a fuel element based on temperature sensing, which can realize real-time online and accurate monitoring of the state of a rod-type fuel element.

[0005] The technical solution of the present invention is as follows: A method for judging the state of a fuel element based on temperature sensing comprises the following steps:

[0006] Step 1: Monitor the temperature in the air gap between the fuel cladding and the pellets to determine the reference value of the air gap temperature change rate when the cladding has different crack sizes;

[0007] Step 2: Determine the status of the fuel element;

[0008] Step 3: After determining that the fuel element is damaged, estimate the size of the rupture of the fuel cladding.

[0009] In the step 1, during the production of the fuel element, a temperature sensor is installed in the fuel cladding to monitor the temperature in the air gap between the fuel cladding and the pellet;

[0010] In step 1, fuel element test pieces with different breach sizes are prepared in advance, and the change rate of the air gap temperature is measured under normal operating conditions in the reactor.

[0011] The step 1 determines the reference value of the air gap temperature change rate when different breach sizes appear in the cladding by means of a theoretical model simulation method.

[0012] In step 2, during the operation of the reactor, the temperature sensor is used to monitor the change of the air gap temperature in real time to judge the status of the fuel element: when the air gap temperature remains stable, the fuel element is judged to be intact; when the air gap temperature is lower than 320°C, the fuel element is judged to be damaged.

[0013] The air gap temperature in step 2 is maintained stable within a fluctuation range of ±5%.

[0014] In the step 3, the change rate of the air gap temperature measurement value is analyzed and compared with the reference value of the change rate of the air gap temperature under different breach sizes obtained in step 1.

[0015] The beneficial effects of the present invention are as follows: the present invention determines the state of fuel elements based on temperature sensing, which can improve the accuracy of fuel element state judgment, instantly reflect the state of fuel elements, shorten the fuel element state judgment process, and independently monitor the state of each fuel element, which can achieve accurate positioning of damaged fuel and facilitate subsequent maintenance and processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of a method for determining the state of a fuel element based on temperature sensing provided by the present invention;

[0017] Figure 2 Schematic diagram of estimating the size of the breach using the rate of change of air gap temperature. DETAILED DESCRIPTION

[0018] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] The air gap between the rod-type fuel element cladding and the pellet is generally filled with helium. When the fuel element cladding is intact, the temperature in the air gap should be maintained at a relatively stable state; when the cladding is damaged, the coolant will quickly enter the air gap in the cladding through the breach, causing the temperature in the air gap to drop sharply;

[0020] The present invention provides a method for judging the state of a fuel element based on temperature sensing. The temperature sensor is used to continuously monitor the temperature in the air gap between the fuel element cladding and the pellet online. When a sharp change in the temperature of the air gap in the fuel element is detected during the operation of the reactor, it can be determined that the fuel element cladding is damaged. After determining that the fuel element is damaged, the size of the rupture can be estimated by the rate of change of the air gap temperature, and the development trend of the rupture can be continuously analyzed.

[0021] like Figure 1 As shown, during the production process of the fuel element, a temperature sensor is installed in the fuel element to monitor the temperature in the air gap between the cladding and the pellet.

[0022] Reactor operators can judge the status of fuel elements by the changes in the air gap temperature inside the fuel elements.

[0023] During reactor operation, the air gap temperature should be maintained at a stable value or have small fluctuations; if the temperature sensor inside the fuel element detects that the air gap temperature is significantly lower than the air gap temperature design value P0, it can be determined that the fuel element cladding is damaged.

[0024] like Figure 2 As shown, the reference value of the air gap temperature change rate under different crack sizes of the fuel element can be set through research; after judging that the fuel element is damaged, the crack size can be estimated by analyzing the air gap temperature change rate, and the crack change trend can be continuously analyzed.

[0025] A method for determining the state of a fuel element based on temperature sensing comprises the following steps:

[0026] Step 1: During the production of fuel elements, a temperature sensor is installed in the fuel cladding to monitor the temperature in the air gap between the fuel cladding and the pellet (hereinafter referred to as the "air gap temperature"). Fuel element test pieces with different breach sizes are prepared in advance, and the rate of change of the air gap temperature is measured under normal operating conditions in the reactor. Alternatively, a reference value of the rate of change of the air gap temperature under different breach sizes in the cladding is determined through theoretical model simulation (the rate of change of the air gap temperature corresponding to different breach sizes).

[0027] Step 2: During reactor operation, the temperature sensor is used to monitor the change of the air gap temperature in real time, and then the status of the fuel element is judged: when the air gap temperature remains stable (fluctuation within the range of ±5%), it can be judged that the fuel element is intact; when the air gap temperature is lower than 320°C, it can be judged that the fuel element is damaged.

[0028] Step 3: After determining that the fuel element is damaged, the change rate of the air gap temperature measurement value over time can be analyzed and compared with the reference value of the air gap temperature change rate under different breach sizes obtained in step 1. When the change rate of the air gap temperature measurement value is close to a certain reference value, the breach size of the current cladding can be estimated to be the breach size corresponding to the reference value. The change trend of the breach size can be continuously analyzed, and then emergency measures such as continuous observation or power reduction and shutdown of the reactor can be taken.

[0029] The above is only one embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiment. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A method for determining the state of a fuel element based on temperature sensing, characterized in that: The steps include: Step 1: Monitor the temperature in the air gap between the fuel cladding and the pellets to determine the reference value of the air gap temperature change rate when the cladding has different crack sizes; Step 2: Determine the status of the fuel element; Step 3: After determining that the fuel element is damaged, estimate the size of the rupture of the fuel cladding.

2. A method for determining the state of a fuel element based on temperature sensing as claimed in claim 1, characterized in that: In step 1, during the production of the fuel element, a temperature sensor is installed in the fuel cladding to monitor the temperature in the air gap between the fuel cladding and the pellet.

3. A method for determining the state of a fuel element based on temperature sensing as claimed in claim 1, characterized in that: In step 1, fuel element test pieces with different breach sizes are prepared in advance, and the change rate of the air gap temperature is measured under normal operating conditions in the reactor.

4. A method for determining the state of a fuel element based on temperature sensing as claimed in claim 1, characterized in that: The step 1 determines the reference value of the air gap temperature change rate when different breach sizes appear in the cladding by means of a theoretical model simulation method.

5. A method for determining the state of a fuel element based on temperature sensing as claimed in claim 1, characterized in that: In step 2, during the operation of the reactor, the temperature sensor is used to monitor the change of the air gap temperature in real time to judge the state of the fuel element: when the air gap temperature remains stable, the fuel element is judged to be intact; When the air gap temperature is lower than 320°C, the fuel element is judged to be damaged.

6. A method for determining the state of a fuel element based on temperature sensing as claimed in claim 5, characterized in that: The air gap temperature in step 2 is maintained stable within a fluctuation range of ±5%.

7. A method for determining the state of a fuel element based on temperature sensing as claimed in claim 5, characterized in that: In the step 3, the change rate of the air gap temperature measurement value is analyzed and compared with the reference value of the change rate of the air gap temperature under different breach sizes obtained in step 1.

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