Method for judging state of fuel element based on pressure 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 pressure sensing. Comprising the following steps that 1, the pressure in an air gap between a fuel cladding and a pellet is monitored; determining an air gap pressure change rate reference value when the cladding has different crevasse sizes; 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 advantages that the states of the fuel elements are judged based on pressure sensing, the accuracy of state judgment of the fuel elements can be improved, the states of the fuel elements can be reflected in real time, the state judgment process of the fuel elements is shortened, state monitoring is independently carried out on each fuel element, damaged fuel can be accurately positioned, and the fuel element state judgment efficiency is improved. 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 pressure 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 the damaged area cannot be located quickly and accurately. 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 pressure 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 pressure sensing comprises the following steps:

[0006] Step 1: Monitor the pressure in the air gap between the fuel cladding and the pellets; determine the reference value of the air gap pressure change rate when the cladding has different breach 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 fuel element production process, a pressure sensor is installed in the fuel cladding to monitor the pressure in the air gap between the fuel cladding and the pellet.

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

[0011] In the step 1 or by a theoretical model simulation method, a reference value of the air gap pressure change rate under different breach sizes of the cladding is determined.

[0012] In the step 2, during the operation of the reactor, the air gap pressure change is monitored in real time by a pressure sensor, and the state of the fuel element is judged: when the air gap pressure remains stable, the fuel element is judged to be intact; when the air gap pressure is higher than 3MPa, the fuel element is judged to be damaged.

[0013] In step 2, the air gap pressure is maintained stable with fluctuations within a range of ±5%.

[0014] In step 3, after determining that the fuel element is damaged, the rupture size of the fuel cladding is estimated by analyzing the change rate of the air gap pressure measurement value and comparing it with the reference value of the air gap pressure change rate under different rupture 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 pressure 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 judging the state of a fuel element based on pressure sensing provided by the present invention;

[0017] Figure 2 Schematic diagram of estimating the breach size using the rate of change of air gap pressure. 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 pressure 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 rupture, causing the pressure in the air gap to rise sharply;

[0020] The present invention provides a method for judging the state of a fuel element based on pressure sensing. The pressure sensor is used to continuously monitor the pressure in the air gap between the fuel element cladding and the pellet online. When a sharp change in the pressure in the air gap of 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 pressure, 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 pressure sensor is installed in the fuel element to monitor the pressure 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 pressure inside the fuel elements.

[0023] During reactor operation, the air gap pressure should be maintained at a stable value or have small fluctuations; if the pressure sensor inside the fuel element detects that the air gap pressure is significantly higher than the air gap pressure 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 pressure change rate under different rupture sizes of the fuel element can be set through research; after judging that the fuel element is damaged, the rupture size can be estimated by analyzing the air gap pressure change rate, and the rupture change trend can be continuously analyzed.

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

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

[0027] Step 2: During reactor operation, the air gap pressure changes are monitored in real time through the pressure sensor, and the status of the fuel element is judged accordingly: when the air gap pressure remains stable (fluctuation within the range of ±5%), the fuel element can be judged to be intact; when the air gap pressure is higher than 3MPa, the fuel element can be judged to be damaged.

[0028] Step 3: After determining that the fuel element is damaged, the change rate of the air gap pressure measurement value over time can be analyzed and compared with the reference value of the air gap pressure change rate under different rupture sizes obtained in step 1. When the change rate of the air gap pressure measurement value is close to a certain reference value, the rupture size of the current cladding can be estimated to be the rupture size corresponding to the reference value. The change trend of the rupture 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 judging the state of a fuel element based on pressure sensing, characterized in that: The steps include: Step 1: Monitor the pressure in the air gap between the fuel cladding and the pellets; determine the reference value of the air gap pressure change rate when the cladding has different breach 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 pressure sensing as claimed in claim 1, characterized in that: In the step 1, during the fuel element production process, a pressure sensor is installed in the fuel cladding to monitor the pressure in the air gap between the fuel cladding and the pellet.

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

4. A method for determining the state of a fuel element based on pressure sensing as claimed in claim 1, characterized in that: In the step 1 or by a theoretical model simulation method, a reference value of the air gap pressure change rate under different breach sizes of the cladding is determined.

5. A method for determining the state of a fuel element based on pressure sensing as claimed in claim 1, characterized in that: In the step 2, during the operation of the reactor, the air gap pressure change is monitored in real time by a pressure sensor, and the state of the fuel element is judged: when the air gap pressure remains stable, the fuel element is judged to be intact; when the air gap pressure is higher than 3MPa, the fuel element is judged to be damaged.

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

7. A method for determining the state of a fuel element based on pressure sensing as claimed in claim 1, characterized in that: In step 3, after determining that the fuel element is damaged, the air gap pressure is measured by analyzing the air gap pressure. The change rate of the value is compared with the reference value of the change rate of the air gap pressure under different breach sizes obtained in step 1. Estimate the breach size of the fuel cladding.

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