JPS58142296A - Method of measuring inside pressure of nuclear fuel rod - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention describes a method for measuring the amount of internal pressurization of a nuclear fuel rod #i, mainly a light water reactor J@O nuclear fuel rod.

Nuclear fuel rods used in so-called light water reactors with 1M of boiling water or pressurized water are loaded with a large number of fuel pellets 2 in a cladding tube l made of zirconium alloy, as shown in Figure 1, to prevent the movement of the fuel pellets 8. upper space 1 for
A coil spring 3 of the required strength is fitted into the cladding tube 14, and ends @5m and 5b made of zirconium alloy are applied to both ends of the cladding tube 10, and these are airtightly attached to the cladding tube 2 by Tllll1i (tungsten inert gas welding) or the like. It's stuck.

In order to efficiently transfer the heat generated in the fuel pellet 2 to the cladding tube 2 and, as a result, to keep the temperature of the fuel pellet 2 low, the upper space 4 and the laminated pellet 2 are Gap Kfl between cladding tubes 1! Usually, an inert atmospheric gas such as helium, which has high conductivity, is charged under pressure.

To do this, either punch a vent hole 6 in the upper end plug 51 in advance, or insert the end plug 5a into the cladding tube IK.
After welding, a vent hole 6 is drilled by laser machining, and the fuel rod path is set so that the vent hole 6 is located in the pressurizing chamber a, as shown in Fig. 112. , the air remaining in the fuel rod path and the pressurizing chamber is removed by an intake means (not shown), and then atmospheric gas is introduced into the pressurizing chamber 7 from the high pressure cylinder b (approximately 150 atm) via the pressure reducing valve C. to bring the room to a specified pressure (
The atmospheric pressure is maintained at about 3 s atmospheric pressure 1ij[), and in this state, atmospheric gas is introduced into the fuel rod path through the vent hole 6 to make the fuel rod passage 6 more airtight. In this case, in a light water reactor, if the pressurized amount of atmospheric gas is small, in the late stage of the fuel life after the fission reaction has progressed, the fuel pellet 2 will be transferred to the vegetative gas, which has a lower thermal conductivity than the atmospheric gas. Volatile components are released, which mix with the initial main gas and form pellets 2 and cladding tube 1.
As a result, when the temperature of the fuel pellet 2 is high, the release of cloudy organic matter O is further increased, the heat transfer coefficient is further reduced, and the temperature of the pellet 2 is lowered. In addition, if the so-called "circle feedback" phenomenon occurs, it will increase.

In a pressurized water reactor, the overcharge cooling water pressure is approximately 1!
Since the pressure reaches up to s7 atm, deformation of the cladding tube l due to the pressure difference between the inside and outside of the fuel tank is a problem. There was a case where a full flexion phenomenon occurred where the pipe was crushed by high coolant pressure.

For this reason, it is important to check the pressurized state of the atmospheric gas in the manufactured fuel rod. pressure needle) to monitor the pressure inside the pressurizing chamber a communicating with the space 4 in the fuel rod during the introduction of atmospheric gas, or use a sound collector to connect the fuel rod from the pressurizer a. It only monitors the blowing sound when atmospheric gas is introduced into the inside of the fuel rod A, and cannot directly check the pressure inside the fuel rod passage. After the communication with 1 & is cut off, the pressure inside fuel rod A cannot be fixed and iim.

Therefore, it has been proposed to insert a member that deforms under pressure into the space 4;

It is difficult to accurately measure the amount of deformation of a member from outside the fuel rod; (2) It costs a considerable amount of money to prepare a system to accurately measure; (3) The effective volume of the space decreases, resulting in nuclear fission. This has not been realized due to reasons such as the lack of O storage capacity for generated gas, etc.

On the other hand, it is generally known that when tension is applied to an object, the natural frequency of that object changes.

Therefore, this invention was devised in view of the above-mentioned circumstances, and utilizes the phenomenon that when tension is applied to an object, its natural frequency changes to apply pressure to a nuclear fuel rod filled with atmospheric gas under pressure. The present invention provides a method for gluing that allows the pressure to be easily adjusted from outside without requiring large-scale equipment.

If atmospheric gas is pressurized and sealed inside a nuclear fuel rod,
An axial tensile stress σt is generated in the cladding tube 1 of the nuclear fuel rod, and this stress can be approximated by the following formula: P: internal pressure (amount of pressurization) γ: radius t of the cladding tube: Also, when tensile stress σt is generated in the cladding tube 1 as described above, the natural frequency (1%) S of the nuclear fuel rod path is expressed by the following equation.

Here, f island: Natural frequency of the nuclear fuel rod before pressurization Am: Cross-sectional area of the cladding tube E: Young's modulus of l: Cross-sectional area of l Therefore, first of all, the atmosphere in the entire internal space has the same pressure as this. A reference nuclear fuel rod rht filled with inert 1kf81 gas is prepared, and as shown in Fig. 3, a steel piece 11 is removably attached to the center of the rod using a band, etc. , B, and an electromagnet 12 on the underside of the iron piece 11.
The electromagnet 12 is connected to the oscillator 13, and a non-contact displacement meter 14 is installed above the electromagnet 120 and connected to the signal analyzer 15. Connect with the oscillator 13.

Then, the electromagnet 12 is operated so that the frequency of the oscillator 13 changes continuously, and forced vibration is applied to the nuclear fuel rod path via the iron piece 11.

The amplitude of the nuclear fuel rod path at that time is detected by the displacement needle 14, and the signal is sent to the signal analyzer 15, which detects the resonance point between the forced vibration applied by the electromagnet 12, that is, the oscillator 13-IIX, and the output vibration of the nuclear fuel rod. Detect the frequency f% of the reference nuclear fuel rod path.

Next, remove the reference nuclear fuel rod port from the above measurement member, remove the iron piece 11 from it, pressurize the atmosphere gas in the entire internal space, and reassign this iron piece 11 to the center of the newly inserted pressurized nuclear fuel rod i. This is placed in the leg member and supported at the same two points A and B, and the natural frequency (fs) s of the pressurized nuclear fuel rod 11 is measured using the same procedure as described above.

Therefore, the pressure of the atmospheric gas, that is, the amount of pressurization is
By rearranging the equation (Hata), it can be expressed as,
By applying the measurement results of the natural frequency f of the reference nuclear fuel rod path and the natural frequency (fs) s of the pressurized nuclear fuel rod to this equation (3), the pressurization amount P of the atmospheric gas can be easily determined. It can be calculated.

Figure 4 shows the relationship between the ratio of the natural frequencies of the reference nuclear fuel rod and the pressurized nuclear fuel rod d and the amount of pressurization of the atmospheric gas in the pressurized nuclear fuel rod d, and the curve shows the pressure of the atmospheric gas. Assuming that 25 Yu7m, 50 Yu/-275 kg/d, 100 &/-......, substitute those values into the above equation (3) to calculate the natural frequency (f) of both fuel rods. ) Calculate Hatake ratio, □- 1.2 , 1.4 , 1.55
, 1.7...) connect the points, while O
The mark indicates 25'Kg/J in the reference nuclear fuel rod path and internal space.
, 50kl? /, j, 75 Yu/- (After the test, the internal pressure was confirmed by destructive inspection) Filled with atmospheric gas, the natural frequency of the friendly nuclear fuel rod was actually measured as described above, and the results were plotted. It can be seen that the values roughly match the calculated values.

As described above, according to the present invention, the natural frequency of the reference nuclear fuel rod with the internal space at atmospheric pressure and the inert 1!
! The surrounding gas is pressurized and sealed, and then the four frequencies of the pressurized nuclear fuel rod are detected, and the amount of pressurization of the atmospheric gas is detected based on the ratio of the two natural frequencies, so the pressurized nuclear fuel It is possible to know the pressure state of the atmospheric gas from the outside without damaging the rod in any way, and it is possible to prevent a decrease in the gap heat transfer coefficient between the cladding tube and the fuel pellet and the phenomenon of total bending. No measuring means required.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a nuclear fuel rod, and 21El is a system IQ0 of the atmospheric gas filling process. FIG. 3 is a system diagram of a means for measuring the natural frequency of a nuclear fuel rod according to the present invention. 4th tl#i - A rough graph showing the relationship between the ratio of the lift frequency and the pressurization amount of the atmospheric gas. In the figure, connection...Reference nuclear fuel rod, Le'... Pressurized Il fueled rod, 1... Cladding tube, 2... Fuel pellet, 4...
・Iku Kusei, 11・-・Iron piece, 12・・Electromagnet, 13・
...Oscillator, 14...Displacement needle, 1G...Signal analyzer.

Claims (1)

[Claims] The inner air barrier is set to atmospheric pressure, forced vibration is applied to the nuclear fuel rod, its natural frequency is detected, and then an inert atmosphere gas is pressurized and sealed in the inner air barrier to create a pressure-covered nuclear fuel rod. The inside of the fueled rod is characterized in that the 70ml frequency is detected by applying forced vibration to the fuel rod, and the pressurized amount of the atmospheric gas is detected based on the ratio of the unique frequency of both nuclear fuel rods. How to determine the amount of pressurization.