JP3981103B2 - Nuclear fuel rod inspection equipment - Google Patents

Description

  The present invention relates to a nuclear fuel rod inspection apparatus and method used in a nuclear power plant.

  Conventionally, the majority of nuclear fuel used in power reactors is ceramic fuel. In particular, as a light water reactor fuel, an oxide fuel using uranium oxide is used. This oxide fuel is molded into sintered cylindrical pellets, this pellet is stacked and loaded in a Zircaloy or stainless steel cladding tube, filled with inert gas, and end plugs are welded to both ends of the cladding tube. It is used as a nuclear fuel rod.

  There is also disclosed a method in which a high density granular fuel is filled in a cladding tube by vibration instead of a molded pellet. (For example, Japanese Patent Publication No. 44-22998 and Japanese Patent Publication No. 49-27916) However, it has not been put into practical use.

  Especially in light water reactors, conditions such as load following are severe, so even with the same fuel body, pellets with different enrichments are filled in the upper and lower parts, or gadolinia (Gd2 O3), a combustible neutron absorber, is mixed. The way to do it is taken.

  Therefore, the present situation is that the fuel is assembled by managing the pellets one by one. As a method of measuring the density distribution in the length direction of these nuclear fuel rods, a scanning method using γ rays is employed.

The conventional method of filling a high density granular fuel into a cladding tube by vibration with respect to a ceramic fuel of a sintered cylindrical pellet is excellent in the following points.
(1) There are few manufacturing processes and remote automation in the hot cell is easy.
(2) The composition of the fuel can be easily changed by blending the granular fuel, and the complex composition can be easily adjusted.
(3) The heat and mechanical interaction between the cladding tube and granular fuel is less than that of pellet fuel.

  As a method for producing these granular fuel particles, there are known a sol-gel method, a method in which uranium hexafluoride (UF6) and water vapor are reacted at a high temperature to coat and grow UO2 around fine particles of uranium dioxide (UO2). .

  However, in the case of the conventional vibration filling method, there is no boundary in the axial direction unlike the nuclear fuel rods in which the pellets are packed one by one in the cladding tube, so it is difficult to adjust the fine concentration in the vertical axis direction and the density distribution. In addition, there is a problem that it is difficult to confirm the distribution in the axial direction and the density distribution.

  Furthermore, when a reprocessed fuel is used as a nuclear fuel material, if the fuel contains a high level of γ-ray nuclides, there is a problem that it is difficult to measure with the conventional method for inspecting nuclear fuel rods by γ-ray scanning. is there.

  The present invention has been made to solve the above-mentioned problems, and the concentration concentration and density distribution of the fuel and the distribution state of the neutron absorbing material, etc., which have been difficult to measure when the conventional granular fuel is used, are determined using neutron beams. It is an object of the present invention to provide a nuclear fuel rod inspection apparatus and inspection method that can measure from the distribution of transmission lines and can simultaneously measure distribution of not only one nuclear fuel rod but also many nuclear fuel rods.

According to the first aspect of the present invention, there is provided an inspection apparatus body composed of a shielding material for shielding radiation, a fuel rod to be inspected alternately filled with a granule mixed fuel region and a mixed ceramic fuel body, A stored neutron source, a moderator provided above the neutron source, a reflector provided surrounding the moderator and the neutron source, a collimator provided above the moderator, and A converter screen provided above the inspected fuel rod provided movably above the collimator and activated by neutrons, a phosphor screen that emits light upon receiving radiation emitted from the converter screen, and the phosphor screen A gamma-ray shielding material that holds the fluorescent screen and the camera, and a fluorescent that drives the gamma-ray shielding material in the vertical direction. And a screen contact mechanism, the fluorescent screen is characterized in that the adherable configuration to said converter screen by the gamma ray provided on the lower surface of the shielding material the fluorescent screen adhesion mechanism.

  According to the first aspect of the present invention, the neutron emitted from the fuel rod itself is considered as a background on the assumption that the fuel element containing the transuranium element is used after reprocessing, and the collimated neutron beam is irradiated from the outside. Then, the amount of permeation can be detected two-dimensionally and β-rays can be measured to measure the fuel rod packing density distribution and the neutron absorber distribution.

  According to the nuclear fuel rod inspection apparatus and inspection method of the present invention, when manufacturing nuclear fuel rods, the density distribution and the distribution state of the neutron absorber are determined according to theory whether or not the fuel is filled up to a predetermined region. Can be measured from the distribution of the transmission lines. Therefore, it is possible to measure the concentration distribution and density distribution of the fuel and the distribution of the neutron absorbers, which are difficult to observe when using the granular fuel in the past, in addition to a single one and a large number of them simultaneously.

A nuclear fuel rod according to an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 (a) is a perspective view showing a nuclear fuel rod according to the present embodiment and a cross-sectional view of the nuclear fuel rod partially cut away to explain the manufacturing method thereof, and FIG. The A section of FIG. FIG. 2 shows four other examples of the mixed ceramic fuel body in FIG. 1, and FIG. 3 shows the upper part of the nuclear fuel rod in FIG. 1 (a).

  In FIG. 1 (a), reference numeral 1 denotes a cladding tube, and the lower end portion of the cladding tube 1 is sealed by a lower end plug 2. The first granular mixed fuel region 3 is filled in the cladding tube 1 by vibration filling. -1 is filled, and the mixed ceramic fuel body 4 in the first mixed ceramic fuel region 4-1 is loaded on top of the first granule mixed fuel region 3-1. The mixed ceramic fuel body 4 (indicated by 4-1) is filled with the second granule mixing region 3-2 by the vibration filling method, and the second mixing portion is placed above the second granule mixing region 3-2. The mixed ceramic fuel body 4 in the ceramic fuel region 4-n is loaded.

  Thus, the granule mixing region 3-1 to n and the mixed ceramic fuel region 4-1 to n are alternately and repeatedly arranged in the cladding tube 1, and the nth granule mixing fuel region is disposed above the cladding tube 1. 3-n and n-th mixed ceramic fuel region 4-n are located.

  When filling the granule mixing region 3-1 to n into the cladding tube 1, a predetermined amount of each granule is supplied into the cladding tube 1 from the nuclear fuel nozzle 5, the non-nuclear fuel nozzle 6, and the neutron absorber nozzle 7, and added. The cladding tube 1 is vibrated and filled by a vibrator (not shown). A tightening portion 8 is formed on the outer surface of the cladding tube 1 where the mixed ceramic fuel body 4 is located. The fastening portion 8 is formed in a ring shape or a dimple shape.

  The mixed ceramic fuel body 4 is a mixture of a predetermined amount of nuclear fuel, non-nuclear fuel and neutron absorber, mixed, compacted and sintered into a ceramic form. When the cladding tube 1 is a cylindrical body, FIG. ) And (b) to form a spherical body.

Further, as shown in FIG. 2, the mixed ceramic fuel body 4 can be arbitrarily formed into a cylindrical body 4a, a chamfered cylindrical body 4b, a conical body 4c, and a football body 4d.
Further, when the cladding tube 1 is not a cylindrical body and the cross section is a polygon such as a hexagon, it can be formed into an arbitrary shape such as a polygonal body, a polygonal pyramid, or a polygonal column.

  When this mixed ceramic fuel body 4 is used to produce a nuclear fuel rod, if the granular mixed fuel region 3 has a filling density distribution or a neutron absorber distribution in the axial direction, different mixed composition ratios above and below the granular mixed fuel region 3 are mixed. It is for not to be. The blending ratio of the mixed ceramic fuel body 4 is set such that an average or one of the granule mixing regions 3 above and below the mixed ceramic fuel region is weighted, and the reactivity distribution in the axial direction is made smooth.

  As shown in FIG. 3, the uppermost portion of the fuel region in the cladding tube 1 is loaded with the pellet fuel 9 having the same composition as the mixed ceramic fuel body 4 on the nth granule mixing region 3-n in the cladding tube 1. Is done. A mesh structure material 10 is provided on the pellet fuel 9, and a plurality of pellet-like vacuum gas plenum structure materials 11 are laminated on the mesh structure material 10.

  The vacuum gas plenum structure material 11 is provided with a thin film 12 so that it can be easily broken by the pressure of the radioactive emission gas 13. The mesh structure material 10 has a purpose of holding the pellet fuel 9 and a purpose of diffusing gas released from the fuel to the upper part.

  A mesh structure material 10 is provided on the upper end of the vacuum gas plenum structure material 11, and a spring 14 is provided on the mesh structure material 10. The upper end of the spring 14 is suppressed by an upper end plug (not shown), and the upper end opening of the cladding tube 1 is sealed.

  The vacuum gas plenum structural material 11 is a pellet in which the inside is evacuated, and is covered with upper and lower thin films 12 to hold the vacuum. In consideration of the soundness of the nuclear fuel rod, the thin film 12 is manufactured so as to be broken when the pressure becomes several times the normal internal pressure, so that the effective volume can be increased.

  Thus, the nuclear fuel rod according to the embodiment having the above-described configuration includes the granular fuel region 3 mainly composed of granular fuel and the mixed ceramic fuel region. This mixed ceramic fuel region is the same as the mixed ceramic fuel body 4, but it may be filled with small-diameter ceramic particles 15 in the gap as shown in FIG. .

  That is, after attaching the lower end plug 2 to the cladding tube 1 and setting the cladding tube 1 upright on a vibration exciter, a predetermined amount of granular nuclear fuel from the nuclear fuel nozzle 5, the non-nuclear fuel nozzle 6 and the neutron absorber nozzle 7 respectively. Then, a predetermined amount of granular non-nuclear fuel and granular neutron absorbing material are introduced from the upper end opening of the cladding tube 1 and vibration-filled to form the first granular mixed fuel region 3-1.

  Next, a spherical first mixed ceramic fuel body 4 formed by mixing a predetermined amount of nuclear fuel, non-nuclear fuel and neutron absorber, compacting and sintering is loaded on the first granule mixed fuel region 3-1. To do. Next, a clamping portion 8 is provided by caulking the outer surface of the cladding tube 1 where the first mixed ceramic fuel body 4 is located so that the first mixed ceramic fuel body 4 is not displaced. That is, the tightening processing unit 8 prevents the mixed ceramic fuel body 4 from moving due to vibration or the like during the process of repeating the loading from the first to the nth.

  The mixed ceramic fuel body 4 is not damaged by being caught in the granule in the granule mixed fuel region 4 adhering to the inner surface of the cladding tube 1 in the cladding tube 1 so that it cannot be loaded at a predetermined position. So that the outer diameter of the cross section of the mixed ceramic fuel body 4 is smaller than the inner diameter of the cross section of the cladding tube 1 and more than twice the maximum outer diameter of the granule in the granule mixed fuel region 3 is subtracted. It is said.

  The gap between the mixed ceramic fuel body 4 and the cladding tube 1 is filled with granules in the second granular mixed fuel region 3-2 to be filled next. This state is shown in an enlarged manner in FIG.

  By repeating the filling of the granule mixed fuel region 3 and the loading of the mixed ceramic fuel region 4 n times, the cladding tube 1 is filled with the nth granule mixed region 3-n and the nth mixed ceramic fuel region 4-n. .

  The nuclear fuel nozzle 5, the non-nuclear fuel nozzle 6 and the neutron absorber nozzle 7 adjust the amount of neutron absorber and the concentration of the nuclear fuel in each region in the cladding tube 1, and have a long half-life radioactivity reprocessed. The isotope particles are charged into the cladding tube 1 and connected to raw material tanks (not shown). Radioactive isotopes with a long half-life are transuranium elements (TRU), such as Np, Pu, Am, and Cm, which are contained in spent fuel.

  After filling the n-th granule mixed fuel region 3-n, the pellet fuel 9 is loaded, a mesh structure material 10 is placed on the pellet fuel 9, and a plurality of vacuum gas plenum structures are placed on the mesh structure material 10. The material 11 is laminated. After placing the mesh structure material 10 on the upper surface of the uppermost vacuum gas plenum structure material 11 and placing the spring 14 thereon, the upper end portion of the cladding tube 1 is sealed with an upper end plug (not shown) to attach the nuclear fuel rod. Constitute.

  FIG. 3 shows a state in which the thin film 12 of the lowermost structural member 11 of the vacuum gas plenum 10 is ruptured, and further, the thin film 12 of the second and third structural members 11 is ruptured from the bottom. Explaining this state, when the pressure in the cladding tube 1 becomes equal to or higher than the set pressure due to the release of radioactive gas, the thin film 12 on the lowermost surface of the vacuum gas plenum 11 is ruptured. Then, since the inside of the vacuum gas plenum 11 is in a reduced pressure state, the effective volumetric gas pressure of the lowermost structural member 11 is reduced. Furthermore, the internal pressure rises, and it begins to burst sequentially from the bottom to the second and third stages.

Next, an embodiment of the nuclear fuel rod inspection apparatus and inspection method will be described with reference to FIGS.
FIG. 4B is an enlarged longitudinal sectional view showing a portion B of FIG. In FIG. 4A, reference numeral 16 denotes an inspection apparatus body, and the inspection apparatus body 16 is formed of a thick shielding material that shields X-rays and γ-rays. The inspection apparatus main body 16 accommodates a neutron source 17 that can be freely inserted and removed from the lower end thereof.

  A collimator 20 is provided above the moderator 18, and the outer side of the collimator 20 and the reflector 19 are surrounded by a neutron absorber 21. On the inspection apparatus main body 16, a nuclear fuel rod 22 to be inspected is mounted so as to be movable in the direction of arrow 23 toward the upper side of the collimator 20.

Above the nuclear fuel rod 22 to be inspected, a converter screen 25 configured in a belt conveyor system is provided so as to be movable in the direction of arrow 24. A box-shaped X and γ-ray shielding material 26 having a lower end opening is installed above the converter screen 24. The lower end opening is formed on the lower surface of the glass substrate 27 as shown in FIG. A fluorescent screen 28 is provided.

  A high-sensitivity camera 29 and a fluorescent screen contact mechanism 30 are attached to the upper end of the X and γ-ray shielding material 26. An X and γ ray shielding material 31 and a neutron absorbing material 32 are inserted into the mechanism for rotating the converter screen 24.

  Thus, the main components of the nuclear fuel rod inspection apparatus according to the present invention are a neutron source 17 that generates neutron beams, a converter screen 24 that records neutron beams that have passed through the nuclear fuel rod 22 to be inspected, and radiation emitted from the converter screen. And a fluorescent screen 28 for reading the emitted radiation.

  The neutron beam generating portion is composed of a neutron source 17, a neutron beam reflector 19, a moderator 18 that decelerates fast neutrons into thermal neutrons, and a collimator 20 that aligns the bundles of rays. The collimated neutron beam passes through the nuclear fuel rod to be measured and activates the converter screen 24 which records the degree of transmission of the neutron beam.

  For the converter screen 24, an indium (In) foil or a dysprosium (Dy) foil having a relatively large heat absorption cross section and a short half-life is used. Further, the activated converter screen 24 is transferred by a belt conveyor to a reading region where neutrons, X-rays, and γ-rays are shielded by the neutron absorbing material 32 and the X, γ-ray shielding material 31.

  In the reading area, the phosphor screen 28 and the activated converter screen 24 are brought into close contact by the fluorescent screen contact mechanism 30. The fluorescent screen 28 is applied or pasted on the glass substrate 27. The fluorescent screen 28 emits light by β rays emitted from the activated portion of the converter screen 24.

  The fluorescent material used for the fluorescent screen 28 is a scintillator in which a dye is dissolved in a solvent to form a resin, Gd2 O2 S: Pr, Ce, Gd3 Ga5 O12: Cr, Ce, Y2 SiO5: Pr, (Y, Gd) 2 O3: Eu. Ceramic type scintillators such as NaI: Tl and CsI: Tl. The glass substrate 27 is also doped with lead to the extent that it does not impede the transmission of the amount of emitted fluorescence.

  The emitted fluorescence is captured by a highly sensitive camera 29 and digitally processed to determine the density distribution, enrichment distribution, and distribution of neutron absorber contained in the fuel. The lens in front of the camera 29 is provided with a filter that matches the wavelength of the emitted fluorescence, thereby increasing the signal to noise ratio.

  When neutrons are emitted from the nuclear fuel rod itself, such as spent fuel and long-lived radionuclides, instead of new fuel, they are emitted from the fuel before the nuclear fuel rod is positioned at the collimator 20 site. The converter screen 24 is activated with neutrons in advance, the background is measured, and the result measured later at the collimator 20 is corrected. The inspection apparatus of FIG. 4 may be used by being rotated 90 degrees counterclockwise.

(A) is the perspective view which cuts out the nuclear fuel rod which concerns on embodiment of this invention, and shows a longitudinal section, (b) is the longitudinal cross-sectional view which expands and shows the A section in (a). The perspective view which shows the other example of the mixed ceramic fuel body in FIG. The perspective view which shows the upper part of the nuclear fuel rod in FIG. (A) is the longitudinal cross-sectional view shown by the partial side surface for demonstrating embodiment of the inspection apparatus of the nuclear fuel rod which concerns on this invention, (b) is the longitudinal cross-sectional view which expands and shows the B section of (a).

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Cladding tube, 2 ... Lower end plug, 3 ... Granule mixed fuel area, 4 ... Mixed ceramic fuel body, 5 ... Nuclear fuel nozzle, 6 ... Non-nuclear fuel nozzle, 7 ... Neutron absorber nozzle, 8 ... Fastening processing part, 9 ... pellet fuel, 10 ... mesh structure material, 11 ... vacuum gas plenum structure material, 12 ... thin film, 13 ... radioactive emission gas, 14 ... spring, 15 ... small ceramic particles, 16 ... inspection device body, 17 ... neutron source, 18 ... Moderator, 19 ... Reflector, 20 ... Collimator, 21, 32 ... Neutron absorber, 22 ... Inspected nuclear fuel rod, 23 ... Arrow, 24 ... Converter screen, 25 ... Arrow, 26, 31 ... X, gamma ray shielding material 27 ... glass substrate, 28 ... fluorescent screen, 29 ... high sensitivity camera, 30 ... fluorescent screen adhesion mechanism.

Claims (1)

An inspection apparatus body composed of a shielding material for shielding radiation, a fuel rod to be inspected that is alternately filled with a granular mixed fuel region and a mixed ceramic fuel body, a neutron source housed in the inspection apparatus body, and the neutron A moderator provided above the source, a reflector provided surrounding the moderator and the neutron source, a collimator provided above the moderator, and movable above the collimator A converter screen provided above the fuel rod to be inspected and activated by neutrons, a fluorescent screen that emits light by receiving radiation emitted from the converter screen, a camera that observes the light of the fluorescent screen, A box-type gamma ray shielding material for holding the phosphor screen and the camera, and a phosphor screen adhesion mechanism for driving the gamma ray shielding material in the vertical direction; Has the phosphor screen inspecting apparatus of a nuclear fuel rod, characterized in that the adherable configuration to said converter screen by the gamma ray provided on the lower surface of the shielding material the fluorescent screen adhesion mechanism.

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