DD301060A7 - METHOD FOR THE AUTOMATED REMOVAL OF FUEL ELEMENTS - Google Patents

Abstract

The invention relates to a method for pickling removal of fuel elements by means of ultrasound after pickling in automatic systems with transverse transport. The object of the invention is to provide a method which makes it possible to achieve a perfect and controlled removal of desiccated pickled fuel elements from zirconium-niobium alloys in an automatic system with transverse transport with continuous flow and high quality assurance. A sequence of movements according to the invention in the sound field of a container of parabolic shape ensures perfect removal of desmudging at all points of the BSE surface. To remove the coating, a dilute nitric acid containing aluminum nitrate of a certain concentration, temperature and exposure time is necessary, a surprising chemical and physical effect occurring under the influence of ultrasound. Apart from fuel elements made of zirconium-niobium alloys, the automatic system is also suitable for other tubular or rod-shaped workpieces. Fig.1

Description

Characteristic of the known technical solutions

In known hand-operated systems for the production of fuel elements, the resulting pickling coating is removed by wiping with textile fabric. The quality of the removal is dependent on the care of the operating personnel. The technical implementation of this Belabetfernungsprinzips in automatic systems with lateral transport is associated with significant shortcomings, such as limited life of the textlien material, back soiling of the fuel element after relatively short time, danger of indentation of Belagresten in the ZrNb surface associated with susceptibility to corrosion, high reject rates and large technical Effort and long downtime when changing the wiping material.

Other principal ways of removal of scale, such as pressure jet method (1), (2), (3), blasting with plastic granules or other suspended material in air or water (4), (5), (6), (7), (8) or chemical detachment in highly concentrated potassium hydroxide (KOH) solution (9) also show significant deficiencies. Due to procedural or technological difficulties, they can not be technically realized or can not be used since the required high quality of the removal of the surface is not achieved. According to (10), niobium is chemically only moderately resistant to phosphoric acid, but it is not possible to use phosphoric acid of any concentration for the fumigation. On the one hand, the solubility is insufficient to achieve a surface of the fuel element which is impermeable in the required purity; On the other hand, new cover layers are immediately formed on the Zr surface which impair the quality-related further processing of the fuel element. Common treatment media for cleaning metallic and non-metallic surfaces are aqueous alkaline solutions with or without additives such as fluorides, emulsifiers and the like. and organic solvents or certain emulsions of various solvents. It has been found that these media are unsuitable both in terms of their effect with and without ultrasound and in terms of process technology and technology in the context of an automatic overall technology.

Known is the intensifying, accelerating effect of the ultrasound or the cavitation caused by ultrasound in aqueous and non-aqueous solutions to chemical and physical processes on material surfaces (10), (11). Evidence has been provided that the use of ultrasound is particularly advantageous in eliminating so-called pigment contaminants (12), (13). Patents (14), (15) describe devices for cleaning, pickling and descaling tubes in liquids by means of ultrasound.

The deficiency of all the mentioned documentation or technical solutions relating to the field of application of the present invention is that they are not suitable for the pickling of ZrNb alloy elements in automatic systems with transverse transport. In oiruGlnon they have the following defects; For example, the metal tube is guided in the axial direction radially about its axis rotatingly past the device for sounding (14). Furthermore, a rotational movement of the tube to be forced by eccentrically offset oscillator heads or so-called concentrators (15). In both cases, they are directly adjacent to the metal surface of the US wall. When applying this principle would be unavoidable by the action of the components of the devices on the surface of the fuel element, a variety moore or less deep running and scratch marks. However, very high demands are placed on the quality of the surface of fuel elements for nuclear reactors. Even slight damage to the relatively soft surface would cause severe corrosion damage and resulting damage to the Roaktors. What is negligible in this regard in the descaling of steel, stainless steel, Kupforrohren etc., is not allowed in fuel elements for nuclear reactors, since especially requirements must be met with high reliability. The bundled by the application of so-called concentrators and striking with great intensity on a tube sound energy bursts from scale surfaces of steel surfaces, but would give the possibility oiner damage to the Pelietsäule in the ducts in fuel pellets filled with fuel elements, resulting in increased wear of the pipe wall or a Breakthrough of the fuel element or an accident of the reactor would result.

Furthermore, it decreases due to the high concentration. Ultrasonic energy the life or service life of the US concentrators or -wsndler, which would have to be replaced constantly, making this proposal is technically unattainable in automated systems and economically not justifiable.

Another deficiency of this device is the localized wiping surface on the surface of the fuel bundle, whereby the pickling is indeed removed before a point, settles .iber partially at adjacent locations again, d. H. only shifts on the surface. This makes it impossible to achieve evenly clean surface before. The mentioned technical solutions are not feasible for the removal of scale of fuel elements in automatic systems with transverse transport. When x-any container with rectangular cross-section and hanging US transducers, as is customary in metal cleaning or in the electroplating, were in this particular application, the removal of pickling from the surface of Brunnstoffelementen, completely insufficient results obtained. In steady state conditions "closed sound fields" with so-called standing waves are formed in all US containers as a result of which sound-deaf zones may develop, which may extend over several λ / 2, on the other hand Cleansing effect advantageous coupling effects occur with a sound compression or an increase in intensity in certain zones of the sonicated space, these favorable conditions can be created by a suitable Behälterkcnvtruktion.

Object of the invention The process of chemical staining of ZrNb alloy fuel elements and in conjunction therewith the process

The pickling distance could not be automated until now.

The inventive solution is a perfect and controlled removal of debris from pickled fuel elements in

an automatic system with transverse transport with continuous flow and high quality assurance can be achieved.

The inventive solution of the lining of Bronnstoffe lementen must assume that this sub-level

procedurally and technologically smoothly into the overall complex of an automatic plant for chemical

Maßbeizen and after-treatment of fuel elements is fitted. Possible damages of surface or filling of fuel elements, inadmissible corrosion, chemical Covering layers and backfilling or covering residues must be avoided in order to increase reactor safety

guarantee. .

Explanation of the essence of the invention According to the invention, the problem is solved by placing the fuel elements in a special container whose Length = 3000mm, whose width = 600mm and desson max.height = 220mm, with parabolic shape Floor and on this longitudinally staggered vibrator plates transversely to the longitudinal axis when performing a

! tight rotational movement and an additional vertical movement while avoiding any possible damage or damage

Deformation of. Surface of the fuel element, d. H. through a suitable constructive solution, not the task of this Invention is, wandered through, this E .hälter contains a suitable medium and the vertical movement of the Fuel element on two verticals goes beyond desson level. Due to the parabolic shaped container bottom in three rows of flanged oscillating plates with each

3 Sandwich Vibrators - with a fuel element length of approximately 2,500 mm 7-8 plates a 300 mm per row - will require the effective removal distance and forming a steady state sound field with a number of 3 x 23 sound sources and multiple reflections on the tank walls and obtains on the surface of the medium in the form of standing waves necessary sound distribution, wherein a concentration of sound energy in the transport plane ensues.

Due to the special container design is achieved in particular that the sound energy concentrated at the two verticals

is, at each of which the lifting movement of the fuel element takes place.

The distance between the two verticals is according to the invention an odd multiple of

"drt 9,15-3,14

η · = - ' ^: = 7.2 mm,

4 4

that is 94mm, where η is an odd number and d is the diameter of the fuel element. The vertical movement dos the fuel element in the treatment medium must be at least λ / 2. Since in the structural design of the container and necessary internals individual antinodes reach very high intensity values, a certain position of the fuel element in the parabolic-shaped container is preferred. According to the invention, the vertical movement of the fuel element is carried out beyond the N .. au of the mode, since there occur in the principle parabolic shape of the oscillator vibration antinodes with about 30% higher sound energy than at all other points of the sound field and thus a überruöJionde effect the desmutting is achieved, which can be achieved by a repeated repetition of the vertical H'ibbewegung in the treatment medium and beyond its level out particularly good Roinigungsergebnlsse.

According to the invention, the value for the vertical lap in the treatment medium is 4.times.λ / 2, wherein both at the surface of the medium and in the horizontal treatment plane an oscillation maximum, i. a vibration belly is present. For procedural and technological reasons, the ultrasound coating formation takes place in a medium consisting essentially of nitric acid, a surprising chemical effect occurring under the US influence which can not be detected without US exposure. The chemical effect of the nitric acid mode can be deduced from the fact that in pre-diluted solutions of about 50 g / l, at a temperature of 15-30 ° C, and at an exposure time of 90 s, particularly good desmutting results are achieved.

Embodiment. The invention will be described below with reference to an embodiment. FIG. 1 shows the movement sequence of the fuel elements 1 in a container 2. In the parabolic trained Bottom of the container 2 are at intervals of 50mm three rows of vibrating plates of dimensions 140 χ 29B χ 1.5mm

arranged, wherein the two outer rows on the two slopes at an angle α = 20 ° to the vertically inclined Bode nfläthe 3befrachten eight Schwingerplanen are in the same flight and dio on the middle horizontally arranged bottom surface 4angellanschten seven Schwinger phantom to the halo length of the vibrator plates, ie to 147th , 5 mm to these vei sotztangeordnet are and each Schwinget plate with 3 Sandwichschwingern 5 is equipped. Dio points P) to P _{4 of} the container * 2 lie on a parabola whose focal point F is on the center line of the container and on the horizontal carrying plane of the container

Fuel element 1 is located, which is by the distance A = 4 λ / 2 - 83.2 mm below the level of the medium. In order to ensure a uniform removal of soil on all sides, the BSE 1 is inserted in point 5 of the container and through

moves the horizontal transport device to point 6 in the sound field.

After the BSE has been picked up by the vertical transport device at point 6, the first vertical one takes place Lifting movement. The BSE moves 7 times within the medium and beyond its level. After that it will be BSE in turn deposited at point 6 and moved by means of the horizontal transport device to point 7, where subsequently

the second vertical lifting movement takes place with 7 strokes in the same area. After completion of the vertical lifting movement of the

BSE is transported by the horizontal transport device to point 8 and into the next treatment step

About lifted.

Dio total exposure time in the ultrasonic field is 90see. As a medium, a dilute nitric acid with a

certain proportion of aluminum nitrate

ENT ₃ 20 70g / l

Al (NOa) ₃ -9HjO 20 70g / l

at a temperature of 15, .. 3O ⁰ C used.

Under these conditions, it is possible to remove the pickling layer with a permissible rust surface less than 20Mg / cm ²

and with less than 0.5 \ / cm ² residual fluoride content on the BSE surface.

Claims (3)

1. A method for removing BeizLelagentfernung of fuel elements by means of ultrasound, characterized in that the removal of casters in an automatic system with transverse transport, consisting of a container having a parabolically shaped bottom and on this in the longitudinal direction in three rows arranged oscillating plates, and thereby transversely to the longitudinal axis transported through this and by the Bohandlungsmedium through and lifted and lowered at 2 lifting points in the vertical direction within the medium and beyond its level. 2. The method according to claim 1, characterized in that the specific movement of the fuel element takes place so that the BSE by horizontal movement with a slight rotational movement transversely to the longitudinal axis of the BSE and in two fixed lifting points in the vertical direction innr '^ aIb the medium and on the Level is transported out, wherein the transport uui vertical movement in the treatment medium is a multiple of λ / 2, preferably 4 · λ / 2 and both at the boundary medium-air and in the horizontal treatment zone each have a maximum vibration and the distance between the two Vertical an odd multiple of - ^ -, preferably 13 times. 3. The method according to claim 1 and 2, characterized in that the treatment medium is nitric acid, preferably between 20 ... 70 g / l with a proportion of aluminum nitrate 20 ... 200g / l, preferably 20 ... 70g / l at a Treatment temperature of 15 ... 75 ⁰ C, preferably 15 ... 3O ⁰ C and an exposure time of 30 ... 300see, preferably 60 ... 120sec is used. Hi9r to 1 page drawing Field of application of the invention Fuel elements made of ZrNb alloys for nuclear power plants must have a very high corrosion resistance under reactor conditions. To smooth the surface profile and to achieve a favorable surface structure, the fuel elements are pickled after a previous mechanical treatment in a HF-HNO ₃ mixture. At the end of a multi-stage reaction remains on the BSE surface, a Beizbelag consisting of Nb and Nb compounds, in particular niobium oxide and a small but impermissible fraction of F 'ions. When using the invention, the gray-brown, dark pickling coating with a coating weight of about 60 pg / cm ^{2 is} removed in automatic Anlagon with transverse transport to allowable residual coating values of ^ 20 ^ g / cm *. At the same time, the fluoride content of the surface of the fuel element drops from about pg g / cm ² to uncritical values of <0 ≦ g / cm ² .