FR2541033A1 - Process for monitoring the leakproofing of containers covered with a neutron-absorbent screen and leakproof jacket - Google Patents

Abstract

Process for monitoring the leakproofing of a storage container for new or irradiated nuclear fuel covered with a neutron-absorbent screen and leakproof jacket, characterised in that a device for monitoring using ultrasonics, calibrated on a dry sample and then impregnated with a sheet of water between coated face and jacket, makes it possible, by comparing the echoes delivered by means of a sensor, to detect the possible presence of water between container and jacketing, this container having previously been immersed or strongly sprayed.

Description

 The subject of the present invention is a method for checking the tightness of a new or irradiated nuclear fuel storage case, provided with a neutron-absorbing screen projected, metallized or deposited, and sealed jacket as suggested in FIG. 1.

The subject of the invention relates to the nuclear technical sector
G 21 g; conversion of chemical elements, production of neutrons, neutron moderators.

 The search for dense storage of irradiated nuclear fuel leads to coating the walls of product storage cases, called neutrophages because of their property of capturing free neutrons.

 These products can be presented, inter alia, by metallic powders based on boron sprayed with plasma or metallized, or else in plates or powders of B4C, or similar products with a high content of Boron 10.

 These neutron-absorbing screens are sometimes confined in an airtight or waterproof jacket of the deactivation pools.

 Checking the tightness of this liner on the case coated with neutron-absorbing screens currently presents implementation difficulties.

such as pressure or vacuum tests with a nozzle to be closed later, penetrant testing with penetrating liquid that does not guarantee core tightness, etc.

 It is to obviate these drawbacks that it appeared necessary to create a non-destructive tightness control process which does not require any subsequent operation which risks destroying this tightness.

 According to the invention, this method is characterized by the fact that a sample faithfully reproducing the case to be checked serves to calibrate an ultrasonic controller whose probe is brought into contact with the liner.

 The calibration is carried out on the one hand with a dry sample, in this case the device indicates an echo corresponding to the thickness of the lining alone, and on the other hand with the sample filled with water between the coated wall and the shirt.

 In this case, the ultrasonic device indicates an echo corresponding to the thickness of the jacket increased approximately by the water layer taking into account the intrinsic ultrasonic qualities of the coating.

 Note that the water can be replaced by any other liquid corresponding to the environment of use.

 Another characteristic of the invention consists in immersing the case to be tested, when it is made of stainless steel, in a heated pickling bath, which allows on the one hand to ensure the finish of the surface and to cause thermal dilations creating internal tensions on the sealing welds and thus favor infiltrations in the event of non-conformity: these infiltrations being detected by the ultrasonic controller at the lowest cost, without requiring an additional immersion operation.

 Another characteristic of the invention consists in immersing the case to be tested in a sealed enclosure, filled with pressurized water so as to simulate the hydraulic pressure of the column of water in operation, for example a height of the order of 14 meters for PWR deactivation pools

 This pressure exerted on the waterproof envelope and the internal faces of the case make it possible to accentuate any infiltration that is insensitive to ambient pressure and to detect it with the ultrasonic controller according to the method described above.

 A variant of the invention consists in adding the immersion effect under pressure to the pickling function by replacing the water with a pickling solution, for example water with about 2m hydrofluoric acid and about 10 y d 'nitric acid in the case of austenitic steels - this solution being possibly heated, for example to 600C, in order to accelerate the pickling but also to simulate the rise in temperature existing in the deactivation pools.

 To fix the subject of the invention without however limiting it in the appended drawings, phase 1 illustrates the calibration of the sample on a dry wall, phase 2 illustrates the calibration of the sample under water slide (or other suitable liquid), phase 3 illustrates the case being checked with the probe at the bottom, the echo delivered is similar to the dry sample and there is no infiltration, phase 4 illustrates the case in During the control, the US controller indicates an echo close to that delivered on the sample with a lamme of water, which corresponds to water infiltration during immersion.

FIG. 5 illustrates the immersion test of a case with temperature pressure and pickling solution.

 The invention is in no way limited to the mode of application described, on the contrary it embraces all variants.

Claims (4)

1- Process for checking the tightness of a storage case for  new or used nuclear fuel coated with a neutron absorbing screen  and waterproof jacket characterized by the fact that an ultra-sound controller  calibrated on a dry sample, then impregnated with a blade of water between  face 'interm and shirt, allows by comparison of possible pregnant  by means of a probe, to detect the possible presence  of water between case and liner, this case having been previously  submerged or heavily watered. 2- tightness control method according to claim 1 characterized  by the fact that water can be replaced by any other liquid  making it possible to differentiate the echoes of the U.S controller. 3- Leakage control method according to claims 1 and 2,  taken together, characterized in that the liquid is a  pickling solution for austenitic steels, which allows  carry out the stripping operation of the stainless case and check  its tightness at the lowest cost, the ultrasonic controller then being  calibrated with a pickling solution slide. 4- Leak test according to claims 1 and 3 taken  sets, characterized in that immersion in decapa solution  ge can eat deca under a temperature - for example 60 C around-1  which promotes pickling, simulates an existing temperature in the pool  deactivation and accelerates any infiltration that may exist and  thus, better detect them. 5- tightness control method according to claim 1. characterized  by the fact that the immersion of the case to be tested is carried out under a pressiop  in order to simulate the height of the water column in operation, such  the deactivation pools for example and also to accentuate the  possible infiltrations. assemblies, leak test according to claim 1,4 and 5 sockets  sets, characterized in that the immersion prior to the control U.S of the case can be carried out in a stripping, hot and pressurized solution in order to combine stripping economically. pressure and temperature control and simulation.