CH684319A5 - Use of scrap image tube glass - Google Patents

Abstract

Scrap glass from image tubes arises in increasingly large quantities from worn out computer equipment and television sets, and also during the manufacture of new tubes of this type. Hitherto there has been virtually no use for such glass, and disposal caused problems because of the high content of lead, barium, strontium and other heavy metals. According to the invention, the use of scrap image tube glass is proposed in the form of pourable granules as a screening material for radioactive sources or X-ray sources, for example as a storage and transport container for industrial or medical radiation sources, for the deposition of radioactive wastes, as a constructional screen or in diagnostic apparatus or treatment apparatus. It is appropriate to admix fine-grain, radiation-absorbing fillers such as barite or anhydrite. The granules can be consolidated to give mouldings by the addition of a binder. - The screening effect (attenuation of "hard" gamma-radiation and X-radiation) is much higher than, for example, in the case of concrete, so that considerable savings in volume and weight result.

Description

1

CH 684 319 A5

2nd

description

Large quantities of disused or defective picture tubes (cathode ray tubes) are mainly associated with “electronic waste” as components of old television sets and computer monitors. Current estimates for picture tubes that have been taken out of use are approximately 4.5 million per year for Germany and approximately 400,000 for Switzerland. In addition, picture tube glass scrap is produced during the production of new picture tubes.

Such picture tubes require special disposal. So far, however, there have been various difficulties opposed to reusing or disposing of the scrap glass:

As is well known, the glass bulb of picture tubes has to be made from special types of glass which shield the «hard» radiation that arises during operation from the outside. Such types of glass (sometimes different for the front part and the cone part of the picture tube) therefore have a high content of lead, barium, strontium and / or calcium and possibly other heavy metals, usually in the form of oxides; the proportion of the elements mentioned in the picture tube glass is regularly 10-15 or more% by weight. The use of such glasses for hollow glass products is therefore out of the question. Attempts to reuse them in the production of new picture tubes encounter technical and economic problems. An admixture in the manufacture of crystal glass (ornamental) objects might be technically possible, but the need for this, measured by the amount of scrap glass, is very low. Above all, the disposal of such glasses in open landfills is not harmless and is already largely prohibited because heavy metals must be washed out (leached) at the broken glass surfaces.

The invention is therefore based on the object of finding a use for picture tube glass scrap which is both technically expedient and economical, but also harmless in terms of disposal technology. According to the invention, it is now proposed to use picture tube glass scrap in the form of pourable granules as shielding material for radioactive or X-ray sources.

Glass scrap parts from picture tubes that have been adequately cleaned can be easily shredded into pourable granules, e.g. by pounding or grinding. With a particle size of e.g. The granulate can be poured into any shape to be used as a radiation shield. When used according to the invention, those properties which have hitherto been a hindrance surprisingly prove to be particularly advantageous and useful: thanks to the high content of lead, barium and other heavy metals, «hard» radioactive radiation (gamma and X-rays) is emitted from such a fill of glass weakened far more effectively than, for example by concrete (an illustrative comparison test is described below). In addition, the glass material is of course largely insoluble, temperature-resistant and chemically stable. The shape of the granules is necessary on the one hand because of the handling and shaping, but also to avoid larger cavities or for the compact, quasi-homogeneous structure of the shielding layers or walls to be formed.

The shielding effect (radiation absorption) can be increased considerably by adding finely ground, radiation-absorbing fillers which, with a suitable grain size distribution, fill the cavities remaining between the granulate grains when mixed with the glass granulate. In particular, the cheap and high radiation absorption minerals barium sulfate (barite BaS04) and calcium sulfate (anhydrite CaS04) are suitable, but e.g. Calcium carbonate, bismuth salts and other heavy metal compounds or heavy metals come into question.

Short glass fiber particles (fiberglass) have also proven to be suitable as a mixture component (filler); It was found that particles such as those obtained from the recycling of electronic circuit boards can also have a high lead content of up to 10% and a corresponding radiation absorption effect.

The glass granulate, if necessary in a mixture, can be used as a loose fill between shaping (container) walls. However, dimensionally stable shielding containers or walls can be produced in a simple manner with the aid of an added binder, in particular cement.

The main, special forms of use within the meaning of the invention are (not exhaustively):

- Storage and transport containers for radioactive consumables, such as nuclear technology and nuclear medicine radiation sources, and in particular for the intermediate and final storage of high and medium-level waste;

- structural shields, e.g. Walls for "hot cells";

- Shields as part of nuclear medical and X-ray diagnostic and treatment devices.

Especially when used for the long-term storage of radioactive waste, considerable volume savings can be achieved thanks to the fact that the wall thicknesses required to achieve the required shielding effect are considerably smaller than with the usual pouring into concrete.

The effectiveness of an example mixture with picture tube glass scrap as the main component, in comparison to concrete, is to be demonstrated by means of the comparison test described below in connection with the drawing. Two cylindrical shielding containers 1 with covers 2 with the same outside diameter D = 43 cm (as shown in the drawing as a vertical section) but different wall thickness w were produced (w not drawn to scale), namely:

5

10th

15

20th

25th

30th

35

40

45

50

55

60

65

2nd

3rd

CH 684 319 A5

4th

Container (A)

with wall thickness w1 = 20 cm made of concrete with 70% sand and 30% cement, and

Container (B)

with wall thickness w2 = 7 cm (interior 3 correspondingly larger) from a mixture of

70% picture tube glass granulate, grain size <approx. 1 mm

20% cement as binder 5% barium sulfate BaSCU dust-fine, as filler 2% calcium sulfate CaSC> 4 dust-fine, as filler 3% fiberglass particles, approx. 1-5 mm long, as fiber reinforcement and filler

A cylindrical gamma radiation source 5 (length H = 10 cm) made of 57 cobalt with an activity of 4.1 · 105 Bq (11.3 nCi) was introduced into the cavity 3 of the two containers A and B in succession and the outside of the container axially emerging (weakened by the container wall) gamma radiation measured; for the measurement a scintillation counter 7 of type 44A and a “900 Series” evaluation and display device 8, both from the English company MINI-IN-STRUMENTS LTD., were used. These measurements gave the following values for the emerging radiation:

For container A

(Concrete, w1 = 20 cm):> 5000 Bq

(Final display value of the device exceeded),

for container B

(Glass granulate, w2 = 7 cm): 2-5 Bq (radiation almost completely absorbed).

This comparative experiment using the example of a container clearly shows the effectiveness of picture tube glass granulate compared to concrete as a shielding material for gamma or X-rays. For the same radiation source, container B made of picture tube glass granulate could be made considerably smaller and correspondingly lighter.

As can easily be seen, significant savings are possible thanks to the invention on the one hand by reducing the volume e.g. in the storage of radioactive waste, but also through weight reduction and thus easier handling and easier transportation of movable containers etc.

Claims (8)

Claims 1. Use of picture tube glass scrap in the form of pourable granules as shielding material for radioactive or X-ray sources. 2. Use of glass granules according to claim 1 in a mixture with fine-grained, radiation-absorbing filler, in particular barite and / or anhydrite. 3. Use according to claim 1 or 2, wherein the granules or the mixture with a binder, e.g. Cement that is solidified. 4. Use according to one of claims 1 to 3, with glass fiber particles as a further mixture component. 5. Use of glass granules according to one of claims 1 to 4 as a storage and / or transport container for nuclear or nuclear medical radiation sources. 6. Use of glass granulate according to one of claims 1 to 4 as a storage and / or transport container for the intermediate and / or final storage of radioactive waste. 7. Use of glass granules according to one of claims 1 to 4 as structural shielding, e.g. for walls of "hot cells". 8. Use of glass granules according to one of claims 1 to 4 as a shield in nuclear medical or X-ray diagnostic or treatment devices. 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 3rd