Cover layer

During the covering (smoothing) of the pile each clay layer of 15-20 cm was compacted by heavy machine. The final depth of covering clay is about 70 - 100 cm. This compacted clay layer is enough to ensure low radiation levels above pile.

On the north to south ridge of the restored pile a service road was built for the later resto-ration and control works.

surolus of waste rock absence of waste rock

direction of relocation^

planned slope

FIG. 3. Relocation plan of the pile 3.

ring ditch ^

a ? 1 1 V

borehole

FIG. 4. Topography of the restored pile 3.

4.4 Radiation protection

During the remedial action of the pile 3 the next radiation levels characterize it:

Dose rate at 1m above the pile in nGy/h

Radon concentration in Bq/m3

Radon f l u x in Bq/cm²/s

Requirement

400

20

0.7

Before restoration

100-1800

20-300

0.1-0.4

After restoration

100-200

10-20

< 0.2 The calculated dose from these data is the following:

External exposure Radon inhalation

Before restoration After restoration mSv/year

0.95 1.3

0.21 0.27

It is stated the radiation situation on the restored pile is acceptable and it is assumed that this state will remain for few hundred years.

4.5 Water quality

According to the assessment, rainfall infiltrates an uncovered pile having the uranium con-tent of 70 - 100 g/t, then the uranium concon-tent of the released water is 10 - 15 mg/ dm³. This value is much more greater than the authorized limit of 2 mg/ dm³. Therefore from the point of view of safety it's practical that the collected water is led into the mining cavity after extraction of ura-nium by an ion exchange process. Similarly, the removal of the stream bed has caused the concen-tration of the radioactive isotopes released to water near the restored pile to be below the autho-rized limit.

4.6 Revegetation

Surrounding the pile 3 is a woodland, therefore the main aim is long term remediation.

The slowness of revegetation is also taken into consideration, so at the first step the grass has to be planted and then shrubs, and at the end different trees.

However, soil (clay) has to be improved for the revegetation task. The clay cover is ac-ceptable for radiation protection, but it is not suitable for the plant cultivation. A humus layer could be produced over clay, if it's overlaid with sewage mud. Nevertheless, the grass-covered re-stored pile is needed to halt the erosion process, too. And the next time shrubs and trees will be planted on the pile.

Besides the climate and spreading of species the shrub and tree plantation will be taken into account:

humidity of soil root extension

no collection for it or for its harvest.

The planting distance is also important because surface water distribution

reduction of soil erosion fire protection.

Therefore the suggested distance for stock is 40 cm and for spacing is 2.2 m.

4.7 Control after restoration work

After the actual remedial action a continuous control measurement program is to be imple-mented. According to this program on the restored pile 3 the next measurements are carried out:

gamma dose rate measurements at 50 points in a mesh at 1 m above the pile radon flux measurements at the same point

radioactive isotopes study in the cover layer considering the migration process water sampling from near streams, ring ditch and pond, the analysis is extended for uranium and radium content.

At present the background level measurements are performed above the restored pile 3.

REFERENCES

[1] Gy. Szomolanyi: The 30-year period of uranium mining at Mecsek Mountain, Mining No. 10 ,1986 (in Hungarian)

[2] L. Juhasz, B. Kanyar, N. Fulop, A. Kerekes, I. Vados: Radiohygienic study of the uranium mining and milling for the promotion of the environmental remedial ac-tion, 18th Workshop on Radiation Protecac-tion, 12-14 May, 1993, Balatonkenese (in Hungarian)

[3] Long-term radiological aspects of management of waste from uranium mining and milling, OECD/NEA,Paris, 1984

[4] J. Csicsak et al.: Annual report on the aspects of hydrology and water supplying in the MOMC, official report, Pecs, 1993, (in Hungarian)

[5] Zs. Lendvai et al.: The restoration plan for the mining pile 3, official study, Pecs, 1993 (in Hungarian)

[6] I. Vados et al.: Report on the continuous control of the restored piles of MOMC, official study, 1993 (in Hungarian)

[7] I. Vados et al.: Report on the continuous control of the restored piles of MOMC, official study, 1994 (in Hungarian)

A PROJECT CARRIED OUT IN ITALY TO SECURE A SITE CONTAMINATED BY Cs-137 OF UNKNOWN ORIGIN C. COCHI, G. MASTING

ENEA/AMB/STRA, Italy

Abstract

This paper describes the final phase of the works carried out to secure the industrial waste disposal situated near Brescia (Italy) contaminated by Csl37 of unknown origin, and represents the logical continuation of the papers presented at the Budapest and Piestany Workshops.

After the campaign survey undertaken to evaluate the amount of the radioactivity on the surface of the facility, the deposition of a first coating, in order to temporary stabilize and immobilize radioactive contamination, and the drilling campaign undertaken to investigate the quantity and the distribution of the contamination inside the mass of waste, the whole surface of the waste disposal was eventually coated with a physical cover and protected with an erosion control net.

In particular, the lecture focuses on the technologies involved, the description of the works undertaken and the results obtained.

INTRODUCTION

The matter of this report is the description of the final intervention carried out in order to secure an industrial waste disposal contaminated by Csl37 of unknown origin.

It is useful, anyway, to briefly remind here the main steps of the intervention already reported in the Budapest and Piestany Workshops.

The contamination of the site was evidenced by geochemical and administrative controls started during the second part of 1989, after an increase of Csl37 in the water of Po river, just near the nuclear Power Plant of Caorso (Piacenza, Italy), had been pointed out during some routine controls. The level recorded was about five times the background value: so, even if that value was far below the safety limit, the presence of that radioisotope in the power plant site of Caorso was immediately monitored, but lucidly no contamination was there evidenced. By Csl37/Csl34 ratio determination, it became then clear that the radiocontamination could not be due to any fission products correlated with used nuclear fuel, and then with any nuclear power plant accidents (Chernobyl included).

Using a well known geochemical survey method applied to the local river network it was possible, going upstream from the signalized place on Po river, to locate the source of the

contamination, found to be two aluminium scraps refineries near Saronno, about fifty kilometers north-west of Milan.

Through further administrative investigations on some correlated foreign suppliers, it was then pointed out that two more scraps aluminium refineries near Brescia, about 90 Km east of Milan, were highly contaminated.

The last step of the control was then toward the industrial dump facility (fig. 1-^-2) where they used to discharge the melting salts from the drum ladles of the latter two refineries, in the aluminium extraction process: and, as a matter of fact, that facility was found to be contaminated, not uniformly, but with some piece of solid salt blocks along the slope highly contaminated (28 Bq/g).

On the other hand, following the hypothesis of an uncontrolled Cs 137 source mixed to the aluminium scraps and submitted to the same refinery process, melting in a drum ladle included, for chemical reasons Caesium could not be linked to aluminium and stay in the final aluminium ingots, but necessarily it had to remain in the melting salts. In fact, aluminium ingots always resulted with very low activity (<1 Bq/gr) and could so be regularly distributed, while salts used in the melting process resulted, more or less, contaminated.

At the same time it was evident that, as a consequence of the refinery process, the Csl37 fragments could not but be scattered everywhere in the mass of waste, in such a way that certainly it could not be possible to separate and pick them all up.

Anyway, by the radiological survey on the surface of the waste plant, it was possible to see that radioactivity was present mostly in some blocks along the slope of basin n° 3; and the blocks were the melting salts directly coming from the drum ladles of one of the two refineries, situated in a buried layer some meters below the surface.

By the drilling campaign (fig.3) in every basin it was then possible to state that significative radioactivity was present only in the basin n° 3, some meters under the surface; the total radioactivity of C^S137 was valued in about l.lxlO¹² Bq (-29 Ci) in that basin, while in the basins 5 and 6 the average concentration of Csl37 was only, respectively, about 125 Bq/Kg and 6 Bq/Kg.

Moreover it was confirmed that the most active samples were the ones from the sault blocks located in the intermediate layers of waste, according to the information on the discharging schedule and according to the previsional model.

Furthermore, the most of the radioactivity concentration was found at the edge of the basin 3, in correspondence with the slope, where the concentration of the salt blocks was maximum.

Fig. 1 - The contaminated waste disposal near Brescia

Fig. 2 - Another view of the contaminated waste disposal

Fig. 3-The drilling campaign

In that situation, as it was impossible to separate the contaminated material, too scattered in something like thousands of cubic meters of waste, and remove it, it was then decided to apply a physical cover, made of different natural coatings, in order to immobilize radioactive contamination.