Microsoft Word - Majersky-eng REMOVAL AND SOLIDIFICATION OF THE HIGH CONTAMINATED
SLUDGES INTO THE ALUMINOSILICATE MATRIX SIAL DURING
DECOMMISSIONING ACTIVITIES

D. Majersky, AllDeco, Slovak Republic

1. INTRODUCTION
The NPP A-1 in Jaslovske Bohunice was gas-cooled and moderated by heavy water. After an
accident in 1977, the 150 MW reactor was shut down.

The company AllDeco is acting in decommissioning of the NPP A-1 as a main subcontractor for
decontamination, dismantling, radiation monitoring works, sampling and handling with old
historical wastes for last ten years. In the previous three years, a lot of research, development and
testing of possible immobilization of frequent radioactive sludge were performed by AllDeco.

The AllDeco Company has developed and in many tasks also applied removal of radioactive
sludges from various tanks, pits, equipments at the NPP A-1. Radioactive sludges have very
often high contents of Cs-137 (as a main gamma emitting radionuclide) and Pu-238, Pu-239,
Pu-240, Am-241, Sr-90.

High contents of transuranic (TRU) radionuclides and fission product radionuclides are a result
of damage of many fuel claddings during operation and cooling. Radioactive substances are
spread widely in the primary and secondary circuit and also in many collecting equipments. In
consequence of the long-term corrosion, erosion of construction carbon steels, cladding of the
fuel rods and chemicals added into the cooling systems, certain amounts of higher contaminated
sludges were accumulated. In the equipments and parts of the primary circuit, the contents of
TRU radionuclides are high and they are very often present in the form of radioactive sludges.
These radioactive sludges are called "historic" waste, because there is an evidence of their
presence from the past but there is also a lack of information about their composition and nature.
Many from these historic sludges are thixotropic, sticky, dense, with high sedimentation rate.
Dry matter content of the sludges varies from 15 to 50 %.

2. LONG-TERM STORAGE
The Long-term storage (DS) at the NPP-A1 was designed as a pool for cooling and storage of
the spent fuel during operation. Fuel elements were inserted into vertically positioned carbon
steel casings (internal diameter 160 mm, height 9500 mm).

External cooling medium for carbon steel casings containing fuel in the pool was water.
Internal medium inside the casings was "chrompik" (water solution of chromate compounds)
or "dowtherm" (mixture of biphenyl and biphenyloxide).

Fuel elements in casings corroded during immersion in "chrompik". Therefore many fuel
elements were transferred into casings with less corrosively aggressive organic medium
"dowtherm". Corrosion and erosion processes on surfaces of fuel rods caused accumulation of
TRU waste at the bottom of all casings with "chrompik" and in many casings with "dowtherm".

Leakages of media from casings and from other manipulations also caused the accumulation
of organic and inorganic sludges at the bottom of the cooling pool.


During the step by step exploring, radiation monitoring and sampling of radioactive wastes
(1999 - 2001) in Long-term storage, an extensive shielding made of lead-steel plates was built
above the pool with casings.

Dose rates recorded at the bottom of the pool were from 50 to 1000 mGy.h
-1
and probably
were resulting from the bottoms of the casings. The volume of 0.2 to 1.5 dm
3
of radioactive
sludge has been expected at the bottom of most casings after the TV inspection.

The bottom of the pool is covered by 200 - 300 mm thick layer of the sludge. This sludge is a
mixture of organic compounds (mainly "dowtherm") and suspension of the water and
insoluble inorganic compounds. Average Cs-137 activities of this sludges after their single
separation are 10
5
Bq.dm
-3
for the water phase, 10
6
Bq.dm
-3
for the organic phase and 10
9

Bq.dm
-3
for inorganic compounds. Total volume of the sludge mixture at the bottom of the
pool is evaluated from 20 to 25 m
3
.

The scheme of the sludge distribution in the cooling pool is on the Fig. 1 and the scheme of
sludge presence in casings as well as the character of both types of sludges are on Fig. 2.
The immobilization of sludges at the bottoms of 73 casings was realised.

The immobilization of sludges at the bottoms of 50 casings with rests of "dowtherm" will be
tested in the end of the year 2004.

Removal, separation and solidification of the sludge from the bottom of the pool are in the
realisation stage and it is performed in the year 2004 after the successive verification in the
year 2003.

3. IMMOBILISATION AND SOLIDIFICATION OF TRU SLUDGES
Since 1997, AllDeco has been remarkably engaged in problems of radioactive sludges
treatment. Having managed and repeatedly realized the procedure of the removal and collection
of different types of sludges, including historical sludges as well as sludges with higher specific
activity, coming from NPPs A-1, V-1 and V-2 in Jaslovske Bohunice, the attention was
particularly aimed to a conversion of the collected sludges into a safe form for direct disposal or
for convenient temporary storage at the NPP. The result of research and pilot-scale tests is a
procedure of the immobilization of collected sludge into the inorganic SIAL matrix directly in
the drum (60 dm
3
, 200 dm
3
) at the room temperature during 30 - 60 minutes.

The developed and tested SIAL matrix, convenient for the radioactive sludge immobilization
at the room temperature with a final volume contraction of resulting product after drying at
the room temperature, is the product of the polycondensation of inorganic compounds, mainly
SiO
2
and Al
2
O
3
.

In the course of immobilization of the sludge, a part of radionuclides in soluble form is physico-
chemically fixed on some compounds of the matrix, the remaining part of radionuclides present
in insoluble or liquid phase of the sludge is encapsulated in the bulk of the matrix.

The SIAL matrix is similar to materials which are known and produced by geopolymerisation.
In the year 2003, Slovak Nuclear Authority (UJD) granted the permission for the NPP A-1 to
use the SIAL matrix for safe disposal of radioactive waste.
































Fig. 1.
Distribution and forms of radioactive sludge at the bottom of the Long-term storage



















Fig. 2:
Forms of radioactive sludge at the bottom of the Long-term storage and casing
Radioactive sludges
at bottoms of

Long-term storage Casing
Samples of radioactive sludges
taken from bottoms of

Long-term storage Casing Majersky-eng
5

4. IN-SITU IMMOBILIZATION OF SLUDGES IN THE CASINGS
An active test with immobilization of the sludge in-situ directly in one casing was performed
in the year 2001. After successive assessment of the test, an extensive dose rate and TV
monitoring at the bottoms of 73 fuel casings (after drainage of "chrompik"), measurement of
the sludge volume was made by special equipment MEZA in the year 2002. A specially
designed columnar equipment MEZA (external diameter 120 mm, height 11 500 mm) for
remotely operated monitoring (TV, dose rate) and sampling of sludges from the bottom of
casings was manufactured and applied. The bar-graph of dose rate distribution at the bottom
of 73 casings is on the Fig. 3.

Before in-situ immobilisation of the sludges in the casing, a few foreign objects were
withdrawn by the equipment MEZA from the bottom of casings.























Fig. 3: Dose rates distribution from measurements at casing bottoms



Fig. 3. Dose rate distribution at the bottom of casings

[mGy.h
-1
] Majersky-eng
6

Table 1: Results of radionuclide analysis of the sludge taken from casing bottoms

Contents of radionuclides

Sludge
sample

241
Am
[Bq/g
d.m.*
]
239, 240
Pu
[Bq/g
d.m.
]
238
Pu
[Bq/g
d.m.
]
90
Sr
[Bq/g
d.m.
]
137
Cs
[Bq/g
d.m.
]
Content of
dry matter in
sludge [%]
Fuel burnup
(MW/t)
3
6,01 97,0 9,80
2,74.10
5
9,93.10
7
6,65 4185
6
6,01.10
5
1,95.10
6
3,55.10
5
6,36.10
7
4,28.10
8
23,9 4849
17
9,31.10
2
2,61.10
3
4,26.10
2
4,51.10
7
1,13.10
8
22,9 5024
25
3,42.10
6
1,85.10
6
1,36.10
5
4,87.10
7
1,49.10
8
20,75 1955
27
2,00.10
3
6,25.10
3
1,25.10
3
7,99.10
6
1,45.10
8
6,76 4453
36
2,43.10
2
4,35.10
2
43,9 1,49.10
5
9,46.10
5
15,47 1269
37
7,36.10
2
1,16.10
3
1,11.10
2
7,53.10
5
6,78.10
5
18,1 871
38
88,9 2,24.10
2
38,7 1,84.10
5
2,39.10
5
10,59 871
45
74,2 2,67.10
2
48,6 3,98.10
5
6,32.10
9
7,07 4593
46
17,1 51,8 5,49
2,11.10
5
2,54.10
6
6,1 2544
* d. m.
Dry matter

Small laboratory samples (120 - 140 cm
3
) of the SIAL matrix with addition of sludge samples
from casings were prepared. Sludges were successfully immobilized and fixed in the selected
matrix composition. Values of compressive strength of the fixed sampl