Method for treating radioactive laundry waste water

The present invention relates to a method for treating radioactive laundry waste water generated from a nuclear power plant, nuclear fuel reprocessing plant, or radioactive nuclides handling facilities, and provides a method for treating the waste water safely and for reducing the volume of generated radioactive waste to a minimum. Radioactive laundry waste water containing a detergent of which major contents are a nonionic surface active agent and inorganic builders is concentrated by an evaporating concentrator, the concentrated waste water is dried and pulverized to dry powder by a rotary centrifugal thin film dryer, and the dry powder is incinerated. By using the above detergent, foaming at the concentration can be reduced, and the concentrated waste water can be easily dried and pulverized. Further, the dried powder can be incinerated stably and safely without influencing undesirable effect on the body of the incinerator. In accordance with the present invention, laundry waste water can be treated simply and safely, and the final volume of radioactive waste can be reduced to minimum.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to a method for treating radioactive laundry 
waste water, and more particularly to a method for treating radioactive 
laundry waste water generated at nuclear power plants, nuclear fuel 
reprocessing plants, and handling facilities for radioactive nuclides. 
(2) Description of the Related Art 
At nuclear power plants, nuclear fuel reprocessing plants, and handling 
facilities of radioactive nuclides, working clothes, underwear, shoes, 
masks and the like for workers in the above facilities are reused after 
laundering. The laundering methods can be divided roughly into two methods 
such as water laundering and dry cleaning. In dry cleaning, freon and 
petroleum group solvents are used, and the solvents are reused after 
recovering by evaporation. Therefore, dry cleaning generates little 
laundry waste liquid. However, currently, use of these solvents has 
gradually come to be restricted in consideration of current environment 
problems, and conversion to water laundering is being performed. 
However, water laundering generates a large amount of waste water which 
contains radioactive nuclides. Although the amount of the radioactive 
nuclides is small, it is necessary to eliminate the radioactive nuclides 
before releasing the waste water. 
A method for treating laundry waste water is disclosed in JP-A-56-35837 
(1981), wherein foaming at concentrating of the waste water is suppressed 
and the waste water is heated to dry or to decompose its content. In 
accordance with the above disclosed method, an antifoamer is added to an 
evaporator for suppressing foaming at the concentration of the waste 
water, and a detergent is used which contains no inorganic builder but a 
nonionic surface active agent which is decomposable by heating, for 
facilitating thermal decomposition. However, no concrete technical content 
is disclosed on heating for drying. 
A feature of the above method is to use a detergent which does not contain 
an inorganic builder for facilitating thermal decomposition. Accordingly, 
the addition of an antifoamer is necessary for suppressing foaming. 
Further, on account of the lack of any inorganic builder, drying and 
pulverization of the content are very difficult. 
The simplest method for final thermal decomposition is incinerating the 
content. In order to incinerate, the waste water must be dried out once 
and, subsequently, the dried residual is treated with an incinerator. 
However, a detergent containing an organic component as a main constituent 
has a low melting point, and the above method has difficulty in processing 
continuously, for drying a large amount of the waste water including the 
detergent. 
Further, a method for treating radioactive waste water containing a surface 
active agent is disclosed in JP-A-63-85498 (1988), wherein radioactive 
waste water containing a surface active agent is mixed with waste water 
containing solid waste and an antifoamer, so that the total amount of the 
surface active agent and the antifoamer in the mixed waste water becomes 
more than an amount necessary for defoaming, and at most 8% by weight to 
an amount of solid waste in the mixed waste water. Subsequently, the mixed 
waste water is dried and pulverized by heating, and obtained powder is 
fabricated to pellets. However, the method disclosed in JP-A-63-85498 
(1988) has a problem such as increasing the amount of final disposing 
solid waste, because the fraction of the total amount of the surface 
active agent and antifoamer to the amount of solid waste is restricted to 
a relatively small level, such as at most 8% by weight. 
SUMMARY OF THE INVENTION 
(1) Objects of the Invention 
An object of the present invention is to provide a method for treating 
radioactive waste water generated by laundering radioactive contaminated 
articles with a detergent and water, and more particularly, a method for 
treating the waste water for reducing its volume and stabilizing it 
safely. 
(2) Methods for Solving the Problem 
The present invention is aimed at realizing a method for treating 
radioactive laundry waste water safely, reducing the generated amount of 
radioactive waste, and solving the above problem of the conventional 
method. 
That is, in accordance with the present invention, the operation of the 
concentration is simplified, a large amount of waste water is treated 
continuously for drying, the dried residual is incinerated simply in an 
incinerator, and a minimum amount of final waste is obtained. In order to 
realize the above objects, a problem of foaming at the concentrating 
process caused by surface active agents in the detergents must be reduced, 
concentrated liquid obtained by the above concentrating process must be 
dried and pulverized continuously and simply, and the dried powder 
obtained by the above drying and pulverizing process must be incinerated 
and its volume reduced safely in an incinerator. 
Foaming caused by the surface active agent can be moderated somewhat by 
using nonionic surface active agents. In view of continuous drying and 
pulverizing of the concentrated liquid, the nonionic surface active agent 
itself is a liquid approximately at room temperature and essentially 
cannot be pulverized. However, by heating the laundry waste water 
containing the nonionic surface active agents up to, for instance, about 
90 degrees, pulverizing the waste water becomes possible even without 
inorganic builders. As for incinerating and reducing the volume with the 
incinerator, it is necessary to prevent undesirable influences such as 
clogging of the filter in an exhaust gas system of the incinerator. For 
instance, a problem is generated when incinerated residual is vitrified by 
melting in a high temperature incinerator. 
The above described problems can be solved by using a detergent containing 
surface active agents, suitable inorganic builders, a small amount of 
redepositing inhibitors, fluorescent agents, enzymes, and chelating 
agents, concentrating the laundry waste water containing the above 
detergent using an evaporating concentrator, pulverizing the concentrated 
waste water with a rotary centrifugal thin film dryer, and incinerating 
the obtained powder using an incinerator. 
Foaming in the evaporating concentrator can be reduced by adding suitable 
inorganic builders into the detergent, and the pulverization can be 
facilitated. Further, in accordance with selecting suitable inorganic 
builders, melting and vitrification of the incinerated residual in the 
incinerator can be prevented and undesirable influences in the 
incinerating facility can be eliminated. 
For the drying and the pulverizing process, continuous and stable drying 
and pulverizing of the concentrated waste water can be achieved by using a 
rotary centrifugal thin film dryer.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The operation of the present invention on foaming at the evaporating 
concentration, drying and pulverizing of the concentrated waste water, and 
incineration of the residual is explained referring to experimental data 
hereinafter. 
The most serious problem in the evaporating concentration of laundry waste 
water is foaming of surface active agents in the detergent, which causes 
migration of a part of the radioactivity in the concentrated waste water 
into condensed water with foam. Accordingly, foaming at the evaporating 
concentration must be suppressed as much as possible. Using a nonionic 
surface active agent can reduce foaming more than using an ionic surface 
active agent. However, the inventor has found that adding suitable 
inorganic ion builders enhances the above mentioned effect. 
An experimental result is shown in FIG. 2. Nonionic surface active agents 
can stop foaming at an elevated temperature, and foam is removed at about 
90.degree. C. without adding the inorganic builders. The experimental 
result shown in FIG. 2 reveals that the temperature at which the foam is 
removed decreases by adding the inorganic builders. Accordingly, foaming 
can be suppressed by adding the inorganic builders. 
For the inorganic builders, any water soluble compound can be used. 
However, in consideration of subsequent processes, an inorganic builder 
which can be dried and pulverized with a rotary centrifugal thin film 
dryer, and which does not melt in the incinerating process, must be 
selected. Concretely, respective single salts or mixed salts of 
hydrochloric acid, sulfuric acid, carbonic acid, nitric acid, and 
aluminosilicic acid are preferable. 
A necessary condition for drying and pulverizing the concentrated waste 
water is that the residual after the evaporating water in the waste water 
must be solid at room temperature. However, the nonionic surface active 
agents are liquid at room temperature. 
Accordingly, if a main component of the residual is the nonionic surface 
active agent, the residual cannot be pulverized. In accordance with the 
present invention, the inventor has found that, if inorganic builders are 
added to the residual, the detergent containing the nonionic surface 
active agent can be dried and pulverized. The inorganic builder can be 
dried and pulverized easily, and the nonionic surface active agent is 
simultaneously dried and pulverized in an absorbed form by the inorganic 
builder. 
Table 1 indicates an experimental result for investigating the possible 
melting and vitrification of the residual when incinerating the pulverized 
powder. 
TABLE 1 
______________________________________ 
Surface Inorganic 
active Builders Causing vitrification 
agent Zeolite NaCl 800.degree. C. 
900.degree. C. 
1000.degree. C. 
______________________________________ 
0.25 1 0 no no no 
0.25 1 0.5 no no no 
0.25 1 1 no no no 
0.25 1 2 no yes yes 
______________________________________ 
Remarks: The numerals indicate parts by weight in 100 parts of pulverized 
powder in total. 
In the incinerator, temperature may rise up to about 1000.degree. C. at 
maximum. Therefore, if the inorganic builder, which is represented by NaCl 
in the experiment, is more than 1 part by weight in 100 parts by weight of 
the pulverized powder, the powder causes melting and possibly clogging of 
filters by spreading the molten powder. Further, the melting of the powder 
may cause deterioration of the incinerator body. 
In order to prevent the vitrification, the most preferable method is to use 
inorganic builders having a high melting temperature. However, water 
soluble inorganic builders do not have a very high melting temperature. 
Therefore, Table 1 indicates an example wherein a mixture of water 
insoluble Zeolite and water soluble NaCl is used as the inorganic builder. 
The result shown in Table 1 reveals that vitrification may be caused when 
the amount of NaCl exceeds a limit. Therefore, it is necessary to control 
the incinerating temperature in correspondence with the composition of the 
inorganic builder. However, a region in the composition of the inorganic 
builder exists wherein the vitrification does not occur even at 
1000.degree. C. by controlling adequately an additive amount of the 
inorganic builder. The region is in a range of the pulverized powder 
containing the nonionic surface active agent 10-30% by weight and the 
inorganic builder 60-90% by weight. 
In accordance with Table 1, the powder having a composition of 400-800 
parts by weight of the inorganic builder to 100 parts by weight of the 
nonionic surface active agent does not melt even at 1000.degree. C., but 
the powder having a composition of 1200 parts by weight of the inorganic 
builder to 100 parts by weight of the nonionic surface active agent melts 
at 1000.degree. C. Therefore, the maximum allowable mixing ratio of the 
inorganic builder in view of preventing the vitrification is 800 parts by 
weight to 100 parts by weight of the nonionic surface active agent. 
Further, the minimum mixing ratio of the inorganic builder is decided by a 
mixing ratio capable of preparing preferable dried powder, as the 
embodiment 1 which is explained later indicates, to be at least 300 parts 
by weight to 100 parts by weight of the nonionic surface active agent. 
Accordingly, a feature of the method for treating radioactive waste water 
in accordance with the present invention is in providing 300-800 parts by 
weight of the inorganic builder to 100 parts by weight of the nonionic 
surface active agent in the radioactive waste water. 
When the composition and contents of the detergent in the radioactive 
laundry waste water are unknown or uncertain owing to mixing or another 
reason prior to executing a series of the above processing steps such as 
evaporation and concentration, drying and pulverization, and incineration, 
the waste water must be analyzed quantitatively for clarifying the 
contents of the surface active agent and the inorganic builder in the 
waste water, and the waste water must be adjusted to ensure a preferable 
mixing ratio of the nonionic surface active agent and the inorganic 
builder in the waste water prior to the series of processing steps. 
The analysis of the waste water is performed by taking a part of the waste 
water as an analytical sample, and the content of the nonionic surface 
active agent in the sample is qualitatively determined by conventional 
methods such as a phosphoric acid tungstate method or cobalt (II) 
tetrathiocyanate absorptiometry. The content of the inorganic builder is 
qualitatively determined by a conventional method such as extraction by 
warm water and ionic chromatography. 
When the result of the above qualitative analysis reveals that the ratio of 
the amount of the inorganic builder to the amount of the nonionic surface 
active agent is within the range indicated above as a feature of the 
present invention, the waste water is transferred to the subsequent 
processing without any treatment. 
When the ratio of the amount of the inorganic builder to the amount of the 
nonionic surface active agent is less than the range indicated above, the 
waste water is adjusted by adding the inorganic builder to the waste water 
from a storage tank of the inorganic builder, so that the ratio of the 
amount of the inorganic builder to the amount of the nonionic surface 
active agent is within the range indicated above. Subsequently, the waste 
water is transferred to the next processing stage. 
When the ratio of the amount of the inorganic builder to the amount of the 
nonionic surface active agent is larger than the range indicated above, 
the waste water is transferred to the subsequent processing stage without 
any treatment. However, in the incinerating process, the incinerating 
temperature of the pulverized powder is lowered down to a temperature 
which does not melt the powder corresponding to the kind and composition 
of the contained inorganic builder. 
In accordance with the present invention, drying, pulverizing, and 
incinerating of the radioactive laundry waste water, which have been 
difficult hitherto, can be performed simply and safely. As a result, the 
radioactive laundry waste water can be reduced in its volume routinely. 
Further, the obtained powder can be solidified with an inorganic 
solidifier such as cement or cement glass, and consequently, the 
radioactive waste water can be disposed safely. 
Embodiment 1 
Referring to FIG. 1, an embodiment of the present invention is explained 
hereinafter. 
Laundry waste water exhausted from a washer 1 is transferred to an 
evaporating concentrator 3 after eliminating coarse insoluble components 
by filtration 2. At the evaporating concentrator 3, evaporated water is 
condensed at a heat exchanger 7, cleaned up at an ion exchanger 8, and 
released after confirmation of its safety by a radiation monitor 9. The 
released water can be reused. 
On the other hand, concentrated water is transferred to a rotary 
centrifugal thin film dryer 4 and dried and pulverized by heating with a 
heated inner wall. Dried powder is filled into a powder vessel 5, and 
transferred for solidification or incineration at an incinerator 6. The 
incinerated powder is also transferred for solidification after the 
incinerating process. Table 2 indicates a composition of simulated laundry 
waste water used in the embodiment. 
TABLE 2 
______________________________________ 
Composition 
Components (% by weight) 
______________________________________ 
Detergent 5 
NaCl 2 
Insoluble components 
0.5 
Inhibitor 0.5 
______________________________________ 
In Table 2, polyoxyethylene derivatives are used as the nonionic surface 
active agent and sodium chloride is used as the inorganic builder. 
The simulated laundry waste water was concentrated by an actual evaporating 
concentrator, and the concentrated water was dried and pulverized by a 
rotary centrifugal thin film dryer. Operating conditions of the rotary 
centrifugal thin film dryer are indicated in Table 3. 
TABLE 3 
______________________________________ 
Items Operating condition 
______________________________________ 
Rotation per minute 
400-500 rpm 
Heating steam temperature 
130.degree. C. 
Treating capacity 60 liter/hour 
______________________________________ 
In accordance with the operating condition shown in Table 3, dried powder 
having water content of at most 5% was obtained. A heating temperature 
higher than 130.degree. C. can be used, but drying with the higher 
temperature may generate dried powder having a lower water content with an 
extremely small diameter. Excessively fine powder is not desirable because 
the powder may cause a problem such as spreading in the air. Therefore, 
the heating temperature of about 130.degree. C. was most adequate. 
The dried powder was filled into a receiving vessel 5 without any trouble 
such as spreading. The dried powder was incinerated in an incinerator 6. A 
major component of the residual of the incineration was sodium chloride 
and its rate of reduction was about 50%. The residual of the incineration 
could be solidified easily to be a stable solid body with an inorganic 
solidifier such as cement, cement glass, and the like. 
In accordance with the present embodiment, laundry with water was performed 
and the volume of the exhausted radioactive laundry waste water could be 
reduced. 
Embodiment 2 
The same procedure of concentration, drying, incineration, and solidifying 
as far as the above embodiment 1 were performed for testing with 
detergents of various composition. As for the inorganic builder, salts of 
hydrochloric acid, sulfuric acid, carbonic acid, nitric acid, or 
aluminosilicic acid were used for the testing. 
The same results as for the embodiment 1 were obtained without any problem. 
Embodiment 3 
The dried powder obtained by the same method as the above embodiment 1 
except without incineration was solidified by a conventional method with 
an inorganic solidifier such as cement, or cement glass. The obtained 
solid body had a mechanical strength of at least 150 kg/cm.sup.2 and was 
stable. In view of volume-reduction, incinerating treatment is effective. 
However, solidifying directly with an inorganic solidifier does not cause 
any special problem. 
Embodiment 4 
Another embodiment of the present invention is explained hereinafter. 
When the amount of the laundry waste water is relatively small, the 
evaporating concentration process can be skipped, and the laundry waste 
water can be concentrated and dried directly by a centrifugal thin film 
dryer. 
In the present embodiment, the same simulated laundry waste water as the 
one used in the embodiment 1 was poured directly into the centrifugal thin 
film dryer. As a result, dried powder having a water content of at most 5% 
was generated continuously, and a problem of foaming did not occur. The 
laundry waste water could be treated safely by solidifying the dried 
powder directly or after incinerating with cement or cement glass. 
Embodiment 5 
Further, another embodiment of the present invention is explained referring 
to FIG. 3. 
FIG. 3 indicates a flow diagram of a case when composition and contents of 
a detergent in laundry waste water are unknown or uncertain by mixing or 
any other unknown reason. The laundry waste water exhausted from a washer 
1 is transferred to an adjusting tank 10 after coarse insoluble components 
are eliminated by a filter 2. At the adjusting tank 10, a part of the 
waste water is taken as an analytical sample and the sample is analyzed by 
an analyzing apparatus 12 for determining contents of nonionic surface 
active agents and inorganic builders in the waste water. 
When the contents of the inorganic builders are in a range of 300-800 parts 
by weight to 100 parts by weight of the nonionic surface active agent in 
the waste water, which is the preferable ratio of the inorganic builder to 
the nonionic surface active agent, the waste water is transferred directly 
to the concentrator 3. 
When the contents of the inorganic builders are less than 300 parts by 
weight to 100 parts by weight of the nonionic surface active agent in the 
waste water, additional inorganic builder is added to the waste water from 
an inorganic builder storage tank 11 and stirred to dissolve the inorganic 
builder in the waste water for adjusting the ratio of the inorganic 
builder to the nonionic surface active agent to be in a range of the above 
preferable ratio. Subsequently, the waste water is transferred to the 
concentrator 3. 
When the contents of the inorganic builders are more than 800 parts by 
weight to 100 parts by weight of the nonionic surface active agent in the 
waste water, the waste water is transferred directly to the concentrator 
3. However, at the incinerating process of the dried powder, the 
incinerating temperature is lowered down to a temperature which does not 
melt the dried powder in consideration of kinds and contents of the 
contained inorganic builder in the dried powder. 
The operation after the concentrator 3 was the same as far the embodiment 
1, and a preferable solid body like that of the embodiment 1 could be 
obtained. 
Embodiment 6 
Furthermore, another embodiment of the present invention is explained 
referring to FIG. 3. 
FIG. 3 indicates a flow diagram of a case when laundry waste water 
containing a detergent which does not use an inorganic builder but which 
use only a surface active agent is treated with the present invention. The 
laundry waste water exhausted from a washer 1 is transferred to an 
adjusting tank 10 after coarse insoluble components are eliminated by a 
filter 2. At the adjusting tank 10, a part of the waste water is taken as 
an analytical sample and the sample is analyzed by an analyzing apparatus 
12 for determining contents of nonionic surface active agents in the waste 
water. 
Subsequently, an inorganic builder is added to the waste water from an 
inorganic builder storage tank 11 and stirred to dissolve the inorganic 
builder in the waste water for adjusting the ratio of the inorganic 
builder to the nonionic surface active agent to be in a range of the above 
preferable ratio. Then, the waste water is transferred to the concentrator 
3. 
The operation after the concentrator 3 was the same as for the embodiment 
1, and a preferable solid body like that of the embodiment 1 could be 
obtained.