JP3014960B2 - How to remove technetium in wastewater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for selectively removing technetium Tc in a waste liquid containing salts dissolved at a high concentration, which is discharged from a process of a nuclear fuel handling facility, and safely treating the waste liquid of radioactive substances. About the method.

[0002]

2. Description of the Related Art In the process of treating uranium fuel used in a nuclear reactor, a waste liquid containing ⁹⁹ Tc, one of fission products, is generated. ⁹⁹ Tc is a stable nuclide with a half-life of 2 × 10 ⁵ years, and ultimately needs to be solidified and disposed of.

[0003] The Tc as a practical method of separating the waste liquid, TcO ₄ ^- and reduced by adding iron powder to the solution in the form,
It has been proposed to precipitate as TcO ₂ , separate the precipitate by filtration, heat and melt the precipitate as it is to form an ingot in which TcO ₂ is dispersed in an Fe matrix (NUCLEA).
R TECHNOLOGY, 19 Jan. 1995, p.161
-2). Here, the waste liquid to be treated has a Tc concentration of 2.7.
It is a 1.5 M nitric acid solution of × 10 ^-6 mol / 1 (170 Bq / ml). In this method, the waste liquid obtained by separating the precipitate by filtration still has radioactivity equivalent to the solubility of Tc (0.6 Bq / ml), and the wastewater standard (ISSN) in Ibaraki Prefecture is used.
0912-036X) 2 × 10 ⁻² Bq / ml, which is insufficient.

The waste liquid to be treated in the present invention has a Tc concentration of about 2 × 10 ⁻⁸ mol / 1 (1.4 Bq / ml) and a concentration of dissolved salts of 10% or more, often as much as 20%. It is a high concentration that is reached and it is not easy to process it to pass the above emission standards.

[0005] Precipitation, distillation, solvent extraction, and chromatographic methods are known as techniques for separating Tc by an analytical method ("Analytical Chemistry Handbook", edited by the Japan Society for Analytical Chemistry).
(Revised third edition) Maruzen p.93), especially when the concentration of dissolved salts is as high as 10 to 20%, it is impossible to carry out industrially with simple equipment.

As a means for separating Tc from the waste liquid generated by the processing of spent nuclear fuel, adsorption with activated carbon (Japanese Patent Application No. 63-37625) and adsorption of Tc
Elution with thiocyanate ion or iodine ion (JP-A-2-54632) or ion exchange with an inorganic ion exchanger (JP-A-5-346493) was known. These methods become impractical when the concentration of the salt dissolved in the waste liquid increases, the adsorption efficiency decreases.

The above-mentioned Japanese Patent Application Laid-Open No. 5-346493 discloses that Tc
Anion Exchange Resin “Amberlite IRA-400”
, But failed (Comparative Example 9). However, the present inventors
As a result of research without giving up the possibility of selective separation of the anion exchange resin Tc, it was found that a specific anion exchange resin effectively exchange-adsorbs TcO ₄ ^- ions.

[0008]

Accordingly, an object of the present invention is to utilize this new knowledge to select Tc from a Tc-containing waste liquid discharged from a process of a nuclear fuel handling facility, particularly a waste liquid in which a high concentration of salt is dissolved. It is an object of the present invention to provide a method for separation and removal of radioactive wastes so that the treatment of radioactive waste can be carried out safely and economically.

[0009]

According to the present invention, there is provided a method for removing technetium in a waste liquid, wherein technetium (Tc) is selectively removed from a waste liquid discharged from a process of a nuclear fuel handling facility and having a high concentration of dissolved salts. In the method, Tc (TcO ₄ ⁻ ) in the waste liquid is converted into particles having a particle size of 0.3 mm or less of a strongly basic anion exchange resin having a water content of 43 to 48% using trimethylbenzyl ammonium salt as an exchange group (for example, The waste liquid is brought into contact with Dowex “Dowex 1 × 8”), and TcO ₄ ⁻ is adsorbed and removed by ion exchange.

The salts dissolved in the waste liquid are usually composed mainly of Na salts, the total amount of which is 10% by weight or more, and often reaches 20% by weight. Also, the waste liquid in which such a high concentration of salt is dissolved can be treated without any trouble.

A typical example of a strongly basic anion exchange resin having a water content of 43 to 48% is a resin having a divinylbenzene content and a degree of crosslinking of about 8%.

In the practice of the present invention, as a method of bringing the waste liquid into contact with the above-mentioned specific anion exchange resin, it is also possible to put resin particles into the waste liquid and stir them, and to separate by filtration after ion exchange. In practice, it is advantageous to use a fixed bed type for contact. That is, particles of a strong base anion exchange resin are packed in a column, and the waste liquid is passed through the column. At this time, the circulation of the liquid is preferably performed at a relatively low speed with a superficial velocity of 10 hr ^-1 or less. In general, 3
About 5 hr ^-1 is appropriate.

For the final treatment of Tc, following the above-mentioned contact, a strong acid is applied to the anion exchange resin on which TcO ₄ ^- is adsorbed, and the eluted TcO ₄ ^- is reduced to form TcO _{2 in} the form of TcO ₂ . A step of precipitation, separation and solidification is performed.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in the data of Examples and Comparative Examples described later, Tc in waste liquid in which salt is dissolved at a high concentration is shown.
(Form of TcO ₄ ⁻ ) is a finely basic anion exchange resin having a specific water content or a degree of crosslinking and having an exchange group of a trimethylbenzylammonium group and having a particle size of 0.3 mm or less. Only in such cases, selective adsorption takes place. The reason why selective adsorption is realized only when such a limited ion exchange resin is used is not sufficiently clear to the inventors, but the molecular weight of the ion exchange resin determined by the water content or the degree of crosslinking is not clear. and network structures micro, macro (mainly grain surface) of the ion exchange resin particles appears to the particle size of the resin affects the time structure is of particular, TcO ₄ ^- make the conditions suitable for adsorption of I guess it will be issued.

[0015] [Example] and the waste gas resulting from the incineration of combustible radioactive waste scrubbed with caustic soda solution, the Tc TcO ₄ ^- give the waste below containing as, which was subjected to ion-exchange .

[0016] Various anion exchange resins were packed in a glass column by 1 ml each, the liquid was passed at a predetermined superficial velocity, the passed liquid was collected in a fraction collector, and the Tc concentration therein was measured by radiation intensity. The Tc concentration ratio (%) of the liquid defined by the following formula (%) (Tc concentration after passing) / (Tc concentration before passing) × 100 is plotted on the vertical axis, and the breakthrough curve is drawn with the amount of the passing liquid on the horizontal axis.

Example: Strongly basic anion exchange resin "Dowex 1-X8" (exchange group trimethylbenzyl ammonium φ-CH ₂ N ₊ (+ means plus ion)) (CH
_{3) 3} Cl ^-, degree of crosslinking 8, using the following particle size 0.3mm moisture content 43-48%), respectively superficial velocity 3.
The liquid was passed at ⁰ , 14.5 or 37 hr ^-1 .

The breakthrough curve shown in FIG. 1 was obtained. From this curve, when contacting at a relatively low superficial velocity, the volume ratio is 35%.
It can be seen that Tc can be almost completely separated by adsorption by treating 0 to 400 or more waste liquids.

COMPARATIVE EXAMPLE 1 A strongly basic anion exchange resin "Dowex 1-X2" (exchange group is the same as above, degree of crosslinking 2, water content about 75%), particle size 0.15 to 0.30 mm
And contacted at a superficial velocity of 14.8.

The breakthrough curve shown in FIG. 2 was obtained. This curve is
This indicates that breakthrough occurred immediately after the start of the liquid passage. Even with the same type of ion exchange resin, if there is a difference in the molecular structure defined by the degree of crosslinking or the water content, the desired adsorption and removal of Tc cannot be realized.

COMPARATIVE EXAMPLE 2 A strongly basic anion exchange resin "Dowex SBR" (exchange group is the same as above, degree of cross-linking 8, water content about 43-48%), particle size 0.3-0.7 mm
And contacted at a superficial velocity of 14.7.

The breakthrough curve is as shown in FIG. Also in this case, breakthrough occurred shortly after the start of the passage of the liquid, and it can be seen that the same anion exchange resin as in the example had no effect when the particle size was different.

Comparative Example 3 Strongly basic anion exchange resin "DIAION SA-20A" (exchange group styrene,
(Equivalent to a degree of crosslinking of 8 and water content of about 39 to 44%).
35 to 0.55 mm was used and contact was made at a superficial velocity of 11.6.

The breakthrough curve shown in FIG. 4 shows that it is not useful that ion exchange resins having the same degree of crosslinking or moisture content and particle size but different exchange groups are different.

[0025]

According to the method of the present invention, Tc contained in a waste liquid in which a salt is dissolved at a high concentration can be selectively adsorbed and removed with a small amount of ion exchange resin. The strong basic anion exchange resin used is relatively expensive among ion exchange resins, but the equipment is sufficient for ordinary and simple equipment. ⁹⁹ Tc-containing waste liquid coming out of the system can be treated.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is data of an embodiment of the present invention, showing a case where a Tc-containing waste liquid discharged from a process of a nuclear fuel handling facility and containing salts at a high concentration is passed through a column of a specific ion exchange resin. It is a breakthrough curve.

FIG. 2 is data of Comparative Example 1 of the present invention, which is a breakthrough curve in a case where an ion exchange resin having a different water content or a different degree of crosslinking from the Example is used.

FIG. 3 is data of Comparative Example 2 of the present invention, which is a breakthrough curve when an ion exchange resin having a different particle diameter from that of the Example is used.

FIG. 4 is data of Comparative Example 3 of the present invention, which is a breakthrough curve when an ion exchange resin having a different exchange group and a different particle diameter from that of the Example is used.

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Masahiro Fukui 4-33 Muramatsu, Oji, Tokai-mura, Naka-gun, Ibaraki Prefecture Within the Tokai Works of the Power Reactor and Nuclear Fuel Development Corporation (72) Inventor Takayuki Ameya Oaraicho, Higashiibaraki-gun, Ibaraki Prefecture 2205 Naritacho JGC Oarai Nuclear Technology Development Center Co., Ltd. (72) Inventor Akira Hasegawa 2205 Oaraicho Naritacho, Higashiibaraki-gun, Ibaraki Prefecture JGC Co., Ltd. Oarai Nuclear Technology Development Center (72) Inventor Kazunori Suzuki Higashiibaraki-gun, Ibaraki Prefecture 2205 Oarai-cho Narita-cho JGC Investigator, Oarai Nuclear Technology Development Center Co., Ltd. Naohide Murata (58) Field of investigation (Int. Cl. ⁷ , DB name) G21F 9/06 G21F 9/12

Claims (5)

(57) [Claims] The effluent discharged from the process of a nuclear fuel handling facility and containing a high concentration of salts dissolves technetium (T
c) for selectively removing Tc in waste liquid,
(TcO ₄ ⁻ ) is brought into contact with a waste liquid with particles of a strongly basic anion exchange resin having a water content of 43 to 48% and having a water content of 43 to 48% and having a trimethylbenzylammonium salt as an exchange group, and the TcO ₄ ⁻ is ionized. A method for removing technetium in a waste liquid, wherein the technetium is removed by adsorption. 2. The method according to claim 1, wherein the main component of the salts is a Na salt, and the total amount of the waste liquid is 10% by weight or more. 3. A strongly basic anion exchange resin having a degree of crosslinking represented by divinylbenzene content of about 8
2. The method of claim 1 wherein the percentage is used. 4. The method according to claim 1, wherein particles of the strongly basic anion exchange resin are packed in a column, and the waste liquid is passed through the column at a superficial velocity of 10 hr ^-1 or less to carry out ion exchange. 5. A strong acid is applied to the anion exchange resin to which TcO ₄ ^- is adsorbed, and the eluted TcO ₄ ^- is reduced to form TcO ₂
2. The method according to claim 1, further comprising the steps of precipitating in the form of, separating and solidifying.