U.S. patent application number 15/984711 was filed with the patent office on 2018-09-20 for purification method for purifying water in a spent fuel pool in a nuclear power plant.
The applicant listed for this patent is EBARA CORPORATION. Invention is credited to Takeshi IZUMI, Makoto KOMATSU.
Application Number | 20180264458 15/984711 |
Document ID | / |
Family ID | 51862093 |
Filed Date | 2018-09-20 |
United States Patent
Application |
20180264458 |
Kind Code |
A1 |
IZUMI; Takeshi ; et
al. |
September 20, 2018 |
PURIFICATION METHOD FOR PURIFYING WATER IN A SPENT FUEL POOL IN A
NUCLEAR POWER PLANT
Abstract
A purification method for spent fuel pool water from nuclear
power generation, the method comprising: passing the water at a
linear flow velocity of 50 m/h or less through a purification
apparatus for the water comprising an ion exchange resin layer and
a metal-doped resin layer which is laid at a bed height of 2 cm or
more on a surface layer of the ion exchange resin layer wherein the
water to be treated is contacted with the metal-doped resin layer
to decompose a pro-oxidant contained in the water; and subsequently
contacting the water with the ion exchange resin.
Inventors: |
IZUMI; Takeshi; (Tokyo,
JP) ; KOMATSU; Makoto; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EBARA CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
51862093 |
Appl. No.: |
15/984711 |
Filed: |
May 21, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14520635 |
Oct 22, 2014 |
9999880 |
|
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15984711 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C02F 1/705 20130101;
C02F 2103/04 20130101; C02F 2101/006 20130101; Y02E 30/30 20130101;
B01J 47/028 20130101; G21C 19/307 20130101; C02F 2001/425 20130101;
C02F 1/42 20130101; C02F 2001/422 20130101; B01J 41/05 20170101;
B01J 47/04 20130101; G21F 9/12 20130101; C02F 2001/427 20130101;
C02F 2101/10 20130101; C02F 2103/023 20130101; B01J 47/026
20130101; B01J 47/04 20130101; B01J 41/05 20170101 |
International
Class: |
B01J 47/028 20170101
B01J047/028; B01J 47/026 20170101 B01J047/026; B01J 47/04 20060101
B01J047/04; C02F 1/42 20060101 C02F001/42; C02F 1/70 20060101
C02F001/70; G21C 19/307 20060101 G21C019/307; G21F 9/12 20060101
G21F009/12; B01J 41/05 20170101 B01J041/05 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 24, 2013 |
JP |
2013-221135 |
Claims
1. A purification apparatus for water in a spent fuel pool in a
nuclear power plant, comprising: a spent fuel pool containing a
spent fuel from a nuclear power plant and water; an ion exchange
resin layer having an inlet side and an outlet side; a metal-doped
resin layer laid at a bed height of from about 2 cm or more to
about 10 cm or less on the surface of the inlet side of the ion
exchange resin layer; and a delivery line configured to deliver the
water from the spent fuel pool to the metal-doped resin layer.
2. The purification apparatus according to claim 1 further
comprising a spent fuel pool water circulation line configured to
return the water from the ion exchange layer to the spent fuel
pool.
3. The purification apparatus according to claim 1, wherein the
water from the spent fuel pool comprises peroxide, and wherein 90%
or more of the peroxide is decomposed by passing the water through
the metal-doped resin layer and the ion exchange resin layer.
4. The purification apparatus according to claim 1, wherein the
metal in the metal-doped resin layer is selected from the group
consisting of fine particles of palladium, platinum, manganese,
iron, and titanium.
5. The purification apparatus according to claim 1, wherein the
water from the spent fuel pool further comprises a hydroperoxyl
radical, a hydroxyl radial, or combination thereof.
6. The purification apparatus according to claim 1, wherein the
delivery line is further configured to deliver the water so that
the water passes through the ion exchange resin layer at a linear
flow velocity of from 30 m/h or more to about 50 m/h or less during
operation.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a division of U.S. patent application Ser. No.
14/520,635 filed on Oct. 22, 2014, which claims priority to
Japanese Patent Application No. 2013-221135 filed on Oct. 24, 2013,
which is hereby incorporated by reference in its entirety
herein.
FIELD OF THE INVENTION
[0002] The present invention relates to a treatment method and
apparatus for spent fuel pool water from nuclear power plants,
particularly to a purification method and apparatus for decomposing
and removing pro-oxidants contained in spent fuel pool water, such
as hydrogen peroxide, and a treatment method and apparatus for
spent fuel pool water that incorporate the purification method and
apparatus.
BACKGROUND
[0003] To purify spent fuel pool water from nuclear power plants
and recycle the purified water as cooling water for spent fuel
rods, a demineralizer using a granular ion exchange resin is placed
as a purification device for fuel pool water. This demineralizer is
placed to inhibit corrosion of stored spent fuels and various
materials and remove radioactive substances from pool water, thus
maintaining long-term soundness, such as decreased radiation
exposure of operators.
[0004] In the demineralizer, it is necessary to replace ion
exchange resins having degraded performance by fresh resins. In
this case, since a volume of spent ion exchange resins are
generated as a radioactive waste, the replacement costs money for
the new ion exchange resins as well as money for disposal of the
radioactive waste and requires a place for the disposal. For these
reasons, it has been desired to prolong the lives of ion exchange
resins.
[0005] However, spent fuel pool water that is obtained from a
nuclear power plant such as a pressurized-water reactor (PWR)
contains pro-oxidants such as hydrogen peroxide which is generated
by decomposition of the water subjected to radiation from fuel rods
and hydroperoxyl radicals and hydroxyl radicals which are generated
from hydrogen peroxide (hereinafter, these pro-oxidants are
referred to as "pro-oxidants") and boron which is derived from
boric acid added for control of nuclear fission reaction of fuels.
In general, spent fuel pool water contains hydrogen peroxide in the
order of a few or several ppm and boron in a concentration of about
2000 to about 3000 ppm. Such spent fuel water is treated directly
by ion exchange in a purification apparatus for fuel pool water.
However, a demineralizer using a granular ion exchange resins
cannot remove those pro-oxidants. Hence, the pro-oxidants remain in
fuel pool water, waste storage bunker water, and condensate storage
water that is recovered after purification of fuel pool water or
waste storage bunker water and then stored. In addition, since the
pro-oxidants have a very strong oxidizing action, they oxidize
cation resins in ion exchange resins and elute polystyrene sulfonic
acid (PSS). The eluted PSS is attached to anion exchange resins and
decreases their reaction rate. Further, hydrogen peroxide oxidizes
and degrades cation exchange resins and, in consequence, sulfate
ions and the like are eluted from the cation exchange resins and
increase the electric conductivity at an outlet of an ion exchange
resins column. The strong oxidizing action of the pro-oxidants
contributes to corrosion of steel materials such as pipes and
tanks.
[0006] It is believed that the main cause of the degradation of ion
exchange resins is oxidation of cation exchange resins that is
caused by their contact with pro-oxidants contained in such water.
To solve this problem, the following methods have been proposed: a
method of alkaline decomposition of pro-oxidant by contacting water
containing the pro-oxidant with anion exchange resins before
contacting the water with cation exchange resins (Patent Document
1: Japanese Patent Publication No. 2000-002787), a method of
removing pro-oxidant by contacting it with granular active carbon
and a method of removing pro-oxidant by contacting it with ion
exchange resins on which platinum group catalyst particles are
doped (Patent Document 2: Japanese Patent Publication No.
H10-111387), a method of removing pro-oxidant by passing water
containing the pro-oxidant through a platinum catalyst coated
membrane (Patent Document 3: Japanese Patent Publication No.
2003-156589), a method of removing pro-oxidants by contacting them
with active carbon to adsorb them (Patent Document 4: Japanese
Patent Publication No. 2008-232773), and a method of removing
pro-oxidants by passing water containing the pro-oxidants through a
manganese filter (Patent Document 5: Japanese Patent Application
No. 2012-217133). However, these methods proposed so far relate to
purification of water having a low pro-oxidant concentration of
about 0.01 to about 0.001 mg/L, such as nuclear reactor cooling
water or radioactive waste water, and there are no examples of
application of those methods to purification of spent fuel pool
water containing pro-oxidants in a high concentration of 1 mg/L or
more as well as boric acid (for example, about 2000 to about 3000
mg/L).
SUMMARY
[0007] The present invention aims to reduce pro-oxidants contained
in spent fuel pool water from nuclear power plants, especially from
pressurized-water reactor (PWR), prolong the life of ion exchange
resins in a purification apparatus for fuel pool water, and lower
the frequency of replacement of the ion exchange resins.
[0008] According to the present invention, there is provided a
technique for water treatment at nuclear power plants of
pressurized-water reactor (PWR); in the technique, before ion
exchange resins are used to demineralize water to be treated that
contains pro-oxidants (e.g., hydrogen peroxide) generated by
radiolysis of spent fuel pool water from the nuclear power plants
of PWR, the water to be treated is contacted with particular
metal-doped resins to reduce the pro-oxidants contained in the
water, decrease load placed on a demineralizer and maintain the
high purity of the treated water as well as prolong the life of the
ion exchange resins and reduce generation of spent ion exchange
resins that are radioactive secondary wastes.
[0009] More specifically, the present invention includes the
following embodiments:
[1] A purification method for spent fuel pool water from nuclear
power generation, the method comprising: passing the water at a
linear flow velocity of about 50 m/h or less through a purification
apparatus for the water comprising an ion exchange resin layer and
a metal-doped resin layer which is laid at a bed height of about 2
cm or more on a surface layer of the ion exchange resin layer
wherein the water to be treated is contacted with the metal-doped
resin layer to decompose a pro-oxidant contained in the water; and
subsequently contacting the water with the ion exchange resins. [2]
The purification method according to [1], wherein the metal in the
metal-doped resin layer is selected from fine particles of
palladium, platinum, manganese, iron, and titanium. [3] The
purification method according to [1] or [2], wherein the
pro-oxidant is hydrogen peroxide, a hydroperoxyl radical, or a
hydroxyl radical. [4] A treatment method for spent fuel pool water
from nuclear power generation, the method comprising: purifying the
water to be treated with a purification apparatus for the water by
the purification method according to any one of[1] to [3]; and then
recycling the purified water to the spent fuel pool to use the
water. [5] A purification apparatus for spent fuel pool water from
nuclear power generation, comprising an ion exchange resin layer
and a metal-doped resin layer which is laid at a bed height of
about 2 cm or more on a surface layer of the ion exchange resin
layer. [6] A treatment apparatus for spent fuel pool water from
nuclear power generation, comprising:
[0010] a spent fuel pool at a nuclear power plant;
[0011] a purification apparatus for the water, comprising an ion
exchange resin layer and a metal-doped resin layer which is laid at
a bed height of about 2 cm or more on a surface layer of the ion
exchange resin layer;
[0012] a delivery line for delivering the water from the spent fuel
pool to the purification apparatus; and
a spent fuel pool water circulation line for returning the water
purified with the purification apparatus to the spent fuel
pool.
Advantageous Effects
[0013] By using the treatment method and apparatus of the present
invention for treating spent fuel pool water from nuclear power
plants, pro-oxidants (e.g., hydrogen peroxide) generated by
radiolysis of the water with radiation from spent fuels can be
decomposed efficiently. Hence, the treatment method and apparatus
can prevent oxidative degradation of ion exchange resins filled in
a demineralizer and maintain the high purity of the treated water
as well as prolong the life of the ion exchange resins and reduce
generation of spent ion exchange resins that are radioactive
secondary wastes. For treatment of spent fuel pool water from
nuclear power plants of PWR, it is an important object to reduce
the volume of radioactive secondary wastes, and the present
invention that can accomplish those achievements is
significant.
BRIEF DESCRIPTION OF DRAWINGS
[0014] FIG. 1 is a schematic flow diagram of a water treatment
apparatus of the present invention for treating spent fuel pool
water from a nuclear power plant.
[0015] FIG. 2 is a graph showing treatment results of Example
1.
[0016] FIG. 3 is a graph showing treatment results of Example
2.
[0017] FIG. 4 is a graph showing treatment results of Example
3.
PREFERRED EMBODIMENTS
[0018] The present invention is described below with reference to
the attached drawings, but they are not intended to limit the scope
of the invention.
[0019] FIG. 1 outlines a flow in a water treatment apparatus of the
present invention for treating spent fuel pool water that is
obtained from a nuclear power plant. A spent fuel pool 1 is filled
with cooling water for cooling storage of a spent fuel rod that is
removed from a nuclear reactor (This cooling water is also referred
to as "spent fuel pool water"). Since the spent fuel rod that is
removed from a nuclear reactor continues emitting radiation even
while being stored in fuel pool water, the spent fuel pool water is
decomposed by the radiation to generate hydrogen peroxide, hydroxyl
radicals or hydroperoxyl radicals. The spent fuel pool water (water
to be treated) that is removed from the spent fuel pool 1 (a
storage tank for the water to be treated) is transferred via a
transfer pump 2 to a fuel pool purification device 3. The fuel pool
purification device 3 comprises an ion exchange resin layer 3a in
which ion exchange resins are filled and a metal-doped resin layer
3b in which metal-doped resins are filled at a bed height of about
2 cm or more, preferably 5 cm or more, on a surface layer of the
ion exchange resin layer 3a. When the bed height is less than about
2 cm, pro-oxidants are not well decomposed. The upper limit of the
bed height of the metal-doped resin layer 3b is not particularly
limited; however, since a bed height exceeding about 10 cm results
in the decreases of the flow velocity and the volume of the treated
water, an appropriate bed height should be determined. The
pro-oxidants contained in the spent fuel pool water are decomposed
when passing through the metal-doped resin layer 3b. Subsequently,
impurity ions are removed through the ion exchange resin layer 3a.
The demineralized water is recycled to the spent fuel pool 1 as
cooling water. The flow volume of water to be treated through the
demineralizer 3 is based on a linear flow velocity of about 10 to
about 50 m/h. When the linear flow velocity is less than about 10
m/h, the volume of the circulated water is decreased and its
cooling effect on the spent fuel rod is diminished. When the linear
flow velocity exceeds about 50 m/h, the efficiency of contact of
the pro-oxidants with the metal-doped resin is reduced and its
capability to decompose the pro-oxidants is diminished.
[0020] The ion exchange resin used in the present invention may be
a common ion exchange resin that is used in purification
apparatuses for spent fuel pool water from nuclear power plants,
and is preferably a mixed bed anion and cation exchange resin. For
example, a mixed bed ion exchange resin (SNM1, a product of
Mitsubishi Chemical Corp.) is suitable.
[0021] The metal-doped resin used in the present invention is
preferably a strongly basic gel-type spherical resin formed of a
polymer resin on which metal particles selected from palladium,
platinum, manganese, iron and titanium fine particles are
doped.
EXAMPLES
[0022] The present invention is described below in more detail by
means of examples.
Example 1
[0023] A metal-doped resin was used to examine its capability to
decompose hydrogen peroxide in an immersion test.
[0024] The metal-doped resin was the Pd-doped resin Lewatit
(registered trademark) K7333, a product of Lanxess. To a 200 ml
beaker, 100 ml of a solution to be treated (Sample 1) containing
H.sub.2O.sub.2 in a concentration of 20 mg/L and boric acid
dissolved in a concentration of 2800 mg/L (as B) was added, 1 ml of
the Pd-doped resin was added, and the hydrogen peroxide
concentration was determined with time. These hydrogen peroxide and
boron concentrations were applied to simulate the quality of fuel
pool water that is obtained from a pressurized-water reactor (PWR)
nuclear power plant. For reference, the same test was conducted
with a boric acid-free solution, i.e., water containing only
hydrogen peroxide (This solution is referred to as Sample 2). The
hydrogen peroxide concentration was calculated based on absorbance
measured at a wavelength of 350 nm with a spectrophotometer by
iodometry (Atomic Energy Society of Japan: PWR Standard Chemical
Analysis 2006). The results are shown in Table 1 and FIG. 2.
TABLE-US-00001 TABLE 1 Conc. (mg/L) Immersion of hydrogen peroxide
time (min) Control Sample 2 Sample 1 0 19.4 19.4 19.4 60 19.4 12.1
12.0 120 19.5 10.8 10.5 180 19.6 9.5 9.8 240 19.5 8.8 9.0
[0025] FIG. 2 shows that the Pd-doped resin had such a high
capability to decompose hydrogen peroxide that about 50% or more of
contained hydrogen peroxide was decomposed at about 2 hours after
the start of immersion. The influence of contained boric acid on
the capability to decompose hydrogen peroxide was not observed.
Example 2
[0026] A metal-doped resin was used to examine its capability to
decompose hydrogen peroxide in a test in which hydrogen
peroxide-containing water was passed through a column.
[0027] The metal-doped resin, which was the Pd-doped resin Lewatit
(registered trademark) K7333, a product of Lanxess, was filled at a
bed height of about 1 to about 10 cm in a glass column with an
inside diameter of about 16 mm. An untreated water comprising
H.sub.2O.sub.2 adjusted to about 2 mg/L was passed through the
column at a linear velocity LV of about 10 to about 70 m/h to
examine the hydrogen peroxide removing performance of the
metal-doped resin. The results are shown in Table 2 and FIG. 3.
TABLE-US-00002 TABLE 2 Hydrogen peroxide decomposition Linear flow
rate (%) by bed height velocity (m/h) 1 cm 2 cm 5 cm 10 cm 1 95 95
95 95 10 80 95 95 95 30 50 95 95 95 50 10 90 93 95 70 2 60 80
90
[0028] FIG. 3 shows that about 90% or more of hydrogen peroxide can
be decomposed at a bed height of about 2 cm or more and an LV of
about 50 m/h or less.
Example 3
[0029] The influence of hydrogen peroxide on degradation of ion
exchange resin was examined.
[0030] Cation resins of the same type were respectively immersed in
solutions having various hydrogen peroxide concentrations for 24
hours and the total organic carbon (TOC) concentrations were
measured with TOC-V, a product of Shimadzu Corp. As shown in FIG.
4, it was confirmed that hydrogen peroxide contained in a
concentration of less than about 1 ppm had little influence on
resin degradation. Hence, it is adequate to decompose 90% or more
of hydrogen peroxide present in the order of a few or several ppm
in fuel pool.
[0031] In general, ion exchange resins are replaced by fresh resins
in a TOC concentration of more than about 20 ppm. FIG. 4 shows that
when the hydrogen peroxide concentration exceeds about 3.5 ppm, the
TOC concentration exceeds about 20 ppm and replacement of ion
exchange resin is required. FIGS. 2 and 4 show that untreated water
(hydrogen peroxide concentration: 20 ppm) has such a high hydrogen
peroxide concentration as to require replacement of ion exchange
resin after the water is passed through the resin once, whereas the
treatment method of the present invention achieves the hydrogen
peroxide decomposition rate of about 95%, decreases the hydrogen
peroxide concentration of water to be treated through an ion
exchange resin to about 1 ppm or less, and considerably lowers the
frequency of replacement of the ion exchange resins.
INDUSTRIAL APPLICABILITY
[0032] Before an ion exchange resin is used to demineralize water
to be treated that contains pro-oxidants (e.g., hydrogen peroxide)
generated by radiolysis of spent fuel pool water from nuclear power
plants of PWR, it is possible according to the present invention to
reduce the pro-oxidants contained in the water to be treated,
decrease load placed on a demineralizer and maintain the high
purity of the treated water as well as prolong the life of the ion
exchange resins and reduce generation of spent ion exchange resins
that are radioactive secondary wastes. Accordingly, the present
invention is significant.
* * * * *