JPS60128393A - Purifier for furnace water of nuclear reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to light water cooled nuclear reactors (hereinafter referred to as light water reactors), such as boiling water reactors (hereinafter referred to as BWRs).

[Technical background of the invention and its problems]

In light water reactors such as BWRs, as the operating time increases, radionuclides from corrosion products accumulate on the inner surface of secondary cooling water piping or equipment, and the radiation dose rate when the reactor is shut down tends to increase.

Such an increase in radiation dose rate, for example, increases the radiation exposure of workers during periodic inspections and causes a decrease in the work growth rate, which in turn causes a decrease in the plant operating rate.

Most of the radionuclides are Co, which has a long half-life, and its proportion increases as the reactor operating time increases.

Furthermore, as described above, these radionuclides are caused by corrosion products eluted from structural materials such as primary cooling water piping or equipment.

Therefore, the above C accounts for the majority of radionuclides.

We will explain how this occurred. In other words, 5? contained in the structural material? Co elutes into the primary cooling water piping due to corrosion of structural materials and becomes ionized. This ionized 59Co is adsorbed to metal oxides such as iron, or is taken into an ion exchanger or other metal oxides, flows into the furnace together with the metal oxides, and is irradiated with neutrons in the furnace. is activated and 60Co is generated. These generated 40COs accumulate in piping equipment outside the core, such as reactor recirculation piping, and the radiation dose rate increases over time. Therefore, if 59Co and 60Co in the reactor can be removed, the amount of radiation that accumulates in the piping outside the core and inside the equipment can be suppressed.

Conventionally, in light water reactors such as BWRs, ion exchange resins are used to remove 59Co and 60Co from reactor water. This will be explained with reference to FIG. FIG. 1 is a system diagram showing a schematic configuration of a BWR power plant. Reference numeral 1 in the figure indicates a reactor pressure vessel.

A reactor core 2 consisting of a plurality of fuel assemblies, control rods, etc. is disposed within the reactor pressure vessel 1, and a coolant (hereinafter referred to as reactor water in this embodiment) 3 is circulated. A recirculation pump 4 is connected to the reactor pressure vessel 1 via a recirculation pipe 4A) to forcefully circulate reactor water 3.

The reactor water 3 rises from the bottom to the top of the reactor core 2, and at this time its temperature rises, resulting in a two-phase flow state of water and steam.

Steam is connected to the reactor pressure vessel 1 and sent to a steam turbine 6 via a main steam pipe 5. The steam driven by the steam turbine 6t is led into the main condenser 7 to become condensate, and is transferred to the condensate demineralizer 9 by the pump 8, and then to the feedwater heater 11 by the pump 10. The water is sent to the reactor pressure vessel 1 again by the pump 12 via the water supply pipe 13t. A purification system pump 14t- is connected to the recirculation pipe 4A.
A low temperature purification system 15 is connected thereto. This low temperature purification system 15. is composed of a regenerative heat exchanger 16, a conventional heat exchanger 17, and an ion exchange resin demineralizer 18.

The ion exchange resin demineralizer 18 is made of a cation exchange resin and an anion exchange resin, each having a withstand temperature of about 12
0℃, about 600 degrees. On the other hand, reactor water 3 is 2
Since it is high temperature and high pressure water of 80℃, 70 to 9/1M2,
3 tons of reactor water is cooled to around 0° C. by the regenerative heat exchanger 16 and is then passed through the ion exchange resin demineralizer 18. Thereafter, the water is heated through the regenerative heat exchanger 16 to the original temperature (280° C.) and returned to the water supply pipe. However, in this method, heat loss occurs in the cooling process of the regenerative heat exchanger 16 and the heat exchanger 17, and for example, increasing the purification capacity leads to an increase in heat exchange loss, an increase in power generation cost, and an increase in the size of the device. In particular, it is not possible to increase the purification efficiency. For this reason, recently, the use of inorganic ion exchangers with excellent heat resistance has been considered in place of the above-mentioned organic ion exchange resins. The inorganic ion exchanger is, for example, a powder of a metal oxide such as titanium oxide or zirconium dioxide having a cobalt ion exchange ability. This metal oxide powder is filled and held in a state where water can pass through the reactor water piping system, thereby reducing Co and C.
This is a configuration for removing o. However, this method makes it difficult to retain metal oxides. That is, in order to increase the cobalt ion exchange capacity in the reactor water, it is necessary to increase the contact area between the reactor water and the metal oxide, and for this purpose, it is necessary to reduce the particle size of the powder. When the particle size of the powder is reduced, the voids are reduced, which increases the pressure loss of the reactor water and changes the flow.

There is a risk of leaching of oxide powder. In other words, the opening of the mesh attached to the outlet of the container is the smallest practical size.
If powder with an average particle diameter of around 0 μm is used, for example, with an average particle diameter of around 1 μm, the powder particles will flow downstream as they are. On the other hand, if an attempt is made to prevent the powder from flowing out, the particle size must be increased, which reduces the contact area between the reactor water and the metal oxide, and reduces the cobalt ion exchange capacity.

Therefore, it is necessary to use a method in which the diameter of the metal oxide powder is reduced to a certain extent and sufficient care is taken to prevent the powder from flowing out, which makes the operation extremely difficult. Furthermore, the powder after cobalt removal has high radioactivity and is difficult to dispose of.

[Purpose of the invention]

The purpose of the present invention is to allow high-temperature, high-pressure reactor water to be directly introduced, to have a high ability to remove cobalt ions contained in the reactor water of a light water reactor, to have good water flow characteristics, and to prevent cobalt adsorbents from flowing out. It's about doing.

[Summary of the invention]

A reactor water purification system for a nuclear reactor according to the present invention includes a container body inserted into a reactor water piping system in a light water-cooled nuclear reactor power generation plant, and a filter housed in the container body, Copal in the reactor water flowing through the reactor water piping system) 1-Construction consisting of a plurality of filter basic elements laminated in the reactor water flow direction, in which adsorbed metal oxide powder is baked and fixed to mesh-like austenitic stainless steel. It is.

Therefore, high-temperature, high-pressure reactor water can be directly introduced, and cobalt in the reactor water can be effectively adsorbed and removed. Furthermore, since the basic filter element is a porous fixed bed and fired body, there is no risk of metal oxides flowing out. Since the mechanical strength and the adhesion strength of the metal oxide are high, it can have sufficient resistance against external forces that act when installed in the ground. Furthermore, since it has good porosity, it has good water permeability and low pressure loss, and it is easy to handle because it is constructed in units of basic filter elements 't-1.

[Embodiment 5 of the Invention An embodiment of the present invention will be described with reference to FIGS. 2 to 5. FIG. 2 is a diagram showing a schematic configuration of the BWR. Reference numeral 101 in the figure indicates a reactor pressure vessel. Inside this reactor pressure vessel 101, a reactor core 102 consisting of a plurality of fuel assemblies, control rods, etc. is arranged, and a coolant (hereinafter referred to as reactor water in this embodiment) 1O3 is circulated.

A recirculation pump 104 is connected to the reactor pressure vessel 101 via a recirculation pipe 104A.
f forced circulation. Reactor water 103 rises from the bottom to the top of the reactor core 102f, and at the same time rises in temperature and becomes a mixture of water and steam.
It becomes a phase flow state. Steam is sent to a steam turbine 106 via a main steam pipe 105 connected to the reactor pressure vessel 101. The steam that drives the steam turbine 106 is stored in the main condenser 107 and converted into condensate, which is transferred to the condensate demineralizer 109 by the υ pump fzos, and sent to the demineralizer 111 by the pump 110. Furthermore, the water supply pipe 113 is connected to the pump 112.
It is again supplied into the reactor pressure vessel 1σ1 through the reactor pressure vessel 1σ1. Recirculation piping 104 on the suction side of the recirculation bomb fxo4
A has a reactor water purification system pump 114 and a low temperature purification system 115.
is connected to the water supply pipe 11 between the pump 112 and the reactor pressure vessel 101 by purifying a part of the reactor water 103.
It is configured to supply within 3 days. The above low temperature purification system 11
5 is composed of a regenerative heat exchanger 116, a heat exchanger 117, and an ion exchange resin demineralizer 118. 1 in the diagram
19 indicates bypass piping.

The configuration is as shown in the figure. Reference numeral 121 in the figure indicates a container body. A filter 12 is provided inside this container body 121.
2 is installed. This filter 122 has a cartridge-type structure in which a plurality of basic filter elements 125, in which manganese ferrite 124 as a cobalt adsorbent is baked and fixed on the surface of a mesh-like austenitic stainless steel 123, are stacked inside an inner container 126. The basic filter element 125 and a partially enlarged view thereof are shown in FIGS. 4 and 5, respectively.

The background of selecting manganese ferrite as the cobalt adsorbent in the above structure is shown below.

First, 1Y types of metal oxides shown in Table 1 were selected based on the following three conditions.

(1) It must be insoluble in hot water f+\\ (2) It must be poisonous, harmful and useful (3) It must be easily and inexpensively available Table 1 And above 1'? We compared and measured the static adsorption characteristics of one type of metal oxide under certain conditions. Commercially available standard reagents were used as samples, and the particle size was fine powder and the specific surface area was 100 x 103 cm2/cm'3 or more.
00 x 103cm2/cm'.

The measurement was performed using 400ml of pure water and 5ml of pure water in a hard glass flask.
One 0 ppm cobalt standard solution was added to set the initial cobalt concentration to 120 pPb. Then, 111/Jl@ of the 17 types of metal oxides were uniformly added and the mixture was kept in a boiling state for 1 hour, after which the residual cobalt concentration in the supernatant was measured by flameless atomic absorption method. As a result, the results shown in Table 2 were obtained.

Table-2 Note) Q2 initial cobalt concentration 120 PP:b (actual value).

As is clear from this table, cobalt ion-adsorbing organic binder impregnated with oxides of V metal elements such as iron, manganese, aluminum, tungsten, ←hh zirconium, tantalum, and two They were mixed in a ratio of 7:3 and kneaded for about 50 hours in a garmill. Thereafter, it was dried and crushed into pieces of 32 meshes or less, and then pressed using a mold into a cylindrical shape with a diameter of 7 mm and a height of 6 mm. Then, in order to blow off the binder, the temperature was slowly raised to 400℃, and the melting point (or decomposition point) shown in the above batter-1 was 5.
It was sintered in a nitrogen (N2) gas atmosphere at a temperature of 0 to 60 degrees for 3 hours to obtain an adsorption element. Sintered top size, eH diameter 5-6 pieces, height 5111I+, weight 0.3-0
．． It is 51. The specific surface area of nine types of metal oxide powder is 10
0 X l 03an2/cm' or more 300 X 10
The specific surface area of the sintered body is less than 'cm2/cm', and the specific surface area is 70
X 10! cm' / cm' or more 200 x 10
'1=-p below cm2/cm3. For the measurement, 80,001 l of pure water and 0.5 ppm cobalt standard solution 1- were placed in a 10-knob stainless steel beaker lined with tetrafluoroethylene resin, and the initial cobalt concentration was set to 62.5 ppt.
And so. And each sintered element is approximately O.1fi.
The sample was immersed in a test liquid at a ratio of 1/l and kept in a boiling state for 1 hour, and then the residual abarth concentration in the supernatant liquid was measured by flameless atomic absorption method. As a result, the results shown in Table 3 were obtained.

Table 3 Initial cobalt concentration 62.5 ppt.

Metal oxide 0.11171 As is clear from these results, tin-iron, manganese and tungsten oxides exhibited excellent cobalt ion adsorption properties. Based on the above background, manganese ferrite was used as an iron oxide in this example, but other Y
Oxides of seed metals such as manganese, aluminum, tungsten, zirconium, tantalum, and niobium may be used, and as iron oxides, in addition to manganese ferrite, nickel ferrite, zinc ferrite, and magnesium ferrite may be used. , barium ferrite, copper ferrite, etc. may be used.

Next, a method for adjusting the filter basic element 125 will be explained. First, manganese ferrite with an average particle size of 0.3 μm and a binder (180-85% by weight): 120-1
5% by weight) to make a mixed solution. This mixed solution is mixed in a butanol/turpentine dispersant in an amount of about 20 to 30% by weight based on the total weight of the total.

The above binder is polyvinyl butyral CPVB)
It is desirable that the mixing ratio of the mixture of B and turpentine is about 10:7 by weight.

The mesh-shaped austenitic stainless steel 123 described above is immersed in the thus prepared ferrite powder mixture. This austenitic stainless steel 123 is thoroughly degreased and cleaned with toluene or xylene, and subjected to surface oxidation treatment in an air oven at 800° C. to 900° C. for 1 to 2 hours. By immersing the austenitic stainless steel 123, the ferrite particles are deposited and adhered to the surface of the austenitic stainless steel 123. and nitrogen (N
2) Dry and bake in a gas atmosphere furnace. At this time, the baking temperature is usually 200 to 220 DEG C., and the baking is carried out for 2 to 3 hours.

Then, this deposition and drying process is repeated several times.

The thus baked and dried material is heat-treated in an inert atmosphere to bake and fix the manganese ferrite powder to the surface of the austenitic stainless steel 123. The firing temperature during heating affects the specific surface area of the filter 122, cobalt adsorption characteristics, etc., but generally the heating temperature is set to 100%.
-200°C is preferably selected within the range of 750°C to 850°C. The sintered body of manganese ferrite thus obtained has a bulk density of 1 to 21 i/cm' and a specific surface area of 45 x 105 cm'/cm', which means it has good porosity. and mechanical strength,
The fixation strength of manganese ferrite is also high, and it has sufficient strength against external forces that act during operation. Note that the bulk density and specific surface area are defined as follows. Inside the fired body, there are sealed closed pores as shown in Figure 6.
d pore ) 126A and an open pore 127 communicating with the outside air are formed, the net volume of the fired body is 1i7vQ, the volume of the closed pore 126A is vl, the volume of the open pore 127 is ν, and the mass t -w, the bulk density is defined as follows.

Furthermore, true density and apparent density are defined as follows.

True density=□...(It) 6 Next, the specific surface area is the sum of the surface areas of all particles contained in a unit volume. In addition, the austenitic stainless steel 1
Reference numeral 23 is a mesh having a mesh opening t-0, which can be selected within a range of 1 to 3 m, and the porosity inside the filter can be changed as appropriate.

The operation of this embodiment shown in FIG. 2 will be explained based on the above configuration. By operating the reactor water purification system pump 114fi, the reactor water 103 containing 59CO and 60CO is passed through the piping/yasu piping 119 and flows into the cobalt removal device 120. C0 and 60CO are captured in this cobalt removal device 120. 59CO and 60C
The reactor water 103 from which O has been removed flows into the water supply pipe 113 together with the reactor water 103 purified by the low-temperature purification system 115, and flows into the reactor pressure vessel 101 again together with the supply water.

After confirming that the target value has been reached, close the on-off valves (not shown) before and after the light water reactor cobalt removal device 120.
Replace the filter 122. According to this embodiment, the reactor water 103 can be introduced without being cooled, and manganese ferrite 124t, which has a large adsorption capacity for conort ions, is used as an adsorbent. 59c o and 60c in water 103
O can be effectively adsorbed and removed. In addition, since the basic filter element 125 is a porous fixed bed and fired body, manganese ferrite 125 is used as a cobalt adsorbent.
There is no risk of leakage to the outside. Since the mechanical strength and the fixing strength of the manganese ferrite 124 are high, it has sufficient resistance against external forces that act when installed in a plant. Also, since it has good porosity, it has good water permeability and low pressure loss. Furthermore, since the cartridge is removable, it is very easy to handle. Next, another embodiment will be described with reference to FIG. 7.

In other words, the light water reactor conalt removal device 1201kJ is inserted into the water supply pipe 113 of the reactor pressure vessel 101 instead of being inserted into the innoce pipe 119.

Therefore, not only can the same effects as in the first embodiment be achieved, but also 59 c can be obtained from the reactor water 103 purified by the low-temperature purification system 115 and the condensate passing through the steam turbine 116. It is extremely effective as it can remove o and 60CO.

The application of the same reference numerals to the same parts as in the above-mentioned embodiment is not limited to the first and second embodiments, but the optimum position may be selected depending on the situation of the plant.

〔Effect of the invention〕

A reactor water purification system for a nuclear reactor according to the present invention includes a container body inserted into a reactor water piping system in a power plant for a light water-cooled nuclear reactor, and a filter housed within the container body, The above-mentioned filter is made by laminating a plurality of filter basic elements in the reactor water flow direction, in which metal oxide powder adsorbing metal oxide in the reactor water flowing through the reactor water piping system is baked and fixed to mesh-like austenitic stainless steel. This is the structure.

Therefore, high-temperature, high-pressure reactor water can be directly introduced, and cobalt in the reactor water can be effectively adsorbed and removed.Furthermore, since the basic filter element is a porous fixed bed and is a fired product, metal oxides can be removed. There is no risk of leakage. Since the mechanical strength and the adhesion strength of the metal oxide are high, it can have sufficient resistance against external forces that act when installed in a plant. Furthermore, since it is housed within the main body, it is easy to handle, and has great effects.

[Brief explanation of drawings]

Figure 1 is a diagram showing a conventional example and is a system diagram showing the configuration of a boiling water reactor, Figures 2 to 5 are diagrams showing an embodiment of the present invention, and Figure 2 is an expanded boiling water type original element. Fig. 5 is a partially enlarged view of Fig. 4. Fig. 6 is a cross-sectional view of a general fired body, Fig. 7 is a plan view of a boiling water reactor showing another embodiment. This is a system diagram. Ikl'1123...Austenitic stainless steel
/14.124...Mangan7 Elite, 125...
- Filter basic elements. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 7 Continued from page 1 0 Inventor Akira Sugatani @ Inventor Takeyu Nawai @ Inventor Hikaru Kubo ] Inventor Noboru Igarashi @ Invention Masahiko Ishiban Inventor Toshikazu Minoshima ■Applicant Toshiba Corporation 3-7-1, Ichiichi-cho Tohoku Electric Power Co., Ltd. 1 Higashi-Shinmachi, Higashi-ku, Uchini City Chubu Electric Power Co., Ltd. 3-1 Sakurabashi-dori, Hokuriku Electric Power Co., Ltd. Co., Ltd. 1-6-1 Otemachi, Chiyoda-ku, Tokyo Japan Atomic Power Co., Ltd. 1-1-6 Uchisaiwai-cho, Chiyoda-ku, Tokyo Tokyo Shibaura Electric Co., Ltd. 1-1-6 Uchisaiwai-cho, Chiyoda-ku, Tokyo No. Tokyo Shibaura Electric Co., Ltd. Tokyo Office 1-1-6 Uchisaiwai-cho, Chiyo, Tokyo Tokyo Shibaura Electric Co., Ltd.

Claims (1)

[Scope of Claims] (1) A light water-cooled nuclear reactor power generation plant, comprising a container body inserted into a reactor water piping system, and a filter housed in the container body, The filter is characterized by a plurality of filter basic elements laminated in the reactor water flow direction, in which metal oxide powder that adsorbs cobalt in the reactor water flowing through the reactor water piping system is baked and fixed to mesh-like austenitic stainless steel. Reactor water purification system for nuclear reactors. (2) The above metal oxide is manganese ferrite (MnFe
2O4)
Reactor water purification system for the nuclear reactor described in Section 1.