JPS59164994A - Cobalt removable device for light water 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 a cobalt removal device for a light water reactor, and more specifically, it has a high adsorption removal ability for a small amount of cobalt contained in the primary cooling water system of a light water reactor, and has a high mechanical strength. The present invention also relates to a cobalt removal device equipped with an excellent high temperature filter element for light water reactors.

[Technical background of the invention and its problems]

Recently, as the number of years of operation of light water reactors has increased, radionuclides have been deposited in various parts of the secondary cooling water system piping, and the radiation dose rate when the reactor is shut down is gradually increasing. Such accumulation of radioactivity leads to an increase in the radiation dose of periodic inspection personnel when the reactor is shut down for periodic inspections, which in turn has negative effects such as a decrease in operating rates. The increase in dose rate at the time of reactor shutdown due to radioactivity accumulation varies widely depending on the type of reactor and maintenance method.
powerResearch Institute,
According to a summary by U-8, A,), the surface dose rate of recirculation lines of some boiling water reactors (BWRs) in the United States exceeds the effective operating period of one year (IFPY: I Full).
Power Year) Yu F) 10100-l
It shows an increase of 50/hr.

It is known that most of the radionuclides that cause this accumulation of radioactivity are "Col 8Co", which has a long half-life, and it is clear that these radionuclides originate from corrosion products from the structural materials of light water reactors. It has become.

That is, corrosion products released into water due to corrosion of structural materials of a light water reactor are composed of various water-soluble ions and various metal oxides dispersed in water. Here, "Co +" Co, which is the main cause of radioactivity accumulation, is
It is generated as follows. That is, first, Co, which is a constituent element of the structural material, is eluted into the cooling water system due to corrosion of the structural material and is ionized. The ionized Co is adsorbed to the metal oxide or is incorporated into the metal oxide through an ion exchange reaction. When the metal oxide is carried into the reactor core, the CO taken in is activated.

If the amount is reduced, the relative amount of co carried into the reactor core and activated can be reduced, and radioactivity accumulation can be suppressed.

From this point of view, several methods have been attempted to reduce the cobalt concentration in reactor water, but all of them are extensions of ion exchange methods that use ion exchange resins at room temperature and atmospheric pressure. High temperature (270-290℃) and high pressure (56-76 atm) such as reactor water environment
) It is not effective for direct application as a cobalt removal method under such conditions, and it has not yet been put into practical use. Furthermore, recently, inorganic ion exchangers with high heat resistance have been attracting attention. This is used, for example, by filling powder or sintered compacts of metal oxides having cobalt ion exchange ability, such as aluminum oxide and zirconium dioxide, in a state in which water can flow through the flow path of the reactor water.

However, when powder is used, its large specific surface area improves cobalt adsorption and removal ability, but on the other hand, if the flow rate of reactor water increases beyond the specified value or flow rate fluctuations such as pulsation occur, There is a risk that the powder will flow out. Therefore, in the operation of the reactor, it is necessary to limit the processing capacity (the amount of water that can pass per unit time) using the flow rate of the reactor water as an index, and strict operational management is also required to prevent flow rate fluctuations. This makes the operation complicated.

That is, it is not preferable to incorporate the powder into an actual machine from the viewpoint of furnace operation.

On the other hand, as for the sintered body, it is a porous structure that has a certain mechanical strength, so compared to the case of powder, the specific surface area is reduced and the contact area with reactor water is reduced. It is easy to incorporate it as a so-called block filter.

However, in the case of a sintered body, there is a drawback that the ability to remove cobalt is low for the reason mentioned above, and so no case has been found where it has been incorporated into an actual machine.

[Purpose of the invention]

The present invention provides a light water reactor equipped with a sintered body type high temperature filter in the reactor water circulation system, which has a large ability to adsorb and remove cobalt contained in the reactor water of a light water reactor, and which has no risk of leakage even when the reactor water flow rate fluctuates. The purpose is to provide a cobalt removal device for

[Summary of the invention]

The present inventors conducted a comparative study on the ability of sintered bodies of various inorganic ion exchangers to adsorb and remove cobalt. We discovered that the removal ability is much superior, and developed the cobalt removal device of the present invention using the sintered body as a filter.

That is, the cobalt removal device for light water reactors of the present invention
It is characterized by a structure in which a filter made of the sintered body α is disposed within the reactor water circulation system.

The filter according to the present invention is a porous structure formed by sintering Snow using a powder metallurgy method. In this case, 5nQt can be sintered by itself, but it has poor mechanical strength, so it is necessary to add a predetermined amount of another metal or alloy as a binder.

The binder used is Cr15 weight or less.

Fe 8% by weight or less, Mn 0.6% by weight or less, Cu
O-05 weight or less, A/1.0.15 weight or less,
'l'i 0.3 weight - or more 0.5 weight - less, Co
An alloy having a composition of 0-(j1% by weight or less and the balance being Ni is preferable, and the amount added is preferably about 50 to 70% by weight based on the total weight.

The filter according to the present invention is prepared, for example, as follows. That is, first, 5n011 powder and binder powder are mixed at a predetermined blending ratio, and the resulting mixed powder is filled into a mold with a predetermined shape and then pressure-molded to form a green compact such as a pellet or block. do.

The molding pressure at this time affects the porosity of the filter, but is usually appropriately selected within the range of 4 to 8 tons/efl.

Next, this green compact is heat-treated and sintered in air or an inert atmosphere. The sintering temperature at this time also affects the porosity of the filter in the same way as the molding pressure, but usually 9
It is appropriately selected within the range of 00 to 1 isoC.

The obtained sintered body is usually a porous structure having a porosity of 30 to 50, has high mechanical strength, and has sufficient resistance to external forces such as vibrations that act during actual furnace operation.

Although the above sintered body may be applied as is to the filter according to the present invention, in order to further increase the contact area with the reactor water and improve the cobalt removal ability, the sintered body may be provided with, for example, the following. It is preferable to perform machining.

Typical examples thereof are shown in FIGS. 1 to 3.

Figure 1 shows a sintered body with slits formed on the peripheral edge of the cylindrical pellet, Figure 2 shows a sintered body with holes drilled in the pellet shape, and Figure 3 shows a sintered body with holes drilled in the pellet. It is rolled into a plate shape and processed into a corrugated plate. Also,
Other embodiments include those in which the sintered body is simply cut into small pieces or in the form of coils. The warts may be machined into a shape that increases the external surface area to increase the contact area with the reactor water.

Now, the cobalt removal device of the present invention is constructed by filling a predetermined container with the above-described filter of the sintered body and disposing it in the reactor water circulation system.

The apparatus of the present invention will be explained in more detail with reference to an example shown in FIG. The figure shows a case where the device of the present invention is installed in a recirculation system. In FIG. 4, 1 is a pressure vessel of a light water reactor, the right side is a condensate system, the lower left side is a recirculation system incorporating an example of the present invention, and z) a removal device.

In the condensing system, 2 is a main steam pipe, 3 is a turbine that performs work with steam, 4 is a condenser that condenses the exhaust gas of the turbine 3,
5 is a water supply pump that supplies the obtained condensate into the pressure vessel 1, and 6 is a condensate pipe.

The cobalt removal device of the present invention includes a cobalt concentration detector installed before and after the filter lO1 in the middle of the loop piping 9 formed between the primary coolant inlet 7 and the primary coolant outlet 8 of the light water reactor. It is arranged as 11°11'. 1
2 is the recirculation yte:/f for conveying the secondary coolant into the pipe 10.

In such a configuration, the cobalt removal operation is performed as follows.

That is, by operating the recirculation pump 2 during operation of the light water reactor, the primary coolant containing cobalt is circulated within the pipe 9 in the direction of the arrow.

The secondary coolant then passes through the filter 10, and the cobalt in the secondary coolant is captured by the filter 10.

The decontaminated coolant passes through the pipe 9 by the recirculation pump 12 and returns to the pressure vessel IK again.

This operation is assisted for a certain period of time, and after it is confirmed by the cobalt concentration detector 11 that the cobalt concentration in the reactor water has decreased to the target value, the recirculation pump 12 is stopped.

Furthermore, by reading the difference between the measured values of the cobalt concentration detectors 11 and 11', if a decrease in the cobalt removal ability of the filter 10 is recognized, the filter is replaced with a new filter to restore the removal ability. It is possible to increase

The above explanation is an example in which the device of the present invention is incorporated into an existing recirculation system, but the location of the device of the present invention is not limited to this. There is no problem in having one.

The device of the present invention can be installed not only in an existing reactor water circulation system, but also in a newly installed reactor water circulation system in parallel with the existing reactor water circulation system.

In addition, in the above-mentioned example, one series of filters was incorporated into one reactor water circulation system (recirculation system), but in order to maintain the cobalt removal ability of the device of the present invention in a steady state at all times, In this case, it is effective to branch one reactor water circulation system into multiple systems and install the filter in each of the systems. An example is shown in FIG.

In FIG. 5, the reactor water circulation system is branched into two lines, A and B. Filters 10 and 10' are applied to each series.
It has been incorporated. First, the pulp 20', 21' on the B side
Close the A side pulp 20.21 and remove the filter 10.
Decontamination was carried out by pouring reactor water into the reactor.

Tracking the measured values of the cobalt concentration detectors 22 and 23, if the removal ability of the A-side filter 10 decreases, the A-side pulp 20
．． 21 and pulp 20' on the B side.

21' and continue decontamination on the B side. During this time, the filter 10 whose removal ability on the A side has decreased is replaced with a new one. In this way, 1, the apparatus of the present invention can always maintain cobalt removal ability in a steady state.

In addition to the above method, it is also effective to simultaneously install filters in a plurality of reactor water circulation systems in order to ensure cobalt removal capacity in a steady state at all times.

The operations in this case are basically the same as in the above example.

〔Effect of the invention〕

As is clear from the above explanation, the device of the present invention can prevent the filter from leaking into the reactor water, selectively capture and remove cobalt in the reactor water, and control the amount of cobalt accumulated in the reactor water. Therefore, its industrial value is great.

FIG. 4 is a diagram showing an example in which the device of the present invention is installed in a recirculation system, and FIG. 5 is a diagram showing another example of application of the device of the present invention.

1...Pressure vessel, 2...Main steam pipe, 3...Turbine, 4...Condenser, 5...Water pump, 6...Condensate pipe, 7...-Secondary cooling Water inlet, 8... - secondary cooling water outlet, 9... loop piping, 10.10''-filter, 11.11'.

22, 22', 23, 23'... Cobalt concentration detector, 12°°° recirculation pump, 20.20', 21
．． 21'...Pulp.

Claims (1)

[Scope of Claims] (1) A cobalt removal device for a light water reactor having a structure in which a filter made of sintered tin oxide is disposed within a reactor water circulation system. 1, 2) The cobalt removal device for a light water reactor according to claim 1, wherein the reactor water circulation system is a recirculation system, a condensate system, or both. (3) The cobalt removal device for a light water reactor according to claim 1 or 2, wherein the reactor water circulation system is a reactor water circulation system newly installed separately from an existing reactor water circulation system. (4) Cobalt removal for a light water reactor according to claim 3, wherein the new reactor water circulation system is arranged in a plurality of series in series with the existing reactor water circulation system, and each of them is provided with the filter. Device. (5) Claim 1 in which the filter has its outer surface machined to increase its surface area.
Cobalt removal equipment for light water reactors as described in .