JP2000162387A - Method and device for judging exchange timing of chemical filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To fully utilize attraction capacity and to reduce the amount of radioactive waste without breaking a filter and any contact, by judging timing when the concentration of a constituent to be eliminated to be measured by a detector or a measurement point being provided before and after a first chemical filter device matches as the exchange timing of the chemical filter. SOLUTION: Iodine filter devices 1 and 2 are composed in series and in two stages and have attraction parts 3 and 4 filled with silver nitrate welding adsorption agent. When a radioactive gas containing iodine is introduced to the devices 1 and 2, iodine is attracted and immobilized by an adsorbent. An exhaust gas where iodine is eliminated is delivered from an outlet nozzle and is released into the atmosphere. Detectors 5 and 6 for detecting the radioactive gas are installed before and after the first filter device 1 for measurement using an Nal scintillation detector or the like for measuring iodine 129. Timing (t) when iodine concentration C01 of the inlet of the first filter coincides with iodine concentration C11 of the outlet finally is judged to be the timing for replacing the filter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for judging the replacement time of a chemical filter, and in particular, to remove radioactive off-gas generated from a nuclear power plant, a reprocessing plant, a radioisotope handling facility, and other nuclear facilities. The present invention relates to a method and an apparatus for determining a replacement time of a chemical filter device.

[0002]

2. Description of the Related Art At nuclear facilities such as a nuclear power plant and a nuclear fuel reprocessing plant, measures to prevent the release of radioactive substances are taken from the viewpoint of environmental protection. In particular, radioactive iodine generated as a gas (chemical form, simple iodine: I2
(Methyl iodide: CH3I, etc.) has been emphasized. As a result, an iodine removal filter filled with an iodine adsorbent such as a silver-impregnated adsorbent is installed in an exhaust system of a nuclear power plant or a nuclear fuel reprocessing plant.

[0003] The silver-impregnated adsorbent is a substance for chemically fixing simple iodine or iodine such as methyl iodide as silver iodide on the silver-impregnated adsorbent. Since these adsorbents are disposed of as radioactive waste after use, they must be used as long as possible from the viewpoint of reducing the amount of waste generated.

[0004] Regarding the time to replace the filter, see HEP
For particulate filter such as A filter and ULPA filter, it can be detected by pressure loss,
Since chemical filters target gas components,
It could not be detected by pressure loss or the like.

As a method for determining the replacement time of a chemical filter, for example, as disclosed in Japanese Patent Application Laid-Open No. 9-280640, the effective life of the chemical filter is determined when the gas concentration at the filter outlet side exceeds a predetermined concentration. As disclosed in Japanese Patent Application Laid-Open No. Hei 10-137522, a bypass filled with the same material as the main body chemical filter is provided, and by measuring the concentration in the bypass, the main body chemical filter is removed. There is a method of determining the replacement time.

[0006]

However, the above prior art has the following problems. A chemical filter that removes a component to be removed by a chemical reaction has a life in which all the reactions are completed in the filter. Its life depends on the concentration of radioactive gas in the environment, humidity, the area and thickness of the filter (the amount of reactants), the amount of air sent to the filter, and the like.

When a radioactive gas is passed through a filter having a certain thickness, the chemical filter first reacts well on the surface (upstream side) and gradually decreases in concentration on the downstream side, so that the reaction becomes slow. Therefore, the filter deteriorates from the upstream side. For this reason, in the replacement time estimation method in which the life is determined only by measuring the concentration on the downstream side, generally, the reaction is completed on the upstream side of the filter, but the reactant remains on the downstream side. . That is, the chemical filter determines that it is time to replace the chemical filter in a state where the entire filter still has the adsorption ability. The service life of a chemical filter is not only directly reflected in the running cost, but also the chemical filter from which the components to be removed have been adsorbed and removed must be disposed of as radioactive waste. Therefore, the amount of radioactive waste must be reduced as much as possible.

Further, a method of determining the replacement time of the main body chemical filter by providing a bypass filled with the same material as the main body chemical filter and measuring the concentration in the bypass is to provide a bypass line separately from the main body. However, since new piping and shielding equipment must be installed, the apparatus cannot be said to be compact. Further, since the chemical filter on the bypass line is also replaced like the main body chemical filter, extra work is required for replacement work, and the running cost is increased.

[0009] An object of the present invention is to reduce the running cost and reduce the amount of radioactive waste by fully utilizing the adsorption capacity without destroying or contacting the chemical filter in the circumstances described above. It is an object of the present invention to provide a method of determining a replacement time of a chemical filter which can be reduced.

[0010]

A feature of the present invention to achieve the above object is that an apparatus for judging the replacement time of a chemical filter is provided by a detector or a measuring point provided before and after at least a first chemical filter apparatus. A chemical filter device is characterized in that a time when the measured concentrations of the components to be removed coincide with each other is determined as a chemical filter replacement time.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described specifically with reference to examples.

FIG. 1 shows an embodiment of a system of an off-gas treatment facility which constitutes an iodine filter device to which the method for judging replacement time of a chemical filter of the present invention is applied.
The iodine filter devices 1 and 2 are configured in two stages in series,
There are adsorption sections 3 and 4 each filled with an iodine adsorbent impregnated with silver nitrate. When a radioactive gas containing iodine is introduced into the iodine filter devices 1 and 2, iodine, which is a radioactive gas, is adsorbed and immobilized by the iodine adsorbent impregnated with silver nitrate in the adsorption units 3 and 4 in the adsorption device. . The exhaust gas from which iodine has been removed is discharged from an outlet nozzle, subjected to appropriate processing such as cooling by a cooling device, and then released to the atmosphere.

Detectors 5 and 6 for detecting iodine such as radioactive gas are provided before and after the first iodine filter device 1. It is desirable that the detector be able to measure iodine concentration directly and without delay using a NaI scintillation detector or semiconductor radiation detector (Ge) for measuring iodine 129 (I-129).

In general, the higher the iodine concentration is, the higher the adsorption efficiency of the chemical filter is. Therefore, iodine is adsorbed with high efficiency on the upstream side of the filter, and the iodine concentration decreases in the filter toward the downstream side. Also, the adsorption efficiency is reduced. Further, the adsorption efficiency of the chemical filter also depends on the amount of the impurities already adsorbed, and the adsorption efficiency of the adsorption of the impurities decreases with time. Since the adsorption proceeds from an early stage on the upstream side of the filter, the adsorption efficiency is greatly deteriorated.

At time t, the iodine concentration at the inlet of the first iodine filter is C _0t . On the other hand, let the concentration of iodine at the outlet of the first iodine filter be C _1t . Initially, since iodine is hardly adsorbed on the iodine adsorbent impregnated with silver nitrate, the removal efficiency is good and the iodine concentration _{Ct + 1} is almost zero. However, as iodine is adsorbed by the iodine adsorbent impregnated with silver nitrate from the upstream side, the removal efficiency also decreases, so that the iodine concentration C _{1t at the} iodine filter outlet also gradually increases. Eventually, the iodine concentration C _0t at the inlet of the first iodine filter and the iodine concentration C _{1t at the} outlet will match. The coincident time t is determined to be the time for replacing the filter, and is set as the time for replacing the filter.

The iodine discharged to the downstream side from the first iodine filter device can achieve adsorption and removal of iodine by the second iodine filter installed in series, so that the amount of iodine released to the environment can be assured. It can be kept below the regulation value.

[0017]

According to the present invention, a detector for measuring the component to be removed is provided before and after the first unit, and the time when the concentration of the component to be removed measured from the detector provided before and after the first matches the chemical is determined. By judging when it is time to replace the filter, the iodine filter can be used up to just before the breakthrough state, making full use of the adsorption capacity without breaking or contacting the chemical filter. The life is extended, and the cost of the adsorbent can be reduced. Further, the amount of radioactive waste can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a configuration of an off-gas processing system according to an embodiment of the present invention.

[Explanation of symbols]

1, 2,... Iodine filter device, 3, 4,.
6 ... Detector.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G01T 1/167 B01D 53/34 134C F-term (Reference) 2G088 EE12 EE25 HH03 KK29 4D002 AA25 AC09 BA04 CA07 DA25 DA70 GA02 GB02 4D012 CA14 CB05 CE02 CF05 CG01 CK10

Claims (3)

[Claims] In the method for determining the replacement time of a chemical filter, the time at which the concentration of the component to be removed measured by a detector provided at least before and after the first chemical filter device coincides with the replacement time of the chemical filter. A method for determining when to replace a chemical filter, characterized by determining. 2. The chemical filter device according to claim 1, wherein at least one backup chemical filter device is installed in series with the chemical filter device. 3. An apparatus according to claim 1, wherein a detector for measuring a component to be removed is provided on pipes before and after at least the first or more chemical filter devices. A chemical filter device.