JP6533714B2 - Determination and monitoring method of radioactive cesium removal rate in volume reduction treatment - Google Patents
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本発明は放射性セシウムを含む減容化対象土壌の減容化処理における除去率を、迅速、高精度に定量する方法に関する。 The present invention relates to a method for rapidly and accurately quantifying the removal rate in the volume reduction treatment of volume reduction target soil containing radioactive cesium.
大気中に拡散した放射性物質は降雨等により地表面に落下する。中でも放射性セシウムは、半減期が比較的長く、長期に亘って土壌中に残留する。また、セシウムは、電子軌道がカリウムに類似しており、植物がカリウムと間違って取り込みやすく、放射性セシウムを取り込んだ穀物、果実、野菜等を摂取すると、人体内に放射性セシウムが取り込まれてしまう。そのため、居住地や耕作地を中心に除染作業が行われ、放射性セシウムを含む土壌が回収されている。回収された土壌量は膨大であり、そのまま保管するには広大なスペースが必要であるため、減容化処理が行われている。 Radioactive substances diffused in the atmosphere fall to the ground surface due to rainfall or the like. Among them, radioactive cesium has a relatively long half-life and remains in the soil for a long time. In addition, cesium has an electron trajectory similar to that of potassium, and plants easily take it as potassium, and when cesium, grains, fruits, vegetables, etc. which have taken in radioactive cesium are ingested, radioactive cesium will be taken into the human body. Therefore, decontamination work is carried out mainly on residential areas and cultivated land, and soil containing radioactive cesium is recovered. The volume of soil collected is huge, and a large amount of space is required to store it as it is, so volume reduction treatment is being performed.
図５に、一般的な減容化処理工程を示す。
放射性セシウムを含む減容化対象土壌１は、洗浄液２とともに洗浄装置１０内で洗浄され、放射性セシウムが吸着した土壌部位が浮泥分として脱離する。洗浄完了後のスラリーは、洗浄篩２０にて回収される粒径の大きな固形分からなる低線量土壌３と、放射性セシウムが吸着した粒径の小さな固形分からなる浮泥分を含む洗浄水４とに分けられる。洗浄水４は、オーバー水受槽３０にいったん受けいれられた後、濁水処理装置４０にて放射性セシウムを含む浮泥分を沈殿させた固相５と液相６とに分離される。固相５はフィルタープレス５０により水分を絞り、放射性セシウムが濃縮された脱水ケーキ７として回収され、液相６は洗浄廃液８として処分される。
FIG. 5 shows a general volume reduction treatment process.
The soil to be reduced in volume 1 containing radioactive cesium is washed in the washing apparatus 10 together with the washing solution 2, and the soil portion to which the radioactive cesium is adsorbed is detached as floating mud. The slurry after completion of the washing is a low-dose soil 3 consisting of a solid of large particle size collected by the washing sieve 20 and a washing water 4 containing floating mud consisting of a solid of small particle size adsorbed by radioactive cesium. It is divided. The washing water 4 is once received in the over water receiving tank 30, and then separated in the turbid water treatment device 40 into the solid phase 5 and the liquid phase 6 in which the floating sediment containing radioactive cesium is precipitated. The solid phase 5 squeezes the water by the filter press 50 and is recovered as a dewatered cake 7 in which radioactive cesium is concentrated, and the liquid phase 6 is discarded as the washing waste liquid 8.
減容化処理には、減容化対象土壌に含まれる放射性セシウム量に対する脱水ケーキへ濃縮される放射性セシウム量の比率であるセシウム除去率が高いことが求められる。減容化処理は、洗浄装置、洗浄篩、濁水処理装置等が組み合わされたプラントで行われるが、セシウム除去率の測定結果を各装置の運転条件にフィードバックし、セシウム除去率を高くすることが行われている。
セシウム除去率は、減容化対象土壌の乾燥重量と放射性セシウム濃度、および、脱水ケーキの乾燥重量と放射性セシウム濃度から求めることができる。放射性セシウム濃度の測定には、ゲルマニウム半導体検出器やＮａＩシンチレーション式ガンマ線スペクトロメータという特殊な測定装置が必要である。これらの測定装置は、大型で冷却に液体窒素が必要であり、専門の研究所等に設置されている。そのため、放射性セシウム濃度を測定するには、測定対象である減容化対象土壌や脱水ケーキをゲルマニウム半導体検出器等が設置されている研究所等まで運搬する必要がある。この際、放射性セシウムが濃縮して高線量となった脱水ケーキの運搬に自治体や道路の管理者等が難色を示すことがある。また、測定結果を得るには一定の時間がかかるため、セシウム除去率の測定結果を運転条件に迅速にフィードバックできないという問題がある。
The volume reduction treatment is required to have a high cesium removal rate, which is a ratio of the amount of radioactive cesium to be concentrated to the dewatered cake to the amount of radioactive cesium contained in the volume-reduced target soil. Volume reduction treatment is performed in a plant combined with a washing device, washing sieve, turbid water treatment device, etc., but the cesium removal rate measurement result can be fed back to the operating conditions of each device to increase the cesium removal rate. It has been done.
The cesium removal rate can be determined from the dry weight and radioactive cesium concentration of the soil to be reduced in volume, and the dry weight and radioactive cesium concentration of the dewatered cake. Measurement of radioactive cesium concentration requires special measuring devices such as a germanium semiconductor detector and a NaI scintillation type gamma ray spectrometer. These measuring devices are large, require liquid nitrogen for cooling, and are installed in specialized laboratories and the like. Therefore, in order to measure the radioactive cesium concentration, it is necessary to transport the soil to be reduced in volume to be measured and the dewatered cake to a laboratory where a germanium semiconductor detector or the like is installed. Under the present circumstances, the administration of a local government, a road manager, etc. may show inconspicuous the conveyance of the dehydration cake which radioactive cesium concentrated and became high dose. In addition, since it takes a certain time to obtain the measurement result, there is a problem that the measurement result of the cesium removal rate can not be quickly fed back to the operating condition.
特許文献１には、サーベイメータを用いる放射性セシウム濃度の簡易分析方法が提案されている。特許文献１に記載の方法は、あらかじめ放射性セシウム濃度の異なる試料でサーベイメータとゲルマニウム半導体検出器にて空間線量値と放射性セシウム濃度を測定し、作成した相関シートと対象物のサーベイメータ測定値から放射性セシウム濃度を推察するものである。特許文献１に記載の方法は、放射性セシウム濃度を簡易に分析することができるものであるが、事前の相関シート作成時と試料測定時のサーベイメータは同一機器、同一条件で測定しなければならない。また、空間線量を測定するサーベイメータを用いるため、バックグラウンド線量が高い場合には測定精度が低下する。さらに、事前の相関シートの作成に加えて、測定対象物周囲の精密なバックグラウンド線量計測が必要であり、高精度での定量は困難であるという問題がある。 Patent Document 1 proposes a simple analysis method of radioactive cesium concentration using a survey meter. In the method described in Patent Document 1, the radioactive cesium is measured from the correlation sheet and the survey meter measurement value of the object prepared beforehand by measuring the spatial dose value and the radioactive cesium concentration with a survey meter and a germanium semiconductor detector with samples having different radioactive cesium concentrations. The concentration is to be inferred. The method described in Patent Document 1 can easily analyze the radioactive cesium concentration, but the survey meters at the time of preparation of the correlation sheet in advance and at the time of sample measurement must be measured under the same equipment and under the same conditions. Moreover, since the survey meter which measures an air dose is used, when background dose is high, measurement accuracy falls. Furthermore, in addition to the preparation of the correlation sheet in advance, there is a problem that precise background dose measurement around the measurement object is necessary, and quantification with high accuracy is difficult.
本発明は、減容化処理プラントにおいて、迅速にセシウム除去率を定量することのできる定量方法を提供することを課題とする。 An object of the present invention is to provide a quantitative method capable of rapidly quantifying a cesium removal rate in a volume reduction treatment plant.
１．減容化対象土壌から洗浄水に溶出したアルミニウム、またはケイ素の量と、前記洗浄水に含まれる放射性セシウム量との相関関係から検量線を作成し、
実プラントでの前記減容化対象土壌の減容化処理において、洗浄水、または洗浄廃液のアルミニウム、またはケイ素濃度の測定値と前記検量線とを用いて、セシウム除去率を定量することを特徴とするセシウム除去率定量方法。
２．予め、事前減容化処理試験を行い、減容化対象土壌から洗浄水に溶出したアルミニウム、またはケイ素の量と、前記洗浄水に含まれる放射性セシウム量との相関関係から検量線を作成し、
実プラントにおける前記減容化対象土壌の減容化処理における、洗浄水、または洗浄廃液のアルミニウム、またはケイ素濃度をリアルタイムで測定した測定値と前記検量線とを用いて、セシウム除去率をモニタリングすることを特徴とするセシウム除去率モニタリング方法。
1. Create a calibration curve from the correlation between the amount of aluminum or silicon eluted from the volume reduction target soil into the wash water and the amount of radioactive cesium contained in the wash water,
In the volume reduction treatment of the above-mentioned volume reduction target soil in an actual plant, the cesium removal rate is quantified using the measurement value of the wash water or wash waste aluminum or silicon concentration and the calibration curve. Determination method of cesium removal rate.
2. Conduct a preliminary volume reduction treatment test beforehand, and create a calibration curve from the correlation between the amount of aluminum or silicon eluted from the volume reduction target soil into the wash water and the amount of radioactive cesium contained in the wash water,
The cesium removal rate is monitored using the calibration curve and the measurement value obtained by measuring the concentration of wash water or wash waste aluminum or silicon concentration in the volume reduction treatment of the volume reduction target soil in a real plant using the calibration curve Cesium removal rate monitoring method characterized by
本発明により、実プラントでの減容化処理におけるセシウム除去率を、放射性セシウム濃度を実際に測定することなく定量することができる。放射性物質を測定施設まで運搬する必要がなく、現場で迅速に、高精度で除去率を定量することができる。除去率を迅速に定量することができるため、減容化処理プラントの各装置の運転条件を短期間で最適化でき、処理能力を高めることができる。
減容化処理条件を一定に保ちながら、Ａｌ、またはＳｉ濃度の測定をリアルタイムで連続的に行うことで、除去率を常時モニタリングできる。
According to the present invention, the cesium removal rate in the volume reduction treatment in an actual plant can be quantified without actually measuring the radioactive cesium concentration. There is no need to transport radioactive material to the measurement facility, and the removal rate can be quantified quickly and accurately on site. Since the removal rate can be quantified quickly, the operating conditions of each device of the volume reduction treatment plant can be optimized in a short period of time, and the processing capacity can be increased.
The removal rate can be constantly monitored by continuously measuring the Al or Si concentration in real time while keeping the volume reduction processing conditions constant.
本発明は、洗浄水、または洗浄廃液中のアルミニウム、またはケイ素の濃度を用いて、放射性セシウム除去率を迅速に高精度で定量する方法に関する。 The present invention relates to a method for rapidly and accurately quantifying a radioactive cesium removal rate using the concentration of aluminum or silicon in washing water or washing waste liquid.
減容化対象土壌の洗浄工程を図１に示す。
減容化対象土壌１を、水酸化カリウム溶液、水酸化ナトリウム溶液等の洗浄液で洗浄すると、土壌粒子に吸着した放射性セシウムが土壌粒子から分離する際に、土壌を構成するアルミニウム、ケイ素が洗浄水中に溶出する。洗浄後のスラリーは、低線量土壌３と洗浄水４とに分けられ、洗浄水４は、放射性セシウム、アルミニウム、ケイ素を含む。なお、セシウムは、洗浄水４中で浮泥分に吸着しており、アルミニウムとケイ素とは、イオンとして存在している。
本発明者らは、洗浄水４中に含まれるアルミニウム量、ケイ素量のいずれか、または両方と、洗浄水４中に含まれる放射性セシウム量との間に、直線的で高い相関関係があることを見出し、本発明を完成させた。
The cleaning process of the soil to be reduced in volume is shown in FIG.
When the soil to be reduced in volume 1 is washed with a washing solution such as potassium hydroxide solution or sodium hydroxide solution, when the radioactive cesium adsorbed to the soil particles is separated from the soil particles, aluminum and silicon constituting the soil are washed water Elute into The slurry after washing is divided into low dose soil 3 and washing water 4, and the washing water 4 contains radioactive cesium, aluminum and silicon. Cesium is adsorbed to the floating mud in the washing water 4, and aluminum and silicon exist as ions.
The present inventors have found that there is a linear high correlation between the amount of aluminum and / or silicon contained in the washing water 4 and the amount of radioactive cesium contained in the washing water 4 And completed the present invention.
以下、本発明について詳述する。
洗浄水４中に含まれるアルミニウム量、ケイ素量は、減容化対象土壌１から溶出した量（以下、溶出量という。）に等しく、洗浄水４中に含まれる放射性セシウム量は、減容化対象土壌１から除去された量（以下、除去量という。）に等しい。
上記したように、溶出量と除去量との間には相関関係が成立する。洗浄水４中に含まれるアルミニウム、ケイ素、放射性セシウムとは、同一の減容化対象土壌１に由来するため、溶出量と除去量のそれぞれを、減容化対象土壌１の重さで割った値の間にも相関関係が成立する。さらに、減容化対象土壌１に含まれる初期放射性セシウム量は一定であるため、溶出量／減容化対象土壌と除去量／初期放射性セシウム量との間にも直線的な相関関係が成立する。減容化対象土壌１に対する溶出量の比（以下、溶出率という。）と、減容化対象土壌１に含まれる放射性セシウム量に対する除去量の比であるセシウム除去率との間には、直線的で高い相関関係が成立するため、溶出率とセシウム除去率との間に成立する回帰直線を、溶出率によりセシウム除去率を求める検量線として利用することができる。
Hereinafter, the present invention will be described in detail.
The amount of aluminum and the amount of silicon contained in the wash water 4 are equal to the amount eluted from the soil to be reduced in volume 1 (hereinafter referred to as the elution amount), and the amount of radioactive cesium contained in the wash water 4 is reduced in volume It is equal to the amount removed from the target soil 1 (hereinafter referred to as the removed amount).
As described above, a correlation is established between the elution amount and the removal amount. Since aluminum, silicon, and radioactive cesium contained in the wash water 4 are derived from the same volume reduction target soil 1, each of the elution amount and the removal amount was divided by the weight of the volume reduction target soil 1 A correlation also holds between values. Furthermore, since the initial amount of radioactive cesium contained in the volume reduction target soil 1 is constant, a linear correlation also holds between the elution amount / volume reduction target soil and the removal amount / initial amount of radioactive cesium . A line between the ratio of the elution amount to the volume reduction target soil 1 (hereinafter referred to as the elution rate) and the cesium removal ratio, which is the ratio of the removal amount to the radioactive cesium amount contained in the volume reduction target soil 1 Since a high correlation is achieved, a regression line that is established between the elution rate and the cesium removal rate can be used as a calibration curve for determining the cesium removal rate by the elution rate.
本発明は、予め、事前減容化処理試験を行い、減容化対象土壌１から洗浄水４に溶出したアルミニウム、またはケイ素の量と、洗浄水４に含まれる放射性セシウムの量との相関関係から検量線を作成し、
実プラントにおける減容化対象土壌１の減容化処理における、洗浄水、または洗浄廃液のアルミニウム、またはケイ素濃度の測定値から溶出率を算出し、前記溶出率と前記検量線とから、セシウム除去率を定量する定量方法に関する。
In the present invention, the volume reduction test was performed in advance, and the correlation between the amount of aluminum or silicon eluted from the volume reduction target soil 1 into the washing water 4 and the amount of radioactive cesium contained in the washing water 4 Create a calibration curve from
Elution rate is calculated from the measured value of wash water or wash waste aluminum or silicon concentration in the volume reduction treatment of soil 1 for volume reduction in real plant, cesium removal is performed from the elution rate and the calibration curve It relates to a quantitative method of quantifying the rate.
「事前減容化処理試験」
予め、実際に処理を行う減容化対象土壌１と洗浄液２とを使用して事前減容化処理試験を行う。事前減容化処理は、相関関係が求められるように、洗浄液濃度、洗浄時間等の洗浄条件を変えた４条件以上で行う。より定量精度を上げるために、事前減容化試験は実プラントを用いることが好ましいが、実プラントでの減容化処理は大規模で行う必要があり高コストであるため、小規模スケールで行ってもよい。
"Preliminary volume reduction test"
A preliminary volume reduction treatment test is performed in advance using the volume reduction target soil 1 to be treated and the washing solution 2 in advance. The prior volume reduction treatment is performed under four or more conditions in which the washing conditions such as the washing liquid concentration and the washing time are changed so as to obtain a correlation. Although it is preferable to use an actual plant in advance for the volume reduction test in order to raise the accuracy of quantification, it is necessary to carry out the volume reduction processing in the actual plant on a large scale and it is expensive. May be
まず、減容化対象土壌１の含水率と放射性セシウム濃度（Ｂｑ）とを測定し、乾燥重量と乾燥時の放射性セシウム濃度（Ｂｑ／ｋｇ−ｄｒｙ）とを算定する。
次いで、減容化対象土壌１の事前減容化処理を行い、脱水ケーキ７と洗浄廃液８とを回収し、脱水ケーキ７の重量、含水率、放射性セシウム濃度（Ｂｑ）と、洗浄廃液８の容量、Ａｌ濃度、Ｓｉ濃度とを測定する。
減容化対象土壌１の乾燥重量、洗浄廃液８の容量、Ａｌ濃度、Ｓｉ濃度とから、Ａｌ溶出率、Ｓｉ溶出率を算出する。また、減容化対象土壌１の重量、含水率、放射性セシウム濃度、脱水ケーキ７の乾燥重量、乾燥時の放射性セシウム濃度（Ｂｑ／ｋｇ−ｄｒｙ）とから、セシウム除去率を算出する。
算出したＡｌ溶出率、Ｓｉ溶出率と、セシウム除去率とを、同一洗浄条件同士でプロットし、相関関係を求める。減容化対象土壌１の性質により、Ａｌ溶出率、Ｓｉ溶出率のどちらが、セシウム除去率とより直線的な相関関係を示すかは異なる。より高い相関を示す溶出率とセシウム除去率とから、回帰直線を作成して検量線として利用する。以下では、Ａｌ溶出率を元に記載する。
First, the moisture content and the radioactive cesium concentration (Bq) of the soil 1 to be reduced in volume are measured, and the dry weight and the radioactive cesium concentration at the time of drying (Bq / kg-dry) are calculated.
Then, the volume reduction target soil 1 is subjected to prior volume reduction treatment, the dewatered cake 7 and the washing waste liquid 8 are recovered, and the weight, the moisture content, the radioactive cesium concentration (Bq) of the dewatering cake 7 and the washing waste liquid 8 Measure the capacity, the Al concentration, and the Si concentration.
The Al elution rate and the Si elution rate are calculated from the dry weight of the soil 1 to be reduced in volume, the volume of the washing waste liquid 8, the Al concentration, and the Si concentration. In addition, the cesium removal rate is calculated from the weight of the soil 1 to be reduced in volume, the moisture content, the radioactive cesium concentration, the dry weight of the dehydrated cake 7 and the radioactive cesium concentration at drying (Bq / kg-dry).
The calculated Al elution rate, Si elution rate, and cesium removal rate are plotted under the same washing conditions to determine the correlation. Depending on the nature of the volume reduction target soil 1, which of the Al elution rate and the Si elution rate exhibits a more linear correlation with the cesium removal rate differs. From the elution rate and the cesium removal rate that show higher correlation, a regression line is created and used as a calibration curve. Below, it describes based on the Al elution rate.
実プラントでの減容化処理における洗浄廃液８のＡｌ濃度を測定し、この測定値と洗浄廃液８の容量、減容化対象土壌１の乾燥重量から、Ａｌ溶出率を算出する。このＡｌ溶出率を、事前減容化試験で作成した検量線に当てはめることにより、実プラントでの減容化処理におけるセシウム除去率を定量することができる。セシウム除去率を迅速に定量することができ、運転条件のセシウム除去率に対する影響をその場で高精度に知ることができ、プラントの各装置の運転条件を短期間で最適化して、処理能力を高めることができる。
なお、実プラントにおける凝集処理は、高分子凝集剤、ポリ硫酸第二鉄、ＰＡＣ（ポリ塩化アルミニウム）等の凝集剤を用いて行われることが一般的である。洗浄水４を凝集剤を用いて固相５と液相６とに分離すると、アルミニウムが固相５に移行することがある。アルミニウムが固相５に移行する場合は、凝集剤を投入する前の洗浄水４をフィルターろ過して浮泥分を取り除いたろ液のＡｌ濃度を測定すればよい。
The Al concentration of the washing waste fluid 8 in the volume reduction treatment in the actual plant is measured, and the Al elution rate is calculated from the measured value, the volume of the washing waste fluid 8, and the dry weight of the volume reduction target soil 1. By applying this Al dissolution rate to the calibration curve prepared in the preliminary volume reduction test, it is possible to quantify the cesium removal rate in the volume reduction treatment in an actual plant. The cesium removal rate can be quantified quickly, the influence of the operating conditions on the cesium removal rate can be known on the spot with high accuracy, the operating conditions of each device of the plant can be optimized in a short period of time, and the processing capacity It can be enhanced.
In addition, it is general to perform aggregation processing in a real plant using coagulant | flocculants, such as a polymer coagulant | flocculant, polyferric sulfate, PAC (poly aluminum chloride). When washing water 4 is separated into solid phase 5 and liquid phase 6 using a coagulant, aluminum may be transferred to solid phase 5. When aluminum is transferred to the solid phase 5, the wash water 4 before adding the flocculant may be filtered by filtration to measure the Al concentration of the filtrate from which the floating mud is removed.
また、減容化処理プラントにおける処理条件を一定に保ちながら減容化処理を行うと、洗浄廃液８の発生量をほぼ同一に保つことができる。洗浄廃液８の発生量が一定であれば、洗浄水４または洗浄廃液８中のＡｌ、またはＳｉ濃度とＡｌ、またはＳｉ溶出率との間に比例関係が成立する。そのため、Ａｌ、またはＳｉ濃度をリアルタイムで測定することにより、セシウム除去率をモニタリングすることができ、プラントに何らかの不具合が起きてセシウム除去率が低下していないかを監視することができる。 In addition, if the volume reduction treatment is performed while maintaining the treatment conditions in the volume reduction treatment plant constant, it is possible to keep the generation amount of the washing waste liquid 8 almost the same. If the generation amount of the washing waste liquid 8 is constant, a proportional relationship is established between Al or Si concentration in the washing water 4 or the washing waste liquid 8 and Al or Si elution rate. Therefore, by measuring the concentration of Al or Si in real time, the cesium removal rate can be monitored, and it can be monitored whether any failure occurs in the plant and the cesium removal rate is reduced.
「実験１」減容化対象土壌の放射性セシウム濃度測定
減容化の対象となる放射性物質汚染土壌の放射性セシウム濃度（Ｂｑ）をゲルマニウム半導体検出器にて測定した。また土壌の含水率も測定し、土壌乾燥重量当たりの放射性セシウム濃度（Ｂｑ／ｋｇ−ｄｒｙ）を算出した。
"Experiment 1" Measurement of radioactive cesium concentration in soil to be reduced in volume The radioactive cesium concentration (Bq) in the radioactive substance-contaminated soil to be reduced in volume was measured with a germanium semiconductor detector. Moreover, the moisture content of soil was also measured, and the radioactive cesium density | concentration (Bq / kg-dry) per soil dry weight was computed.
「実験２」減容化対象土壌の事前減容化処理
土壌洗浄に使用する洗浄液を用い、初期重量と放射性セシウム濃度、及び含水率が測定済みの減容化対象土壌を洗浄剤濃度、洗浄時間が異なる複数の条件で洗浄、分級を行った。洗浄液に水酸化カリウム（ＫＯＨ）溶液を用い、溶液濃度は０、０．１、０．５、１．０ｍｏｌ／Ｌの４条件とし、洗浄時間は５分あるいは６０分とした。
洗浄後の土壌を７５μｍメッシュの篩にて７５μｍ以上と７５μｍ未満で分級し、７５μｍ未満の画分を遠心分離によって固相（脱水ケーキ相当部分）と液相（洗浄廃液）とに分離した。固相は放射性セシウム濃度をゲルマニウム半導体検出器にて測定し、重量及び含水率を計測して乾燥重量当たりの放射性セシウム濃度を算出した。洗浄廃液は、容量を計測した後に硝酸を加えて加熱分解を行い、液中のＡｌ濃度をＡｇｉｌｅｎｔ Ｔｅｃｈｎｏｌｏｇｉｅｓ社の高周波誘導結合プラズマ発光分光分析装置（ＩＣＰ−ＯＥＳ）にて測定した。
"Experiment 2" Prior volume reduction treatment of target soil for volume reduction Using the washing solution used for soil washing, initial concentration, radioactive cesium concentration, and soil for target volume reduction for which water content has already been measured The washing and classification were conducted under different conditions. A potassium hydroxide (KOH) solution was used as the washing solution, the solution concentration was set to four conditions of 0, 0.1, 0.5, and 1.0 mol / L, and the washing time was 5 minutes or 60 minutes.
The soil after washing was classified with a 75 μm mesh sieve at 75 μm or more and less than 75 μm, and the fraction less than 75 μm was separated into a solid phase (dehydrated cake equivalent portion) and a liquid phase (washing waste liquid) by centrifugation. For the solid phase, the radioactive cesium concentration was measured with a germanium semiconductor detector, and the weight and the moisture content were measured to calculate the radioactive cesium concentration per dry weight. After measuring the volume, the washing waste liquid was heated and decomposed by adding nitric acid, and the concentration of Al in the solution was measured with a high frequency inductively coupled plasma emission spectrometer (ICP-OES) of Agilent Technologies.
「実験３」検量線の作成
実験２で計測した事前減容化処理の土壌初期重量：ｗ０（ｋｇ−ｄｒｙ）、及び各洗浄条件における洗浄廃液の容量：ｖ１〜ｖ４（Ｌ）、洗浄廃液中のＡｌ濃度：ａ１〜ａ４（ｍｇ／Ｌ）とから、式１よりＡｌ溶出率：ａｒ１〜ａｒ４を算出した。
式１：ａｒ１〜ａｒ４＝（ａ１〜ａ４／１０００×ｖ１〜ｖ４）／ｗ０
[Experiment 3] Preparation of calibration curve Initial soil weight of the pre-volume reduction treatment measured in Experiment 2: w0 (kg-dry), and volume of washing waste fluid under each washing condition: v1 to v4 (L), in washing waste fluid The Al elution ratio: ar1 to ar4 was calculated from the formula 1 from the Al concentration of: a1 to a4 (mg / L).
Formula 1: ar1 to ar4 = (a1 to a4 / 1000 × v1 to v4) / w0
実験１で計測した減容化体対象土壌の放射性セシウム濃度：ｃ０（Ｂｑ／ｋｇ−ｄｒｙ）と、固相重量：ｗ１〜ｗ４（ｋｇ−ｄｒｙ）、固相の乾燥重量当たりの放射性セシウム濃度：ｃ１〜ｃ４（Ｂｑ／ｋｇ−ｄｒｙ）とから、式２よりセシウム除去率：ｃｒ１〜ｃｒ４を算出した。
式２：ｃｒ１〜ｃｒ４＝（ｃ１〜ｃ４×ｗ１〜ｗ４）／（ｃ０×ｗ０）
Radioactive cesium concentration of the volume-reduced target soil measured in Experiment 1: c0 (Bq / kg-dry), solid phase weight: w1 to w4 (kg-dry), radioactive cesium concentration per dry weight of solid phase: From c1 to c4 (Bq / kg-dry), the cesium removal rate: cr1 to cr4 was calculated from formula 2.
Formula 2: cr1 to cr4 = (c1 to c4 × w1 to w4) / (c0 × w0)
算出したａｒ１〜ａｒ４（Ａｌ溶出率）とｃｒ１〜ｃｒ４（セシウム除去率）とを対応する同一洗浄条件同士でプロットしたグラフを図２に示す。Ａｌ溶出率とセシウム除去率とは、Ｒ２＝０．９９４２の高い相関関係にあることが確かめられた。
Ａｌ溶出率とセシウム除去率とは高い相関関係にあり、この相関関係の回帰直線から信頼性の高い検量線が作成できる。この検量線を用いることにより、実プラントにおける洗浄水、または洗浄排水のＡｌ濃度を測定することで、脱水ケーキの放射性セシウム濃度を測定することなく、放射性セシウム除去率を精度よく定量することができる。
A graph in which the calculated ar1 to ar4 (Al elution rate) and cr1 to cr4 (cesium removal rate) are plotted under the same same washing conditions is shown in FIG. It was confirmed that the Al elution rate and the cesium removal rate were highly correlated with R 2 = 0.9942.
There is a high correlation between the Al elution rate and the cesium removal rate, and a highly reliable calibration curve can be created from the regression line of this correlation. By using this calibration curve, it is possible to accurately quantify the radioactive cesium removal rate without measuring the radioactive cesium concentration of the dewatered cake by measuring the Al concentration of the washing water or washing drainage in the actual plant .
「実験４」
減容化対象土壌として湿重量１０ｇの放射性物質非汚染土壌（真砂土）と、洗浄液としてそれぞれ０、０．５、１．０、１．５、２．０ｍｏｌ／Ｌ濃度のＫＯＨ溶液４０ｍｌとを、１００ｍｌビーカーに入れ、マグネチックスターラーで１０分間室温にて撹拌を行った後、７５μｍメッシュの篩にて、粒径７５μｍ以上と７５μｍ未満とに分級した。
７５μｍ未満の固形分を含む洗浄水を、孔径０．６μｍのフィルターでろ過し、ろ液中のＡｌ及びＳｉの濃度を株式会社日立ハイテクサイエンス製の偏光ゼーマン原子吸光光度計（装置名：ＺＡ２０１０）によって測定した。ろ液中のＡｌ、Ｓｉ濃度から、土壌の乾燥重量当たりのＡｌ、Ｓｉそれぞれの溶出量を求めた。
"Experiment 4"
10 g of radioactive substance non-contaminated soil (true sand soil) with a wet weight of 10 g as soil to be reduced in volume, and 40 ml of a 0, 0.5, 1.0, 1.5, 2.0 mol / L KOH solution as a cleaning liquid The mixture was placed in a 100 ml beaker and stirred at room temperature for 10 minutes with a magnetic stirrer, and then classified with a 75 μm mesh sieve into particle sizes of 75 μm or more and less than 75 μm.
The washing water containing solids less than 75 μm is filtered with a filter with a pore diameter of 0.6 μm, and the concentration of Al and Si in the filtrate is measured by a polarization Zeeman atomic absorption photometer made by Hitachi High-Tech Science Co., Ltd. (apparatus name: ZA2010) Measured by From the concentrations of Al and Si in the filtrate, the elution amount of each of Al and Si per dry weight of soil was determined.
洗浄液のＫＯＨ溶液濃度と、ろ液中のＡｌ、Ｓｉ濃度より求めたＡｌ、Ｓｉ溶出量との関係を図３に示す。洗浄液のＫＯＨ濃度が高くなるに従い、Ａｌ、Ｓｉ溶出量はともに増加傾向にあった。ＫＯＨ濃度と、Ａｌ、Ｓｉ溶出量の関係について一次の近似線を引くと、ＡｌがＲ＝０．６８９４、ＳｉがＲ＝０．９６８８とＳｉの方が洗浄液のＫＯＨ濃度と高い相関係数で比例関係にあった。
また、上記「実験３」における洗浄液のＫＯＨ濃度とセシウム除去率とをプロットしたグラフを図４に示す。洗浄液のＫＯＨ濃度とセシウム除去率とは、Ｒ２＝０．９３９５の高い相関関係を有していた。
The relationship between the KOH solution concentration of the cleaning solution and the Al and Si elution amounts determined from the Al and Si concentrations in the filtrate is shown in FIG. As the KOH concentration in the washing solution increased, the elution amounts of Al and Si both tended to increase. When a first-order approximation line is drawn on the relationship between KOH concentration and Al and Si elution amount, Al is R = 0.6894, Si is R = 0. 9688 and Si has a high correlation coefficient with KOH concentration of the cleaning liquid There was a proportional relationship.
Moreover, the graph which plotted the KOH density | concentration and the cesium removal rate of the washing | cleaning liquid in said "experiment 3" is shown in FIG. The KOH concentration of the cleaning solution and the cesium removal rate had a high correlation of R 2 = 0.9395.
図３より、ＫＯＨ濃度とＳｉ溶出量とは直線的で高い相関関係を有し、図４より、ＫＯＨ濃度とセシウム除去率とは直線的で高い相関関係を有する。したがって、土壌の性質によっては、Ｓｉ溶出量とセシウム除去率との間にも直線的で高い相関関係が成立することが確かめられた。 From FIG. 3, the KOH concentration and the Si elution amount have a linear and high correlation, and from FIG. 4, the KOH concentration and the cesium removal rate have a linear and high correlation. Therefore, depending on the nature of the soil, it was confirmed that a linear and high correlation was established between the Si elution amount and the cesium removal rate.
１ 減容化対象土壌
２ 洗浄液
３ 低線量土壌
４ 洗浄水
５ 固相
６ 液相
７ 脱水ケーキ
１０ 洗浄装置
２０ 洗浄篩
３０ オーバー水受槽
４０ 濁水処理装置
５０ フィルタープレス
1 Volume reduction target soil 2 Washing solution 3 Low dose soil 4 Wash water 5 Solid phase 6 Liquid phase 7 Dehydrated cake
10 Washing device 20 Washing sieve 30 Over water receiving tank 40 Turbid water treatment device 50 Filter press
Claims (2)
実プラントでの前記減容化対象土壌の減容化処理において、洗浄水、または洗浄廃液のアルミニウム、またはケイ素濃度の測定値と前記検量線とを用いて、セシウム除去率を定量することを特徴とするセシウム除去率定量方法。 Create a calibration curve from the correlation between the amount of aluminum or silicon eluted from the volume reduction target soil into the wash water and the amount of radioactive cesium contained in the wash water,
In the volume reduction treatment of the above-mentioned volume reduction target soil in an actual plant, the cesium removal rate is quantified using the measurement value of the wash water or wash waste aluminum or silicon concentration and the calibration curve. Determination method of cesium removal rate.
実プラントにおける前記減容化対象土壌の減容化処理における、洗浄水、または洗浄廃液のアルミニウム、またはケイ素濃度をリアルタイムで測定した測定値と前記検量線とを用いて、セシウム除去率をモニタリングすることを特徴とするセシウム除去率モニタリング方法。 Conduct a preliminary volume reduction treatment test beforehand, and create a calibration curve from the correlation between the amount of aluminum or silicon eluted from the volume reduction target soil into the wash water and the amount of radioactive cesium contained in the wash water,
The cesium removal rate is monitored using the calibration curve and the measurement value obtained by measuring the concentration of wash water or wash waste aluminum or silicon concentration in the volume reduction treatment of the volume reduction target soil in a real plant using the calibration curve Cesium removal rate monitoring method characterized by
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