A device and method for detecting tritium in groundwater in a monitoring well of a nuclear power plant

Abstract

The application discloses a kind of equipment for detecting tritium in groundwater of monitoring well of nuclear power plant, including electric deionization device, collection water tank, switching valve, measuring chamber, dosing mechanism and first waste liquid tank, the electric deionization device is communicated between the monitoring well and collection water tank, the switching valve is arranged between the collection water tank and measuring chamber, the dosing mechanism is communicated with the switching valve, for dosing in the measuring chamber, the electric deionization device and switching valve are all communicated with the first waste liquid tank, direct connecting pipeline is also provided between the electric deionization device and switching valve directly connected.The equipment for detecting tritium in groundwater of the present application can quickly purify water body by setting electric deionization device, and the collected purified water can be directly sent into measuring chamber for detection;Chemical separation and sample measurement are integrated in one device, which can process and detect more samples in a shorter time, greatly shortening the processing time and process.

Description

Technical Field

[0001] This invention relates to the field of environmental monitoring technology, specifically to a detection device for tritium in groundwater from a nuclear power plant monitoring well based on electrodeionization technology, and a detection method based on the device. Background Technology

[0002] Tritium is a radioactive isotope of hydrogen. Tritium decays by emitting low-energy beta particles, with a maximum decay energy of 18.6 keV and a half-life of 12.3 years. The tritium produced in nuclear power plants primarily originates from fission reactions within the reactor and from the primary coolant. 2 H, 6 Li, 10 Neutron activation reaction of B.

[0003] In a megawatt-class pressurized water reactor nuclear power plant, the activation of the coolant produces approximately 37 TBq of tritium. Since it cannot be treated through filtration, desalination, or evaporation, most of it is released into the environment. Tritium has very high mobility and circulation in the biosphere, and it can enter the human body through various pathways, such as skin absorption, inhalation of contaminated water vapor, and ingestion of contaminated food or water. It is rapidly absorbed and utilized by the human body, resulting in relatively significant biological effects.

[0004] The "Technical Specification for Radiation Environment Monitoring" (HJ 61-2021) requires monitoring tritium in groundwater from monitoring wells within nuclear power plants and in potentially affected groundwater during plant operation. Current technology generally employs laboratory analysis methods based on the "Analytical Methods for Tritium in Water" (HJ1126-2020). This involves collecting groundwater, transferring it to a distillation apparatus, adding potassium permanganate, distilling, adding scintillation fluid to the collected distillate, and then placing it in a liquid scintillation counter for measurement. However, this method cannot achieve real-time monitoring, is cumbersome, and time-consuming. Summary of the Invention

[0005] In view of this, in order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a tritium detection device for groundwater in nuclear power plant monitoring wells based on electrodeionization technology, which can quickly and efficiently purify and detect tritium in groundwater.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A detection device for tritium in groundwater from a monitoring well in a nuclear power plant includes an electrodeionization device, a collection tank, a switching valve, a measuring chamber, a dosing mechanism, and a first waste liquid tank. The electrodeionization device is connected between the monitoring well and the collection tank. The switching valve is located between the collection tank and the measuring chamber. The dosing mechanism is connected to the switching valve and is used to add chemicals to the measuring chamber. Both the electrodeionization device and the switching valve are connected to the first waste liquid tank. A direct connection pipe is also provided between the electrodeionization device and the switching valve.

[0008] According to some preferred embodiments of the present invention, one end of the direct connection pipe is connected to a switching valve, and the other end of the direct connection pipe is connected to the top of the electro-deionization device, wherein the electro-deionization device, the collection tank, the switching valve, and the direct connection pipe constitute a purification mechanism.

[0009] According to some preferred embodiments of the present invention, a conductivity meter is installed inside the collection tank to detect the conductivity of the liquid in the collection tank; when the conductivity of the liquid in the collection tank is higher than 10 μS / cm, the water in the collection tank is circulated to the purification mechanism through the switching valve for purification until the conductivity is lower than 10 μS / cm. A level gauge is also installed on the collection tank, and a flow meter is installed between the collection tank and the switching valve.

[0010] According to some preferred embodiments of the present invention, the electro-deionization device is provided with a power supply for providing current to the electro-deionization device, the voltage range of the power supply being 2V to 20V. Preferably, the power supply is a DC power supply.

[0011] According to some preferred embodiments of the present invention, the electro-deionization device has electrodes on both sides, with anion exchange membranes and cation exchange membranes alternately arranged between the two electrodes, and adjacent membranes are separated from the flow channel by a silicon isolation mesh. Specifically, in some embodiments, the electro-deionization device has two titanium electrodes on both sides, with five anion exchange membranes and six cation exchange membranes alternately arranged between the anode and cathode; the effective area of ​​each membrane is preferably 189 cm². 2 The adjacent membranes are separated from the flow channels by a silicon separator (thickness = 0.8 mm).

[0012] According to some preferred embodiments of the invention, a water delivery mechanism is included, the water delivery mechanism comprising a water delivery pipe connecting a monitoring well and an electro-deionization device, and a filter disposed on the water delivery pipe.

[0013] According to some preferred embodiments of the present invention, the filter includes a first filter disposed at the middle end of the water supply pipeline located in the monitoring well and a second filter disposed on the water supply pipeline. In some embodiments, the cross-sectional area of ​​the inlet of the second filter is larger than the cross-sectional area of ​​the outlet, the second filter is connected to the groundwater in the monitoring well and the purification mechanism respectively, and the effective filtration pore size of the second filter is 0.5-2 μm. The first filter is used for coarse filtration of the water, and the second filter is used for fine filtration of the water. Both the first filter and the second filter are ceramic filters, and the filter elements therein are made of ceramic material.

[0014] According to some preferred embodiments of the present invention, the dosing mechanism includes a booster pump and a dosing bottle, the booster pump being used to add the agent in the dosing bottle to the measuring chamber. In some embodiments, a flow meter is provided between the dosing bottle and the switching valve.

[0015] According to some preferred embodiments of the present invention, the measuring chamber is provided with a measuring cell and a photomultiplier tube (PMT), the photomultiplier tube being used to convert photons emitted by tritium in the measuring cell into electrical signals and to receive tritium counting signals, thereby realizing the measurement of tritium in groundwater.

[0016] In some embodiments, a second wastewater tank is also included. The first wastewater tank is used to collect wastewater without scintillation fluid discharged from the electro-deionization device and the measuring cell, and the second wastewater tank is used to collect wastewater containing scintillation fluid discharged from the measuring cell. Before measurement, the water sample is first rinsed in the measuring cell with water from the collection tank through a switching valve and then discharged into the first wastewater tank.

[0017] In some embodiments of the present invention, the switching valve is a five-way switching valve, which simultaneously connects to a booster pump, a collection tank, a dosing bottle, an electro-deionization device, a measuring cell, and a first waste liquid tank. The booster pump is connected to the five-way valve to realize functions such as adding samples to the measuring cell by the dosing mechanism, transporting groundwater to the first filter, circulating and purifying groundwater, cleaning the measuring cell, and collecting waste liquid.

[0018] The present invention also provides a method for detecting tritium in groundwater in a monitoring well using the detection device described above, comprising the following steps:

[0019] Groundwater from the monitoring well is purified by an electro-deionization device and then sent to a collection tank. The conductivity of the liquid in the collection tank is measured. When the conductivity of the liquid in the collection tank is lower than 10 μS / cm, the water sample from the collection tank and the scintillation liquid from the dosing bottle are proportionally transferred into the measuring cell via a switching valve. A photomultiplier tube is used to convert the photons emitted by tritium in the measuring cell into electrical signals. The tritium activity concentration is then measured in real time using the activity concentration calculation formula.

[0020] Formula for calculating the activity concentration of tritium in water:

[0021]

[0022] In the formula:

[0023] A c Tritium activity concentration in water, Bq / L;

[0024] n c Sample count rate, cpm;

[0025] n b Background sample count rate, cpm;

[0026] V: Sample measurement volume, L;

[0027] E: Detection efficiency of the photomultiplier tube for tritium, %.

[0028] V is the volume of groundwater fed into the measuring pool, n c It is the count rate, n, of the groundwater fed into the measuring pool, measured by a photomultiplier tube. b E is the count rate of pure water fed into the measuring cell, measured by a photomultiplier tube. E is the tritium water standard solution fed into the measuring cell, measured by a photomultiplier tube and then calculated.

[0029]

[0030] In the formula:

[0031] E: Detection efficiency of photomultiplier tube for tritium, %;

[0032] n s Count rate of tritium aqueous standard solution, cpm;

[0033] n b Background sample count rate, cpm;

[0034] A s : Activity of tritium water standard solution, Bq.

[0035] Compared with the prior art, the advantages of the present invention are as follows: The tritium detection device in groundwater of this application can quickly purify water by setting an electro-deionization device, and the collected purified water can be directly sent into the measurement chamber for detection; chemical separation and sample measurement are integrated into one device to reduce the workload, time and reagents required for analysis, and can process and detect more samples in a shorter time, greatly shortening the processing time and process, and is suitable for real-time online monitoring of tritium in groundwater in monitoring wells of nuclear power plants. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of the structure of a tritium detection device in groundwater of a nuclear power plant monitoring well, according to a preferred embodiment of the present invention.

[0038] In the attached diagram, the components are: monitoring well-1, first filter-2, second filter-3, three-way valve-4, electro-deionization device-5, DC power supply-6, collection tank-7, level gauge-8, conductivity meter-9, first waste liquid tank-10, flow meter-11, switching valve-12, booster pump-13, flow meter-14, dosing bottle-15, measuring cell-16, photomultiplier tube-17, second waste liquid tank-18, and three-way valve-19. Detailed Implementation

[0039] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0040] Example 1: Detection equipment for tritium in groundwater from monitoring wells in nuclear power plants

[0041] like Figure 1 As shown, the tritium detection equipment in the groundwater of the nuclear power plant monitoring well 1 in this embodiment includes a water delivery mechanism, an electrodeionization device 5, a water collection tank 7, a switching valve 12, a measuring chamber, a dosing mechanism, a first waste liquid tank 10, and a second waste liquid tank 18. The electrodeionization device 5 uses the selective permeation of an exchange membrane to purify the water, ensuring that the subsequent water quality meets the requirements for tritium measurement. It integrates chemical separation and sample measurement into one device to reduce the workload, time, and reagents required for analysis.

[0042] In this embodiment, the electro-deionization device 5 has two titanium electrodes on both sides, and five anion exchange membranes and six cation exchange membranes are alternately arranged between the anode and cathode; the effective area of ​​each membrane is preferably 189 cm². 2 The adjacent membranes are separated from the flow channel by a silicon separator (thickness = 0.8 mm). The electro-deionization device 5 is equipped with a DC power supply 6 to supply a DC electric field to it, and the voltage range of the power supply 6 is 2V to 20V.

[0043] The electro-deionization device 5 is connected between the monitoring well 1 and the collection tank 7. A switching valve 12 is located between the collection tank 7 and the measuring chamber. A dosing mechanism is connected to the switching valve 12 for adding chemicals to the measuring chamber. Both the electro-deionization device 5 and the switching valve 12 are connected to the first waste liquid tank 10. A direct connecting pipe is also provided between the electro-deionization device 5 and the switching valve 12. One end of the direct connecting pipe is connected to the switching valve 12, and the other end is connected to the top of the electro-deionization device 5. A three-way valve 4 is installed at the top of the electro-deionization device 5 to connect the water supply pipe, the direct connecting pipe, and the electro-deionization device 5.

[0044] The electro-deionization device 5, the water collection tank 7, the switching valve 12, and the direct-connection pipeline constitute the purification mechanism to circulate the water sample in the water collection tank 7 to achieve a conductivity of less than 10 μS / cm. A flow meter 11 is installed between the water collection tank 7 and the switching valve 12.

[0045] The water delivery system includes a water delivery pipe connecting the monitoring well 1 and the electro-deionization device 5, and filters installed on the water delivery pipe. The filters include a first filter 2 installed at the middle end of the water delivery pipe in the monitoring well 1, and a second filter 3 installed on the water delivery pipe. The first filter 2 is used for coarse filtration of the water, and the second filter 3 is used for fine filtration of the water. Both the first filter 2 and the second filter 3 are ceramic filters, and the filter elements are made of ceramic material. The effective pore size of the second filter 3 is 0.5-2 μm.

[0046] The second filter 3 connects the groundwater in monitoring well 1 to the purification mechanism, and the cross-sectional area of ​​the inlet of the second filter 3 is larger than the cross-sectional area of ​​the outlet. This setting can increase the fluid flow rate in the pipeline and increase the treatment efficiency of the filter.

[0047] The measurement chamber is equipped with a measurement cell 16 and a photomultiplier tube 17 (PMT). The PMT converts photons emitted by tritium in the measurement cell 16 into electrical signals and receives the tritium counting signals, thereby realizing the measurement of tritium in groundwater. In this embodiment, the dosing bottle 15 contains scintillation fluid; the measurement cell 16 has a capacity of 10 mL. The water sample from the collection tank 7 and the scintillation fluid from the dosing bottle 15 are fed into the measurement cell 16 at a 1:1 ratio through the five-way switching valve 12, and can be adjusted according to the detection limit requirements.

[0048] The dosing mechanism includes a booster pump 13, a dosing bottle 15, and a flow meter 14 located between the dosing bottle 15 and the switching valve 12. The booster pump 13 is used to add the reagent in the dosing bottle 15 into the measuring cell 16. The booster pump 13 can control the flow rate and volume through the flow meters 14 and 11 to achieve constant-rate and quantitative sample addition.

[0049] The water collection tank 7 is equipped with a level gauge 8 and a conductivity meter 9. The conductivity meter 9 is used to detect the conductivity of the liquid in the water collection tank 7. When the conductivity in the water collection tank 7 is higher than 10 μS / cm, the circulation purification mechanism is activated. The water in the water collection tank 7 is circulated to the electro-deionization device 5 for further purification to achieve a conductivity below 10 μS / cm.

[0050] The first wastewater tank 10 is used to collect wastewater without scintillation fluid discharged from the electro-deionization device 5 and the measuring cell 16. The second wastewater tank 18 is used to collect wastewater containing scintillation fluid discharged from the measuring cell 16. Before measurement, the water sample is first rinsed in the measuring cell 16 with water from the collection tank 7 through the switching valve 12, and then discharged into the first wastewater tank 10. The second wastewater tank 18 is connected to the measuring cell 16 and the switching valve 12 through a three-way valve 19.

[0051] In this embodiment, the switching valve 12 is a five-way switching valve 12, which simultaneously connects to the booster pump 13, the collection tank 7, the dosing bottle 15, the electro-deionization device 5, the measuring cell 16, and the first waste liquid tank 10. The booster pump 13, connected to the five-way valve, enables the dosing mechanism to add samples to the measuring cell 16, transport groundwater to the first filter 2, circulate and purify the water sample, clean the measuring cell 16, and collect waste liquid. The use of the five-way switching valve 12 simplifies the control unit and reduces the size of the detection equipment.

[0052] The detection device in this embodiment filters the water in monitoring well 1 through a switching valve 12 into a first filter 2 and a second filter 3, and then purifies it using an electro-deionization device 5. Multiple functional components are simultaneously connected to the switching valve 12 to achieve different functions, saving collection time. The electro-deionization device 5 enables rapid purification of tritium in the water, and the collected purified water can be directly sent to the measurement chamber for testing. Based on this detection device, an accurate, stable, and efficient method for collecting and measuring tritium in groundwater from monitoring wells can be established. By integrating chemical separation and sample measurement into a single device, the workload, time, and reagents required for analysis are reduced. This allows for the processing and testing of a large number of samples in a shorter time, significantly shortening the processing time and workflow. It is suitable for real-time online monitoring of tritium in groundwater from monitoring well 1 in nuclear power plants.

[0053] Example 2: Detection method of tritium in groundwater of monitoring well 1 in nuclear power plant

[0054] This embodiment provides a method for detecting tritium in groundwater in a nuclear power plant monitoring well 1 based on the detection equipment in Embodiment 1, specifically including the following steps:

[0055] Step 1: Clean the measuring tank 16

[0056] Before the formal measurement, the measuring pool 16 is cleaned with water from the collection tank 7 through the switching valve 12 and then discharged into the first waste liquid tank 10.

[0057] Step 2: Background and Detection Efficiency Measurement

[0058] Before purifying the groundwater sample from the monitoring well, a volume V of pure water is taken through switching valve 12, and a volume V of scintillation liquid is simultaneously taken from dosing bottle 15 and transported into measuring cell 16. A photomultiplier tube 17 is used to convert the photons emitted by tritium in measuring cell 16 into an electrical signal to obtain the sample count rate n. b .

[0059] The volume V of the tritium water standard solution is taken through switching valve 12, and simultaneously the volume V of scintillation liquid is taken from dosing bottle 15 and transported into measuring cell 16. The photons emitted by tritium in measuring cell 16 are converted into electrical signals by photomultiplier tube 17 to obtain the count rate n of the tritium water standard solution. s Then, the detection efficiency E of the photomultiplier tube for tritium was obtained through calculation.

[0060]

[0061] In the formula:

[0062] E: Detection efficiency of photomultiplier tube for tritium, %;

[0063] n s Count rate of tritium aqueous standard solution, cpm;

[0064] n b Background sample count rate, cpm;

[0065] A s : Activity of tritium water standard solution, Bq.

[0066] Step 3, Purification

[0067] Groundwater from monitoring well 1 is filtered by booster pump 13 through filters 2 and 3. After filtration, the water sample is purified by electro-deionization device 5 and then transferred to collection tank 7. Conductivity meter 9 measures the conductivity of the liquid in collection tank 7.

[0068] When the conductivity of the water sample in the collection tank 7 is higher than 10 μS / cm, the water in the collection tank 7 is circulated to the purification mechanism through the switching valve 12 for further purification to achieve a conductivity lower than 10 μS / cm.

[0069] Step 4: Adding medicine and measuring

[0070] When the conductivity in the water collection tank 7 is below 10 μS / cm, a water sample volume V is taken from the water collection tank 7 via the five-way switching valve 12, and simultaneously a scintillation liquid volume V is taken from the dosing bottle 15 and transported into the measuring cell 16. A photomultiplier tube 17 is used to convert the photons emitted by tritium in the measuring cell 16 into an electrical signal to obtain the sample count rate n. c The activity concentration of tritium can be measured in real time using the activity concentration calculation formula.

[0071] The formula for calculating the activity concentration of tritium in water is as follows:

[0072]

[0073] In the formula:

[0074] A c Tritium activity concentration in water, Bq / L;

[0075] n c Sample count rate, cpm;

[0076] n b Background count rate, cpm;

[0077] V: Sample measurement volume, L;

[0078] E: Detection efficiency of the photomultiplier tube for tritium, %.

[0079] The relationship between the water sample volume in measuring cell 16 and the detection limit can be calculated using the following formula:

[0080]

[0081] In the formula:

[0082] MDC—Detection Limit, Bq / L;

[0083] n b —Background count rate, cpm;

[0084] t b —Background measurement time, in minutes;

[0085] V—Volume of water sample in measuring cell 16, in L;

[0086] E—Detection efficiency of a photomultiplier tube for tritium, %.

[0087] The tritium detection device in the groundwater of monitoring well 1 in this embodiment uses an electro-deionization device 5 to purify the water sample, achieving a removal rate of over 99% for interfering radionuclides. The purification efficiency is high and stable. It integrates chemical separation and sample measurement into one device to reduce the workload, time, and reagents required for analysis. It can process a large number of samples according to the detection limit requirements, thereby obtaining a very low detection limit (40 Bq / L). It can also process and detect a large number of samples in a short time, greatly shortening the processing time and process. The processing speed is fast and it is suitable for real-time online monitoring of tritium in the groundwater of monitoring well 1 in nuclear power plants.

[0088] The tritium detection equipment in groundwater monitoring wells disclosed in this application is suitable for real-time online monitoring of tritium in groundwater from monitoring wells in nuclear power plants. The method includes ceramic filter filtration, purification and water sample collection using an electro-deionization device, mixing of the water sample with scintillation fluid in a measuring cell, and photomultiplier tube measurement. Electro-deionization purification: Under the action of a DC electric field, dielectric ions in the water undergo directional movement through a partition. The selective permeation of the exchange membrane purifies the water quality, ensuring that the subsequent water quality meets the requirements for tritium measurement. A booster pump connected to a five-way switching valve controls the flow rate and volume, achieving constant-rate, quantitative sample addition. The five-way switching valve controls sampling and injection. Groundwater from the monitoring well is transferred to a ceramic filter via the five-way switching valve for filtration. After filtration, the water sample is purified using an electro-deionization device, achieving a removal rate of over 99% for interfering radionuclides. Photomultiplier tube measurement: A photomultiplier tube is used for real-time measurement of tritium activity concentration.

[0089] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A detection device for tritium in groundwater of a monitoring well in a nuclear power plant, characterized in that: The device includes an electro-deionization unit, a collection tank, a switching valve, a measuring chamber, a dosing mechanism, and a first waste liquid tank. The electro-deionization unit is connected between the monitoring well and the collection tank. The switching valve is located between the collection tank and the measuring chamber. The dosing mechanism is connected to the switching valve and is used to add chemicals to the measuring chamber. Both the electro-deionization unit and the switching valve are connected to the first waste liquid tank. A direct connection pipe is also provided between the electro-deionization unit and the switching valve. One end of the direct connection pipe is connected to the switching valve, and the other end of the direct connection pipe is connected to the top of the electro-deionization device. The electro-deionization device, the collection tank, the switching valve, and the direct connection pipe constitute a purification mechanism. The water collection tank is equipped with a conductivity meter, which is used to detect the conductivity of the liquid in the water collection tank. When the conductivity of the liquid in the water collection tank is higher than 10 μS / cm, the water in the water collection tank is circulated to the purification mechanism through the switching valve for purification until the conductivity is lower than 10 μS / cm. The water collection tank is also equipped with a level gauge, and a flow meter is installed between the water collection tank and the switching valve.

2. The detection device according to claim 1, characterized in that: The electro-deionization device is equipped with a power supply for providing current to the electro-deionization device, and the voltage range of the power supply is 2V~20V.

3. The detection device according to claim 1 or 2, characterized in that: The electrode deionization device has electrodes on both sides, and anion exchange membranes and cation exchange membranes are alternately arranged between the two electrodes. Adjacent exchange membranes are separated from the flow channel by a silicon isolation mesh.

4. The detection device according to claim 1, characterized in that: It includes a water delivery mechanism, which includes a water delivery pipe connecting the monitoring well and the electro-deionization device, and a filter installed on the water delivery pipe.

5. The detection device according to claim 4, characterized in that: The filter includes a first filter installed at the end of the water delivery pipeline located in the monitoring well, and a second filter installed on the water delivery pipeline.

6. The detection device according to claim 1, characterized in that: The dosing mechanism includes a booster pump and a dosing bottle, wherein the booster pump is used to add the drug from the dosing bottle into the measuring chamber.

7. The detection device according to claim 1 or 6, characterized in that: The measuring chamber is equipped with a measuring cell and a photomultiplier tube, which is used to convert photons emitted by tritium in the measuring cell into electrical signals.

8. A method for detecting tritium in groundwater in a monitoring well using the detection equipment described in any one of claims 1-7, characterized in that: Includes the following steps: The groundwater from the monitoring well is purified by an electro-deionization device and then sent to a collection tank. The conductivity of the liquid in the collection tank is measured. When the conductivity of the liquid in the collection tank is lower than 10 μS / cm, the water sample from the collection tank and the scintillation liquid from the dosing bottle are transferred into the measuring cell via a switching valve. A photomultiplier tube is used to convert the photons emitted by tritium in the measuring cell into an electrical signal, thereby realizing the real-time measurement of tritium activity concentration.

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