Estimation method of inhalation dose conversion factor considering particle size distribution after fire accidents

Abstract

The present application relates to a method for estimating the inhalation dose conversion factor considering the particle size distribution after a fire accident, wherein according to the activity intensity of emergency personnel during the rescue of the fire accident, the breathing rate of the person is determined, according to the particle size distribution of the uranium compound in different time periods, the dose conversion factor of different particle size distribution given by domestic and foreign is referred to, and the fine dose conversion factor of the inhalation dose of the worker participating in the emergency is estimated in combination with the temperature and time point of the fire. By using the method disclosed in the present application, the influence of the stage of fire development and the particle size distribution under different combustion temperatures on the inhalation dose conversion factor is considered, thereby the inhalation dose of the worker after the accident is finely evaluated, compared with the previous accident estimation method, the post-accident dose estimation of the worker participating in the fire emergency is more accurate and closer to the actual situation, and the method is suitable for the fine evaluation of the dose of the worker in the emergency accident treatment in the early stage of the accident.

Description

Technical Field

[0001] This invention belongs to the field of radioactive accident consequence assessment, specifically relating to a method for estimating the inhalation dose conversion factor after a fire accident, taking into account particle size distribution. Background Technology

[0002] When assessing the dose of individuals affected by an accident via inhalation, the inhalation dose conversion factor used is based on the dose conversion factors in IAEA No. RS-G-1.2 "Occupational Exposure Assessment Due to Ingestion of Radionuclides" and GB18871-2002 "Basic Standards for Ionizing Radiation Protection and Radiation Source Safety". The standards provide an inhalation dose factor with an AMAD of 5 μm (currently considered the most appropriate default particle size for radionuclides in the workplace [INTERNATIONAL COMMISSION ONRADIOLOGICAL PROTECTION, Human Respiratory Tract Model for Radiological Protection, Publication No. 66, Elsevier Science, Oxford and New York (1994)]); and also provide a dose conversion factor with an AMAD of 1 μm. An AMAD of 1 μm is the default value used in ICRP Publication No. 30 "Limits for Ingestion of Radionuclides by Workers" and is also used as the default value for the public dose conversion factor. High-efficiency particulate air (HEPA) filters in typical nuclear facilities primarily capture particulate dust and various suspended particles larger than 0.3 μm.

[0003] In the event of a fire involving uranium-containing materials in the workplace, the high temperature or pressure can cause radioactive aerosols to penetrate filters, rendering purification devices ineffective. This results in the release of radionuclides of different chemical forms and particle sizes into the near-field environment of the plant. For long-distance transport of uranium-containing radionuclides, particles smaller than 20 μm (AED) are required. Generally, aerosols larger than 10 μm will quickly settle to the ground due to gravity [Cheng Jinxing et al., Prediction and Consequence Assessment of Radioactive Aerosol Diffusion in Nuclear Weapon Accidents. Nuclear Electronics & Detection Technology, 2010, 30(1): 48-51]. However, the particle size of ordinary uranium oxides that can be inhaled by humans is 10 μm (AED).

[0004] In the 2018 IAEA GSG-7 "Occupational Radiation Protection", it was proposed that for AMAD beyond 1 μm and 5 μm, the fraction of inhaled radioactive particles deposited in each region of the respiratory tract should be determined according to the respiratory tract model of ICRP, and appropriate dose coefficients should be calculated.

[0005] It is evident that in the initial stages of a fire, the particle size variation in the release of uranium-containing compounds is significant as the combustion temperature increases. Currently, the dose conversion factor used for estimating worker dose in fire incidents only considers the recommended dose conversion factor corresponding to an AMAD of 5 μm as specified in the standard, without taking into account actual particle size variations. This is unreasonable for the refined assessment of personnel handling emergency incidents. Furthermore, the current dose conversion factor estimation process does not consider particle size distribution, but directly estimates based on the largest inhalation dose conversion factor among all particle sizes, conservatively estimating the actual exposure dose to workers, thus leading to overprotection and increased protection costs. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for estimating the inhalation dose conversion factor after a fire accident, taking into account the particle size distribution. This method considers the particle size distribution of oxides under different combustion and oxidation conditions, and provides a refined estimate of the dose conversion factor. It is suitable for the refined assessment of the dose received by personnel handling emergency accidents in the early stages of an accident, providing guidance for scientific and effective radiation protection and reducing protection costs.

[0007] To achieve the above objectives, the technical solution adopted by this invention is: a method for estimating the inhalation dose conversion factor considering particle size distribution after a fire accident, the method comprising the following steps:

[0008] S1. Determine the respiratory rate B of a person based on the activity intensity of emergency personnel during fire rescue;

[0009] S2. Based on the development and changes of the fire, record the fire's spread and the temperature changes at its center. By recording the temperature, obtain the particle size distribution f at different temperatures. n1 f n2 f n3 and f n4 Based on the acquired data, the relationship between different temperatures and particle size ratios under fire conditions was fitted to determine the DCF (Distributed Direct Current Facility) caused by inhalation of a unit activity radionuclide j at different temperatures as the fire progresses. inh，j Value, i.e., inhaled dose conversion factor;

[0010] S3. The DCF (Distributed Cumulative Dose) caused by inhaling a unit activity radionuclide j at different temperatures. inh，j The inhalation dose value is estimated for different personnel based on the actual situation of emergency personnel.

[0011] S4. Compare the estimated inhalation dose values ​​for different workers with the worker dose limits under accident conditions.

[0012] Furthermore, the particle size distribution f at different temperatures in step S2 n1 f n2 f n3 and f n4 The following relationship f is satisfied between them n1 +f n2 +f n3 +f n4 =1, where n is the number of temperature measurements.

[0013] Furthermore, in step S2, the cumulative dose DCF caused by inhaling a unit activity radionuclide j at different temperatures as the fire progresses is determined according to the following formula. inh，j value,

[0014] DCF inh，j =a×f n1 +b×f n2 +c×f n3 ,

[0015] Where a is the dose conversion factor for AMAD <1μm in GB18871; b is the dose conversion factor for AMAD 1-5μm in GB18871; and c is the inhaled dose conversion factor estimated for the deposition of radioactive particles with AMAD 5-10μm in various regions of the respiratory tract, as determined by the respiratory tract model of ICRP.

[0016] Furthermore, in step S3, the inhaled dose value E for different workers is estimated according to the following formula. inh，j

[0017]

[0018] Among them, C aj,0 (t) is the activity concentration of radionuclide j in the outdoor air at time t; tl is the time the smoke plume stays outdoors as it passes by.

[0019] Furthermore, the respiratory rate B of the person mentioned in step S1 refers to the typical values ​​of respiratory rates of different age groups of the public under different conditions, as given by ICRP in its Technical Report No. 71.

[0020] Furthermore, the DCF caused by inhaling a unit activity radionuclide j at different temperatures in step S2... inh，j The value is the effective dose or equivalent dose to be accumulated caused by inhaling a unit activity radionuclide j.

[0021] Furthermore, the respiratory rate B of a person described in step S1 is related to the person's gender, age, and activities.

[0022] Furthermore, the DCF caused by inhaling a unit activity radionuclide j at different temperatures in step S2... inh，j The value is related to age and the particle size of inhaled aerosols.

[0023] Furthermore, in step S3, the activity concentration C of radionuclide j in the outdoor air at time t... aj,0 (t) is related to time and height above the ground.

[0024] Furthermore, the activity concentration C of radionuclide j in outdoor air aj,0 (t) is obtained by collecting the activity concentration of radionuclide j at a height of 1.5m above the ground.

[0025] The beneficial technical effects of the present invention are as follows: The inhalation dose conversion factor estimation method considering particle size distribution after a fire accident disclosed in the present invention, in order to refine the assessment of the inhalation dose conversion factor of workers under fire accident conditions, provides a dose conversion factor based on different particle size proportions according to the particle size distribution law of different uranium-containing substances released at different combustion temperatures. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating a method for estimating the inhalation dose conversion factor after a fire accident, taking into account particle size distribution, as shown in an embodiment of the present invention. Detailed Implementation

[0027] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0028] Example 1

[0029] In the event of a fire on a uranium-containing nuclear material production line, on-site personnel will conduct emergency rescue operations to extinguish the fire. Normally, an alarm will be sounded and ventilation systems will be shut down upon the occurrence of a fire. However, if the fire spreads rapidly or is large, ventilation systems may remain operational, and filters may be breached, causing purification measures to fail. This allows uranium-containing aerosols and particulate matter to enter the atmosphere through the ventilation system.

[0030] If the exhaust stack is elevated, it may cause sedimentation in areas more than 300m away from the emission point; if the exhaust stack is low, the concentration at the landing point is generally higher in areas within 300m.

[0031] The method for estimating the inhaled dose for emergency rescue personnel during accident handling is as follows:

[0032]

[0033] Among them, E inh，jSv is the effective dose or equivalent dose to a specific organ or tissue caused by the inhalation of radioactive nuclides from the smoke plume as the smoke passes by.

[0034] B is the human respiratory rate, m 3 Respiratory rate is related to a person's sex, age, and activity level. For ease of comparison and dosage assessment, the ICRP, in its Technical Report No. 71, provides typical respiratory rate values ​​for different age groups in the public under various conditions. Furthermore, it provides recommended daily respiratory rate values ​​for adults of different age groups: 2.86 for 3 months, 5.16 for 1 year, 8.72 for 5 years, 15 for 10 years, 20.1 for 15 years, and 22.2 for adults. 3 / d.

[0035] DCF inh，j Sv / Bq is the effective dose or equivalent dose caused by inhaling a unit activity radionuclide j, i.e., the inhalation dose conversion factor. This dose conversion factor is related not only to age but also to the particle size of the inhaled aerosol.

[0036] C aj,0 (t) is the activity concentration of radionuclide j in the outdoor air at time t, Bq / m³. 3 Generally, the activity concentration of radionuclides in the air is related not only to time but also to height above the ground. Typically, for the purpose of internal radiation hazard assessment, airborne radionuclides are monitored at a height of 1.5m above the ground, which is the breathing zone height of an adult standing.

[0037] tl is the time, in seconds, that the smoke cloud stays outdoors as it passes by.

[0038] like Figure 1 As shown, this embodiment of the invention provides a method for estimating the inhalation dose conversion factor considering particle size distribution after a fire accident. The method includes the following steps:

[0039] S1. Determine the activity intensity of emergency personnel during fire rescue and determine the respiratory rate of a person (B).

[0040] S2. Based on the changes in fire development, record the fire's spread and the temperature changes at its center. Using the temperature records, fit the relationship between different temperatures and particle size distributions under fire conditions based on the data obtained from the laboratory. Obtain the particle size distribution f at different temperatures. n1 f n2 f n3 and f n4 Among them, f n1 +f n2 +f n3 +f n4 =1 (n is the number of temperature measurements);

[0041] Based on the determined different particle size relationships, combined with the following formula

[0042] DCF inh，j =a×f n1 +b×f n2 +c×f n3 +d×f n4

[0043] Determine the DCF (Distributed Directional Facility) resulting from inhalation of a unit activity radionuclide j at different temperatures, taking into account variations due to fire conditions. inh，j value.

[0044] Where a is the dose conversion factor for AMAD <1 μm in GB18871; b is the dose conversion factor for AMAD 1–5 μm in GB18871; c is the inhaled dose conversion factor estimated for radioactive particles with AMAD 5–10 μm deposited in various regions of the respiratory tract, determined based on the ICRP respiratory tract model; and d is the inhaled dose conversion factor estimated for radioactive particles with AMAD >10 μm deposited in various regions of the respiratory tract, determined based on the ICRP respiratory tract model.

[0045] For example, in a field combustion experiment of butane gas under temperature condition one (350-450℃), the particle size distribution at different temperatures was obtained as follows: the particle size distribution of <1μm (AED) was f. 11 (0–12.24%); the proportion of particles with a diameter of 1–5 μm (AED) is f 12 (15.16%–30.01%); the proportion of particles with a diameter of 5–10 μm (AED) is f 13 (22.33%–34.29%); the proportion of particles with a diameter >10 μm (AED) is f 14 (35.69%–50.27%).

[0046] Diesel combustion field experiments were conducted under temperature condition two (300–875℃), and the particle size distribution at different temperatures was obtained as follows: <1μm (particle size distribution of AED) f 31 (7.74%–60.42%); the proportion of particles with a diameter of 1–5 μm (AED) f 32 (0.21%–4.97%); the proportion of particles with a diameter of 5–10 μm (AED) f 33 (0–0.74%); the percentage of particles with a diameter >10 μm (AED) 34 (38.64%–87.29%).

[0047] Combustion field experiments were conducted under temperature condition three (600–970℃), and the particle size distribution at different temperatures was obtained as follows: the particle size distribution f of <1μm (AED) 21 (0.19%–17.45%); 1–5 μm (particle size percentage of AED) f 22 (9.82%–14.41%); the proportion of particles with a diameter of 5–10 μm (AED) f 23 (30.32–41.74%); the percentage of particles with a diameter >10 μm (AED) f 24 (0–12.24%).

[0048] Based on the temperature conditions, a power-law curve of "temperature-percentage of different particle sizes" was fitted.

[0049] Value 'a' is set as the dose conversion factor for AMAD <1μm according to GB18871; value 'b' is set as the dose conversion factor for AMAD 1–5μm according to GB18871; and value 'c' is set as the inhalation dose conversion factor estimated based on the respiratory tract model of ICRP for radioactive particles with AMAD 5–10μm deposited in various regions of the respiratory tract. In estimating the inhalation dose conversion factor, it is assumed that uranium particles >10μm will not enter the respiratory tract of personnel handling the accident; therefore, value 'f' needs to be considered in the estimation. n4 This part is deducted.

[0050] Therefore, in the event of a fire, the estimation of the inhalation dose conversion factor for workers is as follows:

[0051] DCF inh，j =a×f n1 +b×f n2 +c×f n3

[0052] S3, According to DCF at different temperatures inh，j Value, based on the actual situation of emergency personnel, estimate the inhalation dose value E for different personnel. inh，j .

[0053]

[0054] S4. Compare the estimated inhalation dose values ​​for different workers with the worker dose limits under accident conditions.

[0055] As can be seen from the above embodiments, the inhalation dose conversion factor estimation method considering particle size distribution after a fire accident disclosed in this invention, after a fire accident, determines the activity intensity of emergency personnel during fire rescue, determines the breathing rate of individuals, and estimates the refined dose conversion factor of inhaled personnel involved in emergency response based on the particle size distribution of uranium-containing compounds at different time periods, referring to dose conversion factors for different particle size distributions given domestically and internationally, and combining the temperature and time of the fire. Using the method disclosed in this invention, considering the stages of fire development and the different effects of particle size distribution on the inhalation dose conversion factor under different combustion temperatures, a refined assessment of the inhalation dose of personnel after the accident is achieved. Compared with previous accident estimation methods, the post-accident dose estimation of personnel involved in fire emergency response is more accurate and closer to reality, and is suitable for the refined assessment of the dose received by personnel in the initial stage of emergency response.

[0056] The method described in this invention is not limited to the embodiments described in the specific implementation. Other implementation methods derived by those skilled in the art based on the technical solution of this invention also fall within the scope of technical innovation of this invention.

Claims

1. A method for estimating the inhalation dose conversion factor considering particle size distribution after a fire accident, the method comprising the following steps: S1. Determine the respiratory rate B of a person based on the activity intensity of emergency personnel during fire rescue; S2. Based on the development and changes of the fire, record the fire's spread and the temperature changes at its center. By recording the temperature, obtain the particle size distribution f at different temperatures. n1 f n2 f n3 and f n4 Based on the acquired data, the relationship between different temperatures and particle size ratios under fire conditions was fitted to determine the DCF (Distributed Direct Current Facility) caused by inhalation of a unit activity radionuclide j at different temperatures as the fire progresses. inh，j Value, i.e., inhaled dose conversion factor; S3. The DCF (Distributed Cumulative Dose) caused by inhaling a unit activity radionuclide j at different temperatures. inh，j The inhalation dose value is estimated for different personnel based on the actual situation of emergency personnel. S4. Compare the estimated inhaled dose values ​​for different workers with the dose limits for workers under accident conditions; The respiratory rate B of a person mentioned in step S1 is related to the person's sex, age, and activities. Particle size distribution f at different temperatures in step S2 n1 f n2 f n3 and f n4 The following relationship f is satisfied between them n1 +f n2 +f n3 +f n4 =1, where n is the number of temperature measurements; In step S2, the DCF (Distributed Cumulative Dose) caused by inhaling a unit activity radionuclide j at different temperatures as the fire progresses is determined according to the following formula. inh，j value, DCF inh，j =a×f n1 +b×f n2 +c×f n3， Where a is the dose conversion factor for AMAD <1μm in GB18871; b is the dose conversion factor for AMAD 1~5μm in GB18871; and c is the inhaled dose conversion factor estimated for the deposition of radioactive particles with AMAD 5~10μm in various regions of the respiratory tract, as determined by the respiratory tract model of ICRP. The DCF caused by inhaling a unit activity radionuclide j at different temperatures in step S2 inh，j The value is the effective dose or equivalent dose to be inhaled caused by the inhalation of a unit activity radionuclide j. In step S3, the inhaled dose value E for different workers is estimated according to the following formula. inh，j Among them, C aj,0 (t) is the activity concentration of radionuclide j in the outdoor air at time t; tl is the time the smoke cloud stays outdoors as it passes by; In step S3, the activity concentration C of radionuclide j in the outdoor air at time t. aj,0 (t) is related to time and height above the ground.

2. The method for estimating the inhalation dose conversion factor considering particle size distribution after a fire accident as described in claim 1, characterized in that: The respiratory rate B of the person mentioned in step S1 refers to the typical values ​​of respiratory rate of different age groups of the public under different conditions given by ICRP in its Technical Report No.

71.

3. The method for estimating the inhalation dose conversion factor considering particle size distribution after a fire accident as described in claim 1, characterized in that: The DCF caused by inhaling a unit activity radionuclide j at different temperatures in step S2 inh，j The value is related to age and the particle size of inhaled aerosols.

4. The method for estimating the inhalation dose conversion factor considering particle size distribution after a fire accident as described in claim 1, characterized in that: Activity concentration C of radionuclide j in outdoor air aj,0 (t) is obtained by collecting the activity concentration of radionuclide j at a height of 1.5 m above the ground.

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