CN110489789B - Radioactive gas diffusion evaluation method in nuclear facility retirement environment - Google Patents
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Abstract
The invention relates to a radioactive gas diffusion assessment method in a nuclear facility decommissioning environment, and belongs to the field of nuclear decommissioning simulation. Constructing a decommissioning scene mathematical model; simulating the diffusion of radioactive gas by adopting a uniform spherical tobacco mass model; correcting the uniform spherical tobacco mass model by using a mathematical model of a retirement scene; and calculating the activity distribution of the radioactive gas to realize the diffusion evaluation of the radioactive gas in the retired environment. The invention adopts a uniform spherical smoke cluster model to simulate the diffusion of radioactive gas; the influence of an actual decommissioning scene on the model is considered, and the dynamic calculation of the concentration distribution of the radioactive gas in the decommissioning environment of the nuclear facility is realized. The invention develops a real-time and efficient radioactive gas diffusion evaluation simulation method in the nuclear facility decommissioning environment, has great practical significance for nuclear facility decommissioning simulation and has wide application prospect.
Description
Technical Field
The invention relates to a radioactive gas diffusion assessment method in a nuclear facility decommissioning environment, and belongs to the field of nuclear decommissioning simulation.
Background
Nuclear facility decommissioning activities generate large amounts of radioactive gases. In order to ensure the safety of workers in retirement activities and to reduce the internal exposure of radioactive gases to workers, the distribution of radioactive gases must be analyzed and evaluated.
The earliest developed radioactive gas diffusion model was a gaussian model, which was mainly applied to point source diffusion studies, including gaussian plume models and gaussian plume models. The former is applied to diffusion studies of continuous sources, and the latter is applied to diffusion studies of transient leakage. CFD modeling fluid flow is an emerging method to address gas flow. The CFD organically combines a numerical calculation method and a data visualization technology, and can perform simulation analysis on related physical phenomena such as flow, heat exchange and the like. However, due to the large space of the retired scene, the occupied space of the equipment is large, the air circulation is slow, the leakage point of the radioactive gas is large, and the existing gas diffusion models are not suitable for the diffusion simulation of the radioactive gas in the retired scene.
In conclusion, the development of the real-time and efficient radioactive gas diffusion assessment simulation method in the nuclear facility decommissioning environment has great practical significance for nuclear facility decommissioning simulation.
Disclosure of Invention
The invention aims to develop a real-time and efficient radioactive gas diffusion evaluation simulation method in a nuclear facility decommissioning environment and provide a radioactive gas diffusion evaluation method in the nuclear facility decommissioning environment.
The invention aims to realize the method for evaluating the diffusion of the radioactive gas in the decommissioning environment of the nuclear facility, which comprises the following steps:
step 4, considering the influence of the retirement scene on the model;
step 5, considering the influence of a plurality of leakage points on the model;
and 6, considering the influence of the exhaust pipeline on the model.
The invention also includes such structural features:
1. the mathematical model in the step 1 comprises a plant, equipment and a wall body, and is described by using a mathematical formula.
2. The step 2 specifically comprises the following steps: the radioactive gas uniform spherical model simulates the diffusion of radioactive gas by continuously releasing a series of spherical uniform concentration smoke clusters, the gas concentration of a certain spatial position is the cumulative sum of the concentrations of all the smoke clusters containing the position, and at the time t, the shape formula of the uniform spherical smoke cluster model is as follows:
(x-x i,t (j)) 2 +(y-y i,t (j)) 2 +(z-z i,t (j)) 2 ≤R i,t (j) 2
in the formula, x i,t (j)、y i,t (j)、z i,t (j) The central position of the jth smoke mass released by the ith leakage point can be obtained by calculation according to the coordinates of the leakage point and the circulation speed of the gas in the plant; r i (j) The radius of the spherical smoke cluster model can be obtained according to the diffusion speed of radioactive gas, and the concentration of the radioactive gas in the spherical smoke cluster model is as follows:
in the formula, C i,t (j) Concentration of radioactive gas in jth plume released at ith leakage point at time t, bq/m 3 ；Q i (j) The release rate, bq/s, of radioactive gas at the leak point when the ith leak point releases the jth smoke mass; delta t is the time interval, s, between the release of adjacent air masses at the leakage point; v i,t (j) Is the volume of the jth plume released at the ith leak point at time t, in m 3 Ideally, the volume of the smoke bolus model is:
3. the step 3 specifically comprises the following steps: considering that the shape of the radioactive gas cigarette mass is limited by the factory space, the shape formula of the uniform spherical cigarette mass model is modified as follows:
in the formula, x min 、y min 、z min 、x max 、y max 、z max For the boundary of the factory space, the volume of the tobacco mass is corrected as follows:
wherein, V out The volume of the tobacco mass outside the factory building boundary.
4. The step 4 specifically comprises the following steps: and correcting the shape formula of the smoke mass by considering the mathematical model difference operation of the radioactive gas smoke mass model and the scene, wherein the volume of the smoke mass after correction is as follows:
wherein, V in Is the volume of the intersection of the plume and the nuclear facility.
5. The step 5 specifically comprises the following steps: since the radioactive gas leakage points are many in the nuclear decommissioning scene, and each soot group is independent, the concentration of the radioactive gas at each spatial position is the sum of the concentrations of the soot groups at the position generated by all the leakage points.
6. The step 6 specifically comprises the following steps: when the cigarette group meets with exhaust duct, the cigarette group model shape is unchangeable, and the gas activity that discharges away through exhaust duct in the unit interval is the gas flow of the concentration product exhaust pipe of cigarette group, and the concentration of cigarette group after the correction is:
wherein, V f Is the volume of gas pumped away by the exhaust duct per unit time.
Compared with the prior art, the invention has the beneficial effects that: the invention develops a simulation method which simplifies radioactive gas into a spherical smoke cluster model with uniform interior and dynamically calculates the spatial distribution of the radioactive gas based on a mathematical modeling method. The invention realizes the simulation of the diffusion of radioactive gas by adopting a uniform spherical smoke cluster model; the invention considers the influence of the actual retirement scene on the model and realizes the dynamic calculation of the concentration distribution of the radioactive gas.
Drawings
FIG. 1 is the concentration of radioactive gas at the (x, y, z) location;
FIG. 2 is a view showing that the volume of the radioactive gas diffusion process is limited by the space of a factory;
FIG. 3 is a view of the volume affected by the scene facility during the diffusion of radioactive gas;
FIG. 4 is the concentration of radioactive gas at the (x, y, z) location for multiple leak point conditions;
FIG. 5 shows the radioactive gas diffusion process affected by the exhaust duct.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
As shown in the figure, FIG. 1 is the concentration of radioactive gas at the (x, y, z) position; FIG. 2 is a view showing that the volume of the radioactive gas diffusion process is limited by the space of a factory; FIG. 3 is a view of the volume affected by the scene facility during the diffusion of radioactive gas; FIG. 4 is the concentration of radioactive gas at the (x, y, z) location for multiple leak point conditions; FIG. 5 shows the radioactive gas diffusion process affected by the exhaust duct.
The invention provides a simulation method for simulating diffusion of radioactive gas by adopting a uniform spherical smoke cluster model and dynamically calculating concentration distribution of the radioactive gas aiming at the radioactive gas leaked in a nuclear retired environment.
The invention adopts C + + language programming, and has the main functions of: and (3) constructing a mathematical model of a decommissioning scene, simulating the diffusion of the radioactive gas by adopting the uniform spherical tobacco mass model, correcting the uniform spherical tobacco mass model by using the mathematical model of the decommissioning scene, and finally calculating the activity distribution of the radioactive gas. The whole system comprises three modules of retired environment modeling, uniform spherical smoke mass model modeling and radioactive gas concentration distribution calculation.
The invention adopts the following technical scheme:
1. and constructing a mathematical model of the virtual retirement environment according to the parameters of the retirement scene of the nuclear facility.
And constructing a mathematical model of the decommissioning environment according to the determined parameters of the decommissioning scene of the nuclear facility. The mathematical model comprises a factory building, equipment, a wall body and the like, and can be described by using a mathematical formula.
2. And constructing a uniform spherical smoke cluster model of radioactive gas.
The radioactive gas uniform spherical smoke cluster model has the following assumed conditions:
(a) The smoke group generated at the leakage part each time is spherical with a boundary, and the concentration distribution of radioactive gas in the smoke group is uniform;
(b) The diffusion gas is not absorbed when contacting with the object;
(c) Neglecting the action of buoyancy and gravity, no chemical reaction occurs in the air mass;
(d) The diffusion speed of the radioactive gas does not change along with time, namely the radioactive gas diffuses to the periphery at a constant speed;
(e) The moving speed of the center of the air mass is equal to the ambient wind speed.
The radioactive gas uniform spherical model simulates the diffusion of radioactive gas by continuously releasing a series of spherical uniform concentration plumes. In the diffusion process, each smoke mass has independent action, and spatial displacement and shape change continuously occur. The gas concentration at a spatial location is the cumulative sum of all the concentrations of the plumes that comprise that location. As shown in fig. 1, the leak source releases 3 boluses over the radioactive gas leak duration, and the concentration of radioactive gas at the (x, y, z) location is equivalent to a superposition that encompasses all the boluses concentrations at that location.
At time t, the shape formula of the uniform spherical smoke mass model is as follows:
(x-x i,t (j)) 2 +(y-y i,t (j)) 2 +(z-z i,t (j)) 2 ≤R i,t (j) 2
in the formula, x i,t (j)、y i,t (j)、z i,t (j) The central position of the jth smoke mass released by the ith leakage point can be measured according to the coordinates of the leakage point and the circulation velocity of the gas in the plantCalculating to obtain; r i (j) Is the radius of the spherical soot model and can be obtained according to the diffusion speed of radioactive gas.
According to the assumed conditions, the concentration of radioactive gas in the smoke mass is uniformly distributed, so that the concentration of radioactive gas in the spherical smoke mass model is:
in the formula, C i,t (j) Concentration of radioactive gas in jth plume released at ith leakage point at time t, bq/m 3 ；Q i (j) The release rate, bq/s, of radioactive gas at the leak point when the ith leak point releases the jth smoke mass; delta t is the time interval, s, between the release of adjacent air masses at the leakage point; v i,t (j) Is the volume of the jth plume released at the ith leakage point at time t, m 3 . Under ideal conditions, the uniform spherical tobacco ball model is spherical and has the volume:
3. the influence of the plant on the model is taken into account.
The shape of the radioactive gas diffusion is limited by the space of the factory, so the formula of the shape of the smoke mass needs to be corrected:
in the formula, x min 、y min 、z min 、x max 、y max 、z max Is the boundary of the factory space. As shown in fig. 2, the volume of the bolus is corrected to be:
wherein, V out For the tobacco mass at the plant boundaryThe outer volume.
4. The influence of the retirement scenario on the model is considered.
Facilities in nuclear decommissioning scenes are bulky and can affect the diffusion of radioactive gases. Therefore, the difference operation needs to be performed on the smoke mass model and the mathematical model of the scene, and the smoke mass shape formula needs to be corrected. As shown in fig. 3, the volume of the bolus is corrected to be:
wherein, V in Is the volume of the intersection of the plume and the nuclear facility.
5. The effect of multiple leak points on the model is considered.
In a nuclear retirement scene, the radioactive gas leakage points are more, and the leakage amount of each leakage point is different. As shown in fig. 4, since each plume is independent, the concentration of radioactive gas at the (x, y, z) location is the cumulative sum of the concentrations of the plumes containing that location for all leak points.
6. The influence of the exhaust duct on the model is taken into account.
The radioactive gas can be discharged to the external environment through the exhaust pipeline after operations such as filtration, absorption and the like. As shown in fig. 5, when the smoke mass is connected to the exhaust duct, assuming that the model shape is unchanged, the activity of the gas exhausted through the exhaust duct per unit time is the product of the concentration of the smoke mass and the gas flow rate of the exhaust duct. The corrected smoke mass concentration is:
wherein, V f Is the volume of gas pumped away by the exhaust duct per unit time.
In summary, the invention discloses a method for evaluating the diffusion of radioactive gas in a nuclear facility decommissioning environment, and particularly relates to a simulation method for simulating the diffusion of the radioactive gas by adopting a uniform spherical smoke cluster model and dynamically calculating the concentration distribution of the radioactive gas aiming at the radioactive gas leaked in the nuclear facility decommissioning environment. The invention comprises the following steps: constructing a decommissioning scene mathematical model; simulating the diffusion of radioactive gas by adopting a uniform spherical smoke cluster model; correcting the uniform spherical cigarette mass model by using a mathematical model of a retired scene; and calculating the activity distribution of the radioactive gas to realize the diffusion evaluation of the radioactive gas in the retired environment. The method comprises three modules of decommissioning environment modeling, uniform spherical smoke cluster model modeling and radioactive gas concentration distribution calculation, and realizes dynamic calculation of radioactive gas diffusion in the decommissioning environment of the nuclear facility.
Claims (3)
1. A radioactive gas diffusion assessment method in a nuclear facility retirement environment is characterized by comprising the following steps:
step 1, constructing a mathematical model of a virtual decommissioning environment according to parameters of a decommissioning scene of a nuclear facility;
step 2, constructing a uniform spherical smoke cluster model of radioactive gas;
the radioactive gas uniform spherical model simulates the diffusion of radioactive gas by continuously releasing a series of spherical uniform concentration smoke clusters, the gas concentration of a certain spatial position is the cumulative sum of the concentrations of all the smoke clusters containing the position, and at the time t, the shape formula of the uniform spherical smoke cluster model is as follows:
(x-x i,t (j)) 2 +(y-y i,t (j)) 2 +(z-z i,t (j)) 2 ≤R i,t (j) 2
in the formula, x i,t (j)、y i,t (j)、z i,t (j) The central position of the jth smoke mass released by the ith leakage point can be obtained by calculation according to the coordinates of the leakage point and the circulation speed of the gas in the plant; r i，t (j) The radius of the spherical smoke mass model can be obtained according to the diffusion speed of radioactive gas, and the concentration of the radioactive gas in the spherical smoke mass model is as follows:
in the formula (I), the compound is shown in the specification,C i,t (j) Concentration of radioactive gas in jth plume released at ith leakage point at time t, bq/m 3 ；Q i (j) The release rate, bq/s, of radioactive gas at the leak point when the ith leak point releases the jth smoke mass; delta t is the time interval, s, between the release of adjacent air masses at the leakage point; v i,t (j) Is the volume of the jth plume released at the ith leakage point at time t, in m 3 Ideally, the volume of the smoke bolus model is:
step 3, considering the influence of the factory building on the model;
considering that the shape of the radioactive gas smoke mass is limited by the space of a factory building, the shape formula of the uniform spherical smoke mass model is modified as follows:
in the formula, x min 、y min 、z min 、x max 、y max 、z max For the boundary of the factory space, the volume of the tobacco mass is corrected as follows:
wherein, V out The volume of the tobacco mass outside the boundary of the factory building;
step 4, considering the influence of the retirement scene on the model;
and (3) correcting the shape formula of the smoke mass by considering the difference operation of the radioactive gas smoke mass model and the mathematical model of the scene, wherein the volume of the corrected smoke mass is as follows:
wherein, V in The volume of the intersection part of the smoke cluster and the nuclear facility;
step 5, considering the influence of a plurality of leakage points on the model;
step 6, considering the influence of the exhaust pipeline on the model;
when the cigarette group meets with exhaust duct, the cigarette group model shape is unchangeable, and the gas activity that discharges away through exhaust duct in the unit interval is the gas flow of the concentration product exhaust pipe of cigarette group, and the concentration of cigarette group after the correction is:
wherein, V f Is the volume of gas pumped away by the exhaust duct per unit time.
2. The method as claimed in claim 1, wherein the mathematical model in step 1 includes plant, equipment, and wall, and is described by mathematical formula.
3. The method according to claim 2, wherein the step 5 is specifically: since the radioactive gas leakage points are many in the nuclear decommissioning scene, and each soot group is independent, the concentration of the radioactive gas at each spatial position is the sum of the concentrations of the soot groups at the position generated by all the leakage points.
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