Method For Searching And Positioning Radioactive Sources By AUV

With the rapid development of the nuclear industry worldwide,incidents of radioactive source loss often occur.At present,the search for lost radioactive sources is basically done through manual search.The use of robots equipped with detectors to replace manual search for radioactive sources has been carried out on land,reducing the risk of personnel exposure to radiation and improving search efficiency.Radioactive sources lost under water also need to be recovered as soon as possible in order to avoid continuous pollution of water resources.Compared with other underwater unmanned vehicles,the Autonomous Underwater Vehicle(AUV)has low cost,self-contained energy,high positioning accuracy,fast mobility,flexible maneuverability,and unmanned autonomous detection.With the advantages of cable and high degree of intelligence,using AUV to search for underwater radioactive sources will become an inevitable trend in this field.This paper takes AUV as the research object,and focuses on the behavior-based search for the source of the point source and the radiation boundary of the radiation source.The main research contents of this paper are as follows:1.AUV motion simulation modeling and Gamma ray radiation field simulation modeling.Based on the "WL-2" AUV developed by Harbin Engineering University,the relevant parameters of the AUV are defined and the movement model of the AUV in the horizontal plane is established.Based on the attenuation law of Gamma rays in a two-dimensional medium environment,a point source ray radiation field is simulated and modeled to simulate the radiation intensity detected by the AUV underwater,which provides the AUV with information on the sensing layer.2.Research on AUV’s behavior-based radiation source search method.Aiming at the research content of AUV searching for ray point sources,a behavior-based radiation source search method was proposed,and three behaviors were redesigned.In view of the randomness of the radiation intensity detected by the sensor,a detailed study was carried out in Behavior 2,and based on the attenuation law of the point source ray,an algorithm for estimating the radiation intensity gradient was improved,and the "∞" search method was proposed.The radiation intensity gradient generated by two circular motions finds the effective intersection point to estimate the position of the point source.Finally,the switching rules between behaviors based on the behavior search method of radiation sources are designed to ensure that only one behavior is running at each moment and to coordinate each behavior in an orderly manner.The effectiveness of AUV’s behavior-based radiation source search method is verified in simulation experiments.3.Research on the radiation boundary search method of radiation source based on behavior.Aiming at the research content of AUV searching for the radiation boundary of the radiation source,the method of acquiring boundary points in the boundary search and reconstructing the boundary is adopted.This paper uses the AUV to continuously drive in and out of the radiation field boundary to obtain discrete boundary points,and then reconstruct the boundary curve of the radiation field through cubic spline curve.Two methods are used to obtain discrete boundary points:(1)Using a wide range of rectangular search method to search the designated radiation area completely;(2)Using local planning to design a "S"-shaped motion curve,using The AUV moves in a circular motion around the center of the circle,and a method for updating the center of the circle is designed to make the AUV drive in and out at the boundary of the radiation field,and obtain boundary points to complete the search for the boundary of the radiation field.Finally,a cubic spline curve is used to fit these discrete boundary points,so that the AUV moves along the curve for verification.In the simulation experiment,the feasibility and effectiveness of the AUV’s behavior-based radiation source boundary search method are verified.