Research On Dose Monitoring System For Nuclear Emergency Situation

The development of nuclear power is an important part of China’s nuclear energy industry,and since the Fukushima nuclear accident in 2011,the operational safety of nuclear power has entered the public eye once again.In the production and utilization environment of nuclear energy,in order to minimize the impact of the accident on the environment,emergency rescue plans and various technical reserves must be prepared before a nuclear accident occurs.Nuclear emergency rescue refers to the special response measures taken by the government and with the cooperation of various parties after a nuclear accident.Rescue work is generally carried out in the order of"Reconnaissance-Decontamination"in nuclear emergency rescue situations.After nuclear accident occurs,before sending relevant personnel and equipment for rescuing,it is necessary to send UAV(Unmanned Aerial Vehicle)platform carrying relevant measuring instruments to detect the scale of the pollution.In this thesis,the research and design of the radiation dose measurement tasks and the corresponding dose measurement instrument platform in the nuclear accident emergency scenario are carried out.The deployment of dose measurement in the nuclear accident scenario is divided into two parts,in the reconnaissance mission,the airborne environmental dose measurement work,and the personal dose monitoring work of the rescuers during the decontamination process,then analyzes the challenges brought to measuring instruments under such special circumstances.The environmental dose measurement requirements in nuclear emergency scenarios are generally realized by special aviation gamma spectrometers mounted on vehicles or manned aircraft nowadays,and there has been no large-scale research on the miniaturized UAV aerial survey platform in recent years.In the design of the airborne environmental dose monitoring system,this Thesis determined the use of CLLB(Cs2LiLaBr6(Ce))crystal detector to achieve dual detection of neutron and gamma by a single detector,which reduced load pressure on the platform effectively.By designing a real-time online neutron-gamma discrimination algorithm,the measurement system can provide real-time neutron and gamma energy spectrum and dose data of the environment,and the circuit parameters were optimized in experiments,which enables it to achieve a high neutron-gamma discrimination ratio while meeting the target of neutron peak resolution better than 5%.As for the problem of high dose radiation in the aerial survey which may interfere with the normal operation of the electronic system,the method of strengthening the electronics in the software and hardware at the same time,and combining with external anti-radiation strengthening materials is proposed.Through modular design and technical means such as hardware redundancy,logic verification,communication link reinforcement,etc.,the dosimeter system can still work normally in the environment with a dose rate of up to 600 Gy/h and a total absorbed dose of 1000 Gy.Finally,after testing and calibration,the development of neutron gamma dose and energy spectrum monitoring equipment with the characteristics of small size,light weight,low power consumption,and high measurement accuracy in nuclear accident emergency situations was completed.In the design of the personal dose monitoring system module,by analyzing the complexity of radionuclides in nuclear accident scenarios,the performance of common commercial personal dose equipment in such scenarios are proposed,and point out that in order to obtain more accurate personal dose information,the gamma spectrum conversion method should be used to improve the accuracy of personal dose measurement.Based on the types of radioactive sources and energy ranges in the nuclear accident scene,in order to meet the requirements of energy spectrum measurement,it is determined to use a quasi-hemispherical cadmium zinc telluride(CdZnTe,CZT)semiconductor detector to design an energy spectrum measurement module for personal dosimeter,and model analysis was carried out for its supporting readout electronics system.Parameters of readout electronics are optimized in experiments so that it can realize the high-precision measurement of the gamma energy spectrum in a very small space volume,the energy resolution of 662 keV gamma ray reaches 2.6%.The modular design method makes it adaptable to various embedded control systems to provide flexible customized personal dose and environmental energy spectrum measurement function.