Nuclear power plant; Intermediate radioactive waste liquid; Transshipment; Cruise ship; Tank car; tankman
With the construction of domestic nuclear power plants and the improvement of nuclear safety standards, the waste liquid treatment system has been separated from the nuclear island and has become an independent waste liquid treatment center. There are limitations in the pipeline transportation of intermediate radioactive waste liquid from NI to the center, which has gradually become a problem to be considered by the new generation of nuclear power plants. This paper introduces a flexible and safe conceptual design of liquid transportation in nuclear power plant, which may be an effective measure to solve this problem.
Keywords nuclear power plant; Moderate liquid waste; Transportation; oil tank car
Introduction to 0
In recent years, China's nuclear power plants have developed rapidly, while nuclear safety has attracted the attention of the state and people, and the technical standards of nuclear power have also been greatly improved. In the new generation of nuclear power plants, radioactive waste liquid treatment facilities will be separated from the nuclear island, and an independent waste liquid treatment center will be built, which will not only save investment, but also improve the safety of the nuclear island. The waste liquid treatment center will centrally treat radioactive waste liquid generated by all facilities in the nuclear power plant. Therefore, it is necessary to develop a brand-new radioactive waste liquid transfer scheme, which can flexibly transfer the medium-level waste liquid produced by different facilities to the waste liquid treatment center under the condition of ensuring safety.
1 Study on Transfer Scheme of Liquid Radioactive Waste
There are many kinds of radioactive wastes produced by nuclear power plants, and their natural characteristics are different. Different treatment technologies have been developed for different wastes, and the equipment and operation cost of the treatment system are expensive. In the case of a small number of units, the amount of waste generated is not enough and the utilization rate of equipment is low. In order to improve the equipment utilization rate and control the investment, the nuclear power plant has built a new waste treatment center to treat the waste generated by multiple nuclear power units in the power plant [1]. As an important part of waste treatment, the waste liquid treatment system is separated from the nuclear island plant, and a waste liquid treatment center (hereinafter referred to as the treatment center) is built in the waste treatment center.
At present, nuclear power plants use pipeline transportation to transport waste liquid to treatment facilities. Restricted by geographical location and topography, pipelines are buried underground for a long time, which poses the risk of leakage of pipelines and valves, and will produce a large amount of radioactive waste when they are retired. In order to avoid all kinds of disadvantages brought by pipeline transportation and increase the flexibility of waste liquid transportation, it is planned to adopt a set of median waste liquid transportation system, including a mobile median waste liquid transportation tanker, waste liquid receiving (discharging) system and flushing system, and transport waste liquid from production facilities to treatment center by vehicle transportation in the factory.
In this scheme, the waste liquid is collected in a high tank (the tank is higher than the top of the tanker), and the middle waste liquid enters the tanker by gravity flow. See Figure 1 for the process of tank car receiving waste liquid. The system can be divided into two parts: waste liquid receiving system and flushing system. The waste liquid receiving system includes medium waste liquid storage tank, valve and corresponding pipeline, quick connector and hose. The flushing system consists of detergent tank, valve and corresponding pipeline. There is a special waste liquid transfer interface between the waste liquid generating facility and the treatment center, which can be connected with the tank car through hoses and quick connectors. After the transfer is completed, clean the waste liquid conveying pipeline and transfer hose with detergent to remove the residual waste liquid in the pipeline.
Fig. 2 is a flow chart of a tanker transporting waste liquid to a treatment center. After the hose is connected, the waste liquid in the tank car is pumped to the treatment center by the middle drainage elevator, and the pipeline and hose are washed by the flushing system after the same transfer is completed.
2 transshipment equipment? Tank car design
Liquid waste transfer scheme adopts liquid waste transfer tank car. According to the relevant provisions in the Transport Rules of Radioactive Materials, the tank car should have good shielding effect and leak detection equipment, meet the requirements of IP-2 package and meet the needs of safe transportation. At the same time, in order to meet the requirements of process transportation, the tank car to be used includes: main device, auxiliary system and safety system.
(1) The main equipment is the basic component of the tanker, including the main frame, shielding container and loading and unloading interface of the tanker.
Main frame: as an important part of tank car, it carries shielded containers and provides installation space and protective measures for equipment and pipelines of other systems. Because the shielding container is made of cast lead and heavy, the frame structure needs to meet the requirements of bearing and transportation.
Shielded container: provides radiation protection barrier for medium-level radioactive waste liquid. A pressure vessel is set inside to store waste liquid, and the outside is shielded by cast lead structure. The surface dose of tanker reaches the working allowable value (surface dose rate of tanker? 2mSv/h, dose rate at a distance of 2m from the tank car surface? 0. 1 msv/h)； At the same time, the shielded container can bear the positive and negative pressure generated by vacuum system and compressed air system.
Loading and unloading interface of tank car: through the connecting hose with quick connector, the tank car can be quickly connected with facilities, reducing the operation time of personnel.
(2) The auxiliary system provides necessary power for the tanker to realize automatic loading and unloading function, including vacuum system, compressed air system and gas purification system.
Vacuum and compressed air system: provide power for the tank car to automatically receive and discharge waste liquid and flush the pipeline.
Gas purification system: the tail gas and vacuum system of the tank car are treated to make them reach the site emission limit.
(3) The safety system provides guarantee for the safe operation of the tank car and prevents tank leakage accidents, including liquid level monitoring system, leakage alarm system and automatic control system.
Liquid level monitoring system: Monitor the liquid level of tank car waste liquid to prevent overflow, stop receiving waste liquid when it reaches a certain liquid level, and provide parameters for the control system.
Leakage alarm system: monitor the environment outside the shielding container to prevent waste liquid from accumulating outside the shielding layer.
Automatic control system: the tank car is automatically controlled, and the loading, unloading and flushing functions of the tank car can be automatically completed after the hose is connected, reducing the operation of personnel.
3 Conclusion
The transportation mode of tank car is flexible, unaffected by earthquake and geological conditions, convenient for cleaning and decontamination when retiring, less radioactive waste, and less potential impact on the surrounding environment. In the case of radioactive waste liquid leakage caused by accidents such as Fukushima nuclear power plant, the transfer tanker will also be able to give full play to its advantages of mobility, convenience, safety and reliability, and transfer the leaked radioactive waste liquid out in time. Even on the premise of pipeline transportation, tanker transportation can be used as a supplementary application means to ensure the safety of facilities, which has great application prospects in nuclear power plants and nuclear facilities.
refer to
Zhang, Yan Cangsheng, Huang Laixi, et al. Reduction of radioactive waste in nuclear power plants [M]. China Atomic Energy Press, 20 13: 3 1-32.