Unloading method for replacing secondary neutron source assembly with central fuel assembly

Abstract

The invention discloses an unloading method for replacing a secondary neutron source assembly with a central fuel assembly, which comprises the following steps of: checking the burnup depth, the refueling pool boron concentration, the temperature and the water level height of the central fuel assembly of a reactor core before overhaul unloading and before unloading, and performing reference counting rate measurement and alarm setting value setting before unloading; and after unloading is started, conducting unloading operation in an oblique diagonal mode, when unloading is carried out to a 58th step, moving the center fuel assembly to an N06 position of the reactor core, conducting reference counting rate calculation and alarm setting value setting again, and then completing reactor core unloading repeatedly in the oblique diagonal unloading mode. Compared with a convention loading method, the unloading method disclosed by the invention does not use a secondary neutron source assemblyany more, a new secondary neutron source assembly does not need to be purchased any more, the purchasing cost can be saved, the tritium generation amount can be reduced, the irradiation risk of operators can be reduced, and good economical efficiency, environmental friendliness and safety are achieved.

Description

technical field [0001] The invention relates to the technical field of reactors, in particular to an unloading method using a central fuel assembly instead of a secondary neutron source assembly. Background technique [0002] The 650MWe pressurized water reactor nuclear power plant is a large-scale commercial nuclear power plant. There are a total of 121 fuel assemblies in the core. The U235 enrichment of the fuel assemblies used does not exceed 4.5%. Heat transfer, currently domestic 650MWe pressurized water reactor nuclear power plants are mainly distributed in coastal economically developed areas such as Zhejiang and Hainan. [0003] Unloading is an important task for nuclear power plant refueling overhaul, such as figure 1 As shown, the traditional PWR unloading method is to arrange the secondary neutron source fuel assembly at a specific position in the core, figure 1 S1 / S2 in middle represent the two secondary neutron source components of the 650MWe pressurized water...

AI Technical Summary

Problems solved by technology

[0004] 1. The design life of the secondary neutron source components is about 15 years, so a new secondary neutron source must be repurchased from abroad every 15 years. At present, the tension in international trade is intensifying, and the secondary neutron source components are used in nuclear power plants. It is becoming more and more difficult to purchase important equipment from abroad;

[0005] 2. The purchase price of the secondary neutron source is relatively expensive. According to the current market price, the design life of the nuclear power plant is calculated as 60 years, and each unit needs to spend about 3 million in purchase costs. The current domestic 650MWe pressurized water reactor nuclear power plant has a total There are 6 units, and a total purchase cost of 18 million is required;

[0006] 3. The components of the secondary neutron source must be re-inserted for each refueling overhaul, which may cause mechanical damage or failure, resulting in no secondary neutron source components available, or even being forced to stop the overhaul, resulting in the serious consequences of being unable to start the stack;

[0007] 4. During the traditional unloading method, it is necessary to move the secondary neutron source components in the stack, and it is necessary to re-measure the neutron count rate reference value and reset the alarm setting value. It takes about 1 hour, there is room for improvement and optimization;

[0008] 5. During the insertion and removal process of secondary neutron source components, the risk of radiation exposure to operators will be increased;

[0009] 6. A large amount of tritium will be produced during the use of secondary neutron sources, accounting for about 15% of the total tritium production, which will increase the environmental discharge pressure;

[0010] 7. Since the pressure vessels of the 650MW and 1000MWe PWRs have the same size, the outer ring of the 650MW PWR core has 36 fewer fuel assemblies than the 1000MW PWR core, so the reflective layer around the core of the 650MW PWR is thicker , there are fewer neutrons escaping the reflective layer, and it is more difficult and challenging to develop passive unloading

Images