On May 25, RIC (In-core Measurement System) of Unit 3 of Ling'Ao Nuclear Power Station was re-qualified, which verified the availability of RIC mechanical and electrical components. This marks the successful application of the new RIC thimble cutting and shifting technology and thimble automatic cutting and grinding tool developed by CGN in the 10th outage of Unit 3 of Ling'Ao Nuclear Power Station, ending the long-time history of using foreign technology for thimble wearing maintenance in China.
Dimensional measurement of thimble before cutting
Each reactor unit of Ling'Ao Nuclear Power Station has 50 thimbles, with length varying from 13.30 to 17.30 meters. The inner wall of thimble is dry and the neutron flux probe can move inside to measure the neutron flux in the core point by point.
During the operation of the unit, the thimble is under the long-time impact of water flow, the sudden change of the guide channel section is easy to produce micro vibration and wearing, which may affect the stable operation of the unit. It needs to be inspected and repaired during the outage.
According to the practice of using foreign technical method in the past, to deal with the wearing of thimble which reaches the wear standard is to shorten the distance of thimble so that the position with serious wearing can avoid the large water impact, that is “Cutting and Shifting”. Due to the limitations of the maintenance process, each thimble is allowed to cut and shift twice at most. If it exceeds twice, it needs to block the channel or replaced the thimble.
Thrust and Extension Section Components after Separating
With the increase of the operation time of the existing units of CGN and more and more new units coming online, the demand for new technologies for thimble wearing maintenance and treatment in power plants is becoming more and more urgent.
Is there a new solution that can improve the current problem? Soon, CGN “Research on Thimble Wear Treatment Technology” Project came into being. As one of the important scientific research projects of CGN, China Nuclear Power Operations Co., Ltd. led and established the project team, with Daya Bay Nuclear Power Operation and Management Co., Ltd. and Fujian Ningde Nuclear Power Co., Ltd. participating.
Based on the length measurement results of wear of thimble, the project team has carried out research on new maintenance technology of the thimble to reduce the cutting length of each cutting and shifting and increase the cutting times within the service life. At the same time, an automatic cutting and grinding tool for cutting and shifting of the thimble is also developed to realize accurate cutting and groove grinding under different displacement lengths, and realize the recycling of cutting and shifting thrust section and extension section components.
After a long-term technical breakthrough, it finally has met the conditions for application . During the 10th outage of Unit 3 of Ling'Ao Nuclear Power Station, taking the advantage of the window period of replacing the seal assembly of the thimble, the project team decided to introduce new technologies and tools in this outage.
The staff are commissioning the tools
Do it now! The project team overcame the difficulties of tight outage schedule, small on-site implementation space and high requirements for cutting centering accuracy, and successfully replaced new sealing components. The new technologies and tools adopted this time shorten the cutting length of 40-45mm to 1mm, breaking the history that each thimble can only be cut and shifted twice, greatly prolonging the service life of the thimble and realizing the reuse of the thrust section and extension section of the thimble.
The employees are handling the thimble.
The technology can be extended to apply in the maintenance of the thimble of CPR1000 and M310 PWR nuclear power plants at home and abroad. It is estimated that the spare part alone contributes to saving of millions of yuans every year which would be spent on importing such spare time otherwise.