Analyze the level measurement of the pressure vessel and regulator of the nuclear power unit and split the K1 differential pressure transmitter. The liquid level measurement plays an extremely important role in the inflow of the primary circuit during the construction of the power plant, the water pressure test, and the primary level monitoring and accident analysis during the operation period. The transmitter's sensor and transmission unit are separately arranged in the containment and the electrical workshop, and are installed directly on the construction site through a unique vacuum, liquid filling, and bubble-free verification test. Filling fluid is the key to technical difficulties and ensuring stable and reliable operation of equipment. Introduce the working principle and characteristics of the primary circuit liquid level measurement, K1 differential pressure transmitter, analyze the on-site vacuum pumping, liquid filling technology, bubble-free verification test, static pressure test and commissioning check results. Finally, the main problems encountered in the installation process are introduced, and the experience of the nuclear power unit is summarized. The vacuum optimization and optimization of the liquid filling process and installation management are proposed to provide reference for the follow-up units.
The nuclear pressure vessel and regulator liquid level measurement is used for condition monitoring and accident analysis, and is extremely important for nuclear power operation safety. The transmitter consists of an isolation module, a sensing unit and a transmission unit, wherein the isolation module is directly connected with the process pipeline. The transmitter's isolation module, capillary tube, and sensing unit are installed in the nuclear island. The transmission unit is installed in the electrical plant and connected through the junction box and cables. The split structure prevents the transmission unit from working in the high-irradiation, high-temperature, and high-pressure working environment under Local conditions, ensuring the life, maintainability, stability, and reliability of the transmitter.
Transmitters are sent to the site in the form of loose parts to be installed on site, involving vacuum, liquid filling, bubble-free verification tests, static pressure tests and other special processes. The harsh construction environment on site, and the vacuum process requirements are very high. For example, the HP vacuum is 0.02 mBar. In the high-temperature and high-humidity environment of nuclear islands, to achieve such a high degree of vacuum, all aspects of the process must be strictly controlled, otherwise it will directly affect the measurement accuracy and service life of the transmitter.
1 RCP level measurement and split K1 differential pressure transmitter
1.1 RCP level measurement
The level measurement of the reactor coolant system (RCP) is divided into the measurement of the pressure stage and the measurement of the pressure relief stage. The liquid level in the RCP pressure stage is measured by the supplied split K1 differential pressure transmitter and is divided into the level measurement under normal hot operation conditions and the liquid level measurement under the water loss accident during the primary circuit.
Under normal hot working conditions, the reactor pressure vessel is full of water with an average temperature of 314°C and a pressure of 15.5 MPa. The entire RCP system has only vapor space above the regulator, and the RCP water level is equivalent to the regulator water level. Regulator water level sensor RCP007, 008, 011MN measurement, signal accuracy, for reactor protection system and regulator water level adjustment system [1].
In the case of one-loop water loss accidents, the RCP level may drop directly below the reactor core and monitor the core flooding condition using four pressure vessel water level gauges RCP090, 091, 092, and 093MN, for a total of 6 differential pressure transmitters. A, B series, each column 3, as shown in Figure 1.
1.2 Split K1 Differential Pressure Transmitter
The transmitter is a split type differential pressure inductive type and consists of a high-voltage isolation module, a low-voltage isolation module, a transmission unit, a signal processing drawer, etc. [2]. Figure 2 shows the working principle of the split-type K1 differential pressure transmitter.
1.3 JUV Vacuum Assembly
The transmitter uses a special tool JUV for vacuuming and filling. Evacuation refers to pumping the vacuum level of the transmitter and Class A water to the required value to avoid pressure transmission, level measurement accuracy, and response time due to air bubbles between the transmitter and the isolation module. Liquid filling means that after the degree of vacuum has been reached, type A water is injected into the transmitter according to the specified operating procedure and filling container. The JUV structure is shown in Figure 3.
2 Installation of Split K1 Pressure Transmitter
The installation work of the split type K1 pressure transmitter mainly includes prerequisite check, calibration of transmission module, sensor vacuum and liquid filling, sensor no bubble verification test and static pressure verification test.
2.1 Prerequisite check
The first task is to check on-site installation conditions and check the main work sequence.
(1) Referring to the drawings, check and measure the installation route of the capillary of the transmitter, the installation of the capillary bridge and the mounting position of the transmitter bracket.
(2) Check the installation of the separation area in the installation room, air conditioning and dehumidifier settings, scaffolding, temporary power supply, and temporary lighting.
(3) Apply for transmitter components and professional tools: vacuum pump assembly (JUV) and simulation tester (JUS).
(4) Preparation of Class A decontamination water, compressed air, hygrometer, capillary sealant, bolt anti-biting agent, anhydrous alcohol and other consumables.
2.2 Isolation Block Inspection and Transmitter Calibration
According to metrology regulations, calibration is performed before the transmitter is installed. Split K1 transmitters must be calibrated before installation. The flow is as follows. (1) Isolation Module Check: Check if the diaphragm is deformed and there is foreign matter in the chamber. (2) Transmitter calibration: Perform zero and full-scale calibration. (3) Linearity test: The linearity is checked and the linearity is higher than 98.5% as qualified.
2.3 Vacuum and liquid filling
Vacuum pumping and liquid filling are the core processes in transmitter installation and directly relate to the measurement accuracy and service life of the transmitter. The workflow is as follows.
(1) The transmitter low-voltage isolation module LP and the high-voltage isolation module HP are capillary-connected to the sensor's low-voltage "-" and high-voltage "+" terminals.
(2) LP vacuum and liquid filling: loosen the ball screw on the LP moderately, connect the filling hose to the LP filling connector and the JUV filling connector, and connect the vacuum gauge on the low pressure side of the sensor. LP continues to pump vacuum continuously for 4 hours for regulator LP and 24 hours for LP.
(3) The JUV is connected to the sensor, and the vacuum gauge is connected to the JUV. HP continues to pump vacuum for 36 hours.
2.4 Verification test
During evacuation, the Class A water and transmitter in JUV Tank1 cannot be fully evacuated, and the seal between the isolation module, capillary tube, and sensor may leak. To ensure high accuracy of the split K1 transmitter, Sensitivity and reliability must be verified on the volume and sealing performance of the bubble in the transmitter.
After the filling is completed, a bubble-free verification test and a static pressure test are specifically set to verify the filling result. The bubble-free verification test is used to determine whether or not vacuuming and filling are acceptable.
2.4.1 Bubble-free verification test
The bubble-free verification test uses a syringe to pressurize the low pressure side of the transmitter. The measurement of the syringe to the LP container changes the actual volume change V2 reflected by the V1 and transmitter output values, and finally calculates, analyzes, and compares the V1 and V2 relationships. Verify the total bubble size between the transmitter LP/HP and the sensor.
Figure 4. Schematic diagram of a bubble-free verification test. The bubble value of all split type K1 pressure transmitters of a nuclear power unit determined by the no-bubble verification test was less than 0.1 mL, and all qualified passed [3].
2.4.2 Static pressure test
The split K1 differential pressure transmitter is directly connected to the primary circuit. In order to ensure the integrity of the seal boundary of the primary circuit and the reliable operation of the transmitter, the transmitter must be hydrostatically tested. Hydraulic pressure test diagram 5.
All split type K1 pressure transmitters of a nuclear power unit were all qualified in the static pressure test [3].
2.4.3 Commissioning Check Results
After the transmitter is installed, the commissioning team conducts on-site verification. The split type K1 differential pressure transmitter has passed all calibrations and is stable and reliable in the hot test process. The calibration record is shown in Table 1. The differential K1 differential pressure transmitter calibration record [4].
3 Problems and Optimization Solutions During Installation
3.1 Installation Problems
The problems encountered in the installation process of the split K1 differential pressure transmitter for measurement of the pressure vessel and voltage regulator of a nuclear power unit are as follows:
(1) The nuclear island plant ventilation system is often not available. The on-site working environment is harsh and the temperature is often above 40 °C and humidity above 80%. The vacuum pump will continue uninterrupted at a temperature of 25 °C and a humidity of 50% to reach the target value (eg HP 0.02 mbar). The fact that the on-site environment is difficult to control results in multiple failures in vacuuming, the vacuum pump's working efficiency is degraded, and the schedule delay affects the on-site schedule.
(2) The transmitter rack is installed in the KCS801-804AR nuclear small three boxes. The rack and cabinet are purchased separately. The specification book does not consider the boundary interface, there is no matching special terminals.
(3) NNSA witnessed the installation of the split K1 differential pressure transmitter and asked questions about the process flow and quality control of the installation process. There is no on-site service qualification for equipment manufacturers' operating scope.
(4) There is dirt on the diaphragm of the transmitter isolation module and must be repaired. At the same time, after RCP091MN was evacuated and filled with liquid, the linear offset was found to exceed the standard when the air bubble verification test and the static pressure test were performed, and it could not be used.
(5) Transmitters The capillary bridges were not laid according to the construction drawings, and some wall penetrators were not installed, resulting in insufficient capillary length and direct capillary contact with the cement.
3.2 Optimization Program
3.2.1 Optimization of Prerequisite Preparation
(1) Before installing the split type K1 differential pressure transmitter, check the installation position and quality of the capillary bridge and the penetrating parts with the construction unit with reference to the construction drawings, and if necessary, carry out rectification.
(2) Before the supplier comes to the site, ensure that the transmitter's packaging is intact. The supplier unpacks and checks if the transmitter is qualified.
(3) Set up the on-site installation quality plan for the split-type K1 differential pressure transmitter, including the construction company, general contractor, and supplier, so as to ensure that the supplier's filling work at the site can meet the HAF604 regulatory requirements.
3.2.2 Optimization of the quarantine area
The follow-up unit established a tightly sealed isolation zone. At the same time, the isolation zone was equipped with one air-conditioner with good cooling effect and two dehumidifiers with good dehumidification effect. Strictly control the temperature and humidity of the environment and add air conditioners and dehumidifiers when necessary. As far as possible, fill the service time in winter or spring.
3.2.3 Vacuum and sampling optimization
Process optimization. (1) Change the JUV vacuum pump assembly to change its rubber connection to a metal sealing connection to improve the sealing performance of JUV and increase the vacuum efficiency. Change the structure of the JUV while vacuuming multiple transmitters in one room to shorten the duration.
(2) Regenerate the JUV every week to remove water vapor from the pump. The implementation of JUV regeneration was changed from the implementation of the nuclear island to the implementation of the office. The temperature and humidity of the office was controlled at 20 °C and 45% to improve the performance of the vacuum pump.
(3) A drying package is set at the suction port of the vacuum pump, and the air is sucked into the pump after the primary dehumidification of the drying package. At the same time, the insulation resistance wire is wound around the pump casing and heated and dehumidified if necessary.
(3) Vacuum sequence of a nuclear power unit is RCP007MN, 008MN, 011MN, 090MN to 094MN. In view of the in-situ water inflow and water pressure test on the primary loop, only the RCP090 and RCP091MN need to use the narrow range to monitor the primary circuit level. After the RCP090 and RCP091MN are fully charged, the remaining split type K1 transmitter is filled.
Optimization of work arrangements. (1) The evacuation time of the split type K1 differential pressure transmitter is relatively long, and HP needs to continuously vacuum for 36 hours. Arrange the vacuum plan rationally and make full use of the time period during the weekend for vacuuming.
(2) Optimize the manufacturer's split-type K1 differential pressure transmitter vacuum team, from 2 to 3 teams. The vacuum efficiency of the 3-person team is equivalent to two 2-person teams, saving labor and improving work efficiency.
4 Conclusion
Due to the large difficulties encountered in the field installation of the split K1 transmitter, it was once stagnant. Under the coordination of the author, through the efforts and improvement of each link, the difficulties of uncontrollable ambient temperature and humidity, unacceptable transmitter components, and tight schedules were overcome. Finally, a bubble-free verification test, a static pressure test, and a commissioning check were adopted. Ensure the quality and progress of the equipment to meet the requirements of hydrostatic test nodes.
This paper summarizes and optimizes the installation experience of a nuclear power unit, and has important reference significance for the follow-up unit of a nuclear power project and other nuclear power projects.
Goldshell Miner:Goldshell Mini-DOGE Pro,Goldshell LT Lite,Goldshell X5,Goldshell LT5,Goldshell LT5 Pro,Goldshell LT6,Goldshell Mini-DOGE
Goldshell Miner is an industry-leading technology company. The company was founded in 2017, we are focusing on high-performance miners and application fields. In the past few years, Goldshell Miner has successfully completed the R&D, mass production, and sales of multiple miners in LTC, CKB, HNS, Sia and other cryptocurrencies. The headquartered is based in Shanghai, Goldshell Miner has offices in Hangzhou, Hong Kong, Singapore,etc. The current R&D personnel account for more than 70% of the company. The core team has more than 10 years of experience in the integrated circuit field. Aiming to become an excellent blockchain computing power provider, and promoting the development of the industry, Goldshell has established an efficient operation system from algorithm research, batch production and delivery, which based on a strong core team and excellent system capabilities. Goldshell continuously improved the computing performance and competitiveness of products, to provide high-performance and high-reliable computing infrastructure and services for the development of digital economy. Especially our household miner-BOX series, allow more customers to join in the market since our product are small, quiet, affordable, and friendly to beginners so that everyone could start mining at home.
goldshell mining machine,goldshell ltc miner,goldshel lt5,goldshell mini doge pro,goldshell lt6
Shenzhen YLHM Technology Co., Ltd. , https://www.sggminer.com