 ·Home
·Table of Contents
·Methods and Instrumentation | Development of Ultrasonic Measurement Device for the Sagging of Calandria Tubes and Liquid Injection Shutdown System Tubes
Chul Hoon Park, Jong Po Lee, Hyung Taik Lim, Byung Guk Um,
Research Institute of Korea Advanced Inspection Technology (KAITEC)
Tae Ryong Kim, Suk Man Sohn, Jun Shin Lee,
Korea Electric Power Research Institute, Korea Electric Power Corporation
Contact
|
ABSTRACT
The gaps between calandria tubes (CT) and liquid injection shutdown system (LISS) tubes in pressurized heavy water reactors (PHWR) are very important because it is known that the tube saggings take place with plant operation time. The problems may come not only from the saggings but also from the different saggings in between CT and LISS tubes. Therefore, sagging measurements for both tubes and their proximities are needed to verify that CT and LISS tubes do not contact within the service lifetime. In order to measure the saggings and the gaps between CT and LISS tubes, ultrasonic measurement device was developed. This device is fed through the view port #1 and #2 and enables us to know actual positions of both tubes. The feature of this device is different from that developed in Canada which is inserted through LISS Tubes or horizontal flux detectors. Ultrasonic measurement data can be utilized to calculate tube saggings in different locations other than measuring locations.
INTRODUCTION
PHWR consists of many components such as calandria tubes, liquid injection shutdown system nozzles, and flux detectors. The gap between CT and LISS tubes is very important because they may contact each other and result in serious safety problems. Therefore, the equipment to measure the saggings and the gap was developed and applied to the actual measurements. This was done in Canadian plants, namely Bruce Nuclear Generating Station "A" and Point Lepreau Nuclear Generating Station (NGS).
The first technique is to insert an inspection probe assembly containing four ultrasonic probes inside LISS tubes[1-2]. The measurements were fed to a system computer that was programmed to convert the readings into compensated gaps. The second technique is to insert an inspection probe inside horizontal flux detector (HFD). These techniques have some advantages that the gaps between CT and LISS are measured directly, but some disadvantages that individual saggings of CT and LISS/HFD tubes are not measured, respectively. In the case of the first technique, if a flange exists within the straight LISS tubes, inserting an inspection probe is possible. If not, this is difficult unless design change and modification are made. In the case of the latter technique, a redundant and empty HFD can be used to insert an inspection probe for measurements. Four PHWRs, the Wolsong nuclear power plant (NPP), Unit 1, 2, 3, & 4 are now in operation in Korea. Unfortunately, PHWRs at the Wolsong site neither have a flange within the straight LISS tubes nor have a redundant HFD. Those techniques and equipment developed and applied to the PHWR such as Bruce "A" or Point Lepreau cannot be used in PHWR in Korea. Therefore, it is inevitable to develop a new system to measure saggings and the gaps of those tubes at the Wolsong nuclear power plants.
Fig 1: Distribution of CT, LISS, and view ports in PHWR |
Wolsong PHWR units have the following features. The number of calandria tubes is 380 and the lattice between CT is 11.25 inches. LISS tubes are horizontally installed and perpendicularly to the CT. In addition to these tubes, horizontal and vertical flux detectors are located in reactors. Fig. 1 shows CT & LISS tubes relative to the view port #1 & #2. In this paper, a new ultrasonic measurement system developed and applied to the field is introduced. This system is fed to view ports(#1 & #2) to get actual position values of CT and LISS tubes, thus saggings and gaps between them can be measured. It was successfully applied to the Wolsong NPP, Unit 1.[6-7]
ULTRASONIC MEASUREMENT SYSTEM THRU VIEW PORT
Measurement system consists of mechanical driving mechanism and ultrasonic data acquisition & analysis system as shown in Fig. 2. Any of the parts which is fed into the reactor must not be loosened. Thus, a guide tube which contains ultrasonic probe assembly and protects possible loose parts in it has been designed and fabricated. Ultrasonic probe assembly is attached to the end of mechanical driving units. Transducer assembly is controlled by either joystick or main computer.
Fig 2: The diagram of ultrasonic sagging and gap measuring systems |
Mechanical driving mechanism and UT probe assembly
Mechanical driving parts are driven up and down inside the guide tube installed through the view port and ultrasound is incident perpendicularly to the axis of the CT or LISS tubes, respectively. Ultrasound incident to the tubes is reflected back to the transducer and maximum reflection is obtained when ultrasonic beam reaches the tube center. Then, actual elevations of CT and LISS tubes are measured. Ultrasonic probes are immersion type and their characteristics are shown in Table 1.[3-5]
| Frequency
| Size
| 6 dB Bandwidth
|
| 2.25 MHz
| 15.6mm
| 20%, 24%, 33%
|
| Table 1: Ultrasonic transducers
|
AC servomotor was employed to control linear motion of ultrasonic transducer assembly using ball screw. Ball screw emits 720 counts per revolution and encoder signals and ultrasonic data are transmitted to the computer. These tubes are consisted of several pieces that enable UT probes to reach the lowest CT. Then, transducer positions are analyzed versus to the signal amplitude. Guide tubes have a guide flange which makes leakage minimum from the reactor. The length of ball screw is limited and the height from top of the view port to the reactor ceiling is not enough to encompass the total length of guide tubes.
Data acquisition hardware and software
Data acquisition system consists of ultrasonic pulser and receiver and analogue to digital converter. It includes multitasking and real time operation software by using Lynx operating system. In addition, TCP/IP LAN protocol is used. So, we can achieve 10Mbps data from data acquisition computer to data analysis computer. Data acquisition computer encompasses ultrasonic information with DAS. Data acquisition software transfers ultrasonic data with real time and stores them to optical and/or hard disk. Concurrently, ultrasonic signals and probe positions are displayed on CRT. A-scan, B-scan, and C-scan can be displayed by computer processing. The other features of the software for data acquisition and data analysis are as follows.
Fig 3: Data acquisition system and mechanical driving units |
- Ultrasonic data is received from 2 channel ultrasonic transducers,
- Acquired data is stored with real time to the optical and/or hard disk and these data can be used for reprocessing,
- UT probe position information and UT data can be displayed simultaneously with data acquisition,
- Acquired data can be analyzed and evaluated off-line.
- All the data can be printed out graphically
Fig. 3 shows the data acquisition system and mechanical driving units. The main program for data acquisition uses X/Motif window and provides graphics window interface. Users can select an appropriate window(s) and control system motion. Main program uses pull down menu.
All input and controls are carried out by "point & click". Main menu consists of "ultrasonic calibration", "ultrasonic examination", "signal analysis", "sagging analysis", and "system utility". Sagging analysis menu is the program to find out probe positions at peak amplitude which mean the elevations of actual CT and/or LISS tubes. Ultrasonic calibration program has the following functions.
- digitization of gated RF wave form
- A-scan display of selected RF or full wave form
- Input or control of all system variables
- Gain control by 0.5 dB
- Determination of sampling rate (maximum 100 MHz)
- Calibration of ultrasonic transducer
- System calibration
MOCK-UP TEST AND FIELD APPLICATION
In order to verify the accuracy of ultrasonic measurement system, a partial mock-up was designed and fabricated. The UT system was installed and tested to measure the CT and LISS tube positions. The position data obtained by ultrasonic measurement system was compared with physical measurements. The results are shown in Table 2. From the mock-up test, the errors are within 1 mm that we established the target of the accuracy. This new ultrasonic measurement device was applied to measure the saggings and the lattice between CT and LISS tubes of the Wolsong NPP, Unit 1. The results will be presented in this conference.[6]
| Tubes
| Location
| Number
| Physical data
| Ultrasonic data
| Errors
|
| CT
| Left
| 1
| 1338.0
| 1338.0
| 0.0
|
| CT
| Left
| 2
| 1623.5
| 1624.0
| 0.5
|
| CT
| Left
| 3
| 1908.9
| 1909.5
| 0.6
|
| CT
| Left
| 4
| 2193.5
| 2194.5
| 1.0
|
| CT
| Right
| 5
| 2479.2
| 2479.5
| 0.3
|
| CT
| Right
| 6
| 1337.7
| 1337.5
| -0.2
|
| CT
| Right
| 7
| 1622.9
| 1623.5
| 0.6
|
| CT
| Right
| 8
| 1908.5
| 1908.5
| 0.0
|
| CT
| Right
| 9
| 2194.2
| 2194.5
| 0.3
|
| CT
| Right
| 10
| 2478.7
| 2479.0
| 0.3
|
| LISS
| Right
| 1
| 1481.0
| 1481.0
| 0.0
|
| LISS
| Right
| 2
| 1767.0
| 1767.0
| 0.0
|
| LISS
| Right
| 3
| 2053.1
| 2052.5
| -0.6
|
| LISS
| Right
| 4
| 2336.7
| 2337.0
| 0.3
|
| Table 2: Mock-up test results (Comparisons of ultrasonic data with physical data) unit : mm |
CONCLUDING REMARKS
A new ultrasonic system measuring the saggings of CT and LISS tubes at CANDU reactors was developed. This equipment is fed through view port #1 & #2 from the top of reactor without any plant system design change or modification. Partial mock-up was designed and fabricated in order to verify that the accuracy of measurements is within the specified limit. It was confirmed that the errors of measurements for CT and LISS tubes using mock-up was
within ±
1mm. This ultrasonic measurement system was successfully applied to the Wolsong nuclear power plant, unit 1 in May 2000. The saggings of CT and LISS tubes can be measured periodically in order to verify whether possible contact takes place.
REFERENCES
- R. C. Abucay, K. S. Mahil and J.J Goszczynski, "Recent Experience in Ultrasonic Gap Measurement between Calandria Tubes and Liquid Injection Shutdown System Nozzle in Bruce Nuclear Generating Station," Proc. of 13th Int. Conf. on NDE in the Nuclear and Pressure Vessel Industry, Kyoto, Japan, 1995.5
- J. Goszczynski and A. B. Mitchell, "Development of Ultrasonic Measurement of Calandria Tubes/ Horizontal Flux Monitor Guide Tube Proximity in CANDU Nuclear Reactors,"
- Jong Po Lee, et al, "Development of Data Acquisition and analysis system for the nuclear vessel weld", Annual Report (KAERI/CM-379/99), KAERI, 2000.3
- Jong Po Lee, et al, "Improvement of remote control system of automatic ultrasonic equipment for inspection of reactor pressure vessel", Final Report (KAERI/RR-1936/98), MOST, 1999.12
- Jong Po Lee, et al, "Enhancement of the Automatic Ultrasonic Signal Processing System Using Digital Technology", Final Report (KAERI/RR-1941/98), MOST, 1999,11
- Tae Ryong Kim, et al, "Ultrasonic measurement of saggings of calandria tubes and liquid injection shutdown system tubes using newly developed device", IDN-65 in this Conference
- T. R. Kim, et al, Development of Measurement and Prediction Methods for Calandria Tube Sagging, Interim Report (TM.98NJ15.M1999.292), KEPRI, 1999.6
Fig 3: Data acquisition system and mechanical driving units