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Ultrasonic Inspections of Reactor Pressure Vessels in Slovakia Author: Mr. V.Chmelik Co-Author: Mr. G.Engl Contact

1. Reaktortest - Company profile

Reaktortest (company with limited liability) was established in 1991 as a joint venture, its founders are the Slovak utility Slovenské elektrárne a.s.(SE) (Slovak Power Plants, joint stock company) and Siemens' Power Generation Group (KWU). Reaktortest inspects the integrity of reactor pressure vessels (RPV) type VVER-440 and VVER-1000 and other primary circuit components with state of the art equipment and methods.
The Slovak share of the work consists of newest equipment supplied by Siemens AG and operating personnel for in-service inspections. Siemens´ share represents complementing measuring and evaluation instruments with controlling, supervising and evaluating personnel. For the advantage of our customers, Reaktortest is thereby able to combine advanced international technologies and international required standards on quality with highly competitive economic conditions. The main scope of activities of REAKTORTEST consists of monitoring the RPV by means of:

• ultrasonic testing
• eddy current testing
• visual inspections
• extraction of material samples
The evidence of our successfull cooperation shows the enclosed list of Siemens - Reaktortest VVER RPV inspections (Tabl. 1).

YEAR	NPP	SCOPE	NR
1980	Loviisa 2	ET-Examination of the RPV-cladding incl. nozzles,	1
		UT-Examinations of the welds and nozzles
	Loviisa 1	ET-Examination of the RPV-cladding incl. nozzles with	1
		repair -grindings, UT-Examination of the welds and nozzles
1982	Loviisa 2	ET-Examination of the RPV-cladding incl. nozzles	1
		UT-Examination of the welds and nozzles	1
1986	Loviisa 2	ET-Examination of the RPV-cladding	1
		UT-Examination of the welds and nozzles	1
1987	Loviisa 1	UT-Examination of the RPV incl. emergency core cooling nozzle	1
	Greifswald 1	UT-Examination of the welds and nozzles, TV-Inspection 1
1988	Loviisa 1	ET-Examination of the RPV-cladding, UT-Examination of the nozzle edges	1
	Greifswald 3	UT-Examination of the welds and nozzle edges	1
	Greifswald 1	UT-Examination of the welds and nozzle edges, previous	2
		and after heattreatment incl. grinding and erodiation
	Greifswald 5	UT-Examination of the welds and nozzle edges	1
1989	Greifswald 1	UT-Examination of the RPV-head welding	1
	Greifswald 2	UT-Examination of the RPV-head welding	1
	Greifswald 3	UT-Examination of the RPV-head welding	1
	Greifswald 4	UT-Examination of the welds, nozzles edges and cladding	1
1987	Loviisa 1	UT-Examination of the RPV incl. emergency core cooling nozzle	1
	Greifswald 1	UT-Examination of the welds and nozzles, TV-Inspection	1
1988	Loviisa 1	ET-Examination of the RPV-cladding, UT-Examination of the nozzle edges	1
	Greifswald 3	UT-Examination of the welds and nozzle edges	1
	Greifswald 1	UT-Examination of the welds and nozzle edges, previous	2
		and after heattreatment incl. grinding and erodiation
	Greifswald 5	UT-Examination of the welds and nozzle edges	1
1989	Greifswald 1	UT-Examination of the RPV-head welding	1
	Greifswald 2	UT-Examination of the RPV-head welding	1
	Greifswald 3	UT-Examination of the RPV-head welding	1
	Greifswald 4	UT-Examination of the welds, nozzles edges and cladding	1
1990	Greifswald 2	UT-Examination of the welds and nozzle edges	2
		previous and after heattreatment incl. grinding and erodiation
	Greifswald 3	UT-Examination of the welds, nozzle edges and cladding,	2
		previous and after heattreatment
	Greifswald 3	ET-Examination of the RPV-claddings, previous and after heattreatment	2
1992	EBO 1	UT/ET-Examination of the RPV and its bolts and nuts,	1
		of the threaded holes RPV-flange and dome section, visuale TV-Inspection
	EBO 4	UT/ET-Examinationof the RPV and its bolts and nuts,	1
		of the threaded holes RPV-flange and dome section, visuale TV-Inspection
1993	EBO 2	UT/ET-Examination of the RPV and its bolts and nuts,
		of the threaded holes RPV-flange and dome section,	2
		visuale TV-Inspection , previous and after heattreatment
	EBO 1	UT/ET-Examination of the RPV and dome section,	2
		visuale TV-Inspection , previous and after heattreatment
1995	Paks 1	UT/ET-Examination of the RPV, ligaments and dome section,	1
		visuale TV-Inspection, Examinations of the SG
	EBO 3	UT/ET-Examination of the RPV and dome section, visuale TV-Inspection	1
1996	EBO 4	UT/ET-Examination of the RPV and dome section, visuale TV-Inspection	1
	Paks 2	UT/ET-Examination of the RPV, ligaments and dome sections,	1
		visuale TV-Inspection, Examinations of the SG
	EBO 2	UT/ET-Examination of the RPV and dome section, visuale TV-Inspection	1
1997	EBO 1	UT/ET-Examination of the RPV and dome section, visuale TV-Inspection	1
	Paks 3	UT/ET-Examination of the RPV, ligaments and dome sections,	1
		visual TV-Inspection, Examinations of the SG
1998	EMO 1	Pre Service Inspection	1
	Paks 4	UT/ET-Examination of the RPV, ligaments and dome sections,	1
		visual TV-Inspection, Examinations of the SG
1999	Paks 1	UT/ET-Examination of the RPV and ligaments, visual TV-Inspection	1
	EBO 3	UT/ET-Examination of the RPV, visuale TV-Inspection	1
	EMO 2	Pre Service Inspection	1
	EBO 2	UT/ET-Examination of the RPV, visuale TV-Inspection	1
2000	Paks 2	UT/ET-Examination of the RPV and ligaments, visual TV-Inspection	1
	EBO 4	UT/ET-Examination of the RPV, visuale TV-Inspection	1
Table 1: Non-destructive UT/ET-Examinations of WWER-RPV performed by Siemens, since 1992 by Reaktortest/Siemens

2. Inspection of a VVER 440 Reactor Pressure Vessel

We present examination of the reactor pressure vessel type VVER-440 as an example of the scope of inspections performed in compliance with the requirements of the regulatory bodies and the operator. The main examinations contain the UT/ET Inspection of :

• the reactor pressure vessel shell areas
• the reactor nozzles and nozzle inner radii
• the threaded holes, bolts and nuts
The reactor pressure vessel inspection areas that are all welds and adjoing cladding, are determined mostly for ultrasonic testing. The same testing areas are foreseen for ET and the Visual Inspection. The examination scope is complemented by the inspection of bolts, nuts and the threaded holes in the flange area. Technical descriptions specifying the parameters of the applied technology as well as the proceeding of Reaktortest are stipulated for each type of examination performed to the scope agreed upon with the customer. They are presented in the next paragraphs.


2.1 BASIC SYSTEM DESIGN
The basic reactor pressure vessel inspection system design is prepared for simultaneous UT /ET testing. Data of the reactor pressure vessel are acquired by UT/ET probes and a video system located on the support of the Central Mast Manipulator (CMM5). The data are recorded and evaluated in the DEA container.
The control unit SIMACON 5 allows the staff for remote control of CMM5.
The position data provide continuous information about the actually tested position.


2.2 CMM5 CENTRAL MAST MANIPULATOR
It is the biggest component of the inner surface examination of the reactor pressure vessel. It is placed directly in the reactor building during the inspection and the mast is standing in the centre of the reactor vessel.
Based on the type of reactor vessel inspection the same inspection systems may be mounted on the support, like nozzle inspection system, shell section inspection system, bottom head inspection system etc. There are probes on the end effectors, which have to be selected in compliance with the examination type and location.
The extent of movement of the CMM5 manipulator in its function is adaptable to the requirements of the inspection, i.e. height and diameter of the reactor pressure vessel, its circular or nozzles cross-section. The extent of movement of the CMM5 and its adaptability to these different tasks allows its utilisation also for other types of reactors than that of type VVER.


2.3 UT Equipment
Ultrasonic examination is performed by means of a set of equipment necessary for the generation and reception of ultrasonic signals, including the connecting cable and data aquisition and evaluation equipment. The main components of the ultrasonic equipment are:


• US examination system SAPHIR
• 16-element phased-array in combination with standard ultrasonic probes
• DATA EVALUATION AND AQUISITION (DEA) equipment in a separate container outside the reactor building
More details , as well as a main topic of presentation, will be given in the point 3.


2.4 TV System
The inner surface of the reactor vessel is visually inspected with a high-resolution scanning and recording video technique. The main components of the visual inspection system are:


• a CCD video camera with colour monitor
• video-recorder and
• control unit.
The camera motion is controlled internally from the control board, eventually externally from the DEA container. The visual inspection is continuously recorded in compliance with the customer specified inspection areas.


2.5 Eddy current testing equipment
The eddy current testing is performed by a modular assembly of equipment for scanning, aquisition and evaluation of data of the surface of the tested areas. The main components for the eddy current testing are:


• probes
• control unit
• the ET data acquisition and evaluation equipment.
Special small manipulators with ET equipment are used for inspection of connecting elements.


2.6 DEA container
The equipment for the external control of the CMM5 and the complete recording and evaluating centre of the reactor pressure vessel inspection data are situated in the DEA container outside the reactor building.

2.7 Documentation
Once the inspecton is finished, REAKTORTEST will elaborate a detailed documentation covering the performed testing for the purpose of long-term filing of the inspection data:


• Interpretation as well as documentation and the resulting analysis of the components are performed according to criteria valid in operation.
• The documentation will include work documentation as colour video records on video tapes, records of all UT-examinations on MOD´s, optionally all records of ET-examinations etc.
• Evaluation comparing the inspection results with the results of previous examinations.
• Preliminary report and Final report.

3. Experience with ultrasonic inspections by phased array method

Since 1992 Reaktortest´s offer of equipment has developed continually with the development of technology, particularly in the area of the UT examination systems, supplied by our partner Siemens KWU. In the years 1992 and 1993 ultrasonic examinations were performed by the system TIMLOK with the individually adjustable monitoring gates. Then we applied the system ALOK for the purpose of acquiring a more complete sonic information about the presence and characteristic of an eventual defect. Since the year 1997 we have innovated the offered examination equipment by the examination system SAPHIR which combines the advantages of the ALOK system with the latest evaluation software and with application of the phased array probes with a variable angle of incidence, controlled by electronic activation of the individual elements - usually 16 elements by Siemens phased array probe design. This new equipment has reduced the inspection time and provided more detailed and accurate examination information.
In this connection, it is certainly most interesting and with reference to the above - mentioned claims even demonstrable to compare individual examinations and theit results. However, the comparison of all in-service inspections (ISI) of every NPP´s reactor is a matter of extensive data and beyond the scope of this presentation. Therefore we will state the comparison of the results of only one examination place and that is a shell weld between nozzle rings of RPV, with 4-years ISI period on NPP Bohunice Unit 1 (Tab.2).


Indication Number				Reflector Size (FBH , mm)				Notice
ISI´85	ISI´88	RT´92	RT´97	ISI´85	ISI´88	RT´92	RT´97	to ISI´97 by Reaktortest
15	62	3	18	7,1	5,7	4,8	7,5
	60	3	18		7,1	4,8	7,5
	61	1	16		5,0	3,0	2,8	voluntarily registred
		2	17			3,8	3,3	voluntarily registred
		4	19			3,8	3,5	voluntarily registred
		5	20			4,0	4,2	voluntarily registred
		6	21			3,8	3,5	voluntarily registred
		7				3,0		97 under registration level
		8	14			4,8	7,5
		9				3,0		97 under registration level
Table 2: Comparison of ISI Results 1985 - 1997, Weld Nr. 0.1.6 NPP EBO 1

According to the above - mentioned comparisons it is obvious that reproducibility of the examinations is very good and does not exceed the expected tolerance. It is a consequence of using different techniques of examinations, probes, sensitivity etc. between the individual inspections. The accomplished comparative measurements prove excellent continuity of the inspections after the change of the inspection company - the previous supplier performed the ISI in the years 1985 and 1988; Reaktoertest in 1992 and 1997; the next ISI is scheduled in the year 2001. Some differences in individual examinations are a result of the impossibility to capture each reflector during the renewed examinations precisely from exactly the same direction and point of incidence bearing in mind that even a small change of examination parameters has a considerable influence on the evaluated reflectors.

Conclusion

In general neither new indications have been found nor a relevant increase of the known indications has been recorded - in other words, the quality of reactors and the safety of the operation of the NPPs in the Slovak Republic is proved and still being proved on the international, independent and accredited level.

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