Final results of quality inspections of the pipeline components
In its statement of 4th May 2020, Nuclear Regulatory Authority of the Slovak Republic (UJD SR) informed the public about the ongoing inspection of pipeline components at Unit 3 of Mochovce NPP.
In abovementioned statement UJD SR informed the public about the following facts:
- the reason which led to the need to performed inspections of pipeline components,
- the methods used during the inspections,
- the scope of inspections and the application of a graded approach to inspections, which shall be carried out according to: “… the importance of components from the point of view of nuclear safety. For the most important components, every single piece will be inspected. In the case of minor samples, a percentage random sample of each delivery shall be inspected to cover each delivery and lot, and in the event of negative findings, the scope of the inspection shall be extended”,
- the current status of ongoing inspections,
- and on the inspection of the entire material testing process by UJD SR and the approach of UJD SR to non-conforming pipeline components (“if it is not possible to prove reliably enough the quality and properties of the materials used … such components will be replaced”).
UJD SR informed in another statement of 2nd September 2020, among others, about the course of the process of material inspections at Unit 3 of Mochovce NPP.
The process of material inspections and evaluation of the results of these inspections at Unit 3 of Mochovce NPP was completed in April 2021. Slovenské elektrárne, a. s., in cooperation with its suppliers, prepared the final Summary Report “Verification of the quality of specified deliveries of pipeline components used on classify equipment at Unit 3 of Mochovce NPP”. With the aim of transparency and objective informing of the public in the given matter, UJD SR publishes this report*.
Note: The summary report is available in the Slovak language only.
All quality tests of pipeline components at Unit 3, prescribed by the inspection methodology accepted by UJD SR, were performed.
The summary report “Verification of the quality of specified deliveries of pipeline components used on classify equipment at Unit 3 of Mochovce NPP” is intended primarily for the professional public (specialists of materials used in nuclear energy and specialists in the field of power engineering). The effort of the team of authors was to write it so that it clearly describes the course and results of inspections of materials at Unit 3 of Mochovce NPP and so that it can be read with understanding even by people who are not specialists in the field.
The summary report provides readers with data in the following structure:
- Reasons for inspecting pipeline components at Unit 3 of Mochovce NPP (Chapter 6).
- Information on the control methodology used with a view to explaining the scope of inspections and the use of a graded approach to inspections (Chapter 7).
- The methods used to verify the quality of the materials at the various stages of verification (Chapter 8). It is possible to assume that this chapter may be of interest mainly to the professional public. For the sake of completeness, it should be added that the testing was time consuming. The testing itself was preceded by the preparation of the test equipment – dismantling of the insulation and possibly also to build scaffolding, surface preparation, sampling for the given type of test and after testing – and re-installation of the insulation. From this point of view, the scope of work performed is extremely large.
- Summary of results of inspections/tests performed in Chapters 9 to 11.
- Evaluation of the results of the performed tests from the point of view of the applicability of the given pipeline parts at Unit 3 of Mochovce NPP (Chapters 12 to 17),
- Final evaluation of results (Chapter 18).
Key data on performed inspections of pipeline components at Unit 3 of Mochovce NPP:
- Total number of tested pipeline components: 3410
- Number of pipeline components for which insignificant deviations in their chemical composition from the recommended values defined in the technical conditions for the given steel brand were found: 293
Each such deviation was evaluated individually and it was confirmed that it doesn’t affect the final characteristics of the pipeline component. The probable cause of these insignificant deviations could be the course of further processing of metallurgical semi-finished products, unequal distribution of alloying elements in the production process, different method of measurement, statistical error of used measurements or use of secondary raw materials in metallurgical production (e.g. slightly increased content of Co and Cu). The measured values of the parameters of these piping components became part of their accompanying technical documentation. These parts were left installed in the Unit 3 technology after proper evaluation.
- Number of pipeline components for which a material brand other than that declared in the documentation (certificates) has been identified: 61
The most common case was the replacement of steel brand according to GOST 08Ch18N10T with steel according to EN X6CrNiTi18-10 with analogous properties and similar chemical composition. Analyses of chemical composition and mechanical properties of these pipeline components were performed in accredited laboratories. The identified parameters were included in the accompanying technical documentation. After a detailed evaluation, these pipeline parts were left installed in the technology of Unit 3 of Mochovce NPP as satisfactory. These pipeline components represent approximately 1.8% of the inspected piping components.
- Number of pipe parts that have been replaced: 12*
9 replaced pipeline components were made of low-alloy carbon steel. 5 of these pipeline components were replaced due to the finding of the substitution with a brand which is not certified for use on the Unit 3 of Mochovce NPP (material of the brand 21MnCr5 or 33NiCrMo14-5). In 4 cases, the use of an inappropriate brand was found (12 050 instead of P265GH). All 9 mentioned pipe parts were replaced by pipeline components made of certified materials. The 3 replaced pipeline components were made of austenitic steel and were replaced due to an unsatisfactory result of the chemical composition test and an unsatisfactory intergranular corrosion resistance test. Replaced pipe sections make up approximately 0.35% of the tested pipe sections.
* Note: the number of replaced pipe sections does not include those that had to be replaced due to the use of destructive testing methods.
UJD SR inspectors performed checks of the quality testing of pipeline parts at Unit 3 of Mochovce NPP on a daily basis. They checked compliance with the testing procedures and were kept informed on its results. In some cases, they performed their own reference measurements through technical support and guided the scope of testing in order to achieve the maximally conservative results.
The evaluation of the results of the quality tests of the material of the pipe parts of Unit 3 of Mochovce NPP was provided by acclaimed specialists in the field of materials of nuclear installations:
- For Slovenské elektrárne, a. s.: experts of the Institute of Materials and Machine Mechanics of the Slovak Academy of Sciences, experts of the Faculty of Materials Technology of the Slovak University of Technology, internal specialists of Slovenské elektrárne, material specialists and design engineers of suppliers of Slovenské elektrárne, a. s., specialists of Železiarne Podbrezová and Authorized Legal Entities (Technical Inspection),
- For UJD SR: experts of the University of Žilina and internal specialists of UJD SR.
The current results indicate that some measures will need to be taken:
- to improve inspections in the process of production and processing of metal products before their delivery to the customer; the aim is that the documents issued to prove the quality and characteristics of the products are credible and that the characteristics of the pipe parts are identical to those declared,
- to introduce additional inspections of piping parts before their acceptance at the customer and also before their installation in technological units.
Any questions on the quality control of pipeline parts at Unit 3 of Mochovce NPP and on the final Summary Report “Verification of the quality of selected supplies of pipeline parts used at selected facilities at Unit 3 of Mochovce NPP” can be sent to UJD SR by e-mail (email@example.com) or in writing to address of UJD SR.
The final Summary Report “Verification of the quality of selected supplies of pipeline parts used at selected facilities at Unit 3 of Mochovce NPP” contains sensitive information in terms of their definition, which is given in § 3 para. 16 of the Atomic Act. Such documentation shall be made available after the exclusion of sensitive information. UJD SR removed sensitive information from the Summary Report as follows:
- title page: names of employees of Slovenské elektrárne, a. s., and their suppliers,
- page no. 31: the numbers of operating systems.
Removed sensitive information has no effect on the comprehensibility of the text. The removal of sensitive information was performed in accordance with the UJD SR Directive on the identification and removal of sensitive information, criteria L1 and T3. The UJD SR Directive on the identification of the removal of sensitive information is published on the UJD SR website. Access: UJD SR Directive on the identification of the removal of sensitive information