Completed webinar talks

Answer of John Wise, NRC: NRC preparations for U.S. license extensions generally evaluated regulatory and technical issues on a 20-year basis (i.e., 40-60 years, 60-80 years), without an explicit consideration of the next period. However, the NRC maintains an LTO research program on materials ageing that is not limited to a specific operating period. In addition, the underlying regulatory framework across all periods has emphasized stability and predictability. The 40-60 year licensing process did not fundamentally change for the 60-80 year period, except for enhancements to recommended ageing management activities to address technical issues unique to the longer service life.

Answer of Garry Young, EPRI: It is a good practice to give some thought to the longer term when performing aging management reviews and plans for asset management.  One good example is in the area of time limited aging analysis (TLAA).  When evaluating metal fatigue, neutron embrittlement, environmental qualification, etc., consider performing the evaluation based on threshold values (e.g., max. number of fatigue cycles, fluence threshold, etc.) rather than time limits (e.g., 60 years).  The result is that the analysis that justifies 60 years (based on threshold values) may also be good for 80 years or even longer.  This makes the subsequent LTO evaluation easier since some of the work has already been done to justify the first LTO period.

Answer of Robert Krivanek, NRG: Ageing management is a process to manage ageing effects of SSCs important to safety and other in-scope SSCs  while LTO (long term operation) is a period of the NPP life cycle which is beyond original design life time. Ageing management is one of the main tools to demonstrate preparedness for safe LTO. Demonstration (and justification) of safe LTO typically includes also design aspects, human resources aspects and environment impact aspects which are covered but different processes.

Answer of Robert Krivanek, NRG: From technical perspective, an essential part of each ageing management programme according to the IAEA SSG-48 is an attribute 8 ‘Operating experience feedback and feedback from research and development’. This attribute should provide a ‘mechanism that ensures timely feedback of operating experience and research and development results (if applicable) and provides objective evidence that they are taken into account in the ageing management programme’. External operating experience has a key importance and the IAEA IGALL programme facilitates this area globally.

Unfortunately, changes in political decisions and national nuclear strategies belong in some countries to the category of ‘unknown uknowns’ and may have a serious impact on LTO decision making.

Answer of John Wise, NRC: Yes, there can be “unknown unknowns,” and those uncertainties should be considered in guidance or requirements for LTO. A few examples of how such technical issues may be addressed include the use of sampling-based inspections of components that are not expected to degrade and ongoing assessments to ensure that newly discovered ageing issues in plants promptly lead to enhancements to plant programs and are shared with the wider industry, as appropriate.

Answer of Garry Young, EPRI: Yes, this could happen.  Specific to management of aging effects, new information is always being collected via the inspections, monitoring, and surveillance activities.  The result may be the identification of previously unknown aging effects.  This new information (operating experience) is required to be addressed by a corrective action program, which requires an extent of condition evaluation and, if necessary, changes to the aging management program(s) to address the new information.  Because of this continuous review of operating experience and the use of an effective corrective action process, “unknown unknowns” are properly addressed for the life of the plant.

Answer of John Wise, NRC: The NRC oversight inspections of nuclear power plants address such concerns by verifying that age-related degradation is being promptly identified, addressed, and considered in adjustments to plant programs to prevent recurrence, as appropriate. These plant practices become evident in reliable and available plant SSCs.

Answer of John Wise, NRC: The NRC provides guidance for safe operation in LTO; however, simply committing to following that guidance is not necessarily appropriate for each particular plant (checking the box is not sufficient). As a result, the NRC approval process for license extension includes an evaluation of plant operating experience and unique plant materials and service environments that would warrant a plant-specific approach to address ageing. Also, while plants are in LTO, NRC oversight inspections verify that plants are implementing their approved ageing management activities and that those activities are effectively identifying and addressing degradation.

Answer of Garry Young, EPRI: The U.S. process of renewing an operating license to allow for LTO involves a comprehensive safety and environmental review to ensure relevant issues (e.g., aging management issues) are addressed each time a license is extended.  The plant owner performs the initial safety and environmental review, submits the results to the regulator for an independent review, which includes provisions for public involvement and intervention.  This comprehensive and extensive evaluation and regulatory review ensures that LTO does not become a “box-ticking” exercise.

The US NRC is not required by agency regulations or US law to consult with organizations in either Canada or Mexico, and we have not had inquiries from either government on any license renewal actions.

My SALTO experiences have been as a reviewer of ageing management of mechanical SSCs. My experiences from plants on three continents (South America, Africa and Asia) have engendered a high level of respect and admiration for the technical proficiency and knowledge of the staff at the various plants. The overall quality of the plant documentation and the safety-focused attitudes of the staff at each site have been impressive to witness. The differences in regulatory approaches for LTO for these countries, as compared to the US license renewal approach, have been fascinating to understand. These experiences have reinforced to me the need for high levels of competence and commitment by plant staff as the first line of safety at plants.

The US NRC approach to plant safety is focused on maintaining the level of safety in plants. We accomplish this in part through implementation of the “Regulatory Process Essential Elements” identified in my slides. Separate from the license renewal review, plants are required to implement later editions of the American Society of Mechanical Engineers (ASME) Code Section XI every 10 years consistent with 10 CFR 50.55a.  The NRC does not regulate obsolescence issues per se, instead relying on performance-based safety and operability requirements to ensure that the plant is continued to operate consistent with its current licensing basis.

Borssele NPP still has access to a decent number of suppliers for safety-classified SSCs but for some SSCs it becomes challenging. So far this is solved on a case by case basis. Borssele NPP is now doing a project to set up a more structured obsolescence programme to reduce the risk as much as possible. However, Borssele NPP was not built on KTA standards but particularly on the Dutch “Stoomwezen” guidelines, supported by the 1968 ASME section III and addenda. Qualified structures and components needed the approval from Siemens and Stoomwezen for their quality assurance (Vorprüfung), based on Stoomwezen and generic German rules. ASME III was not used for qualification purposes. For some SSCs (later modifications), KTA standards are applicable. In the design phase of Borssele NPP, KTA standards were not in place or still in development.

In case that an SSC is produced under a different nuclear code or standard, a justification has to be made that the requirements of the original used code are also fulfilled. In case of a modification of the plant, the applicable standards are part of the modification plan which needs approval by the regulator. See also the last part of the answer on question 1.

Borssele NPP is thinking about using commercial grade SSCs in future. In the PSR which is done at the moment, a project is done to update the safety classification system to a system in line with the current standards. Particularly for electrical and I&C SSCs, current IEC standards (for instance IEC61226) give the possibility of using commercial grade SSCs for the lower safety classified equipment. Of course this will be reviewed in detail to make sure that these SSCs fulfill all the necessary requirements.

Yes, COMSY is used as a tool for ageing management not only to manage flow-accelerated corrosion which COMSY was originally developed for. Nowadays, COMSY contains several modules and comprises all aspects of ageing management. Several modules of COMSY have been used in Borssele NPP and in cooperation with Framatome GmbH, COMSY has been developed into Borssele NPP IT instrument for ageing management.

We were able to monitor realistic thermal loadings with FAMOS. It was possible to prove safe operation for almost all locations until 2034 without a need for any extra inspections or replacements. Environmental fatigue was also taken into account. A rather high usage factor for one location (attachment of a thermal sleeve) was calculated with taking into account environmental fatigue. Although this was not a safety issue, it was decided to perform ultrasonic testing of this location. No cracks were found.  

Time to develop an ageing management programme can differ very much because there are big differences among ageing management programmes. Some are really specific and some are quite comprehensive. The other thing is that in Borssele NPP case, the most of the ageing management activities were already in place and are now credited in an ageing management programme. In most of the cases, when the ageing management review was done, it took not so much time to develop an ageing management programme. The real work was in doing a sound ageing management review which in Borssele NPP case took about three years in close cooperation with NRG and Framatome. The scope of the ageing management process comprises about 50 systems and 10 000 of structures and components.

I only can say that also in the Netherlands people realize that all options are needed with regard to the future of energy and the climate. Nuclear energy is seen as a serious option. The government is now studying on the possibility of new built but also on the possibility to further operation Borssele NPP after 2034.   

First, I received SALTO missions at my own plant as an NPP team leader. This really helped us to rethink about the project and adapt to the latest standards. It was also very important for the management of the plant to realize that ageing management is very important and must be dealt with in a broad sense. Now, as a reviewer in SALTO missions at other NPPs I experience several benefits. Every time I perform such a mission, I reflect on the way we do it in Borssele NPP and this often leads to new insights. The principle of ageing management is everywhere the same, but it can be done in practice in different ways. As a reviewer, you can learn a lot from other plants not only on ageing management but also on other aspects of the business.   

Continuous improvement, new standards and obsolescence issues re very important for LTO. Improvement on safety including new safety standards are dealt within our 10-yearly PSR. This already resulted in very big safety upgrades of the plant. Technological obsolescence is also very important from the economical perspective and here we are looking for improvement. So far we managed this with measures on a project basis for specific problems. We are trying to go for a more proactive approach on this.