Austrian-Hungarian bilateral expert meeting on the site characteristics of the new nuclear power plant units

An Austrian-Hungarian expert meeting was held on February 15, 2022, at Austria's request, to discuss the site characteristics of the new nuclear power plant units, including the question of the fault. Based on the outcome of the event, it is the firm position of the Hungarian Atomic Energy Authority that the selected site is suitable for the construction of the new units. The authority is evaluating whether the technologies and plans to be used adequately address the site's specific characteristics as part of the ongoing construction licensing process.

The study, which was ordered by the Austrian government and analyzed the geological features of the new units' Paks site, was published in Austria in May 2021 and sent to the HAEA. On the initiative of Austria, the Hungarian Atomic Energy Authority hosted an Austrian-Hungarian expert meeting on the topic on 15 February 2022. In addition to the experts of the HAEA and the Supervisory Authority of Regulatory Affairs (the legal successor of the Mining and Geological Survey of Hungary and the government offices designated as state geological functions), the representatives and experts of Paks II Ltd., as well as the members of the Federal Environment Agency of Austria and their external (Austrian, German and French) experts participated in the event.

The Austrian study, despite the significant amount of documents taken into account, is based on not entirely complete information. On the other hand, significantly more documentation and information were considered during the elaboration of the HAEA's professional position (e.g. the complete documentation and – as required by law – external peer review of the Geological Research Program and its implementation, as well as the full documentation of the IAEA's "Site and External Events Design Review Service" (SEED) mission, etc.).

Regular expert discussions with Austria

In its international relations, the HAEA gives priority to bilateral relations with the authorities of neighbouring countries, especially the member states of the European Union. The Austrian-Hungarian bilateral cooperation dates back to more than three decades. During meetings held (at least) once a year, experts from the HAEA and the Austrian counterpart discuss current issues of mutual interest, such as the Paks II project.

Along this line, an Austrian-Hungarian bilateral (online) meeting took place twice last year (in April and October).

It is important to emphasize that Austria does not use nuclear power for electricity production and it does not support such projects in other countries. Respecting this, the HAEA informs regularly the Austrian counterpart and does its best to maintain an honest dialogue.

What is needed to be known about the Paks site

The Paks site is in an intraplate area, further away from the typical occurrence points of larger earthquakes, which are typically found at crustal plate junctions. It is one of Hungary's least seismic (earthquake-prone) areas, with loose sedimentary layers covering it. As a result of these characteristics of the site, it behaves very differently from areas where permanent surface displacement due to faulting typically occurs in terms of earthquake surface appearance and effects (e.g., Japan, California, New Zealand, etc.). This difference and these aspects must be taken into account during site investigation and evaluation. The loose sedimentary layers of the Paks site due to their damping effect are particularly advantageous in terms of surface displacements caused by earthquakes. However, due to the possibility of soil liquefaction, they pose a serious but manageable technical challenge to the planned facilities. Accordingly, the HAEA continuously analyses and evaluates the tests and plans of the related technical solutions and their implementation with special attention.

The focus is on issues concerning the fault

The Dunaszentgyörgy-Harta fault segment, which runs beneath the site, is active in neotectonic terms and on a neotectonic time scale, i.e. minor earthquakes occurred on this fault during the quarternary period of Earth's history (approximately 2.7 million years perspective). One of the main questions in the survey to confirm the new units' site license was whether an occasional earthquake on this fault segment could cause significant permanent surface displacement. Despite the fact that the Paks site was already one of the geologically best-surveyed area in the country, an extensive and multi-year survey program was conducted to justify the adequacy of the site for the regulatory decision. The survey was not limited to the data gathered at the Paks location. It covered a 50-kilometer radius and included connections to large, remote structures. Relying on the knowledge accumulated over the past thirty years, and using complex geological-geophysical examinations in the framework of the program, the section of the fault where the possibility of permanent surface, near-surface displacement could be assumed was identified at the site. This section was subjected to direct exploration via trenching excavation, and local deformations were discovered at the trenching excavation. Due to the conservative analysis and design approach formulated as a basic requirement in the nuclear industry, the local deformations identified at the site were modelled and taken into account as fault displacement despite the fact that results of the trenching assumed it only to be a local deformation. An analysis of the hazard of permanent surface displacement was also performed using conservative modelling approach as well. It was determined that no permanent surface displacement in the fault segment is expected, which could jeopardize the safety of the nuclear power plant to be constructed, or the nuclear facilities that are already operational there. The units are designed with significant safety margins arising from different loads, even when compared to the regulatory limit, allowing them to withstand a higher level of displacement than the conservatively assumed maximum. Therefore the nuclear power plant has to be protected against this hazard, too.

Examination of earthquake impacts is of utmost importance

A key issue is determining the potential effects of earthquakes as a source of hazard and protecting the units that will be built or operated from earthquakes. Instrumental measurements over the past nearly century have confirmed the Paks site in the Pannonian Basin's moderately earthquake-prone classification, with no significant seismic activity in the area.

Since the 1990s, extremely precise measurement data have been available in addition to historical earthquake data. The Paks site's monitoring stations were built with more advanced technology than those in the surrounding countries, and their sensitivity is still considered exceptional in the region. If there had been an earthquake caused by tectonic movements in the last few decades, the results of the measurements would have revealed it. These measurements are continuous (including right now) and are available to anyone in real time (www.foldrenges.hu).

Summary

Based on the examination of the Austrian study and the professional discussions with the Austrian party, it can be stated that no new, relevant information has emerged that would justify the review of the site license issued in 2017 or question its validity. The HAEA maintains its position that the site of the new nuclear power plant units complies with legal requirements and is thus suitable for the construction of the new nuclear power plant units, based on the measurements, the performed analyses and the submitted documentation.

During the ongoing construction licence procedure and the subsequent building permit procedures the authority will examine the adequacy of the specific technical solutions of the new nuclear power plant units to ensure that the technologies and plans to be used adequately address the specific characteristics of the site, such as the behaviour of the fault (which has been known for decades) and its impacts on the facility even during a possible earthquake.

The Hungarian Atomic Energy Authority's main task is to ensure the safe use of nuclear energy in Hungary, so meeting nuclear safety requirements is the highest priority in all new unit licensing procedures.