Reactor Harmonisation Working Group (RHWG)

The Reactor Harmonization Working Group (RHWG) is mandated by WENRA to develop a harmonized approach to nuclear safety of operating Nuclear Power Plants (NPPs). To achieve this, the RHWG has developed the WENRA Safety Reference Levels (SRLs) for Existing Plants. The SRLs are agreed by the WENRA members. They reflect expected practices to be implemented in the WENRA countries.

In addition, the RHWG undertakes work in the following areas:

  • SRLs for Existing Plants
  • Annual Review of Implementations of SRLs in National Regulatory Framework
  • Revision of SRLs for NPPs
  • Topical Peer Review (TPR)
  • Production of Guidance on technical areas such as, Practical Elimination and Long Term Operation (LTO)
  • Applicability of SRLs to Small Modular Reactors and New Reactors

Safety Reference Levels for Existing Plants 

In 2006, the RHWG published its first revision of Safety Reference Levels (SRLs) for operating nuclear power plants (NPPs). The SRLs were then revised in 2014, after the TEPCO Fukushima Dai-ichi nuclear accident to take into account the lessons learned, including the insight from the EU stress tests. Most recently, in 2020, the RHWG has revised the SRLs to addresses issues not revised in the 2014 revision.

As the WENRA members have different responsibilities, the emphasis of the SRLs has been on nuclear safety, primarily focussing on the main safety functions for ensuring the integrity of the reactor core and spent fuel. The SRLs specifically exclude nuclear security and, with a few exceptions, radiation safety.

As SRLs have been established for greater harmonization within WENRA countries, the areas and issues they address were selected to cover important aspects of nuclear safety where differences in substance between WENRA countries might be expected. They do not seek to cover everything that could have an impact upon nuclear safety or to form a basis for determining the overall level of nuclear safety in operating NPPs.

Given the various regulatory regimes and range of types of plants (Pressurised Water Reactor (PWR), Boiling Water Reactor (BWR), CANDU and gas-cooled reactors) in operation in WENRA countries, the SRLs do not go into legal and technical details.

There are significant interactions between some of the issues and hence each issue should not necessarily be considered self-standing and the SRLs need to be considered as a whole set.

Annual Review of Implementation of SRLs in National Regulatory Framework

WENRA members made a formal commitment to implement these SRLs into their national regulatory framework so that, in time, these SRLs are actually implemented at the nuclear power plants.

Since 2011, RHWG has reported to WENRA on the progress made towards harmonization in WENRA countries, specifically on implementation of SRLs into each national regulatory framework. To this end, RHWG developed a yearly summary report – a one-page factsheet with quantitative status – restricted to WENRA. The implementation reports are publicly available and can be found at the end of the webpage.

Revision of SRLs for NPPs

WENRA is committed to continuous improvement of nuclear safety. To this end WENRA is committed to regularly revising the SRLs when new knowledge and experience are available. The 2014 revision, was after the TEPCO Fukushima Dai-ichi nuclear accident to take into account the lessons learned, including the insight from the EU stress tests.

The 2020 revision of the SRLs addresses issues not revised in the 2014 revision. Reviews against changes in knowledge, international standards and other factors have identified the need to introduce the notion of leadership into Issue C (Leadership and Management for Safety) and obsolescence into Issue I (Ageing Management), which also addresses the outcome of the recent ENSREG Topical Peer Review on the topic. There was also a need to complete the hazards to be addressed in the safety demonstration. To achieve this Issue S (Protection against Internal Fires) has been extended to cover all internal hazards (Issue SV), and Issue T (Natural Hazards) has been extended to address all external hazards (Issue TU).  All other issues remain unchanged from the previous version.

By issuing the revised SRLs WENRA aims at further convergence of national requirements and safety improvements at NPPs in WENRA member countries, as necessary.

Topical Peer Review

The European Union’s Nuclear Safety Directive 2014/87/EURATOM (NSD) requires the member states to undertake topical peer reviews (TPR) every 6 years with the first starting in 2017.

For each review the directive requires the following:

(a) a national assessment is performed, based on a specific topic related to nuclear safety of the relevant nuclear installations on their territory;

(b) all other Member States, and the Commission as observer, are invited to peer review the national assessment referred to in point (a);

(c) appropriate follow-up measures are taken of relevant findings resulting from the peer review process;

(d) relevant reports are published on the above-mentioned process and its main outcome when results are available.

The member states, acting through the European Nuclear Safety Regulators Group (ENSREG), have decided that the topic for the first topical peer review is ageing management. The Technical Specification for the TPR 2017 can be found here.

Production of Guidance on technical areas

The RHWG considers relevant regulatory challenges and opportunities. As such, the RHWG has produced guidance which has been approved by its members. A sample of the guidance reports are presented below. For a full list please see the web-links at the end of this page.

Long Term Operation (LTO)

RHWG has also discussed about the safety aspects of continued operation of nuclear power plants longer than foreseen by their original design (this is referred to as “long term operation” or LTO). WENRA published in 2011 an overview of the LTO practices in WENRA countries. The report discusses also the link between the periodic safety review and LTO. 

Practical Elimination Applied to New NPP Designs

This report provides a common understanding of the approach to demonstrate the avoidance of early releases and large releases by using the notion of practical elimination. This notion is widely used in this context, inter alia by WENRA and IAEA. The report applies to new nuclear power plants. It deals exclusively with nuclear safety aspects. Existing plants and other nuclear installations, as well as security aspects, are outside its scope.

Periodic Safety Review (PSR)

One of the key aspects of nuclear safety and continuous improvement is the periodic safety review (PSR). According to the WENRA SRLs, PSRs shall be made periodically, at least every ten years. The review shall confirm the compliance of the plant with its licensing basis and any deviations shall be resolved. In addition, the review must consider any issues that might limit the future life of the facility or its components and explain how they will be managed.

In light of the accident in Fukushima, in 2013 the RHWG presented a position paper regarding PSRs taking into account the lessons learned from the accident. 

Applicability of SRLs to Small Modular Reactors and New Reactors

The RHWG considers the relevant applicability of SRLs to New NPPs and SMRs.

After the RHWG RLs were published for the existing NPPs, WENRA initiated work in new reactors. WENRA tasked RHWG to define and express a common view on the safety of new reactors, so that:

  • new reactors to be licensed across Europe in the next years offer improved levels of protection compared to existing ones;
  • regulators press for safety improvements in the same direction and ensure that these new reactors will have high and comparable levels of safety;
  • applicants take into account this common view when formulating their regulatory submissions.

In addition, this common view could provide insights for the periodic safety reviews of existing reactors.

In 2009 WENRA published a statement concerning the WENRA Safety Objectives for new nuclear power plants, followed by a WENRA statement on these objectives in 2010. As a follow-up to the WENRA statement, the RHWG presented a report outlining safety objectives for new NPPs in 2013. Further information is included below.

Safety Objectives for NPPs

The safety objectives for new reactors have been proposed on the basis of the IAEA Fundamental Safety Principles and of a review of the existing relevant documentation. These safety objectives are formulated as expected improvement compared to existing reactors, which is in line with the commitment of WENRA members to continuously improve safety. They are formulated in a qualitative manner, so that they can be more easily understandable by the public.

Safety of New NPP Designs

The RHWG produced a Report on Safety of new NPP designs. This was published by WENRA in 2013. This report (Booklet) provides some more detail to support a practical approach on how to achieve the safety level set by the objectives and the lessons learnt from the Fukushima Daiichi accident.

As almost ten years have passed since, it has been considered necessary to identify possible need for revising these objectives. Therefore, the RHWG has completed a review of the need for a revision.

Upon completing its review, the RHWG has not found a real need to modify either the Safety Objectives or the Booklet.

Report on the Applicability of the SRLs for Existing Reactors to SMRs

WENRA RHWG established in May 2019 a subgroup dedicated to SMRs. The task given to the group was to evaluate the impacts of different safety features of SMRs on the Safety Objectives for new NPPs. However, when considering the wide variety of SMR designs currently under development, it is not easy to identify safety features that would be common to all the designs. Instead, the group considered generic design features and features of different deployment schemes of the new concepts that may affect the applicability of the Safety Objectives.

The conclusion is that the Safety Objectives are applicable to SMR designs, including evolutionary LWR (Gen III+) and Gen IV technologies. Widening the scope of Safety Objective O5 to also cover safeguards would be beneficial. O5 obliges to design and implement safety and security measures in an integrated manner.