Design change management in the nuclear sector5 March 2015
A new report from the World Nuclear Association looks at mechanisms for utilities, vendors and the regulatory bodies to work together to support reactor design standardisation throughout a reactor fleet’s operational lifetime. By Barry Kaufer
In January 2007 the World Nuclear Association (WNA) established a working group to stimulate dialogue between the nuclear industry (including reactor vendors, operators and utilities) and nuclear regulators on achieving worldwide convergence of safety standards for reactor designs.
The Cooperation in Reactor Design Evaluation and Licensing (CORDEL) working group evolved from a group of experts discussing international standardisation in nuclear safety design and standards. It is now an established and recognised WG dedicated to analysing and forging common understanding in key areas of nuclear energy policy.
The CORDEL working group's mission is to promote the standardisation of nuclear reactor designs. This can be achieved only by the development of a worldwide nuclear regulatory environment where internationally accepted standardised reactor designs, certified and approved by a recognised competent authority in the country of origin, can be widely deployed without major design changes due to national regulations. In practice, this would mean that generic design certification and safety evaluations approved in the country of origin would be acceptable in other countries without the need to duplicate or repeat the entire design certification process.
A 'roadmap' in the CORDEL report, 'International Standardisation of Nuclear Reactor Designs,' published in 2010 describes a way forward:
- Share design assessment. Once a design is licensed in one country, the approving regulator should share information with other national regulators, conveying its full experience in the safety assessment of the design. If several regulators are concurrently reviewing the same design, they could form a collaborative network to discuss their assessment methodology and assessment results. This sharing process, which can be undertaken without any change in existing regulatory frameworks, may facilitate harmonisation of licensing standards and procedures.
- Validate and accept design approval. If a design is already licensed in one country and is subsequently proposed for other countries, the existing approval could be used by the other countries following a simplified validation procedure. This may require some adjustments in regulations and legislation.
- Issue international design certification. A procedure could be created by international agreement, whereby a design could be certified by a team of national regulators (from countries with a direct interest in the design). Under the agreement, participating countries would accept this certification. Alternatively, such international certification could be facilitated by a designated international organisation. National regulators would remain responsible for assessing the adaptation of the internationally certified design to the local circumstances, and for supervising construction, commissioning and operation.
Standardisation is a major tool to improve nuclear plant economics during design approvals, licensing and construction. It also has the potential to bring significant benefits to operational safety, based on the fact that there would be fleets of standard plants operating worldwide that could act as a international basis for experience exchange.
The standardised reactor design concept does not require everything to be identical. It means that the 'core' is the same in all projects that use the standardised design. The 'core' in this case refers to the global architecture of the plant and at least the nuclear steam supply system design and components.
Design change management
In 2010 the CORDEL working group organised a Task Force on Design Change Management (DCMTF). Its mandate was to analyse and determine potential enhancements to international institutional mechanisms in the industry in order to maintain standardisation throughout a standard fleet's lifetime. The enhancements should also reduce the potential for divergence in the design of current fleets of reactors that were originally of common design. DCMTF issued a number of position papers followed by a report on 'Design Change Management in Regulation of Nuclear Fleets,' published in 2012.
Further insights gained from discussions following publication showed a need to clarify the roles and responsibilities of utilities, owners and the regulatory body. A new edition of the report will be published in early 2015. The updated report considers the causes for design changes and the ability of responsible operating organisations to manage this process, including maintaining the underlying design knowledge, with the involvement of the plant's original vendor as needed. Significant elements in the new report include:
- A new look at the principle 'the operator is responsible for safety'. As a 'responsible designer' the vendor has an important role along with its involvement in the long-term design knowledge management, especially for a standardised fleet.
- Re-emphasis that the nuclear industry is responsible for knowledge management and design change within a standardised fleet. Consideration of the kinds of agreements between the utilities and the vendors.
- Reconsidering the roles played in the design change process by vendors, utilities, owners' groups, regulators and other international bodies, such as the World Association of Nuclear Operators (WANO).
- Recommendations to various industry stakeholders to support better cooperation in design change control.
Incorporating operating experience, feedback and safety reassessments means that a plant will undergo change during its 60 plus years of operations. To ensure continuing safety, changes must be made with a full understanding of the design intent. Regulators require that each operating organisation includes a designated entity that is responsible for the safety of the plant design to ensure that the knowledge of the design that is needed for safe operation, maintenance and modification of the plant is available (IAEA SSS-2/1). INSAG 19 calls this entity the design authority.
As the number of countries and nuclear utilities increases this requirement might be difficult to achieve. Some operating organisations will be new and some will be small. For Generation III plants acquired on a turnkey basis it is even more challenging for the operating company to develop and retain full knowledge of the design of the plant.
The report highlights the importance and challenges of controlling the plant configuration throughout the plant life. It calls for more clarity on the level of design knowledge that should be retained by an operator and how the knowledge of the designer should be maintained.
This discussion has led to the development of a separate report on design authority. Issues discussed in this report include:
- Defining 'design authority,' and other relevant concepts
- Describing configuration management
- Methods that can be implemented by licensees to manage plant configuration throughout the plant's lifetime
- Looking at the responsibilities of the design authority and ways that these can be implemented
- Identifying challenges in gathering the information necessary to maintain configuration control and ways in which these can be addressed
- Types of information that a licensee should receive from the NSSS vendor and the architect/engineering organisation.
The existing mechanism of the owners group (OG) provides a good point of interaction between a vendor and utilities, which could potentially aid design standardisation. The involvement of responsible utilities within OGs allows the sharing of experience, feedback and drawing of common lessons in order to improve safety at the fleet level. This can increase opportunities for standardisation.
DCMTF is looking at the potential role of OGs in more detail, including by addressing the following issues:
- Possibility of increased opportunities by OGs for standardisation through joint review and implementation of design changes, and by developing clear benchmarks in case of alternative solutions, with a goal to maintain the benefit of standardisation.
- Strengthening as appropriate the involvement of the original vendors in OGs including the use of vendor 'Service and Advisory Bulletins'.
- Strengthening the role of the OGs, in identification of significant safety issues, which should result in recommendations and decision to be benchmarked through all OG members.
- Production of reliability data and a standard probabilistic safety assessment for a design by OGs.
Aerospace industry approaches
The DCMTF held a number of discussions with aerospace industry representatives who also operate in a high-technology sector where reliability and safety are vital.
The aerospace industry developed techniques for adhering to standard designs at an international level many years ago and there are lessons to be learned from this industry. These were covered in a separate report, 'Aviation Licensing and Lifetime Management - What Can Nuclear Learn?,' published in early 2013.
Throughout the life of an aircraft design the original designer is always involved in the response to events and safety-relevant findings. For serious events, the aviation authority of the country of design may issue an airworthiness directive which will be based on solutions proposed by the original aircraft designer. This airworthiness directive requires other national authorities to implement remedial measures to their regulated entities, making sure that changes are applied consistently over the entire fleet of aircraft of the same design.
It is difficult to apply some of the aerospace industry practice directly to the nuclear industry: nuclear power plant operators have more time to react in severe accident management; there are many more aircraft and accountability and legal paradigms are totally different.
Three other key issues were studied in developing the report:
- Fukushima. While the magnitude of the external hazard was clearly not taken into account in the original design basis and the subsequent modifications of the original plants, the sequence of events that played out highlighted the differences in fleet implementation of features such as the containment hardened vent. It provides a good case study for improving fleet design change management process for the next generation of plants within a standardised fleet.
- Alongside the responsible operator the role of the original plant vendor is also important. The vendor often retains the detailed knowledge of why the design is how it is. Responsible designers are to be involved to a greater extent in keeping and improving the safety of a design during operation. The vendor can also play a role in keeping up to speed with new research findings and developments, particularly as they impact the understanding of the design basis for the plant, as well as the changes in the design of the plant.
- Regulators are making efforts to harmonise their activities and share their assessment of new designs. The Multinational Design Evaluation Programme is the best known initiative. It might be expected that the results of this work will not only benefit the standardisation of designs during licensing, but also will support the benefit of standardised solutions during plant life.
The CORDEL working group DCMTF's updated report 'Design Knowledge and Design Change Management in the Operation of Nuclear Fleets' will be published in early 2015.
It provides recommendations to the nuclear community on the establishment of institutional mechanisms for effective design change management across international fleets of similar plants. The objective is to maintain the original standardised design throughout the fleet's lifetime. The recommendations envisage enhanced international cooperation within industry and between regulators.
The full report Design Knowledge and Design Change Management in the Operation of Nuclear Fleets will be available on the World Nuclear Association's website (www.world-nuclear.org). ¦