The interest in harmonising approaches to the design, the evaluation and the certification of nuclear installations is universally recognised. Recently, the need for a “paradigm shift” has been recognized; “ …I think the time is now to think boldly and look critically at regulatory frameworks and be open to the need to re-engineer them. It may be time for a paradigm shift in the regulatory space.” (ref. CNSC President Rumina Velshi)
Without claiming to indicate miracle solutions to achieve the desired harmonisation, this “Perspectives” report provides innovative proposals which can help paving the way for the definition of programs which realisation could contribute to the advancement of the reflection.
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Interest in harmonising approaches to the design, evaluation and certification of nuclear installations is universally recognised since longtime. Significant progress has been made but the process has not yet been completed and the situation now appears to be stagnating. To make further progress in this difficult area, radical actions should be engaged as suggested by CNSC President Rumina Velshi at the International Framework for Nuclear Energy Cooperation’s (IFNEC) Global Ministerial Conference: “ …I think the time is now to think boldly and look critically at regulatory frameworks and be open to the need to re-engineer them. It may be time for a paradigm shift in the regulatory space.” Practical proposals are necessary to characterise this “Paradigm shift” and to identify how this can be translated into an innovative harmonised approach.
All the stakeholders involved in nuclear technologies are engaged in an effort to improve the conditions for harmonisation on a planetary scale.
This is the case for regulators with actions that continue at regional or international scales as well as for the designers, vendors, operators and, generally speaking, all the involved stakeholders. The education is also an essential mean to help the spreading and the achievement of the harmonisation.
A good level of consensus already exists on the applicable generic terminology, on the Safety Objectives and on the Principles, also generic, on which must lie the definition of requirements applicable to the design and evaluation of nuclear installations; however, differences still exist as regards to the interpretation of their content and the ways for their implementation.
Theis Perspectives report addresses examples which deserve discussion in order to identify the actions needed to achieve a full consensus about their content. The notion of Risk is discussed through the use of the so-called “Farmer curve” and the “Risk space”. The need for a really technology neutral approach is pointed out to go further compared with the currently available set of requirements. The important specification to harmonise the safety / security approach is recalled. Concerning the safety objectives, it is agreed that the harmonisation can be organized through the extension of the safety demonstration (and the strengthening of its robustness) and the reinforcement of the defence in depth (DiD).
The objective – extremely ambitious – is to build a universally accepted paradigm for the safety / security of nuclear installations, that is to say a “model of thought” which organises and directs the analysis. The development of a new paradigm necessarily involves both compromises on current positions and, where appropriate, the introduction of new tools to facilitate this development. This new paradigm must be: 1) Compliant with fundamental safety principles; 2) Simple, pragmatic and understandable by all; 3) Applicable to all the nuclear installations and organised following a Top > Down approach. The certification approach which materialises the implementation of such paradigm shall be based on criteria and metrics which allow assessing the conformity of the design with the fundamental principles and the compliance with the available requirements and the safety objectives.
When discussing the elements for the new paradigm, the first element of reflection is the notion of safety (/security) architecture. This is expressed by the capability to answer the question when the plant is facing a specific situation: “who/what does what, when, how ?”. The principle being relatively simple, it is essential to find an easy and understandable way to represent this architecture unequivocally.
As a corollary to this notion of Safety Architecture comes first the concept of defense in depth (DiD) which must be fully implemented with the related associated principles such as the requested reliability for each of the DiD levels and the independence between the levels. However, if the concept of DiD is universally accepted, the principles that govern it and their implementation are still subject to different interpretations as for example the notion of independence. The document provides suggestions to overcome the issue.
The notion of “Line of protection”, developed within the context of the IAEA activities and endorsed, among others, by the Generation IV International Forum / Risk & Safety Working Group (GIF/RSWG), replaces the current notion of “Line of defence”, complementing the Defence in depth and allowing sketching the safety (/ security) architecture.
The concept of risk space evoked above can be used to define the deterministic or probabilistic success criteria, in terms of required performances and reliability for the lines of protection. Other key concepts are discussed such as the “Graded/proportional approach”, the “Reasonably practicable” the “Practical Elimination” and finally the notion of “Risk Informed”.
One of the key issues being the assessment of the DiD, the document provides suggestions and elements as to how to perform it using the PSA to verify that the implemented safety architecture complies with the principles of the DiD while meeting the probabilistic objectives.
The regulation of the transport of nuclear materials is undoubtedly the best example for the harmonisation between the regulators worldwide. The transport of nuclear material shall comply with the IAEA Safety Fundamentals and IAEA Requirements. The safety objectives and the required performances are clearly and quantitatively defined and easily accessible and measurable. Additional parameters allow unambiguous categorisation of packages.
In these conditions, an essential lesson that can be drawn from this experience is the need for an available set of criteria and metrics – measurable and controllable – which characterise the level of safety unanimously considered acceptable. However, the major difficulty is to extrapolate the availability of easily quantifiable and measurable criteria and metrics defined for relatively simple architectures to the otherwise more complex architecture of a nuclear installation.
A key issue is represented by the need to guarantee the independence of the national safety regulatory authorities that shall remain a national prerogative worldwide. To reconcile this requirement and the objective of harmonisation, the corresponding work must be organised step by step with the primary objective of finding compromises that can facilitate dialogue and understanding between the various safety authorities; this is the raison d’être of the new paradigm that the nuclear safety / security international community must try to define and share as widely as possible.
The first step is the critical review of the whole document in order to reach a consensus on the analysis, positions and proposals that are put forward. Once an agreement achieved, the activity should proceed with the preparation of “position papers” on different selected items such as:
Each of these positions papers should develop and detail the subject matter and define the technical tasks necessary, in particular, to overcome the identified bottlenecks.
The interest in harmonising approaches to the design, the evaluation and the certification of nuclear installations is universally recognized. Efforts for this harmonisation have been underway for several tens of years; significant progress have been made but the process has not yet been completed. In parallel with work carried out on a permanent basis the need for a “paradigm shift” has been recognised.
The discussion on the practical content of the new paradigm prompts us to propose innovative tools for the representation of the safety / security characteristics of the installation, representation which is essential to assess its conformity with the objectives that should also be defined and harmonised as a first step.
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