Office for Nuclear Regulation

Technical specialisms

Control and instrumentation / Electrical engineering

C&I research is primarily concerned with the issue of producing appropriate safety cases for safety and safety-related computer and complex hardware based systems. This is an extremely difficult topic and requires in-depth research into often complex areas of software engineering, computer aided hardware design and associated mathematical methods. The research undertaken has revealed a wider range of issues than originally envisaged. The need for continuing research in this area follows a pattern that is well established when researching novel and complex technologies, i.e. the harder you look the more there is to see.

Radioactive waste management and decommissioning

The principal challenge for radioactive waste management is the need to maintain safety over very long periods and to avoid 'legacy' problems in the future. Decommissioning faces the challenge of safely managing short-term increases in risk with the longer-term need to reduce the hazard on the site.

Research and development on radioactive waste and decommissioning should address the short, medium and long-term aspects of managing waste streams and the full site lifecycle.

It is generally accepted that the Nuclear Decommissioning Authority (NDA) and the UK nuclear industry need to take steps to ensure the availability of adequate knowledge and expertise in order to ensure radioactive waste management and decommissioning can be undertaken safely. ONR's research & development will be focussed to ensuring that it has the appropriate technical competence to underpin its regulatory decision making on these topics.

Fuel and core

Commercial nuclear fuel comprises of pellets of fuel material clad in sealed metal tubes to form individual fuel rods. As the fuel is consumed, the fissile material content is slowly transformed into fission products. These fission products include hazardous radioactive isotopes which must be immobilised as far as reasonably practical. Most of the fission products remain trapped in the fuel material itself, but a fraction diffuses out of the pellets and is retained in the rods by the metal cladding tube.

The fuel rods are fabricated into self-contained fuel assemblies to allow the fuel to be handled and the correct core geometry to be maintained to ensure the intended distribution of neutrons in the core. The design and dimensions of the fuel rods and assemblies are determined by the requirements of the particular reactor.

The main focus of fuel research is to identify the conditions required to maintain the integrity of the fuel assembly and the rods in both normal operation and anticipated fault conditions.

Chemistry & Chemical Engineering

Chemistry can have a major impact on nuclear safety and a number of the hazards posed by the design and operation of nuclear installations, ranging from nuclear chemical plants to nuclear power reactors.

Assessment of the chemistry aspects of safety cases for these facilities may therefore require an examination of the chemistry based safety claims being made for normal operations and fault or accident conditions. This means the chemistry discipline is broad and interacts with a number of others, including: structural integrity, radiological protection, internal hazards, fault studies, and nuclear liabilities management.

Civil Nuclear Security

Effective security arrangements in the civil nuclear industry are essential to prevent the theft or sabotage of nuclear or other radioactive materials, the sabotage of nuclear facilities and to protect sensitive nuclear information. ONR regulates this through the Civil Nuclear Security and Safeguards (CNSS) division. In ONR, security is sub-divided into the broad topics of physical protection (including site and nuclear material transport), personnel security and information security. The obligations placed upon all those involved in security in the civil nuclear industry are laid down in the Nuclear Industries Security Regulations 2003 (NISR 03), as amended.

Security in the civil nuclear industry reflects the UK's international obligations and good practice. In particular, the UK is a party to the Convention on the Physical Protection of Nuclear Material, and it takes account of the recommendations made by the International Atomic Energy Agency (IAEA) in The Physical Protection of Nuclear Material and Nuclear Facilities (INFCIRC/225/Rev5).

Conventional Health and Safety

ONR delivers focused and proactive regulation of, and exerts a positive influence over, the management of CHS on GB nuclear sites in order to hold the industry to account for its health & safety performance, and to foster a culture to prevent injuries and ill-health. ONR delivers focused and proactive regulation to ensure dutyholders meet the statutory requirements for the protection of life safety from fire. These are achieved through a proactive programme of compliance inspections, engagement with stakeholders, and the provision of information and advice.

Fault Studies - DSA

Deterministic safety analysis is primarily used within safety cases to demonstrate the safety of nuclear facilities against design basis faults. It is also used to support Probabilistic Safety Analysis (PSA) and the analysis of severe accidents. The analysis techniques vary dependent on the facility, but for reactors typically take the form of reactor physics and thermal hydraulic calculations using complex computer codes that are validated by experimental data.

Human and Organisational Capability

Human and Organisational Factors (HOF) is concerned with the way that human beings interact with, and respond to, the technical and managerial systems, culture and environment at work. In the context of nuclear safety, the science of HOF underpins the design, commissioning, operation, and decommissioning of all nuclear facilities. It provides a basis for principles and guidance to optimise the role that the human plays in these facilities during the lifecycle stages, and also provides analytical methods to qualitatively and quantitatively assess the positive and negative impacts that the human has on overall system performance. Importantly, it also interacts and links with other safety disciplines such as: Instrumentation and Control, Fault Studies, and Emergency Arrangements.

Internal hazards

Internal hazards are defined in ONR publication 'Safety Assessment Principles' 2014 Edition, Revision 0, paragraph 229; as: Internal hazards are those hazards to the facility or its structures, systems and components that originate within the site boundary and over which the dutyholder has control in some form. The term is usually limited to apply to hazards external to the process, in the case of nuclear chemical plant, or external to the primary circuit in the case of power reactors. Internal hazards include internal flooding, fire, toxic gas release, dropped loads or impact and explosion/missiles. Again, this list is not exhaustive.

Engineering principles EHA.1 to EHA.19 within the SAPs identify the general and specific principles attributable to internal and external hazards. There are linkages between internal and external hazards. Also an internal hazard or hazards may be part of the consequence chain from another hazard or another fault (for example, fires following a seismic event, a dropped load causing fires and flooding consequences). For this reason, the discipline of internal hazards is an integrating one, requiring high levels of co-ordination and co-operation with other design and assessment disciplines.

Mechanical Engineering

The mechanical engineering specialism considers Structures, Systems and Components (SSCs) that contain both dynamic and static elements used in nuclear plant across the range of sites regulated by ONR. The specialism considers many aspects associated with the safe use of SSC's and encompasses:

  • Material properties and behaviour affecting mechanical performance;
  • Load analysis;
  • Thermodynamic and fluid flow characteristics;
  • Design processes;
  • Procurement processes;
  • Examination, Inspection, Maintenance, and Testing (EMIT) affecting mechanical performance;
  • Associated safety justifications.
  • Computer modelling of mechanical systems
  • Regulatory Challenges and Opportunities

Continued safety and reliability of SSC's requires duty holders to have maintenance management strategies that ensure their performance and safety function whilst controlling degradation mechanisms. There are various commercial products and techniques available aimed at improving asset management of SSC's that could benefit the nuclear industry. The regulatory challenge that fits within the mechanical engineering specialism is that the ONR does not have a full picture of these available products and techniques and their risk potential when used for predicting asset care strategies. There is an opportunity to improve this knowledge through research and this knowledge can then be used by ONR to make informed regulatory decisions on the adequacy of maintenance management strategies in the future.

Design and construction of new power generating reactors, replacement of obsolete equipment, nuclear decommissioning and life extension all present opportunities to exploit state of the art technology to improve safety. One huge area of potential interest is in the development of products, materials and processes utilising Graphene. This is a relatively new area of technology that is a rapidly increasing in popularity outside the nuclear industry and is an area where nuclear safety could potentially find benefits from its use in a wide variety of applications. The regulatory challenge, that fits within the mechanical engineering specialism, comes in so far as neither ONR or the nuclear industry have so far got a full understanding of the benefits or limitations of products containing this technology. Research into this technology would improve ONR's knowledge to assist in making informed regulatory decisions when assessing the use of such products in the future.

Probabalistic safety analysis

Probabilistic Safety Analysis (PSA) has a vital role to play in safety analysis of complex nuclear plant. PSA is a generic term for the integrated analysis of risks arising from plant and processes which is undertaken by applying structured and systematic analysis techniques. These techniques can be used to provide anything from a basic qualitative (engineering judgement) analysis of a single piece of equipment, up to a full integrated analysis of an entire facility with the numerical determination of the identified risks (quantitative analysis). This in turn enables complex interactions between plant and process to be identified and examined, and provides an objective, logical basis for determining the probability that a hazard will arise and the likely consequences that could occur as a result. PSA is used to facilitate risk-informed judgements both at the design stage and in the operation of nuclear installations.

Radiological Protection Criticality and EP&R

Research into this technical area helps fulfil fundamental supporting roles in nuclear safety cases aims to reduce and limit radiation exposure to the public and workers from normal and emergency situations. Criticality addresses the risk from nuclear criticality faults, emergency preparedness and response deals with response to accidents and radiological protection is concerned with reducing and limiting radiological exposure during normal operation and consequence assessment for faults.


Nuclear safeguards are measures used to verify that countries comply with their international obligations not to misuse nuclear materials (plutonium, uranium and thorium) for nuclear explosives purposes with the State itself regarded as the potential diverter of nuclear material. Such verification is reflected in the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) for the application of safeguards by the International Atomic Energy Agency (IAEA). The Treaty Establishing the European Atomic Energy Community (the Euratom Treaty) includes requirements for the application of safeguards in the European Union by the European Commission.

The primary safeguards 'regulators' are the international safeguards inspectorates. Nevertheless, safeguards obligations in the UK are a direct consequence of the UK's signature of Treaties and Safeguards Agreements. ONR Safeguards:

  • Provide the UK Government with informed independent assessment of safeguards application and compliance in the UK;
  • Fulfil the international and domestic safeguards-related reporting obligations that are the direct responsibility of the UK Government ; and
  • Provide advice and support to BEIS and other Government Departments (OGDs) on safeguards implementation in the UK.

Structural Integrity

Safety related components and structures in nuclear reactors, nuclear chemical plants, decommissioned reactors and other safety related plant may be subjected to high pressure, high temperature and/or corrosive environments, or other challenges. Those in the reactor core area are also subjected to high levels of irradiation, which over time, can degrade material properties of the steels. Defects may be present in safety related structures due to the methods of construction, or arising during operation; which must be detected and assessed. ONR will conduct research to address specific regulatory issues arising from our work in this area and to monitor and influence more general developments in structural integrity assessment.

Each AGR in the UK features a large graphite core, which is essential to sustain a controllable fission reaction. It contains the fuel and control rods and allows for the flow of coolant gas. Assessment of the condition of the graphite core is of fundamental importance because the core degrades over time due to a number of factors, including irradiation and radiolytic oxidation. If the graphite core is compromised it could lead to a number of fault conditions, including failure to shut-down and hold-down the reactor, failure to ensure adequate cooling of the fuel and core structure and loss of the ability to remove fuel safely from the core. ONR will conduct research in this area to support our activities to regulate the continued safe operation of the UK AGR fleet.


The Transport Specialisms (comprising the Assessment and the Inspection and Enforcement functions) deliver principally to the ONR Transport Sub-Programmes which are part of the Cross ONR Programme (COP) and perform on behalf of ONR the GB Competent Authority function for the transport of radioactive materials by road and rail. This function involves the regulation of safety (and in some cases security) of radioactive material in the public domain and performing certain functions on behalf of, and providing advice to, the UK Competent Authority for the transport of radioactive material by air and sea (and by road in Northern Ireland).

As well as enforcing compliance, ONR Transport Specialisms inspect a wide variety of duty-holders and assess submissions for Competent Authority approval of certain radioactive materials, transport package designs and shipments. Regulations governing the transport of radioactive material are based on standards developed by the International Atomic Energy Agency (IAEA).

Civil Engineering and External Hazards

The Civil Engineering Specialism considers Structures, Systems and Components (SSCs) that deliver a range of safety functions. These functions include shielding and containment / confinement of nuclear matter and radioactive materials and supporting and or protecting other safety related plant and equipment.

Safety and reliability should be considered throughout the lifecycle of a civil engineering SSC including during the design, construction, operation and decommissioning phases. These considerations are applicable to the safety cases of existing facilities, new nuclear build and advanced nuclear technologies.

Areas of potential ONR research include the following topics and their specific application to the nuclear industry:

  • Analysis and design practices for assessment of civil engineering SSCs.
  • Novel materials and technologies used in construction of civil engineering SSCs.
  • Identification and quantification of ageing, degradation mechanisms and time-dependent phenomena relevant to the materials used in construction of civil engineering SSCs.
  • Development and evaluation of techniques for monitoring, repairing and managing the progress of ageing and degradation mechanisms.
  • The response of civil engineering SSCs to different faults / hazards and their potential impact on the delivery of safety functions.

Civil engineering SSCs are typically the primary means of protection against external hazard loadings. External hazards are those natural or man-made hazards to a site and facilities that originate externally to both the site and its processes.

There are many external hazards that could impact nuclear safety or impair operations such as earthquakes and flooding, as well as more obscure hazards such as space weather. The Fukushima-Daiichi incident demonstrated the importance of understanding the nuclear safety impacts of external hazards occurring in combination.

External hazards is also an active area of research, particularly in relation to climate change. Therefore, it is important that ONR remains up-to-date on these developments and proactively undertakes research in relation to external hazards topics to ensure regulatory guidance remains fit-for-purpose. Areas of potential ONR research include the following topics:

  • Characterising the role of natural process and phenomena on hazard frequency-magnitude relationships and temporal changes in these relationships.
  • Techniques for deriving hazard frequency-magnitude relationships, particularly for obscure hazards and hazard combinations.
  • Analysis and evaluation techniques for hazards, and their potential impact on nuclear safety.

Research into the civil engineering and external hazards topics will improve ONR's knowledge and assist in making well-informed regulatory decisions when assessing dutyholder safety cases.