PSR Safety Factors

Safety Factor 1: Plant Design

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This factor assesses the adequacy of the NPP design and its documentation in accordance with the Current Licensing Basis (CLB) and national and international standards, requirements, and practices. The scope of this review will depend on the extent of changes in standards and the licensing basis since the previous PSR or the start of operation.

A review of this safety factor should be carried out for all SSCs important to safety. It should seek to identify deviations between the plant design and current safety requirements and standards and to determine their safety significance.

In addition, the review should consider the adequacy of defense in depth in the plant design, and it might include an examination of the degree of independence of levels of defense in depth; the adequacy of delivery of preventive and mitigatory safety functions; redundancy, separation, and diversity of SSCs important to safety; and defense in depth in the design of structures.

A design re-evaluation should be undertaken if the design information is inadequate or there is significant uncertainty over the adequacy of an SSC important to safety to fulfil its safety function.

For more details on the scope and tasks of this safety factor, as well as the methodology to carry out its analysis, refer to sections 5.15 to 5.26 of SSG-25.

Safety Factor 2: Condition of Structure, Systems and Components (SSCs) Important to Safety

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This factor is used to determine the current condition of SSCs important to safety using knowledge of any existing or anticipated aging processes or obsolescence. The operating history of the plant’s equipment and consideration of whether the SSCs are capable and adequate to fulfill the design requirements is included, at least until the next PSR.

Inputs to perform the assessment must be available from the existing maintenance programs, and these will be checked to confirm that they represent the current condition of SSCs. If a lack of information is identified, and it is necessary to assess the status of SCCs, specific inspections, tests or walkdowns will be carried out.

Depending on plant configuration, or operational conditions, it may not be possible to determine the status of all SSCs important to safety. In these situations, evidence from similar components from other plants that are subject to similar conditions could be considered as well as knowledge of the relevant aging processes and operating conditions.

After determining the actual condition of the SSCs important to safety, each SSC should be assessed against the current design to confirm that design basis assumptions have not been significantly challenged and that design basis assumptions will remain valid until the next PSR.

In cases where consistency with the design basis has been significantly questioned, the PSR should propose corrective actions such as additional inspections, further safety analysis or even the replacement of components. These proposals should be evaluated as part of the global assessment, taking into account the results of the rest of the safety factors.

For more details on the scope and tasks of this safety factor, as well as the methodology to carry out its analysis, refer to sections 5.27 to 5.36 of SSG-25.

Safety Factor 3: Equipment Qualification

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Plant components important to safety should be properly qualified to ensure their capability to perform their safety functions under all applicable operating states and both normal and predicted accident conditions, including those arising from internal and external events or accidents (i.e. high energy line break, loss of coolant accidents, seismic events or other vibration conditions, etc.).

The aim of the review of equipment qualification is to assess whether SSCs important to safety (including cables) have been properly qualified; taking into account environmental conditions, and to verify if this qualification is maintained by a maintenance program, inspection, or testing that provides confidence that safety functions will be preserved until the next PSR or later.

The assessment of equipment qualification should include seismic conditions, vibration, temperature, pressure, jet impingement, electromagnetic interference, irradiation, corrosive atmosphere and humidity, fire, and combinations thereof and other anticipated events. It also considers the effects of aging degradation of components during service, equipment repairs and refurbishment, equipment failures and replacements and any possible changes in environmental conditions during normal operation since the EQ program began.

The review of equipment qualification should determine whether existing equipment qualification specifications and procedures are in place. The review will also determine if equipment performance has been maintained through ongoing measures such as scheduled maintenance, condition monitoring, testing and/or calibration, and whether or not these programs have been properly documented.

Finally, the review will assess the results of tests, inspections and walkdowns carried out to confirm the current condition of equipment in the environmental qualification program, and also verify that the installed equipment complies with the required qualification described in the safety documentation and should be the input to the review of the plant’s procedures for maintaining equipment qualification.

For more details on the scope and tasks of this safety factor, as well as the methodology to carry out its analysis, refer to sections 5.37 to 5.44 of SSG-25.

Safety Factor 4: Aging

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The aim of this safety factor is to determine whether physical changes caused by aging in SSCs important to safety are being effectively managed and if an effective aging management program (AMP) is in place to ensure that all required safety functions will be fulfilled during the design lifetime of the plant and, if proposed, during long term operation.

This factor should confirm that an AMP provides adequate tools to detect and prevent degradation of components due to aging that may affect the safety functions and the service life of SSCs important to safety. It also contains measures to ensure that an adequate maintenance program for their safety functions is in place. The review should focus on the results of periodic inspection and testing programs, and trends in safety parameters.

The review should ensure that a systematic and effective aging management process is in place which is based on plant operations which minimize the rate of aging degradation, establish preventive maintenance activities to avoid loss of component intended function, conduct inspections, and monitor in line with applicable requirements in order to detect and characterize early any indication of aging degradation. Upon identification of an aging degradation, assess the integrity and verify if the intended function of the component is maintained.

For more details on the scope and tasks of this safety factor, as well as the methodology to carry out its analysis, refer to sections 5.45 to 5.51 of SSG-25.

Safety Factor 5: Deterministic Safety Analysis

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The development of this safety factor should be conducted for each NPP in order to confirm the design basis for SSCs and evaluate the plants behavior for postulated initiating events.

The objective of this safety factor is to determine to what extent the current deterministic safety analysis is in place and remains valid. This determination will take into account the actual plant design including all SSCs’ modifications since the last update of safety analysis report or the last PSR, current safety standards and knowledge, current deterministic methods, the existence and adequacy of safety margins, etc.

The review should include an evaluation of the supporting analyses for design extension conditions. This should determine whether the arrangements aimed at preventing or mitigating severe core damage continue to be sufficient and whether any improvements are reasonable and practical.

For more details on the scope and tasks of this safety factor, as well as the methodology to carry out its analysis, refer to sections 5.52 to 5.60 of SSG-25.

Safety Factor 6: Probabilistic Safety Assessment

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A review of the probabilistic safety assessment (PSA) should be conducted to identify weaknesses in the design and operation of the plant and, as part of the global assessment, to evaluate and compare proposed safety improvements.

The PSA should be reviewed to confirm that the modeling reflects current design and operating characteristics, takes into account all operating experience, includes all modes of operation and, where appropriate, has a scope agreed upon with the regulatory body. The results of the PSA should be compared with relevant probabilistic safety criteria defined for the plant or set by the regulatory body.

Although it would be desirable to maintain a living PSA; when this is not feasible, the PSA should be kept sufficiently up to date throughout the life of the plant to make it useful for safety decision making.

For more details on the scope and tasks of this safety factor, as well as the methodology to carry out its analysis, refer to sections 5.61 to 5.72 of SSG-25.

Safety Factor 7: Hazard Analysis

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The objective of this safety factor is reviewing the hazard analysis to determine the adequacy of the protection of the NPP against internal and external hazards. This review should take into account the plant design, the site characteristics, the current condition of the SSCs important for safety and their expected condition at the end of the period covered by the PSR, as well as the analytical methods, safety standards and current knowledge.

The description of this factor included in SSG-25 lists representative internal and external hazards that may affect the safety of the plant, so their impact on the plant should be reviewed.

For each relevant hazard, the assessment should verify, using current analytical techniques and data, that:

• The frequency of occurrence and/or the consequences of the hazard are sufficiently low that specific protective measures are not required, or
• That existing preventive and mitigating measures are adequate.

For more details on the scope and tasks of this safety factor, as well as the methodology to carry out its analysis, refer to sections 5.73 to 5.83 of SSG-25.

Safety Factor 8: Safety Performance

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The safety performance review's objective is to determine whether plant safety indicators and operating experience records, including root cause assessment of plant occurrences, indicate any need for safety improvement.

The assessment of safety performance should evaluate whether appropriate processes for the routine recording and evaluation of safety related internal operating experience are in place. Examples are safety related incidents, safety related operational data, maintenance, inspection and testing, replacements of SSCs important to safety owing to failure or obsolescence, unavailability of safety systems, radiation doses, off-site contamination and radiation levels, discharges of radioactive effluents, among others.

Where available, the review should use a set of safety performance indicators, which should systematically cover all aspects of the operation important to safety. These indicators should provide information on both positive and negative aspects of safety performance. The IAEA safety performance indicators, and the World Association of Nuclear Operators (WANO) safety performance indicators could be used for this purpose.

The following IAEA references provide recommendations and guidance on the use of safety indicators to verify compliance with the requirements for the safe plant operation.

• IAEA Specific Safety Guide Nº 74 (SSG-74), “Maintenance, testing, surveillance and inspection in nuclear power plants”, 2022
• IAEA-TECDOC-1141 “Operational safety performance indicators for nuclear power plants”, 2000
• PI Reference Manual MN 2014-02 Rev 2, WANO. 2023

For more details on the scope and tasks of this safety factor, as well as the methodology to carry out its analysis, refer to sections 5.84 to 5.102 of SSG-25.

Safety Factor 9: Use of Experience From Other Plants and Research Findings

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The review of this safety factor is focused on determining whether there is feedback of relevant experience from other nuclear power plants and research findings, and whether it is used to introduce reasonable and feasible safety improvements at the plant or in the operating organization.

During the review process, reports of operating experience and other information that may be relevant to nuclear safety at other plants should be identified, together with national and international experience and research results from nuclear and non-nuclear facilities. It should be verified that this information has been considered as part of the plant's routine evaluation processes and that appropriate action has been taken.

The PSR should document a summary of the results of this process and assess the effectiveness of it. Where the effectiveness review indicates significant weaknesses in the process, appropriate action should be taken, including a repeat review of relevant events and information.

The following IAEA references provide recommendations and guidance on the development of an adequate operating experience process:

• IAEA Specific Safety Guide Nº 50 (SSG-50), “Operating Experience Feedback for Nuclear Installations”, 2018
• International Nuclear Safety Group, INSAG-23, “Improving the International System for Operating Experience Feedback”, 2008
• IAEA Database Incident Reporting Systems for Nuclear Installations
• NEA Component Operational Experience, Degradation and Ageing Programme (CODAP) Project Database

For more details on the scope and tasks of this safety factor, as well as the methodology to carry out its analysis, refer to sections 5.103 to 5.110 of SSG-25.

Safety Factor 10: Organization, the Management System and Safety Culture

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The operating organization must have a management system in place to ensure that policies and targets are implemented in an efficient and effective manner. Likewise, the organization must have a safety culture, so everyone performs safety-relevant duties properly, with alertness, due thought, full knowledge, sound judgment and a proper sense of responsibility.

The aim of the review of this safety factor is to determine whether the organization, management system and safety culture are both adequate and effective to ensure the safe operation of the nuclear power plant.

Periodic and systematic reviews of the management system are necessary to ensure that the organization's safety policies, goals and objectives are being met as intended. This can be accomplished through the review of independent audits conducted on behalf of top management, task observations, self-assessments and supporting corrective action plans.

The review should also examine if weaknesses and barriers have been identified, assessed, and addressed promptly. It should also examine whether improvements or changes need to be made to policies, goals, strategies, plans, objectives, and processes.

For more details on the scope and tasks of this safety factor, as well as the methodology to carry out its analysis, refer to sections 5.111 to 5.120 of SSG-25.

Safety Factor 11: Procedures

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Safety-relevant procedures should be comprehensive, validated, formally approved, properly distributed and subject to rigorous management control. In addition, they should be unambiguously relevant to the actual plant, and reflect current operating practices. Human factor aspects should be given due consideration.

The aim of the review of this factor is to determine if the processes of the organization to manage, implement and comply with operating and work procedures, and to maintain compliance with operating conditions and regulatory requirements are adequate and effective and ensure the safety of the plant.

For more details on the scope and tasks of this safety factor, as well as the methodology to carry out its analysis, refer to sections 5.121 to 5.126 of SSG-25.

Safety Factor 12: Human Factors

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This safety factor focuses on assessing the different human factors that may affect the safe operation of the NPP and trying to identify improvements that are reasonable and feasible.

The review should examine human factors at the plant and within the operating organization to determine whether they are consistent with accepted good practice and verify that they do not present an unacceptable contribution to risk. In particular, the review should determine whether the operator's actions claimed to be in support of safety are feasible and adequately supported.

The review of human factors should include aspects related to design of the control room and other safety-relevant workplaces, human information requirements and workloads, and clarity and feasibility of procedures. The review should take into account recognized national and international good practices.

If deficiencies in procedures and processes or in the design of the human-machine interface, are a potentially significant adverse contribution to risk, the PSR should formulate proposals for corrective actions to be included in the overall assessment. These may include improvements in training and procedures or redesigning human-machine interfaces.

For more details on the scope and tasks of this safety factor, as well as the methodology to carry out its analysis, refer to sections 5.127 to 5.134 of SSG-25.

Safety Factor 13: Emergency Planning

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According to SSG-25, the aim of the review of this safety factor is to determine a) whether the licensee has in place adequate contingency plans, staff, facilities, and equipment to deal with emergencies; and b) whether the actions taken by the licensee have been coordinated with the arrangements of the local and national authorities and are being implemented on a regular basis.

The PSR should include a general overview to ensure that emergency planning for the plant remains satisfactory and that emergency plans are maintained in accordance with safety analyses, accident studies and good practices.

Records of emergency exercises should be reviewed to assess the effectiveness and competence of the staff of the operating organization and external organizations, the required functional capability of the team, and the adequacy of emergency planning. In addition, it is important to assess interactions with relevant external organizations, such as police, fire, hospitals, ambulance services, regulatory agencies, local authorities, government, public welfare authorities and the media.

The following IAEA reference provides recommendations and guidance for nuclear or radiological emergency preparedness and response:

- IAEA General Safety Guide GSG-2, “Criteria for Use in Preparedness and Response for a Nuclear or Radiological Emergency”, 2011

For more details on the scope and tasks of this safety factor, as well as the methodology to carry out its analysis, refer to sections 5.135 to 5.145 of SSG-25.

Safety Factor 14: Radiological Impact on the Environment

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The objective of the assessment of this safety factor is to determine whether the licensee has an adequate and effective program in place to monitor the radiological impact of the plant on the environment, ensuring that emissions are adequately controlled and as low as reasonably achievable.

Radiological monitoring data should be compared with the values measured prior to the commissioning of the NPP and the historical values examined in the last PSR.

The review should determine whether the monitoring program is both adequate and sufficiently comprehensive. In particular, the assessment should verify that the radiological impact of the plant on the environment is not significant compared to that due to other sources of radiation.

There are countries in which these surveillance programs are also carried out by public organizations. This can facilitate independent validation of the data provided by the operating organization.

For more details on the scope and tasks of this safety factor, as well as the methodology to carry out its analysis, refer to sections 5.146 to 5.153 of SSG-25.

Record of Revisions

Number	Date	Description of Changes
0	6/11/2024	Initial version

Nuclear Power Plant

Current Licensing Basis - 10 CFR 54.3 under references

Periodic Safety Review

Systems, Structures, and Components

Environmental Qualification - A process for ensuring that equipment will be capable of withstanding the ambient conditions that could exist when the specific function to be performed by the equipment is actually called upon to be performed under accident conditions.

Aging Management Program

Probabilistic Safety Assessment

International Atomic Energy Agency

World Association of Nuclear Operators