Hazards PSA for New Build Reactor Designs

There are currently several different new build reactor designs in various stages of the licencing process within the UK each of which must satisfy the relevant assessment criteria set out by the Office for Nuclear Regulation (ONR). A fundamental part of the assessment criteria relates to the need for, and use of, probabilistic safety assessment (PSA) and specifically internal and external hazards PSA. The next generation of reactor designs offer improved safety performance through multiple, redundant and diverse methods for performing the critical safety functions meaning that combinations of random failures are rendered highly improbable. However, hazards pose a unique threat to plant safety and operability meaning that developing ... Continue reading ...

Is risk-informed fire safety design coming?

Jacobsen Analytics' experts were invited by British Standards Institution (BSI) to support the preparation of a new document, titled "Application of fire safety engineering principles to the design of buildings".

The document discusses the implementation of both deterministic and probabilistic methods to fire safety analysis during the building design process. Jacobsen Analytics experts contributed to the "Probabilistic Risk Assessment (PRA)" section adding information on internationally accepted methods and tools employed in Fire PRA. The main purpose of this document is to provide guidance and recommendations regarding the process, models and data that can be used in order to apply probabilistic methods in the design of buildings. Altho ... Continue reading ...

Fire PSA Task 11: Detailed Fire Modelling Case Study

In 2016, Jacobsen Analytics Limited (JA) was contracted to support a project to perform fire PSAs for five units, across two nuclear power plants with an ambitious schedule. Working in an international team, JA's specific task was to provide expert support and to lead the Task 11 detailed fire modelling analyses, specifically for the Main Control Rooms (MCR), Main Relay Rooms and back-up Control and Main Relay Rooms. The analyses conducted previously for these rooms had yielded higher than expected risk-estimates when compared to similar power plants. Therefore, the task set for Jacobsen was to refine and update the analyses to obtain more realistic results.

A Fire PSA effectively overlays the potential likelihood and impact of fire ... Continue reading ...

Target Selection for Main Control Room Fire Modelling

The Main Control Room (MCR) is the eyes and ears of a nuclear power plant. From this central location all parameters are monitored and operations are coordinated. Being the nerve centre of the plant, the MCR is usually one of the most risk significant compartments in all the plant. Fires in MCR can therefore lead to major disruptions in plant operation, but due to the high level of control and indication instruments in the room, it is a challenging room to evaluate for fire risk and perform detailed fire modelling. Apart from the high concentration of instruments and controls which could be lost, you also have to consider false or spurious signal generation, hot gas layer (HGL) development and deterioration in environmental conditions ... Continue reading ...

Support to the UK Office for Nuclear Regulation in the Generic Design Assessment review of the AP1000 PSA

Jacobsen Analytics was selected by the UK Office for Nuclear Regulation (ONR) to perform the Generic Design Assessment (GDA) of the Probabilistic Safety Assessment (PSA) for the UK submission of the Westinghouse AP1000 reactor design. The final report of the assessment of the AP1000 PSA [1] by the Health and Safety Executive (HSE), based on Jacobsen Analytics' supporting analysis, has been released to the public and can be found on the HSE website. The GDA was a process of four steps whereby the requesting parties submitted their designs for regulatory approval for potential new-build in the UK.

The PSA review covered all the technical areas of the Level 1 and L ... Continue reading ...

Level 2 PSA for the US and UK EPR

Jacobsen Analytics have provided support over the last 5 years to Areva NP Inc (USA) and Areva NP SAS (France) throughout the development of the Level 2 PSA for the EPR design. Our initial involvement in the project was for the US Design Certification project, and we subsequently supported Areva NP SAS for the adaptation of the Level 2 PSA for use in the submission to the UK Generic Design Assessment process. We have also continued to support the US Design Certification process for the EPR in the area of Level 2 PSA during the USNRC's regulatory review of the submission.

The EPR Level 2 PSA is a fully linked model, integrated with the Level 1.

Our scope of work for the US EPR Design Certification Level 2 PSA included:

  1. Development ... Continue reading ...

Fire PRA and the NFPA 805 Transition Process

To date approximately 50 of the 104 licensees in the US have committed to transitioning their fire protection licensing basis to the NFPA 805 standard. NFPA 805 is intended to be an alternate method to meet the intent of existing fire protection requirements in 10 CFR 50.48, Appendix R, and General Design Criterion (GDC) 3. While earlier methods relied solely upon a deterministic (rule based) approach, the NFPA standard provides flexibility to a nuclear power plant licensee through implementation of a mix of both deterministic and performance-based methods to analyse and manage fires.

NFPA 805 image

Managing fire risk at a nuclear power plant is not simple for a variety of reas ... Continue reading ...

Fire PRA Uncertainty

Fire PRA Quantitative Uncertainty and Sensitivity Analyses to Support Fire PRAs for US Nuclear Utilities

Fire PRAs are complex and can consist of in the order of 1,000 fire damage states (similar to an internal events initiating event). The development and quantification of these fire damage states has considerable uncertainty, which has not been fully addressed in recently conducted fire PRAs. Furthermore the PRA Standard includes requirements to address uncertainties in a fire PRA and applications of a fire PRA are expected to address uncertainties. Whilst US industry and NRC documents (EPRI 1016737 and NUREG 1855) provide guidance for addressing uncertainties, neither guidance document explicitly addresses fire or other hazards with the same level of ... Continue reading ...

Review of the Fukushima Accident Sequence for the Office for Nuclear Regulation

Jacobsen Analytics performed a review for the UK Office for Nuclear Regulation (ONR) which was aimed at providing a reference discussion of the events of the accident sequences that occurred at the three Fukushima units, as well as the code analyses performed in Japan to understand the sequences and the conclusions that could be drawn from these analyses.

The report prepared by Jacobsen contains:

  1. short overview of BWR containment and reactor systems,
  2. discussion of general features and phenomena expected in severe accident scenarios for BWR units with Mark I containments,
  3. summary of the timelines at Fukushima Daiichi units 1, 2 and 3, and
  4. discussion of the accident analyses perform ... Continue reading ...

Safety Performance Indicators (SPI)

Within any safety management system there is a requirement to monitor performance against health and safety goals. However for nuclear safety there may be many aspects for which performance indicators may be justified. The IAEA has provided guidance to utilities for the development of Safety Performance Indicators (SPIs) initially through IAEA-TECDOC-1141, 'Operational safety performance indicators for nuclear power plants', which provides a framework for the identification of performance indicators which have a relationship to the desired safety attributes 'Smooth Operation', 'Operate with Low Risk' and 'Operate with a Positive Safety Attitude'.


Jacobsen has provided support to th ... Continue reading ...