Executive summary
Date(s) of inspection: February 2024
Aim of inspection
The aim of the inspection was to gather sufficient evidence, proportionate to current project maturity, of the selection and implementation of suitable and sufficient user interfaces within the main control room (MCR) to provide effective control of the Hinkley Point C (HPC) facility once it is operational. The inspection had a specific focus on how the provision of alarms, and other aspects of the MCR human machine interfaces (HMIs), will facilitate the implementation of the future operational safety case and support ongoing compliance with the limits and conditions defined within it.
ONR human factors (HF) and control and instrumentation (C&I) specialist inspectors undertook the inspection, on a sampling basis, to form a judgement on the adequacy of the arrangements associated with identification and selection of user interfaces important to nuclear safety. This was followed by sampling the implementation of those arrangements for user interfaces associated with two of the three main nuclear safety functions, namely control of reactivity and residual heat removal.
Subject(s) of inspection
- LC14 - Safety documentation - Rating: Green
Key findings, inspector's opinions and reasons for judgement made
Based on the evidence presented, the following areas of good practice relating to the processes, procedures and implementation of requirements traceability, were noted:
- the availability of high-fidelity simulator facilities during the construction of the facility;
- the knowledge and competence of reactor operators (ROs) in operation of the simulated process information and control system (PICS) HMIs;
- the use of PICS functionality to reduce the number of alarms received during plant disturbances to levels considered as manageable;
- the ability of the automatic diagnosis (AD) system to significantly reduce MCR distractions during the most challenging periods of operation in terms of nuclear safety; and
- the maturity of the design along with the availability of simulator facilities and trained ROs provide NNB Generation Company (HPC) Ltd (NNB GenCo) the opportunity to test and continue to improve HMIs, training and procedures prior to the commencement of power generation.
The following shortfalls were identified:
- inconsistencies and omissions in the safety case linkage ‘golden thread’ from the nuclear safety requirement to specific MCR alarms;
- the absence of a consolidated master schedule / database for all MCR alarms; and
- robust arrangements for systematic assessment, modification and subsequent configuration control of the HMIs to ensure an overall optimum solution is achieved.
In addition, the inspection highlighted a number of areas where potential gaps to relevant good practice (RGP) were observed within the alarm system, as demonstrated during the inspection. Whilst, these shortfalls might not constitute a nuclear safety risk currently, given the absence of nuclear hazards on the HPC site, they could, if not rectified, be a source of risk in the future. For example, limitations in the ‘golden thread’ and consolidated alarm schedule, if not resolved in a timely manner, will likely make it significantly more difficult for NNB GenCo to maintain effective configuration control over the developing / operational alarm system. The inspection highlighted the need for NNB GenCo to demonstrate the effectiveness of its arrangements to systematically identify potential human factors issues, and rectify them, to give confidence that a HMI aligned with RGP will be delivered.
However, I am satisfied that the inspection did not identify any fundamental issues with the proposed alarm system design that foreclose options to ultimately deliver a solution which reduces risk as low as reasonably practicable (ALARP).
Conclusion
Based on the evidence obtained via this inspection, I judge that a rating of green (no formal action) is appropriate for Licence Condition 14 (safety documentation).
Whilst shortfalls against regulatory expectations were identified, these were not fundamental given the current phase of the project, and recognising that currently there is no nuclear hazard arising from the HPC site and there is time to resolve them. In assigning a green rating, I judged there is a need for improvements to ensure appropriate and robust configuration control of the developing / operational system is maintained going forward. ONR will oversee delivery of these improvements via a level 4 regulatory issue (RI).