Office for Nuclear Regulation

System Based Inspection of Submarine Refit Complex Water Retaining Boundary

Executive summary

Purpose of Intervention

The Office for Nuclear Regulation (ONR) undertakes all interactions at the Devonport Licensed Site (Operated by Devonport Royal Dockyard Ltd. ((DRDL)), in accordance with ONR’s integrated intervention strategy plan.

The purpose of this intervention was for ONR to conduct a system based inspection, to examine whether the Licensee’s safety case claims, relating to the submarine refit complex water retaining boundary, have been adequately implemented.

This intervention was undertaken remotely, by an ONR inspection team comprising fault studies, mechanical engineering, civil engineering and site inspection specialists.  A member of the Licensee’s Independent Nuclear Oversight team supported the intervention and conducted certain site-based activities as required.

Interventions Carried Out by ONR

For this intervention, ONR performed a planned safety case informed system based inspection of the safety systems and structures associated with the submarine refit complex water retaining boundary, to judge performance against the safety functional requirements and examine the adequacy of implementation of the safety case.  The following systems, structures and components, were sampled by this intervention:

Through sampled examination of the arrangements made for the water retaining boundary safety systems and structures, ONR inspectors performed compliance inspections against the following licence conditions (LCs) where applicable:

The intervention was performed in line with ONR's guidance requirements (as described in our technical inspection guides) in the areas inspected.

Explanation of Judgement if Safety System Not Judged to be Adequate

The Licensee has demonstrated that the safety systems and structures sampled in relation to the water retaining boundary are able to fulfil their safety functional requirements adequately, in line with the safety case. 

A new Regulatory Issue will be raised to track the Licensee’s progress in relation to the LC28 shortfalls identified with respect to its maintenance instructions, the storing of records, handling of reported defects and gaps to relevant good practice.

A number of observations were made during this inspection and the associated recommendations were shared with the Licensee.

Key Findings, Inspector's Opinions and Reasons for Judgements Made

During the inspection, it was identified that a temporary cover had been installed by the Licensee, to prevent the potential ingress of rainwater into an electrical cabinet.  Due to the poor condition of the cover, and the potential for water ingress, which could present a risk to workers, this was judged as requiring immediate attention during the conduct of this system based inspection.  The Licensee promptly investigated the issue and undertook necessary tests and remedial works, prior to confirming that the electrical installation was safe and suitable for continued use until the next outage.  In addition, the Licensee has actioned requests and recommendations made by its Technical Authority.

Based on the specific areas sampled during the course of the inspection, ONR found that overall, the Licensee has adequate arrangements in place to ensure that the safety systems and structures associated with the water retaining boundary are operated and maintained in accordance with the appropriate safety cases.  Ratings for each of the LC are as follows:

LC10 (training) – IIS Rating GREEN.  The inspection team judged that jobs and roles that may affect safety were identified and defined (along with the competencies required), adequate arrangements were in place to review and develop training, and that records were available for individuals that confirmed that all training required had been completed.  An observation was recorded regarding a potential opportunity to develop some additional training material.

LC 23 (Operating rules) – IIS Rating GREEN.  The inspection team were satisfied that the safety case limits were identified through an adequate set of operating rules and that these were appropriately implemented.  An observation was raised against IOI/1.03.14 & IOI/1.03.15 commentary in PSC-220 Addendum 7, which has the potential to improve the consistency of this commentary and align it with other relevant documentation.

LC 24 (Operating instructions) – IIS Rating GREEN.  In the areas sampled, the inspection team found operating instructions were written in clear and unambiguous terms and contained relevant prerequisites and precautions. An observation was raised to highlight the opportunity to credit margin between the operational 15 Dock caisson level and the relevant IOI limit, in relevant operating instructions.

LC 27 (Safety mechanisms, devices, and circuits) – IIS Rating GREEN.  The inspection team found that sampled SMDC’s were clearly identified (along with their applicability) with adequate tests to confirm availability and links to LC28 Plant Maintenance Schedule.  However, an Observation was recorded with respect to it not being possible to fully determine the availability and reliability of an SMDC due to related maintenance shortfalls (see LC 28).

LC 28 (Examination, inspection, maintenance, and testing) – IIS Rating AMBER.  The inspection team judged that the Licensee is not fully compliant with the legal standards for LC28 (8).  The sampled EIMT arrangements do not adequately identify conditions (as set out within the design substantiation) that require results to be brought to the attention of the appropriate person(s) within the Licensee forthwith, so that appropriate action is taken to ensure that safe conditions (substantiated limits) are not compromised.  Specific shortfalls against NS-INSP-GD-028 expectations were recorded in relation to the storing of output records and the handling of reported defects.  A gap was also reported against relevant good practice acceptable limits.  It is judged that, the ongoing deterioration of monitoring equipment is challenging the implementation of associated maintenance activities concerned with ensuring that structures, systems, and components will function with adequate reliability and remain within substantiated limits.

LC 34 (Leakage and escape of radioactive material and radioactive waste) – IIS Rating N/A.  No LC 34 rating not awarded, as it was judged this licence condition was not sufficiently relevant to the safety systems and structures under consideration.

Conclusion of Intervention

From the evidence sampled during the inspection, ONR considers that overall, the safety systems and structures associated with the submarine refit complex water retaining boundary adequately meet the claims in the relevant safety cases and that there are no findings from this inspection that could significantly undermine nuclear safety. 

It was judged through this intervention, that the Licensee is not fully compliant with the legal standards for LC28 (8).  Sampled maintenance arrangements do not adequately identify conditions (as set out within the design substantiation) that require results to be brought to the attention of the appropriate person(s) within the Licensee forthwith, so that appropriate action is taken to ensure that safe conditions (substantiated limits) are not compromised. 

Specific shortfalls against NS-INSP-GD-028 expectations were recorded in relation to the storing of maintenance output records and the handling of reported defects.  A gap was also reported against relevant good practice acceptable limits.  It is judged that, the ongoing deterioration of monitoring equipment is challenging the implementation of associated maintenance activities concerned with the ensuring that structures, systems, and components will function with adequate reliability and remain within substantiated limits.

The above have been put forward to ONR for consideration as a Regulatory Issue.  No additional regulatory action is needed over and above ONR’s planned interventions as set out in our integrated intervention strategy plan.