Office for Nuclear Regulation

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Planned Intervention - SBI 22 (CO2 Storage and Distribution)

Executive summary

Purpose of intervention

The purpose of this intervention was to conduct a Licence Condition (LC) compliance inspection of the carbon dioxide (CO2) storage and distribution plant at Dungeness B power station. The work was carried out as part of the planned intervention programme contained in the Dungeness B Integrated Intervention Strategy (IIS).

I undertook this inspection along with a specialist mechanical engineering inspector and a graduate mechanical engineer. The inspection was completed over a two-day period, which involved interviewing several of the licensee's employees responsible for the day-to-day operation and safety of the plant.

Interventions Carried Out by ONR

The objective of the inspection was to determine whether the licensee's arrangements for plant operational limits, plant maintenance schedules, staff training requirements and inspection plans were adequate in accordance with safety case requirements.

The inspection was based on sampling the compliance arrangements against several site licence conditions. These were LC10 (training), LC23 (operating rules), LC24 (operating instructions), LC27 (safety mechanisms, devices and circuits), LC28 (examination, maintenance, inspection and testing) and LC 34 (leakage and escape of radioactive material and radioactive waste). Following review of the system and consultation with site staff, it was judged that the CO2 system being inspected was not applicable for inspection against the requirements of LC 34 because the system only contained 'clean', non-contaminated gas.

The licence conditions were inspected against ONR's published guidance requirements (as described in our technical inspection guides).

Explanation of Judgement if Safety System Not Judged to be Adequate

We judged that the arrangements and their implementation, associated with CO2 storage and distribution plant, met the requirements of the safety case and are adequate.

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

From an LC10 perspective, the inspection of staff training records and profiles were generally in accordance with the role requirements. There was no evidence of a system engineer handover being completed when the system health engineer took charge of the system, which is a shortfall against the licensee's own procedures. A condition report (CR00884603) was raised to capture this shortfall and the handover process is planned for completion later this year. We are content that this condition report will be tracked and closed through the licensee's own arrangements; therefore, we consider the LC10 element of this inspection to be adequate, warranting an associated IIS rating of 3.

From an LC23 and LC24 perspective, based on the evidence sampled during this inspection, the implementation of the technical specifications, commentaries, and schedules has been demonstrated to be consistent with the claims presented within the living safety document for the CO2 storage and distribution plant. The overview of the safety case by the licensee demonstrated that there was adequate knowledge and understanding in the areas of the safety case and how they relate to the operating rules and instructions in place for the CO2 storage and distribution plant. We consider the LC23 and LC24 element of this inspection to be adequate, warranting an associated IIS rating of 3.

From an LC27 perspective, there was mutual agreement on what mechanisms, devices and circuits were considered relevant on the CO2 storage and distribution plant. The duty holder was able to demonstrate an adequate level of compliance against LC 27. We consider that the LC27 element of this inspection to be adequate, warranting an associated IIS rating of 3.

From an LC28 perspective, shortfalls were observed during the site inspection for several plant items that do not significantly affect the claim on nuclear safety. We are content that the licensee have captured these observations within their own arrangements and will implement a programme for improvement. There is no apparent risk to nuclear safety in the short term; however, the condition of non-safety significant plant could be improved. For this reason, we consider the LC28 compliance of this inspection to be below standard, warranting an associated IIS rating of 4.

Conclusion of Intervention

From the evidence sampled, witnessed and collected during the inspection against LCs 10, 23, 24 and 27, the structural integrity and mechanical engineering aspects for this system based inspection meet the requirements of the safety case and its implementation is considered adequate.

Observations made during the inspection against LC28 have demonstrated that the arrangements for the CO2 storage and distribution plant are below standard. The shortfall in expectations was against some items, components and structures not considered to have a significant impact on nuclear safety. We are content that they will be addressed by the licensee in accordance with their own arrangements.

One Category 4 Issue was raised following an observation of corroded seismically qualified restraint bolts, pending a response from site.