Office for Nuclear Regulation

COMAH intervention - PTS inspection

Executive summary

Purpose of Intervention

The purpose of this intervention was to provide regulatory confidence in the management of conventional health and safety (CHS) hazards, specifically relating to Control of major Accident Hazards (COMAH) Regulations present at EDF Energy Nuclear Generation Limited’s (NGL) Dungeness B (DNB) power station whilst it is currently offline. This is in line with the annual COMAH intervention programme agreed with the facility.

Previous interventions had identified a need to examine arrangements in place for the management of the risks posed by corrosion to storage tanks and pipework and related tertiary containment. This visit provided a site familiarisation opportunity to allow effective prioritisation and targeting of future intervention strategies by the new COMAH inspectors.

I was accompanied and supported by the Dungeness B nominated site inspector during this inspection that was at the station as part of his routing station planned visit.

Interventions Carried Out by ONR

The key regulatory activities undertaken during the one day inspection were based around:

Explanation of Judgement if Safety System Not Judged to be Adequate


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

Inventory Management – The site is managing their inventory to remain within the thresholds of lower tier. The current level of hydrazine is being reduced due to temporary storage of Sodium Hypochlorite this being required during refurbishment works. These and other COMAH substances are being stored and controlled in compliance with the COMAH regulations.

Emergency Preparedness – The station has conducted two separate process hazard reviews (PHRs) in 2012 and 2016. The hazard areas identified were mechanical corrosion and potential reactions from accidental mixing of incompatible chemicals. The consequences of these are environmental; and thus constitute the Major Accident Hazards for the site. The site has undertaken a detailed assessment of these environmental risks.

Major work has been undertaken on site to reduce the corrosion risk including removal of external insulation on tanks where it is not required. A programme of replacement of corroded tanks and pipework is also underway.

The MAH identification has fed directly into the MAPP, this was not reviewed in depth but was seen to meet legal requirements. This should be reviewed in future intervention in conjunction with the site SMS.

Maintenance, Systems & Process – There is a schedule/programme for routine inspections of tanks and bunds. The station has aligned these inspections into 1 yearly external and 5 yearly external and internal inspections.

ONR found visible cracks on the hydrazine bund. The station confirmed the coating inside the bund prevents leakage through the bund wall. There were poorly sealed pipework penetrations through the lubrication oil tank bund. This has been raised as a regulatory issue.

The maintenance and management responsibility of the BOC nitrogen tank was unclear. There were clear signs of corrosion, however, it did not appear to be part of the site inspection programme and was understood to be managed by BOC themselves. Site will follow up and ensure adequate inspection and maintenance is performed.

Workplace Transport (Issue 6619) – A follow up to a regulatory Issue was undertaken regarding  Workplace Transport. Little progress has been completed due to the extended outage requiring large areas of the site being disturbed therefore preventing road/pavement painting and installing of barriers etc. Work has been completed in the contractors compound area, with barriers installed.

Conclusion of Intervention

A small number of areas of concern where improvements are required in addition to examples of good standards were seen during the visit. These were summarised during feedback provided at the conclusion of the visit, as were the visit outcomes/actions required by EDF. The Environmental Compliance Coordinator, Plant Manager, Engineering Manager, Operations Manager and Company Safety Advisor were present at the feedback session.

Despite the minor issues raised, the overall impression gained from the inspection in relation to COMAH was a satisfactory one. EDF have undertaken a programme of improvement to repair or replace corroded tanks and pipework across the site, which included COMAH products.  The ongoing inventory will need careful management to ensure the site remains lower tier. Maintenance of bunds including cracks and bund wall penetrations require attention, which will be tracked via a regulatory issue. Ownership of the BOC nitrogen tank in relation to inspection and maintenance will be followed up by the site.

These shortcomings aside, health and safety management standards met legal requirements. . Therefore, an inspection rating of ‘green – acceptable’ should be applied to all parts of the intervention.