Office for Nuclear Regulation

Compliance inspection CD35 - Backfilling, Surcharge Management and Waterproofing

Executive summary

Purpose of Intervention

In accordance with the Office for Nuclear Regulation’s (ONR’s) Hinkley Point C (HPC) Construction Inspection Plan, ONR performs a series of planned compliance inspections of applicable licence conditions. This is to ensure that the licensee, NNB Generation Company (HPC) Ltd (NNB GenCo), is adequately developing and implementing its compliance arrangements in a manner that is commensurate with the stage of the project under consideration.

This intervention was an inspection carried out to assess NNB GenCo’s compliance with licence condition 19 (LC19); Construction or Installation of New Plant. LC19 requires that where the licensee proposes to construct or install any new plant, which may affect safety, the licensee makes and implements adequate arrangements to control the construction or installation.

Intervention Aims

The aim of this intervention was to assess the adequacy of NNB GenCo’s management and quality control arrangements at site together with its application of relevant good practice in the areas of structural backfilling, surcharge controls and structural waterproofing. It sampled nuclear safety classified structures of both Unit 1 and Unit 2.

A number of the nuclear safety classified structures are either partially or wholly embedded within the ground. As such, they have been designed to resist lateral earth pressures arising from the backfill material. In the majority of cases at HPC, embedded structures have been designed to resist seismic lateral earth pressures transmitted through the backfill, under both seismic and normal loading. The magnitude of lateral earth pressures acting upon embedded structures can be significantly affected by a number of factors, including: the properties of the backfill material, the methods employed for its compaction and by the action of surcharge loads associated with construction plant.

A number of the nuclear safety classified structures at HPC employ structural waterproofing systems. In the context of HPC, the principal functions of structural waterproofing are either to fulfil an internal containment function or to provide external protection to the structure from degradation through contact with aggressive ground conditions.

At the time of this intervention, the physical backfilling and waterproofing operations covered by this intervention were underway at site. I took the opportunity to sample a number of areas where relevant work was ongoing.

Explanation of Judgement if Safety System Not Judged to be Adequate

This section is not applicable as this was not a safety system inspection.

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

Responses to questioning were forthcoming, informative and provided me with confidence that the planned operations were being adequately managed, with due consideration of the risks involved.

Overall, I was satisfied that the licensee’s current arrangements in relation to the planning of implementation of structural backfilling, surcharge management and waterproofing.

Conclusion of Intervention

On the basis of the evidence sampled, I was satisfied that the arrangements in place comply with LC19. Accordingly, I assign an inspection rating of GREEN (No formal action) to this intervention. No regulatory issues were raised.