Office for Nuclear Regulation

CD19 - Intake and Outfall Heads Construction Assurance (Level 3)

Executive summary

Purpose of Intervention

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

The primary purpose of the intervention was to derive regulatory confidence over the licensee’s application of relevant good practice, principally on the topic of construction management, of the in-situ construction of the intake and outfall heads; including their connecting shafts and adits.

Interventions Carried out by ONR

This intervention was an inspection carried out to assess the licensee’s compliance with Licence Condition (LC) 19: Construction or Installation of New Plant. LC19 requires that where the licensee proposes to construct or install any new safety-related plant, it shall make and implement adequate arrangements to control the construction or installation.

Through this intervention, I sought to assess the licensee’s application of ┬árelevant good practice in construction management with a focus on ensuring the structural safety of the intake and outfall heads and the shafts that connect the heads to the main bores of the intake and outfall tunnels. The scope of the intervention was confined to an assessment of the buildability of the execution design and proposed in-situ construction methods for the intake and outfall heads. It excluded precasting operations for the head elements themselves; this topic having been covered in previous interventions. It also excluded the tunnelling works of the main bores; these being well advanced at the time of the intervention.

The risks considered in the intervention pertained principally to structural safety during the period of construction. Such risks, if unresolved, could nonetheless conceivably impinge on future engineering performance of the nuclear safety classified system in question.

The intervention took place prior to commencement of physical works at the site of the intake / outfall heads, but at a time when the heads themselves had been precast and the main intake tunnel bores were well advanced.

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

Overall, I was satisfied with the licensee’s construction management arrangements to manage risks associated with insitu construction of the intake and outfall heads, their associated connection shafts and adits to the main bores.

The proposed method of construction has been heavily influenced by early contractor engagement and there is, in my opinion, a sound appreciation of the intrinsic relationship that exists between buildability and safety. The original design concept has consequently evolved in its configuration to one that eliminates certain buildability risks that were once present.

Conclusion of Intervention

My overall opinion, based on the evidence sampled, is that the licensee’s arrangements for assuring conformant construction of the intake and outfall heads, together with their associated shafts and adits, conforms with relevant good practice. I therefore judge that a rating of GREEN (no formal action) is appropriate against this LC19 intervention.