Case study 05 · Nuclear marine works

Learning from one tunnel to de-risk the next

Each cooling-water tunnel has to be stripped of temporary services, repaired and handed over to the client section by section. The first handover took 90 days, and the larger tunnels risked taking twice as long, with contractual penalties at stake. We captured what the team had learned and turned it into a plan for the next tunnel.

Download the PDF About the programme

At a glance

149 of 152 non-conformance reports shown to be closable

7–9 days of engineering time freed

12 weeks fixed window for the next handover

Context

The challenge

After tunnelling, each tunnel is stripped of the services that supported construction, then scanned and repaired before the client’s surveillance and delivery teams sign it off. The first, shorter tunnel took 90 days to hand over, and the two larger tunnels risked taking up to 180.

The final tunnel had a fixed window of around 12 weeks and a very different repair profile, with low cover repairs up from 25 to 1,111 and radial joint repairs up from 5 to 330.

Our approach

How we tackled it

We ran two lessons-learned workshops, one internal and one with the client’s surveillance and delivery teams. We observed strip-out, repairs, snagging and handover over several days, and analysed scan and repair data for the next tunnel.

What worked

Strong collaboration with the client, early engagement with the surveillance team and lessons carried over from the previous tunnel had already improved section handovers.

What held the team back

Slow defect logging, resources split across areas with no logical sequence, little time to plan between tunnels, snagging that relied on repeat inspections and limited hands-on training.

Where the risk sat

About 75% of the next tunnel’s repairs were in the invert and front-loaded. One platform zone had held 1,656 recorded issues, against 121 across the rest of the tunnel.

Outcome

The results

149 of 152 non-conformance reports, covering 2,108 defects, were shown to fall within the standard repair procedure and could be closed, freeing 7 to 9 days of engineering time.
Disposable templates trialled for low cover repairs save about four minutes a segment: around 74 hours across the tunnel for about £1,500 of material.
Pre-start works planned for the gap before handover, including moving services to reach the repairs behind them.
Resource plans built around where the repairs actually are, with shorter sections for more frequent sign-off.
A dedicated construction manager recommended to strengthen planning, team structure and programme control.