When the tide is high, dangerous things can happen – and when you are building a new nuclear power plant in an estuary where the tidal forces are some of the highest in the world, mitigating risk is the highest priority. Luckily, advancements in technology can make the most dangerous situations into ones that are safer and more manageable.

In the last few months, a public inquiry has been conducted into whether a fish protection measure, known as an acoustic fish deterrent (AFD), should be installed at Hinkley Point C Nuclear Power Plant. The AFD is an underwater system to be placed in front of the Low Velocity Intake Heads, which draw water into the plant to cool the reactor. The initial design and the subsequent Design Consent Order (DCO) both stipulated that an AFD must be installed, but EDF is now challenging this on safety grounds due to the use of divers to maintain the system.

At the inquiry it was highlighted that ROVs could be used to eliminate this risk. ROV stands for remote operated underwater vehicles – and are used to perform tasks such as maintenance and repair when the conditions might be too dangerous for even experienced divers. Because the ROV can be operated from a ship above the maintenance site there is no risk to life to any divers – because there is no need for anyone to be in the water.

And in addition, since the original optioneering phase in 2017, great strides have been made to improve ROVs. A great example of this is the developments being made on High Tidal ROVs.

‘Vehicle has already been deployed on offshore renewables projects.’

In a recent article for Offshore Magazine, three product managers from Oceaneering, manufacturer of one of the world’s leading ROV ranges, Isarus, discussed the need for ROVs in strong tidal situations, and how they have worked with both the fossil and renewables industry to create machines that can deal with the challenging conditions.

In the article, they state “Four Isurus ROV systems are currently in operation in regions such as Northwest Europe and East Asia, performing offshore wind and tidal project construction without encountering currents that have exceeded the systems’ capabilities to maintain station and execute work-class tasks. Prior to the implementation of Isurus, regular work-class ROVs were often unable to execute these same construction tasks for a period of up to 25% of any given day due to severe tidal currents.”

Within the limits of Sizewell and Hinkley Water Speeds

The article states, ‘When compared to traditional ROV systems that were limited to speeds of 1.5 to 2 knots, the Isurus ROV stands out. While achieving speeds up to 5 knots — 2.5 times faster than any other work-class vehicle in the fleet.’

Five knots, when converted to meters per seconds is 1.8m/s. Which is well within the water speeds of Sizewell C and all but the most extreme ranges of Hinkley Point C. And with maintenance plans able to work around short-term extreme water speeds, ROVs such as the Isaurus could provide the maintenance required to reduce the risk considerably. These ROVs are also equipped with 2D and 3D sonar which enables them to operate in minimal visibility.

In addition the authors state that ‘After more than two years in operation, the Isurus ROV has not encountered a current that could shut down operations. It has performed with better than 99.73% uptime for more than 3,500 dive hours.’