High risk and restricted areas

Each nuclear power plant has its own cooling system requiring regular inspection and maintenance to be carried out by professional commercial divers. Such operations may be performed in high-risk & restricted areas.

At DIKO Subsea, we have a comprehensive nuclear power plant maintenance, cleaning, and service program for all facets of the nuclear industry, including outages and on-line maintenance.


Hyperbaric operations in high-risk areas include;
  • Dismantling
  • Cutting
  • Decommissioning
  • Cleaning
  • Clearing out waste and debris
Materials placed underwater to prevent the diffusion of radioactive elements being generated on the cutting phrase of the dismantling process can be dismantled and placed on a subaquatic cutting workshop to follow the same technical treatment.


The range of maintenance activities in a nuclear power plant includes monitoring, surveillance, inspection, assessment, calibration, repair and replacement of parts which main purposes are;
  • Promoting reliable, safe and effective working conditions and minimizing personnel radiation exposure
  • Maintaining working areas in clean and orderly condition preserving correct environmental conditions and guarding against hazards such as fire and chemical spills
  • Optimization of outages minimizing their occurrence and/or avoiding time extensions
  • Implementing an appropriate radioactive waste management system to minimize and effectively control the production of radioactive waste
Mechanical dismantling may also be performed during maintenance operations. In fact, dismantling activities are often required to access confined and restricted areas in order to remove radioactive contaminants during maintenance operations.
Such operations are carried out under the supervision of qualified Operation Managers and the competent authority at the nuclear facility.


Sanitation activities are intended to minimize the radiation exposure of the personnel while performing pool maintenance activities.
Clean-up of the Reactor Building (RB) and the SPF with high-pressure jet and suction equipment including;
  • Essential elements for nuclear plant’s security
  • Tube transfer connecting the PR and the SPF
  • Loading mast
  • Fuel Handling and Storage (FHS) system
  • Drain lines
  • Fuel transfer tippers
Underwater sanitation requires specific equipment used for the performance of filtering and suctioning activities underwater. Suction equipment is directly connected to air supply piping systems in order to conduct the following procedure;
  • An initial suctioning is carried out in order to pull out the largest radioactive particles
  • High-pressure cleaning (max 300 bars) is performed so that smaller radioactive particles may get unstuck from structures
  • A second suctioning is performed to remove the remaining radioactive particles
Underwater sanitation covers underwater decontamination activities which may include;
  • Decontamination of FHS and grappling hooks
  • Decontamination of transfer tunnels
  • Decontamination of fuel transfer tippers
DIKO Subsea’s know-how and expertise in relation to underwater decontamination guarantees excellent results in terms of quality, time and cost with the application of traditional methods (heavy or chemical). DIKO Subsea hyperbaric divers’ excellent mobility allows them to effectively and efficiently work on all structures without complimentary scaffoldings, resulting in time and cost savings, this being critical during outages (for instance, 2 shifts, each one of which lasting 3 hours, are required for the decontamination of a Safety Injection System).

Equipment replacement & assembly

Following Fukushima nuclear disaster, many nuclear regulators are requiring the development and implementation of stricter security measures for reactors of nuclear power plants including increased inspection and maintenance activities such as;
  • Installation of filters in PTRs
  • Modification of PTR grips
  • Assembly of equipment and expansion joints and site monitoring
  • Multi-site modifications
  • Coordination of scaffolding, insulation, non-destructive testing and instrumentation activities

Decontamination & dismantling

Decontamination plays an important role in ensuring the safe and long-term operation of nuclear power plants.
DIKO Subsea supports decontamination of equipment and components within operating and non-operating nuclear facilities including decontamination operations during refueling, maintenance and upgrade activities or decontamination and recovery of rooms and buildings.
Dismantling operations are often required to access inaccessible contaminated sections.
Such operations are carried out under the supervision of qualified Operation Managers and the competent authority at the nuclear facility.

Emergency situations & unexpected events

DIKO Subsea can respond quickly and efficiently to address emergency situations and unexpected events helping nuclear plant operators recover from unscheduled events and minimize plant downtime safely and rapidly.
DIKO Subsea’s know-how allows a prompt and diligent prevention of operational inefficiencies and downtime especially during the execution of critical activities like charging and discharging of nuclear reactors. DIKO Subsea may perform the inspection, maintenance and operation of
  • FHS equipment and structures
  • Loading mast
  • Pebbles
  • Opening and closing doors
  • Extraction of clasp on EIS