Diving into nuclear power plants is specific to only a few companies rigorously selected by the operators. For this reason and to ensure relevant information, I have contacted Patrick Lucon, the diving manager of “Onet Technologies CN”, a company specializing in these activities, headquartered in Marseille, France. who provided me with a presentation I have adapted for this article. Note that in addition to services to the nuclear industry, this group, which operates worldwide, is specialized in the design and production of specific communication systems, asbestos removal, waste management services, and many other activities. The diving department of “Onet Technologies CN” was initially “COMEX Nucleaire”, a company created in 1990 by the COMEX group that was bought in 1999 by “Onet Technologies CN”. The need to work and dismantle installations in contaminated nuclear pools created this diving activity that initially employed divers who previously worked on military experimentation sites. SOGETRAM, a subsidiary of the COMEX group that specialized in interventions in unhealthy surroundings in addition to onshore and inland diving operations, was one the 1st company involved with this market in France before the creation of “COMEX Nucleaire” (Note that SOGETRAM no longer exists). The company operates for clients such as EDF (1), ORANO (2), and CEA (3), and all types of diving work are done in their nuclear facilities (mechanical, inspection, welding, etc.). These interventions can be anticipated or incidental, requiring continuous personnel and material availability. Nuclear diving is an activity in a radioactive environment, and no school trains divers for it. For this reason, Onet Technologies CN trains its divers in specific gestures and procedures to allow them to work in the very closed nuclear industry environment safely. Trainings are regularly carried out in the COMEX swimming pool in Marseille, France, or in pools similar to those of the nuclear facilities in service at the "Centre d'expérimentation des techniques d'intervention sur les chaudières nucléaires" (Experimentation centre for technical interventions on nuclear boilers), also know under the acronym "CETIC". This makes it possible to carry out the most appropriate gesture for saving time and limiting the ionising radiation dose absorbed by the diver during his exposure time (measured by dosimetry). The study and manufacture of suitable equipment are necessary. For this reason, a close collaboration is established with the Onet Technologies design office and the well-known nuclear power plants manufacturer "Framatome" (4). Also, based on the 30 years of experience acquired by the company, the diving department continuously improves the diving systems, which are standardized as follows: • Fully sealed reinforced rubber dry suits, like those made by "Viking" or "Gates", equipped with waterproof rubber gloves, so that no part of the body is exposed to the water, are the only type of suits used currently. Note that for ionising radiation exposure reasons, the diving team uses only one suit, which result that the divers of a team should be of similar mensuration to be able to use this suit safely. • The helmets used are continuous flow types. The company has successfully used the Aquadyne AH3 and AH4 in the past, and now the AH5, which is the latest evolution of this helmet (Aquadyne is a Brand of JFD). However, the exhaust valve of these helmets has been modified as the original model did not allow working in any position without water intrusion: As a reminder, this adjustable exhaust valve is provided with a "Head button" that can be operated by a movement of the head for the accelerated evacuation of the air contained in the suit, allowing the diver to quickly adjust his buoyancy and avoid an uncontrolled ascent (blow-up). As water intrusions were noticeable when the diver operated this button in the laid position, and because a perfect sealing is essential, this exhaust valve had to be modified. This problem has been solved with the help of COMEX Pro diving systems designers and then those of COMEX Nucléaire. In addition to the above, the company has closely worked with Beat Engel (Composite - Beat Engel) on designing a new helmet better adapted to its nuclear diving activities. This project, started five years ago, results in a new model equipped with a removable weight that allows additional comfort during the diver's long dressing and undressing phases. These long phases are linked to the fact that the diver must be fully assisted during the dressing phase, as he must never touch the outside of the suit for obvious contamination reasons. It is the same for the undressing phase, where in addition, a thorough decontamination must be done by the assistants to guarantee an undressing without risk before being allowed to get out of the suit. As the helmets are calculated to have a neutral buoyancy, they are quite heavy outside the water. For this reason, a helmet with a removable weight has been considered an advantage regarding comfort and, thus, fatigue of the diver. Specific and strict operational procedures must be in place: A radiation dosimetry must be conducted to identify and quantify the nature and impact of the radiological risks to which the divers will be exposed before starting the diving campaign. A map identifying the radiation context is established under the responsibility of the Radiation Protection Department of the site: • A first mapping is carried out from the surface before any diving campaign. absorbed in real time. This makes it possible to better manage the traveling and gestures of the diver. • In function of the cartography, more precise measurements are carried out at the start of the dive in areas inaccessible from the surface. • The volumetric activity of the water and the nature of the radioelements* are also requested. (*Radioelements = Element that are radioactive). For information, underwater, the radiological dose rate decreases by a factor of 2 when moving away from 10 cm. This is why nuclear diving is considered suitable. Another point to take into account is that the water of nuclear pools is often hot (consider temperatures between 24 and 34 °C). For safety reasons (hyperthermia), the company considers that the water temperature for diving intervention should be below 28 °C. Depending on the intervention criteria, a specific study by the hyperbaric doctor and the company's hyperbaric prevention advisor can be considered. The composition of a diving team is 5 people, organized as follows: - 1 diving supervisor - 1 working diver - 1 standby diver - 2 divers operating as tenders Therefore, the functions of the team members are identical to those in force in the offshore industry, with a diving supervisor managing the dive and a standby diver ready to intervene as quickly as possible in an organized manner on the supervisor's instruction in case of an incident or accident. For this reason, the standby diver is not involved in any other activity than waiting for the instruction to rescue the diver at work, and is partially equipped, as it is the case in the offshore industry. In addition to the precautions already mentioned, the intervention of the diver is organized to manage and minimize the radiological risks: • The diver’s suit is provided with several radiological probes (one on each foot, one on each wrist, one at chest level, and one in the back), allowing the diving supervisor to know the radioactive dose absorbed in real time. This makes it possible to better manage the traveling and gestures of the diver. • The diver moves along a path previously defined in the work procedure according to the radiological mapping of the environment. • A precise radiological survey is carried out in the intervention area, and the diver is equipped with a radiological probe for this reason. This submerged probe must remain available and close to the diver throughout the intervention. Nuclear diving remains a particular activity where errors are not allowed. For this reason, in addition to the working methodology and intervention procedures mentioned above, the mentality of the divers contributes to working safely in this very closed field of activity. Notes: 1. Orano SA is a multinational company headquartered in Châtillon, France, specializing in uranium mining, conversion, and recycling. The company also provides logistical, engineering, and intervention services to the nuclear industry. 2. EDF is the acronym of “Electricite De France” (Electricity of France), a French multinational electricity producer mainly owned by the French state and headquartered in Paris, France. The company operates various types of power plants worldwide and is one of the major operators of nuclear power plants. 3. CEA stands for “Commissariat a l'energie atomique” (Atomic Energy Commission). As suggested by its name, it is a French public research organization initially specialized in the civil and defense nuclear industry whose function is to create synergies between fundamental research and advanced technology, including designing nuclear reactors and manufacturing specific systems. For a few years, the mission of the commission has been extended to the study of other energies, resulting that its name is now changed to “Commissariat a l'energie atomique et aux energies alternatives” (Alternative Energies and Atomic Energy Commission), without changing the acronym under which it is known. 4. Framatome is a nuclear systems and power plants manufacturer operating worldwide and headquartered in Paris, France. Contact: Patrick Lucon: LuconP@onet.fr Complemetary paper: The document “Diving protection against nuclear contaminants”, published in 2020 by Nicusor Chiripici, Amil Avram, & Laurentiu Mocanu can be read in the section “Diving equipment”

Underwater welding training in a swimming pool

New Composite Beat Engel helmet model DSL B2 CN. Note the removable weight also acting as a protector.

Diver dressing (above) and cleaning before undressing (below). Note the protective suits of the assistants.

Launching the dive in a reactor pool

Intervention in a combustible pool