The Life of a Nuclear Diver

All material in this article is copyrighted © by William L. Sheaffer

Introduction

Commercial diving comes with its fair share of problems and challenges.  Disorientation, temperature, strong currents, depth, and low visibility are a few of the challenges that divers face daily.  Now consider those are gone and a new challenge is presented, one that cannot be seen, touched, tasted, or smelled.  This challenge is radiation and to a nuclear diver it is a very real and potentially hazardous occupation.

In today’s world of heightened security due to the risk of terrorism, the nuclear power industry is always on watch.  For a worker just to get through the door, a series of prerequisites must be fulfilled.  A psychological evaluation, FBI back ground screening, drug screening, and many hours of education are required.  The classroom training is on how the plant operates, fall protection, confined space, foreign material exclusion, and of course, full radiation worker knowledge.  Once all these are completed and accepted, an unescorted access will be granted and the worker can then enter the plant property.  To enter the plant, the worker must pass through a bomb detector, a metal detector, and then a key card gate that also requires the worker’s hand geometry to be scanned.  Once past the guard house, the nuclear workers can begin the role for with they were hired, nuclear divers.

Depending on the location of the dive operation, many hours of meetings with engineers, radiation protection, and the client are required.  The dive crew must have a full understanding of the work location, work to be performed, water temperature, water depth, and potential radiation dose sources.  Generally these meetings are referred to as briefs, but by no means are they brief.  These briefs can normally take up to several hours and much patience, but that is all part of the job.

In water temperatures exceeding 95 degrees F, a diver can quickly become fatigued and run the risk of possible heat stress.  If the dive location is found to exceed this temperature level, several options must be considered.  The use of temperature reducing gear for the diver is one option or the possibility of postponing the job until temperatures can be reduced is another.  Normally the second option is not possible due to the time it would take to reduce temperatures.  So the option of gear used by the diver is on the top of the list.  The modern nuclear diver has two reliable options to reduce the temperature inside the suit, one is an ice vest and the other is a cool suit.  An ice vest is a good option if the dive will be short, since the ice in the vest will melt, eventually causing the diver’s temperature to rise.  A cool suit is a much better option since it is more reliable and will keep temperatures low during the full length of the dive.  The cool suit was a joint design conducted by divers and astronaut suit engineers, allowing for bottom times of over an hour in water exceeding 120 degrees F.  It is a light weight Dacron material with small diameter Tygon tubing sewn into the exterior of the suit.  The Tygon tubing allows for chilled water to pass through, constantly keeping the diver’s body temperature much cooler than the surrounding water.  The chilled water is normally kept in a small cooler that is mixed with ice and circulated to the diver using a small air powered pump.  On larger dive jobs involving more than one diver in the water at a time, a refrigerator pump unit is used.

Radiation Protection

Before any diving can be done, a meeting with Radiation Protection (RPs) needs to be scheduled so understandings between both groups can be achieved.  The RPs should have up to date dose rates for the job location, so the divers know what they can expect underwater.  The RPs and divers also need to agree upon where dosimetry packs will be placed on the diver’s body.  The packs are small electronic dosimeters (EDs) that record the amount of radiation dose the diver is receiving.  Each ED is placed on a section of the diver’s body, which normally is on the feet, legs, chest, arms, and head (picture 1).  The EDs are linked by wires to a central transmitter unit usually attached to the diver’s back.  On the outside of the suit is a receiving unit antenna attached to a cable mated to the dive umbilical.  Topside this cable is attached to a computer for the RPs to monitor in real time the radiation field and the dose the diver has received.  This is one of the most vital portions of the nuclear diver’s equipment.  If one of these units were to fail, most likely the dive is terminated until the problem can be located and fixed.


Picture 1: Diver with EDs attached

The divers' outfit



   Picture 2: Diver in “Nuke” dress out

 On the day of the dive it is time to get dressed up; the diver has on a cool suit with all EDs attached to the outside.  As the diver marches up to the fuel floor, RPs are in tow to make sure everything is ok and the EDs aren’t bumped.  The rest of the dive crew has been on station for nearly an hour now, to do their last minute checks and make sure everything is ready for the diver.  Once the diver is on the floor, all attention is directed to the diver for a timely suit up and water entry.  The diver’s suit is made of vulcanized rubber (ex. Viking, Hunter..) which limits the amount of contamination, is easily cleaned, and waterproof “most of the time”.  The cool suit has hook-ups inside the dry suit which look similar to the inflator valve on any dry suit.  On the exterior of the suit is an identical hook-up which is attached to the cool water hose.  At this time the cool suit will be hooked up to make sure the diver’s cool suit is working correctly and to start cooling the diver who is already beginning to heat up.  After the suit is zipped up, two layers of rubber gloves are attached to the hard cuffs on the dry suit.  This allows the diver to have dexterity while limiting the amount of contamination to the hands, especially if the outer layer happens to rip.  Next up is the external antenna attached to the divers harness.  This will enable the RPs to verify all the dosimetry is working and all the packs are transmitting.  As with normal dry suit diving, weight is essential, so on comes the heavy belt with solid weights.  In the past small shot lead weights have broken and caused foreign material issues, thus the reason for solid weights.  Last but not least is the helmet, which normally is a Desco air hat, due to it’s positive pressure free flow, and smooth cleanable surface, it is the preferred hat for nuke work.  The suit is fitted with a Desco neck yoke that mates up to the hat and makes a water proof seal.  Once the hat is on and cammed up the diver quickly but safely enters the water, that is a lot of weight to have on in the dry (picture 2).

 The Amp 100

Once the diver is in the water, an Amp 100 is lowered.  The Amp 100 is a radiation sensing device that allows the diver to give a more accurate survey of the work area.  This device is also very useful for acquiring dose rates on items that might be found on the bottom.  Due to the possibility of irradiated items, this will tell the diver if that item can be picked up or just pushed off to the side.  After the RPs have given the ok, the diver can then proceed with the objective at hand (picture 3)(picture 4)(picture 5).  If dose rates are found to be higher than expected an underwater vacuum can be used to help remove contaminates from that area.  If a vacuum is not an option, the placement of lead blankets can be used to help lower the amount of dose the diver will receive.   


Picture 3: Using an Amp 100


Picture 4: Diver at work


Picture 5: Diver welding 

Once the diver has completed the assigned task, it is time to clean up the work area.  The tenders will start to bring items up to the surface as with normal clean diving operations.  As these items are being raised, anything coming out of the water must be rinsed with de-mineralized water and wiped down.  Thoroughly cleaning these items will ensure the prevention of the top side personnel from being exposed to potentially hot particles.  Hot particles are small bits of irradiated material, which are usually too small to see with the naked eye.  If these particles are left out of their water shielding, it could cause extreme dose to be received by the workers.  After all the tools and equipment are cleaned up, it’s time for the diver to come up.  As with everything leaving the water the umbilical and the diver must be washed down.  Special attention must be placed on rinsing the diver’s hands and feet which come in the most contact with contaminates on the bottom.  Once the diver is clear of the water, the tenders and RPs go into action.  The tenders quickly wipe the diver down, trying to get all drops of water off the suit.  While the tenders are drying, the RPs are using meters to survey the diver and assure there are no hot particles on the suit.  By this time the diver is tired, so in reverse order of donning the equipment, the tenders assist in quickly but carefully removing the gear.  Once clear of all the gear the diver is marched back off the floor by the RPs.  They will first ensure there are not contaminates on the cool suit or dosimeters, if clean the packs are removed and the diver is clean to change back into clothes.  If the diver is found to be contaminated, then it’s off to the showers to clean up and hopefully make it past the radiation contamination monitors, thus ending another nuclear dive (picture 6).


 Picture 6: RPs & Tenders in action

Conclusion

Over the many years, the nuclear power industry and commercial diving companies have been working together to form a state of the art partnership.  Cooperation by both groups have developed solutions to problems in a more practical format.  Instead of draining an entire pool to perform a job that would be costly to the plant and cause extreme dose rates for its workers, divers have been implemented.  When emergencies happen, divers are usually the first to be called in to assist.  They have worked in spent fuel pools, performing re-racks, which allow for more storage of spent fuel rods.  They’ve gone into fuel transfer canals to replace sensors and repaired broken transfer carts which move the fuel bundles.  They’ve welded on steam dryers, which have been cracked and needed modifications.  They’ve mended broken equipment above the reactor which would have left the plant in a complete shut down unless repaired.  They’ve even worked in the reactor several feet above live fuel to repair flow nozzles, and recover lost items which could damage the fuel rods.  All the while performing their work as professionals even knowing that for each day the plant is not producing power, it’s loosing upwards of a million dollars a day.  No time pressure!

About the DESCO air hat

When diving in a nuclear plant, time and cost become a huge factor in planning for work.  As stated in the Nuke diver article, a nuclear plant can loose upwards of a million dollars a day, when it is not producing power.  If the diving operations are in the power producing areas, the divers will be under a magnifying glass.  The divers will be expected to perform their work quickly and efficiently, and questions will arise when they fall behind planned hours.  To decrease down time due to diver problems, the Desco air hat has been found to be one of the easiest hats to maintain in the field.  With its basic engineering, any repairs that may arise, can be dealt with rapidly and normally will be back in the water in less than an hour.  As stated before, the other issue with nuclear plants is cost.  When diving in radioactive pools, any dive gear that comes in contact with the water is regarded as contaminated.  Also depending on the dive station location and potential for airborne contaminates, that too may be contaminated.  All this contaminated equipment can no longer be placed back into normal service.  If the equipment is new and brought into the plant by the diving contractor, then the plant becomes the proud owner of this diving equipment.  Since diving gear is not cheap, they look for the contractor to lean towards less costly equipment.  Dive umbilicals, radios, harnesses, and weight belts are normally at a set price, but helmets can come cheaper, thus the Desco air hat.

As with normal diving, it is not uncommon for the diver to hit his head on a support or obstruction.  Through out the industry fiberglass helmets have been seen with scrapes and gouges on the surface that will attract dirt and other debris.  In a nuclear pool, the debris now becomes radioactive contaminates, that may be hard to clean off, in turn raising the acquired dose on the helmet.  The copper of the Desco air hat is a much nicer and easier material to clean, even with the scratches, helping to keep dose rates lower.  The last thing the diver and the plant want is a high dose source on the head.

Another benefit of the Desco air hat is its positive pressure, free flow design.  In the event the neck ring leaks, the positive air will push out the leak, and prevent water from entering.  Even if the diver is working hard, the chance of the diver over breathing the hat causing a negative pressure is slim.  The potential for leaking hats is always on a divers mind, and it has happened, but for the majority of all nuclear dives, the head is the driest part of the body.

I hope this sheds a little light on what type of diving helmets the nuclear side prefers.  The Desco air hat is the preferred hat in the US , but through out the world, other hats are being used and I have no intention on down playing other manufacturers helmets.  This article is based on what my company dives and what I’ve had experience with the length of my nuclear diving career.

Many thanks to Bill Sheaffer for his fantastic help on this part!

Continue to page 2 to see more Nuclear divers in action

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