Radiation is a valuable asset in the sterilization of materials, and because of this hundreds
of facilities across the world harness radioisotopes, from irradiating food, equipment and even
blood.
But history has shown that these facilities are often overlooked when it comes to maintenance
funding and training.
This is because they offer little risk to the outside world in the same way that a facility
that regularly assembles critical assemblies or a nuclear reactor.
And due to many being operated for profit production schedules offer a unique pressure
on operators.
An industrial sterilization facility in Nesvizh nezvitz, Belarus would become center stage
in the early 1990s for an over exposure event which would result in death.
The story would follow a similar route to other incidents where an operator would enter
an irradiation room when it was certainly not safe to do so.
However what is different in this event was that the facility had multiple features that
should have stopped an exposure event and on the day they were working, and the operator
was highly qualified, meaning they had to actively avoid these safety measures.
My name is John and today we are looking at the Nesvizh Radiological Accident.
//////////// Background
It is 1981 and a new irradiation facility is being planned for use at the Biochemical
Plant of the Pharma Industry Corporation in Nesvizh, USSR, modern day Belarus.
It is going to be built by the All-Union Scientific Research Institute of Radiation Technology
of the USSR, and is designed to a standard set out by soviet relegatory athurotiroes.
It is intended to irradiate peat for use in fertilizers and makes use of gamma radiation
from an original capacity of 6.72 PBq of cobalt 60.
3 years after conception the site would become operational in 1984, but would undergo a significant
refurbishment in 1989 where the capacity would be upped by over 3 times to 30 PBq of Co 60.
Along with the greater reactivity of its source the plant was further modified to irradiate
other types of materials including medical equipment such as syringes.
The design of the facility is of a 'Pepel' model type and is different to what we've
seen on this channel so far when it comes to irradiation plants.
And whilst we are here let's look at the Pepel Irradiation system.
There are a number of differences to say a western irradiation machine, the first is
the way that the source is stored when out of use, instead of a pool, the radioactive
material is in a shielded dry storage pit.
However, the system still makes use of gravity in that when in use the source is raised out
of its pit and in the event of a power outage or a safety system trip the source is dropped
to a safe position.
Another difference from say an Atomic Energy of Canada Limited (AECL) design is the way
the products to be irradiated are given their sweet dose of radiation.
Instead of pistons rollers and conveyors, the products are rotated at a constant rate
around the source in a transport container suspended from an overhead rail.
The whole irradiation room is surrounded by concrete shielding up to 1.8 meters thick,
and like many other facilities entry is via an area called the maze.
The maze here is far more intricate than other facilities I've looked at and this is primarily
due to its pretty impressive safety systems that are aimed at preventing and mitigating
the risks from unauthorized entry.
The first reminds me of something from Indiana Jones, when the source rack is in the irradiation
or up position a section of the floor at the entrance to the maze is driven back by a motor
to reveal a deep pit, the only usable ledge is the top of the motor housing.
This acts as a physical barrier to entry but that isn't all there is, further down the
maze hallway is a full width pressure plate, too big to be jumped across, if stepped on
then the source rack would be lowered.
The sauce is made up of a rack of pencils and spacers; each pencil can have as much
as 70 TBq of radioactivity.
Control of the facility is done at a panel in the control room next to the loading bay
for the transport system.
From here operators can control the source and the transport mechanism as well as the
gamma monitoring system.
The Gamma monitoring system is interlocked to the control panel if either of the 2 monitors
outside the room take a reading that exceeds 14 uSv/hr then the rack is dropped into the
pit.
During operation the product transport system and the movement of material to be irradiated
is monitored from its control panel; this has illuminated signals that are triggered
by micro switches along the track.
The first hint of a product jam is if a light doesn't illuminate in sequence, this requires
the operators to remain vigilant from a radiation dose point of view as if a product is held
in a position for too long it can damage it.
But unlike the gamma monitors the transport system is not interlocked with the source
rack, and thus if there is a jam then its is solely down to the operator to make the
irradiation room safe by dropping the rack via the source down button.
Now before we get onto the fateful event we need to mention the correct procedure for
entering the irradiation room, as no matter the amount of safety systems you can have
proper control of staff actions can be the difference between life or death.
To gain entry to the facility an operator must first Push the 'down' button on the control
panel.
This illuminates the 'down' light until the microswitches sense the irradiator is 'fully
down.
The operator is then required to wait 4 minutes, then the key on the control panel should be
turned from the 'ready' to the 'off position, and then removed.
Then the dose rate is monitored from the gamma probes, if at an acceptable level then they
must check their portable dose rate monitor on a test source attached to it.
The key has to be taken to the maze entrance panel, where it is inserted and turned to
the 'on' position that moves the motorized floor section to cover the entrance pit.
A final check of the portable monitor to see if there are higher than anticipated radiation
levels.
You should see between 0.2-0.5 uSv/h when the rack is lowered, and if fully exposed,
3-4 uSv/h.
Upon entry to the irradiation room, the operator must keep on checking their portable monitor.
Now we know how it's meant to be done, we must now look at the disaster.
The Disaster It is the early hours of Saturday, 26 October
1991 and 2 workers are operating the Nesvizh radiation facility, this morning the team
consisted of the site's most experienced operator and his assistant.
The operator was 34 years old, had a degree in engineering and had worked at Nesvizh since
the site's construction.
He was in the control room reading a newspaper whilst the assistant was on the loading bay
loading the product into the carriers.
The assistant became aware of a product jam when the drive motor noise made a noticeable
change, he called out to the operator.
The operator pushed the source down button as per the rules but failed to remove his
key before making his way to the maze entrance, investigators would later speculate that this
was to speed up the resumption of operations after the jam was cleared.
Without his key the operator had a problem, how to move the motorized floor to bridge
the entrance pit gap, well, his experience from previous incidents had shown an alternative
method of entry.
You may remember that I mentioned that the motor housing is the only pretrouding thing
in the entrance pit as it turns out it is enough to support the weight of a person and
gives a big enough ledge to step over the gap.
He did however take a portable radiation monitor with him, and he approached the pressure plate.
This is where the narrative gets a little bit shaky, the operator post event was reluctant
to tell investigators how he managed to go over the plate, without triggering an emergency
source down situation.
But there are a couple of theories, 1 was that he climbed over the plate by grabbing
the transport rails, or the other was that he did walk on it but the rack was jammed
and thus didn't go down into the shielding pit, the final theory was that the rack raised
on its own accord.
Regardless the operator made his way into the irradiator room, upon entry the transport
containers would have obscured the view of the rack, but its counterweights would have
been visible which could have indicated its position.
It's unlikely that he realized the position of the rack as he started to clear the obscuration,
after approximately 1 minute he started to experience a headache, he looked around the
room and discovered the rack was in the irradiation position.
He ran out of the irradiation chamber and told the assistant that he had been exposed,
immediately telephone calls were made to the local hospital and the police.
Within 20 minutes an ambulance had arrived on the scene and transported the operator
to hospital.
Quickly it was realized after the operator explained what they had been exposed to that
the Nesvizh hospital didn't have the appropriate experience needed to deal with the patient.
He was transferred via Minsk, to the clinic at the Biophysics Institute in Moscow for
specialized care.
Within the first 7 days bone marrow and gastrional issues started to manifest themselves in the
operator, during this period investigations were made into the dose received during the
incident.
The operator's clothing was analyzed and this gave an estimation of between 11 and 18 gray,
roughly 3 times a fatal full body dose.
8 days post exposure the patient had started to experience a fever, and 11 days post exposure
he began to manifest severe skin injury.
Around day 40 his general state was relatively stable but would start to show symptoms of
pneumonia, and his condition would deteriorate, by day 104 he was showing a typical acute
adult respiratory distress syndrome.
The patient's blood pressure decreased on day 112, and sadly the following day he would
die while in a hypoxaemic coma, caused by respiratory distress.
Aftermath We have to jump back to the day of the disaster
after the exposure and before he was transferred to moscow, local authorities spoke to the
operator to try and find out how the event played out.
He was not particularly forthcoming and tried to pass off many questions to feeling tired
during his shift and not being able to remember.
A government led investigation looked into the event, and concluded that the following
facility modifications be implemented: Enlarging the size of the pit and moving the
motor, Providing an audible alarm for movement of the source rack within the facility and
Providing visible warning signals inside the facility to indicate the position of the source
rack.
The sites license was suspended until these modifications were implemented, but there
was still the looming question, if the operator pressed the source down button how did the
rack go back up in the time between walking from the control room to the entrance of the
maze.
The rack being jammed seemed unlikely as no debris was found that could have caused an
obstruction, the other cause is likely linked to the fact the operator did not remove the
key, and thus in theory left the system with power.
This left the system open to the rack being raised either from Accidental and unnoticed
depression of the exposure button, Temporary failure of a component in the control circuit
or The logic of the electrical circuits which could have provided power to the lift circuit.
The initiating events are all too common with these types of facilities, and that is a product
jam, this coupled with the pressures of production targets has shown to lead operators to undertake
reckless actions.
If the rules had been followed properly then the overexposure would have likely not happened.
Now as always if you want to read into this event more then check out the IAEA report
the link will be in the description below.
This video is a Plainly Difficult production.
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https://www-pub.iaea.org/MTCD/Publications/PDF/Pub1010_web.pdf