It is the 15th October 1958 and a little known nuclear disaster is about to unfold in vinca,
Yugoslav republic, modern day Serbia.
In its wake 1 would be dead and 4 would be seriously injured, although largely forgotten
now… in the aftermath.. an uncharacteristic cooperation agreement between east and west
would result in several medical and nuclear research firsts.
The desire to explore the radiological consequences of the accident resulted in French British
and Yugoslav Cooperation, the results would benefit all sides of the political spectrum
and prove the usefulness of a budding international nuclear organisation.
My name is John and this is a brief history of the vinca reactor excursion and doesemetery
experiment.
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Background a politically charged project.
Our story starts in the late 1940s and the establishment of the Vinča Institute of Nuclear
Sciences.
Yugoslavia had become a communist country in 1946… after the country had been liberated
at the end of ww2 and it abolished its monarchy in November 1945.
In its early years Yugoslavia was tentatively aligned with the USSR and it was amongst this
background that the Vinca institute was formed.
Politically the country would start to become more independent from the Soviet Union in
1948 with the Tito-Stalin split, needless to say this brought the fear of war between
the two communist countries.
Rumers were floating around that the ussr was close to its own atomic bomb and as such
Tito wanted to match his new rivals.
75 billion dinars (about $35 million at the 1953 exchange rate) was spent on building
and operating the country's fledgling nuclear industry; this constituted a significant part
of the country’s gdp.
In the early 1950s several organisations were set up at vinca in preparation to develop
an atomic weapon.
A Department for Spent Fuel Reprocessing was created in 1956; and a heavy water-moderated
zero-power critical assembly “RB reactor” was constructed in 1958.
This RB reactor was the first to be built inside Yugoslavia and strangely for the political
landscape was of a soviet design.
The whole vinca site was named the boris kedric institute.
The Reactor, an experimental design.
The reactor made use of roughly four tonnes of natural uranium in the form of 216 aluminium-clad
fuel rods.
Each rod was 2.5 cm in diameter and 210 cm long. The fuel rods, with a lattice spacing
of 12 cm, were contained in a cylindrical tank made of aluminium of 1 cm thickness.
One end of each fuel rod rested on the bottom of the tank.
The assembly used heavy water du02 as a moderator of the neutrons created during chain reaction.
Interestingly instead of control rods the system made use of the level of heavy water
in the tank to control the reactor.
2 safety rods were provided and were held out of the core by electromagnetics and if
power is cut then the rods fall into the core by gravity stopping the chain reaction thus
being fail safe.
A storage tank was provided under the reactor for excess heavy water.
The design was to also not have any form of neutron reflection as such it was mounted
on a supporting rack to ensure the tank was always at least 4m away from any potential
reflection surfaces.
As well as no reflective surfaces, the reactor had virtually no shielding which the operators
would find out later was not a good thing.
Now I need to quickly mention the reactor's name as it is considered a zero power installation.
You see, a zero power nuclear reactor is capable of sustaining a stable fission chain reaction
with no significant increase or decline in the reaction rate.
This type of installation is essential to gain practical experience of reactor operation,
but can still be deadly if the delicate balance isnt maintained.
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The accident “noone knew the danger they were in”.
It is the 15th october 1958 and an experiment is being undertaken at the Vinca reactor at
the Boris kedric institute.
6 operators are workinging inside the reactor hall on a subcritical foil counting experiment,
the workers rely on BF3 counters to monitor the reactivity of the reactor.
On the day the reactor had 3,995 kg of aluminum-clad natural uranium fuel inside its core.
Because the liquid level was normally used to control the system reactivity and the operators
wanted to obtain as much activation of the foils as possible, the heavy water level was
raised in increments, but it was intended to keep the assembly sub critical.
To do this at each level the bf3 counters needed to be closely monitored. ******
Two of the BF3 counters maxed out at maximum saturation level, but the 3rd was acting erratically,
this was disconnected and technical assistance was requested.
But what the operators didn't know was that the reactivity of the assembly was increasing
ever closer to super criticality.
After the assembly had been at this D2O level for around 5 to 8 minutes, one of the operators
started to smell ozone.
Originally it was thought that a valve may have been leaking but after investigation
it was realized that the system was supercritical at some unknown power level.
Upon realizing this the reactor was scrammed with its safety rods and the hall was evacuated.
A paper recorder based 540m away recorded an increased background gamma ray level for
around 10 minutes.
The heavy water level was at 183 cm and the reactor was in an uncontrolled state for 433
seconds.
During the excursion The total energy release was about 80 million joules (about 2 kg of
TNT equivalent).
A terrific amount of energy to be exposed to especially in an unshielded assembly, definitely
somewhere you would not want to be standing next to.
6 personnel had received varying doses of radiation…initially they received first
aid onsite before being sent to paris for specialist care.
The hospital they were transferred to was the world famous Curie Foundation and there
they were placed under the care of Dr. H. Jammet.
Of the 6 exposed individuals 1 was to be treated conventionally with blood transfusion this
was due to his exposure being significantly lower than the others.
But it was quickly realized that the others would require some drastic treatment, as they
had received in some cases close to and well over a lethal dose.
The radiation had destroyed tissues in their bone marrow, resulting in the number of white
blood cells falling sharply.
At the time the concept of bone marrow transplants was in its early stages, great strides had
been made in the field in the US but in the late 1950s it was still very much an experimental
science.
The bone marrow grafts were performed by Georges Mathe, an oncologist, and made use of donors
That were all French: Marcel Pabion, Albert Biron, Raymond Castanier and Odette Dragh.
The fifth donor was Léon Schwartzenberg, a member of Mathé's team.
The grafts and subsequent treatment helped further the concept of bone marrow grafts,
immunotherapy and how it could be used to treat cancer.
28 days post exposure treatment began, but for one of the men this was too late, they
had received too high of a dose and the treatment didn't help reverse his outcome and sadly
passed away.
However for the other 4 the grafts worked and they gradually made a recovery, reportedly
still being alive in 1980 19 years post exposure with at least 1 of the men becoming a father
to a healthy child.
You see what was interesting with the transplants, was that host versus graft disease was not
observed in the patients who received the bone marrow.
One theory that was posed was that the high radiation exposure had actually prevented
the creation of antibodies and in a happy side effect facilitated the incorporation
of the grafted marrow.
It was estimated that the doses of each man who was ages between 23-26 had revived in
descending order 433, 422, 415, 410, 320, and 205 rem respectively.
For reference 500 rem without any treatment is fatal and between 400-1000 can result in
early death.
It really depends on how much was received where in the body and health of the victim
prior to exposure, as will as a multitude of other factors.
Now the doses of the patients was very inaccurate due to the fact that the reactor was supercritical
for a rather long period of time, and studies into Acute radiation sickness were not very
abundant at the time.
But the reactor now powered down offered an opportunity for the scientific community in
which a study could be undertaken to further understand dose effects on humans.
The vinca dosimetric study
The situation presented to the international community and Yugoslav nuclear officials was
that if the exact doses could be ascertained through an experiment then it could be linked
up to the treatment and ars symptoms of the patients.
Post Stalin Tito split Yugoslavia was more open to collaboration with the west and in
February 1960 an agreement was signed between the federal nuclear energy committee and the
iaea where the reactor would be reactivated and prepared for an experiment.
Part of the reactivation required around 6.5 tonnes of heavy water, as the original stock
had been reused in Vincas other reactors, after negotiations with a number of IAEA member
states the United Kingdom offered the required material for free for the length of the experiment.
The French Commissariat a l 'Energie Atomique offered to make modifications to the reactor
for free as well.
The modifications consisted of detector and more comprehensive control equipment which
allowed the reactor to be placed into different reactivity states more effectively.
More obvious alterations were a wall of sandbags and concrete between the reactor hall and
control room to protect the operators from any fast neutrons.
For the experiment the reactor was to be operated in two power ranges, low and high.
This was to take place at the end of April 1960.
The low power test ran the reactor at 5w and used multiple positions to measure fast neutrons
and gamma doses.
But the high power tests were where things really got interesting as this would involve
these rather creepily characters named phantoms.
They were designed to mimic a human body to allow greater dosimetric accuracy.
The phantoms were filled with an aqueous solution of NaCl at a concentration of 15.7 mg Na per
gram of solution.
After each experiment the sodium activation was measured.
The high power experiment ran at two power levels 1kw and 5kw.
For each run the phantoms were placed in different positions with the lower being closer to the
reactor and the higher being further away.
After the experiments the iaea released its report in 1962 and its well worth reading
The study helped create a greater understanding of potential dose a person can receive in
certain circumstances.
This also Inturn helped in the understanding of the types of shielding needed to protect
staff from fast neutrons and gamma rays.
However the experiment wasn’t the magic catch all bullet but rather another tool available
to nuclear industry.
Even in the iaea reports own concluding remarks this is hinted upon.
“It can (thus) not be expected that data for any one accident can solve all the basic
questions at once or even any of them completely.”
What the experiment did show was the benefits of cross border cooperation when it comes
to radiological investigation.
The disaster and subsequent experiment showed that the young iaea which was founded in 1957
could work as a concept for interstate nuclear industry Cooperation.
After all, it did successfully broker an agreement where an experiment in a Soviet designed reactor
based in Yugoslavia modified by the french and filled with British heavy water could
be used for the greater good of dosimetry discovery.
Now where would you rate this disaster on my scale? I’m going to give it a 3 on my
disaster scale due to the death of a young operator and the horrible pain the other must
have gone through, but an 8 on my legacy scale because of international cooperation, valuable
information gained from the experiement and the successful use of bone marrow grafts.
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John, in a sunny Southeastern corner of london, uk.
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https://www.johnstonsarchive.net/nuclear/radevents/1958YUG1.html
https://nonproliferation.org/titos-nuclear-legacy/
https://www.iaea.org/sites/default/files/publications/magazines/bulletin/bull2-2/02205800405.pdf
https://inis.iaea.org/collection/NCLCollectionStore/_Public/38/085/38085294.pdf?r=1
https://www.osti.gov/etdeweb/servlets/purl/20918988
https://www.nrc.gov/docs/ML0037/ML003731912.pdf page 96
https://www.vin.bg.ac.rs/en/about-institute/history-of-the-institute