Nuclear criticality accident in Russia last 7 days, kills one technician.

[NNadir]

This is actually a relatively old tale, from 1997, but I'd never heard about it.

The incident did not take place in a nuclear power reactor but in a research institution.

http://www-pub.iaea.org/MTCD/publications/PDF/Pub1106_scr.pdf

Some excerpts:

The critical assembly, which is described in Refs <26, 27>, was designed as an
experimental tool to study fission reactions relevant to the design and development of power reactors and research and impulse reactors. It is located in a purpose built facility (see Fig. 3).

In accordance with documented procedures, a known subcritical portion of the assembly is constructed and then moved to a position from which it can be raised and lowered by a motor (see Figs 4 and 5). Thorough preliminary calculations as well as experience from previous experiments are employed in ensuring that the assembly remains in a subcritical state during this stage of the work. Safety measures taken include a requirement for an experiment controller (supervisor) to be present in the experimental hall (in addition to the technician who constructs the assembly). Additionally, the neutron flux from a 252Cf source placed at the centre of the fissile material is observed. This flux is constantly measured and is displayed visually in the working area as well as being converted into a click audible on a loudspeaker.

Here's what happened:

On the morning of 17 June 1997 at about 09:30 a technician, a 41 year old male of height 1.80 m and weight 81 kg, reportedly started to assemble a previously functioning and familiar critical assembly comprising a high enriched uranium core and a predominantly copper reflector. The victim was an experienced technician who had carried out several hundred previous criticality experiments. He was reportedly working with a well known system and was not expecting any problems. However, he was working alone in the experimental hall, which was a violation of documented procedures.


At 10:50, during the construction of the assembly, a component from the upper reflector slipped from the technician’s rubber gloved hand and fell on to the lower part of the assembly, which had already been constructed and contained the enriched uranium core. (Gloves were routinely worn to prevent contamination of the components of the assembly.) The point of criticality was exceeded, there was a flash of light and a wave of heat, and the lower part of the assembly was ejected downwards into the bottom of the stand (Fig. 5).

The technician reportedly realized that a criticality accident had happened. He left the experimental hall and closed the sliding doors connecting the experimental hall to the adjoining rooms, as shown in Fig. 3. He informed his supervisors and colleagues of the event, reportedly telling them that he thought his exposure was likely to prove fatal.

During this first few minutes after the criticality event he was fully conscious and fully active. As soon as they were alerted, radiation protection personnel performed an initial direct radiological survey of the technician, which detected the neutron induced gamma radiation emitted by radionuclides in his body.

The critical system he had fired up was still critical and stayed critical for :

By 13:00 it had reportedly been firmly established there was no airborne or surface contamination within the experimental hall. However, the assembly was still in a state of criticality and was emitting significant amounts of neutron and gamma radiation. Of a number of neutron detectors used to measure the neutron flux in normal operations in the room in which the accident occurred, all except the detector furthest from the assembly read off the scale. Another detector was introduced through a channel in the shielding to permit monitoring of changes in the neutron flux. By means of this detector, it was determined that the neutron flux was relatively
stable, indicating that the chain reaction was self-regulating...

...To terminate the chain reaction it was necessary to remove remotely part of the critical assembly or to change its configuration in some other way. Personal access to the experimental hall was precluded owing to high radiation levels. The only option readily available to those dealing with the emergency was to use the remotely operated overhead crane in the experimental hall. A significant difficulty was the fact that moving any object close to the assembly would increase its reactivity and hence the heat and radiation generated by the system. In any method of dismantling the assembly, positioning any sizeable object near to it had to be avoided.

An ad hoc committee of specialists proposed and discussed a number of possible approaches to the problem. These included changing the configuration of the assembly remotely by mechanical or chemical means, by the use of a controlled explosion or by gas or plasma cutting. Promising ideas were investigated using specially designed models constructed in a nearby experimental facility in which similar work with critical assemblies was being done. In parallel, separate calculations were made to model the effects of various actions on the system’s criticality, including the likely effects on the generation of heat and radiation.

The first step taken was to remove from the experimental hall those containers of nuclear materials which had not been used in the construction of the assembly. The operation was conducted using a robot constructed by the Bauman University of Computer Engineering in Moscow (see Fig. 6). Once this first stage was completed, specialists began remotely altering the configuration of the critical assembly. Using the robot manipulator, a thin walled conical vacuum suction device connected to a hose was suspended on the hook of the overhead crane. The suction device was then placed over the pper (copper) hemisphere covering the enriched uranium core. The movement of the critical assembly as this was done resulted in an approximately fourfold increase in neutron flux and an increase in temperature. Once the suction device was actuated and the configuration of the assembly altered, the chain reaction was stopped and the neutron output decreased as expected to the background level. The assembly was then removed using the crane and placed on to a stand for final dismantling at a later stage. The operation to make safe the critical assembly was concluded at about 01:20 on 24 June 1997.

I guess the thing didn't burn through the floor and go all the way to California.

One can read in great deal about the hour by hour medical condition of the technician up to his death

The technician arrived at the Sarov occupational medical service at 11:45 on 17 June 1997, slightly less than one hour after the accident, and was immediately examined. At this stage he was experiencing nausea and he began to vomit, with vomiting increasing in frequency over the following two hours. He was treated with antiemetic drugs, and vomiting stopped at around 14:00. At the clinic of the occupational medical service, the severity of his exposure was clinically evaluated and some symptomatic treatment provided. His general condition was already poor, and he was experiencing fatigue, dizziness and headache. He showed paleness and excessive perspiration. His hands showed a rapidly invasive erythema (skin reddening). His blood pressure was 90/50 mm Hg, pulse 104/min and body temperature normal. It was known from previous health surveillance records that the individual was hypotonic, with a low blood pressure of 90/60 mm Hg.

A summary of haematological findings is presented in Table V. As soon as the technician arrived at the clinic of the occupational medical service, a blood sample was taken, and this showed that (one hour after the accident) there was already a tendency towards lymphopenia. This became more evident in a further blood sample taken an hour later (two hours after exposure)...

...Monitoring of the patient for contamination at 15:30 showed that he was not externally contaminated, but the observation of neutron induced gamma activity in the body, the symptoms seen so far and the description of the accident all indicated a very high dose with a very poor prognosis. Accordingly, it was decided to send the patient to a specialized hospital, and he was transferred by air to Moscow. He arrived in the Clinical Department of the Institute of Biophysics in the Ministry of Health at 20:50 on the day of the accident, ten hours after his exposure...

...the patient was placed in an isolated room assigned to patients exposed in radiation accidents. He was still active, could move by himself and was stable in a vertical position. He was fully conscious but fatigue and headache were persistent. He mentioned a slight pain in the area of the parotid glands which was made worse by swallowing and palpation. His blood pressure was 90/70 mm Hg (which was an improvement over that when he left Sarov) and his pulse was stable at around 100/min.
The hands showed rapid deterioration with pronounced erythema and oedema...

...On the day after the accident (18 June 1997) blood pressure remained low at 80/60 mm Hg. The first signs of oliguria appeared, despite the volume of liquids infused (1500 mL) and the administration of furosemide. The urine volume for the first 12 h after admission to the clinic in the Institute of Biophysics in Moscow was only 800 mL, and the patient had no voiding between 12:00 and 18:00 on the second...

...At this stage, following a discussion among the medical specialists treating the patient which concluded that the various injuries were life threatening, it was decided that amputation of both arms was necessary in order to save his life. Accordingly, the infusion of sodium heparine, aprotinin and acyclovir was discontinued and blood flow was improved by the administration of Rheopolyglucine. Amputation of both arms was performed at about 16:20 on 19 June 1997 under endotracheal narcosis. The left arm was amputated at mid-humerus level and the right arm at the upper humerus...

...At 02:45 on the next day (20 June 1997) the blood pressure dropped dramatically and bradycardia developed. At 03:20 in the morning, 66.5 hours after exposure, the patient died. The apparent cause of death was heart failure.
day.

So that's what happened.

[MADem]

1. Geez, that's pretty terrible.

The headline made me initially think it was a "Vlad put some polonium in the coffee maker, the bum!" type incident.

Nuke power is just so 'zero tolerance' when it comes to screwing up. I'm sure there are plenty of noncritical screw ups that have happened, but when it's a critical screwup, there's no turning back...

[NNadir]

2. I don't know about that.

This is a very detailed report. It doesn't speak in very secretive terms. If this guy had been 1,000 coal miners killed in a mining accident you just wouldn't have heard about it at all. There'd be no medical reports accessible on line giving, in great detail, the status of their health nearly a decade after the accident.

I often recall the 65 mexican coal miners who disappeared beneath the earth earlier this year. I can't find out if their bodies were ever recovered.

As for screw ups and tolerance, I have heard, so as to believe it, that fossil fuels are causing a screw-up that will prove to be zero tolerance. It's called "climate change."

The interesting thing about this accident is that the critical mass was self regulating. The nuclear reaction continued for 7 days without intervention without killing anyone else. This is very unlike say, "air pollution."

This is something like the Oklo natural nuclear reactors that operated without human design or human intervention, for some 200,000 years almost 2 billion years ago.

[nealmhughes]

3. OK, this was an experimental reactor -- a toy, by power reactor terms.

Some of the terms employed in nuke jargon are "scary." Such as "critical" as in "The reactor reached citicality" or "critical assembly" or "critical mass."

Critical simply means that the chain reaction is self-sustaining -- that due to its geometry and other factors, such as moderation temp, etc. that when the neutrons are "flying around" in the reactor, enough of them are "reflected" back into the assembly ("core") to cause the fission rate to remain "constant."

A reactor can be critical and produce only miniscule heat/power.

I performed over 150 reactor startups/fast scram recoveries during my 6 years in the USN. Believe me, you either want the reactor critical or shutdown with no way of starting back up without a great deal of effort! It is during transients controlled by control rods that the reactor is most difficult to control -- not by the "natural" effect of the moderator.

This is analogous to yanking a control rod out of a core. Not good.

As to "burning thru the floor to California"...get real.

The uncontained fission products were a real "scare" factor -- not some horrific "China Syndrome."

This is what happens when one thinks they can superceed the established safety procedures and take a day to day operation lightly. I also note that the article does not address any emergency poisoning methods such as flooding the reactor with borax in place.

[NNadir]

4. I understand reactor physics very well.

There is a good deal of sarcasm in my post.

My point was that this accident is covered in enormous detail and has considerable attention paid to it. If a fellow working at a Russian petroleum facility researching new catalysts had been blown to bits, or painfully burned to death, lingering for days, no one would care.

[hatrack]

5. Jesus - shades of Louis Slotin

No Kyshtym, but exceedingly unpleasant to contemplate.

[NNadir]

6. The accident is nearly identical to Slotin's case.

Slotin was holding the two hemisphere's apart with a screwdriver. He twitched and got the exposure that killed him. Slotin of course, was working with a bomb core.

Reading this case it looks like the guy dropped a neutron reflector - copper - into the assembly. In this sense it is a slightly different case.

IIRC, Slotin was pushed the spheres apart and the critical mass was present only for a short time. That's a big difference in the two events. The mass was critical for many days in the Russian case.

The spherical nature of the assembly here sort of makes one wonder what he was really up to, whether this was weapons work, but I can imagine lots of experiments that are not weapons related in which this configuration might be useful. It seems that they manipulated this device by changing the leakage probability. Of course one of the reasons that many nuclear weapons are spheres is involved in the volume to surface area maximization. If one were looking to measure the nuclear properties of a certain type of alloy or substance, say the cross sections for fission, one might want a sphere to minimize the amount of material needed. In fact that situation probably minimized the problems to others that this accident might have caused otherwise.

Kyshtym from what I've read was the equivalent of one our Hanford tanks exploding. I believe that they were using nitrate extractions of plutonium and that the coolant system failed. The decay heat in the tanks caused the nitrates to denotate. That was a very, very, very unpleasant accident, probably the worst up until Chernobyl.

When you think about it, the Soviets were nuclear slobs but frankly our Hanford tanks do not represent the height of cleanliness and safety. To be sure we have nitrates in some of those tanks. We have no idea what the hell is in some of those tanks, since we developed lots of actinide chemistry there under experimental (and highly secret) conditions.

The Japanese also had a criticality accident in the late 1990's. It killed 4 people.

[hatrack]

7. Yeah, Tokaimura - I recall it well

I was working for the Japanese government at the time. LOTS of press, as you might imagine . . .

Seriously, how technical does "Don't dump a whole shitload into the machine" have to BE to get the point across? One wonders.

[NNadir]

8. Well, I don't know too many details about the Japanese accident.

I heard that they were working with highly enriched fuel with which the technicians were not all that familiar. I believe they were working in an area where low enriched uranium was consistently used.

I think I'm right, am I?

Criticality calculations are not always that simple and they are very sensitive to the type of fuel. There are fudge factors for geometry and the nature of the materials in the area.

If you read about this Russian accident, you see that they weren't totally sure that putting the robot near the system would not change the neutronics of the system. You can, for instance, make a subcritical system critical just by dropping it in a beryllium or aluminum box. It is not trivial to bring a piece of metal near a mass that either is critical or is nearly critical.

It is inevitable that using any kind of energetic materials will result in some accidents. I certainly don't want to represent that nuclear energy related accidents will never again happen - surely they will. On the other hand, the scale of these accidents is different than say, becoming so dependent on petroleum that you accidentally "elect" a President darkly obsessed with petroleum, who then, in service to that obsession, goes off on an adventure that kills hundreds of thousands of people on the other side of the globe. It's different too than "accidentally" changing the chemistry of the atmosphere in such a profound way that the entire planetary ecosystem "accidentally" is modified forever in an irreversible fashion.

One has to compare a lot of things, including scale. As long as we are using energy, there will be injuries and deaths and environmental cost. We cannot eliminate those things. All we can do is to minimize them.