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IAEAInternational Atomic Energy Agency
IAEA Seibersdorf Pu-240 incident,clean-up and lessons learnt
John Hunt, Rudolf Hochmann, Hugo Eisenwagner,Tobias Benesch and Christian Schmitzer.
HPS 2009 MeetingMinneapolis
12 - 16 July 2009
IAEA Pu-240/Page 2
Safeguards inspectors
Safeguards samples
Safeguards Analytical Laboratory
IAEA safeguards operations
IAEA Pu-240/Page 3
Safeguards inspectors
Safeguards samples
Safeguards Analytical Laboratory
Reference Pu, U,
Am, Cf solutions (CRM)
IAEA safeguards operations
IAEA Pu-240/Page 4
Safeguards inspectors
Safeguards samples
Safeguards Analytical Laboratory
Reference Pu, U,
Am, Cm solutions (CRM)
IAEA safeguards operations
Austrian Research Center
IAEA Pu-240/Page 5
Pu - 240
Alpha emitter
Physical half-life 6563 years
Biological half-lives
• 50 years in bone
• 20 years in liver.
Used as tracer or reference material.
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Plutonium CRM vial
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Plutonium vial
PuNO3
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Plutonium vial
PuNO3
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Pu-240 solution
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Alpha emission and radiolysis
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Ionized water
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Recombination
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Recombination
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Pressure build-up
PuNO3
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The pressure build-up in the vial depends on:
• The time passed since sealing (1993 – 2008)
• The activity of the solution (GBq of Pu-240)
• The molarity of the solution (1.5 M).
• The air space above the solution.
Pressure build-up
IAEA Pu-240/Page 16
The incident
3rd of August, Sunday, a bit before 02:31 am a Pu-240 vial stored in a fire proof safe burst, and caused the breaking of a further four vials.
Around 0.8 g or 6.7 GBq (0.2 Ci) of Pu-240 was released, mostly to inside the safe.
The release was detected by the continuous air monitor in the room.
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• The actions foreseen in the SAL emergency plan were carried out.
• Early in the first day it was seen that no release to the environment had happened.
• The incident was reported, also to the Incident and Emergency Centre of the IAEA.
• A press release was made.
Immediate actions (first day)
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Was there a release to the environment?
• HEPA filter efficiency 99.999 % for a 0.3 micron particle.
• Total HEPA filter bank efficiency 99.999999 %
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No release to the environment
• The final Austrian Research Center report of 2008/09/08 states:
• ‘The measured values of activity of the “incident” in the environmental samples do not deviate from the routinely performed environmental monitoring results.’
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• Money spent on safety related systems is money well spent.
lesson learnt
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INES level 1
• The IEC classified the incident as an INES level 1 anomaly. We were lucky that the incident happened on a Sunday morning.
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Visit by Dr. Richard Toohey
• Dr. Richard Toohey made an “expert visit” to IAEA Seibersdorf over the 8th to the 12th of September 2008.
• The objective of the visit was to review the Plutonium-in-wound measurement system and emergency procedures related to Plutonium work at the Safeguards Analytical Laboratory.
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The clean-up in three phases
• Safe temporary storage of other Pu vials with overpressure.
• Removal of the rest of the vials and clean-up of safe.
• Stabilization of the Pu vials with overpressure.
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Safe temporary storage
• The SAL inventory of reference standards was searched for similar ampoules with overpressure.
• 5 similar vials were found.
• Work-plans were prepared and approved by the IAEA Regulator.
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Modified Type B container
The vials (already packed in a steel container) were stored in a modifyed type B transport container.
HEPA filter
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The clean-up of the safe
The safe was covered by a plastic tent, and the remaining vials were removed through a bagging-out port, as in a glove box.
Positive pressure respiratory protection was used, and appropriate PPEs.
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The clean-up of the safe
After the removal of the vials, the internal walls of the safe were decontaminated and finally painted.
The final surface contamination was lower than 0.1 Bq/cm2 of alpha emitters.
The floor and other surfaces of the affected room were also decontaminated down to the same level.
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Doses from first and second phases
• Urine analysis was carried out for actinides for the staff involved in the clean-up. No Pu-240 above the detection limit was measured.
• The external effective doses were very low (< 10 μSv.)
• Many thanks to ARC medical team and fire brigade who gave us very good support.
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Third phase: stabilization
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Third phase: stabilization
Proposed stabilization procedure:
1. Cool down the internal part of the modified Type B container to – 600 C with CO2 (dry ice). The Pu solution will freeze.
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2. Remove the steel vial containers.
3. Transfer the steel container to a glove box.
4. Open the steel container and fill it with liquid N2.
5. Crack the vial through remote-controlled mechanical means.
Third phase: stabilization
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Vial cracking
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Lessons learnt
• The phenomenon of radiolysis (gas formation and pressure build-up) in Plutonium solutions is well known. However this type of event in CRM vials had not been reported in the open literature before.
• Therefore no safety measures were taken to prevent such an event happening (periodic pressure release).
• The suppliers of CRM do not inform storage problems.
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Lessons learnt – safety culture
• It is always important to continue learning, through seminars, congresses, reports, the internet.
• Learn through the problems and incidents that have happened in other facilities, and report on incidents and accidents that happen in your installation.
