HPS 2009 Meeting Minneapolis 12 - 16 July 2009

1. HPS 2009 MeetingMinneapolis 12 - 16 July 2009 IAEA Seibersdorf Pu-240 incident, clean-up and lessons learnt John Hunt, Rudolf Hochmann, Hugo Eisenwagner, Tobias Benesch and Christian Schmitzer. j.hunt@iaea.org

2. IAEA safeguards operations Safeguards inspectors Safeguards samples Safeguards Analytical Laboratory

3. IAEA safeguards operations Safeguards inspectors Safeguards samples Reference Pu, U, Am, Cf solutions (CRM) Safeguards Analytical Laboratory

4. IAEA safeguards operations Safeguards inspectors Safeguards samples Austrian Research Center Reference Pu, U, Am, Cm solutions (CRM) Safeguards Analytical Laboratory

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.

6. Plutonium CRM vial

7. Plutonium vial PuNO3

8. Plutonium vial PuNO3

9. Pu-240 solution

10. Alpha emission and radiolysis

11. Ionized water

12. Recombination

13. Recombination

14. Pressure build-up PuNO3

15. Pressure build-up 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.

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.

17. Immediate actions (first day) • 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.

18. 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 %

19. 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.’

20. lesson learnt • Money spent on safety related systems is money well spent.

21. 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.

22. 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.

23. The clean-upin 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.

24. 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.

25. Modified Type B container HEPA filter The vials (already packed in a steel container) were stored in a modifyed type B transport container.

26. 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.

27. 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.

28. 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.

29. Third phase: stabilization

30. 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.

31. Third phase: stabilization • Remove the steel vial containers. • Transfer the steel container to a glove box. • Open the steel container and fill it with liquid N2. • Crack the vial through remote-controlled mechanical means.

32. Vial cracking

33. 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.

34. 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.

35. Any questions or comments? j.hunt@iaea.org