HPS 2009 Meeting Minneapolis 12 16 July 2009

HPS 2009 Meeting Minneapolis 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 IAEA International Atomic Energy Agency

IAEA safeguards operations Safeguards inspectors Safeguards samples Safeguards Analytical Laboratory IAEA Pu-240/Page 2

IAEA safeguards operations Safeguards inspectors Safeguards samples Safeguards Analytical Laboratory IAEA Reference Pu, U, Am, Cf solutions (CRM) Pu-240/Page 3

IAEA safeguards operations Safeguards inspectors Safeguards samples Austrian Research Center Safeguards Analytical Laboratory IAEA Reference Pu, U, Am, Cm solutions (CRM) Pu-240/Page 4

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. IAEA Pu-240/Page 5

Plutonium CRM vial IAEA Pu-240/Page 6

Plutonium vial Pu. NO 3 IAEA Pu-240/Page 7

Plutonium vial Pu. NO 3 IAEA Pu-240/Page 8

Pu-240 solution IAEA Pu-240/Page 9

Alpha emission and radiolysis IAEA Pu-240/Page 10

Ionized water IAEA Pu-240/Page 11

Recombination IAEA Pu-240/Page 12

Recombination IAEA Pu-240/Page 13

Pressure build-up Pu. NO 3 IAEA Pu-240/Page 14

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. IAEA Pu-240/Page 15

The incident 3 rd 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. IAEA Pu-240/Page 16

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. IAEA Pu-240/Page 17

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 % IAEA Pu-240/Page 18

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. ’ IAEA Pu-240/Page 19

lesson learnt • Money spent on safety related systems is money well spent. IAEA Pu-240/Page 20

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. IAEA Pu-240/Page 21

Visit by Dr. Richard Toohey • Dr. Richard Toohey made an “expert visit” to IAEA Seibersdorf over the 8 th to the 12 th 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. IAEA Pu-240/Page 22

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. IAEA Pu-240/Page 23

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. IAEA Pu-240/Page 24

Modified Type B container HEPA filter The vials (already packed in a steel container) were stored in a modifyed type B transport container. IAEA Pu-240/Page 25

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. IAEA Pu-240/Page 26

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/cm 2 of alpha emitters. The floor and other surfaces of the affected room were also decontaminated down to the same level. IAEA Pu-240/Page 27

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. IAEA Pu-240/Page 28

Third phase: stabilization IAEA Pu-240/Page 29

Third phase: stabilization Proposed stabilization procedure: 1. IAEA Cool down the internal part of the modified Type B container to – 600 C with CO 2 (dry ice). The Pu solution will freeze. Pu-240/Page 30

Third phase: stabilization 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 N 2. 5. Crack the vial through remote-controlled mechanical means. IAEA Pu-240/Page 31

Vial cracking IAEA Pu-240/Page 32

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. IAEA Pu-240/Page 33

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. IAEA Pu-240/Page 34

Any questions or comments? j. hunt@iaea. org IAEA Pu-240/Page 35