Decommissioning of MAX-lab Magnus Hörling 9 th International Workshop on Radiation Safety at Synchrotron Radiation Sources April 19-21, 2017 Taiwan Photon Source, Hsinchu, Taiwan
Outline ● Facility Description ● Objective & Conditions ● Regulations ● Approach ● Phase 1 - Radiological Characterization ● Phase 2 - Dismantling & Radiological Clearance ● Outcome & Costs Decommissioning of MAX-lab / Outline
Facility Description
Facility Description (1/4) ● Former Swedish national laboratory for accelerator development, synchrotron light and nuclear physics research ● The history of MAX-lab dates back to the early 80’s ● About 1000 users per year Decommissioning of MAX-lab / Facility Description
Facility Description (2/4) Injector ● Microtron 95 MeV 1984-2002 ● Linac 200/400 MeV 2001-2015 MAX I ● Ø 32 m 200/550 MeV 1986-2015 MAX II ● Ø 90 m 1500 MeV 1996-2015 MAX III ● Ø 36 m 700 MeV 2007-2015 Nuclear physics ● Prolonged runs at 10 Hz using MAX I as a pulse-stretcher ● Significant losses in the injector and MAX I Decommissioning of MAX-lab / Facility Description
Facility description (3/4) MAX I MAX III MAX II Injector Nuclear physics Decommissioning of MAX-lab / Facility Description
Facility Description (4/4) Decommissioning of MAX-lab / Facility Description
Objective & Conditions
Objective & Conditions (1/2) Objective: ● Building to be emptied and returned to the landlord ● Building to be “cleared for free use” – i.e. no longer subject to the terms and requirements of the Radiation Protection Act Physical conditions: ● Local decay storage not an option ● No dedicated or suited space for decay storage on the MAX IV property ● Alternate solutions for decay storage were briefly considered, but decided not to be an option ● → 3 rd objective: Disposal of activated material Decommissioning of MAX-lab / Objective & Conditions
Objective & Conditions (2/2) Time constraints: ● Facility to remain in operation until mid December 2015 ● Dismantling to start immediately after shutdown ● Goal for (physical) completion set by the management to the summer of 2016 Budget: ● Total budget: 1500 k€ ● Estimated radiological cost: 650 k€ Decommissioning of MAX-lab / Objective & Conditions
Regulations
Regulations The Swedish requirements for radiological clearance procedures are given by the regulatory code SSMFS 2011:2. ● Nuclide specific clearance levels (Bq/g or kBq/m 2 ) ● Generally harmonized to levels in related EC RP publications ● Before any clearance, a control program has to be notified to the authority ● Decisions on the clearance of buildings are taken by the authority on application by the licensee Decommissioning of MAX-lab / Regulations
Approach
Approach Given the time frame, personnel resources, legal requirements and lack of space the implementation of a comprehensive measuring and clearance program within the organization was not considered feasible. The decision was made to hire a contractor specialized in the field of radiological decommissioning and radioactive waste management. The radiological decommissioning was divided into two phases. Decommissioning of MAX-lab / Approach
Phase 1 – Radiological Characterization
Phase 1 - Radiological Characterization (1/5) The characterization - performed during the first half of 2015 - included: ● Summary of operating history ● Risk categorization of rooms and material ● Inventory and marking, database – ~800 objects/sections/surfaces ● Pulse and dose rate measurements ● Sampling of concrete and metal ● Determination of nuclide vectors Decommissioning of MAX-lab / Phase 1 – Radiological Characterization
Phase 1 - Radiological Characterization (2/5) Risk categorization of rooms and material: ● Initially based on operating history and facility knowledge ● Protected (and normal) areas deemed Extremely Low Risk (~6700 m 2 ) ● Conservative approach for controlled areas (~1500 m 2 ) Decommissioning of MAX-lab / Phase 1 – Radiological Characterization
Phase 1 - Radiological Characterization (3/5) Risk categorization of rooms and material: ● Pulse rate measurements used primarily to confirm initial categorization ● Results allowed for modifications of the categorization (less conservative) – mainly exclusion of stands in MAX II and MAX III and recategorization of less critical room surfaces Decommissioning of MAX-lab / Phase 1 – Radiological Characterization
Phase 1 - Radiological Characterization (4/5) General categorization of controlled areas and material inside. Injector, MAX I and Nuclear Physics BL: Above Clearance Level ● Vacuum system, magnets etc Risk Low Risk ● Other equipment, incl. stands Extremely Low Risk ● Room surfaces MAX II and MAX III: ● Vacuum system ● Magnets, incl. IDs etc ● Stands and peripheral equipment ● Room surfaces Decommissioning of MAX-lab / Phase 1 – Radiological Characterization
Phase 1 - Radiological Characterization (5/5) Determination of nuclide vectors Radionuclides measured in samples and average ratios to 60 Co ● Sampling of concrete, wall filling Concrete Wall Filling Material Steel material and activated metal Co-60 1,0E+00 Co-60 1,0E+00 Co-60 1,0E+00 Na-22 1,1E+00 Mn-54 1,9E+00 Sc-46 1,6E-01 ● Large uncertainties Sc-46 1,9E-01 Zn-65 8,2E-01 Cr-51 1,6E+01 Mn-54 4,0E-01 Cs-134 3,7E-01 Mn-54 3,4E+01 ● Concrete samples showed induced Co-58 1,0E+00 Eu-152 1,6E+00 Co-56 2,4E+00 Cs-134 3,8E-01 Co-57 4,8E+01 activity, but only up to ~ 60% of the Cs-137 2,9E-01 Co-58 2,2E+00 Eu-152 2,1E+00 Fe-59 1,8E-02 clearance level Eu-154 5,2E-01 Y-88 5,0E-02 ● For all concrete samples, the naturally Eu-155 6,8E-01 Zn-65 2,1E-02 Nb-95 2,6E-01 occurring radionuclides (mainly 40 K and 232 Th) still dominated the activity content Decommissioning of MAX-lab / Phase 1 – Radiological Characterization
Phase 2 – Dismantling & Radiological Clearance
Phase 2 – Dismantling & Radiological Clearance (1/7) Dismantling began with categorized material in controlled areas in January 2016. ● Dismantling ● Separation & Sorting ● Packaging ● Registration (contractor’s data base) ● Shipping to contractor’s site A separate contractor, hired for general dismantling and demolition of (the rest of) the facility started work two months later. Decommissioning of MAX-lab / Phase 2 – Dismantling & Radiological Clearance
Phase 2 – Dismantling & Radiological Clearance (2/7) Bulk shielding of the injector, nuclear physics and parts of MAX I: ● Walls of 2-3 m thickness ● Made out of gravel including stones of varying sizes, supported by corrugated metal and beams ● ~800 m 3 of concrete like mass ● Probably a great idea back in the day… ● Turned out to be very challenging (and costly) to remove Decommissioning of MAX-lab / Phase 2 – Dismantling & Radiological Clearance
Phase 2 – Dismantling & Radiological Clearance (3/7) Bulk shielding of the injector, nuclear physics and parts of MAX I: ● Innermost 40 cm of the wall filling material were separated for clearance measurments ● Filled into big-bags and measured ● When the innermost parts had been separated and removed, the remaining masses could be dealt with in a less delicate way Decommissioning of MAX-lab / Phase 2 – Dismantling & Radiological Clearance
Phase 2 – Dismantling & Radiological Clearance (4/7) Local clearance of material: ● Concrete blocks and wall filling material was not shipped to the contractor – measured for clearance at MAX-lab ● Dedicated measuring station set up by the contractor (NaI probes) ● 60 Co content quantified and nuclide vector applied ● < 1000 kg material per measurement ● Formally cleared by MAX-lab (control program notified to authority) Decommissioning of MAX-lab / Phase 2 – Dismantling & Radiological Clearance
Phase 2 – Dismantling & Radiological Clearance (5/7) Clearance measurements of concrete bulk shielding and room surfaces: ● Rooms completely emptied ● HPGe equipment, collimated ● Low Risk – one measurement per surface, critically chosen area ● Risk – measurements in a 1 x 1 m 2 grid ● 5 m 2 measured at once when practical ( t m increased accordingly) Decommissioning of MAX-lab / Phase 2 – Dismantling & Radiological Clearance
Phase 2 – Dismantling & Radiological Clearance (6/7) Demolition of bulk shielding: ● Could start when the data from the clearance measurements had been analyzed ● Cast concrete was segmented by circular cutting and wire sawing ● None of the bulk shielding concrete could leave MAX-lab until the decision by the authority on the clearance of the building was received Decommissioning of MAX-lab / Phase 2 – Dismantling & Radiological Clearance
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