8 th International Workshop on Radiation Safety at Synchrotron Radiation Sources

Transcription

1 8 th International Workshop on Radiation Safety at Synchrotron Radiation Sources DESY Hamburg, 3 5 June 2015 Proposed material release plan for The decommissioning of the ESRF storage ring Paul Berkvens

2 DECOMMISSIONING OF EXISTING STORAGE RING new machine existing machine magnet cell #/cell iron (kg) copper (kg) iron (kg) copper (kg) quadrupole 40 cm , quadrupole 50 cm , quadrupole 90 cm 2 1, , sextupole , dipole 2 3, ,200 1,400 total cell 19 15,980 2,570 storage ring ,360 82,240 vacuum vessels stainless steel (kg) aluminium (kg) cell storage ring 9, Page 2 supports km cables

3 DEFINITION OF RADIOACTIVE WASTE IN FRENCH LEGISLATION Article L of French Environmental Act definition of radioactive waste A radioactive material is a material containing radionuclides, natural or artificial, whose activity or concentration justify radiation protection control measures. Radioactive waste is a radioactive material for which no further use is foreseen or envisaged. Table A, Part 1 of annex VII of the 2013/59/EURATOM Directive defines clearance levels for radioactive waste. H 3 Cr 51 Mn 52 Mn 54 Fe 55 Co 56 Co 57 Co 58 Co 60 Ni Clearance levels (Bq/g) defined in the 2013/59/EURATOM Directive French legislation however does not define clearance levels. Page 3

4 DISCUSSIONS BETWEEN ESRF AND ASN Discussions between ESRF and the French Nuclear Safety Authority (ASN) started several years ago. A formal meeting with the ASN took place on 13 April Following several exchanges it was decided that ESRF should carry out a technical study and propose a methodology for the possible clearance of certain accelerator components. The design study should be based, in particular, on 3D Monte Carlo calculations, and special attention should be placed on the presence of possible activation hot spots. A first technical study should be submitted to ASN beginning of Page 4

5 PROCESS KNOWLEDGE: BEAM LOSSES 2500 Injected electron charge recorded Presently: 400 µc/year small beam loss power Injected charge [µc] Injected charge [µc] 20,000 18,000 16,000 14,000 12, ,000 8, ,000 4, , Page year 400 µc/year Days since 01/05/1998

6 PROCESS KNOWLEDGE: BEAM LOSSES Ionisation chambers beamloss monitors stored beam (ma) total beam loss (ma s -1 ) E E-04 3 ionisation chamber reading (µsv h -1 ) 50 2 cell days Typical stored beam decay in uniform filling mode. Red curve: stored beam intensity; blue curve: corresponding total beam losses 0.E cell 6 cell 9 cell 32 cell days Readings from the 32 beam loss ionisation chambers, during the same period Page 6

7 PROCESS KNOWLEDGE: BEAM LOSSES total beam loss (ma s -1 ) 1.5E E E E+00 Page days Reproduction of the total beam loss power via the weighted sum of the readings of the 32 beam loss ionisation chambers. Blue curve: total beam loss power Red curve: weighted sum of ionisation chamber readings

8 PROCESS KNOWLEDGE: BEAM LOSSES Standard cells: losses 1 % of total losses 400 µc/year 0.76 mw per cell A few cells 10 % of total losses 400 µc/year 7.6 mw per cell total beam loss (ma s -1 ) 1.5E % of total beam losses 1 1.0E E E+00 Page days c1 c2 c3 c4 c5 c6 c7 c8 c9 c10 c11 c12 c13 c14 c15 c16 c17 c18 c19 c20 c21 c22 c23 c24 c25 c26 c27 c28 c29 c30 c31 c32 Typical beam loss distribution along storage ring cell

9 MONTE CARLO CALCULATIONS: FLUKA q Page 9

10 FLUKA ACTIVATION CALCULATIONS: EXAMPLES Bq/g q Total specific activity (all isotopes), integrated over all z Quadrupole 1 Total specific activity (all isotopes), integrated over x = [2.6 cm, 3.8 cm] Cooling down time = 1 month 1 % local losses Page 10

11 FLUKA ACTIVATION CALCULATIONS: EXAMPLES Σ i (AS i /SE i ) q Sum specific activities/clearance levels (all isotopes), integrated over all z Quadrupole 1 Sum specific activities/clearance levels(all isotopes), integrated over x = [ cm] Cooling down time = 1 month 1 % local losses Page 11

12 FLUKA ACTIVATION CALCULATIONS: EXAMPLES Bq/g q Total specific activity (all isotopes), integrated over all z Sextupole 2 Total specific activity (all isotopes), integrated over x = [-1 cm, 1 cm] Cooling down time = 1 month 1 % local losses Page 12

13 FLUKA ACTIVATION CALCULATIONS: EXAMPLES Σ i (AS i /SE i ) q Sum specific activities/clearance levels (all isotopes), integrated over all z Sextupole 2 Sum specific activities/clearance levels(all isotopes), integrated over x = [-1 1 cm] Cooling down time = 1 month 1 % local losses Page 13

14 FLUKA ACTIVATION CALCULATIONS: EXAMPLES Bq/g q Total specific activity (all isotopes), integrated over z = [910 cm, 930 cm] dipole 1 Total specific activity (all isotopes), integrated over z = [930 cm, 950 cm] Cooling down time = 1 month 1 % local losses Page 14

15 FLUKA ACTIVATION CALCULATIONS: EXAMPLES Σ i (AS i /SE i ) q Sum specific activities/clearance levels (all isotopes), z = [ cm] dipole 1 Sum specific activities/clearance levels (all isotopes), z = [ cm] Cooling down time = 1 month 1 % local losses Page 15

16 FLUKA ACTIVATION CALCULATIONS: EXAMPLES Bq/g q Total specific activity (all isotopes), integrated over z = [851 cm, 871 cm] dipole vessel 1 Total specific activity (all isotopes), integrated over z = [931 cm, 951 cm] Cooling down time = 1 month 1 % local losses Page 16

17 FLUKA ACTIVATION CALCULATIONS: EXAMPLES Σ i (AS i /SE i ) q Sum specific activities/clearance levels (all isotopes), z = [ cm] dipole vessel 1 Sum specific activities/clearance levels (all isotopes), z = [ cm] Cooling down time = 1 month 1 % local losses Page 17

18 Proposed material release plan o Proposed zoning for the measurement protocols. Σ i (AS i /SE i ) 100 % local losses Page 18

19 INDISTINGUISHABLE FROM BACKGROUND Proposed criterion for definition of non-radioactive material o Surface dose measurements: indistinguishable from background count rate distributions 1.E+00 y* y# ISO standard, May E-01 1.E-02 1.E-03 1.E u(y 0 ) 3.1 u(y#) Detector Exploranium Gr-130 minispec ( NaI(Tl) scintillator) (count rate: 1.37 cps per nsv/h) 1.E-05 1.E-06 1 minute integration time: Decision threshold: 3.62 cps 1.E-07 Detection limit: 7.4 cps 1.E-08 0 β = α = net count rate (for 30 nsv/h background) Page 19

20 INDISTINGUISHABLE FROM BACKGROUND AND EURATOM CLEARANCE LEVELS Exploranium Gr-130 calibrated in terms of air kerma between 60 kev and 3 MeV. Relate detection threshold (cps) to residual ambient dose equivalent rates obtained from FLUKA. detector efficiency η [counts per second (photons s -1 cm-2 ) -1 ] : table A.21, ICRU Report Count rate [counts per second] Air kerma [ngy h -1 ] photon energy [kev] Cs kev ± ± 5.52 Na kev ± ± kev ± ± 0.28 Am kev ± ± 1.30 Co kev ± ± 10. Measured net count rates and net air kerma rates Page 20

21 INDISTINGUISHABLE FROM BACKGROUND AND EURATOM CLEARANCE LEVELS ratio κ between the ambient dose equivalent rate and the count rate for a given spectrum. : table A.21, ICRU Report 57 κ [nsv h -1 cps -1 ] Background spectrum: Stainless steel: Magnet yoke: E+08 1.E+07 1.E+06 1.E+05 1.E+04 photons per bin [relative units] Detection limit Stainless steel: 4.5 nsv/h Magnet yoke: 5.8 nsv/h (for 30 nsv/h background) 1.E+03 1.E+02 Co 57 Mn 54 1.E Page 21 photon energy [kev] Spectrum calculated with FLUKA for stainless steel vessel

22 INDISTINGUISHABLE FROM BACKGROUND AND EURATOM CLEARANCE LEVELS Compliance with clearance levels defined in Council Directive 2013/59/EURATOM Surface dose measurements (indistinguishable form background) Σ i (AS i /SE i ) guaranteed for 1 cm 3 hotspots. Detection limit of 5.8 nsv h -1 µsv/h 1 cm 3 hotspots with Page 22

23 INDISTINGUISHABLE FROM BACKGROUND AND EURATOM CLEARANCE LEVELS Compliance with clearance levels defined in Council Directive 2013/59/EURATOM Surface dose measurements (indistinguishable form background) cm Σ i(as i/se i) Σ i (AS i /SE i ) guaranteed for 1 cm 3 hotspots. cm Detection limit of 4.5 nsv h -1 µsv/h 1 cm 3 hotspots with Page 23

24 INDISTINGUISHABLE FROM BACKGROUND AND EURATOM CLEARANCE LEVELS Compliance with clearance levels defined in Council Directive 2013/59/EURATOM Surface dose measurements (indistinguishable form background) cm Σ i(as i/se i) Σ i (AS i /SE i ) guaranteed for 1 cm 3 hotspots. cm cm µsv/h Detection limit of 3.2 nsv h -1 µsv/h 1 cm 3 hotspots with (for 15 ns/h background) cm Page 24

25 PROPOSED MEASUREMENT PROTOCOL more than one measurement positive Initial clearance test all measurements negative unrestricted release at least one confirmation measurement positive confirmation of positive result via 3 new measurements only one measurement positive all confirmation measurements negative unrestricted release 0 12 months after shutdown radioactive waste no component expected to meet clearance criteria within 5 years yes Intermediate storage at ESRF radioactive waste radioactive waste more than one measurement positive at least one confirmation measurement positive second clearance test confirmation of positive result via 3 new measurements only one measurement positive all measurements negative all confirmation measurements negative unrestricted release Unrestricted release 0 5 years after initial clearance tests Page 25

26 STATUS AND NEXT STEPS Technical study sent to ASN on 25 February 2015 o o Proposed material release plan Detailed activation calculations of standard cell Meeting with ASN on 22 May 2015 o Outcome of meeting: yes, but. o ESRF should rephrase criteria to make it criteria for radiological zoning. Next steps q o Submit formal authorisation request end of 2015 o Public hearing beginning 2016 o Authorisation expected 2017 Page 26

27 ACKNOWLEDGEMENTS: S. ROKNI & J. LIU (SLAC), S. ROESLER (CERN) Page 27