CArbon-14 Source Term CAST

CArbon-14 Source Term CAST
EC 428 ECCN= N CArbon-14 Source Term CAST Name: Eva de Visser-Týnová Organisation: NRG Date: 16 January 2018

Carbon-14 release from irradiated stainless steel
Outline Samples Leaching experiments Analytical methods Results to date (to 60 weeks) C-14 liquid phase C-14 gas phase Co-60 liquid phase Interim conclusions Ongoing work Reporting WOOD/NRG WP2 C-14 release from irradiated steels

Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels
Samples 316L(N) austenitic stainless steel from single sheet 6 CT specimens irradiated at HFR, Petten – SIWAS O7 experiment (2dpa, 80°C, 5 28-day cycles) in 1996/97 C-14 and Co-60 inventory assessed by ORIGEN calculations Unirradiated steel from same sheet 3 experiments each with 3 CT specimens Due to high dose rates from samples, they require handling in a shielded cell (a hot cell) CT specimen 30x28.8x12 mm3 Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

Final container design
Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

AMEC/NRG WP2 C-14 release from irradiated steels
CT specimen support AMEC/NRG WP2 C-14 release from irradiated steels

Liquid phase analysis Co-60 by gamma spectrometry, Canberra High purity Ge detector C-14 inorganic measurement done by acidification of solution and release of C-14 as 14CO2, measured by LSC (Packard TriCarb 3180 TR/SL) N2 NaOH 20ml/min 5ml/min H2O Carbosorb Ice bath Acid Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

Gas phase sampling apparatus
Designed and made at RCD in UK Captures 14CO2, 14CO and 14CH4 fractions by selective oxidation/ absorption on 3 soda lime columns Concern over potential CO sorption to metal surfaces replaced all nickel-based fittings with stainless steel Efficiency and selectivity of 2 catalysts were measured CO 94.5% (CuO) remainder oxidised on CH4 catalyst CH4 95% (Pt) with <2% removed after CO catalyst Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

Leaching experiments Leaching in 600 ml 0.1M NaOH (pH 13) under N2 at the ambient temperature in the hot cell (~30°C) Gas and solution phase sampled periodically purge with N2 for collection of gas phase C-14, with selective capture and oxidation of 14CO2, 14CO and 14C-hydrocarbons (14CH4) as CO2 then collect solution sample via dip leg for γ-spec (Co-60) and C-14 Please add volume of solution used in the blank experiment Setup for tests: 1 is soda lime column for removing C-14 from N2 feed, 2 is leaching container where A is N2 inlet, B is dip leg and C is N2 outlet, Unit 1 and Unit 2 are the parts of RCD rig Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

Leaching experiments AMEC/NRG WP2 C-14 release from irradiated steels

Progress with experiments
Experiments started 31 May to 2 June 2016 Added 600 ml 0.1M NaOH via dip leg Sampling after 1, 3 and 6 weeks and 3, 5 & 13 months Purged vessel with nitrogen for 7 hours Collected gas phase C-14 in RCD samplers Sequential oxidation and capture of 14CO2, 14CO and 14C-hydrocarbons (14CH4) as CO2 on soda lime columns Collected ~7ml (from week 6 ~15ml) solution sample via dip leg Analysis Co-60 and inorganic C-14 in solution to 13 months (NRG) C-14 gas phase to 13 months (RCD) AMEC/NRG WP2 C-14 release from irradiated steels

Results – C-14 inorganic solution phase
Containers 2, MBq C-14 C-14 release from Container 2: corrosion rate ~ 3nm/yr, at congruent release of C-14 with corrosion and uniform C-14 distribution through steel Note that the NRG method for separating C-14 from solution has only been validated with C-14 carbonate and not with a soluble organic species. There is uncertainty whether the method is measuring just inorganic C-14, total C-14 or somewhere between the two. The amount of carbon-14 released is much higher than was expected. In region of 5 parts in a million C-14 after 3 months. Not consistent with expected long-term rate of C-14 release, based on corrosion of unirradiated steel, which was expected to be about 20 Bq/year! Points to presence of carbon-14 on surface of the samples Fast initial C-14 release, then rate decreases Container 2 – C-14 activity still increasing at steady rate Container 3 – C-14 activity has changed little between 6 and 60 weeks, with an unexplained peak after 13 weeks Container 1 – no C-14 measurable Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

Results – C-14 gas phase Container 1 – unirradiated steel
Don’t know why these 2 measurements give a positive C-14 measurement. Not seen this in blank experiment. Both are after catalysts. Not C-14 from CO2 in air . LoD <0.04 Bq 2 analyses give positive C-14 measurement above LoD AMEC/NRG WP2 C-14 release from irradiated steels

Results – C-14 gas phase Container 2 – irradiated steel
C.f ±8 Bq to solution phase over 13 months Majority C-14 release to gas phase as hydrocarbons ~10% CO or volatile oxygenated organic compounds No measurable gas phase CO2 AMEC/NRG WP2 C-14 release from irradiated steels

Results – C-14 gas phase Container 3 – irradiated steel
C.f ± 8 Bq C-14 to solution phase over 13 months Majority C-14 release to gas phase as hydrocarbons ~6% CO and/or volatile oxygenated organic compounds No measurable gas phase CO2 Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

Results – Co-60 solution phase
Container 2,3 16 GBq Co-60 Much higher Co-60 release in the first week as well. Scoping calculations suggest that if we assume uniform distribution of Co-60, 1 week release corresponds to a corrosion rate of 125nm/yr, this is significantly higher than long-term corrosion rate of ~1nm/yr measured for unirradiated steel under alkaline anaerobic conditions. Steel contains 0.08wt% Co. Note that NRG performing an additional test to investigate loss of Co-60 from solution to the zirconia insert. Drop in Co-60 concentration in solution to a plateau may be consistent with a Co solubility limitation with respect to steel solid solution; however, 13 week container 2 result of <LoD suggests sorption (to walls and steel surface itself) may also be a factor. High Co-60 activity in leachates after 1 week 1 part in 106 of Co-60 inventory Then solution activity decreases possible solubility limitation and/or sorption Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

Additional tests 2 tests of Co-60 sorption/solubility: Setup filled with NaOH (600 g) and Co-60 spike (11,2 kBq) Samples taken at T0 and after 6 weeks, under N2 atm., RT Test 1 – without stainless steels Test 2 - with stainless steels Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

Conclusions I There is a relatively fast initial release of accessible C-14 species from the surface of the steel on immersion in alkaline water Predominantly to solution phase but also to gas phase Higher proportion and rate of release to gas phase initially in Container 3 Gas phase release predominantly hydrocarbons with up to 10% released as CO or volatile oxygenated compounds This seems consistent with findings from inactive studies of bulk carbon release from iron powders (Deng et al and PSI work), where the presence of carbon species on the surface of the material was found to dominate the initial release. Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

Conclusions II Rate of carbon-14 release declines beyond 3-6 weeks in both Containers 2 and 3 Release continues at measurable rate to both gas and solution phases in Container 2 Rate of release to the gas phase decreases more quickly in Container 3; little change in solution phase concentration between 6 and 60 weeks Reasons for differences in carbon-14 release between Containers 2 and 3 are not yet understood Release of Co-60 was investigated as a possible marker of the rate of steel corrosion, but is not suitable due to possible solubility limitation and/or sorption to the irradiated steel Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

Ongoing work (outside CAST scope)
Experiments extended with one year Leaching experiments continuing 2 years sampling – June 2018 Results July –August 2018 Experiments terminated after 2 years vessels acid washed to recover deposits for γ-spec Some of the solution samples taken during periodic sampling will be analysed for total C-14 total by pyrolysis Also additional Co-60 experiment and trying to find information on surface examination of similar samples from the irradiation. Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

Reporting D2.8 - NRG Final Report on C-14 release and speciation from irradiated stainless steel under alkaline reducing conditions Contribution to D WP2 synthesis report Final Report to RWM drafted Work presented at KONTEC Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

CArbon-14 Source Term (CAST) project
The project has received funding from the European Union’s European Atomic Energy Community’s (Euratom) Seventh Framework Programme FP7/ under grant agreement no , the CAST project. Co-funding from Radioactive Waste Management is gratefully acknowledged.

Additional slides AMEC/NRG WP2 C-14 release from irradiated steels

Samples - NRG 316L(N) EHRII-type austenitic stainless steel from single sheet CT specimens irradiated at HFR, Petten – SIWAS O7 experiment (2dpa, 80°C, 5 cycles) Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

Sample inventory - NRG Activation calculations performed using ORIGEN (‘zero dimension’) code Units: Bq/g 60Co measured by γ-spec. for b107 in 2010: ± 0.4 x 108 Bq/g C, N content confirmed by independent analysis on unirradiated sample Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

Inventory in experiments
Container 1 unirradiated steel contains ~0.1Bq C-14 from irradiated steels

Irradiated steel leaching experiments - NRG
To be performed by NRG in the shielded chemical cell G1 in Hot Cell Laboratory (HCL) at Petten, NL Required installation of a new glove box to hold gas phase sampling rig adjacent to the G1 hot cell Authorisation for hot cell modification received from Dutch regulator New glovebox installed G1 cell inbox cleaning is finished Connection between the glovebox and G1 cell being made This slides feels rather out of date now. Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

Liquid phase analysis The rate of release of Co-60 into solution shall be measured by means of gamma spectrometry, in order to provide additional information on the corrosion of the sample. C-14 measurement will be done by LSC (Packard TriCarb 3180 TR/SL) N2 NaOH 20ml/min 5ml/min H2O Carbosorb Ice bath Acid Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

C-14 solution analysis Recovery ˃ 90% Teflon replaced by glass tubing Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

Gas phase sampling apparatus
Designed and made at RCD in UK Captures 14CO2, 14CO and 14CH4 fractions by selective oxidation/ absorption on 3 soda lime columns Concern over potential CO sorption to metal surfaces replaced all nickel-based fittings with stainless steel Efficiency and selectivity of 2 catalysts were measured CO 94.5% (CuO) remainder oxidised on CH4 catalyst CH4 95% (Pt) with <2% removed after CO catalyst Delivered to Petten on 26 March 2015 Used for blank tests Placed in the glove box Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

Blank experiment Container filled with 600 ml 0.1M NaOH solution Gas and solution phase sampled after 1 day (24 hours collection of gas phase C-14) and after 10 days (9x 24 hours collection of gas phase C-14) Please add volume of solution used in the blank experiment Setup for blank tests: 1 is soda lime column for removing C-14 from nitrogen feed, 2 is leaching container where A is N2 inlet, B is dip leg and C is N2 outlet, Unit 1 and Unit 2 are the parts of RCD rig Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

Solution phase results
Sample name CPM Efficiency (%) Activity (Bq) in sample Blank A (0.1 M NaOH) 5.39 78.9 - Blank B (0.1 M NaOH) 6.15 78.6 Average Blank A&B 5.77 78.8 Blank C (Carbosorb + InstaGel, 50:50) 4.86 78.5 Standard A (C-14 tracer) 109.83 79.5 2.18 Standard B (C-14 tracer) 112.08 79.2 2.24 Sample A (1-day sampling) 5.34 ˂0.1 Sample B (1-day sampling) 6.33 78.7 Sample C (10-days sampling) 5.04 79.0 Sample D (10-days sampling) 4.43 This slide needs explanation. What are Standards A and B? What is the conclusion? Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

Gas phase C-14 results Results of 14C analysis of 3 soda lime absorbent columns after 1 and 9 days continuous gas phase sampling during the blank experiment compared to soda lime background Day CO2 (Bq) CO (Bq) CH4 (Bq) 1 0.023 ± 0.003 0.021 ± 0.002 10 0.020 ± 0.002 0.025 ± 0.003 Soda lime background 0.026 ± 0.003 No difference between the 14C activities measured in the sample columns and those measured in equivalent amounts of pre-loaded soda lime No measurable 14C was absorbed from gas phase during the blank test Only measurable source of background 14C in gas phase measurements is from the soda lime absorbent (pre-loaded with fossil CO2 as carrier) – intrinsic background AMEC/NRG WP2 C-14 release from irradiated steels

Recommendations from the blank experiment
The blank tests aimed also to validate the proposed experimental procedure and the leaching setup, including the leaching container prototype. Observations During the running of the tests, a condensation in the container and in the tubing of the container and even between the tubing of unit 1 and unit 2 of the RCD rig has been observed. The position of the sample valve is unhandy, mainly because quite some amount of the liquid sample stays in this valve between samplings. Dip leg has too big inner diameter, which gives problems during liquid sampling (vacuum has to be applied in two steps). Please explain how these have been addressed. AMEC/NRG WP2 C-14 release from irradiated steels

Liquid sampling AMEC/NRG WP2 C-14 release from irradiated steels

Co-60 analysis Sub-samples transferred to 400μl polythene container Gamma spectrometry – Canberra High purity Ge detector Sample to detector - 10 cm Measurement - 48 hours Minimum detectable activity Bq Amec Foster Wheeler/NRG WP2 C-14 release from irradiated steels

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