Geological disposal of higher-activity radioactive waste. June 2010

Transcription

1 Geological disposal of higher-activity radioactive waste June

2 Nuclear Decommissioning Authority Delivering the largest environmental clean-up programme in Europe at 19 existing nuclear facilities Retrieving, making safe and disposing of some of the most hazardous material in the world Transforming the UK s decommissioning programme into a competitive market introducing skills and innovation to achieve greater value for money 18,000-strong workforce across the NDA s estate Annual budget currently 2.8 billion Responsible for the implementation of geological disposal of higher-activity radioactive waste 2

3 NDA activities Demolition of towers at Chapelcross Chapelcross begins Reactor 3 defuelling Trawsfynydd ILW store opens New Sellafield product store under construction VRR back overseas Dounreay Puma Cell cleared out and cleaned up 3

4 Radioactive waste - key issues UK a nuclear nation since the 1940s Challenges and lessons from the past Existing waste legacy Other materials? Future new build waste? Will remain hazardous for hundreds of thousands of years Previous failed attempts to find a solution 4

5 Managing Radioactive Waste Safely Managing Radioactive Waste Safely Programme established (2001) Committee on Radioactive Waste Management (CoRWM) set up (2003) CoRWM recommendations (2006) Geological disposal Safe and robust interim storage Flexible and staged-decision making process Intensified programme of research and development Government consultation (2007) MRWS White Paper, A framework for implementing geological disposal (2008) 5

6 The organisations involved 6

7 Geological disposal Preferred international approach Learned society support Geological disposal facility (GDF): metres deep Area of several square km years until ready for waste 100+ years to fill 7

8 A concept for intermediate-level waste 8

9 MRWS site assessment process Stage 1: Invitation issued and Expressions of Interest from communities Advise Community not suitable Stage 2: Consistently applied sub-surface unsuitability test Unsuitable Suitable Stage 3: Community consideration leading to Decision to Participate Stage 4: Desk-based studies in participating areas Stage 5: Surface investigations on remaining candidates Final Community Right of Withdrawal Stage 6: Underground operations 9

10 Current progress Currently in Stages 1 and 2 Stage 1 Expressions of interest received, but still open for more West Cumbria MRWS Partnership established Stage 2 Unsuitability test in progress for Copeland and Allerdale Stage 3 Decision to participate ~ 2011? 10

11 The importance of chemistry in our needs-driven research programme Current Nuclear Power Issues, RSC Workshop June

12 Our research programme Our research programme is needs driven and supports geological disposal in the UK. Research supports our key programme activities of: Specification what are the requirements from a geological disposal facility (GDF) Design what will a geological disposal facility look like? Assessment will a GDF meet the safety requirements? Chemistry is important in each of these activities. 12

13 The role of research 13

14 Chemistry in EBS design International programmes have used knowledge of: What their waste/wasteforms are The geology of their site(s) To design an appropriate engineered barrier system. A range of designs exist and these are shown in the following slides. 14

15 Nagra s proposed layout for a deep geological disposal facility in Opalinus Clay 15

16 Illustrative concept example for disposal of HLW/SF in a lower strength sedimentary host rock 16

17 Illustrative concept example for disposal of ILW/LLW in a lower strength sedimentary host rock 17

18 Contact-handled TRU waste packages being stacked in a disposal room in the WIPP 18

19 Illustrative concept example for disposal of ILW/LLW in an evaporite host rock 19

20 Safety assessment The GDF would be designed so that the majority of radionuclides would decay within the engineered system. One of the aims of the safety assessment is to consider the impact of the small fraction of radionuclides that could be released from the engineered barrier system and migrate back to the surface environment Key pathways are in gas or groundwater 20

21 Chemistry in the safety assessment Key parameters in the assessment model: Leaching rate for the waste or wasteform Gas generation rates Solublity in the porewater / groundwater Sorption to the engineered barriers Sorption in the geosphere Biosphere factor We need appropriate values for these parameters, including an understanding of the associated uncertainty. 21

22 Example carbon-14 from ILW A programme of work looking at: Leaching of C-14 from irradiated materials Demonstration of carbonation in the near field Field-scale biosphere experiment 22

23 Irradiated graphite first experiment WAGR Graphite contacted with highly alkaline water Volatile C-14 and tritiated species collected and analysed Short term experiment Small release of volatile C-14 Follow up studies using improved methodology and looking at BEPO graphite 23

24 Gas sampler First column traps HTO Pd catalyst then oxidises C-14 species to CO 2 and remaining T to HTO Third column traps HTO Fourth column traps 14 CO 2 C-14 and H-3 recovered from columns and analysed Sampler now developed with 2- stage oxidation to distinguish CO and hydrocarbons 24

25 Future graphite work Obtain sample of irradiated Magnox reactor graphite Study effect of aqueous conditions e.g. ph, T, oxic/reducing Study to start this year 25

26 C-14 release from irradiated steels Serco/NRG measuring release of C-14 from irradiated stainless steel Sample of high nitrogen content steel (316N) Main experimental work starts next year Analysis methodology for gas will be similar to graphite experiments 26

27 Carbonation of NRVB RH = 75%, T = 20 C, P = 3 bar 27

28 Drum-scale carbonation experiment 28

29 Carbon-14 in the biosphere New study Serco / Nottingham University Obtain experimental data on behaviour of CH 4 and CO 2 in soil zone and plant uptake Laboratory (year 1) Field study (years 2 & 3) Interpret results Updated (or new) assessment model for C-14 in plants from below ground flux of C-14 gas 29

30 Conceptual model 30

31 Field-scale experiment Head space analysis 31

32 Summary Chemistry is important in: Designing GDF concept Assessing the safety of the GDF Example - Carbon-14 Low rate of release of gaseous C-14 from irradiated BEPO graphite at high ph Studies to be extended to Magnox reactor graphite Study has commenced on irradiated stainless steel Demonstration of carbonation Plant uptake study including field scale experiment is now underway 32