Embed Size (px)
Citation preview
Irradiated Graphite Processing Approaches: an
Update on Project ‘GRAPA’
A.J. Wickham,
W.Meyer and P. O’Sullivan
INGSM-20
Bruges, September 2019
An Update since INGSM-19 in Shanghai
• KEY ISSUES REMAIN UNCHANGED!
• >250,000 tonnes irradiated graphite world-wide (“i-graphite”)
• Graphite has been ‘damaged’ by neutron irradiation… may be distorted, cracked, difficult to extract conventionally (especially where other materials such as pins/wires are present): if irradiated at low temperature, Wigner energy may be present
• Impurities have become activated by slow neutrons and 14C produced from 13C: also 3H from moisture and fuel and, in some cases, contamination from failed fuel fission products
• If irradiated in air or carbon dioxide, structure also weakened by chemical oxidation
• An issue not only for major historical producers (e.g. UK, Russia, France) but also for any country with small reactors containing graphite reflectors or thermal columns
• GLACIAL progress (i.e. lack of) in some domains, urgency to find a solution in others
• New build programmes require disposal routes to be established ahead of licensing (for HTR including graphite/carbon in fuel elements: for MSR graphite with salt/fuel within its pores)
The Role of IAEA in i-Graphite Management
• The IAEA does NOT prescribe policy on radwaste management.
• The objective of GRAPA has been to maintain awareness of previous and ongoing work in other programmes, to collate information, and to develop potential technological solutions – then to invite the IAEA to advise Member States of the various options which are available, to enable them to make an informed decision on the correct policy for their situation… currently through the INTERNATIONAL DECOMMISSIONING NETWORK and the INTERNATIONAL PRE-DISPOSAL NETWORK
• One problem is that few waste authorities seem to have actually defined any acceptance criteria!
DISMANTLING...
DISPOSAL...
TemporaryStorage
?
Treatment
?
...or WAIT?
Useful Product
?
Reduced activity or
reduced waste category
?
REPOSITORYOTHER
HOW?
...may be decided on basis of what happens next (other boxes here)...
...or another reason entirely ...e.g. underwater
Options include:
• ‘Safe Storage’ in reactor vessels or containments•Treatment of fuel pebbles/particles and/or graphite• Progress with deep repository construction•Case for shallow repository disposal – maybe in
association with pre-treatment• Do nothing Plant-specific or
design-specific solution
The selected method of graphite removal/recovery should relate to the next stage in the operation: this had led to proposals for an international ‘pilot plant’ but this is impractical with the number of possible permutations: however, as will be seen later, this is entirely practical for a specific family of reactors of similar type
GRAPA Topic 1 - Characterisation:
Investigate the isotopics, understand their chemical form, and their potential for leaching short term and long termExtent of irradiation damageMechanical properties (for removal methodology and subsequent handling)Wigner energy? Seen as a minefield, but for the wrong reasons.Why measure ‘weight loss’?Don’t overlook existing data!!!
The extent of characterisation should be focussed on ‘what you need to know’ – the default position of reulators (and waste authorities) is always to ask for more information: this is also sometimes an excuse for delays which would have been inevitable anyway
Newly developed rapid characterisation technique –CPST Lithuania
GRAPA Topic 2 – Removal and Retrieval:
Whole blocks? Ask ‘why?’ If you end up smashing the graphite to immobilise it in containers, then this complex mechanical operation may not be necessary. Equally, if you are going to treat it in some process then you may want small lumps or even dust…
The selected method of graphite removal/recovery should relate to the next stage in the operation: this had led to proposals for an international ‘pilot plant’ but this is impractical with the number of possible permutations: however, as will be seen later, this is entirely practical for a specific family of reactors of similar type
ADE-5 Graphite-Block Removal – A Success During GRAPA
GRAPA Topic 3 - Treatments:
What are you trying to achieve? Reduction in radioactivity for handling, personnel dose or reduction of waste category? Make re-use [in some form] an easier process?
whence: Thermal decontamination, incineration, electro-disintegration, supercritical extraction, etc.
In-Situ (before dismantling) or a subsequent process?Novel immobilisation? As glass, filled with glass, as filler in cement for other waste…
An Integrated Process - Example
GRAPA Topic 4 – Packaging, Storage and Disposal:
All available planned methodologies for packaging, shallow and deep disposal, have been reviewed. Member States have generally planned for deep repositories they do not yet have – the UK is unique (!) in having different regional policies for Scotland compared with England and Wales!
Russia is adopting a variablestrategy, as we have seen:whereas one reactor is alreadybeing dismantled, another has simply been buried: “entombment” or “in-situdisposal”.
USA is thought to still have this inmind for Hanford reactors, but they declined to take part in GRAPA
Application to Specific Reactor Projects
• The output from GRAPA has been closely aligned with a number of decommissioning projects:
• Ignalina NPP (planning, characterisation, special wigner-energy issues in control-rod displacers);
• CIRUS (India), L54-M (Politecnico Milano) and VVR-S (Romania) – research-reactors at end of life)
• Chernobyl (special case for RBMK)
• Chinon (EdF developing pilot plant for all UNGG aactivities)
• Latina (for all Magnox reactors, focus particularly on mechanical handling of graphite components)
• Russian production-reactor disposal (both entombment and dismantling) and development of thermal treatments and also vitrification for highly-contaminated graphite (ongoing concern)
Concept Development (An Example):“Potential Exposure Reduction”
As part of the ‘core-to-capture’ integrated process mentioned earlier, mixing the 14C from heat treatment (as CO2) with CO2 from fossil-fuel burning (depleted in 14C compared with current natural background) ensure that future re-concentration is not possible because chemical separation is not possible.
Avoidance of the possibility of future re-concentration of radioisotopes:
Some Personal Observations
• Utilities should focus down on ‘what do we need to know’ through characterisation: in some instances there seems to be too much reliance on ‘maybe we should get more information’ – and in some instances irrelevantinformation - as an excuse not to move ahead with dismantling;
Some More Personal Observations
• There needs to be a recognition from regulators and waste authorities that if the data do not match the modelling, it is the data that matter;
• We still have to convince regulators ‘Health and Safety’ and waste authorities of two things: (1) that graphite does not burn; (2) that total stored energy is of little importance but that the potential rate of release per unit temperature rise is… [and learn the lessons of BGRR dismantling success];
• We need a proper debate on the logic of creating interim storage facilities where the ‘problem’ is simply moved from one part of the site (reactor) to another at considerable cost;
• We are not going to fully understand things like C-14 mobility in and from graphite until we can understand some really important issues about graphite structural behaviour on the micro-scale under irradiation… so…
• TWO CHALLENGES…
Two Challenges (neither relates entirely to i-graphite issues: both have come up in recent technical discussions relating to
operational nuclear-graphite behaviour)
1. Is highly-irradiated nuclear graphite a collection of particles with interconnected spaces between them (like a sand bed) OR is it a cave system of enlarging interconnected passages with solid walls around them? This has arisen as an important question when considering graphite oxidation in the
presence of an inhibitor which has a spatial distribution: the former may facilitate ‘dispersion’ or ‘spreading’: either is important in the consideration of radioisotope mobility
Two Challenges (neither relates entirely to i-graphite issues: both have come up in recent technical discussions relating to
operational nuclear-graphite behaviour)
2.You’re in there, inside the ‘cave’ or sand bed, gazing between the crystallite
layers as the atoms are displaced by fast neutron “collisions” and (for example) as 13C atoms are converted to 14C by slow neutrons and spin towards you, out of control, because of the recoil energy. With more than 20 displacements per atom, and the known ‘zoo’ of damage structures along with Malcolm Heggie’s ‘Buckle, Ruck and Tuck’, how does this materialpossibly retain the structure and properties of graphite, and
what is happening to the contained radioisotopes?
End of the GRAPA Road… Possible New Directions
• Draft GRAPA Report: will be presented to Member State’s representatives at…
• Technical Meeting, Vienna, Lithuania, 1-4 October 2019
• Next Consultancy Meeting (all interested can request an invitation), March 3-6 2020 (date to be confirmed), Vienna: objective to prepare the final GRAPA report as a TECDOC (see later) and to make recommendations to the IAEA for future i-graphite work under the IPN
• If you would like to have your current work on irradiated graphite disposal issues to be associated with any new IAEA project, please talk to us!
• Tony Wickham [email protected] Willie Meyer [email protected]
Tetiana Kilochytska [email protected]
“…further international collaboration through IAEA…” (1)
• Need to align with other international initiatives, for example:
A current INNOGRAPH proposal for international collaboration on an ‘Industrial Demonstrator’ at Chinon led by EdF – an excellent initiative aimed at working through the practical detail of dismantling UNGG reactors
“…further international collaboration through IAEA…” (2)
• Issues left over from GRAPA and TECDOC 1790 an deserving of further study:
• Importance of CHEMICAL FORM of radioisotopes;
• Mobility of radioisotopes;
• Focussing sampling programmes on the clear objectives;
• Remain open-minded about alternative dismantling, treatment and disposal strategies;
• Further development of characterisation instrumentation, handling and lifting equipment, techniques for immobilisation and packaging…
Step Back and Consider Every Stage of Your Programme
• Some people have strong views: need to balance the science and the politics with the economics and with informing the public. This balance is rarely correct!
• Some will determinedly hold on to their strong views: “IF YOUR DECOMMMISSIONING PLAN INVOLVES BUILDILNG A NEW BUILDING, THEN IT’S THE WRONG PLAN!” - (EPRI Decommissioning Workshop, Kendal UK, October, 2006).
Then: “Stop Worrying and Get On With It”
Windscale Piles to be left for 100 years to ~2050
Whereas BGRR…
Gone!
Going…
And, lastly…
THANK YOU FOR YOUR ATTENTION
KEYWORDS
• decommissioning
• disposal
• waste characterisation
• treatment
• i-graphite
