The NDA group of Site
Licensed Companies
Making a difference for future generations

Steve Hardy
Director of Environment
Nuclear Decommissioning Authority
United Kingdom

Our mission
We’re charged with the mission, on behalf of Government, to clean up
the UK’s earliest nuclear sites safely, securely and cost effectively.
Doing this with care for our people, communities and the environmentis at the heart of our work.

We’re committed to overcoming the challenges of nuclear clean-up anddecommissioning, leaving our 17 nuclear sites ready for their next use.

Our sites
Our work to clean up the UK’s nuclear
legacy is the largest, most importantenvironmental restoration project in Europe.
Our mission is so long-term it spans the next
century and beyond.
Our 17 sites are at different stages ofdecommissioning and all have unique challenges.

The UK’s nuclear legacy
The UK’s nuclear landscape began totake shape in the post-war period andhas evolved over many decades.
Our 17 sites reflect this and include
the first fleet of nuclear power stations,research centres, fuel-related facilities
and Sellafield, which has the largest
radioactive inventory and the mostcomplex facilities to decommission.
Current plans indicate it will take morethan 100 years to complete our core
mission of nuclear clean-up and waste
management. The ultimate goal is toachieve the end state at all sites by2125.

Innovation throughresearch and development
The NDA collaborated on R&D
projects with the wider nuclear
sector and beyond, both in the UKand overseas.
• We’re supporting more than 50
PhD projects at over 20
universities• More than 70 supply chainorganisations are involved withour R&D projects• Around 80% of total R&D
spending is targeted at Sellafield’s
technical challenges

We’re doing
more internationally
We place great importance on
collaborating with international partners toshare learning and best practice, helping us
develop better solutions for the UK’s mostpressing technical challenges.
We’re working closely with international
committees such as the IAEA and the OECD
NEA, and with decommissioning and waste
management companies in France, USAand Japan.

We’re also helping to identify opportunities
for the UK’s nuclear supply chain to workinternationally.

Introduction

The presentation will include an example from the UK to present the challenge
in managing higher activity waste following either accident scenario and wherethe records and provenance of the waste is poor
Sellafield Magnox Swarf Storage SilosBriefly UK Radioactive Waste Characterisation Good practice guide(which is summarised in NEA Expert Group on Characterisation of
Unconventional and Legacy Waste 2020 paper) will is now publishedSellafield

Current key activities• Focus on high hazard risk reduction• We have had a number of significant accidents
at the site over the past 7 decades and have anumber of facilities in a degraded condition
which are a priority for us• In order to make the progress needed toaddress those High Hazard facilities and reduce
the risk they present in a priority manner wework very closely as part of G6 approach, with
our government, our two key regulators (Officefor Nuclear Regulation and Environment
Agency)9High Hazard programmes represent 90% of
the nuclear hazard potential on theSellafield site
5. Highly Active
Liquor (HAL)

1. Pile Fuel
Storage Pond
2. Pile Fuel
Cladding Silo
3. First
Generation
Magnox Fuel
PondFourLegacy Ponds& Silos

6. Managementof Plutonium

4. Magnox SwarfStorage Silos10

Discrete item retrievals now completely
removed from the Pile Fuel Storage Pond atSellafield

Magnox Swarf Storage Silo – balance
between certainty and progress
Credit to my colleague John Clifford, Head of Retrievals and Higher Activity
Waste of Sellafield Ltd for content

Balancing uncertainty and progress• A selected forward direction requires a certain level of confidence which is
influenced by levels of risk, hazard, stakeholder requirements and legislation.
• Confidence can be gained through removal of uncertainty and tolerance orprotection to uncertainty and there is an appropriate balance between
elements which can be struck to allow progression.
• The appropriate balance is bespoke to the problem in hand.
• The role of characterisation is one means to provide data to inform decisions(utilising Data Quality Objectives principles) where the nature and extent ofcharacterisation provides the level of confidence in that data.
• However, for certain scenarios characterisation activities that provide sufficientlevels of quality and confidence may prove a significant challenge.
• The Magnox Swarf Storage Silo is one such case study where the driver to makeprogress in removal of its inventory is significantly important.

Magnox Swarf Storage Silo (MSSS)

There is a high hazard and risk reduction driver to remove the inventory fromMSSS and store in a safer form under modern arrangements.
The outcome was the Alternative ILW Approach where the material was to be
stored unconditioned in high integrity multi-barrier containers.

MSSS - Inventory Overview &Uncertainty
There are 22 compartments each approximately 600 m3 containing a range ofIntermediate Level Waste.

MSSS waste can be broadly categorised into five waste types which are of interest:
Magnox swarf and its corrosion product magnesium hydroxide sludge;
Uranium metal and its corrosion products e.g. uranium dioxide sludge;
MBGW;
Mixtures of the above three types.
Stainless steel and Zircaloy hulls from reprocessing operations.
Majority of MBGW items consisted ofgeneral waste e.g. filters, cave items,
graphite sleeves and distance pieces,
drums of sludge, tins/drums of softwastes, lead, pond tools.

MSSS – Inventory Overview –Swarf/Sludge• Metal corrosion rate is temperature, pH and surface area dependent.
• Magnox wastes in the older compartments exhibit a specific set of behaviours
identified by characterisation and are referred to as “Type 1” Magnox behaviour.
• Applying this Type 1 Magnox behaviour to the MSSS results in the prediction thatmost of the Magnox in all the Compartments of the MSSS has corroded duringstorage, with the waste now consisting of magnesium hydroxide sludge.
• In 2014 and during 2015 a series of video camera surveys were carried out in theMSSS. These showed that at least at the visible surface of the waste in theSecond and Third Extensions the Magnox had corroded to a much lesser extent
than would be expected if it had exhibited Type 1 behaviour. This Magnox waste,
which has shown a lower corrosion extent than Type 1 behaviour Magnox isreferred to as exhibiting “Type 2” behaviour Magnox.

Technical, Safety and Engineering
Cases
Requirement to consider the lifecycle of the waste:
In-situ inventory
Retrievals and containerisation
Safe interim storage
Final disposal to the GDF
Undertaking characterisation is extremely challenging – difficult to access the waste,radiological considerations for handling and analysis, and to provide high levels ofconfidence significant numbers of samples would be required - uncertainty would
always remain.
For all current adopted waste management processes and identified waste behaviours
all available information has been used e.g Historic records and accounts, visualinspections and historic sampling data, On-plant measurement data.
Significant supplementary work was also undertaken to provide a sufficiently
conservative basis and assumption set, through;Fundamental research and development related to waste behaviours,Demonstrations and predictive modelling
Where each element of uncertainty is duly considered to ensure that sufficientmargins of tolerance are incorporated into the solution to protect people, process andplant.

Example - Robust Waste Containers
The 3m3 Box and internal waste storage skip
provide significant robustness to a numberof any adverse waste behaviours. This
provides protection against a range ofuncertainties.

Key Box Features:• Multi and diverse-barrier container
robust to corrosion mechanisms inducedby the waste or external environment.
• Filters to allow egress of hydrogen andretain particulate.
• Robust to impacts and deflagration

Example - Hydrogen TechnicalArguments• With respect to hydrogen generation the inventory of significance arethose wastes that can generate hydrogen or retain and release hydrogensuch that levels within the waste container exceed the lower flammable
limit.
• Conservative skip filling has been adopted to ensure the rate of H2generation is always manageable.
• Conservative waste behaviours have been assumed.

Assurance through Condition
Monitoring and Inspection• Condition Monitoring and Inspection (CM&I) takes
account of the technical risks, the potential waste
evolution and the performance requirements of boththe store and waste container.
• The approach provides reassurance that the overall
performance of the storage system is protective ofpeople and the wider environment.
• Monitoring of evolution of the waste packages will
aim to understand any long-term risks that could
complicate package retrieval, as well as supporting
the understanding of the waste prior to finishing anddisposal.
• The currently available and proposed future CM&I
capabilities provide for wide ranging interrogation
techniques.

Conclusions : MSSS Optimisation,Continued Improvement and Learning• Although a conservative basis has been adopted, it is understood
where known uncertainties reside and conservatisms have beenmade.
• Tolerance and robustness has been built into the engineered systems
and technical basis.
• Caution is adopted for the filling of skips and this means a suboptimal case but allowed retrievals and storage to commence.
• Waste behaviour and the silos content will be better understood once
it is retrieved and observed.
• Strategy is now to improve on this position to reduce conservatism
through learning activities, further R&D, engineering optimisation andlimited characterisation; whilst having considered means ofresponding to deviations.

NDA Solid Radioactive Waste
Characterisation Good Practice Guide

Chapter 1 describes the aims, scope and intended
readership of the GPG.
Chapter 2 describes the United Kingdom classification
system for solid radioactive waste and introduces theUK regulatory framework for radioactive waste
management.
Chapter 3 describes the characterisation requirementsof organisations responsible for treating or disposing ofradioactive waste, the responsibilities of the wasteproducer.

Chapter 4 presents a systematic process forcharacterising solid radioactive waste and gives
guidance on the application of this process.
Chapters 5 to 7 consider specific important aspects of
the waste characterisation process
Chapters 8 to 10 describe and provide guidance on
the three approaches to waste characterisation

Optimised Approach to Acquiring New Data

Summary
There is a balance to be struck between making progress and managing
uncertainty
If there is an imperative to make progress then uncertainty must be managed.
Where it is not feasible or characterise to the extent you might like, one canadopt conservative safety cases and robust engineered containers to provide
the safety envelope and hence allow the progress.

Progress can best be made by developing and agreeing that strategy with key
stakeholders, aiming for a shared and agreed outcome.
Progress may only be to the next interim step but this is still good and important
progress as long as the end goal is kept in mind.