nuclear decommissioning in the uk2017.radioactivewastemanagement.org/images/slide/session... ·...

NUCLEAR DECOMMISSIONING

IN THE UK

Pete Burgess

Radiation Metrology Ltd 1

Radiation Metrology Ltd

Where • Government nuclear research sites, e.g. Harwell, Winfrith

and Dounreay

• Materials test reactors – high neutron flux reactors for

determining the consequences of neutron irradiation such

as embrittlement

• Plutonium production reactors at Sellafield – see first slide

• Research reactors at universities etc.

• Reactor designs that were not taken forward into series

production – the SGHWR at Winfrith for example

• The earlier power reactors – power reactors have been

operating since 1956

• Weapons sites – mainly AWE at Aldermaston



2

Where (2)

• Nuclear submarine dockyards

• Uranium production facilities – a surprising number in the

early days

• Enrichment plants

• Fuel manufacture sites

• Fuel reprocessing sites

• Waste disposal sites now deemed inadequate

• Minor university and commercially operated research

facilities

• Radiopharmaceutical manufacturing plants at Amersham

and Cardiff



3

Waste in the UK

•“By 2030 Britain will have

generated approximately 1.4 million

cubic metres of LLW, 260 thousand

cubic metres of ILW and 3 thousand

cubic metres of HLW”



4

Clean

•Only by history. NOT by

measurement • No reasonable possibility of contamination or activation

• Difficult on old sites

• All measurement does is to give you, at best, a Less Than value

• Measuring for longer or using better equipment can reduce this

• But not eliminate it.

• Think on Limit of Detection or, I think more usefully, Maximum

Missable Activity



5

Out of Scope • Can’t be clean by history but levels are trivial, and

possibly undetectable – e.g. the desks in an

administrative building – or detectable (just) but very

low

• Most of the mass – building concrete, building cladding,

generators, soil, “clean side” plant, service piping etc.

• Uses values derived (currently) from EU RP122 but

may move to IAEA RS-G-1.7

• We have a very useful guidance document

• http://www.nuclearinst.com/write/MediaUploads/SDF%2

0documents/CEWG/Clearance_and_Exemption_GPG_

2.01.pdf



6

Higher categories

• Surface contaminated but can be cleaned

• Metal, in particular, with surface contamination

• Process pipework, ventilation ducting

• Strip, clean by grit blasting mainly

• Residue (pipe scale, surface paint, rust and used grit) goes as LLW

• The product goes as Out of Scope

• Studsvik in Workington are the main contractors

• Ship to Studsvik in Sweden

• Magnox heat exchangers

• Significant surface activity – activation products mainly

• https://www.youtube.com/watch?v=oysSDAZpEg8



7

Further categories • VLLW

• Most of the rest of the mass

• Definitely radioactive – concrete from pond walls, soil contaminated

by pipe leaks, low level activated concrete from close to reactors

• Nuclide specific but limit is typically 200 Bq/g

• NORM scale from oil production - http://www.nsnorm.com/services

• Goes to specified hazardous waste disposal sites

http://www.augeanplc.com/FileDepository/locations/enrmf/Permit%

20-

%20receipt%20and%20disposal%20of%20radioactive%20waste.p

df-

• Most protests were about the number of trucks, not the radioactivity



8

LLW • Building rubble, active pipework

• Sludge from cooling circuits and ponds

• Glove boxes and soft waste

• Main site is the Low Level Waste Repository (LLWR) at

Drigg in Cumbria

• Nuclide specific limits for LLWR but overall 12 GBq/tonne

beta and 4 GBq/tonne alpha

• Been in use since the 1950s. Well managed to begin with

• Then a (very) casual period – see photo

• Now properly managed again

• Very keen on grouted half-height ISOs – no voids,

basically a solid block



9

Map and pictures

• The old way – tumble tipping

• And now

• But Very Close to the sea



10

ILW

• Reactor components

• Debris from fuel reprocessing

• Steel components cropped off fuel elements

• Redundant sources

• Plutonium contaminated material from fuel and weapons

manufacture

• No disposal route as yet – sites are building their own

storage. Winfrith shown above

• And not likely to be for a long time

• Probably will end up at Sellafield (somewhere). Most is

already there

• Local council volunteered to host a site but Cumbria

Council blocked it



11

Treatment • Compacted and grouted in 500 litre stainless steel drums

• Or packed into Mosaik boxes – hugely expensive

• http://www.gns.de/language=en/23371/gns-yellow-box



12

High level waste

• The really scary stuff – Sv/h at metres from the cannisters

• Mainly from fuel reprocessing at Sellafield and Dounreay

• Requires cooling as it generates kW/litre

• Was mainly in liquid form – not a good idea!

• Now converted into glass blocks and stored inside

stainless steel containers in a tube store



13

UK progress -reactors

• All the Magnox reactors shut down and very nearly

completely defueled.

• All materials test reactors closed and defueled

• All research and prototype reactors closed. Many now

completely removed

• Magnox turbine halls demolished – mostly Out of Scope

• Fuelling machines removed

• Some of the heat exchangers removed –contaminated but

most not activated. Gas reactor ones are much less

contaminated than PWR heat exchangers

• Some recycled at Studsvik



14

Magnox reactor



15

Magnox

• Reactor pressure vessel is huge compared to PWR and

BWR designs. Typically 7m in diameter

• Reactor buildings will remain but reduced in height

• Fuel element debris vaults being emptied – high end LLW

and ILW – Co-60 dominated

• Other debris vaults being cleared – control rods

• Steel rods with boron ends

• Out of scope to ILW on one rod!



16

Berkeley then and now

• Two 138 MW(E) Magnox

• Quite low power

• 1962 to 1989 – unusually short life

• On site ILW store operating



17

Harwell (where I work)

• Started in 1946

• Peaked at 5000 workers in the 1960s

• 14 reactors in total

• Two significant air cooled “atomic piles”, GLEEP and

BEPO – very low power. Graphite with natural uranium in

aluminium cans. GLEEP ran from 1947 to 1990

• De-fuel, remove the concrete bioshield

• Break up the moderator

• Incinerate to remove the tritium

• Store

• Plus 2 materials test reactors

• HEU and higher power



18

Then and now

• Only the

most active

buildings

remain –

reactor

vessels,

stored

waste,

plutonium

chemistry



19

Chemical plant

• B351 – uranium contam

• Lots of asbestos

• Brick – recycled after crushing

• Steel structure recycled

• Pipework etc. as low level waste

• All the steel flooring plates

recycled after monitoring



20

Harwell Liquid Effluent Treatment Plant

• Everything that went into any building drain

• Cs-137, Sr-90, uranium, plutonium, Co-60, C-14 etc.

• We had to cut the trees down – we tried hard not to

• Soil, brick, pipework and concrete contamination



21

Liquid effluent treatment plant

• “Main active drain” – excavated as low level waste,

significant number of MBq particles trapped inside

• Trade waste drain – less active levels

• Domestic waste

• LETP provided treatment and filtration

• Big range of activity levels

• Major project success – for one area, an estimated 22

Half Height ISO containers reduced to 2

• Good monitoring, careful radiochemical analysis

• Use of Exemption Orders



22

Springfields Gaseous Diffusion Plant

• Enrichment by diffusion of UF6

• Designed to concentrate the lighter fissile U-235 (0.7 % of

mass) from the heavier non-fissile U-238 (99.3 % of

mass)

• High value metals wet decontaminated

• Then smelted to reduce volume

• Ingots assayed for radioactivity

• Most released as out of Scope



23

Delicensing

• Major facilities operate under a nuclear site license

• Nuclear Installations Act 1965 and subsequent

modifications

• Delicensing on the basis of “no danger”

• On the basis of existing, published guidance6, HSE

considers that an additional risk of death to an individual

of one in a million per year, is ‘broadly acceptable’ to

society.

• http://www.onr.org.uk/delicensing.pdf

• Interpreted as less than 10 µSv/annum to a future

occupier

• ALARP still applies. If you can reduce doses even further

without huge expenditure, then do so.



24

Approach

• Post operational clean-out (POCO)

• Assess what is left

• Strip buildings and dispose of the waste appropriately

• Demolish and dispose of unwanted buildings

• Monitor and remediate drains

• Remove any contaminated soil generated by spills

• Produce a detailed site gamma map

• Pull together all the evidence that the site has been

cleaned up well enough

• Activity limits based on IAEA RS-G-1.7 sum of quotients

• Submit to the Office for Nuclear Regulation



25

Fingerprints • Waste characterisation often refers to a

fingerprint, rather than quantifying individual nuclides

• Any detection mechanism is radiation type and energy dependent

• Only gammas are easily detectable on a metre by metre basis

• Many assessments rely on one or two gamma emitting easily detectable nuclides

• Which are not always the ones that dominate radiologically

• Cs-137 for fission (662 keV at 85 %), Co-60 for activation (1.17 and 1.31 MeV at 100 % each, Bi-214 for radium (609 keV)

• So getting the fingerprint right is vital

Gamma map

The limiting activity – nuclide specific

• Express each nuclide as a fraction of the total activity (e.g. 15% Co-60, 85 % low toxicity at 100 Bq/g)

• Divide each fraction by the limiting activity (e.g. 15% Co-60/0.1 + 85% others/100)

• Sum the results (in the example above this will be 1.509)

• Invert that to get the limiting fingerprint activity in Bq/g

• Divide the fraction of the nuclide to be measured by this sum to get a limiting Bq g-1 value for that nuclide

• Taking Co-60 as the most likely nuclide to be measured this is 15%/1.509 = 0.099 Bq g-1

• Sounds complicated but isn’t

• Easy with a spreadsheet

Example - Fuel cooling pond concrete

• Total activity limit =

0.16 Bq g-1

• Two useful gamma

emitters

• Easy gamma

monitoring target –

lots of Cs-137 and

Co-60

Nuclide Major

emission

Fraction

(%)

RS-G-

1.7

limit

(Bq/g)

Cs-137

Gamma +

medium E

Beta

46 0.1

Co-60 Gamma +

low E Beta 17 0.1

H-3 Very low E

beta 23 100

Fe-55 Very low E

X-ray 4 100

Ni-63 Low E beta 7 100

C-14 Low E beta 2 1

Sr-90

(+Y-90) High E beta 1 1

And then? • They appoint a contractor to review the submission,

particularly the monitoring aspects.

• PHE is currently the main one.

• They do not duplicate measurements.

• They think about what was measured and where.

• What could be missed?

• Example: sloping flask loading area.

• It had been monitored in strips from the high end to the

low end.

• PHE concentrated on walking along the low end.

• Contaminated paint flakes in the gutter!



30

The difficult bits 1

• Fingerprints with no useful detectable gammas and bulk

contamination

• Options include gross beta measurement if there is a high

energy beta

• Sampling followed by radiochemistry – slow, expensive

and very, very easy to miss localised spills



31

Contamination by the naturals • Uranium and thorium are everywhere, in the mg/kg

region.

• Equivalent to several times 0.01 Bq/g, the Out of Scope

level

• The way out is to take lots of samples around the site

• Then look at on site samples

• If they fall within the same distribution, claim for zero

contamination



32

Essential reading

• The DQO process – how to put together a credible

monitoring plan

• https://www.epa.gov/sites/production/files/documents/guid

ance_systematic_planning_dqo_process.pdf

• -----------------------------------------------------------------------------

• An excellent guide to the statistics of detection

• Lloyd A. Currie, Limits for Qualitative Detection and

Quantitative Determination: Application to Radiochemistry,

Anal. Chem. 40, 586-593 (1968).

• Unfortunately, not freely available on the web.

• Worth Paying For



33

https://www.epa.gov/sites/production/files/documents/guidance_systematic_planning_dqo_process.pdf



Very useful

• But very hard work!

• Marssim

• https://www.epa.gov/radiation/multi-agency-radiation-

survey-and-site-investigation-manual-marssim

• Needs lots of translation from ancient units into SI



34

https://www.epa.gov/radiation/multi-agency-radiation-survey-and-site-investigation-manual-marssim


















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