Dalgety Bay Radium Contamination Dr Paul Dale 4 th November 2011 - - PowerPoint PPT Presentation

Dalgety Bay Radium Contamination

Dr Paul Dale 4th November 2011

Work undertaken

• Dalgety Bay hazard reports
• Dalgety Bay intrusive work
• Dalgety Bay inter tidal work

Hazard reports

• Released 26th September 2011. Two reports
• Skin doses
• Ingestion doses
• Both reports based on sources recovered

by DE (now DIO) and SEPA

Skin Assessment

• Undertaken on sources recovered in 2008
• Direct measurements of energy deposited

Skin doses

Skin thickness

• Max. dose rate

15 4 m 1031 mGy/h 51 4 m 214 mGy/h 77 4 m 210 mGy/h 289 4 m 121 mGy/h

Inhalation

• No further work to date on this pathway.
• 2009 report “Assuming a particle of 1 kBq Ra-226 (+

daughters at 0.9 kBq: Pb-214, Bi-214, Pb-210, Po-210) was sufficiently small to deposit in the alveolar or bronchial regions

• f the lung, and assuming Type M[1] solubility, rough first

estimates of committed effective dose are:

• Deposition in the alveolar region of an adult: 10 – 25 mSv
• Deposition in the alveolar region of a 1 year-old child: 50

– 150 mSv

• Potentially higher doses if deposited in the bronchiolar

region.

• Thus, it may be worthwhile investigating the ashy layer, to

determine if sources of a few kBq are present or otherwise. Given the likely costs of this work, if further work is to be undertaken at Dalgety Bay, it is recommended that this is given consideration.

Ingestion

• Assessment of potential CED using more

realistic solution

• Selection of DE recovered sources (30 of 128)

for characterisation

• Sources initially screened for alpha
• Initial segregation of sources from matrix

S084 - particle

Before Separation After Separation

S120 – source break down?

Before Separation After Separation

Artefacts – dial and fuel gauge

Activities

• Assessed by gamma spec
• 700,000 Bq Ra-226
• 170,000 Bq Ra-226 Dial
• 11,000 Bq Ra-226 Fuel sign

Solubility

• Ten sources tested
• “Replicated” stomach acid and lower ingestion

solutions used

• No relationship between activity and solubility

nor form and solubility

Solubility (2)

• Maximum solubility 25% (previous studies max 15%)
• Effect of variable source or more realistic solution?

Doses from ingestion

• For the most soluble source up to 128 mSv for

a three month old infant

• Issue of higher solubility needs to be carefully

considered

• Sources on the beach could give doses in

excess of 100mSv.

Pathways

• Member of the public removing stones/objects

from the beach as a memoir

• Possible pathway of preferential selection
• f artefacts
• Reported that they either did not see the signs
• r the message was not clear.

Summary

• Skin – hazard remained similar
• Inhalation – no further work undertaken
• Ingestion – previous estimates of dose may

have under estimated the true dose

• Doses from inadvertent ingestion of

ingestible particles would be above the 100mSv level for at least very young children in 2011 work. Earlier work previously shown doses in excess of 100mSv to older age groups.

Conclusion of SEPA Sept 2011 Reports

• Skin doses unlikely to exceed RCL threshold

values.

• Ingestion doses again exceed criteria in RCL.

Intrusive work

• Focus on the headland at Dalgety Bay
• Ground Penetrating Radar (GPR) work

undertaken on 5th September to provide information on the construction of the made ground

• Coring of the headland began on 12th

September

Intrusive work

Undermining of headland?

Headland Results

• Source recovered from within the eroding

edge of the headland

• Ra-226 positively identified at face of

headland

• Sources identified in the headland at depth

which appeared to be a tipping face

Dalgety Bay - Headland Area’s where Ra-226 has been detected

DIO Contractor

• Detect and remove sources from the affected

inter-tidal area including

• In front of the headland
• Slipway area
• Eastern side of sailing club area
• In front of Ross plantation

Contamination zone and DIO contractor finds

Contamination zone and DIO contractor + SEPA finds

Further Monitoring of Slipway area

Further SEPA Monitoring

Second Area of Made Ground

High Activity Source

• Recovered from 75 cm
• Multiple other sources

present

• In field activity 13MBq

Ra-226

• Type A container

required

• 1mSv per hour at 5 cm
• Laboratory analysis
• 10 MBq (detector 70

dead time)

• Further analysis

require detailed risk assessment

High Activity Sources

Source recovered (together with at least 10 further sources) Other high activity source(s) remain which require to be removed before winter erosion begins

Signs

• As other sources may be present near surface
• f high activity signs erected with

demarcation.

Hazard 10 MBq Source

• Assumed: activity 10 MBq Ra-226 in equilibrium with

daughters, physical size 20 x 20 mm, M type solubility.

• Ingestion doses
• Assume 10 % soluble (range from 0 to 25 %)
• If broke into 4 x 4 mm bits and activity evenly

distributed

• Activity of 4 x 4 mm source = 400,00 Ra-226 (similar

activity to other sources found)

• If ingested dose 534mSv to 1 year old, 86mSv adult
• Worse case 25% solubility 1.3 Sv 1 year old, 217 mSv

adult

Skin doses - gamma

• Initial field measurement of 1mSv /hr at

5cm

• Laboratory measurement – saturation

at close distances.

• Modelled response at distance appears

valid

• Current best estimate: “Thus for skin

contact (assuming 100 µm) we would estimate the dose rate from gamma to be around 220 Sv/h or 190 Gy/h, with a 95% confidence interval of 50 Sv/h”.

Beta and alpha skin doses

• Not possible at present (saturation)
• Likely to be high

Sources recovered

• 12th September to 4th November
• 396 sources in total
• Some sources have been recovered close to

the surface which have high activity (100’000Bq + Ra-226)

• Two sources recovered from made ground on

public access area (at surface)

Sources recovered to date

Ingestible?

• Estimated Activity 41,000 Bq Ra-226

Conclusions (1)

• More sources present than recent monitoring

has suggested.

• High activity source(s) remain at depth in

demarcated area at Dalgety Bay, which could give deterministic effects and could pose a significant hazard to human health.

• Inhalation pathways need to be revisited.
• In light of findings (above) current signs are

not appropriate.

• The criteria for RCL at Dalgety Bay appear to

have been exceeded and; given recent findings, the historic management arrangements may no longer be adequate.

Conclusions (2)

• An erosional event could release further

significant radiological hazards into the environment

• Monitoring and recovery will not prevent re-

contamination of the beach and appears unable to resolve the contamination issue.

• There appears to be a number of caches of

contamination which could be managed to prevent their release into the environment