Plutonium in depleted uranium penetrators

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275

PLUTONIUM IN DEPLETED URANIUM PENETRATORS

J.P. Mc Laughlin, L.León Vintró, K.Smith and P.I. Mitchell, Z.S.Žunić*

Dept of Experimental Physics, University College Dublin, Ireland

VINČA Institute of Nuclear Sciences, Belgrade, Yugoslavia

ABSTRACT

Depleted Uranium (DU) penetrators used in the recent Balkan conflicts have

been found to be contaminated with trace amounts of transuranic materials

such as plutonium. This contamination is usually a consequence of DU

fabrication being carried out in facilities also using uranium recycled from

spent military and civilian nuclear reactor fuel. Specific activities of

239+240

Plutonium generally in the range 1 to 12 Bq/kg have been found to be

present in DU penetrators recovered from the attack sites of the 1999 NATO

bombardment of Kosovo. A DU penetrator recovered from a May 1999 at-

tack site at Bratoselce in southern Serbia and analysed by University College

Dublin was found to contain 43.7 +/- 1.9 Bq/kg of

239+240

Plutonium. This

analysis is described. An account is also given of the general population radi-

ation dose implications arising from both the DU itself and from the presence

of plutonium in the penetrators. According to current dosimetric models ,in

all scenarios considered likely ,the dose from the plutonium is estimated to be

much smaller than that due to the uranium isotopes present in the penetrators.

Key words: natural radionuclides, transuranic materials, depleted uranium,

plutonium, DU ammunition

INTRODUCTION

In the 1990s starting with the Gulf War, again in Bosnia and Herzogvina and most recently

in 1999 in Kosovo and Serbia ammunition made from depleted uranium (DU) was used by

forces from NATO countries. Although it has not been confirmed it is considered possible

that DU ammunition originating from the DU stock of the former Soviet Union or other

non-western sources may also have been used on occasions in conflicts in other parts of the

world in the 1990s. It is variously estimated that about 30000 rounds of DU armour pene-

trating ammunition were used in the NATO aerial bombardment of Kosovo in 1999. The

majority of these penetrators having missed hard targets remain buried in the ground at

depths that make them very difficult to detect and recover.. In addition to the main targets

which were in Kosovo it is estimated that perhaps another 3000-5000 30-mm-caliber DU

rounds were directed at a number of targets in Serbia. Up to the present only a small

276

number of DU penetrators recovered from Kosovo and Serbia have been analysed for their

radionuclide content

. All these analyses are in general good agreement and have confir-

med that the penetrators are in fact composed of metallic depleted uranium having the

following approximate uranium isotope specific activities (Bq/kg):

238

U (12 x 10

) ,

234

(1.5 x10

) ,

235

U (1.5 x10

) and

236

U (5.5 x 10

). The presence of

236

U indicates that recyc-

led uranium from nuclear fuel was probably part of the DU production. In February 2001 it

was also confirmed that trace amounts of plutonium were present in some DU penetrators

. The presence of this plutonium was further confirmation that recycled uranium was

probably involved in the production of the DU. With the connotations that exist in the pub-

lic mind between plutonium and nuclear weapons its presence in the DU penetrators will

be perceived by the general public to present an even greater health hazard than that of

the DU itself. While such a perception may be grossly incorrect its existance needs to be

confronted objectively and addressed. It was therefore considered appropriate to present in

this paper information relating to possible radiological health implications of plutonium in

DU penetrators used in the 1999 conflict in Yugoslavia. (Other papers in the proceedings of

this conference deal in greater detail with the radiological health implications of the ura-

nium isotopes in the penetrators.) In order to help quantify the possible doses and risks

from the plutonium contamination of the DU penetrators a description is first given in this

paper of the analysis of a 300 g DU penetrator recovered intact from a May 1999 target

site in the southern Serbian community of Bratoselce which is 10 km northeast of Preševo.

1 0 0

1 0 0 0

1 0 0 0 0

1 0 0 0 0 0

5 0

7 5

1 0 0

1 2 5

1 5 0

1 7 5

2 0 0

2 2 5

E n e rg y (k e V )

oun

hanne

2 3 4

T h

2 3 4

T h

2 3 5

U

Figure 1. Gamma spectrum of the DU penetrator

ANALYSIS OF DU PENETRATOR

Two grams of DU fragments machined from the penetrator were used for alpha and

gamma spectrometry analyses. After the non-destructive gamma analysis was performed ,

the DU samples went through a variety of strictly controlled chemical treatment stages

involving its careful dissolution in acid and other treatments. From the resulting solution

two precise 0.5 ml aliquots were taken for a duplicate uranium analysis, and the rest of the

solution was reserved for the plutonium analysis.

In the non-destructive gamma analysis fragments from the penetrator were combined in a

polyethylene vial and measured by high-resolution gamma spectrometry using an n-type

germanium detector with a relative efficiency of 30% and resolution of 1.70 keV (FWHM)

at 1.33 MeV. The accumulated gamma spectrum is shown in Figure 1.

277

In addition the material of the penetrator was confirmed by our analysis to be DU by using

a recently proposed convenient and rapid method for discriminating between natural and

depleted uranium using gamma spectrometry

URANIUM AND PLUTONIUM ANALYSES.

In order to quantify the activities of the uranium and plutonium in the penetrator appropri-

ate amounts of tracer or chemical yield monitor materials were added to a known amount of

dissolved sample. In the case of the uranium analyses

232

U chemical yield monitor (NIST

SRM 4324A) was used and in the case of plutonium analysis the chemical yield monitor

was

242

Pu (NIST SRM 433D). A detailed description of the radiochemical methods emplo-

yed can be found in León Vintró and Mitchell

At the end of the radiochemical processing samples of the resulting solution were transfer-

red to an electrolytic cell and plated onto stainless steel discs. The alpha activities of the

electroplated discs were measured using a multiple alpha spectrometer detector system,

specially designed for low-level analysis using Canberra, passivated (ion-) implanted

planar silicon (PIPS) detectors.

Uranium Analysis : The alpha spectrum of the purified uranium fraction contains a number

of well-resolved peaks including that of the

232

U tracer, as shown in Figure 2. The results

for all uranium isotopes are in good agreement with those determined by other researchers

(Table 1). The presence of

236

U in the penetrator indicates likely contact of the DU during

its production with recycled nuclear fuel.

Plutonium Analysis: The pulse height spectrum for plutonium, following radiochemical

separation by ion exchange and solvent extraction with TIOA – xylene, is shown in Figures

3. The specific mass activity of

239+240

Pu in the DU penetrator analysed is given in Table 2,

together with

239+240

Pu specific mass activities reported by other laboratories for other DU

penetrators used in the Balkans. Although the specific mass activity of

239+240

Pu in the DU

penetrator analysed at University College Dublin (UCD) at about 44 Bq/kg is higher than

that reported by other laboratories, it is in good accord with values quoted for mean

239+240

Pu concentrations in DU armour used in tanks, at 85 Bq kg

–1

. The

238

Pu/

239+240

activity ratio as determined from the alpha spectra, at 0.039

0.008, is typical of low burn-

up plutonium. The presence of plutonium indicates that the DU employed to manufacture

the penetrator was mildly contaminated with plutonium, at some point in time, most likely

during the enrichment process.

1 0

1 5

2 0

2 5

3 0

3 7 0 0

4 1 0 0

4 5 0 0

4 9 0 0

5 3 0 0

5 7 0 0

oun

E nergy (keV )

2 3 8

2 3 5 + 23 6

2 3 4

2 3 2

2 2 8

T h

Figure 2. Pulse height spectrum of uranium from the DU penetrator

278

1 0

1 2

1 4

1 6

1 8

3 7 0 0

4 1 0 0

4 5 0 0

4 9 0 0

5 3 0 0

5 7 0 0

oun

E ne rg y (keV )

2 4 2

P u

2 3 8

2 3 9 + 2 4 0

P u

2 3 8

P u

Figure 3. Pulse height spectrum of plutonium from the DU penetrator

following TIOA solvent extraction

Table 1. Uranium specific activities (Bq kg

–1

) in DU penetrators

1,2

Sample

Analysis

Lab

238

U

234

U

235

U

236

U

UCD-01

UCD

12.13

1.38

1.43

5.15

UCD-02

UCD

12.22

1.41

–

ZA/R-00-505-01

AC Spiez

12.37

1.16

1.60

6.10

ZA/R-00-505-02

AC Spiez

12.37

1.39

6.19

ZA/R-00-500-16

AC Spiez

12.37

1.62

6.10

Kokouce

STUK

12.70

1.55

5.72

4

Table 2. Plutonium specific activities in DU penetrators

1,2

Sample

Laboratory

239+240

Pu (Bq kg

–1

)

UCD-01

UCD

43.7

1.9

ZA/R-00-505-01

AC Spiez

<0.8

ZA/R-00-505-02

AC Spiez

ZA/R-00-500-16

AC Spiez

Kokouce

STUK

<0.8

Ceja Mountain

SSI

12

HUMAN EXPOSURE IMPLICATIONS

Uranium : The overwhelming majority of the DU penetrators used by NATO forces in

Yugoslavia in 1999 still remain buried in the ground and did not strike targets of sufficient

279

hardness ,such as armour, to cause them to be aerosolised. It remains to be confirmed but it

is likely therefore that only a very small number of persons may have inhaled or ingested

DU in aerosol or small particle form during and in the immediate aftermath of hostilities.

International attention up to now has focussed primarily on the possible health effects from

DU on servicemen or other personnel from abroad stationed in the Balkans with the effects

on the local population receiving minor attention. For the local population in target areas

the most likely long term future exposure to DU in the Yugoslav environment will therefore

be by skin contact when penetrators are picked up or by ingestion of drinking water or

perhaps food contaminated by the DU which has dissolved and migrated in the

environment. In the case of small children ingestion of soil contaminated by DU is another

possible pathway. In the case of handling the penetrators the radiation dose from skin

contact with DU metal is about 2.5 mSv /hour but as the skin is a tissue relatively

insensitive to radiation damage deterministic effects such as erythema or radiation burns

should not occur for short term contact with the DU. However for prolonged (i.e .some

weeks ) direct skin contact with DU there will be a non-trivial increase above the baseline

risk of skin cancer both fatal and non-fatal

. For DU which is inhaled or ingested its

partitioning within the body is governed by many factors such as its chemical state and

biological parameters. While uranium deposits on bone surfaces and may remain there for

many years in most cases nearly 90% of the intake will be excreted in the urine within a

few weeks. A detailed discussion of uranium metabolism and both its chemical- and radio-

toxicities is outside the scope of this paper (see other papers in the proceedings of this

conference). Recent reviews of the extensive literature dealing with these topics suggest

that DU health effects to communities living in target areas will in most cases be negligible

with DU intake at any conceivable level unlikely to have an appreciable potential for

chemical or radiological carcinosis

. In this context it is appropriate to point out that the

two largest human studies to date on the health effects of uranium were cohort studies,

mainly carried out some decades ago , of adult (mainly male) uranium workers in the US

and in the UK

. By the exacting standards of present day radiation and chemical epide-

miology these studies had numerous deficiencies which in some degree calls into question

their transferability and usefullness in assessing the long term health effects of DU

exposure in a general population ,which includes children and persons with existing health

problems

. It is therefore considered prudent and equitable to the general populations in the

target areas that as a pre-requisite to actual health studies a properly designed and executed

assessment of their exposure to DU should be carried out. In a pilot study earlier this year

for the first time DU was found to be present and was measured in the urine of a small

number of persons from Bosnia and Kosovo

. Estimates of DU burdens as high as 288 μg

were made. If, to a first approximation, it is assumed that DU body burdens are log-nor-

mally distributed in an exposed general population then a small percentage of the populati-

on may have DU body burdens much higher than this. This suggests that DU concentrati-

ons in the urine of the general population in target areas should be measured systematically

and also the dissolution and migration rates of DU from buried penetrators into local

drinking water supplies should be investigated. These and other related proposed investi-

gations are to be encouraged by the appropriate Yugoslav authorities. In view of the multi-

disciplinary nature of such work and the need for access to specialised analytical equipment

collaboration on an international basis in this work would seem to be scientifically

desirable.

Plutonium : There are traces of

239

Pu in the environment which occur naturally due to the

capture by

238

U in rocks of neutrons from spontaneous fission and alpha-neutron

280

reactions. The mass concentrations of plutonium which are formed naturally are of the

order of 1 part in 10

which is exceeding low

. The plutonium of most interest from the

radiological health perspective is anthropogenic and is produced as

239

Pu in a nuclear

reactor as a result of neutron capture by uranium (

238

U).

239

Pu has a radioactive half-life of 24360 years and emits alpha particles of energies

between 5.115 (73.2%) and 5.51 (10.6%) MeV (The MeV is a unit of energy used to

describe the energy of the radiation emitted from radioactive substances). Plutonium

concentrations found in DU ammunition are commonly quoted as being

239+240

Pu because it

is technically difficult using alpha spectrometry to distinguish between these alpha particles

from

239

Pu and those from another isotope

240

Pu .

The most important pathway into the body for plutonium is by inhalation. On the other

hand for ingested plutonium only about 1 part in 10

passes through the gut wall into the

bloodstream with the rest being excreted. As wide variations in the ingested plutonium

uptake by animals have been reported considerable fluctuations should also be anticipated

in man . Inhaled plutonium activity deposited in the lung may , depending on factors such

as its solubility, transfer into other body tissue and will concentrate mainly in the

liver,kidneys and in particular in the skeleton. In the case of plutonium in the skeleton in

common with other multivalent metals the activity will be concentrated in the bone surfaces

as distinct from the internal volume of the bone. Plutonium seems to bond with the

phosphate groups found in organic compounds on bone surfaces. Of particular note in this

regard is the fact that internal bone surfaces surround bone marrow. Therefore alpha

particle emitting radionuclides such as plutonium deposited on internal bone surfaces may

irradiate bone marrow. The possibility that this could cause leukaemia in children and

young adults has been the focus of much research in recent decades. In particular many

studies have taken place in the UK to determine if ,inter alia, plutonium in the environment

as a result of activities at the British Nuclear Fuels Limited (BNFL) reprocessing plant at

Sellafield in Cumbria (UK) could be a contributor to the incidence of leukaemia in the

region . Due to the confounding effects of other environmental and socio-economic factors

it has yet to be scientifically established if the leukaemia incidence in Cumbria is enhanced

by the presence of radionuclides such as plutonium discharged to the environment by the

operations at Sellafield

. Nevertheless it is considered prudent by most radiological

protection agencies to avoid contamination of the environment by plutonium.

DOSES AND RISKS

One can consider the health implications of the radioactive heavy metals uranium and

plutonium from both radiological and chemically toxic perspectives . Uranium is nephro-

toxic but even its toxic effects on the kidneys at most appear to cause minor and reversible

renal damage. The plutonium concentration of about 44 Bq/kg of DU which we have mea-

sured in a 300 gram DU penetrator recovered from south Serbia means that the total mass

of plutonium present in such a penetrator is about 5.5 x 10

-9

grams equivalent to about

0.019 ppb (ppb = parts per billion = 10

-9

). While this is comparable to the level of

plutonium naturally produced and present in uranium ores the removal of natural plutonium

by chemical processing of the ore means that the plutonium in the penetrators almost

completely originates from reactors. Due to its minute mass concentration even if it were

possible for all the plutonium from a single DU penetrator to be ingested or inhaled its

chemical toxic effects are incalculable and in any case would not be possible to detect. In a

similar manner the radiological risk posed by the plutonium present in the DU will be

281

exceedingly low. In this case however it is possible to calculate the radiation dose from the

plutonium and to compare it to both the doses from the DU itself and also with the natural

radiation doses that the population always receives. To make a worst case estimate we will

consider the radiation doses arising from inhaled DU particles. This is because the radiation

doses from both uranium and plutonium arising from inhalation

are much greater than

those if the same mass of material is ingested. Based on current models of the ICRP (Inter-

national Commission on Radiological Protection) we estimated the radiation doses that

would arise from the inhalation of 1 mg of insoluble DU particles containing the plutonium

at a specific activity of 44 Bq/kg

11,12

. For the DU itself the dose was estimated to be about

0.15 mSv and that from the plutonium to be about 0.7 nSv (nSv = 10

-9

Sievert). For the

DU the ALI (Annual Limit of Intake ) ,based on the public annual dose limit of 1 mSv,

would be about 5 mg. At the uranium ALI the plutonium contribution to dose would be

only about 5 nSv which is by any standards an exceedingly low dose. If the DU conta-

minated with plutonium were ingested rather than inhaled the doses would be even smaller.

It should be noted that the average annual radiation dose from natural radiation (i.e. radon

,external gamma ,cosmic radiation) in Yugoslavia is probably about 2.5 mSv while in parts

of Kosovo due to uranium mineralisation much higher natural radiation levels are known

to exist

. On the basis of these calculations there is no likely scenario of human intake in

which the radiation doses and associated risks from the plutonium in these DU penetrators

could even approach a level that would be considered a matter of health concern for

radiological reasons by such bodies as the ICRP or for reasons of chemical toxicity by the

WHO. This is not however the case for the chemical toxic effects of the uranium isotopes

in the DU. On the basis of the chemical toxicity of uranium the WHO has derived a

provisional guideline for drinking-water quality of 0.002 mg/l which for a 500 l/year

consumer corresponds to an ALI of 1 mg

. It should however be pointed out that this is

provisional and is substantially more stringent (due to still existing uncertainties in our

knowledge of uranium chemical toxicity ) than the corresponding guidelines of other

agencies. Depending on the isotopic mix in the DU based on a 1 mSv/year public limit the

radiological ALI for ingested uranium is about 1 g and the radiologically based DDWC

(Derived Drinking Water Concentration) is about 2 mg /l. (Even in this case the WHO has

the more stringent guideline of 0.28 mg/l.) These observations further emphasise the

greater importance of chemical toxicity relative to radiological toxicity in the case of

uranium. It also strengthens the recommendations, already given above in this paper, that a

careful study of the dissolution and migration of DU into the drinking water supplies in

target areas coupled to urine analyses of the general population should be given priorities

by the relevant national and international agencies,.

CONCLUSIONS

Plutonium has been detected in trace amounts in DU penetrators recovered from 1999

attack sites in Kosovo and Serbia. In this paper the level of plutonium measured in one

such penetrator was about 44 Bq/kg of DU. The associated dose from the plutonium for an

inhaled intake of 1 mg is estimated to be about 0.7 nSv ( 10

-9

Sv) . Even allowing for the

uncertainties in such an estimate this is an exceedingly low radiation dose and is a minute

fraction of natural radiation doses. The presence of plutonium in the DU penetrators does

however raise a number of ethical questions. For example its presence would seem to be in

conflict with the basic radiation protection principle of justification as the plutonium serves

no useful purpose as part of the penetrator. The fact that the DU penetrators used so far

282

would appear to have plutonium contamination at a very low level of almost no

radiological health significance does not mean high levels of plutonium may not appear in

DU from other sources used in future conflicts. In contrast to plutonium it would appear

that studies should be carried out both into the dissolution and migration of the DU into

drinking water supplies in target areas and also that the DU content of the urine of the local

population should be assessed

ACKNOWLEDGEMENT

The authors wish to acknowledge the assistance of Professor S. Milovanović, Military

Medical Academy ,Belgrade in the procurement of the DU penetrator.

REFERENCES

UNEP (a) . Depleted Uranium in Kosovo – Post conflict Environmental Assessment .

Report of United Nations Environmental Program. 6 April 2001. Switzerland. (2001)

UNEP(b).BalkansPressRelease,February2001.

http://balkans.unep.ch/press/press010216.html

(2001)

Shoji, M., Hamajima, Y., Takatsuka, K., Honoki, H., Nakajima, T., Kondo, T. &

Nakanishim T. A convenient method for discriminating between natural and depleted

uranium by

-ray spectrometry. Applied Radiation and Isotopes, 55, 221– 227 (2001)

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alpha-emitters. In: Encyclopedia of Analytical Chemistry (pp. 12847–12884), R.A.

Meyers (Ed.). Chichester: John Wiley and Sons Ltd (2000)

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(TACOM) and army Material command (AMC) review of transuranics (TRU) in

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century

mankind. Environmental Plutonium, 1-14, Vol 1 Radioactivity in the Environment

Series , Ed A.Kudo, Elsevier Press.(2001).

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Doll, R. The Seascale Cluster – a probable explanation. British Journal of

Cancer , Vol 81, Issue 1, 3-5,. (1999).

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ICRP Publication 67. Age-Dependent Doses to Members of the Public from Intake of

Radionuclides : Part 2 . Annals of the ICRP 24(4) (1993)

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Diehl, P. Hazards from depleted uranium produced from reprocessed uranium ,WISE

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Document Outline

PLUTONIUM IN DEPLETED URANIUM PENETRATORS
- - - - INTRODUCTION
- Analysis Lab
  - - - HUMAN EXPOSURE IMPLICATIONS
The most important pathway into the body for plutonium is by inhalation. On the other hand for ingested plutonium only about 1 part in 104 passes through the gut wall into the bloodstream with the rest being excreted. As wide variations in the ingested p
- - DOSES AND RISKS
CONCLUSIONS
- - ACKNOWLEDGEMENT
Doll, R. The Seascale Cluster – a probable explanation. British Journal of
Cancer , Vol 81, Issue 1, 3-5,. (1999).

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