The nature of radioactive waste health now and in the future

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The nature of radioactive waste health now and
in the future

• Keith Baverstock
• Department of Environmental Science

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Life and radiation

• are defining features of planet Earth.
• Life needs radiation, in the form of light to
  fuel photosynthesis, and convert its waste
  products (CO2) back to oxygen.
• Light is just one component of the spectrum of
  radiation that illuminates the Earth and which
  is also generated by the radioactive material
  that constitutes the Earth, that is
  terrestrially.
• Radiation is, therefore, an unavoidable natural
  feature that life has to deal with.

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Life has evolved .

• in such a way as to deal with radiation so why
  do we need to talk about risk in connection with
  radiation?
• Oxygen is a pretty toxic substance yet we all
  breath it, many may well die of oxygen related
  damage, but few complain about the risks of
  breathing oxygen.
• Should we not accept that radiation exposure is
  unavoidable and forget about the risks?

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The analogy with oxygen

• . is not quite fair a better analogy would be
  with the ubiquitous toxic heavy metal Uranium.
  Life has also evolved to deal with the toxic
  effects of this element provided it is INGESTED.
  If it is INHALED in soluble form, a circumstance
  not met in the natural course of events, it is
  highly toxic. It is reasonable to minimise the
  risk of this route of exposure.

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So we are not concerned

• . so much with the risk of radiation per se but
  with the particular circumstances in which the
  exposure takes place.
• This is part of the complex of reasons for the
  considerable social concern about the risks of
  exposure to so called man-made radiation
  sources.
• But what do we mean when we say man-made?

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There are man-made .

• . radiation sources in the form of generators
  (X-ray machines) but these dont concern us here.
  By man-made, particularly in the context of
  waste, we mean nuclides that have been generated
  through mans exploitation of the nuclear
  fission, fusion and activation processes,
  themselves natural and mostly resulting in
  natural products.

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So radioactive waste .

• contains little that is unnatural. More than
  half the naturally occurring isotopes are
  radioactive and most of those we regard as
  unnatural, such as plutonium, are that because
  their radio-active precursors had such short half
  lives that they are no longer present on the
  Earth, the decay chain that generated them has
  ended.

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But natural radiation .

• . is damaging to health and that damage can only
  be partially avoided.
• Natural background radiation (NBR) is unavoidable
  and is assumed to cause a number of ill effects
  including cancer. There is something of the order
  of a 1 chance of dying of a NBR induced cancer.
  If thyroid cancer occurs in childhood it is
  likely that it was caused by NBR.

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NBR can be regarded as

• a baseline against which we can judge other
  exposures to man-made sources.
• We shall now see how radioactive waste poses
  risks to health and the environment.

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Risks from radioactive waste

• Radioactive waste, initially as spent fuel (SF),
  is first stored in such a way as to isolate it
  from the surrounding environment. In the case of
  spent nuclear fuels it may be kept under several
  metres of water in so called cooling ponds.
  After that it may be packed in shielded
  containers for transport and finally packaged for
  disposal, here in Finland in deep geological
  repositories.

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If this process works .

• as it is intended there will be complete
  isolation from the environment and no risk of
  exposure for several thousand years.
• Other countries, the UK for instance, spent fuel
  is reprocessed to reclaim unused U and the Pu
  produced. This involves dissolving up the spent
  fuel after an initial storage (cooling) phase,
  chemically processing the solution and producing
  high level liquid waste (HLLW).

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HLLW requires cooling .

• . and so is stored in tanks for several years
  before being vitrified (made into a glass) and
  packed for further storage or disposal (the UK
  still has no strategy for the management of its
  high level waste (HLW) beyond indefinite storage
  in a vitrified form).
• The handling of HLW (and to a lesser extent SF)
  leads to contamination and the generation of
  intermediate level waste (ILW) which also has to
  be managed.

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Thus we have the following .

• .. stages to consider as potential health and
  environmental risk situations
• Initial local storage of spent fuel
• Transport to a central facility for reprocessing,
  vitrification, packaging
• Storage and handling at the central facility
• Transport to and management at, a waste
  management facility
• Long-term storage or disposal

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Basically there are two .

• .. health risk situations we need to consider
  apart from the occupational exposure risk (which
  is controlled through the normal radiological
  protection procedures) to those responsible for
  the handling of the material
• Accidents involving dispersal of radioactivity to
  the environment (safety)
• Deliberate dispersal of the waste to the
  environment (security)

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Risk

• we will consider the risks now (stages 1 to 4)
  separately from the far future risks (stage 5).
  Typically by now we mean the next few 100 years
  and by far future we mean from about a few 100
  years onwards, for the moment indefinitely. We
  will discuss the ultimate limit later.

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Accidents now

• The early phases of storage require cooling but
  SF is highly resistant to dispersal of its
  contents so the health risk is low.
• Transport of spent fuel carries an accident risk
  but again it is low.
• Reprocessing and the storage of HLW, particularly
  HLLW is less resistant to the dispersal of
  radioactivity and indeed happened at Kystym in
  the Urals in 1957.

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Kystym

• HLLW in an organic solvent was stored in concrete
  silos and a spark from a faulty fan caused an
  explosion which dispersed long lived fission
  products (mainly Cs and Sr) over a large area
  downwind (125 km).
• Inhabitants of the contaminated zone ingested
  radioactivity through the food chain and were
  subject to an external radiation field over and
  above the NBR. There was undoubtedly a public
  health detriment in the form of cancer.

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Sellafield in the UK

• is the site where large quantities of HLLW are
  stored in tanks that require continuous cooling.
  A failure in the cooling for several hours would
  lead to the evaporation of the liquid and
  possible penetration of waste into the ground
  water below, leading to ground water
  contamination and steam explosions and dispersal
  of a waste aerosol over significant distances.

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Deliberate dispersal now

• This is possible at any of the four stages. An
  explosion or intense fire (resulting from
  aircraft fuel for example) would in theory result
  in dispersal of spent fuel or more so, HLLW.
  Theft of material for use in a dirty bomb is also
  a risk. Security, as opposed to safety, of waste
  is an increasingly important issue as terrorist
  actions seem to have increased in frequency.

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Risk in the far future

• As safety and security should be among the
  primary considerations in choosing how to manage
  stage 5, it will be expected that the health
  risks from accidents and deliberate dispersal are
  reduced close to zero, at least for some
  specified time, e.g. 10,000 years.
• For stage 5 the primary risk is containment
  failure. Over infinite time this is inevitable,
  the question is how long do we need the
  containment to last.

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This is partly a technical .

• question and partly an ethical question.
• Technically there are clear limits on what
  materials science can offer and then there is the
  question of what level of radioactivity in the
  waste can we neglect as a risk.
• Ethically there is the question of how we view
  our responsibilities to future generations, are
  we concerned only about our grandchildren or do
  we need to consider future generations ad
  infinitum?

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This is an important issue

• as it influences the cost of the management
  process. The longer we want to contain the
  radioactivity the more it will cost and as
  resources are limited this means we have to
  balance this cost against other quite different
  priorities.
• Here we are deciding what risk future generations
  will be subject to against how much we are
  prepared to spend now.

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A technical issue

• we can influence is the point at which we can
  assume that the health risk is acceptable or
  negligible when the containment fails.
• As the radioactivity is decaying we could say
  that when it reaches the activity level of the
  local natural radioactivity it no longer needs to
  be contained. This, however, does not imply that
  the level of risk will fall to the same level as
  that from NBR.

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Why?

• Because here we are dealing with radioactivity
  entering the body through water and food and some
  isotopes and some chemical forms of the isotopes,
  will be more or less dangerous than others. The
  level of radioactivity in Bq/l alone, even
  measured in food and water, let alone in the
  ground, is NOT a good predictor of risk.

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We therefore need to carry

• out complex modelling of the radioactive decay
  process, how waste leaks from failed containers
  at different times, diffuses into ground water,
  and enters the food chain and is metabolised by
  the local inhabitants, who ever they may be. And
  all this looking ahead say 10 to 100 thousand
  years.

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This is a daunting task .

• and how much confidence can we have in such
  long range projections?
• Perhaps a more certain projection is that there
  will be an ice age in some 20,000 years and thus
  we could make that the cut-off.
• Alternatively, given that the oldest remnants of
  civilisation date back no more than 10,000 years
  need we think beyond this timescale into the
  future?

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So far we have confined

• . ourselves to the effects on humans and their
  health what about other species and the
  non-living environment. Could the radioactivity
  from a failing repository decrease biodiversity
  in the future or might it influence the direction
  of evolution by modifying the environment, and if
  it did should we worry?
• The world we live in today has been formed by the
  past activities of living organisms,
  micro-organisms as well as man is leaking
  radioactive waste such a special problem?

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Some would argue

• . that at least radioactivity decays, some
  elements and chemicals that also are wastes from
  mans activities dont and we are less concerned
  about them. Is it rational to be so concerned
  (and spend so much) on dealing with radiation?
• Others have argued that on time scales of
  100,000s years we cannot even be sure that
  geology will be stable and that, e.g.
  un-predicted volcanic activity might disperse the
  stored material from a repository with dramatic
  consequences for the environment.

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What is clear is that

• how we deal with the waste from mans nuclear
  activities is a highly contentious and complex
  issue a blend of technical and ethical
  considerations that constantly poses the
  essentially social question
• How much of todays resources should we spend to
  minimise the risk of harm to ourselves, our
  descendents and the environment?

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.. and the technical question

• How do we answer that question, i.e. make the
  necessary decision?