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  • rods in the reactor #4 spent fuel pool also lost their cooling.

    Radiation from the crippled reactors began to leak no later than

    12 March 2011.2 The radiation release poisoned local water and

    food supplies and created a dead-zone of several hundred square

    kilometers around the site that may not be safe to inhabit for

    decades to centuries.3 Some radiation was also transported long

    distances, and was detected as far away as North America and

    Europe.4,5 Although emissions after a month were orders of

    magnitude lower than during the first few days, minimal releases

    continued until a total cold shutdown of the plant was achieved

    in December 2011.6

    Several studies have tracked the emission, transport, and

    deposition of radionuclides from Fukushima using observa-

    tional datasets and chemical transport models.1,4,7–11 Initial

    studies have suggested that less than one quarter of the

    radioactivity was deposited over land in Japan, and only 1% of

    the radiation reached Europe.4 However, no study to date has

    examined the global health effects of such radioactivity or

    simulated the radioactivity with a model that treats size-

    resolved aerosol particle microphysics or gas–aerosol–cloud

    interactions. Here, we used the GATOR-GCMOM global

    model to simulate the emissions, advection, decay, dissolution,

    aerosol–aerosol coagulation, aerosol–cloud coagulation, aero-

    sol nucleation scavenging, rainout, washout, and dry deposi-

    tion of radionuclides from the Fukushima Daiichi nuclear

    accident.12,13 Atmospheric and ocean circulation, clouds,

    precipitation, aerosol processes, cloud processes, aerosol–cloud

    interactions, air–surface interactions, and radiation were all

    treated online in the model.13 Results were evaluated against

    daily worldwide Comprehensive Nuclear-Test-Ban Treaty

    Organization (CTBTO) airborne radionuclide concentrations

    and deposition rates from around Japan.14,15 Atmospheric

    and ground concentrations of iodine-131 (I-131), cesium-137

    (Cs-137) and cesium-134 (Cs-134) were then used to

    estimate the worldwide health effects from the radioactive

    fallout.

    Previous studies have modeled the dispersion and health

    effects of radioactive plumes from the Chernobyl nuclear

    accident.16–20 Some of these studies have attributed thousands

    of cancer-related mortalities in Europe and Asia to the accident

    from a combination of acute and low-dose radiation expo-

    sure.16,18,19 An increase in thyroid cancer attributed to the

    Chernobyl accident has been found in children and adolescents

    living in highly contaminated areas and an increase in leukemia

    has been detected among recovery and clean-up workers.16

    Overall, radioactive emissions from Fukushima were roughly

    an order of magnitude lower than from Chernobyl.3 In addi-

    tion, over 80% of the radioactivity from Fukushima was

    advected over the Pacific Ocean whereas the radioactivity from

    Chernobyl was largely deposited over land. Furthermore,

    collective radiation exposure to workers and local populations

    appears to be lower from Fukushima compared with Cher-

    nobyl due to stricter safety precautions taken after the

    Fukushima accident.21–23 For these reasons, some have sug-

    gested that radiation exposure from the Fukushima nuclear

    accident had no health effects.24,25 This contention is evaluated

    here.

    Inhaled or ingested I-131 at low doses becomes localized in

    the thyroid gland increasing the risk of latent thyroid cancer

    Energy Environ. Sci.

    and other thyroid diseases, whereas inhaled or ingested Cs-137

    becomes distributed in soft tissues increasing the risk of various

    cancers.26 A linear no-threshold (LNT) model of human expo-

    sure was used to calculate radiological health effects, similar to

    previous Chernobyl studies.18,27,28 The LNT model assumes that

    each radionuclide disintegration has the same probability of

    causing cell transformation and that each transformed cell has

    the same probability of developing into a cancer. The LNT

    model has been employed extensively in the radiation safety and

    prevention communities,27–30 yet some studies have questioned

    its validity at low doses31–35 resulting in an ongoing debate.36

    Epidemiological studies have shown a statistically significant

    increase in stochastic cancer risk for doses above 100 mSv,

    however at doses below 100 mSv, significance or insignificance

    has not been demonstrated.30 Similarly, linearity between dose

    and cancer risk has been detected for moderate doses with a

    lower bound of 45 mGy according to Japanese atomic bomb

    survivor data, but has not been demonstrated for low doses.30,34

    Some studies even suggest that low doses of ionizing radiation

    may instead be beneficial by stimulating immune response.37

    Yet, supporters of the LNT model claim that the difficulty in

    detecting and attributing a small number of cancers to low

    doses in a large population does not necessarily indicate there is

    an absence of risk at these low doses.38 The U.S. Nuclear

    Regulatory Commission (NRC) states ‘‘The radiation protec-

    tion community conservatively assumes that any amount of

    radiation may pose some risk for causing cancer and hereditary

    effect, and that the risk is higher for higher radiation exposures.

    The LNT hypothesis is accepted by the NRC as a conservative

    model for determining radiation dose standards, recognizing

    that the model may overestimate radiation risk’’.39 The United

    Nations Scientific Committee on the Effects of Atomic Radia-

    tion (UNSCEAR) also supports a non-threshold response of

    radiation-induced cancer development at low doses.30 Future

    developments in the field of health physics may confirm or

    refute the LNT hypothesis at low doses, but currently the

    analysis here remains within the accepted standards of radiation

    health methodologies.

    In addition to modeling the radioactive release from

    Fukushima Daiichi, this study also examines the impact of

    radioactive release with identical emissions to Fukushima from

    a hypothetical nuclear accident at the Diablo Canyon Nuclear

    Power Plant in Avila Beach, CA during the months of March

    and September. These simulations were conducted to study the

    impact of geographic location and seasonality on health effects

    of a nuclear accident in comparison with Fukushima. The

    Diablo Canyon nuclear plant uses pressurized water reactors

    (PWRs) rather than the boiling water reactors used at the

    Fukushima Daiichi plant, yet PWRs are also susceptible to

    meltdown if reactor cooling is not continuously applied after

    the insertion of control rods, such as during the Three Mile

    Island nuclear accident.40 The Diablo Canyon plant is also

    situated near multiple fault lines, and a 20-year extension of the

    plant’s operating lifetime beyond 2025 is currently in doubt

    until new seismic studies can be conducted.41 If the plant

    receives its license renewal, the chance that it will be subject to

    an earthquake exceeding its ‘‘safe shutdown earthquake’’ level

    is 13%.42 Furthermore, an inspection of the Diablo Canyon

    Power Plant by the U.S. NRC following the disaster at

    This journal is ª The Royal Society of Chemistry 2012

  • Fukushima Daiichi found a series of problems that could

    impact the ability to respond to a Fukushima-like event,

    including a susceptibility of the diesel generators to common

    failures due to similarities in design and location and a lack of

    training on how to operate diesel generators in adverse condi-

    tions.43 We chose Diablo Canyon due to its earthquake

    vulnerability; however, every nuclear plant is susceptible to

    natural disaster or terrorist attack to some degree.42

    Methods

    Estimating radionuclide emissions based on observations

    Emission rates of I-131 and Cs-137 in the model were constrained

    by emission estimates based on inverse modeling of worldwide

    Comprehensive Nuclear-Test-Ban Treaty Organization

    (CTBTO) observed concentrations. The CTBTO is a network of

    over 80 radionuclide monitoring stations used to detect and

    quantify radioactive species from nuclear explosions as well as

    fission-based products from nuclear power plants.14 Stations

    located in Japan, Alaska, California, Hawaii, and the Pacific

    Islands were used to estimate source strengths in Becquerels (Bq)

    on the majority of days following the accident. The data were

    provided by the U.S. National Data Center and the Zentralan-

    stalt f€ur Meteorologie und Geodynamik (ZAMG).44 The ZAMG

    estimated I-131 emissions between 1 � 1014 and 1 � 1017 Bq per day and Cs-137 emissions between 1 � 1013 and 1 � 1016 Bq per day, which compare well with our estimates provided in Table 1.

    We estimate total I-131 (Cs-137) emissions as 6.53 � 1016 Bq (1.70 � 1016 Bq) during the month following the accident. Our estimates are generally conservative by a factor of two with

    respect to I-131 and in line with respect

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