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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.1,4,711 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 gasaerosolcloud

interactions. Here, we used the GATOR-GCMOM global

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

aerosolaerosol coagulation, aerosolcloud 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, aerosolcloud

interactions, airsurface 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.1620 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.2123 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,2730 yet some studies have questioned

its validity at low doses3135 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

plants 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 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 fur Meteorologie und Geodynamik (ZAMG).44 The ZAMG

estimated I-131 emissions between 1 1014 and 1 1017 Bq perday and Cs-137 emissions between 1 1013 and 1 1016 Bq perday, 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. Ourestimates are generally conservative by a factor of two with

respect to I-131 and in line with respect to Cs-137 compared with

estimates made by the Japanese government, including the

Nuclear and Industria

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