Category Archives: Isotope

Possible Melted Fuel Seen for First Time at Fukushima Plant

by Mari Yamaguchi
July 21, 2017
Originally published by the Associated Press

TOKYO (AP) — An underwater robot captured images of solidified lava-like rocks Friday inside a damaged reactor at Japan’s crippled Fukushima nuclear plant, spotting for the first time what is believed to be nuclear fuel that melted six years ago. Continue reading Possible Melted Fuel Seen for First Time at Fukushima Plant

Measuring Fukushima Contamination in Fish Caught in Hawaii

Yellowfin tuna, Thunnus albacares leaping from the water

By Jay T. Cullen

The purpose of this post is to summarize a recently published, peer reviewed, scientific study that investigated levels of Fukushima derived contamination in fish caught in the North Pacific and sold at market in Hawai’i.  This post is part of an ongoing series dedicated to bringing quality scientifically derived information to readers so that they can form an evidence based opinion regarding the environmental impact of the Fukushima Daiichi Nuclear Power Plant meltdowns. The paper by Azouz and Dulai (both at the University of Hawai’i at Manoa) summarizes levels of human made 134-Cesium (134Cs half life ~2 years) and 137-Cesium (137Cs half life ~30 years) and naturally occurring 40-Potassium (40K half life 1.25 billion years) in 13 different fish purchased in Hawai’i in 2015.  The findings of the study were that:

  1. 3 of the 13 fish had detectable levels (above the 95% confidence interval) of 134Cs which can be linked to the Fukushima disaster
  2. Highest levels of radiocesium were found in ‘ahi tuna with 134Cs and 137Cs of 0.10 ± 0.04 Bq kg-1 and 0.62 ± 0.05 Bq kg-1 respectively
  3. Most of the fish carried no fingerprint of the Fukushima disaster
  4. Levels of radiocesium were well below intervention levels of 1,200 Bq kg-1 set by the United States Food and Drug Administration
  5. Doses to fish consumers from human made radioisotopes were 30-1,000 fold lower than the dose experienced because of naturally occurring 40K in the fish
  6. Neither the effective dose from the natural nor the human made radioisotopes represent a significant health risk to consumers of the fish given scientifically established dose-response relationships

These results agree with the results of the Integrated Fukushima Ocean Radionuclide Monitoring Project (InFORM) I head up at the University of Victoria which has been making similar measurements on North Pacific fish returning to rivers in North America.

The Azouz and Dulai paper was published recently in the journal Pacific Science and can be found here.  The authors obtained 13 different species (Ahi, Albacore Tuna, King Salmon, Cod, Dover Sole, Halibut, Mahi Mahi, Monchong, Onaga, Opah, Opakapaka, Swordfish and Yellowfin Tuna) of fish that were caught in the North Pacific (>20oN) and commonly consumed in Hawai’i at local markets.  Information about the range and size of the fish are given in Table 1:

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Levels of Radiocesium in Fish From Hawai’i

Samples of the fish tissue were freeze dried and homogenized before gamma emitting radioisotopes were measured using a gamma spectrometer by counting samples for a period of 7 days. Levels of 134Cs, because of its short half life, serve as a fingerprint of Fukushima in samples as previous sources of this human made isotope (e.g. 20th century nuclear weapons testing and the Chernobyl disaster) are sufficiently far in the past that all of the isotope has decayed away and is no longer present in the environment.  Results of the analyses are summarized in the following figure:

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Fig. 1 Cesium activities in fish collected in the North Pacific in 2015 and available for consumption in Hawai’i

In 3 fish statistically significant (>95% confidence interval) but trace levels of 134Cs was detected.  Given that 137Cs/134Cs ratio in vast majority of the release from the Fukushima site was ~1 the authors were able to determine the fraction of radiocesium present in these fish owing to Fukushima versus legacy sources like atmospheric weapons testing.  Maximum radiocesium levels in the fish approached 0.7-0.8 Bq kg-1 which is more than 1,500 fold lower than conservative levels thought be a health risk set by the FDA (1,200 Bq kg-1).  Most fish had radiocesium attributable to weapons testing fallout. Fukushima radiocesium accounted for ~60% of the radiocesium detected in an Ahi measured by the authors.

Levels of Naturally Occurring 40-Potassium in Fish

Naturally occurring 40K decays with a half life of 1.25 billion years and in taken up into the tissue of marine fish.  The levels of 40K in the fish measured by the authors are summarized in the table below:

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Levels of artificial radiocesium and naturally occurring 40-K in fish from Hawai’i

Activity of 40K (Bq kg-1) tended be ~100 fold higher in the fish tissue than radiocesium activities.

Effective Dose of Ionizing Radiation and Health Impact to Fish Consumers

The authors determined the impact of fish consumption on the ionizing radiation dose experienced by individuals consuming an average amount of fish per year (24.1 kg per year or 53.1 pounds per year).  The table below compares the dose in nanoSieverts per year (10-9 Sv yr-1) owing to historic and Fukushima sourced radiocesium and naturally occurring 40K in seafood.

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Committed effective dose to fish consumers from artificial (human made) and naturally occurring 40-K

Converting isotope activities in the fish to dose demonstrates that 40K is responsible for ~100 times higher dose than 134Cs + 137Cs. Doses to humans from consuming the fish owing to radiocesium were 0.02–0.2 µ Sv yr-1, while doses of 6–20 µ Sv yr-1 were contributed by the natural 40K present in the same fish. These levels of radioisotopes and the calculated doses to consumers are similar to those reported by the InFORM project who have looked at Pacific salmon returning to rivers and streams in North America over the last 3-4 years. It is important to note that the bulk of ionizing radiation dose to fish consumers normally results from 210-Polonium (210Po half life 138 days) naturally present in the fish but this isotope was not measured in the Azouz and Dulai study.

Conclusion

Fukushima derived radioisotopes 134Cs and 137Cs were detected (at 95% confidence interval) in 3 of 13 fish caught in the North Pacific and commonly consumed by people living in the Hawaiian islands.  The radiocesium in most fish reflected contamination largely present in the North Pacific Ocean owing to atmospheric weapons testing during the last century.  The levels of radiocesium in the fish were a small fraction of the levels of naturally occurring radioisotopes like 40K.  The committed effective dose of ionizing radiation to fish consumers is dominated by the naturally occurring isotopes and do not remotely approach levels known to represent a significant or measurable health risk to human beings.  The results of this study agree with previously published research and results of the InFORM project which focuses on the impact of the Fukushima disaster on the marine ecosystem and public health in North America.

The fate of atmospheric Fukushima radiation

Did you enjoy your trip? If you were alive during the Fukushima meltdown in 2011, you received an extra dose of radiation equal to that received on a roundtrip flight from Vancouver to Tokyo. This is the result according to research presented by Nikolaos Evangeliou of the Norwegian Institute for Air Research at the annual meeting of the European Geophysical Union earlier this year.

Continue reading The fate of atmospheric Fukushima radiation

The Apollo 13 Mission and Rescue: How much plutonium was added to the Earth’s environment?

By Jay T. Cullen

The purpose of this short post is to compare the relative amounts of radioactive plutonium released to our environment from the Apollo 13 mission in April 1970 and the

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Apollo 13 mission patch/emblem with a depiction of the Greek god of the Sun and latin phrase “Ex Luna, Scientia” which means “From the Moon, Knowledge.”

Fukushima Daiichi nuclear power plant disaster that began in March 2011.  Apollo 13 was the third mission planned to bring American astronauts to land on the moon and conduct scientific studies there.  On April 11 1970 the Saturn V rocket carrying astronauts James Lovell (Commander), Fred Haise (Lunar Module Pilot) and Jack Swigert (Command Module Pilot) was launched from the Kennedy Space Center in Florida.

The mission plan was to land Lovell and Haise in the Fra Mauro highland area of the moon but, due to unforeseen circumstances, that never came to pass.  As many of you know as was popularized in the 1995 film directed by Ron Howard and starring Tom Hanks (Lovell), the late Bill Paxton (Haise) and Kevin Bacon (Swigert) the lunar landing was aborted after a malfunction in one of the service module oxygen tanks caused an explosion that crippled the spacecraft.

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Photo of the damaged Service Module taken shortly after it was jettisoned by the Apollo 13 crew.

What followed was a technical problem solving masterpiece to bring the astronauts safely back to Earth with limited power and life support systems. The rescue of Lovell, Haise and Swigert has been characterized as a “successful failure” and NASA’s finest hour.

Plutonium in the Environment from Apollo 13

A consequence of not having landed on the moon was that the descent stage of the Lunar Module (LM; which would normally have brought Lovell and Haise down to the surface and been left behind when they returned) was now being brought back to Earth.  The power and life support afforded by the LM was central to the successful rescue of the crew.  What is significant about this is that the power supply attached to the descent stage of the LM to be left on the lunar surface to provide electric power for the Apollo Lunar Surface Experiment Packages (ALSEP) was a SNAP-27 Radioisotope Thermal Generator (RTG) containing 1,650 TBq (TBq = 1012 Becquerel) or roughly 3.9 kilograms of plutonium oxide fuel.  While the RTG was essential to bring astronauts home safely the high velocity reentry of the LM raised the possibility of contaminating the atmosphere and surface Earth with worrying amounts of Pu.  To avoid the possibility of the RTG coming down in a populated area the flight engineers had the LM enter the Earth’s atmosphere such that the RTG would be deposited in the remote Pacific Ocean near the Tonga Trench where water depth is about 6-9 kilometers.  Measurements in the atmosphere and ocean following the reentry of the LM suggested that the RTG had survived intact and little of the Pu was broadcast in the environment.  Tests of the RTG casing suggest that this 3.9 kg of Pu, somewhere on the seafloor of the Pacific, will not be mobilized for another ~800 years.
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Plutonium Released From Fukushima

The triple meltdown and hydrogen explosions at the Fukushima Daiichi Nuclear Power Plant (FDNPP) are known to have released some of FDNPP Pu isotope inventory to the environment.  Direct measurements of air, water and soil and modeling of the temperature and pressure in the reactors during the meltdowns by the international scientific community have allowed the total amount of Pu broadcast to the environment during the period of peak releases in the weeks to month following the disaster. These direct measurements made globally, the models and comparisons with isotopes that were released in much greater quantities (e.g. 137-Cesium and 131-Iodine) indicate that about 2.3 x 109 Bq or about 580 milligrams of Pu left the FDNPP in the wake of the disaster.  This is about 700,000 fold less Pu than Apollo 13’s RTG.  While the Apollo 13 Pu is likely to have little environmental impact given that it will be released slowly to the deep ocean over time I think it is interesting to compare the total amounts given the perceived impact of the FDNPP releases.  Both the FDNPP and Apollo 13 Pu are dwarfed by the ~11 PBq (PBq = 1015 Bq) of Pu-239,240 released to the atmosphere as a result of nuclear weapons testing in the 20th century.

Fukushima residents exposed to far less radiation than thought

by Katherine Kornei
Published in Science
23 Jan 2017

Citizen science usually isn’t this personal. In 2011, roughly 65,000 Japanese citizens living near the crippled Fukushima Daiichi Nuclear Power Plant started measuring their own radiation exposure in the wake of the Tōhoku earthquake and tsunami. That’s because no one, not even experts, knew how accurate the traditional method of estimating dosage—taking readings from aircraft hundreds of meters above the ground—really was. Now, in a first-of-its-kind study, scientists analyzing the thousands of citizen readings have come to a surprising conclusion: The airborne observations in this region of Japan overestimated the true radiation level by a factor of four.

Continue reading Fukushima residents exposed to far less radiation than thought