Laboratories outside Japan have validated the results. Marine radioactivity levels from the nuclear disaster have fallen, but questions remain years after the meltdown. Continue reading IAEA Affirms Japan’s Fukushima-Related Radioactivity Monitoring
By Jay T. Cullen
The purpose of this post is to conduct a thought experiment to arrive at (I hope) a useful estimate of how much radioactive contamination might occur if North Korea detonates a thermonuclear weapon in the lower atmosphere over the North Pacific Ocean. There are a significant number of unknowns, not the least of which is the fundamental uncertainty as to whether the rogue nation has successfully tested a Teller-Ulam style thermonuclear weapon or not. I explain my assumptions and compare the resulting global release of radioisotopes that represent a radiological health concern from such a test to the amounts recently released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) disaster, the Chernobyl disaster and aggregate atmospheric weapons testing in the last century. I invite comments and an accounting of the approach used here and how it might be improved. Continue reading North Korean Atmospheric Thermonuclear Test: How much contamination can we expect?
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
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.
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.
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.
By Jay T. Cullen
@JayTCullen and @FukushimaInFORM
The purpose of this post is to report results from two recently published studies on plutonium releases from Fukushima to the Pacific Ocean. The post contributes to an ongoing series where results from peer-reviewed studies on the impact of the triple meltdowns at the Fukushima Dai-ichii nuclear power plant on the health of the Pacific ecosystem and residents of the west coast of North America are reported. A frequently asked question of those involved in monitoring the health of the North Pacific is why more measurements of the long lived, alpha-emitting isotopes of plutonium (239Pu half-life 24,100 years; 240Pu 6,570 years) are not being made given the potential for these isotopes to pose radiological health risks. Previous work indicates that 239+240Pu releases from Fukushima were about 100,000 and 5,000,000 times lower than releases from the Chernobyl disaster in 1986 and 20th century weapons testing respectively. Initial measurements of Pu isotopes in seawater and marine sediments off the coast from Fukushima indicated no detectable change occurred in Pu inventories in the western Pacific after the disaster. These two most recent studies monitored the activity and isotopic composition of Pu in seawater and marine sediments off of Japan from 2008-2013. Similar to earlier work these studies find that the release of Pu isotopes by the Fukushima accident to the Pacific Ocean has been negligible. The Fukushima signal is not detectable in the ocean off Japan relative to legacy sources from atmospheric weapons testing in the 20th century. Given these accumulating results 239+240Pu from Fukushima is unlikely to negatively impact the health of the Pacific Ocean ecosystem and levels in the environment from Fukushima will not pose a danger to the population of North America.
Continue reading Most Recent Measurements of Plutonium in Pacific: Fukushima Fallout Undetectable
The purpose of this post is to provide estimates of the plutonium (Pu) isotopes present at the Fukushima Dai-ichi nuclear power plant (NPP) at the beginning of the disaster in March 2011. The post is part of an ongoing effort to communicate facts about Fukushima obtained through scientific study of the impact of the meltdowns on the environment. Comments on this site and in other public forums highlight the fact that Unit 3 at the NPP was burning mixed oxide (MOX) fuel at the time of the accident which, because it is enriched in Pu, suggests that these releases are potentially more harmful. Here I report estimates of Pu present in the reactors (Units 1, 2 and 3) and spent fuel pools (Units 1-4) at the site based on burnup calculations. Because fission of low enriched uranium (LEU) fuel produces Pu isotopes during operation there was a significant amount of Pu on site in Units 1-4. During extended operation a MOX fuel burning reactor can produce multiple times the Pu of LEU but this was not so at the time of the Fukushima meltdowns. The amount of additional Pu present due to Unit 3’s MOX fuel is small compared to the other reactor cores and the inventory of the spent fuel pools. The differences between environmental impact of MOX versus LEU reactor core meltdown in this case are small. Estimates of the release of Pu isotopes from Fukushima, based on measurements of air, soil and water suggest 100,000 fold less was broadcast to the environment compared to Chernobyl and 5,000,000 fold lower than releases from nuclear weapons testing in the 20th century. Continue reading Plutonium Inventories at Fukushima Dai-ichi Nuclear Power Plant and Mixed Oxide (MOX) Fuel at Unit 3