FUKUSHIMA, DESCRIPTION OF THE ACCIDENT AND FUKUSHIMA, DESCRIPTION OF THE ACCIDENT AND CONSEQUENCES TO THE ENVIRONMENTCONSEQUENCES TO THE ENVIRONMENT

Dragoslav NikezicDragoslav NikezicFaculty of Science, University of Faculty of Science, University of

Kragujevac, SerbiaKragujevac, Serbianikezic@kg.ac.rsnikezic@kg.ac.rs

http://www.pmf.kg.ac.rs/radijacionafizika/http://www.pmf.kg.ac.rs/radijacionafizika/

EARTHQUAKEEARTHQUAKE

ON 11.03.2011 large scale tsunami, followed after ON 11.03.2011 large scale tsunami, followed after strong earthquake of M=9 overflow nuclear power strong earthquake of M=9 overflow nuclear power plant Fukushima Daiichi. The earthquake occurred plant Fukushima Daiichi. The earthquake occurred under the sea about 70 km eastern of Oshika under the sea about 70 km eastern of Oshika peninsula at the depth of about 32 km. It was the peninsula at the depth of about 32 km. It was the most powerful earthquake that had ever hit Japan, most powerful earthquake that had ever hit Japan, and fifth the strongest in the world since official and fifth the strongest in the world since official modern record began in 1900. This earthquake modern record began in 1900. This earthquake triggered big tsunami which wave reach up to 40 triggered big tsunami which wave reach up to 40 m in Iwate prefecture. The wave height was m in Iwate prefecture. The wave height was smaller on another locations, being about 8 m in smaller on another locations, being about 8 m in Fukushima area. Japanese authorities reported Fukushima area. Japanese authorities reported 15854 death, and 3155 missing people. In 15854 death, and 3155 missing people. In addition, about 27000 was injured. addition, about 27000 was injured.

FUKUSHIMA DAIICHI POWER FUKUSHIMA DAIICHI POWER PLANT PLANT

Fukushima Daiichi plant comprised by six Fukushima Daiichi plant comprised by six separate nuclear reactors. All reactors separate nuclear reactors. All reactors were water boiled type, maintained by were water boiled type, maintained by Tokyo Electric Power Company TEPCO.Tokyo Electric Power Company TEPCO.

The plant was protected by a seawall The plant was protected by a seawall protection designed to withstand a 5.7 m protection designed to withstand a 5.7 m tsunami. Obviously this was not enough tsunami. Obviously this was not enough high to protect against tsunami on high to protect against tsunami on 11.03.2011.11.03.2011.

LOCATION of FNPPLOCATION of FNPP

BEFORE THE ACCIDENTBEFORE THE ACCIDENT

Parameters of power plant Parameters of power plant

SITUATION AT THE TIME OF THE SITUATION AT THE TIME OF THE QUAKEQUAKE

At the time of the quake, reactor 4 had At the time of the quake, reactor 4 had been de-fueled while 5 and 6 were in been de-fueled while 5 and 6 were in cold shutdown for planned regular cold shutdown for planned regular maintenance (refueling).maintenance (refueling).

Reactors 1,2 and 3 were operating. At Reactors 1,2 and 3 were operating. At the moment of the quake, reactors were the moment of the quake, reactors were shut down automatically. Emergency shut down automatically. Emergency generators started to run to pump the generators started to run to pump the water needed to cool the reactors.water needed to cool the reactors.

TSUNAMITSUNAMI The plant was protected by a seawall The plant was protected by a seawall

protection designed to withstand a 5.7 m protection designed to withstand a 5.7 m tsunami. However, the tsunami. However, the 8-148-14-metre tsunami -metre tsunami wave arrived wave arrived 1515 minutes after the minutes after the earthquake.earthquake.

The entire plant was flooded, including low-The entire plant was flooded, including low-lying generators and electrical devices in lying generators and electrical devices in reactor basements.reactor basements.

Connection to the electrical grid was broken. Connection to the electrical grid was broken.

HEAT PRODUCTIONHEAT PRODUCTION

Although the reactors were cooled down, there were a Although the reactors were cooled down, there were a large amount of fission products in reactor core. large amount of fission products in reactor core.

About About 6 % 6 % of total energy of fission is released through of total energy of fission is released through beta and gamma decay of fission products. It amounts beta and gamma decay of fission products. It amounts about about 12 MeV 12 MeV per one fission. This energy is ultimately per one fission. This energy is ultimately transformed into the transformed into the heat. heat.

Although the chain reaction was stopped, it is necessary Although the chain reaction was stopped, it is necessary to cool down reactor core, until the radioactivity of fission to cool down reactor core, until the radioactivity of fission products decreases significantly below certain level. products decreases significantly below certain level.

Similar is true for Similar is true for spent fuel spent fuel which must be cooled down which must be cooled down for some period of time. Radioactivity of fission product for some period of time. Radioactivity of fission product decreases with the time in complicated manner. Many decreases with the time in complicated manner. Many different radioactive isotopes are presented in fresh spent different radioactive isotopes are presented in fresh spent nuclear fuel. All of them are BETA/GAMMA radioactive.nuclear fuel. All of them are BETA/GAMMA radioactive.

OVERHEATING OF REACTORS OVERHEATING OF REACTORS AND SPENT FUEL POOLAND SPENT FUEL POOL

There were three independent cooling There were three independent cooling systems. All three cooling systems failed; systems. All three cooling systems failed; some of them because connection to the some of them because connection to the electricity was interrupted. Independent electricity was interrupted. Independent cooling based on generators was also broken, cooling based on generators was also broken, because they were flooded by tsunami.because they were flooded by tsunami.

Without any cooling, reactors and spent fuel Without any cooling, reactors and spent fuel pool started to heat due to the radioactive pool started to heat due to the radioactive decay of fission products. decay of fission products.

Soon after the tsunami, evidence arose of Soon after the tsunami, evidence arose of partial core meltdown in reactors 1, 2, and 3. partial core meltdown in reactors 1, 2, and 3.

Intriguing questionIntriguing question In many document was written that hydrogen In many document was written that hydrogen

exploded. However, there was not any exploded. However, there was not any explanation on the following question:explanation on the following question:

From where did hydrogen come from? From where did hydrogen come from? This was intriguing question for me. To This was intriguing question for me. To

resolve this issue consultations with resolve this issue consultations with chemists were necessary. chemists were necessary.

Need to know chemical behavior of water Need to know chemical behavior of water vapor at temperatures between 200 vapor at temperatures between 200 00C C and 300 and 300 00C in contact with some metals.C in contact with some metals.

INTERACTION OF WATER INTERACTION OF WATER VAPOR WITH ZIRCONIUM AND VAPOR WITH ZIRCONIUM AND

METALSMETALS Zirconium was used in construction elements. Zirconium was used in construction elements.

The most important reaction was between The most important reaction was between water vapor and zirconium (and other metals water vapor and zirconium (and other metals presented in construction elements), which presented in construction elements), which occur at high temperature. As the result of occur at high temperature. As the result of this chemical reaction water molecules were this chemical reaction water molecules were disrupted and only hydrogen remained in disrupted and only hydrogen remained in gaseous phase, while, oxygen atoms were gaseous phase, while, oxygen atoms were combined with zirconium (and other metals). combined with zirconium (and other metals).

Explosions and firesExplosions and fires

Hydrogen formed in chemical reactions exploded Hydrogen formed in chemical reactions exploded and destroyed the upper cladding of the buildings and destroyed the upper cladding of the buildings housing of reactors 1, 3, and 4.housing of reactors 1, 3, and 4.

Explosion on reactor No3 severely damaged Explosion on reactor No3 severely damaged reactor building No4. There are speculations that reactor building No4. There are speculations that hydrogen leak from reactor No3 to No4 through hydrogen leak from reactor No3 to No4 through underground tunnels.underground tunnels.

There were explosion and fire on reactor No2. There were explosion and fire on reactor No2. Spent fuel rods stored in spent fuel pools of units Spent fuel rods stored in spent fuel pools of units

1–4 began to overheat as water levels in the pools 1–4 began to overheat as water levels in the pools dropped. Constant production of heat also due to dropped. Constant production of heat also due to gamma and beta radioactive decay of fission gamma and beta radioactive decay of fission product.product.

Anatomy of Fukushima Daiichi blastsAnatomy of Fukushima Daiichi blasts

The most complex nuclear accident The most complex nuclear accident in history. All units were involved in in history. All units were involved in some way. some way.

Much more complex than Chernobyl Much more complex than Chernobyl accident, where only one reactor was accident, where only one reactor was destroyed. destroyed.

Each reactor has its own story in this Each reactor has its own story in this accident. Difficult to manage. accident. Difficult to manage.

More photos, 11.03.2011.More photos, 11.03.2011.

More photos, 20.03.2011.More photos, 20.03.2011.

20.03.2011, 20.03.2011, reactors 1,2,3 (from left to reactors 1,2,3 (from left to

right)right)

17.03.2011. Reactor No3.17.03.2011. Reactor No3.

MANAGING OF THE MANAGING OF THE ACCIDENTACCIDENT

Evacuation of population within 20 km, Evacuation of population within 20 km, immediately after the accident. immediately after the accident.

The main problem was to enable cooling of The main problem was to enable cooling of all damaged reactors and spent fuel pools. all damaged reactors and spent fuel pools. All work on damaged reactors was seriously All work on damaged reactors was seriously hindered by high level of radiation within hindered by high level of radiation within reactors building and around them. It has reactors building and around them. It has been reported that dose was up to 400 been reported that dose was up to 400 mSv/h at some position within the power mSv/h at some position within the power plant.plant.

Let we remind that average lethal dose is Let we remind that average lethal dose is between 4 and 8 Sv. between 4 and 8 Sv.

There were some information that There were some information that dose was as high as 1 Sv/h. This dose was as high as 1 Sv/h. This result was taken with reserves result was taken with reserves because instruments were calibrated because instruments were calibrated up to 1 Sv/h.up to 1 Sv/h.

In order to cool down in Units 1, 2 and 3 In order to cool down in Units 1, 2 and 3 fresh water has been continuously fresh water has been continuously injected both via the feed water system injected both via the feed water system lines and the fire extinguishers lines into lines and the fire extinguishers lines into the reactor pressure vessel; the reactor pressure vessel; temperatures and pressures were temperatures and pressures were stabilized.stabilized.

Sea water was used in the first phase of Sea water was used in the first phase of the accident, but it caused the accident, but it caused contamination of sea water.contamination of sea water.

TEPCO started work on 9 May of 2011 to install a TEPCO started work on 9 May of 2011 to install a supporting structure for the floor of the spent fuel supporting structure for the floor of the spent fuel pool of Unit 4.pool of Unit 4.

Fresh water was injected into the spent fuel pools Fresh water was injected into the spent fuel pools of Units 1 - 4.of Units 1 - 4.

One generator at unit 6 was restarted on 17 One generator at unit 6 was restarted on 17 March allowing some cooling at units 5 and 6 March allowing some cooling at units 5 and 6 which were least damaged.which were least damaged.

Grid power was restored to parts of the plant from Grid power was restored to parts of the plant from 20 March, but machinery for reactors 1–4 20 March, but machinery for reactors 1–4 damaged by floods, fires and explosions remained damaged by floods, fires and explosions remained inoperable.inoperable.

Spread out of radioactive Spread out of radioactive contamination in atmospherecontamination in atmosphere

Spread out in ocean waterSpread out in ocean water

Overall, the situation at the Overall, the situation at the Fukushima Daiichi nuclear power Fukushima Daiichi nuclear power plant remains very serious. TEPCO plant remains very serious. TEPCO planned to completely demolish planned to completely demolish four reactors in 30-40 yearsfour reactors in 30-40 years

CONTAMINATION CONTAMINATION Large scale releasing of radioactivity in Large scale releasing of radioactivity in

environment. Power plant was very environment. Power plant was very contaminated, but, as it can be seen in contaminated, but, as it can be seen in previous images, radioactivity was airborne previous images, radioactivity was airborne toward the east (Pacific ocean). Many toward the east (Pacific ocean). Many measurements of radiation level in Japan, measurements of radiation level in Japan, were performed close and further from were performed close and further from Fukushima NPP. Fukushima NPP.

Fission product, Fission product, 131131I, I, 137,134137,134Cs, Cs, 131,134131,134Xe detected Xe detected soon after the accident, constituted large soon after the accident, constituted large part of radioactivity released in environment. part of radioactivity released in environment.

Spread out of contaminationSpread out of contamination

Contamination of sea water spread Contamination of sea water spread by ocean stream.by ocean stream.

Airborne contamination by Airborne contamination by permanent atmospheric motion. permanent atmospheric motion.

Effective dose for population around power Effective dose for population around power plant was estimated up to 30 mSv. This is plant was estimated up to 30 mSv. This is larger than dose limit for professional larger than dose limit for professional persons which amounts 20 mSv per persons which amounts 20 mSv per annum, (in average for 5 years). This is annum, (in average for 5 years). This is much larger than dose limit for general much larger than dose limit for general population ( 1 mSv per annum). Evacuation population ( 1 mSv per annum). Evacuation that was undertaken immediately after the that was undertaken immediately after the accident was justified.accident was justified.

Contamination of the rest of the worldContamination of the rest of the world

Radioactive contamination was observed in Radioactive contamination was observed in many parts of the northern hemisphere, many parts of the northern hemisphere, including Europe, Central Asia, North America.including Europe, Central Asia, North America.

There are many papers published in last several There are many papers published in last several months about radioactivity levels in different months about radioactivity levels in different media (air, rain water, soil deposition etc. ). media (air, rain water, soil deposition etc. ).

General conclusion is that radioactivity level in General conclusion is that radioactivity level in Europe is rather small, and somewhere below Europe is rather small, and somewhere below detection limit. detection limit.

Contamination of EuropeContamination of Europe

Rain water was found contaminated Rain water was found contaminated with with 131131I up to 1.0 Bq/L . Also I up to 1.0 Bq/L . Also 137137Cs Cs was below 1 Bq/L.was below 1 Bq/L.

Radioactivity in air was measured by Radioactivity in air was measured by air pumping through some filters and air pumping through some filters and measuring on gamma spectrometry. measuring on gamma spectrometry.

Europe contamination wit Europe contamination wit 131131I.I.Scale mBq/mScale mBq/m3 3 of air. (Bosew of air. (Bosew

etc)etc)

DoseDose

Dose estimated for Europe is order of Dose estimated for Europe is order of 1 µSv from 1 µSv from 131131I. This dose is negligible I. This dose is negligible and cannot contribute to any and cannot contribute to any measurable effect.measurable effect.

Our measurementsOur measurements

Radioactivity of rain water well below 1 Bq/LRadioactivity of rain water well below 1 Bq/L Radioactivity of air, below 0.1 Bq/mRadioactivity of air, below 0.1 Bq/m33

External doses unchangedExternal doses unchanged

Comparison to Chernobyl accidentComparison to Chernobyl accident Radioactivity of Radioactivity of 131131I in rain water 6900 Bq/LI in rain water 6900 Bq/L Radioactivity of Radioactivity of 137137Cs in rain water 170 Bq/LCs in rain water 170 Bq/L More than 20 other radionuclides. Fall out More than 20 other radionuclides. Fall out

about 11 L/mabout 11 L/m22

External doses increased 20 times more than External doses increased 20 times more than normal.normal.