Experience feedback on the Fukushima NPS accident- Sanitary and environmental consequences

Transcription

1 Experience feedback on the Fukushima NPS accident- Sanitary and environmental consequences Harald Thielen (GRS), Olivier Isnard (IRSN), Kurt Couckvyt (BelV), Harutaka Hoshi (JNES), Serge Lobach (SSTC NRS) Abstract: As the accident developed at the Fukushima Dai-ichi nuclear power station (NPS) there were phases of massive releases of radionuclides. These releases caused sanitary and environmental consequences for the workers onsite and for the members of the public. These radiological consequences were discussed with respect to the different pathways, like: external radiation or the ingestion of contaminated foodstuffs. This paper also shows the effects of different distances from Fukushima Dai-ichi NPS, starting with the situation onsite and ending with effects on Europe. 1 INTRODUCTION The Fukushima Dai-ichi nuclear accident on 11 March 211 was a consequence of the 9. magnitude Tōhoku earthquake and the following tsunami. A series of on-going equipment failures in several blocks of the power plant led to releases of radioactive material into the atmosphere and the seawater. The emissions caused significant values of radiation and isotope concentrations measured by the involved institutions in the environment and especially, in different media namely: soil, water and foodstuffs. Based on this monitoring data, the authorities in Japan implemented emergency measures to protect the population of the region. Also, in Europe the direct and indirect effects of the releases in Japan can be observed. 2 RADIOLOGICAL SITUATION ON SITE OF FUKUSHIMA DAI-ICHI NPS At the seventh stage: International Nuclear and Radiological Event Scale (INES) of the assessment of events in Nuclear Power Plants, the accident in Fukushima Dai-ichi was rated at level 7 by the Japanese authority NISA on 12 April 211. The major release to the atmosphere corresponds to a quantity of radioactivity equivalent of about 4 to 6 x 1 17 Bq iodine-equivalent. In connection to the spread of radioactive material, due to the hydrogen explosions, these emissions caused contaminations and high activity concentrations inside the plant area, the buildings and the sea water.

2 2.1 Dose rate measurements outside and inside the buildings The assessment of the radiological situation at the Fukushima Dai-ichi NPS (onsite), is mainly based on measurements performed by the operator of the Tokyo Electric Power Company (TEPCO). Measurement data of local dose rates were published on the TEPCO website [1] for various locations shortly after the beginning of the accident. Progressing further, some of these locations were moved, added or removed. Fig. 1 shows the position of the measuring stations for local dose rates. Fig. 2 shows the time variation of the dose rates at selected locations beginning with 11 March 211. Single peaks can be observed which are closely connected to the events during the accident development. The peak values of dose rates of about 12, µsv hr -1 were observed near the main gate. After the end of March, the temporal development of the local dose rates were characterized by decreasing values, which were now caused by direct radiation from radionuclide deposited on the ground. At the end of May the maximum values were about 35 µsv hr -1. In the vicinity of units 1 to 4 and inside buildings considerably higher values were measured. The local dose rates reached some msv hr -1 up to 1 msv hr -1. Nuclide specific analysis of soil samples showed the deposition of 131 I and 137 Cs and 134 Cs respectively. Due to the short half life time of 131 I of 8 days, the local dose rate is dominated by the caesium isotopes after some weeks. In the soil samples, also, small amounts of plutonium, uranium and strontium isotopes were detected [2]. Fig. 1: Position of the measuring stations for dose rates at Fukushima Dai-ichi

3 12 1 MP 4 Dose rate in µsv/h Near Main Gate North of Main Building Near Main Gate North of Main Building South of Main Building 2 MP 4 Near Main Gate South of Main Building Time of measurement (local time) Fig. 2: Dose rate measurements performed by TEPCO at selected locations 2.2 Activity concentrations in seawater The water which was used for cooling the reactors and fuel storage pools accumulated in the lower levels of the reactor buildings and turbine halls. The total amount of water is estimated by TEPCO at being 1, tons. One fraction of this highly contaminated water flowed into the Pacific Ocean uncontrolled. As a consequence, the concentrations of iodine and caesium isotopes in the seawater increased. To estimate the contamination of the seawater TEPCO and the Ministry of Education, Culture, Sports, Science and Technology (MEXT) performed nuclide specific measurements of activity concentrations. These were taken in the proximity of Fukushima Dai-ichi NPS and at 1 km to 3 km distance from the coastline. Fig. 3 shows the measured concentrations of 137 Cs at two different locations. High concentrations of caesium and iodine in March and beginning of April could be observed. These values had a high potential for high concentrations in fish, mussels and algae. Since mid-may the concentrations of caesium in seawater were below the limiting value. 2.3 Exposition of workers The operations and works performed by TEPCO to get the situation under control were heavily affected by the radiation fields in the facility area. Between March 211 and July 211, about 3 people per month were involved in clean-up efforts and emergency measures onsite Fukushima Dai-ichi. The individual dose values were assessed via Whole Body Counter (WBC) for the internal dose and with personal dosimeters for the external dose for TEPCO employees as well as for contractors [3] (see Fig. 4). As a result 1264 of 3757 workers received effective Doses in March above 2 msv (internal + external dose). Six workers were exposed with a total dose of more than 25 msv, which is

4 the permissible dosage limit for a worker in an emergency situation in Japan. Since May 211 no total effective dose above 5 msv was observed. 1 3 m to the north 1 1 km to the south limit value for cesium Bq/cm 3 1,1,1,1 Time of measurement (local time) Fig. 3: 137 Cs contamination of seawater (data by TEPCO) < dose range [msv] > 25 2 July 1 5 March 6 April May June Fig. 4: Total radiation exposure of workers on Fukushima Dai-ichi NPS from March to July 211 (data by TEPCO)

5 2.4 Counter measures by TEPCO Besides the activities to restore cooling of the reactors and the spent fuel pools, TEPCO performed measures to reduce the exposure of the workers. First of all, there is the monitoring program which helps to identify regions with high radiation levels inside and outside buildings. To prevent diffusion of radioactive material, spraying of dust inhibitors was carried out at different locations of the facility. To reduce contamination of the sea, sand bags with zeolite were positioned in several places in the water. Furthermore, a Water Treatment Facility was installed, so that highly contaminated water could be decontaminated and used for cooling again in a closed circuit. Local exhausters were used to decrease radiation level inside buildings before the workers carried out emergency measures. 3 RADIOLOGICAL SITUATION IN THE VICINITY OF FUKUSHIMA DAI-ICHI NPS From 11 to 27 March 211, the main accidental releases occurred, winds from westerly directions predominated so that the major part of the released radionuclides were dispersed over the Pacific Ocean. Only in some situations (e.g. on 15 March 211) there were meteorological conditions in connection with precipitation and winds from southeast which supported the transportation of radioactive substance inland. During this phase, there were important depositions of iodine and caesium up to distances of 5 km from the power plant. 3.1 Dose rate measurements Since 16 March 211 MEXT published data of dose rate measurements at different locations in the Fukushima region. In 3 km distance in the northwest direction on 17 March 211 a value of 17 µsv hr -1 was reported [4]. Since there were no major releases anymore, the radiation level decreases with time. Fig. 5 shows the local dose rate map for June 6 to July 8 by MEXT. The dose rate maps were verified with results of aerial monitoring by the American National Nuclear Security Administration (NNSA) of the DOE [5]. Fig. 5: Air dose rate map June 6 to July 8 (by MEXT)

6 3.2 Exposition of members of the public On the basis of the time series of the air dose rates and with respect to the half life time of the main nuclides 134 Cs, 137 Cs and 131 I, an estimation of effective external dose at various point of interest could be performed. Fig. 6 shows the estimations of external dose based on US DOE-NNSA aerial measurements. The estimations were performed for the first year. In some regions, in northwest direction out of the 3 km zone, there were some hotspots with doses of more than 3 msv. In other regions near the Fukushima Dai-ichi NPS, the radiation level was so high that - assuming a permanent stay the external dose in the first year could exceed 1 msv. Estimation of external dose for the first year more than 3 msv more than 4 msv more than 18 msv more than.5 msv Fig. 6: External dose estimation for members of the public in the Fukushima region for the first year. 3.3 Countermeasures of the authorities For the protection of the people living in the vicinity of Fukushima Dai-ichi NPS, the authorities ordered some emergency measures. On 11 March 211, the evacuation of an area of a 3 km radius began. Sheltering (stay inside buildings) was ordered within a 1 km radius. Until 15 March 211, the evacuation inside the 2 km radius and sheltering inside 3 km radius was declared. Furthermore, iodine tablets were distributed. At the end of April some special evacuation areas existed (Fig. 7): First the restricted area within the 2 km radius. Secondly, the evacuation prepared area in case of emergency connected to future accident development with new releases into the atmosphere. The third area is the deliberate evacuation area. In this area, there is a possibility for individual doses that exceed 2mSv in

7 one year. Some locations with unacceptably high doses in this area were designated to be evacuated in future. Deliberate Evacuation Areas Restricted Area Evacuation Prepared Areas Fig. 7: Evacuation areas near Fukushima Dai-ichi NPS A further instruction of the authorities was the ban of sale and consumption of contaminated food (leafy vegetables, rice, tea). Restrictions on drinking water were mostly limited in time. Additionally, a lot of people who lived inside the 2 km zone were controlled and if necessary, decontaminated. 4 RADIOLOGICAL SITUATION IN JAPAN 4.1 Spread of contamination (dose rate measurements) In some cases there were also winds from northerly directions observed. This led to increased radiation levels in the south of Fukushima towards the direction to Tokyo. In the province of Ibaraki, the measured values of local dose rate reached 3 µsv hr -1 on 2 March 211. Until May these values decreased to.2 µsv hr -1 (see Fig. 8).

8 Fig. 8: Measured dose rates at several locations on the Honshu Island 4.2 Exposition of members of the public As a consequence of the dispersion and deposition of radionuclides, the concentrations of 137 Cs and 131 I in foodstuffs were observed. Fig. 9 shows an example of maximum values of the concentrations in spinach measured by the Ministry of Health, Labor and Welfare (MHLW) [6]. In the region close to Fukushima, the provisional limiting values were surpassed by more than one order of magnitude. In the Tokyo region, the concentrations also exceeded the limiting values but are in the same magnitude. A similar behavior could be observed for other foodstuffs like shiitake, beef, rice or tea. The concentrations reached their highest values at the end of March and decreased in the following months. For Tokyo region there were no restictions on foodstuffs. For drinking water the situation was not as severe as for other foodstuffs. The limiting values for 131 I for small children were reached in the early phase: up until 18 March 211 in the Fukushima prefecture. In most of the other regions of the Honshu Island, the measurements were far below the limitig value or even below the detectable values. In Tokyo there was a limited restiction on drinking water from 23 to 24 March 211 for infants.

9 Provisional limiting values for leafy vegetables: I-131: 2, Bq/kg Cs-137: 5 Bq/kg Spinach up to: I-131: 54,1 Bq/kg Cs-137: 2, Bq/kg Spinach up to: I-131: 5,7 Bq/kg Cs-137: 89 Bq/kg Fig. 9: Maximum cesium and iodine concentrations in spinach (data by MHLW) 5 RADIOLOGICAL SITUATION IN EUROPE Also, in Europe the consequences of the Fukushima nuclear accident could be observed. Due to the long distance transport of radionuclides in the atmosphere via global circulation systems 131 I and 137 Cs from Japan reached Europe and were detected by highly sensitive measuring equipment. With maximum values of about 1 mbq m -3, the values were far below those values which could affect human health. Fig. 1 shows the activity concentration of 137 Cs at selected German stations (by BfS). Measurements and control actions together with precautionary radiation protection measures were ordered by the authorities. To avoid importing contaminated foodstuffs, measurements were performed and the results compared to the EU-limits. Also, airplanes and ships were checked to avoid spreading contamination. Furthermore, people returning from Japan were checked for internal and external contamination on a voluntary basis. The precautionary actions in Belgium are more or less the same as mentioned obove, except there was no action ordered by the authorities for airplanes, since there are no direct flights (as well for the transportation of people as for cargo) between Belgium and Japan.

10 Bq/m³ caesium-137 Fig. 7: Activity concentration of 137 Cs at selected German stations (by BfS) In accordance with data available at the State Nuclear Regulatory Inspectorate of Ukraine (snrc.gov.ua), minor releases of radionuclide activity were detected in April 211.It should be noted that starting on 25 March, minimally detectable levels of 131 I concentration in air (in the range Bq/m 3 ) were detected by stationary facilities of the automated radiation monitoring system (ARMS) within the 3-km observation areas around NPPs in the Rivne, Khmelnitsky and Mykolaiv regions. In the Zaporizhzhya region, the 131 I concentration was below the detectable limits. On 28 March, minimally detectable levels were recorded. Increase in the amount of 137 Cs in the observation areas around NPPs cannot be totally addressed to the Fukushima event due to presence of 137 Cs having Chernobyl origin. In accordance with Radiation Safety Standards of Ukraine (NRBU-97), the acceptable concentration of 131 I for the public is 4 Bq/m 3 and of 137 Cs is.8 Bq/m 3. Data representing records of monitoring facilities is given in Figure 11 below. Fig. 11: Activity concentration of 131 I in the vicinity of Ukrainian NPPs

11 6 CONCLUSIONS The Earthquake and following Tsunami lead to a station blackout and loss of cooling of Fukushima Dai-ichi NPS units. There is significant core damage in units 1 to 3. The massive release of radionuclides into the atmosphere and the Pacific Ocean leads to INES rating 7 (major accident). Increased levels of dose rates on-site and offsite of Fukushima Dai-ichi NPS forced emergency measures by the authorities. The contamination of foodstuffs and drinking water above the regulatory limits was detected for 131 I and 134 Cs/ 137 Cs. Recent measurements confirm high concentrations of radionuclides in seawater. The pathways to Europe are monitored and are controlled via measurements. The radiological situation for the people in Japan is serious but regionally limited, if no further releases occur. 7 REFERENCES [1] Tokyo Electric Power Compay (TEPCO) Radiation dose measured in the Fukushima Daiichi Nuclear Power Station. Available at Accessed 29 September 211 [2] Tokyo Electric Power Compay (TEPCO) Detection of radioactive material in the soil in Fukushima Daiichi Nuclear Power Station. Available at Accessed 29 September 211 [3] Tokyo Electric Power Compay (TEPCO) Enhancing Controls of Internal Exposure at Fukushima Daiichi Nuclear Power Station, , Available at Accessed 19 September 211 [4] Ministry of Education, Culture, Sports, Science and Technology (MEXT), Readings at Monitoring Post out of 2 Km Zone of Fukushi-ma Dai-ichi NPP, 17 March 211, 16:. Available at around_fukushimanpp _monitoring_out_of_2km/211/3/133972_1716.pdf, Accessed 15 September 211 [5] U.S. Department of Energy, Radiological Assessment of Effects from Fukushima Daiichi Nuclear Power Plant, 13 May 211, Available at Accessed 19 September 211 [6] Ministry of Education, Culture, Sports, Science and Technology (MEXT), Reading of radioactivity level in drinking water by prefecture(be collected in September 27, 211). Available at, 6/index.html Accessed 28 September 211