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The dependence of the total cross section with energy changes very fast for neutron energies close to the resonances of the compound nucleus. In this case, the cross section is characterized by a series of narrow resonance peaks, and is expressed by the Breit-Wigner formula [ 10 ].

These peaks are due to the exited states of the compound nucleus see fig 9. The principal elements in the fuel of a reactor are uranium and uranium, which are found in the nature in the proportions 0.

The neutron absorption cross section can be divided into two parts, the fission cross section and the radiative cross section. In the radiative capture, a compound nucleus is formed with gamma ray emission for example U. In addition some of the neutrons can suffer inelastic or elastic scattering from the nucleus without being absorbed.

The total cross section for U at energies below 0. In the range between 1 eV and 1 keV is the resonance region. In this region the cross section varies very rapidly with the energy. In the third region for energies larger than 1 keV, the cross section for U is predominantly due to scattering inelastic at energies larger than 14 keV.

The fission cross section is lower than the total cross section, and much lower than in the first energy range [ 10 ]. The cross section for U is almost constant in the low energy region, and is predominantly due to elastic scattering and radiative absorption.

The fission cross section starts to be significant above 1. As described above the neutron cross section for U fission, is much higher for low energy neutrons. The fission process produces fast neutrons with energies in the interval 0. Thus, the neutrons must be slowed down in the reactor to energies at which they can be captured in the U with greater probability.

The neutrons transfer their energy to the nuclei by multiple scattering, until reaching an approximately thermal distribution, in which they can be captured by the fissionable fuel [ 13 ]. The so called thermal neutrons have a range of energies in the interval 0. The mean free path of a neutron of 2 MeV in the fuel is around 3 cm [ 10 ]. The probability q depends on the geometry and size of the sample, and on the energy of the neutrons. The critical radius for a sphere of U is about 8. The reactors have control rods containing boron, or cadmium, which can absorb neutrons in the thermal range.

So, inserting or withdrawing the control rods in the reactor core can modify the reactor power. The reactor must be operated at criticality, but is important that criticality is achieved taking into account the delayed neutrons, and not the prompt neutrons alone.

This is because, the prompt neutrons have lifetimes of the order of 10 -3 s, and this is a very short time to mechanically control the power output of the reactors. The delayed neutrons led to a better timescale to control the reactor. Moreover, the reactors must be designed for thermal stability, i. When a neutron is emitted in the fission process at 2 MeV, it will more probably interact with the U, through inelastic scattering, leaving it in an exited state.

After a few scatterings the neutron will lose its energy capable to induce fission in U. So, the neutron must find a U to induce fission, but as it is so much less abundant it is more probable the neutron is captured in a U resonance to form U with the emission of a gamma ray. Thus, the proportion of fission neutrons that induce further fission in natural uranium is rather low, and a chain reaction can not be sustained [ 10 ].

However, a technology has been developed to produce a chain reaction from natural uranium. The Fukushima Daiichi reactors are thermal reactors.

In a thermal reactor the fuel is the ceramic uranium dioxide, and is contained in an array of thin rods containing the fuel pellets. In the reactor the fuel is surrounded by a large volume filled with a material of low mass number, called the moderator. The neutrons can lose their energy in the moderator before encountering a uranium nucleus. Thus the neutron cross section for U fission increase and is much larger than for U, compensating the low concentration of uranium The neutrons are called thermal because their energy corresponds to the operation temperature of the reactor 0.

The capture of neutrons at thermal energies, lead to the fission of the U with large probability, and thus, the chain reaction is made possible with natural uranium using this technology. The moderator can be 12 C, or heavy water D 2 O. But, if the reactors use enriched uranium, the reactor can be moderated using ordinary water.

The thermal power generated by a nuclear reactor is approximated by the formula [ 12 ]:. There is a distinction in the notation between units of megawatt of thermal power -which is the total generated power- indicated as MWt, and the total generated electric power -the energy converted to work- indicated as MWe.

After the scram of the reactors the control rods were inserted into the core, and the uranium fission stopped. However, the fuel rods containing the fission products which are neutron rich, decay emitting beta rays and gamma rays as well. So, the fuel rods continued producing heat after the scram. The empirical expression for the power of heat decay P is given by the formula [ 10 , 12 ]:. This expression has an acceptable error in a certain time interval ranging from 10 seconds and days.

The nominal power for reactor 2 and 3 is MWt. If the rods have a life of one year, the decay power after one day is: If the lifetime of the rods is larger the decay power will be higher.

However, this data was not very accessible for processing, as was published in html format and in Japanese. Radiation dose measured by the stations. The measurements are made every ten minutes in more than two hundred stations along Japan, and the file starts in March 1, , until the present. So, the archive has more than Mbytes today, and it requires near 2 Gbytes of free RAM memory to read it with conventional text processors.

The data must be combined with another archive providing information on each station: site name, site identifier, location, city, prefecture, and geographic coordinates see [ 24 ]. The authors of the present chapter programmed a Fortran code to retrieve information from this data base.

In addition, several stations close to the nuclear power plant stopped measuring dose rates on March 11, and restarted on September 21, [ 21 ]. The action of bloggers helped to understand the critical situation at Fukushima and bring calm to the general population.

It was an alternative and reliable source to retrieve information about the crisis and in several cases the information provided was not so confusing like in the main news channels. In a simplified model of the radiation emitted from the nuclear power plant, it could be assumed that the particles will travel radially out from a point source, emitting S particles per second isotropically.

The particles can survive a certain distance without scattering with other particles, depending on the macroscopic cross section for scattering and the density of target nuclei. If there is a certain amount of radioactive particles being emitted from the site accident, the flux of particles will be attenuated by a geometric factor with the distance and by the scattering with the atoms of the atmosphere.

Of course, the hypothesis of isotropic emission of particles is not true in the case of Fukushima, since there was an important wind carrying the radioactive emission to the sea in the days following the accident.

This was a good factor within the disgrace of the accident, since the wind dragged the radiation out from populated zones. It is difficult to make correct predictions on the nuclear fallout without a detailed numeric simulation taking into account the full meteorological data: including wind direction, wind speed, and rain fall at each date.

The database of dose measurements was surveyed to provide a description of the dependence of the radiation versus time, and radiation versus distance from Fukushima Daiichi nuclear power plant. Since there are two widely used systems of units to measure the radiation dose, we clarify the definitions and the conversion between the two systems of units. A dose is the quantity of energy absorbed by a kilogram of exposed tissue to the radiation. As the damage produced on the tissue depends on the radiation type, i.

Radiation contour map as November 15, For fast interpretation and comparison of the results with the data found in the literature, the Table 4 gives the conversion between commonly used units and its multiples for the measured dose equivalent rate, spanning all the relevant range of values for the Fukushima accident.

In the analysis of the data is implicitly assumed that the quality factor is one, as is commonly assumed in the literature about Fukushima, i. The occupational annual dose to individual adults, except for planned special exposures, is a total effective dose equivalent equal to 50 mSv [ 25 ]. For the individuals the radiation dose equivalent limit is 5 mSv [ 25 ]. This means that in normal conditions a person must not receive a dose equivalent larger than 0.

In the next set of figures we show the results of the database analysis. The silhouette of the island is representative. Caveat: the radiation contour map displayed could be scary, but as it will be shown the radiation falls with time due to the half life of the radioactive isotopes and by the action of the wind. There is an important contribution from atmospheric radiation to this map, and not necessarily all the radiation was deposited in the ground.

Moreover, this is a contour map and do not mean that a high radiation level was actually measured in all the shadowed areas, but on some point located within it at the date indicated. The map is more representative of the spatial distribution of the radiation at the indicated date.

Spatial distribution of the radiation as function of the geographic coordinates. The release of radioactive isotopes was due to the necessary venting of the reactor pressure vessel and of the dry well of the reactor. The venting was done to reduce the pressure inside the reactor. The release of radioactive particles was worsened with the explosion of the secondary containment that occurred due to the hydrogen explosions of units 1 and 3, and a breach in the suppression chamber of unit 2 see the Appendix.

The incident was rated at level 7 according to the International Nuclear Event Scale. The main isotopes released at Fukushima have been iodine; caesium; strontium; and plutonium. These radioactive elements have been released to the atmosphere and to the Pacific Ocean. The second peak was at Ono Ookuma distance 2. The following figures show the decrease of the radiation with the radial distance from the nuclear power plant. In this date, there are no stations collecting data closer than km from the nuclear plant.

There was a blackout of several stations that recovered after September 21, , thus the data is incomplete. There is a large scatter of the data, which may be due to the topography of Japan, the action of the wind, and the rain fall in each location. Radiation versus distance as March 15, A non-linear fit of the data was performed with Origin 8. The result of the fit is shown as the red curve in the figures. As March 15, , due to the stations blackout in Fukushima the largest radiation measurements made were in the Ibaraki prefecture as shown in the Table 6.

It is possible to appreciate the large dispersion in the measured radiation with the distance. For example, there is a large difference in the dose measured at Funaishikawa Tokai with what is measured at its neighbor Kadobe Naka city. It is seen that the non-linear fit decrease slower with the distance. This could be to the action of the wind, not taken into account in the Equation Moreover, the radioactive particulate could act as nucleation centers to form rain drops, and the rain could significantly modify the radiation distribution.

In addition, is observed that the radiation distribution at this date is more scattered. It is seen that the maximum radiation dose rate at Ibaraki decreased respect to the measurements made in March. The Figure 5 shows the radiation decrease with distance as November 15, The stations were recovered near Fukushima, so the readings are higher. Radiation versus the radial distance at July 15, The following figures show the decrease of radiation with time at two locations.

The Figure 6 shows the decrease of radiation with time at the nuclear power station. It is seen that the time evolution can be approximated with a straight line in the indicated period of time.

A decreasing exponential with a half life of 3. Download Free PDF. Learning how to learn from failures: The Fukushima nuclear disaster. Ashraf Labib. Abstract Analysis of the Fukushima nuclear reactor disaster will show how to learn from failures using multi-models. Related Papers. An Inextinguishable Fire. Fukushima Daiichi accident study : status as of April Chronicle of the disaster of Fukushima I. Analysis of Possible Causes of Fukushima Disaster. Impact of accidents on organizational aspects of nuclear utilities.

Harris b,2 a University of Portsmouth, UK b University of Manchester, UK a r t i c l e i n f o a b s t r a c t Article history: Analysis of the Fukushima nuclear reactor disaster will show how to learn from failures Received 8 July using multi-models. This type of analysis can enrich the modelling of causal factors, Received in revised form 20 September provide insight into policy making and support decisions for resource allocations to Accepted 6 October prevent such disasters.

They were then given a brief Fukushima Hydrogen explosion in the form of a narrative of the accident derived from investigation reports and divided Common mode failure into small groups tasked to analyse the disaster and to present their recommendations Loss of cooling both orally and in a written report. Fault tree All the participants were asked to follow a certain presentation format.

All rights reserved. Introduction In the wake of the Fukushima disaster few investigation reports, aimed at explaining the accident and outlining the lessons learnt, have been published. Most notably, it has been suggested that in the nuclear power industry, probabilistic safety assessment PSA is under-utilised. Labib, M. Others have also supported the use of PRA approaches in the nuclear industry [24,17].

In this paper the Fukushima disaster is analysed and a hybrid modelling approach, using PSA-related techniques, is developed. Also, there have been few text books on this topic, other than those of Turner [34] on man-made disasters and Kletz [15] on learning from accidents.

Recently, however, there has been a revival of interest and research activity, the Journal of Safety Science dedicating an issue to learning from events and near-misses [6] and another to learning from accident reports [9], The Journal of Contingencies and Crisis Management running an issue on learning from crises and major accidents [8] and The Journal of Organization Science publishing a special on rare events and organisational learning [19].

Also recently pub- lished have been reviews of the literature on learning from incidents, accidents and disasters [21,22,20,10]. In a recent work by Saleh et al. Unfortunately, these have not been matched with guidance on how this could be achieved [35]. One unique feature of nuclear power plants is that they are initially designed for a very long operational life, typically sixty years.

This poses major challenges such as those of having to cope with technical developments, new safety requirements and sustaining skills and competencies, over two or three gen- erations of staff [35].

The following section is a narrative summarising the abundance of information in the literature on the Fukushima acci- dent. It is suggested that, the disaster having happened a while ago, a primary data collection would be of lower quality, as memories have faded and key observers have dispersed, and a secondary data analysis which is a proven and widely used research method is therefore employed for structuring the problem.

This also offers the possibility of triangulating sources and easy checking by other researchers. The background of the participants were practitioners from different industries such as oil and gas, power and nuclear power generation.

They workshop was part of a masters class related to learning from failures. They were also initially provided with the theoretical background of the tools used in the analysis such as FTA and RBD. The evolution of the disaster On 11 March Japan suffered its worst ever recorded earthquake, known as the Great East Japan Earthquake.

The epi- centre was miles E. On detection of the earthquake all the units shutdown tripped safely. Initially, on-site power was used to provide essential post-trip cooling. About an hour after shutdown a massive tsunami, generated by the earthquake, swamped the site and took out the AC electrical power capability.

Sometime later, alternative back-up cooling was also lost. With the loss of these cooling systems Reactor Units 1 to 3 overheated, as did a spent-fuel pond in the building containing Reactor Unit 4. This resulted in several disruptive explosions, because the overheated zirconium- containing fuel-cladding reacted with water and steam and generated a hydrogen cloud which was then ignited. Major releases of radioactivity occurred, initially to air but later via leakage to the sea.

The operators struggled to restore full control. The Japanese authorities imposed a 20 km radius evacuation zone, a 30 km sheltering zone and other countermeasures. Governments across the world watched with concern and considered how best to protect those of their citizens who were residents in Japan from any major radioactive release that might occur [36].

Some have commented on reports of plant damage caused by the earthquake itself, concluding that the loss of effective cooling for the reactors stemmed directly from the earthquake rather than the subsequent tsunami. However, the information available about the emergency cooling systems, and analysis of the circumstances, do not support such a hypothesis [37].

This, coupled with land movement, ensured that the tsu- nami caused enormous damage along the coast [13]. The consequences of the failure The earthquake, occurring under the sea near the north east coast of Japan, lasted over 90 s, and caused widespread dam- age to property, although, due to the civil building design standards most structures did not collapse.

As a result of the earth- quake Japan has moved 2. This was by any measure a major global event. The 14 m high tsunami travelled up to 10 km inland, devastating infrastructure already weakened by the earthquake.

The infrastructure affected included many different types of facility: homes, hospitals, electricity and water supplies, pet- rochemical and oil installations. Fukushima itself is a city in the Tohoku Region of Japan, lying km north of Tokyo and covering an area of As of May , it had a population of , The damaged caused by the earthquake and subsequent tsunami, which arrived at In the short to medium term the Japanese government has suspended operations at Tohoku until the sea defences are improved, which is estimated could take years to complete.

Currently in , all nuclear power plants are stopped for safety enhancement, and some of them are preparing for restart by submitting the additional safety analysis to regulatory body. In an article in the Guardian newspaper [33] Mr. Think about all different kinds of small counter-measures, not just one big solution.

We made a lot of excuses to ourselves. The scale is intended to be logarithmic, similar to the movement magnitude scale that is used to describe the comparative magnitude of earthquakes. Each increasing level represents an accident approximately ten times more severe than one on the previous level INES, Compared to earthquakes, where the event intensity can be quantitatively evaluated, the level of severity of a man-made disaster such as a nuclear accident is more subject to interpretation.

Because of this the INES level is assigned well after the incident of interest occurs. Therefore, the scale has a very limited ability to assist in disaster- aid deployment. The INES scale of nuclear accidents [12]. In the next sections the analysis provided by one of the groups are presented. This argument was encapsulated in a fault tree. It consisted of six BWRs with a combined power output of 4.

In the case of Fukushima-Daiichi NPP, only unit 3 was operated with mixed oxide MOX fuel, while the other two reac- tors under operation were loaded with only uranium-dioxide UO2 fuel at the time of the accident. The steam is conditioned heated to ensure it is suitably dry and then used to produce electricity via a turbo-generator. The steam is then cooled and condensed, the resultant water being returned to the reactor via variable-speed pumps see Fig. Cooling system schematic for a BWR reactor [4].

When the earthquake struck, Reactors 1, 2 and 3 were operational and at full output. Reactors 4, 5 and 6 were not on-line, but were shut down for routine periodic inspection. Assuming that water could flow in both directions resulted in only a 0. In Figures 2. Once the leakage rate is computed, water levels in the reactor well and dryer-separator pit can be estimated using the mass balance as discussed in Appendix 2B.

The reactor well and dryer-separator pit are estimated to have a combined volume of 1, m 3 and surface area of m 2 ; these values are given by TEPCO a, Attachment , Table 3; b and are consistent with other published data. The gates are just hung in place; their sealing depends on the force created by differential water levels between the pool and reactor well.

This force increased substantially with the water addition to the pool on April Congress asked the National Academy of Sciences to conduct a technical study on lessons learned from the Fukushima Daiichi nuclear accident for improving safety and security of commercial nuclear power plants in the United States. This study was carried out in two phases: Phase 1, issued in , focused on the causes of the Fukushima Daiichi accident and safety-related lessons learned for improving nuclear plant systems, operations, and regulations exclusive of spent fuel storage.

This Phase 2 report focuses on three issues: 1 lessons learned from the accident for nuclear plant security, 2 lessons learned for spent fuel storage, and 3 reevaluation of conclusions from previous Academies studies on spent fuel storage.

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Get This Book. Visit NAP. Looking for other ways to read this? No thanks. Nuclear Plants: Phase 2. Page 20 Share Cite. Note: Spent fuel was being stored in the Unit reactor buildings, the common pool, and in a dry cask storage facility. Page 21 Share Cite. Page 22 Share Cite. Notes: The features shown in the figure are described in the text.

This is not an engineering drawing; some features are simplified or omitted, and not all components are drawn to scale. Note: The rack is approximately 4. Page 23 Share Cite. Fuel is moved underwater between the reactor and pool using a fuel handling machine that runs on rails located on the refueling floor FIGURE 2. Notes: The fuel from the reactor was stored in the spent fuel pool, the dryer-separator pit and reactor well were flooded with water, the concrete barriers between the dryer-separator pit and reactor well and the spent fuel pool and reactor well see Figure 2.

Water levels m relative to the bottom of the spent fuel pool are shown on the right-hand side of the figure. Note: This is not an engineering drawing; some features are simplified or omitted, and not all components are drawn to scale. Page 24 Share Cite. Notes: The spent fuel pool is shown in the foreground; the fuel racks are visible at the bottom of the pool. The reactor well background is separated from the pool by the steel gate shown on the far wall of the pool.

The green apparatus located above the reactor well is used to lift the gates and runs along tracks on the sides of the pool, The green apparatus that is partially visible in the foreground is the fuel handling machine.

It also runs along tracks on the sides of the pool. The photo is distorted because it was taken with an ultra-wide-angle lens. Page 25 Share Cite. Page 26 Share Cite. Page 27 Share Cite. Page 28 Share Cite. Page 29 Share Cite. Page 30 Share Cite.

Page 31 Share Cite. Page 32 Share Cite. Page 33 Share Cite. Page 34 Share Cite. Left image: Side view of the tops of the racks. Three fuel assembly handles are partially visible in the foreground of the image. Right image: Top view of the racks.

Page 35 Share Cite. Note: The large green object 8 is the fuel handling machine. Page 36 Share Cite. Page 37 Share Cite. Note: The pool is the dark region at the bottom of the two left-hand images and the left-hand side of the right-hand image.

The canal and reactor well plug are visible in the center and right-hand sides of the right-hand image. The gate closest to the canal has been displaced. Page 38 Share Cite. Notes: The red squares indicate the hottest, most recently offloaded fuel assemblies. The grey squares indicate unirradiated new fuel assemblies. Page 39 Share Cite. Page 40 Share Cite. Page 41 Share Cite. Page 42 Share Cite. Page 43 Share Cite. Page 44 Share Cite. The negative additions i.

Page 45 Share Cite. Page 46 Share Cite. The mathematical model and limitations are described in Appendix 2B , and the key features are as follows: Evaporative water losses from the pool, which are driven by thermal heating of the pool water from radioactive decay in the stored spent fuel, were estimated using the steady-state energy-balance model described in Appendix 2B.

Water losses from the pool from sloshing were assumed to be 0. Page 47 Share Cite. Water additions to the pool from leakage around the gate seals were estimated using the orifice flow-rate correlation described in Appendix 2C.

Water was assumed to flow in one direction from the reactor well to the spent fuel pool and only if the reactor water level was higher than the pool level; see Appendix 2C for further discussion of this issue.

Following the earthquake, evaporative losses of water from the pool remained low until the pool temperature reached equilibrium, 21 at which point heat gained in the water from radioactive decay in the stored spent fuel balanced heat lost from water evaporation. The increase in pool-water evaporation rates is indicated by the change in the slope of the pool water-level curve starting around March 13, The explosion on March 15, , caused an additional 1 m of water to slosh from the pool and reactor well and dryer-separator pit according to TEPCO.

The model predicts that water began to leak from the reactor well into the pool on March 16, This leakage is indicated by the decrease in slope of the pool water-level curve blue curve and increase in slope of the reactor well and dryer-separator pit water-level curve orange curve. Pool water levels are predicted to drop to within about 3. Subsequently, the combination of water leakage around the gates and external water additions Figure 2.

Page 48 Share Cite. Notes: The black curve shows a hypothetical scenario in which there is no water leakage from the reactor well and dryer-separator pit into the pool. The vertical scale in this figure is different from that in Figure 2. Pool water levels dropped to less than 2 m above the tops of the racks on April 13 and again on April 20, Operators used a water-level indicator in the skimmer surge tank to determine whether the pool was full.

They subsequently realized TEPCO, a , Attachment that water oversprays onto the refueling deck were entering the skimmer surge tank through floor drains, bypassing the pool altogether, so less water was being added to the pool than estimated. Page 49 Share Cite. Page 50 Share Cite. The estimates were likely based on engineering judgment.

Pool water levels prior to April 12, , were not measured. As noted previously, the water-level indicator in the skimmer surge tank provided misleading information on pool water levels prior to this date. A number of effects not accounted for in the model become important once the water level drops below the top of the racks, most notably the reduction in cross-sectional water area.

Consequently, the water-level estimate without gate leakage shown in Figure 2. This estimate is increasingly unreliable below this level because of geometrical inaccuracy and also because of other physical phenomena not accounted for by the model, including rack and fuel heat capacity, multiphase flow, film boiling, cladding oxidation, flow blockage, and change in geometry with loss of cladding integrity.

Computations that include many of these effects are discussed in the Sandia analysis of a hypothetical loss-of-cooling accident in Unit 4 see Chapter 8 of Gauntt et al. Page 51 Share Cite. Page 52 Share Cite. Note: This estimate was developed using the model in Appendix 2B with the same assumptions about the fuel and Unit 4 building condition as Scenario 2 of Gauntt et al. The black filled circle indicates a hypothetical situation in which, if the fuel had been offloaded only 48 days before the accident, the first water additions to the Unit 4 pool would have taken place just as the water level was reaching the midheight of fuel.

Page 53 Share Cite. Page 54 Share Cite. Plant operators had not planned for or trained to respond to the conditions that existed in the Unit spent fuel pools following the March 11, , earthquake and tsunami: Primary and backup pool cooling systems had failed because of the loss of all power.

There were no plans or equipment available for adding emergency makeup water or implementing alternate cooling strategies. Water-level and temperature monitoring instrumentation had also failed because of the loss of power. The limited range of monitoring instrumentation greatly reduced its effectiveness even after power was restored.

Explosions in Units 1, 3, and 4 damaged the reactor buildings, introduced debris onto the refueling decks and into the spent fuel pools, and hindered visual observations of pool conditions. Radiological conditions hindered access to areas around the buildings and limited personnel access to the refueling decks and pools. The recommended improvements in plant monitoring systems include the following: Remote surveillance of pools and refueling decks, Radiation levels on the refueling deck, Pool temperatures, and Pool water levels.

Page 55 Share Cite. Page 56 Share Cite. Page 57 Share Cite. TEPCO has also performed whole-body counting on each worker to derive his or her internal dose. Slight discrepancies in the reported number of workers monitored are due to a handful of individuals where external and internal dose results are not both available.

As of the most recent monitoring period, no observable health effects have been reported in any of the workers. It should be noted that acute health effects are not expected at these doses to workers, although all are being closely monitored. For chronic health effects above 0. For example, the occupational worker who received a dose of 0. Estimating cancer risks to the general public is complicated by the low dose rates outside of the NPS and significant overall cancer rates from various environmental factors [2].

The maximum external dose recorded is mSv 0. The maximum total dose recorded to one worker was mSv, and six workers have received doses in excess of the emergency dose limits established. Although workers have received doses above the normal annual limit of 50 mSv, the average dose for emergency workers is still relatively low and has decreased steadily during the months following the accident.

For workers performing emergency work since March, the average total accumulated dose is The total collective dose for all emergency workers is estimated to be person-Sv. In addition to whole-body doses, two male employees received significant skin dose while laying electric cables from standing in contaminated water that flooded their boots.

The actions in the immediate aftermath of the accident on March 11 resulted in doses to a handful of workers in excess of established limits and elevated doses to a larger group, as noted above. Since that time, TEPCO has been improving the working conditions and safety measures for its workers.

Currently, seven designated rest areas have been created, and four additional rest areas are in preparation. Also, improvements in living conditions have been made at the gymnasium that houses these workers. At this time there are not enough data collected and publicly reported by the Japanese government or the IAEA to reach any definitive conclusions on off-site health effects.

The doses received by members of the public have come from four different pathways:. The first two of these items cannot be measured retrospectively but can only be predicted from dispersion modeling.

A few crude dispersion models have been made public, but no validated models have been made available for review to date in the United States. Airborne radioactivity is transitory, and the dose from inhalation is many times greater than the submersion dose for all but the inert gases.

Food and water contamination has been documented through extensive measurements. Most contaminated foodstuffs have been restricted, but there is no public information regarding their actual level of consumption at this time.

Conversely, the external exposure from ground contamination can be predicted with relative accuracy from the distribution of ground contamination. A similar estimate was provided by the U. This estimate, although not definitive, suggests that health effects to the public will be minimal. The information provided below comes from the Japanese Health Monitoring Program.

By July more than , residents had been screened by experts from related organizations, universities, and local governments [5]. Initial measurements were taken between June 27 and July The survey focused on residents who lived in areas associated with high doses.

A total of participants—90 residents from Namie Town, 20 residents from Iitate Village, and 12 residents from Kawamata Town—were initially enrolled in the survey, and subjects were surveyed in follow-up examinations.

Whole-body counters were used to detect activity from Cs, Cs, and I. Urine bioassays were used to determine a cutoff value for the whole-body counter measurements. Cesium was detected in 52 out of people Cesium was detected in 32 out of people Both Cs and Cs were detected in 26 out of people Iodine was not detected in any subject. JAEA began internal exposure surveying of 2, evacuees on July Currently, a two-step plan is being considered. First, a preliminary study began in early July on a sample of about residents who were located in regions of high radiation levels.

Those selected will undergo thorough testing for internal radiation contamination. All Fukushima residents will be considered in the primary study. Questionnaires will be distributed to all residents in order to help experts determine the radiation dose received by the residents. The data will be stored for 30 years to conduct follow-up health checks.

An estimated 2 million residents need to be monitored. The United Nations Scientific Committee on the Effects of Atomic Radiation has also announced that it will conduct a study on the health impact to Fukushima residents [7].

The long-term land contamination off-site is due to the deposition of Cs and Cs because of their comparatively long half-lives the half-life of Cs is 2. The other radionuclides identified as being released have half-lives on the order of less than days or tens of days.

The other isotopes of concern from a reactor accident include strontium strontium and yttrium yttrium and the actinides, but none of these have been measured in any detectable quantities within or beyond the established evacuation zone.

The initial measurement of ground contamination was performed by the Ministry of Education, Culture, Sports, Science and Technology—Japan MEXT , with substantial assistance from the DOE NNSA and DOE Office of Nuclear Energy, by measuring exposure levels aboveground using fixed-wing airplanes and helicopter flyovers, extrapolating to the exposure rate at ground level, and converting that value to an area concentration of cesium, given the relative proportions of Cs and Cs expected.

One example is shown in Fig. This method has the potential to miss small hot and cold spots in the survey area but provides a reasonable distribution of the deposition of these radionuclides. A significant number of soil samples throughout the region have been collected and measured with gamma spectroscopy to obtain cesium concentration.

A summary map is shown in Fig. This careful work provides a detailed quantification of Cs environmental contamination. Such data will be needed to better inform off-site cleanup or remediation activities. A direct correlation between these various maps has not been completed at this time. But, the patterns observed are quite similar. We were not able to precisely compare this to the Japanese government relocation land area, but the relocation area is larger. The Committee collected and compiled data for contamination of foodstuffs by Cs, Cs, and I.

These detailed data, as well as detailed spreadsheets, are provided at the Japanese Ministry of Health, Labor and Welfare Web site [10]. Actions taken by the Japanese government to restrict consumption of contaminated meats are given in [11]. No data were available regarding the partition between public water supplies and bottled water that was used after the accident.

Data do exist for some public water supplies. These measured data for public water supplies indicate that radiation levels were falling after March and were trending toward levels below allowable limits. Early in the accident, radioactive materials were released with water coolant into the sea. The measurements taken near the Fukushima Daiichi NPS indicate these releases were dispersed quite quickly.

The accident at the Fukushima Daiichi NPS has resulted in significant challenges for accident cleanup and waste management. These issues include processing the large volume of contaminated water, debris, soil, secondary wastes, potentially damaged spent fuel within the reactor SFPs, and damaged fuel and fuel debris within the reactors and primary containment structures.

Progress has been made in cooling of the reactors, and all the units have reached ambient pressure and temperature conditions, i. Mid-term to long-term waste management issues will continue to be the major technical issues that must be overcome as recovery actions continue toward an acceptable end state.

TEPCO see [13] for TEPCO information on cleanup status has established a road map that describes elements of the site cleanup and water management, and it is currently developing more detailed mid-range to long-range plans. There are also waste management challenges associated with. Resolving these challenges will be required to allow continued progress for removal of the spent fuel stored within the SFPs and ultimately the retrieval and processing of the damaged fuel within and outside of the RPVs.

As the planning for the cleanup continues to evolve, in early November, the Japanese government ordered TEPCO to draw up a road map to decommission the four damaged reactors at the Fukushima Daiichi NPS in a process that could take decades. The plan, developed by TEPCO in collaboration with the Japanese government, is based on removing fuel rods in SFPs within 2 years and damaged fuel in each of the reactors within 10 years, according to the minister in charge of the nuclear disaster response.

TEPCO is developing a road map to be provided early in Decommissioning the four reactors is estimated to cost at least 1. Substantial government involvement will be necessary in the decommissioning process.

Normal decommissioning takes about half as long according to the JAEC committee. This dose level is approximately the same amount of radiation exposure a patient would receive from a full-body CT computed tomography scan. The current government policy is that areas where the annual dose levels are above this level are to be given priority in scheduling decontamination activities.

The current government policy may prove to be problematic for implementation. The Fukushima Daiichi accident produced radioactive gaseous, liquid, and solid wastes. The gaseous emissions were released in the early days of the accident and have dispersed and decayed to small levels and are no longer a health threat.

Liquid waste management and the cleanup and management of the water that was injected into the reactors and SFPs had been a major concern.

For many weeks following the accident, rainwater mixed with the water that had been injected into the reactors and SFPs was accumulating in NPS buildings and tanks.

As the buildings and tanks filled up, additional temporary storage tanks were brought in to hold the water. In June, the first of two temporary wastewater cleanup systems was started.

Water levels in the buildings are slowly decreasing, and plans are in place to start work in on a new, more permanent long-term wastewater processing facility. Plans are being developed and implemented to monitor and, if necessary, clean up or remove radioactive contamination from surrounding areas on the Fukushima NPS site.

Much of the contaminated rubble and materials around the NPS buildings and in the roadways has been removed, and work has started on rubble removal from the refueling floors of Units 3 and 4. Planning is in progress to start moving the fuel from the SFPs to interim or long-term storage or reprocessing facilities within the next couple of years. Studies are in progress or planned to determine the best methods to be used to defuel the reactors, remove the spent fuel from the SFPs, and treat and dispose of the accumulated radioactive wastes.

The initial phase of the complete plan for removal of fuel from the reactor is illustrated below. Because of damage to the RPVs, PCVs, and reactor buildings, contaminated water injected into the reactor cores is leaking into the turbine buildings.

This situation required the quick design of two water treatment systems. One was a short-time-frame installation, and the other was a mid-term installation Fig.

The two water treatment systems are still being used to process wastewater to remove oil, contamination, and brine. The processed water is being reused to inject into the RPVs to minimize the volume of new water used. The systems initially experienced equipment and operational problems caused by quick installation and operator unfamiliarity.

TEPCO has been able to reduce the inventory of contaminated water creating enough margin to increase the cooling injection rates into the RPVs. The waste sludge from the oil separator, reverse osmosis membrane, and desalination units is being stored on-site in temporary tanks. This volume will eventually challenge the storage capacity. A similar portable skid-mounted water treatment and desalination system is being used to reduce contamination and chlorine levels in the SFPs of Units 2, 3, and 4.

These SFPs had seawater injected into them during the event. In many ways, the Fukushima Daiichi NPS has evolved from a nuclear power electric generation site into a large water treatment facility Fig. Site cleanup has been accomplished through the use of ten remotely controlled vehicles including backhoes, bulldozers, and dump trucks. The site has two remote vehicle control rooms that are used to control all the debris-removal construction equipment. One control room operates a backhoe, a dump truck, and a lift truck.

The second control room operates two backhoes, a bulldozer, two dump trucks, and two lift trucks. All the items and materials removed from the yard area around the NPS have been stored in metal containers 4- to 8-m3 volume. Larger and less contaminated items are stored in bulk in a new solid-waste building. Each container has an assigned number and is labeled with its container number, where the debris is from, dose rate, and type of debris.

This will be used to maintain inventory control during eventual transport off-site and waste disposal. Removal of reactor building structures damaged by the explosions will be required to allow removal of spent fuel and ultimately core material.

Planning is currently in progress for removal of fuel from the SFPs Fig. Frequent monitoring and development of plans for environmental cleanup or removal of harmful levels of radioactive contamination from areas surrounding the NPS are progressing. The magnitude of the cleanup outside of the NPS site has required the Japanese government to take ownership for these tasks. A number of demonstration projects have been initiated, and the complete road map is to be provided in early As the Committee reviewed and analyzed the information regarding aspects of the Fukushima Daiichi accident, we, the members, raised a series of questions regarding safety issues, i.

In this section we provide a summary of our safety-related recommendations that evolved from the discussion of these questions. We want to emphasize that these recommendations are consistent with most of the regulatory issues that have been raised by national and international bodies.

However, our emphasis is not to directly suggest what regulatory rules or process changes are needed; rather, we focus on the key technical issues that would be the basis for any specific set of regulatory actions. There is no aspect of the Fukushima Daiichi accident that a priori indicates that the level of safety of NPPs in the United States is unacceptable.

The Committee agrees with the U. However, from a public confidence viewpoint, it is unacceptable to have an accident of the visibility and societal consequences of the Fukushima accident occurring somewhere in the world every 25 to 30 years. There are some major lessons to be learned from the accident that relate to observed vulnerabilities in the design and operation of the Fukushima Daiichi NPPs and to weaknesses in the ability of the NPPs to respond to such an extreme event.

We need to examine each of these observed vulnerabilities to see how they relate to U. NPPs and address those issues, as necessary. The following recommendations are consistent with our general conclusion. These recommendations are strictly motivated by our understanding of the Fukushima Daiichi accident and technical shortcomings observed.

These recommendations are largely embodied within the suggested regulatory actions proposed by the NTTF. The scope of reactor safety design and regulation should be reviewed to consider the adequacy of design bases for natural-phenomenon hazards and the need for extension of the design basis in a graded manner, using risk information, into what have previously been considered beyond-design-basis accidents BDBAs. Historically, nuclear reactor regulations have focused on providing high assurance that events within the design basis of the NPP would not result in severe fuel damage or in a substantial off-site release of radioactive material.

Some requirements have been imposed on licensees related to beyond-design-basis conditions, such as hydrogen mitigation devices in some NPP designs.

In general, though, the insights from risk information and safety assessments have been used to reduce design vulnerabilities that would lead to beyond-design-basis events rather than the mitigation of the consequences of those events. We are quite aware that a risk-informed approach is a long-term effort and is technically complex.

It may lead to a change in the scope of regulatory requirements for beyond-design-basis events, including the development of deterministic acceptance criteria for risk-dominant accident sequences and end states.

This could impact both existing and future NPPs. If the return period for a tsunami of the magnitude experienced in Japan is as short as reported once every years , a risk-informed regulatory approach would have identified the existing design bases as inadequate.

It has long been recognized that external events, particularly seismic and external flooding events, could be substantial contributors to risk because of the potential for multiple common-cause failures. The Fukushima Daiichi accident raises the issue of whether past risk assessments have underestimated the relative importance of natural-phenomenon hazards to NPP risk.

There is little question that the methods of analysis used for analyzing internal event risk are more developed and have smaller associated uncertainties than those used to assess the risk of low-frequency natural-phenomenon hazards. The NRC is requiring that the design bases for all U. NPPs be reviewed for natural-phenomenon hazards to assure that they are consistent with the existing regulations.

The NRC should also undertake a review of regulations for each of the natural-phenomenon hazards to determine whether they are appropriately risk-informed. For example, the current regulatory approach in the United States for establishing a design basis for floods is deterministic, based on the concept of the maximum possible rainfall.

This type of concept, even though inconsistent with nature, may work effectively when dealing with common engineering concerns like assurance of a low frequency of dam failures or bridge failures. However, the criteria that we have established for NPPs are much more stringent.

Although it is very difficult to deal with low-probability events, this is the perspective needed for a risk-informed treatment of natural-phenomenon hazards. Such an approach to regulating hazards from extreme natural phenomena should be undertaken. As part of this approach, the NRC should periodically reanalyze and potentially redefine the design and licensing basis for severe natural events earthquakes, floods, tsunamis, hurricanes, tornadoes, and fires using the latest, accepted, best-estimate methodologies with quantified uncertainties and data available that are well vetted and have a strong consensus of technical experts.

All risks to NPPs from severe natural events should be periodically e. Based on the outcome of the assessment, the NRC may mandate improvements based on cost-benefit analyses. Recognizing that the high cost and lengthy schedule to obtain site approval are powerful incentives for multiple-unit sites, we recommend that a multiple-unit risk assessment be performed whenever a unit is added to a site.

Such a risk analysis should include sensitivities to determine the extent to which multiple-unit considerations increase or decrease the risk.



The Fukushima Daiichi Nuclear Accident | SpringerLink


Am Mittwoch im Kontrollraum von Reaktor 1 und 2 Bild: dapd. In dem Ort Namie wurden Mikrosievert pro Stunde gemessen. Die Regierung empfahl, Kinder unter einem Jahr sollten das Wasser nicht trinken. In vielen Stadtvierteln war Mineralwasser am Mittwoch ausverkauft. Wiederum versicherte Regierungssprecher Edano, dass keine unmittelbare Gesundheitsgefahr bestehe.

Damit will man vermeiden, dass der Druck im Reaktor zu stark steigt. Es gelang, die Beleuchtung im Kontrollraum von Reaktor 3 wieder in Betrieb zu nehmen. Im Turbinenraum wurde eine Strahlung von Millisievert pro Stunde gemessen. Zwei Arbeiter wurden leicht verletzt, aber nach Angaben von Tepco waren sie keiner Strahlung ausgesetzt. Ein Gastbeitrag. Doch so einfach ist die Sache nicht. Atomkatastrophe in Fukushima: Nichts scheint gut zu werden. Warum sehe ich FAZ.

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Fukushima reaktor 5 und 6 free download

Mar 15,  · Der Reaktor Nummer 4 registrierte einen neuen Brand. In den Reaktoren 1 und 2 wurden auch die Kernbrennstäbe ganz oder teilweise beschädigt. Reaktor 5, der bereits ausgeschaltet war, fiel der Wasserstand der verbrauchten Kernbrennstoffpools aufgrund von Verdampfung weiter ab. Fukushima Donnerstag Estimated Reading Time: 6 mins. May 30,  · Im Kernkraftwerk Fukushima sind am Wochenende die Kühlpumpen ausgefallen. Die Temperatur in Reaktor 5 stieg stak an. Nach Angaben der Betreiberfirma Tepco konnte das Problem aber behoben werden. Mar 23,  · Am Mittwoch im Kontrollraum von Reaktor 1 und 2 In Fukushima gab es am Mittwoch zwei Nachbeben einer Stärke von 5,8. und 6. In dem Ort .