放射性物質の大気中への放出量の推定について
http://www.tepco.co.jp/cc/press/betu12_j/images/120524j0105.pdf
平成２４年５月
東京電力株式会社
=========================================================
Estimation of Radioactive Material Released to the Atmosphere
during the Fukushima Daiichi NPS Accident
May 2012
Tokyo Electric Power Company
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Cf. Following extract: (PDF 104P)
Contents
1 Introduction .......................................................................................................................................1
2 Release of Radioactive Material ........................................................................................................1
3 Method of Assessing Amounts Released ..........................................................................................1
3.1 Assessment Sequence......................................................................................................................2
3.2 DIANA (Figure 3-①)......................................................................................................................3
3.3 Meteorological Data Used in Assessment (Figure 3-②)................................................................5
3.4 Air Does Rates Used in Assessment (Figure 3-③).........................................................................7
3.5 Release Circumstances at Each Time (Figure 3-④) ......................................................................8
3.6 Sorting According to Nuclide (Figure 3-⑤) ..................................................................................8
4 Assessment Results ...........................................................................................................................9
4.1 Assessment Results of Amounts Released .....................................................................................9
4.2 Time Variation of Amount Released ..............................................................................................9
4.3 Results of Assessment of Amount of Radioactive Material Deposited...........................................9
5 Discussion.........................................................................................................................................11
5.1 Comparison of Amounts Released Against Assessment Results of Other Institutions ................11
5.2 Comparison Against Actually Measured Deposition Amounts ....................................................12
5.3 Assessed Values for Periods Where Air Dose Rate Data Fluctuate ..............................................13
5.4 Assessed Values for Periods Where Air Dose Rate Data Do Not Fluctuate..................................15
5.5 Assessment of Each Event .............................................................................................................16
5.5.1 Amount of Radioactive Material Released at Time of Building Explosion...............................18
5.5.2 Amount of Radioactive Material Released Accompanying Primary Containment Vessel
Venting.................................................................................................................................................20
5.5.3 Amounts Released from Reactor Buildings ................................................................................20
5.6 Factors in Contamination of Area Northwest as Viewed from Fukushima Daiichi Nuclear
Power Station ......................................................................................................................................21
6 Summary...........................................................................................................................................23
7 Attachments ..................................................................................................................................... 23
Reference Material .............................................................................................................................. 24
1 Plume Movement and Changes in Air Dose Rates........................................................................... 24
1.1 Case Where Plume Approaches the Sky above Monitoring Location............................................24
1.2 Case Where Plume Does Not Approach the Sky above Monitoring Location ..............................25
2 Ratio of Susceptibility of Radioactive Nuclides to Release..............................................................26
1 Introduction
The Tohoku-Chihou-Taiheiyou-Oki Earthquake, which had its hypocenter off the coast of Sanriku striking at 14:46 on March 11, 2011, and the accompanying tsunami led to the accident at Units 1~3 of the Fukushima Daiichi Nuclear Power Station where a situation continued in which all
AC and DC power sources as well as the ultimate heat sink were lost, fuel was damaged and melted, and damage occurred to the primary containment vessel, resulting in radioactive material being released to the atmosphere.
In connection with the investigation into this accident, the purpose of this document is to estimate the amount of each principal nuclide released to the atmosphere from the power station accompanying the accident, and to clarify the time sequence of releases, the effectiveness of primary ontainment vessel venting, and factors pertaining to deposition in a northwesterly direction.
Because of uncertainties in computational conditions and the limits on systems used in the estimation, the content of this document may be revised as the investigation into the accident develops in the future.
2 Release of Radioactive Material
After the accident, radioactive material was released from Units 1~3. In addition to releases accompanying venting and building explosions, there were continuing releases of radioactive material to the atmosphere from buildings after the building explosions.
The established monitoring posts and stack monitors should have been able to ascertain releases of radioactive material to the atmosphere, but the power source for monitoring posts was lost due to the earthquake and the power source for stack monitors was lost in the wake of the tsunami, so function of stack monitors and other such equipment was lost. Therefore, monitoring cars were posted around the power station to measure the air dose rate, meteorological data (wind direction and velocity) and other data in an effort to ascertain the status of radioactive material release.
Of the radioactive materials released to the atmosphere as shown in Figure 1, noble gases, which are not affected by gravity or rainfall, are carried off on the wind and dispersed. On the other hand, iodine, cesium and other such nuclides are affected by gravity and rainfall, and fall to the ground surface or sea surface while they are dispersed by the wind. Moreover, even after depositing on the ground surface, they exhibit complex behavior, such as being carried by rainwater to rivers and migrating thereafter to the ocean.
In addition, of the radioactive material released from the primary containment vessel which does not migrate to the atmosphere as shown in Figure 2, that associated with water injected into the reactor from outside the primary containment vessel leaks from the primary containment vessel, traverses through the interior of the reactor building, and accumulates in the turbine building (In this report, the amount of such radioactive material is not subject to the assessment.).
3 Method of Assessing Amounts Released
Based on air dose rates and other data measured by monitoring cars and other equipment as well as rainfall and other meteorological data measured at the Meteorological Agency’s meteorological stations, the amount of radioactive material released to the atmosphere from the
power station was assessed.
3.1 Assessment Sequence
The sequence through which amounts released are assessed is as follows. This sequence is shown in Figure 3. In addition, specifics are listed in the following paragraphs indicated by numerals ①~⑤.
Step 1: Observed data (air dose rates, meteorological data (wind direction, wind velocity, rainfall amounts, sunshine duration)) are input into TEPCO’s
system for assessing the atmospheric dispersion of radioactive material (see section 3.2 DIANA) to estimate the amounts released to the atmosphere.
Step 2: Based on time variations in the air dose rate, the percentages of noble gases, iodine and cesium released are assessed for the amounts releases
as obtained in Step 1.
Step 3: From amount of cesium-137 released as obtained in Step 2 and meteorological data, the amount deposited on the ground surface is assessed.
3.2 DIANA (Figure 3-①)
The Dose Information Analysis for Nuclear Accident (DIANA) is a system which assumes an event in which radioactive noble gases, iodine, and
particulate matter have been released to the atmosphere. The system is capable of simulating three-dimensional advection dispersion phenomenon in the area surrounding a nuclear power station for each 10-minute period as well as assessing the air dose rate at arbitrary points. The system’s detailed
specifications are given below.
Calculation method: Based on measured meteorological data (wind direction and velocity at the power station), a three-dimensional windy spot within the area assessed (range extending 50km east-west × 50km north-south × height of 2000m which includes the power station; calculation mesh: 1km×1km×100m) is prepared with consideration given to geographical influences, and particle-based advection-dispersion is calculated.
Dispersed particles: 0.5MeV-equivalent particles are assumed
Assessment of windy spots: Assessment of windy spots satisfying the law of conservation of mass
Advection-dispersion: Lagrangian virtual particle dispersion model
Release location: A points assuming release at the same time is one point
Calculation steps: Every 10 minutes (10-minute period is assumed to be the uniform release
rate)
Deposition rate: The deposition rate expresses the susceptibility of radioactive material to
deposition, and the numerical values in the tables below have been used to assess the
concentration of deposition on ground surface. These numerical values have been noted in
the following papers and are common numerical values in calculations of atmospheric
dispersion.
Engelmann, R.J. (1968) The Calculation of Precipitation Scavenging
in Meteorology and Atomic Energy – 1968, D.H.Slade, Ed.,
US AEC, TID-24190
Crandall, W.K. et. al, An Investigation Of Scavenging Of Radioactivity
From Nuclear Debris Clouds: Research In Progress,
Larwence Livermore Laboratory, 1973.
UCRL-51328, TID-4500
Sehmel, G.A., Particle And Gas Dry Deposition: A Review,
Atmospheric Environment, 14, pp.983-1011, 1980
(Dry deposition)
| Atmospheric | lodine (cm/s) | Cesiun (cm/s) |
| stability | ||
| A~F | 0.3 | 0.3 |
(Wet deposition)
| Atmospheric stability | Iodine (1/s)/(mm/hr) | Cesium (1/s)/(mm/hr) |
| A~D | 1.0E-03 | 2.0E-04 |
| E, F | 1.0E-04 |
Range assessed for deposition:
25km to the north of the power station
25km to the south of the power station
20km to the east (sea side) of the power station
30km to the west (land side) of the power station
Due to limitations imposed by the aforementioned specifications, there is uncertainty in the assessment.
3.3 Meteorological Data Used in Assessment (Figure 3-②)
The meteorological data input into DIANA comprises wind direction, wind velocity, atmospheric stability and rainfall, but, due to the loss of power following the earthquake and other such influences, the data is not limited to meteorological data from the Meteorological Observation System installed on site.
Wind direction and velocity were measured using monitoring cars (2m aboveground), which were arranged on the premises of the Fukushima Daiichi Nuclear Power Station at the time of the
accident.
Atmospheric stability was determined using the values for sunshine duration obtained at the Japan Meteorological Agency’s Funehiki AMEDAS observation station, which was not missing any observations due to power failure and is located comparatively close to the Fukushima Daiichi Nuclear Power Station.
The wind velocity at 10m aboveground, which was used in the assessment, was determined in accordance with the “Manual of Methodology for Environmental Impact Forecasting in Areas Surrounding the Source of Hazardous Air Contaminants (Ministry of Economy Trade and Industry, February 2008)” by using the atmospheric stability and wind velocity at 2m aboveground as measured by the monitoring cars.
With regard to wind direction, 16 directions measured by the monitoring cars were used.
DIANA takes into account geographical influences, and assesses changes in wind direction due to geographical influences at the time of dispersion.
With regard to rainfall, basically, those observation stations around the power station that were downwind at the time of the release of radioactive material were selected. It was confirmed whether or not the deposition amount actually measured by the Ministry of Education, Culture, Sports, Science and Technology was reproduced, and the rainfall amounts at the optimum observations stations (see Table 1 and Figure 4) were used.
| Table 1. AMEDAS Observation Points Used | ||
| Time period | Hourly rainfall | AMEDAS observation |
| (mm/h) | point used | |
| March 15 11:10~21:20 | 0~3 | Iitate |
| March 15 21:30~24:00 | 0~3 | Haramachi |
| March 16 | 0~3 | Kawamae |
| March 21 AM | 0~3 | Hirono |
| March 21 PM | 0~3 | Kawamae |
| March 22~23 AM | 0~3 | Hirono Note 1 |
| March 23 PM | 0~3 | Kawamae |
| March 25 0:00~18:00 | 0~3 | Tsushima |
| March 25 18:10~21:00 | 0~3 | Funehiki |
| March 25 21:10~March 26 | 0~3 | Hirono |
| March 30~31 | 0~3 | Namie Note 2 |
10-minute periods before and after, rainfall has been set at 3mm/h after taking into consideration the circumstances of other points and radar AMEDAS.
Note 2: The measurement for 8:00 on March 31 is missing. At the same point, there was no rainfall at 7:50, and there was rainfall (3mm/h) at 8:10. Rainfall has been set at 3mm/h after taking into consideration the circumstances of other points and radar AMEDAS.
3.4 Air Does Rates Used in Assessment (Figure 3-③)
Monitoring posts (Figure 5) are set up around the power station for ordinarily monitoring the release of radioactive material to monitor air dose rates. During the accident at Fukushima Daiichi Nuclear Power Station, the function of monitoring posts was lost following the loss of power sources, so monitoring cars were arranged within the power station premises to measure air dose rates and other indices during the accident. The monitoring data, which provides a record of the measurement results and events, is shown in Figures 6~25.
In addition to the times when events occurred such as venting of the primary containment vessel and building explosions, the release of radioactive material during the accident at the Fukushima Daiichi Nuclear Power Station is regarded to have been radioactive material released to the atmosphere from damaged primary containment vessels.
In cases where the air dose rate fluctuates significantly, the air dose rate data varies due to a plume passing directly over the area around an observation station, as shown in the reference materials. Also, even when a plume does not pass directly over the observation station, the air dose rate data fluctuates due to the impact of direct radiation from the plume.
From the aforementioned, in time periods when the air dose rate data fluctuates, it is possible to assess the release at that point in time as a time-course release rate by performing a dispersion calculation in detail based on the range in the rise of the air dose rate data.
In addition, when the air dose rate data do not vary, there are cases where there was a release event but no fluctuation in the air dose rate data and cases where there was no release per se. For periods where the air dose rate data do not vary, it is believed that there was no release large enough such as to cause a peak in the amount released. However, it has not been assumed that there was no release, but the assessment has been conducted in which it is postulated that there was a continuing release of radioactive material equivalent to 1 percent of the air dose rate data. Also, when fluctuations in actual measured data for the air dose rate are calculated, because of the fact that such were less than roughly 1% of the air dose rate (Table 2 and Figure 26), it can be said to be conservative in making the assessment to assume a release rate of 1% which is larger than even the fluctuation in the measured value for periods where the air dose rate data do not vary.
Table 2. Standard Deviation of Air Dose Rates in Time Periods where Peaks not Observed
| Time period | Location | Air dose rate | Standard |
| (μSv/h) | deviation (%) | ||
| March 12 22:00~22:30 | MP-4 vicinity | ~50 | 0.07% |
| March 14 0:00~2:00 | MP-2 vicinity | ~400 | 0.00% |
| March 15 15:30~16:30 | Main gate vicinity | ~500 | 0.89% |
| March 19 18:00~21:00 | Administrative building - North | ~3000 | 0.10% |
3.5 Release Circumstances at Each Time (Figure 3-④)
In cases where the unit releasing due to explosion, venting or other event has been identified, the assessment is performed as a release of the unit in question. However, from March 13 on, core damage and the release of radioactive material accompanying such damage occurred at multiple units, and radioactive material is thought to have been released from multiple locations (units) at the same time. However, the DIANA system specifications limit the releasing locations to one location, so the unit emitting the major release was estimated based on in-core conditions, various operating conditions, Fukuichi live camera video and other data, and the assessments were conducted using an event tree for the unit.
Release from stack height has been assumed in the case of venting, and release from the height of a building in the case of releases from an explosion or building.
3.6 Sorting According to Nuclide (Figure 3-⑤)
As stated above, DIANA, which treats radioactive material as the object of a dispersion calculation of 0.5MeV-equivalent virtual particles, was used to assess the amount of 0.5MeV-equivalent virtual particle released.
Then, energy conversion factors and other quotients pertaining to each nuclide are used to sort the amount of 0.5MeV-equivalent virtual particle released into the amount of radioactivity of the nuclides targeted for assessment, and to determine the amounts released.
Using the method described in section 3.4, where the release rate of 0.5MeV-equivalent virtual particles is assessed using DIANA at time t (R(t)), the approach to sorting by nuclide is given in the following equation.
R(t)=Q’(t)（100X(t)*C1＋10Y(t)*C2＋Z(t)*C3）
R(t): 0.5MeV-equivalent virtual particle release rate (Bq/s) calculated backwards using
DIANA from the air dose rate
X(t): Noble gas inventory (Bq) at time t
Y(t): Iodine inventory (Bq) at time t
Z(t): Cesium inventory (Bq) at time t
C1: Coefficient converting the noble gas inventory to 0.5MeV-equivalent value
C2: Coefficient converting the iodine inventory to 0.5MeV-equivalent value
C3: Coefficient converting the cesium inventory to 0.5MeV-equivalent value
Q’(t): Coefficient (1/s) for converting a certain released amount (0.5MeV-equivalent value) to a release rate determined from the air dose rate
Because the numerical values other than for Q’(t) are determined for each time t, Q’(t)
is determined. From the above equation, the release rate for each nuclide at time t is as
given below.
Noble gasNote 1: Q’(t)* 100C1* X(t)Bq/s
Iodine: Q’(t)*10C2* Y(t) Bq/s
Cesium: Q’(t)*C3* Z(t) Bq/s
Based on the above approach, the release rate has been assessed. The ORIGEN code has been used for in-core inventories, and, assuming a five-batch fuel conversion, it is assessed as the average composition. The ORIGEN code uses the characteristics of atomic nuclei (fission cross section, fission yield, decay constant, etc.), which are known as the nuclear data library, to find the amount of radioactivity resulting from disintegration and formation of fission products inside a reactor.
The results of an examination of ratio of the susceptibility of radioactive nuclides to release, such as reproducing the shape of a peak in the air dose rate, showed that the ratio of noble gases, iodine and cesium was 100:10:1. (See Chapter 2 of the Reference Material)
Noble gases are treated as not having been released from the time at which the entire
amount is assessed to have been released and thereafter. With regard to cesium, a ratio of
susceptibility to release which is the same respectively for both Cs-134 and Cs-137 was
used.
Note 1: The nuclides assessed are as follows:
Kr-79.80.81.81m.82.83.83m.84.85.85m.86.87.88.89.90.91.92.93.94.95.96.97.98
Xe-126.127.128.129.129m.130.131.131m.132.133.133m.134.134m.135.135m.136.
137.138.139.140.141.142.143.144.145.146.147
4 Assessment Results
4.1 Assessment Results of Amounts Released
The amounts released to the atmosphere during March 2011 as assessed using the
method described in the previous chapter (sum total of amount of radioactivity (Bq) at the time
of release) are given in Table 3. The assessment period is from March 12, 2011 until March 31,
and assessments for April and later account for less than 1% of the total amount for March as
shown in Attachment 1.
| Table 3. Assessment Results (Unit: PBq=1015Bq) | ||||
| INES assessment | ||||
| (0.5MeV-equivalent value) | I-131 | Cs-134 | Cs-137 | Note 1 |
| Approx. 500 | Approx. 500 | Approx. 10 | Approx. 10 | Approx. 900 |
Note 1: The International Nuclear Event Scale (INES) assessment is an iodine-converted
value of the amount of radioactivity. Here, because only limited nuclides are able to be
assessed, I-131 and Cs-137 were used to assess the scale of the accident. It has been
added to the assessment of only Cs-137.
(Ex.: Approx. 500PBq＋approx. 10PBq×40 (conversion factor) = approx. 900PBq)
4.2 Time Variation of Amount Released
The time variation of the amount released as described in section 4.1 is shown in Figure
27, and the time variation of the release rate is shown in Figure 28.
4.3 Results of Assessment of Amount of Radioactive Material Deposited
When the Cs-137 deposition amounts were assessed within the DIANA assessment range
based on the amount released as assessed by DIANA, it was assessed that there was
deposition of 0.6PBq on the land to the north (range of 30km west × 25km north) and
deposition of 0.5PBq on the land to the south ((range of 30km west × 25km south) of the
Fukushima Daiichi Nuclear Power Station, as shown in Table 4 (simplified illustration is
below the table). The deposition was 0.9PBq over a range extending 20km east (sea side)
× 50km north-south.
| Table 4. Amount of Cs-137 Deposited in Area | |
| Surrounding Fukushima Daiichi Nuclear Power Station (as of April 1 at 0:00) | |
| Deposition amount according to DIANA | |
| North side (25km) | 0.6PBq |
| South side (25km) | 0.5PBq |
| Total amount | 1PBq |
| (Illustration of range assessed for deposition amounts) | |
| Land | Sea | |||
| ↑ | 25km | |||
| 0.6PBq | 0.9PBq | |||
| ● | Fukushima Daiichi NPS | |||
| North | ||||
| 25km | 0.5PBq | |||
| 30km | 20km | |||
5 Discussion
5.1 Comparison of Amounts Released Against Assessment Results of Other Institutions
The results of assessments conducted by other institutions of the amounts released are
shown in Table 5. From these results, the amount of Cs-137 released is almost on par with
that announced by other institutions. Also, with regard to I-131, the results ended up being
approximately three times more than the assessment results of other institutions. Because
this assessment used a fixed ratio for the rate of the susceptibility to release from the in-core
inventory at Units 1~3 across the entire assessment period (However, the in-core inventory
for each time uses a calculated value which takes into consideration decay. See Chapter 2 of
the Reference Materials for specific details.), there is the possibility that the amount of I-131
released is greater. For instance, in the estimation of the amount of atmospheric discharge by
the Japan Atomic Energy AgencyNote 1, the results were that I-131 measured in the
environment and the release rate of Cs-137 fluctuated depending on the time of release (form
equivalent to approx. 100 times greater), and the ratio of susceptibility to release needs to
continue to be examined.
Note 1: Open workshop held on March 6, 2012
“Reconstructing the Dispersion Process and Environmental Release Resulting from the
Accident at Fukushima Daiichi Nuclear Power Station” (Sponsor: Japan Atomic Energy
Agency)
| Table 5. Assessment Results of Other Institutions | |||||||
| Announcement date | Amount Released (PBq) | ||||||
| Institution | Period Assessed | Noble | INES | ||||
| gases | I-131 | Cs-134 | Cs-137 | assessment | |||
| Japan Atomic Energy Agency | |||||||
| and | April 12, 2011 | March 11 ~ | － | 150 | － | 13 | 670 |
| Nuclear Safety Commission | April 5, 2011 | ||||||
| of Japan | |||||||
| Japan Atomic Energy Agency | |||||||
| and | August 22, 2011 | March 11 ~ | 130 | 11 | 570 | ||
| Nuclear Safety Commission | April 5, 2011 | ||||||
| of Japan | |||||||
| March 6, 2012 | March 11 ~ | 120 | 9 | 480 | |||
| Japan Atomic Energy Agency | April 10, 2011 | ||||||
| Nuclear and Industrial Safety | April 12, 2011 | － | － | 130 | － | 6.1 | 370 |
| Agency | |||||||
| Nuclear and Industrial Safety | June 6, 2011 | － | － | 160 | 18 | 15 | 770 |
| Agency | |||||||
| Nuclear and Industrial Safety | February 16, 2012 | － | － | 150 | － | 8.2 | 480 |
| Agency | |||||||
| French Institute de | March 12 ~ | ||||||
| radioprotection et de sûreté | March 22, 2011 | 2000 | 200 | 30 | |||
| nucléaire ( IRSN Note 2 ) | March 22, 2011 | ||||||
| Note 2: IRSN assessed noble gases, iodine and cesium. The data were not arranged according | |||||||
| to each nuclide, so a simple comparison cannot be made against this assessment | |||||||
5.2 Comparison Against Actually Measured Deposition Amounts
Surveys have been conducted of deposition amounts of radioactive materials by the Panel
on Creation of Maps of Distributions of Radiation Doses, etc. of the Ministry of Education,
Culture, Sports, Science and Technology. The surveys were conducted over the period from
June until July 2011, and the revised results (amount of radioactivity) were released for
deposition amounts as of June 14, 2011. (See Figure 29) Based on those survey results, the
deposition amounts for Cs-137, Cs-134 and I-131 were computed for a land range extending
50km north-south and 30km east-west, which includes the Fukushima Daiichi Nuclear Power
Station. The results are as follows. With DIANA, it was decided to make a comparison of the
deposition amounts as of March 31, and, because the half-life of Cs-137 is longer than
Cs-134 or I-131, the comparison was against the deposition amount of Cs-137 as of June 14.
| Table 6. Calculated from Results (Deposition Amounts) of Surveys Conducted by | ||
| Ministry of Education, Culture, Sports, Science and Technology | ||
| Cs-137 | (Reference) Cs-134 | (Reference) I-131 |
| (North side) 0.8PBq | (North side) 0.7PBq | (North side) 1E-3 PBq |
| (South side) 0.3PBq | (South side) 0.3PBq | (South side) 8E-4 PBq |
| (Total) 1 PBq | (Total) 1 PBq | (Total) 2E-3 PBq |
From a comparison of the DIANA assessment results and the survey results of the Ministry
of Education, Culture, Sports, Science and Technology regarding Cs-137, the following were
found.
① The total deposition amounts largely coincided.
② According to the survey results of the Ministry of Education, Culture, Sports, Science
and Technology, the deposition amounts for Cs-134 and Cs-137 were almost the
same, so the amount of Cs-134 and Cs-137 released from the power station is
regarded as having been the same, and the amounts were consistent also with the
results of this assessment.
③ According to the survey results of the Ministry of Education, Culture, Sports, Science
and Technology, the deposition amount on the north side was larger than that on the
south side, but the south and north had equal values in the results of our estimation.
When making this assessment of the deposition amount, wind directions were
reproduced for 16 directions using a monitoring car within the site, so it is
conceivable that an error of measurement occurred for the south-north direction.
A comparison of the results of airborne monitoring by the Ministry of Education, Culture,
Sports, Science and Technology (Figure 30) and the deposition assessment results by
DIANA is shown in Figure 31. According to this comparison, although there are some
differences regarding the direction of high contamination in assessment of the northwest
direction, DIANA also reproduced a trend in which there was large deposition in the
northwest direction. This is considered to have been able to largely recreate the release
trend by employing rainfall data from observation stations downwind at times of rainfall when
the deposition amount increases.
5.3 Assessed Values for Periods Where Air Dose Rate Data Fluctuate
Of the assessments of release amounts as stated above, the assessed values for periods
where the air dose rate fluctuated are shown in Table 7, and a more detailed breakdown is
given in Table 8. The assessed values for the amounts released during the period where
the air dose rate fluctuated account for a large proportion of the total amount of the period
from March 12 thru 31, 2011.
Table 7. Sum Total of Assessed Values for Period Where Air Dose Rate Fluctuated (Unit: PBq)
| Noble gases | I-131 | Cs-134 | Cs-137 |
| Approx. 500 | Approx. 400 | Approx. 10 | Approx. 8 |
| Table 8. Assessed Values for Periods Where Air Dose Rates Fluctuated | ||||||||||
| NO | Putative | Release | Noble | Basis for unit selection (due to limitations in terms of DIANA specifications, the unit with the largest release has been selected) | ||||||
| TIME | Time | releasing | height | gases | I-131 | Cs-134 | Cs-137 | |||
| unit | (m) | (PBq) | (PBq) | (PBq) | (PBq) | |||||
| 1 | March 12 | 04:00 | 10:10 | 1 | ~30 | 20 | 3 | 0.06 | 0.04 | Only Unit 1 had core damage and venting operations were not executed, so this is regarded as a building release. |
| 2 | 10:10 | 10:50 | 1 | ~120 | 3 | 0.5 | 0.01 | 0.008 | Because S/C vent valve operation was implemented at Unit 1, this is regarded as a stack release. (Actually, it is unclear whether or not venting was able to be performed.) | |
| 3 | 10:50 | 14:00 | 1 | ~30 | 0.2 | 0.03 | 6E-04 | 4E-04 | Same as No. 1. | |
| 4 | 14:00 | 15:10 | 1 | ~120 | 4 | 0.7 | 0.01 | 0.01 | Same as No. 2. | |
| 5 | 15:30 | 15:40 | 1 | ~30 | 10 | 3 | 0.05 | 0.04 | Because a building explosion occurred at Unit 1, this is regarded as a building release. | |
| 6 | 18:00 | 24:00 | 1 | ~30 | 3 | 0.5 | 0.01 | 0.008 | Same as No. 1. | |
| 7 | March 13 | 08:00 | 09:00 | 1 | ~30 | 3 | 0.7 | 0.02 | 0.01 | The timing was prior to Unit 3 sustaining core damage, and the Unit 1 building where the refueling floor was blown off is regarded as the release location. |
| 8 | 09:00 | 09:10 | 3 | ~120 | 1 | 0.3 | 0.005 | 0.003 | Based on the venting results, this is regarded as a stack release. | |
| 9 | 13:30 | 17:00 | 3 | ~30 | 20 | 4 | 0.07 | 0.05 | Because no major fluctuations were seen in D/W pressure at Units 1 and 2 and a vent valve operation was not executed for Unit 3, this is regarded as a building release. | |
| 10 | March 14 | 02:00 | 04:00 | 3 | ~30 | 10 | 7 | 0.1 | 0.09 | Because the reproducibility of changes in dose rate was good compared to cases where other release locations are hypothesized, the Unit 3 building is regarded as the release location. |
| 11 | 07:20 | 09:20 | 3 | ~30 | 2 | 1 | 0.02 | 0.02 | Same as No. 9. | |
| 12 | 11:00 | 11:10 | 3 | ~30 | 1 | 0.7 | 0.01 | 0.009 | Because a building explosion occurred at Unit 3, this is regarded as a building release. | |
| 13 | 21:20 | 22:20 | 2 | ~120 | 60 | 40 | 0.9 | 0.6 | Although it is unclear where the release location is, the assessment was made assuming that the release came from the Unit 1 and 2 stack. (See Attachment 3 Chapter 3.2) | |
| 14 | March 15 | 06:10 | 07:20 | 1 | ~30 | 5 | 4 | 0.1 | 0.07 | Because there was no change in the D/W internal pressure at Units 2 and 3, this is regarded as a Unit 1 building release. |
| 15 | 07:20 | 10:20 | 2 | ~30 | 80 | 60 | 1 | 0.9 | See Chapter 5.5. | |
| 16 | 21:30 | 24:00 | 2 | ~30 | 50 | 40 | 0.9 | 0.6 | Same as above. | |
| 17 | March 16 | 10:00 | 13:00 | 3 | ~30 | 100 | 100 | 2 | 2 | Because a large volume of white smoke was confirmed to have been emitted from the reactor building at 8:30 and the Unit 3 D/W pressure decreased, this is regarded as a building release. |
| 18 | March 18 | 15:20 | 17:30 | 1 | ~30 | 20 | 20 | 0.7 | 0.5 | Because there was no change in the D/W pressure at Units 2 and 3, this is regarded as a Unit 1 building release. |
| 19 | March 19 | 07:50 | 08:00 | 3 | ~30 | 30 | 30 | 0.9 | 0.6 | Because the Unit 3 D/W pressure changed, this is regarded as a building release. |
| 20 | 08:30 | 08:40 | 3 | ~30 | 7 | 6 | 0.2 | 0.1 | ||
| 21 | 09:30 | 09:40 | 3 | ~30 | 2 | 1 | 0.04 | 0.03 | ||
| 22 | March 20 | 03:40 | 03:50 | 2 | ~30 | 0 | 1 | 0.03 | 0.02 | Because the reproducibility of changes in dose rate was good compared to cases where other release locations are hypothesized, the Unit 2 building is regarded as the release location. |
| 23 | 09:30 | 09:50 | 2 | ~30 | 0 | 0.2 | 0.008 | 0.006 | ||
| 24 | 13:50 | 16:40 | 2 | ~30 | 0 | 20 | 0.5 | 0.4 | ||
| 25 | 19:50 | 20:10 | 2 | ~30 | 0 | 4 | 0.1 | 0.09 | ||
| 26 | March 21 | 16:20 | 16:30 | 2 | ~30 | 0 | 2 | 0.07 | 0.05 | Because it was confirmed that steam was rising from Unit 2 at 18:20, the Unit 2 building is regarded as the release location. |
| 27 | 17:00 | 18:00 | 2 | ~30 | 0 | 5 | 0.2 | 0.1 | ||
| 28 | March 22 | 15:10 | 16:30 | 3 | ~30 | 0.2 | 0.3 | 0.01 | 0.007 | Because it was confirmed that smoke was rising from Unit 3 at 7:11, the Unit 3 building is regarded as the release location. |
| 29 | March 23 | 13:40 | 16:00 | 3 | ~30 | 2 | 6 | 0.2 | 0.2 | Because it was confirmed that black smoke was rising from Unit 3 reactor building at 16:20, the Unit 3 building is regarded as the release location. |
| 30 | March 25 | 10:10 | 10:30 | 1 | ~30 | 8 | 10 | 0.6 | 0.4 | Because the Unit 1 D/W pressure changed, the Unit 1 building is regarded as the release location. |
| 31 | 18:30 | 21:00 | 1 | ~30 | 0.6 | 0.8 | 0.05 | 0.04 | ||
| 32 | March 28 | 08:40 | 08:50 | 2 | ~30 | 0 | 0.6 | 0.04 | 0.03 | Because the Unit 2 D/W pressure changed, the Unit 2 building is regarded as the release location. |
| 33 | 09:40 | 17:00 | 2 | ~30 | 0 | 20 | 1 | 0.9 | ||
| 34 | March 29 | 04:20 | 05:50 | 1 | ~30 | 1 | 2 | 0.2 | 0.1 | Because the Unit 1 D/W pressure changed, the Unit 1 building is regarded as the release location. |
| 35 | 06:50 | 11:50 | 1 | ~30 | 4 | 6 | 0.5 | 0.4 | ||
| 36 | 14:50 | 16:20 | 1 | ~30 | 0.7 | 1 | 0.1 | 0,07 | ||
| 37 | 16:50 | 18:20 | 1 | ~30 | 0.1 | 0.2 | 0.02 | 0.01 | ||
| TOTAL | 500 | 400 | 10 | 8 | ||||||
| Guide: S/C: Suppression chamber; D/W: Dry well; MAAP: Modular Accident Analysis Program | ||||||||||
5.4 Assessed Values for Periods Where Air Dose Rate Data Do Not Fluctuate
The assessed values for the amount released during periods where air dose rate data do
not fluctuate are shown in Table 9.
| Table 9. Amounts Released in Periods Where Air Dose Rate Data Do Not Fluctuate | ||||||||
| No | Date | Time | Release height | Novle gases | I-131 | Cs-134 | Cs-137 | |
| (m) | (PBq) | (PBq) | (PBq) | (PBq) | ||||
| 1 | March 12 | 03:00 | 04:00 | ~30 | 0.000002 | 0.0000002 | 0.000000004 | 0.000000003 |
| 2 | 15:10 | 15:30 | ~30 | 0.00008 | 0.00002 | 0.0000004 | 0.0000003 | |
| 3 | 15:40 | 18:00 | ~30 | 0.003 | 0.0006 | 0.00001 | 0.00001 | |
| 4 | March 13 | 00:00 | 08:00 | ~30 | 0.001 | 0.0003 | 0.000006 | 0.000004 |
| 5 | 09:10 | 11:00 | ~120 | 0.001 | 0.0003 | 0.000005 | 0.000003 | |
| 6 | 11:00 | 12:30 | ~30 | 0.002 | 0.0004 | 0.000007 | 0.000005 | |
| 7 | 12:30 | 3:30 | ~120 | 0.04 | 0.009 | 0.0002 | 0.0001 | |
| 8 | 17:00 | 20:40 | ~30 | 0.003 | 0.001 | 0.00003 | 0.00002 | |
| 9 | 20:40 | 24:00 | ~120 | 0.003 | 0.001 | 0.00002 | 0.00002 | |
| 10 | March 14 | 00:00 | 02:00 | ~30 | 0.01 | 0.007 | 0.0001 | 0.00009 |
| 11 | 04:00 | 05:20 | ~30 | 0.01 | 0.005 | 0.00009 | 0.00006 | |
| 12 | 05:20 | 07:20 | ~30 | 0.07 | 0.04 | 0.0007 | 0.0005 | |
| 13 | 09:20 | 11:00 | ~30 | 0.004 | 0.002 | 0.00004 | 0.00003 | |
| 14 | 11:10 | 21:20 | ~30 | 0.002 | 0.001 | 0.00002 | 0.00002 | |
| 15 | 22:20 | 23:40 | ~120 | 0.00003 | 0.00002 | 0.0000005 | 0.0000003 | |
| 16 | 23:40 | 24:00 | ~30 | 0.008 | 0.005 | 0.0001 | 0.00008 | |
| 17 | March 15 | 00:00 | 06:10 | ~30 | 0.02 | 0.02 | 0.0003 | 0.0002 |
| 18 | 10:20 | 16:10 | ~30 | 7 | 5 | 0.1 | 0.08 | |
| 19 | 16:10 | 20:50 | ~30 | 0.5 | 0.4 | 0.009 | 0.006 | |
| 20 | 20:50 | 21:30 | ~30 | 1 | 0.9 | 0.02 | 0.01 | |
| 21 | March 16 | 00:00 | 02:20 | ~30 | 0.3 | 0.3 | 0.006 | 0.004 |
| 22 | 02:20 | 06:20 | ~30 | 6 | 4 | 0.1 | 0.07 | |
| 23 | 06:20 | 08:30 | ~30 | 1 | 0.8 | 0.02 | 0.01 | |
| 24 | 08:30 | 10:00 | ~30 | 0.7 | 0.6 | 0.01 | 0.009 | |
| 25 | 13:00 | 24:00 | ~30 | 1 | 1 | 0.02 | 0.02 | |
| 26 | March 17 | 00:00 | 21:30 | ~30 | 0.03 | 0.03 | 0.0007 | 0.0005 |
| 27 | 21:30 | 21:40 | ~30 | 30 | 40 | 1 | 0.8 | |
| 28 | 21:40 | 24:00 | ~30 | 0.004 | 0.003 | 0.00009 | 0.00006 | |
| 29 | March 18 | 00:00 | 05:30 | ~30 | 0.09 | 0.08 | 0.003 | 0.002 |
| 30 | 05:30 | 07:20 | ~30 | 0 | 2 | 0.07 | 0.05 | |
| 31 | 07:20 | 15:20 | ~30 | 0.1 | 0.1 | 0.004 | 0.003 | |
| 32 | 17:30 | 24:00 | ~30 | 0.1 | 0.1 | 0.004 | 0.003 | |
| 33 | March 19 | 00:00 | 07:50 | ~30 | 0.06 | 0.06 | 0.002 | 0.001 |
| 34 | 08:00 | 08:30 | ~30 | 0.004 | 0.004 | 0.0001 | 0.00008 | |
| 35 | 08:40 | 09:30 | ~30 | 0.007 | 0.006 | 0.0002 | 0.0001 | |
| 36 | 09:40 | 24:00 | ~30 | 0.1 | 0.1 | 0.004 | 0.003 | |
| 37 | March 20 | 00:00 | 03:40 | ~30 | 0 | 0.9 | 0.03 | 0.02 |
| 38 | 03:50 | 09:30 | ~30 | 0 | 0.5 | 0.01 | 0.01 | |
| 39 | 09:50 | 11:20 | ~30 | 0 | 0.2 | 0.006 | 0.004 | |
| 40 | 11:20 | 12:50 | ~30 | 0 | 0.2 | 0.006 | 0.004 | |
| 41 | 12:50 | 13:50 | ~30 | 0 | 0.1 | 0.004 | 0.003 | |
| 42 | 16:40 | 19:50 | ~30 | 0 | 0.7 | 0.02 | 0.02 | |
| 43 | 20:10 | 24:00 | ~30 | 0 | 7 | 0.2 | 0.2 | |
| 44 | March 21 | 00:00 | 16:20 | ~30 | 0 | 1 | 0.04 | 0.02 |
| 45 | 16:30 | 17:00 | ~30 | 0 | 0.03 | 0.001 | 0.0007 | |
| 46 | 18:00 | 24:00 | ~30 | 0 | 0.2 | 0.008 | 0.006 | |
| 47 | March 22 | 00:00 | 15:10 | ~30 | 0.3 | 0.3 | 0.01 | 0.007 |
| 48 | 16:30 | 24:00 | ~30 | 0.1 | 0.1 | 0.005 | 0.003 | |
| 49 | March 23 | 00:00 | 13:40 | ~30 | 0.3 | 0.3 | 0.01 | 0.008 |
| 50 | 16:00 | 24:00 | ~30 | 0 | 0.2 | 0.008 | 0.005 | |
| 51 | March 24 | 00:00 | 24:00 | ~30 | 0 | 3 | 0.1 | 0.1 |
| 52 | March 25 | 00:00 | 10:10 | ~30 | 0.04 | 0.04 | 0.003 | 0.002 |
| 53 | 10:30 | 18:30 | ~30 | 0.03 | 0.03 | 0.002 | 0.002 | |
| 54 | 21:00 | 24:00 | ~30 | 0.01 | 0.01 | 0.0009 | 0.0006 | |
| 55 | March 26 | 00:00 | 24:00 | ~30 | 0 | 0.2 | 0.01 | 0.008 |
| 56 | March 27 | 00:00 | 24:00 | ~30 | 0 | 0.2 | 0.01 | 0.009 |
| 57 | March 28 | 00:00 | 08:40 | ~30 | 0 | 0.09 | 0.006 | 0.004 |
| 58 | 08:50 | 09:40 | ~30 | 0 | 0.009 | 0.0006 | 0.0004 | |
| 59 | 17:00 | 24:00 | ~30 | 0 | 0.08 | 0.006 | 0.004 | |
| 60 | March 29 | 00:00 | 04:20 | ~30 | 0.02 | 0.03 | 0.002 | 0.002 |
| 61 | 05:50 | 06:50 | ~30 | 0.004 | 0.006 | 0.0005 | 0.0004 | |
| 62 | 11:50 | 14:50 | ~30 | 0.01 | 0.02 | 0.002 | 0.001 | |
| 63 | 16:20 | 16:50 | ~30 | 0.002 | 0.003 | 0.0003 | 0.0002 | |
| 64 | 18:20 | 24:00 | ~30 | 0.02 | 0.4 | 0.003 | 0.002 | |
| 65 | March 30 | 00:00 | 24:00 | ~30 | 0.02 | 0.4 | 0.003 | 0.002 |
| 66 | March 31 | 00:00 | 24:00 | ~30 | 0.02 | 0.4 | 0.004 | 0.003 |
| Total | 50 | 70 | 2 | 1 | ||||
5.5 Assessment of Each Event
The results in the previous chapter have been compiled and the assessment results for
the release amounts as assessed for each event, including explosions which occurred at
Units 1~3, venting and so on, are shown in Table 10.
The sum total released due to these events is approximately 1/10 of the sum total
calculated in regard to Cs-137. As stated previously, in addition to calculation of the
amounts released being premised on conservative assumptions, it is believed that these
results are because of continuing building releases due to leaks from the primary
containment vessel as well as these events.
Table 10. Amounts Released by Event
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