Transcript Level 3 PSA Accident Consequence Assessment Methodology

Consideration of Off-site Emergency Planning
and Response using Probabilistic Accident
Consequence Assessment Models
M. Kimura, J. Ishikawa and T. Homma
Nuclear Safety Research Center
Japan Atomic Energy Agency (JAEA)
NREP Conference, April 22, 2009
Background
 IAEA Safety Requirements (GS-R-2, 2002)
Safety Guide (GS-G-2.1, 2007)
– Management approach
– Practical goals (8 goals)
 Prevent the occurrence of deterministic health effects
 Prevent, to the extent practicable, the occurrence of stochastic health
effects
– Intervention principles
– Efficient and cost-effective system
 ICRP (Publ.103, 2007)
Optimization of overall strategy
 Japan (NSC’s Guideline on emergency preparedness)
– No practical guidance for protective measure strategy
–
2
Objectives
Perform a risk informed analysis of protective measures
using Level 3PSA code (OSCAAR), in order to formulate
the technical basis for the effective strategy of protective
measures
– Introduce a metabolic model of iodine to accurately
evaluate the effect of reducing thyroid dose by
administration of stable iodine
– Combination of protective measures, sheltering and
evacuation with administration of stable iodine
3
Accident Consequence Model
OSCAAR (Off-Site Consequence Analysis of
Atmospheric Releases of radionuclides)
CURRENT
Meteorological
data
Meteorological
sampling
HEINPUT
DOSDAC
Population
Agricultural
data
MS
Source
term
Atmospheric
dispersion
HE
Early
exposure
EARLY
Protective
measure
PM
Deposition
ADD
Health
effect
Economic
loss
Chronic
exposure
HINAN
ECONO
CHRONIC
OSCAAR module
Preprocessor code
4
Models of OSCAAR
Atmospheric Dispersion and Deposition
 Multi-puff trajectory model with two scale wind fields
 Take account of temporal changes in weather conditions and variable
long duration releases
Meteorological Sampling
 Stratified sampling scheme appropriate for use with the trajectory
dispersion model was designed and developed
 Select a representative sample of weather sequences for analysis
Exposure Pathways
 Realistic estimates for all possible exposure pathways with protective
measures with simple models such as sheltering, evacuation, relocation
and food ban
– Shielding and filtering factors for sheltering
– Radial evacuation
5
Metabolic Model of Iodine
Reduction in the committed thyroid dose to man
(for adult, 100mg)
Johnson model (1981)
1  192 d 1
INORGANIC
INORGANIC
5  1.92 d 1
IODINE, Y
2
IODINE,
Y2
s2
r2
4  0.053 d 1
BLADDER
EXCRETA
EXCRETA
THYROID, Y3
Y3
THYROID,
3  s2 / M t
ORGANIC
ORGANIC
IODINE, Y4
Y4
IODINE,
6  0.005 d
1
r2  s2 (Y2r / Y2s )
r2 , s2 : the rate of uptake of radioactive and stable
iodine by the thyroid
 : the rate constant for uptake or excretion of
iodine from each compartment
Reduction factor
(Intake of stable iodine/ No measurement)
GUT
Y1
GUT or
or LUNG,
LUNG, Y
1
1.0
0.8
0.6
0.4
0.2
0.0
-80
-60
-40
-20
0
20
40
Time (h) before or after an intake of radioiodine
6
0
-1
10
-1
10
-2
10
-2
10
-3
10
-3
10
-4
10
-4
10
-5
10
-5
10
-6
10
-6
10
-7
10
-7
10
-8
10
-8
10
-9
10
-9
10
-10
TQUV-ψ-l
TBU-ψ-l
AE-ψ-l
TQUV-υ-l
TQUX-υ-l
TB-υ-l
TBU-υ-l
AE-υ-l
V-ν
TW-θ
TC-θ
▲ JAEA evaluation
TQUV-δ
TQUX-δ
TB-δ
TBU-δ
AE-δ
10
-10
:Relative failure frequency
(each / all containment failure scenarios)
10
TQUX-σ
TB-σ
TBU-σ
10
BWR5/Mk-II
of iodine
● Release fraction
環境へのヨウ素の放出割合
□ Relative failure発生頻度/全格納容器破損頻度
frequency (from INS/M03-22)
TQUX-μ
TB-μ
TBU-μ
10
0
TQUV-α
TQUX-α
TB-α
TBU-α
AE-α
●: Release fraction of Iodine
Source Term Development
・10-1 Iodine release fraction ：Energetic events, Overpressure, ISLOCA
・10-5～10-4
：Containment vent
・10-7～10-8
：Termination
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炉内
水蒸気爆発
高圧溶融物
DCH
噴出
ISLOCA 格納容器
ベント
TQUV-ψ-l
TBU-ψ-l
AE-ψ-l
TQUV-υ-l
TQUX-υ-l
TB-υ-l
TBU-υ-l
AE-υ-l
過圧破損
V-ν
TW-θ
TC-θ
TQUV-δ
TQUX-δ
TB-δ
TBU-δ
AE-δ
●Release 環境への放出開始時刻
time (hr)
発生頻度/全格納容器破損頻度
□Relative failure frequency (from INS/M03-22)
▲JAEA
evaluation
JAEAにおける評価値
10-1
80
10-2
70
10-3
60
10-4
50
10-5
40
10-6
30
10-7
20
10-8
10
10-9
0
10-10
100
(each / all containment failure scenarios)
:Relative failure frequency [-]
発生頻度/全格納容器破損頻度
BWR5/Mk-II
TQUX-σ
TB-σ
TBU-σ
90
TQUX-μ
TB-μ
TBU-μ
100
TQUV-α
TQUX-α
TB-α
TBU-α
AE-α
●: Release time (hr)
環境への放出開始時刻[hr]
Source Term Development (Cont’d)
事故終息
8
Source terms and PM strategy
Three source term scenarios
Release scenario
Release time
(hr after scram)
Duration of
release (hr)
Release fraction
of iodine (%)
Large early release
3
1
7.9
Large late release
27
7
3.3
Control release
12
22
0.09
Strategies of protective measures
Large early release: precautionary evacuation with stable iodine intake
Large late release: evacuation and sheltering with stable iodine intake
Control release: sheltering with stable iodine intake
Site data
A reference site is assumed to be located at a coastal area facing the Pacific
Ocean (JAEA site at Tokai)
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Steps for Consequence Evaluation
 Calculation
of dose from each pathway and time-dependent iodine
concentrations in air at receptor points using OSCAAR
‒ 248 weather sequences selected by a stratified sampling method
 Calculation
of dose reduction effects by various combinations of
protective measures
‒ Intervention levels for implementing each protective measure (NSC’s Guideline)
Sheltering：10 mSv, Evacuation：50 mSv（effective dose）
Administration of stable iodine ：100 mSv (thyroid equivalent dose for infants)
‒ Inhalation dose due to isotope iodine based on I-131~135 contents in thyroid using
Johnson model
 Calculation
of maximum dose at
each distance from the site and
its probability of weather sequence
‒ Probability of exceeding a specific dose level
‒ Dose at each distance from the site at a specific
cumulative probability of weather sequences
Find a maximum dose
at each distance and
each weather sequence
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Large Early Release
 Effect of the reduction for the thyroid dose
due to the delay of evacuation and SI intake
 Effect of the reduction for the effective dose
due to protective measures
2
10
95% Met
10
Thyroid dose (Sv)
50% Met
1
Effective dose (Sv)
No
Shl
Evac
0
10
-1
10
Evacuation
-2
10
Sheltering
-3
10
10
4
10
3
10
2
10
1
10
0
10
-1
10
-2
10
-3
10
-4
10
-5
No
Evac
Evac(3h)
Evac(3h)+SI(0h)
Evac(3h)+SI(3h)
95% Met
50% Met
Stable
iodine
-4
10
-5
10
0.1
1
10
Distance from the release point (km)
100
0.1
1
10
100
Distance from the release point (km)
 For large early release, precautionary evacuation is needed before the start of release.
‒ It is important to develop the preparedness action before occurring accident (e.g. EAL:
emergency action level, PAZ: precautionary action zone)
 Early stable iodine intake can be very effective to reduce the thyroid dose for the people within
about 20 km from the site even the delay of evacuation (consideration of distribution method).
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Large Late Release
 Effect of the reduction for the thyroid dose
due to protective measures
 Effect of the reduction for the effective dose
due to protective measures
1
2
10
95% Met
50% Met
No
Shl
Evac
0
1
10
-1
10
Evacuation
-2
10
Sheltering
-3
-1
10
Stable
iodine
10
-4
0.1
0
10
-2
10
10
No
Shl
Shl+SI
Evac
Evac+SI
95% Met
50% Met
Thyroid dose (Sv)
10
Effective dose (Sv)
10
-3
1
10
Distance from the release point (km)
100
10
0.1
1
10
100
Distance from the release point (km)
 For large late release, evacuation and sheltering areas can be decided to consider weather
conditions at the time of accident.
 In this scenario, evacuation and sheltering area are unlikely to occur beyond 20 km and 50 km.
 Sheltering or evacuation with administration of stable iodine is very important to reduce the thyroid
dose.
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Control Release

 Effect of the reduction for the thyroid dose
due to sheltering and intake of stable iodine
Effective dose for distance from the release
point
0
1
10
10
-1
10
Evacuation
Sheltering
-2
10
-3
10
0.1
Thyroid dose (Sv)
Effective dose (Sv)
Met 50%
Met 95%
95% Met
50% Met
No
Shl
Shl+SI
0
10
-1
10
Stable
iodine
-2
10
-3
1
10
Distance from the release point (km)
100
10
0.1
1
10
100
Distance from the release point (km)
 For control release, evacuation area is unlikely to occur beyond a few kilometers and
sheltering area is unlikely to occur beyond about 10 km.
 For very severe weather conditions, sheltering with stable iodine intake is needed.
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Conclusions
For the representative source terms, the preliminary analysis has been performed using
the probabilistic accident consequence model (OSCAAR) to evaluate the effectiveness
of protective action strategy involving a combination of evacuation, sheltering and
administration of stable iodine.
The study indicated following findings for three release scenarios.
Large early release
Precautionary evacuation is needed before the start of release.
Early stable iodine intake can be very effective to reduce the thyroid dose even the delay of
evacuation.
It is important to develop the preparedness action before occurring accident (e.g. EAL, PAZ,
method for distribution of stable iodine).
Large late release
Evacuation and sheltering areas can be decided to consider weather conditions at the time
of accident.
Sheltering or evacuation with administration of stable iodine is very important to reduce the
thyroid dose.
Control release
Evacuation area is unlikely to occur beyond a few kilometers and sheltering area is unlikely
to occur beyond about 10 km.
For very severe weather conditions, sheltering with stable iodine intake is needed.
14