Consideration of Off-site Emergency Planning Consideration of Off-site Emergency Planning and Response using Probabilistic Accident and Response using Probabilistic Accident

Consequence Assessment ModelsConsequence Assessment Models

Consideration of Off-site Emergency Planning Consideration of Off-site Emergency Planning and Response using Probabilistic Accident and Response using Probabilistic Accident

Consequence Assessment ModelsConsequence Assessment Models

M. Kimura, J. Ishikawa and T. Homma

Nuclear Safety Research Center

Japan Atomic Energy Agency (JAEA)

NREP Conference, April 22, 2009

2

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 e

ffects

– 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

BackgroundBackground

3

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

ObjectivesObjectives

4

Accident Consequence ModelAccident Consequence Model

CHRONIC

Atmosphericdispersion

ProtectivemeasureSource

term

MS

Chronicexposure

ADD

EARLY PM

ECONO

PopulationAgricultural

data

HE

Healtheffect

HEINPUT

HINAN

CURRENT

DOSDAC

Economicloss

Earlyexposure

Meteorologicalsampling

Deposition

Meteorologicaldata

OSCAAR (Off-Site Consequence Analysis of Atmospheric Releases of radionuclides)

OSCAAR module

Preprocessor code

5

Models of OSCAARModels of OSCAAR

Atmospheric Dispersion and DepositionMulti-puff trajectory model with two scale wind fieldsTake account of temporal changes in weather conditions and variable long duration releases

Meteorological SamplingStratified sampling scheme appropriate for use with the trajectory dispersion model was

designed and developedSelect a representative sample of weather sequences for analysis

Exposure PathwaysRealistic 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

6

Metabolic Model of IodineMetabolic Model of Iodine

GUT or LUNG, Y1

THYROID, Y3

ORGANIC IODINE, Y4

BLADDEREXCRETA

INORGANIC IODINE, Y2

s2 r2

GUT or LUNG, Y1

THYROID, Y3

ORGANIC

IODINE, Y4

BLADDEREXCRETA

INORGANIC

IODINE, Y2

s2 r2

11 192 d

14 053.0 d

15 92.1 d

16 005.0 d

tMs /23

)/( 2222sr YYsr

Johnson model (1981) Reduction in the committed thyroid dose to man (for adult, 100mg)

Reduction in the committed thyroid dose to man (for adult, 100mg)

: the rate of uptake of radioactive and stable iodine by the thyroid

22 , sr

: the rate constant for uptake or excretion of iodine from each compartment

0.0

0.2

0.4

0.6

0.8

1.0

-80 -60 -40 -20 0 20 40

Time (h) before or after an intake of radioiodine

Red

uct

ion

fac

tor

(In

take

of

stab

le i

od

ine/

No

me

asu

rem

ent)

7

Source Term DevelopmentSource Term Development

　・ 10-1 Iodine release fraction 　： Energetic events, Overpressure, ISLOCA　・ 10-5 ～ 10-4 　　　　　　　　　　　　　　　　　　： Containment vent　・ 10-7 ～ 10-8 　　　　　　　　　　　　　　　　　　： Termination

環境へのヨウ素の放出割合 発生頻度 / 全格納容器破損頻度

:Rel

ativ

e fa

ilur

e fr

eque

ncy

(eac

h /

all c

onta

inm

ent f

ailu

re s

cena

rios

)

TQUV-α

TQUX-α

TB-α

TBU-α

AE-α

TQUX-μ

TB-μ

TBU-μ

TQUX-σ

TB-σ

TBU-σ

TQUV-δ

TQUX-δ

TB-δ

TBU-δ

AE-δ

TW-θ

TC-θ

V-ν

TQUV

-υ-l

TQUX

-υ-l

TB-υ

-lTB

U-υ-

lAE

-υ-l

TQUV

-ψ-l

TBU-

ψ-l

AE-ψ

-l

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100BWR5/Mk-II

●: R

elea

se f

ract

ion

of I

odin

e

●□ Relative failure frequency (from INS/M03-22)

▲ JAEA evaluation

Release fraction of iodine

8

●Release time (hr) □Relative failure frequency (from INS/M03-22)

●:

Rel

ease

tim

e (h

r)

▲JAEA evaluation

Source Term Development (Cont’d)

:Rel

ativ

e fa

ilur

e fr

eque

ncy

(eac

h /

all c

onta

inm

ent f

ailu

re s

cena

rios

)

9

Strategies of protective measuresLarge early release: precautionary evacuation with stable iodine intakeLarge late release: evacuation and sheltering with stable iodine intakeControl release: sheltering with stable iodine intake

Site dataA reference site is assumed to be located at a coastal area facing the Pacific

Ocean (JAEA site at Tokai)

Source terms and PM strategy

Release scenarioRelease 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

Three source term scenarios

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全方位の 最大値

rn ri r2 r1

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) Sh

eltering ： 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

Steps for Consequence Evaluation

Find a maximum dose at each distance and each weather sequence

Calculation of maximum dose ateach 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

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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).

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).

Large Early Release

0.1 1 10 10010-5

10-4

10-3

10-2

10-1

100

101

102

No Shl Evac

Distance from the release point (km)

Eff

ect

ive

do

se (

Sv)

95% Met

50% Met

Sheltering

Evacuation

0.1 1 10 10010-5

10-4

10-3

10-2

10-1

100

101

102

103

104

No Evac Evac(3h) Evac(3h)+SI(0h) Evac(3h)+SI(3h)

Distance from the release point (km)T

hyr

oid

do

se (

Sv)

95% Met

50% Met

Stable iodine

Effect of the reduction for the effective dosedue to protective measures

Effect of the reduction for the thyroid dosedue to the delay of evacuation and SI intake

12

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.

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.

Large Late Release

0.1 1 10 10010-3

10-2

10-1

100

101

102

No Shl Shl+SI Evac Evac+SI

Distance from the release point (km)T

hyr

oid

do

se (

Sv)

95% Met

50% Met

Stable iodine

0.1 1 10 10010-4

10-3

10-2

10-1

100

101

No Shl Evac

Distance from the release point (km)

Eff

ect

ive

do

se (

Sv)

95% Met

50% Met

Sheltering

Evacuation

Effect of the reduction for the effective dosedue to protective measures

Effect of the reduction for the thyroid dosedue to protective measures

13

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.

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.

Control Release

0.1 1 10 10010-3

10-2

10-1

100

Met 50% Met 95%

Eff

ecti

ve d

ose

(S

v)

Distance from the release point (km)

Sheltering

Evacuation

0.1 1 10 10010-3

10-2

10-1

100

101

No Shl Shl+SI

Distance from the release point (km)T

hyr

oid

do

se (

Sv)

95% Met

50% Met

Stable iodine

Effective dose for distance from the release point

Effect of the reduction for the thyroid dosedue to sheltering and intake of stable iodine

14

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 releaseEvacuation 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.

Conclusions