6 Source terms for EPZ and Response - Nucleus · Source terms for the determination of Emergency...

Source terms for the determination of

Emergency Planning Area and during

response to an Radiological Emergency

O. Isnard

Emergency Response Department

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Role of a Source Term

Evaluation of a source

term

Objectives

What for?

3

Some definitions

Emergency Planning Zones

PAZ (Precautionary Action Zone): take urgent protective action before the start of the release.

Zone to prevent highly dose to the public – close to the plant.

UPZ (Urgent Protective Zone): shelter in place and monitor for hot spots.

Dose reduced by 10 from PAZ.

No evacuation needed at distance over the UPZ.

LPZ (Long Term Zone): Mostly food restriction.

Can cover hundreds of kilometer to an entire country.

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Emergency Planning Zones

Most countries translated the EPZ concept to

distance over which protection measures

have to be applied (evacuation, sheltering,

iodine prophylaxis)

Rationales for the selection of EPZ are based

on possible consequences of accidents but

not only. Other considerations shall be (are)

incorporated (population, civil response,

cost…)

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Technical basis

Most of the EPZ are made from the choice of:

�Accident(s)

�DBA, BDBA, SA (level of the atmospheric releases)

�Kinetics

�Radionuclides composition

�From a deterministic/probabilistic method

�Meteorological situation(s)

�Exposure pathways (ingestion)

�Reference level for doses (intervention levels)

�Time frame

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One example

Example for France (deterministic approach)

�ST1: Accidents resulting in early failure of the

containment

�ST2: Accidents resulting in delayed failure of the

containment (24h) without filtration

�ST3: Accidents resulting in delayed failure of the

containment (24h) with some filtration

Use of ST3 for Emergency Planning

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Source Term characteristics

Important features for a source term for EPZ

�Represent some plausible accident

�The evaluation shall be realistic (in magnitude)

�The kinetic of releases shall be realistic

�Composition of the releases (radionuclides) shall be

adapted for the emergency and late phase

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Importance of the composition of the releases

Family Noble

gas

Iodine Caesiu

m

Tellurium Strontium Ruthenium Zirconium Lanthanum Plutonium

Radionuclides

Xe-Kr

I2,

I_IM,

CsI

CS-Rb Te-Sb Sr-Ba-Mo Ru-Rh-Tc Nb-Zr Y-La-Ce Pu-Np-Cm

Total release9,2.1015 6,7.1014 3.1013 8,9.1013 2,5.1014 1,6.1014 1,8.1013 3,6.1013 5,7.1013

Mo, Ba, La, Zr and Pu represent only 5% (in activity) of the release

Example of a core melt with water injection after 24h

External dose

due to deposition

Internal dose

due to inhalation

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Importance of the composition of the releases

Complete source term Difference Usual source term

Pathway Dose at 24h (mSv) % Dose at 24h (mSv) Pathway

External due to deposition 19 25 14.5 External due to deposition

External due to plume 19 6 18 External due to plume

Internal due to inhalation of the plume 184 27 135 Internal due to inhalation of the plume

Total effective dose 223 25 168 Total effective dose

Internal due to inhalation at the thyroid 2350 0.2 2353 Internal due to inhalation at the thyroid

Complete source term Difference Usual source term

Pathway Dose at 1 month % Dose at 1 month Pathway

External due to deposition 173 75 43 External due to deposition

Inhalation due to re-suspension 6.5 10-2 70 2.1 10-2 Inhalation due to re-suspension

Internal due to ingestion 713 22 555 Internal due to ingestion

Total effective dose without ingestion 173 74 45 Total effective dose without ingestion

Total effective dose 885 32 601 Total effective dose

Internal due to inhalation at the thyroid 9244 0.1 9235 Internal due to inhalation at the thyroid

Emergency Phase

Post-Accidental Phase

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Importance of the kinetic of the releases

(with meteorology)

Example of the Fukushima accident @ local scale

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Importance of the meteorology

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Importance of the meteorology

Statistical approach from the meteorological point of view

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An example with ST3 release

Scenario:

� Large LOCA with no safety injection

� Core melt in 1 hour

� Opening of the U5 sand filter after 24h

Amount of releases in Bq

Caesium Iodine Noble gas Total

LOCA with venting 1.8 1013 2.6 1016 4.9 1018 4.9 1018

Fukushima 5.8 1016 4.1 1017 6.5 1018 7.2 1018

ST3 with U5 filter 6.7 1013 8.6 1017 9 1018 1019

Chernobyl 1.7 1017 5.4 1018 6.5 1018 1.4 1019

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Distance (km) Evacuation Shelter in place Iodine

prophylaxis

Minimum 13 37 81

Maximum 71 181 555

Mean 36 108 238

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Source term during response

�Have some objectives to drive your evaluation

�Protection of the public

�Avoid unnecessary exposure

�Have a methodology in place

�France (IRSN & EdF) is using a comprehensive

methodology to assess the D/P of the plant

�Your software shall use a simple set of parameters

�Focus on the main phenomena

�…And be able to evaluate a source term in minutes!

�Evaluations shall be comparable with what is observed

in the environment

During response

Make it simple

Release

PERSAN

Auxiliary buildings

Reactor buildings

FP deposit

Spray system (O/N)

Collected leakage

Non-collected leakage

VentilationO/N

1) claddings

2) Primary circuit

3) containment

FP deposit

FP deposit

4 FP family: NG, I, Cs et Te

Pressure variation

leak rate

FP retention in the RCS

Stack flow rate

Filters efficiency and iodine traps

Extraction rates through ventilation systems of the auxiliary buildings

Initial RCS activity

Ci(t+dt) = Ci(t) + [ Si(t) - Di(t) - Fi(t) ] * dt

Example with the IRSN system

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Use of inverse modelling approach to assess

the source term by using environmental

measurements

Air concentration

Dose rate

Daily deposition

Observations + -

Air

concentration

Easy to use

(Model

parameter &

Isotopic

composition)

Number & frequency (Very

few data

& Time averaged)

Deposition

Easy to use

(Model

parameter &

Isotopic

composition)

Number & frequency (Very

few data during the

release

& Time integrated)

Dose rateNumber &

Frequency

Difficult to use (Not a

model parameter &

Aggregate all the gamma

radiations emitted by any

radionuclides present on

the ground and in the air)

Inverse modelling using dose rate

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▌Gamma dose rate observations

▌ How to use dose rate signal ?

� Plume detection when it blew over the station timing of the release events.

� The slope due to the radioactive decay of the deposit isotopic composition.

� The value of the observed dose rate quantities released.

Of I-131

� Objective: estimate the release rate of 5 radionuclides: 134Cs, 136Cs, 132Te, 131I and 133Xe

Inverse

modeling

▌The inverse problem to solve can be formalized by:

▌ The objective is to assess the ST σ so that the error ε is minimized.

Cost function (minimized by using L-BFGS-B algorithm)

▌ Hypothesis

� No prior knowledge of the ST (σb = 0)

� Simple parameterizations (Winiarek et al., 2011): R = B = I

Ingredients of the reconstruction: the inverse problem

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Hε σ µ= − Vector of

measurements

Estimator of the STSource receptor matrix

computed with the forward atm. model (Abida et al.

2011)

Vector of

errors

( ) ( )1 11 1( ) ( ) ( )

2 2

T T

b bJ H R H Bσ µ σ µ σ σ σ σ σ− −= − − + − −

Dispersion

model H+

Observations

µ

Estimation of

the ST σ

Source term (ST): temporal evolution of the release rate + distribution between radionuclides

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Measurements: dose rate due to the plume component for 7O stations

Potential release periods

Step 1: Inverse modelling to identify the potential release periods

Plume extraction

Inverse

modeling

Reconstruction of the Fukushima Daiichi source term

381 initial time stepsInverse

modeling120 potential release instants

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Inverse

modeling


Cs-137 Inverted ST

Step 2: Inverse modelling to assess the release rates during periods identified in step 1

� Measurements: the complete dose rate signal on 70 stations

� Soft constraints on isotopic ratio are imposed (based on analysis of core reactor and air

concentrations measurements in Japan)

0.6 � � ��

� �� 16; 2 � � ��

� �� 100; 0.1 � � ��

� �� 10000

� The cost function to minimize uses a regularization function which contains information

about isotopic ratios

� � � 12 � � �� 1

2 � � �� !"�#!

▌ Comparisons with other ST

▌ Inverted quantities are consistent with the other estimations.

▌ Underestimation in iodine and cesium in comparison with Mathieu et al ST (several

events are not identified by inversion).

▌ Amount of noble gases is similar to Stohl et al estimation: probably overestimated


Source Term (PBq) 133Xe 131I 132I 137Cs 136Cs

Inverted ST 12100 103 35.5 15.5 3.7

Mathieu et al. (2012) 5950 197 56.4 20.6 9.8

Winiarek et al. (2012) - 190-380 - 12-19 -

Terada et al. (2012) - 150 13 -

Stohl et al. (2012a) 13400-20000 - - 23.3-50.1 -

TEPCO (2012) 500 500 10

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▌ Good agreement between model and observations.

▌ Additional releases are identified with the inverse modeling method.

▌ Discrepancies are due mainly to inaccurate meteorological fields.

6 Source terms for EPZ and Response - Nucleus · Source terms for the determination of Emergency...

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