Vg# 1

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,for the United States Department of Energy’s National Nuclear Security Administration

under contract DE-AC04-94AL85000.

Treatment of MSIV Leakage in BWR Dose Analysis

R.O. Gauntt – Sandia National LaboratoriesM. Blumberg – USNRC - NRR

M. Salay – USNRC -RES

Vg# 2

Overview

• Up Front – summarize briefly the central issue and the proposed methodology for analyzing MSIV leakage

• Questions so far• MELCOR code overview• MELCOR applied to MSIV analysis

– Vessel head source versus drywell source– Effect of reflooding vessel– Attenuation in steam lines and condenser

Vg# 3

History• Regulatory Guide 1.183

– Details use of NUREG-1465 Alternative Source Term in evaluating containment performance

– MSIV leakage may be assessed using containment airborne fission product concentrations as a surrogate for the MSIV leakage environment

• NUREG-1465 is a containment source term• Problem is, the containment is not the source volume for the MSIV

leakage– Staff recognition of issue dates toNUREG-1169

Vg# 4

MAIN Steam Lines

• Inboard/outboard valves• Tech spec leak based on standard test

– Pressurize between valve and bleed down• Characterize valve performance

– SCFH @ test pressure– Implies a leak area– Necessary to scale standard leak to accident conditions

Vg# 5

Current RG Method

• Source - Drywell airborne from NUREG-1465• Lambdas derived using AEB 98-03 • Flow rates - ideal gas law

drywell

inboardsteamLine

inboardMSIV

intermediatesteamLine

outboardMSIV

outboardsteamLine

environment

1 2 3C

time

Vg# 6

Reg Guide View Not Consistent with DBA Scenario

• Reg guide assumes uniform f.p. in drywell – NUREG-1465 is a containment source

– Valve leak source assumed to be drywell• MELCOR shows vessel concentrations exceed drywell concentrations

– Core and vessel ongoing source of f.p. to containment and steam lines

drywell

vessel

realistic behaviorin release

phase

drywell

vessel

reg guideidealized behaviorin release

phase

Vg# 7

DG-1199 ModelSource

• Recognize vessel as MSIV leakage source prior to reflood• Modify NUREG-1465 containment source to reflect vessel

concentrations during first hour • After 1 hour – assume drywell is MSIV leakage source (like before)

drywell

inboardsteamLine

inboardMSIV

intermediatesteamLine

outboardMSIV

outboardsteamLine

environment

1 2 3

vessel

RxC

time

C

time

in-vesselreleaseperiod

postrefloodperiod

Vg# 8

DG-1199 Model Lambdas

• Lambdas calculated by MELCOR• Integrated phenomenology (ie. Thermal hydraulics, aerosol

physics) provides a best estimate of removal in steamline• Same method as used to model settling and sprays in

containment• Use of “filter efficiencies” are not technically correct

– Fails to capture time dependencies of filling the volumes

Vg# 9

DG-1199 Model Flowrates

• Flow equations proposed match the flow calculated by MELCOR and are more realistic

• Based on (mostly) critical flow through a nozzle• Originally documented in Air Cleaning Conference

Paper• Standard engineering approach

Vg# 10

DG-1199 Flowrates in Steamline

• Flow equations proposed match the flow calculated by MELCOR and are more realistic• Based on nozzle flow• When sonic (most of the time), downstream pressure replaced with critical pressure• Test conditions determine leakage area “A”• Accident conditions determine actual flows• In accident conditions, volume flow after second MSIV increases significantly owing to

expansion• Flow in condenser reduces due to cooling

kk

up

dnk

up

dnupup P

PPP

kkPAw

12

12

1

12

kk

upcr kPP

Vg# 11

MELCOR Source to RADTRAD

• Source implemented in *.RTF file• Lambdas and flow rates are directly input into

RADTRAD GUI

drywell

inboardsteamLine

inboardMSIV

intermediatesteamLine

outboardMSIV

outboardsteamLine

environment

1 2 3

vessel

MELCORIntegrated

Source

Vg# 12

DG-1199 Model

team Dome (0 .0.5 hr)(1)

Steam Dome (0.5·1 hr) (8)

team Dome (>1 hr)(9)

Coltairmeft Leakage

0W!> Void (2)

1(13,14,19 U~led

Line

CD MSL·A 0

r----> (5) t----'

~ 0 MSL·B

[------< (5) ----0

~

MSL·A (6)

MSL·B (6)

)== Control Room

(4)

0 ® S MSL·A ~

j--=-> (7) }----l :::. ~ ~ ... ~

~B " ID

0 1/1 0 !E c:: " 'C c::

0 ® 0

MSL·B U Environment ----0 (7) f--'-o 0) (3)

"==

Vg# 13

Lambdas vs. Filter Efficiencies

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 1 2 3 4 5 6 7 8 9 10time (hr)

RN

mas

s (g

)

RN in Env (MELCOR)RADTRAD (lambda)RADTRAD (Feff)

Use of filter efficiency Use of filter efficiency capturescapturesCorrect rate of attenuationCorrect rate of attenuationBut does not recognize the But does not recognize the storage of material in the storage of material in the volumevolume

Vg# 14

Questions so Far ?

Vg# 15

Details on Work Done

• Overview of MELCOR Code• Realistic unrecovered DBA analysis of source

from core/vessel to MSIV’s

Vg# 16

What has Been Done

• Perform MELCOR analyses of DBA sequences– MSLB and RLB– With and without Drywell sprays– Couple releases to RADTRAD

• Perform uncertainty analyses on main steam line deposition behavior (determining lambdas)

– Aerosol physics– Leak area– Piping length

• Explore potential modifications to Regulatory Guide– Correct for drywell versus steam dome source term

• Clarify other Regulatory Guidance issues

Vg# 17

Timeline of Nuclear Safety Technology Evolution

Timeline of Nuclear Safety Technology Evolution

Nuclear PowerOutlook

Optimistic

Guarded

Pessimistic

Risk Informing Regulation- Modernization, NUREG-1465

License Amendments and Extension- MOX, High Burnup- Plant aging

Emergency Response PlanningAdvanced Reactors

- AP1000, ESBWR, US-EPRNGNP - HTGR, VHTGR, H2 EconomyGNEP - Fast Burner Reactor, Reprocessing

Probabilistic Risk Informed AnalysisRisk Informed Regulation

Deterministic Bounding Analysis

NRC

Chicago Critical Pile Shippingport

Atomic Energy Act of 1954

WASH 1400

TMI-2 Chernobyl

1940 1950 1960 1970 1980 1990 2000 2010

NUREG-1150AEC

1982 SandiaSiting Study

Windscale

TID 14844source term

SOARCAStudy

NUREG 1465alternative

source term

QUENCH, Phebus FP, VERCORS, MASCA

Phenomenological Experiments(PBF, ACRR, ACE, HI/VI, HEVA)

Tier 1: Integrated Codes: MELCOR, MAAP, ASTEC

Tier 2: Mechanistic CodesSCDAP, CONTAIN, VICTORIA

detailed best estimate

US Research International Research

Emerging Issues.....

simplified parametric

Vg# 18

Vg# 19

Aerosols: MAEROS• MAEROS sectional model of Gelbard

– 10 sections [.1 - 50 m]– Condensed FP vapor sourced into smallest

section• Particles grow in size

– Agglomeration– Water condensation

• Particle fallout by gravitational settling• Particle deposition processes

– Thermophoresis– Diffusiophoresis– Brownian motion

• Cs chemisorption in RCS modeled– Iodine from CsI revolatilizes when

reheated

0.1 1 10 100aerosol diameter [m]

sect

ion

mas

s

0.1 1 10 100aerosol diameter [m]

sect

ion

mas

s Aerosol size distribution evolves in time, depending on sources, agglomeration and removal processes

Time 1

Time 2

Validation ExperimentsPANDA, DEHBI, CVTR, FALCON, LACE-LA4, ABCOVE, Wisconsin flat plate

Vg# 20

Aerosol Size vs. Time

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.0E-07 1.0E-06 1.0E-05 1.0E-04

particle diameter [m]

prob

abili

ty [-

]

1 hr3 hr5 hr7 hr9 hr11 hrPowers

SNL ESBWR MELCOR Model Drywell Aerosol

Particle Size Distributions

Accident Scanario 1(using median values for uncertain parameters)

Initial source term particle size distribution in Powers MSIV Code (using median values for mean particle diameter and standard deviation)

Vg# 21

vaporcondensation

aerosol

thermophoresis

impaction

chem

isor

ptio

n

RadioNuclide Overview

Fission product transport & natural deposition processes

steamaerosol

stefan flow

sedimentation

diffusion

condensation

Vg# 22

MELCOR Analysis of Full Plant DBA

• Mark-I and III• MSLB and

RLB• With and

without drywell sprays

• Assess drywell airborne versus steam dome

Vg# 23

23

Issues

• Source – Steam dome vs. Drywell• Pathway• Removal in Steamline• Flow in Steamline• Lambdas vs. filter efficiency• Other - Sprays

Vg# 24 24

Source Term Steam Dome vs. Drywell

• MSLs are connected to the reactor vessel.• NUREG – 1465 • Provides Magnitude, Mix, Speciation for Containment Source

Term• Does not provide aerosol size distribution for Source Term• Does not provide source term for reactor vessel• Regulatory Guide 1.183 • Assumes the source for MSIV leakage is the drywell activity

(NUREG-1465) up to two hours• At two hours reactor assumed to be re-flooded and 1465

homogenized over DW & WW free space • MELCOR analyses show that during the first two hours of the

SL break in containment and RLB that the concentrations in the steam dome are much greater than in the DW.

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25

Source TermSteam Dome to Drywell Concentration MELCOR,

Mark I

0

5

10

15

20

25

30

35

0.0 0.5 1.0 1.5 2.0 2.5

Time (hr)

Stea

m D

ome

to D

ryw

ell C

once

ntra

tion

Rat

io RN2RN3RN4

Vg# 26

26

Source TermSteam Dome to Drywell Concentration

MELCOR, Mark III

0

10

20

30

40

50

60

70

0.0 0.5 1.0 1.5 2.0 2.5

Time (hr)

Stea

m D

ome

to D

ryw

ell C

once

ntra

tion

Rat

io RN2RN3RN4

Vg# 27

27

Source Term after after Reflood

Mk-III RLB with Reflood - Aerosol Distribution

0.0000001

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

10

100

1000

-2 0 2 4 6 8 10 12

Time (hr)

Aer

osol

mas

s (k

g)

Rx steam domeDrywellWetwell atmWetwell pool

Core spray established

Vg# 28

DG-1199 ModelSource

• Recognize vessel as MSIV leakage source prior to reflood• Modify NUREG-1465 containment source to reflect vessel

concentrations during first hour (to keep it simple)• After 1 hour – assume drywell is MSIV leakage source (like before)• Containment spray does not reduce vessel concentration but can

reduce driving pressure

drywell

inboardsteamLine

inboardMSIV

intermediatesteamLine

outboardMSIV

outboardsteamLine

environment

1 2 3

vessel

RxC

time

C

time

in-vesselreleaseperiod

postrefloodperiod

Vg# 29

29

Removal/Attenuation in Steamline

• Credited Mechanisms for SSE qualified piping and condenser

• Gravitational Settling• Holdup• Elemental I2 Plateout

Vg# 30

30

Gravitational Settling

• Removal coefficient (or lambda value) dependent on settling velocity.

• Settling velocity depends on shape, diameter, density and shape factor of aerosol and viscosity of fluid.

Vg# 31

Uncertainty Study on MSL Deposition

• RADTRAD often requires “lambda” values to assess attenuation of source term

• MELCOR uncertainty analysis of MSL piping was done to bound aerosol removal coefficients used on RADTRAD

• MELCOR estimates instantaneous lambda from known deposition rate and airborne concentrations

• Uncertainties considered aerosol physics, valve leak area and piping length variations

mmdep

Vg# 32

MELCOR Main Steam Line Deposition Analyses

• Reduced nodalization• Boundary conditions from RLB analysis• Monte Carlo sampling used to derive distributions• Removal coefficients determined for each piping section• Inboard line experienced revaporization

inboardsteamLine

inboardMSIV

intermediatesteamLine

outboardMSIV

outboardsteamLine

condenser volumesteamdome

Pre-RecordedMELCORConditions

pressuretemperaturegas compositionaerosol mass and size distribution

Vg# 33

Example Results from Deposition AnalysisAerosol Deposition Physics Uncertainty

inboardinboard between valvesbetween valves

outboardoutboard condensercondenser

Vg# 34

34

MSL and Condenser Removal Coefficients (50th Percentile)

MSL section 0 - 2 (hr) 2 - 12 (hr) 12+ (hr)

in-board 0* 0* 0*

between MSIVs 3.1 2.4 2.0

out-board 1.4 1.2 1.0

condenser 0.021 0.018 0.015

note. removal coefficients are given in 1/hr

* Not credited because of Re‐evolution, thermal bi‐directional Flow, turbulence, containment boundary

• Circulation and mixing in inboard piping one reason for disallowing deposition credit

– Size distribution effect is important• Lambdas decrease as remaining aerosol becomes smaller• Condenser lambdas strongly affected (reduced) by geometry

– Significant deposition results from long residence time

Vg# 35

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