SPES3FacilityRELAP5SensitivityAnalyseson ...4Research and Technology Unit, Westinghouse Electric Company LLC, Cranberry Township, PA 16066, USA Correspondence should be addressed to

Hindawi Publishing CorporationScience and Technology of Nuclear InstallationsVolume 2012, Article ID 173637, 19 pagesdoi:10.1155/2012/173637

Research Article

SPES3 Facility RELAP5 Sensitivity Analyses onthe Containment System for Design Review

Andrea Achilli,1 Cinzia Congiu,1 Roberta Ferri,1 Fosco Bianchi,2 Paride Meloni,2

Davor Grgic,3 and Milorad Dzodzo4

1 SIET S.p.A., UdP, Via Nino Bixio 27/c, 29121 Piacenza, Italy2 ENEA, UTFISSM, Via Martiri di Monte Sole 4, 40129 Bologna, Italy3 FER, University of Zagreb, Unska 3, 10000 Zagreb, Croatia4 Research and Technology Unit, Westinghouse Electric Company LLC, Cranberry Township, PA 16066, USA

Correspondence should be addressed to Roberta Ferri, [email protected]

Received 11 March 2011; Accepted 27 July 2011

Academic Editor: Alessandro Del Nevo

Copyright © 2012 Andrea Achilli et al. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

An Italian MSE R&D programme on Nuclear Fission is funding, through ENEA, the design and testing of SPES3 facility at SIET,for IRIS reactor simulation. IRIS is a modular, medium size, advanced, integral PWR, developed by an international consortiumof utilities, industries, research centres and universities. SPES3 simulates the primary, secondary and containment systems of IRIS,with 1:100 volume scale, full elevation and prototypical thermal-hydraulic conditions. The RELAP5 code was extensively used insupport to the design of the facility to identify criticalities and weak points in the reactor simulation. FER, at Zagreb University,performed the IRIS reactor analyses with the RELAP5 and GOTHIC coupled codes. The comparison between IRIS and SPES3simulation results led to a simulation-design feedback process with step-by-step modifications of the facility design, up to the finalconfiguration. For this, a series of sensitivity cases was run to investigate specific aspects affecting the trend of the main parametersof the plant, as the containment pressure and EHRS removed power, to limit fuel clad temperature excursions during accidentaltransients. This paper summarizes the sensitivity analyses on the containment system that allowed to review the SPES3 facilitydesign and confirm its capability to appropriately simulate the IRIS plant.

1. Introduction

The IRIS reactor, with its integral design, is an advancedengineering solution of the latest LWR technology. Medium-sized, safe, modular, and economic, it provides a viablebridge to generation IV and satisfies the GNEP requirementsfor grid-appropriate NPPs [1–3].

In the frame of an R&D program on nuclear fission,funded by the Italian Ministry of Economic Development,ENEA, as member of the IRIS consortium, is supporting thedesign, construction, and testing of the SPES3 ITF at SIETlaboratories [4–6].

The SPES3 design was carried out following the subse-quent steps: (a) definition of a preliminary facility design,based on specified system geometry; (b) setup of theRELAP5 facility model and DBA simulation; (c) comparisonof SPES3 and IRIS results against the same transient;

(d) identification of the main differences and understandingof related reasons; (e) FSA application to selected thermo-fluid-dynamic parameters in order to assess and quantify thediscrepancies; (f) updating of the SPES3 design to matchthe IRIS behaviour; (g) final result comparison; (h) finalFSA application and assessment of acceptability criteria forconsidering SPES3 correctly simulating IRIS.

The above-mentioned process allowed to verify theSBLOCA PIRT objectives for the IRIS reactor, as defined bya group of international experts [7]. The Phenomena Iden-tification and Ranking Table put in evidence the thermal-hydraulic phenomena playing an important role in operationof IRIS safety systems. Two figures of merit were consideredfundamental for the accident sequence control: containmentpressure and reactor vessel mass inventory. Sufficient waterin the vessel allows to remove stored energy, and decay heatwithout fuel clad temperature excursions and adequate heat

2 Science and Technology of Nuclear Installations

SGs

Pump

PRZ

CRDM

Core

FL nozzles

SL nozzles

DCRPV

LP

Figure 1: IRIS integral layout.

Figure 2: IRIS containment systems.

rejection to the RWST prevents containment overpressuriza-tion and contributes to core cooling also thanks to dynamiccoupling between the primary and containment systems.

The DBA simulation on the facility allowed to under-stand the transient plant behaviour and the mutual systeminteraction. The comparison with the IRIS results led torunning many sensitivity cases that required the SPES3design review for better matching the IRIS transients.

The SPES3 tests will provide a qualified data base for theassessment of codes to be used in the reactor safety analyses.

The SPES3 facility is under construction, based on theIRIS reactor design. The availability of such a complex plantopens the way to other possibilities of exploitation, and

RWST

DW

RPV LGMS

PSS

RC

EHRS

EBT

QT

Figure 3: SPES3 facility layout.

studies are foreseen for using it in a wider field of applicationfor integral layout SMR simulation [8].

2. IRIS Plant and SPES3 FacilityLayout and Nodalization

The IRIS pressure vessel and containment are shown inFigures 1 and 2, whereas the SPES3 facility is presented inFigure 3.

The SPES3 facility reproduces all parts and compo-nents of the IRIS plant with 1 : 100 volume scaling factor,1 : 1 elevation scaling factor, and prototypical fluid andthermal-hydraulic conditions. The reactor vessel includesthe internals, consisting of the electrically heated coresimulator, the riser with control rod device mechanisms,the pressurizer, the pump suction plenum, the helical coilsteam generators, the downcomer, and the lower plenum.Three SGs simulate the eight IRIS SGs. A pump, locatedoutside of the RPV, for room reasons, and connected toit by pipes, simulates eight IRIS pumps. Two emergencyboration tanks are simulated and connected to the DVIlines, devoted to direct injection of emergency fluid into thevessel. Three secondary loops simulate four IRIS loops. Eachsecondary loop is simulated up to the main isolation valvesand includes the feed line, the SG, the steam line, and theemergency heat removal system with a vertical tube heatexchanger immersed in a refuelling water storage tank. TheIRIS spherical containment compartments are simulated bytanks, connected to each other by pipes and to the RPV bybreak lines [4, 5]. They include dry-well and reactor cavity,representing the dry zone surrounding the RPV, respectivelyabove and below the mid-deck plane; pressure suppressionsystems representing the wet zone around the lower part

Science and Technology of Nuclear Installations 3

Figure 4: IRIS primary and secondary circuit nodalization for RELAP5 code.

of the RPV, suitable to dump pressure in case of contain-ment pressurization; long-term gravity make-up systemsrepresenting the cold water reservoir to be poured into theRPV when depressurized. The two stages of the automaticdepressurization system are simulated, connected to thepressurizer top, with stage I discharging into the quench tankand stage II directly connecting RPV and DW at high plantelevation.

The facility allows to test both LOCAs and secondary sidebreaks (DBA and BDBA) as well as to perform separate effecttests on particular components such as SG-EHRS thermallycoupled to RWST.

The IRIS nodalization was developed in two parts: theprimary and secondary circuits for the RELAP5 code and thecontainment system for the GOTHIC code (Figures 4 and 5).The RELAP5 nodalization includes 1845 volumes, and 1940junctions, 1015 heat structures with 8600 mesh points, whilethe GOTHIC model includes 85 volumes, 28 junctions, and57 heat structures.

The SPES3 nodalization was completely developed forthe RELAP5 code (Figures 6, 7, and 8). It includes 1499 vol-umes, 1639 junctions, 1839 heat structures, and 19322 meshpoints.

3. Design-Calculation Feedback Process forSPES3 Facility Final Design

The RELAP5 model for SPES3 was initially developed onthe basis of the preliminary design of the facility, and thesteady-state conditions are based on the actual IRIS nominaloperation [9]. Five DBAs were simulated with particularattention to the occurring phenomena and sequence ofevents. In particular, three SB-LOCAs and two secondaryside breaks were simulated, according to the specified testmatrix [10].

Once the phenomena occurring in the DBAs were in-vestigated, attention was focused on the most challengingtransient scenario, the DVI line DEG break, for a directcomparison of the SPES3 and IRIS results.

WEC, in collaboration with the University of Pisa andPolitecnico di Milano, developed the Fractional ScalingAnalysis for IRIS and SPES3. The method, based on systemand time sequence decomposition, allowed to identify theparameters mostly affecting the transient and to quantify thedistortions between IRIS and SPES3 simulations introducedby such parameters (e.g., containment tank metal mass, heattransfer at core side wall, etc.).


2

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PSS vent PSS vent

QT

DVI-A

LGMS-ALGMS-B

DVI-B

Ventextension

Ventextension

Figure 5: IRIS containment nodalization for GOTHIC code.

The first application of the DVI line DEG break ev-idenced important differences on containment pressure,especially in early phase of the accident, at pressure peak, andalso on the long term.

The need of understanding the reasons and reducingdiscrepancies led to performing a series of sensitivity caseson SPES3 containment, making SPES3 response closer toreactor one, and finalizing the facility design [11, 12].

The main events, identified in the DVI line breaktransient, are listed below for better understanding all sen-sitivity analyses and the design-calculation feedback process.Approximate timing of events is reported too. The long-termphase of the transient was simulated to verify the safe, stableplant operation.

(i) The break opening (0 s) causes the RPV blowdownand depressurization, containment pressurization,steam dumping into PSS with air build-up at PSS top,and consequent pressurization;

(ii) the signal of high containment pressure (∼30 s) trig-gers the reactor scram, the secondary loop isolation,and the actuation of two out of four EHRSs;

(iii) the signal of low PRZ water level (∼120 s) triggersthe pump coastdown, and the natural circulationin the core is guaranteed through the check valves,connecting riser and downcomer at one-third of theSG height;

(iv) the signal of low PRZ pressure (∼200 s) actuates theremaining EHRS and triggers the ADS stage I, to help

RPV depressurization, and the EBT intervention, toinject cold water into the primary circuit;

(v) the signal of low differential pressure between RPVand DW (∼2250 s) triggers the LGMS injection intothe DVI line and opens the valves connecting RCand DVI line to allow water reverse flow from thecontainment to the primary side;

(vi) when PSS pressurization is sufficiently high, coldwater flows from PSS to DW (3500 s), increasing theRC flooding and allowing water to enter the RPV;

(vii) the signal of low LGMS mass (∼25000 s) opens theADS stage II with possible reverse steam flow fromDW to RPV;

(viii) on the long term (simulation up to 100000 s), theplant is cooled by EHRSs that reject core decay heatto RWST.

The starting point for the sensitivity analyses was thecomparison between cases SPES3-97 and IRIS-HT1 results,which showed qualitatively good agreement in occurringphenomena, but also quantitative discrepancies in contain-ment pressure, affecting the sequence of events and transientevolution (Figure 9).

A series of parameters identifying and potentially affect-ing containment pressure is: (a) SPES3 containment over-volume of about 10% with respect to 1 : 100 scaled IRIS;(b) SPES3 containment metal mass greater than IRIS formechanical resistance to the same design conditions; (c)


Figure 6: SPES3 primary circuit nodalization for RELAP5 code.

SPES3 component surface-to-volume ratio ten times greaterthan IRIS, due to volume scaling and component heightconservation; (d) containment metal structure temperature;(e) containment piping pressure drops; (f) EHRS and RWSTmodelling and heat transfer coefficients.

A synthesis of the performed sensitivity cases on SPES3 isreported in Table 1, where they are grouped according to theinvestigated parameters. A synthesis of IRIS cases, utilised forthe comparison, is reported in Table 2.

A reduction of DW volume, for correctly scaling IRIS(1 : 100), did not provide great improvements (a few percent)in the containment pressure response. An improvement wasobserved only in the long term related to lower heat losses toenvironment due to DW size reduction (Figure 10).

In order to compensate for the extra surface in SPES3,a thermal insulation of DW inner surface was tested withdifferent thickness of Aluminium Silicate Rescor 902. Asshown in Figure 11, the introduction of an increasing


Figure 7: SPES3 secondary circuit and EHRS nodalization for RELAP5 code.

Figure 8: SPES3 containment nodalization for RELAP5 code.

thickness of thermal insulation increased pressure in the veryshort term, but the additional mass reduced the containmentpressure peak. The result was that the DW insulation ledto worse effects on pressure than with noninsulated DW,showing that masses have larger effects than surfaces.

The influence of DW heat structure mass on containmentpressure response was investigated by reducing DW thicknessby 40% (25 mm to 15 mm), approximately correspondingto a design pressure of 1.5 MPa, instead of the original2 MPa. As shown in Figure 12, pressure increase in the early


0E + 00

2E + 05

4E + 05

6E + 05

8E + 05

1E + 06

1.2E + 06

0 20000 40000 60000 80000 100000

Time (s)

Pre

ssu

re(P

a)

p 401140000PR1s54∗1000

SPES3-97IRIS-HT1

Figure 9: SPES3-97 and IRIS-HT1 DW pressure. Note: The IRISDrywell Volume was subdivided in 4x4x4 sub-volumes in the threedirections, marked 1s1, 1s2. . . up to 1s64. Pressure from a cell at thetop of the model was used as reference.

0E + 00

2E + 05

4E + 05

6E + 05

8E + 05

1E + 06

1.2E + 06

0 20000 40000 60000 80000 100000

Time (s)

Pre

ssu

re(P

a)

IRIS-HT1

p 401140000p 401140000PR1s54∗1000

SPES3-97SPES3-99

Figure 10: SPES3-97, 99 and IRIS-HT1 DW pressure.

phase of the transient was steeper and pressure peak higher.Containment pressure was still below the IRIS one, showingthat such DW metal mass reduction was not enough to havethe desired pressure response.

A further DW mass reduction was performed in atheoretical case, where concrete plus carbon steel IRIS DWequivalent mass was distributed on SPES3 DW surface,resulting in a thickness of 10 mm AISI 304. As shown inFigure 13, the further DW mass reduction allowed to getpressure values closer to IRIS both in the early phases ofthe transient and at the pressure peak, but still below IRISpressure. That showed that other parameters affected theresults.

An attempt to investigate how a greater DW volumereduction affects containment pressure was performed byscaling it 1 : 150 with respect to IRIS. Figure 14 shows apressure gain only in the early phases of the transient

0E + 00

2E + 05

4E + 05

6E + 05

8E + 05

1E + 06

1.2E + 06

0 2000 4000 6000 8000 10000

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ssu

re(P

a)

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p 401140000p 401140000p 401140000PR1s54 1000

SPES3-100SPES3-103

SPES3-99

Figure 11: SPES3-99, 100, 103 and IRIS-HT1 DW pressure (shortterm).

0E + 00

2E + 05

4E + 05

6E + 05

8E + 05

1E + 06

1.2E + 06

Time (s)

Pre

ssu

re(P

a)

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p 401140000p 401140000PR1s54 1000

SPES3-104SPES3-99

0 2000 4000 6000 8000 10000

Figure 12: SPES3-99, 104 and IRIS-HT1 DW pressure (short term).

0E + 00

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Pre

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re(P

a)

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p 401140000p 401140000PR1s54 1000

SPES3-99SPES3-105

0 2000 4000 6000 8000 10000

Figure 13: SPES3-99, 105 and IRIS-HT1 DW pressure (short term).


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late

IRIS

surf

ace.

Sen

siti

vity

onth

eco

nta

inm

ent

pipi

ng

pres

sure

drop

s

SPE

S3-1

09P

SSm

ain

ven

tpi

pere

sizi

ng

from

2.5′′ t

o2′′ S

ch.4

0.P

SSve

nt

pipe

exte

nsi

onre

sizi

ng

from

3/4′′ t

o1/

2′′ S

ch.4

0P

SSto

DW

mas

sfl

owcl

oser

toIR

ISon

e.

SPE

S3-1

10P

SSm

ain

ven

tpi

pead

diti

onal

rest

rict

ion

atth

ech

eck

valv

e(D

orifi

ce14

.19

mm

)O

nly

earl

yst

eep

but

limit

edco

nta

inm

ent

pres

sure

incr

ease

.

SPE

S3-1

18

Con

tain

men

tvo

lum

esc

aled

1:1

00on

IRIS

.LG

MS

toD

VI

line

calib

rate

dor

ifice

from

3.2

mm

to2.

3m

m.

EH

RS-

CC

Lca

libra

ted

orifi

cefr

om8.

5m

mto

6.5

mm

.P

SSve

nt

pipe

exte

nsi

onad

diti

onal

rest

rict

ion

(Dor

ifice

5.2

mm

).C

onta

inm

ent

hea

tst

ruct

ure

init

ialt

empe

ratu

re48

.9◦ C

Att

empt

tom

atch

IRIS

inje

ctio

nm

ass

flow

s.

SPE

S3-1

20

Con

tain

men

tvo

lum

esc

aled

1:1

00on

IRIS

.T

hic

knes

sto

resi

st1.

5M

Pade

sign

pres

sure

.A

irsp

ace

met

alst

ruct

ure

init

ialt

empe

ratu

re84

◦ C.Q

Tin

itia

ltem

pera

ture

48.9◦ C

.LG

MS

toD

VI

line

calib

rate

dor

ifice

from

2.3

mm

to2.

5m

m

IRIS

inje

ctio

nm

ass

flow

repr

odu

ced,

but

diff

eren

tpr

essu

redr

ops

inth

epi

pes.

SPE

S3-1

24

PSS

mai

nve

nt

pipe

resi

zin

gfr

om2′′ t

o2.

5′′ S

ch.4

0P

SSve

nt

pipe

exte

nsi

onre

sizi

ng

from

1/2′′ t

o1′′ S

ch.4

0LG

MS

toD

VI

line

calib

rate

dor

ifice

from

2.5

mm

to3.

6m

m.

PSS

ven

tpi

peex

ten

sion

orifi

cefr

om7.

3to

19m

m.

PSS

ven

tpi

peex

ten

sion

con

nec

tion

toD

Wel

evat

ion

decr

ease

of1.

5m

tom

atch

IRIS

.P

SSsp

arge

rel

evat

ion

decr

ease

of0.

25m

tom

atch

IRIS

.P

SSbo

ttom

mod

elle

dw

ith

abr

anch

.C

onta

inm

ent

air

spac

em

etal

stru

ctu

rein

itia

ltem

pera

ture

84◦ C

,wat

ersp

ace

48.9◦ C

Mas

sfl

owde

term

ined

byac

tual

pipi

ng

pres

sure

drop

sas

inIR

IS.C

onta

inm

ent

pres

sure

resp

onse

qual

itat

ivel

yan

dqu

anti

tati

vely

clos

eto

IRIS

.T

he

PSS

bott

omm

odel

ling

did

not

affec

tth

eP

SSve

nt

pipe

empt

yin

gm

ode.


Ta

ble

1:C

onti

nu

ed.

SPE

S3ca

ses

Ch

arac

teri

stic

seff

ect

for

mas

sR

esu

lts

SPE

S3-1

27A

sSP

ES3

-124

PSS

bott

omm

odel

led

wit

hth

ree

bran

ches

.T

he

PSS

bott

omm

odel

ling

did

not

stro

ngl

yaff

ect

the

PSS

ven

tpi

peem

ptyi

ng

mod

e.

SPE

S3-1

30A

sSP

ES3

-127

RW

STto

ppi

pein

trod

uct

ion

for

con

nec

tion

toat

mos

pher

e.R

edu

ced

loss

ofm

ass

atR

WST

top

due

todr

yai

ran

dw

ater

con

tact

.

SPE

S3-1

35

AS

SPE

S3-1

32C

ompl

etel

yre

view

edth

eE

HR

Sci

rcu

its

and

RW

STm

odel

:E

HR

S-A

and

Btu

be4%

surf

ace

ther

mal

lyin

sula

ted

wit

hTe

flon

oth

erth

anth

eor

igin

ally

insu

late

d0.

6tu

bes.

EH

RS-

C4%

surf

ace

ther

mal

lyin

sula

ted

oth

erth

anth

eor

igin

ally

insu

late

d0.

2tu

bes.

EH

RS-

Aan

dB

HL

resi

zed

from

2′′ t

o1.

25′′

Sch

.80.

EH

RS-

Aan

dB

CL

resi

zed

from

1.25

′′to

1.5′′ S

ch.8

0.E

HR

S-C

HL

resi

zed

from

2.5′′ t

o2′′ S

ch.8

0.E

HR

S-C

CL

resi

zed

from

1.5′′ t

o3′′ S

ch.8

0.H

L-A

and

Bad

diti

onal

orifi

ceD=

17m

m.

HL-

Cad

diti

onal

orifi

ceD

=24

mm

.C

L-A

and

Bor

ifice

resi

zed

from

5m

mto

5.9

mm

.C

L-C

orifi

cere

size

dfr

om7

mm

to8.

3m

m.

EH

RS

tube

hea

tst

ruct

ure

fou

ling

fact

orse

tto

2.9

left

and

2.77

righ

t(o

rigi

nal

valu

es2.

725

left

,3.5

4284

righ

t)[1

3].

RW

ST-A

Ban

dC

risi

ng

slic

ear

eare

size

dfr

om0.

491

m2

to0.

1191

67m

2;r

ecir

cula

tion

slic

ere

size

dfr

om1.

217

m2

to1.

6011

69m

2[1

3].

RW

ST-A

Ban

dC

slic

esi

deju

nct

ion

area

from

0.15

1m

2to

0.13

5m

2[1

3].

Th

eco

mpl

ete

revi

sion

ofth

eE

HR

Spi

pin

gan

dh

eat

exch

ange

rpa

ram

eter

sle

dto

mat

chin

gtr

ansf

erre

den

ergy

.

SPE

S3-1

46A

sSP

ES3

-135

.P

SSve

nt

pipe

exte

nsi

onor

ifice

from

19m

mto

17.5

mm

.SG

tube

inle

tor

ifice

from

12.5

mm

to11

.7m

m

Goo

dsi

mila

rity

betw

een

SPE

S3an

dIR

ISB

ASE

CA

SEfo

rFS

Afi

nal

appl

icat

ion

.


Table 2: Characteristics of the IRIS cases.

IRIS cases Characteristics Results

IRIS-HT1 Containment heat structures simulated only for the DW. Starting point for comparison with SPES3.

IRIS-HT5g

Heat structures added to all containment compartments and secondarysidepiping.PSS main vent pipe connection to DW rise of 4 m.PSS sparger set at 0.75 m from PSS bottom.RWST remodelled with parallel slice approach.

Similar containment pressure response withSPES3.

IRIS-HT6 rwstc

SG tubes inner layer removed which simulated the Fouling.ADS stage II actuation signal corrected to intervene on low LGMS mass.RWST remodelling according to PERSEO area ratio and HTC calibrationon experimental data. EHRS heat transfer parameters set as in SPES3 (bymultiplier fouling factors) [12, 13].RWST top pipe introduction for connection to atmosphere.Correction of energy transfer parameters at the GOTHIC and RELAP5code couplings.

Better matching of EHRS long-term energytransfer to RWST.

IRIS-HT6 rwstc1a

Corrected elevation difference between the RELAP5 and GOTHIC parts ofthe model: the ADS stage I vent pipe end should be 0.5 m from QT bottom(it was connected to QT top); LGMS tanks rise of 0.75 m.

Results very similar to IRIS-HT6 rwstcBASE CASE for FSA final application.

0E + 00

2E + 05

4E + 05

6E + 05

8E + 05

1E + 06

1.2E + 06

Time (s)

Pre

ssu

re(P

a)

SPES3-106SPES3-104IRIS-HT1

p 401140000p 401140000PR1s54 1000

0 2000 4000 6000 8000 10000

Figure 14: SPES3-104, 106 and IRIS-HT1 DW pressure (shortterm).

with a lower peak value. No improvement was obtained byoverreducing the DW volume with a scaling factor differentfrom 1 : 100.

A theoretical case, where IRIS DW structures weredirectly scaled 1 : 100 in mass and surface, was investigated.A one-hundredth vertical slice of IRIS DW structures wasattributed to SPES3 DW, maintaining the same thickness andmaterial composition. Figure 15 compares two cases withequivalent heat structure masses, but different surfaces andmaterial properties. Pressure increase was similar in IRIS andSPES3, in the early phase of the transient, when surface hasa greater impact, but later energy transfer to heat structuresprevailed and SPES3 pressure did not increase as expected,with all SPES3 containment structures being completelysimulated against the only IRIS DW structure simulation.Moreover, gas space volume at the PSS and LGMS topwas about 14% higher in SPES3 than IRIS, so limiting

0E + 00

2E + 05

4E + 05

6E + 05

8E + 05

1E + 06

1.2E + 06

Time (s)

Pre

ssu

re(P

a)

IRIS-HT1

p 401140000p 401140000PR1s54 1000

SPES3-108SPES3-105

0 2000 4000 6000 8000 10000


the containment pressure peak. Containment pressure trendshowed also differences in the depressurization phase, relatedto steam condensation in RC and DW due to broken loopLGMS water entering the RC (∼2000 s in SPES3) throughthe DVI break line, containment side, and PSS injection intothe DW (∼3000 s in SPES3). Injection mass flows are shownin Figures 16 and 17, and they depended on different pipepressure drops and containment pressurization.

An attempt to make closer SPES3 and IRIS PSS toDW injection mass flows was performed: size of PSS mainvent pipe and extension was decreased and the resultscompared with a base case (SPES3-107) equivalent to SPES-99, where minor input mistakes were corrected. PSS injectionresults were effectively closer to IRIS with consequent slowercontainment depressurization (Figures 18 and 19).

The attempt was performed to see how a restriction at thePSS main vent pipe check valve affects the steam-air transfer


−0.020

0.020.040.060.08

0.10.120.140.160.18

0.2

0 1000 2000 3000 4000 5000 6000 7000 8000900010000

Time (s)

Mas

sfl

ow(k

g/s)

mflowj 423000000 LGMS-Amflowj 433000000 LGMS-B

FL7/100 LGMS-AFL12/100 LGMS-B

SPES3-108

IRIS-HT1

Figure 16: SPES3-108 and IRIS-HT1 LGMS to DVI injection massflow (short term).

−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

2.5

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Time (s)

Mas

sfl

ow(k

g/s)

mflowj 47002 + 473 VENT-Amflowj 48002 + 483 VENT-BFV + FL + FD04 VENT-AFV + FL + FD09 VENT-B

IRIS-HT1

SPES3-108

Figure 17: SPES3-108 and IRIS-HT1 PSS to DW injection massflow (short term). Note: for IRIS, the total mass flow (FL + FV +FD) is obtained by the sum of phasic mass flows (liquid, gas anddroplets.

from DW to PSS and eventually rise DW pressure. The resultwas a steep but limited pressure increase (Figure 20).

The impossibility of reducing the DW thickness under15 mm, to resist 1.5 MPa design pressure, led necessarily toan excess of mass with respect to IRIS 1 : 100 scaled mass.In SPES3-105 case, the IRIS scaled mass was distributed onthe SPES3 DW surface obtaining an equivalent thicknessof 10 mm. The possibility of compensating for 5 mm extramass, by preheating the DW heat structures, was investigated.The preheating temperature of 84◦C was estimated byan energy balance between the cases with 10 mm and15 mm thickness from the specified initial temperature of48.9◦C and regime temperature of 172◦C after the heat-uptransient. Figure 21 compares the cases with 15 mm (SPES3-104), 10 mm (SPES3-105), and 15 mm (SPES3-111) pre-heated DW thickness. The 10 mm and 15 mm pre-heated

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Time (s)−3

−2

−1

0

1

2

3

Mas

sfl

ow(k

g/s)

mflowj 47002 + 473 VENT-Amflowj 48002 + 483 VENT-Bmflowj 47002 + 473 VENT-Amflowj 48002 + 483 VENT-BFV + FL + FD04 VENT-AFV + FL + FD09 VENT-B

IRIS-HT1

SPES3-107

SPES3-109

Figure 18: SPES3-109, 107 and IRIS-HT1 PSS to DW injectionmass flow (short term).

SPES3-109SPES3-107

0E + 00

2E + 05

4E + 05

6E + 05

8E + 05

1E + 06

1.2E + 06

Time (s)

Pre

ssu

re(P

a)

IRIS-HT1

p 401140000p 401140000PR1s54 1000

0 2000 4000 6000 8000 10000


DWs are equivalent showing that heat structure preheatingcompensates for the excess of mass in SPES3. Only DWpreheating is not enough to have the same IRIS pressureresponse.

The comparison between the cases with and withoutPSS heat structures allowed to quantify the phenomenonof air cooling when steam-air mixture flowed from DW toPSS. The run was interrupted by a nonconvergence erroron noncondensable gas properties in the PSS, but availableresults allowed to evaluate the pressure gain, with respect tothe theoretical case with 1 : 100 IRIS DW volume and surfacescaled structures, as shown in Figure 22.

In order to reduce distortions on pressure as muchas possible, related to scaling mismatching, all the SPES3containment compartments were scaled 1 : 100 on IRISvolumes and all thicknesses were sized to resist 1.5 MPa


SPES3-110SPES3-109

0E + 00

2E + 05

4E + 05

6E + 05

8E + 05

1E + 06

1.2E + 06

Time (s)

Pre

ssu

re(P

a)

IRIS-HT1

p 401140000p 401140000PR1s54 1000

0 2000 4000 6000 8000 10000


0E + 00

2E + 05

4E + 05

6E + 05

8E + 05

1E + 06

1.2E + 06

Time (s)

Pre

ssu

re(P

a)

IRIS-HT1

p 401140000p 401140000p 401140000

PR1s54 1000

SPES3-111SPES3-105SPES3-104

0 2000 4000 6000 8000 10000


pressure, so limiting the thermal inertia of the metal walls.In particular, the containment air zone heat structures werepreheated at 84◦C, while those in the liquid zone werekept at 48.9◦C. Moreover, the calibrated orifices on theLGMS to DVI lines, the ADS stage I, and EHRS-C CL wereresized to match IRIS mass flows. Figure 23 shows that,notwithstanding a slower DW pressure increase, that case issimilar to the case with IRIS DW scaled 1 : 100 in mass andsurface (SPES3-108), confirming that containment volumeresizing and heat structure preheating are good solutionstoward IRIS containment pressure response. Orifice resizingwas not enough to match the IRIS LGMS to DVI andEHRS-C CL mass flows, while it was correct to scale ADSstage I mass flow (Figure 24), even if a stronger waterentrainment was evidenced in IRIS at the second flow peak.

0E + 00

2E + 05

4E + 05

6E + 05

8E + 05

1E + 06

1.2E + 06

Time (s)

Pre

ssu

re(P

a)

IRIS-HT1

p 401140000p 401140000

PR1s54 1000

SPES3-112SPES3-108

0 2000 4000 6000 8000 10000


0E + 00

2E + 05

4E + 05

6E + 05

8E + 05

1E + 06

1.2E + 06

Time (s)

Pre

ssu

re(P

a)

IRIS-HT1

p 401140000p 401140000p 401140000

PR1s54 1000

SPES3-115SPES3-108SPES3-107

0 2000 4000 6000 8000 10000


Further calibrations of the injection line orifices wereperformed that evidenced contact condensation stronger inSPES3 (RELAP5) than in IRIS (GOTHIC).

A case was run where IRIS containment heat structureswere reproduced on SPES3 with the DW 1 : 100 scaled inmass and surface and all other tanks with 1 mm thick wallsto avoid code convergence errors in case of complete heatstructure removal. Figure 25 shows very similar SPES3 andIRIS containment pressure rising phase and a pressure peakonly 0.1 MPa lower in SPES3 than in IRIS, demonstrating theimportance of a correct simulation of the heat structures.

The containment piping orifice, sized to match IRISinjection mass flows, allowed a direct comparison betweenthe plants, but it did not meet the piping pressure dropscaling criteria. It allowed to understand two important


−0.4

−0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Time (s)

Mas

sfl

ow(k

g/s)

mflowj 143000000 DTmflowj 153000000 STmflowj 982 + 983/100 DTmflowj 981/100 ST

SPES3-115

IRIS-HT1

Figure 24: SPES3-115 and IRIS-HT1 ADS stage I ST and DT massflow (short term).

0E + 00

2E + 05

4E + 05

6E + 05

8E + 05

1E + 06

1.2E + 06

Pre

ssu

re(P

a)

0 5000 10000 15000 20000 25000 30000Time (s)

p 401140000PR1s54∗1000 IRIS-HT1

SPES3-119

Figure 25: SPES3-119 and IRIS-HT1 DW pressure (short term).

differences related to the injection of LGMS into the DVIlines and of PSS into the DW. As shown in Figures 26and 27, IRIS LGMS injection into the DVI line is alwaysdriven by differential pressure between LGMS and DVI line(until about 18700 s), instead in SPES3, such differentialpressure extinguishes earlier (around 9200 s) and later LGMSinjection is driven only by gravity with a large mass flowdecrease. The reason for such early pressure equalizationin SPES3 is related to the PSS injection stop, vent pipeemptying, and gas flow from PSS to DW. That phenomenondid not occur in IRIS, where the vent pipes did not emptyavoiding air transfer from PSS to DW, keeping the PSSpressurized with respect to DW and DVI (Figure 28).

The sensitivity cases on containment tank geometry, heatstructures, and piping pressure drops led to reviewing boththe IRIS and SPES3 models in IRIS-HT5g and SPES3-124. AllIRIS containment heat structures were simulated and SPES3piping geometry was adjusted to match IRIS pressure drops.

0 5000 10000 15000 20000 25000 30000 35000 40000

Time (s)−0.02

0

0.02

0.04

0.06

0.08

0.1

0.12

Mas

sfl

ow(k

g/s)

mflowj 423000000 LGMS-Amflowj 433000000 LGMS-BFL7/100 LGMS-AFL12/100 LGMS-B

IRIS-HT1

SPES3-120

Figure 26: SPES3-120 and IRIS-HT1 LGMS injection mass flow.

0E + 00

2E + 05

4E + 05

6E + 05

8E + 05

1E + 06

1.2E + 06

1.4E + 06

1.6E + 06

1.8E + 06

2E + 06

0 5000 10000 15000 20000 25000 30000 35000 40000

Time (s)

Pre

ssu

re(P

a)

p 406060000 LGMS-Ap 408060000 LGMS-Bp 6010100000 DVI-Ap 630100000 DVI-BPR7∗1000 LGMS-APR8∗1000 LGMS-BP 604401 DVI-AP 62401 DVI-B

IRIS-HT1

SPES3-120

Figure 27: SPES3-120 and IRIS-HT1 LGMS and DVI pressure.

Figure 29 compares SPES3 and IRIS containment pres-sures, showing a good qualitative and quantitative agree-ment. The LGMS to DVI and PSS to DW injection massflows are shown in Figures 30 and 31. With the samesimulated pressure drops in the piping, different values ofmass flow are evidenced due to greater differential pressuresin SPES3 between LGMS and DVI and PSS and DW. Variousreasons could explain these differences and the most likelyis the different code simulation of contact condensationwith the consequent different pressurization of containmentcompartments. Remodelling of IRIS RWST led to similarRWST water temperatures, but greater exchanged power inSPES3 caused faster heat-up (Figure 32).


0

5

10

15

20

25

0 5000 10000 15000 20000 25000 30000 35000 40000Time (s)

Leve

l(m

)

cntrlvar 1439 VENT-Acntrlvar 1441 VENT-BLL14-12 + LL4-1.5 VENT-ALL15-12 + LL6-1.5 VENT-B

IRIS-HT1

SPES3-120

Figure 28: SPES3-120 and IRIS-HT1 PSS vent pipe level.

0E + 001E + 052E + 053E + 054E + 055E + 056E + 057E + 058E + 059E + 051E + 06

0 20000 40000 60000 80000 100000

Time (s)

Pre

ssu

re(P

a)

p 401140000PR1s54∗1000 IRIS-HT5g

SPES3-124

Figure 29: SPES3-124 and IRIS-HT5g DW pressure.

−0.02

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0 10000 20000 30000 40000 50000

Time (s)

Mas

sfl

ow(k

g/s)


IRIS-HT5g

SPES3-124

Figure 30: SPES3-124 and IRIS-HT5g LGMS to DVI mass flow(short term).

−3

−2.5

−2.0

−1.5

−1

−0.5

0

0.5

1

0 1000 2000 3000 4000 5000 6000 7000 8000 900010000

Time (s)

Mas

sfl

ow(k

g/s)

mflowj 47002 + 473 VENT-Amflowj 48002 + 483 VENT-B(FV + FL + FD4)/100 VENT-A(FV + FL + FD9)/100 VENT-B

IRIS-HT5g

SPES3-124

Figure 31: SPES3-124 and IRIS-HT5g PSS to DW mass flow (shortterm).

0

50

100

150

200

250

300

350

400

450

0 20000 40000 60000 80000 100000

Time (s)

Tem

pera

ture

(K)

tempf 520180000 RWST-ABtempf 825010000 RWST-Ctempf 58001 RWST-Atempf 59001 RWST-B

IRIS-HT5g

SPES3-124

Figure 32: SPES3-124 and IRIS-HT5g RWST temperature.

0 20000 40000 60000 80000 100000

Time (s)

0E + 001E + 052E + 053E + 054E + 055E + 056E + 057E + 058E + 059E + 051E + 06

Pre

ssu

re(P

a)

p 401140000

PR1s54∗1000 IRIS-HT5g

SPES3-127

Figure 33: SPES3-127 and IRIS-HT5g DW pressure.


0 20000 40000 60000 80000 100000

Time (s)

IRIS-HT5g

SPES3-127

0

50

100

150

200

250

300

350

400

Tem

per

atu

re(K

)

tempf 520180000 RWST-ABtempf 820180000 RWST-Ctempf 58001 RWST-Atempf 59001 RWST-B

Figure 34: SPES3-127 and IRIS-HT5g RWST temperature.

0 20000 40000 60000 80000 100000

Time (s)−200

0

200

400

600

800

1000

1200

1400

Mas

s(k

g)

RWST out tot massRWST out tot mass IRIS-HT5g

SPES3-127

Figure 35: SPES3-127 and IRIS-HT5g RWST top integral massflow.

The SPES3 PSS bottom remodelling was the furtherattempt to investigate PSS vent pipe emptying at the end ofPSS injection into the DW. No important differences wereobserved. The SPES3-127 results were used to investigatethe EHRS heat transfer to RWST, considered the cause ofthe different containment pressure trend in the long term,where IRIS increased after 50000 s while SPES3 continued todecrease (Figure 33). RWST temperature in SPES3 did notreach saturation, but established at lower values (Figure 34),due to the direct connection, in the model, of RWST topwith the atmosphere control volume, and mass lost throughRWST top caused by water solution in dry air with energyremoval and temperature limitation (Figure 35).

That phenomenon led to a further modification of themodel with the introduction of a discharge pipe at RWSTtop, limiting the contact surface with air and solving theproblem of RWST water temperature that, finally, could

0 20000 40000 60000 80000 100000

Time (s)

250

270

290

310

330

350

370

390

Tem

per

atu

re(K

)

tempf 520180000 RWST-ABtempf 820180000 RWST-Ctempf 520180000 RWST-ABtempf 820180000 RWST-Ctempf 58001 RWST-Atempf 59001 RWST-B

SPES3-130

IRIS-HT5g

SPES3-127

Figure 36: SPES3-130, 127 and IRIS-HT5g RWST temperature.

0 20000 40000 60000 80000 100000

Time (s)

0E + 00

1E + 05

2E + 05

3E + 05

4E + 05

5E + 05

6E + 05

7E + 05

8E + 05

9E + 05

1E + 06

Pre

ssu

re(P

a)

p 401140000

PR1s54∗1000

SPES3-146

IRIS-HT6 rwstc

Figure 37: SPES3-146 and IRIS-HT6 rwstc DW pressure.

0 20000 40000 60000 80000 100000

Time (s)

SPES3-146

IRIS-HT6 rwstc

0E + 00

2E + 06

4E + 06

6E + 06

8E + 06

1E + 07

1.2E + 07

1.4E + 07

1.6E + 07

1.8E + 07

Pre

ssu

re(P

a)

p 130150000P 13015

Figure 38: SPES3-146 and IRIS-HT6 rwstc PRZ pressure.


0

Time (s)−0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Mas

sfl

ow(k

g/s)

mflowj 607000000 EBT-Amflowj 627000000 EBT-BMFLOWJ 605/100 EBT-AMFLOWJ 625/100 EBT-B

SPES3-146

IRIS-HT6 rwstc

0 2000 4000 6000 8000 10000

Figure 39: SPES3-146 and IRIS-HT6 rwstc EBT injection massflow (short term).

0 20000 40000 60000 80000 100000

Time (s)

SPES3-146

IRIS-HT6 rwstc

−0.02

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

Mas

sfl

ow(k

g/s)


Figure 40: SPES3-146 and IRIS-HT6 rwstc LGMS to DVI injectionmass flow.

reach saturation (Figure 36). Faster water heat-up in SPES3showed that EHRS energy transfer to the RWST is greaterthan IRIS. That led to a series of sensitivity cases on astand-alone model of EHRS-RWST that led to investigatingthe differences between the models and finding a commonmodelling approach based on experimental data on anin-pool heat exchanger and literature values of the heattransfer coefficients [13]. The method provided propermultiplying factors for the HTC to be applied to tube heatstructures, condensing and boiling side, in the form offouling factors [14] and a criterion to set the area of the poolslice containing the heat exchanger. IRIS EHRS-RWST wasmodified accordingly in the IRIS-HT6 rwstc case. A stand-alone model was also utilized to calibrate pressure drops in

Time (s)−3

−2.5

−2

−1.5

−1

−0.5

0

0.5

1

Mas

sfl

ow(k

g/s)

mflowj 47002 + 473 VENT-Amflowj 48002 + 483 VENT-B(FV + FL4 + FD4)/100 VENT-A(FV9 + FL9 + FD9)/100 VENT-B

SPES3-146

IRIS-HT6 rwstc

0 2000 4000 6000 8000 10000

Figure 41: SPES3-146 and IRIS-HT6 rwstc PSS to DW injectionmass flow (short term).

Time (s)−2E + 06

0E + 00

2E + 06

4E + 06

6E + 06

8E + 06

1E + 07

1.2E + 07

Pow

er(W

)

cntrlvar 541SG total power (CNTRLVAR51 + 52 + 53 + 54 + 55 + 56 + 57 + 58)/100

SPES3-146

IRIS-HT6 rwstc

0 2000 4000 6000 8000 10000

Figure 42: SPES3-146 and IRIS-HT6 rwstc SG power (short term).

0E + 00

1E + 05

2E + 05

3E + 05

4E + 05

5E + 05

6E + 05

7E + 05

8E + 05

Pow

er(W

)

cntrlvar 582 RWST-ABcntrlvar 585 RWST-CCNTRLVAR 3510/100 RWST-ACNTRLVAR 3520/100 RWST-B

SPES3-146

IRIS-HT6 rwstc

0 20000 40000 60000 80000 100000

Time (s)

Figure 43: SPES3-146 and IRIS-HT6 rwstc RWST power.


0 20000 40000 60000 80000 100000

Time (s)

0

500

1000

1500

2000

2500

3000

3500

Mas

s(k

g)

cntrlvar 408CNTRLVAR 3219/100

SPES3-146IRIS-HT6 rwstc

Figure 44: SPES3-146 and IRIS-HT6 rwstc RV mass.

0 20000 40000 60000 80000 100000

Time (s)

300

350

400

450

500

550

600

650

Tem

pera

ture

(K)

httemp 110100110 bottomhttemp 110101110 middlehttemp 110102110 topHTTEMP 110100110 bottomHTTEMP 110101110 middleHTTEMP 110102110 top

SPES3–146

IRIS-HT6 rwstc

Figure 45: SPES3-146 and IRIS-HT6 rwstc core heater rod outersurface temperature.

EHRS hot legs and cold legs to properly reproduce the IRISloops with adjustment to calibrated orifices. Moreover, theneed of thermally insulating 4% of SPES3 HX heat transfersurface was evidenced to compensate for AISI 304 thermalconductivity greater than IRIS Inconel 600.

The SPES3-146 case included all design and modelupdates previously described and was considered the basecase to compare to IRIS-HT6 rwstc. The main quantitiesof the transient and those that were objective of the SPES3facility model and design optimization are shown in Figures37, 38, 39, 40, 41, 42, 43, 44, and 45.

The last IRIS case was successively run to correct somedifferences, found in RELAP5 and GOTHIC models, aboutthe end elevations of LGMS and ADS stage I lines. Smalldifferences, compared to IRIS-HT6 rwstc results, were foundin LGMS flows as well as some changes in ADS stage I

flow, after initial discharge. Such differences do not affect ormodify the results of the analysis previously described.

The final FSA is planned to be performed on the SPES3-146 and IRIS-HT6 rwstc1a results.

4. Conclusions

The design of the SPES3 facility was finalized thanks to aniterative calculation-design feedback process that allowed toverify the adequacy of containment pressure and reactorvessel mass inventory simulation, objectives of the SBLOCAPIRT for the IRIS reactor [7].

Since the early simulations, efficiency of IRIS safetysystems was demonstrated in coping with SBLOCAs. Thecomparison with the SPES3 results and the early applicationof the FSA allowed to identify the main causes of discrep-ancy between the results and to put in evidence specificphenomena particularly affected by simulation choices. Thecontainment heat structures, the heat transfer from EHRSto RWST, and piping pressure drops were found to be themost affecting parameters in matching the IRIS results. Thereview of the SPES3 design, in accordance to the above-mentioned parameter optimization, led to demonstratingthat the PIRT identified FoMs are satisfied and that theresidual discrepancies can be considered conservative: SPES3RPV mass lower than IRIS mass and SPES3 heater rodtemperatures higher than IRIS ones.

Besides the SPES3 design review, the main outcomeof this work is the availability of a set of data suitablefor the final FSA application, in progress at the moment,and the quantification of SPES3 facility distortions in IRISsimulation.

The SPES3 facility is under construction at SIET labora-tories.

Nomenclature

ADS: Automatic depressurization systemCIRTEN: Consorzio Interuniversitario per la Ricerca

Tecnologica Nucleare (University Consortiumfor Nuclear Technologic Research)

CL: Cold Legcntrlvar: (CNTRLVAR) control variable (RELAP5

variable)CRDM: Control rod drive mechanismDBA: Design basis accidentDC: DowncomerDEG: Double ended guillotineDT: Double trainDVI: Direct vessel injectionDW: Dry wellEBT: Emergency boration tankEHRS: Emergency heat removal system (EHRS-A, B, C

for loops A, B, C)ENEA: Agenzia Nazionale per le Nuove Tecnologie,

l’Energia e lo Sviluppo Economico Sostenibile(Italian National Agency for New Technologies,Energy and Sustainable EconomicDevelopment)


FD: Droplet mass flow rate (GOTHIC variable)FER: Fakultet Elektrotehnike i Racunarstva (Faculty

of Electric Engineering and Computing) FLFeed Line

FL: Liquid mass flow rate (GOTHIC variable in thegraphs)

FoM: Figure of meritFSA: Fractional scaling analysisFV: Gas mass flow rate (GOTHIC variable)GNEP: Global nuclear energy partnershipGOTHIC: Generation of thermal-hydraulic information

for containmentsHTC: Heat transfer coefficienthttemp: (HTEMP) heat structure temperature

(RELAP5 variable)HX: Heat exchangerIRIS: International reactor innovative and secureITF: Integral test facilityLGMS: Long-term gravity make-up systemLL: Liquid level (GOTHIC variable)LOCA: Loss of coolant accidentLP: Lower plenumLWR: Light water reactormflowj: (MFLOWJ) mass flow rate (RELAP5 variable)NPP: Nuclear power plantp: (P) Pressure (RELAP5 variable)PIRT: Phenomena identification and ranking tablePR: Pressure (GOTHIC variable)PRZ: PressurizerPSS: Pressure suppression systemQT: Quench tankRC: Reactor cavityRELAP: REactor loss of coolant analysis programRPV: Reactor pressure vesselRV: Reactor vesselRWST: Refueling water storage tankR&D: Research and developmentSB: Small breakSET: Separate effect testsSIET: Societa Informazioni Esperienze

Termoidrauliche (company for informationand experiences on thermal-hydraulics)

SG: Steam generatorSL: Steam lineSMR: Small and medium-sized reactorSPES: Simulatore pressurizzato per esperienze di

sicurezza (pressurized simulator for safety tests)ST: Single traintempf: (TEMPF) liquid temperature (RELAP5

variable)WEC: Westinghouse Electric Company LLC.

References

[1] M. D. Carelli, L. E. Conway, L. Oriani et al., “The design andsafety features of the IRIS reactor,” Nuclear Engineering andDesign, vol. 230, no. 1–3, pp. 151–167, 2004.

[2] M. D. Carelli, B. Petrovic, L. E. Conway et al., “IRIS designoverview and status update,” in Proceedings of the 13th

International Conference on Nuclear Engineering (ICONE13-50442 ’05), Beijing, China, May 2005.

[3] B. Petrovic, M. D. Carelli, and N. Cavlina, “IRIS—international reactor innovative and secure: progress in devel-opment, licensing and deployment activities,” in Proceedings ofthe 6th International Conference on Nuclear Option in Coun-tries with Small and Medium Electricity Grids, Dubrovnik,Croatia, May 2006.

[4] M. D. Carelli, B. Petrovic, M. Dzodzo et al., “SPES-3experimental facility design for IRIS reactor integral testing,”in Proceedings of the European Nuclear Conference (ENC ’07),Brussels, Belgium, September 2007.

[5] M. Carelli, L. Conway, M. Dzodzo et al., “The SPES3experimental facility design for the IRIS Reactor simulation,”Science and Technology of Nuclear Installations, vol. 2009,Article ID 579430, 12 pages, 2009.

[6] R. Ferri, A. Achilli, C. Congiu et al., “SPES3 facility and IRISreactor numerical simulations for the SPES3 final design,” inProceedings of the European Nuclear Conference (ENC ’10),Barcelona, Spain, May June 2010.

[7] T. K. Larson, F. J. Moody, G. E. Wilson et al., “Iris small breakloca phenomena identification and ranking table (PIRT),”Nuclear Engineering and Design, vol. 237, no. 6, pp. 618–626,2007.

[8] IAEA-TECDOC 1536, “Status of small reactor designs withouton-site refuelling (IAEA ’07),” 2007.

[9] R. Ferri and C. Congiu, SPES3-IRIS facility nodalization forRELAP5 Mod.3.3 code and steady state qualification. SIET 01423 RT 08 Rev.0, ENEA FPN-P9LU-017, 2009.

[10] R. Ferri and C. Congiu, SPES3-IRIS facility RELAP5 base casetransient analyses for design support. SIET 01 489 RT 09Rev.0., ENEA FPN-P9LU-035, 2009.

[11] R. Ferri and C. Congiu, SPES3-IRIS facility RELAP5 sensitivityanalyses of the Lower Break transient for design support. SIET01 499 RT 09 Rev.0., FPN- P9LU-040, 2009.

[12] R. Ferri, SPES3-IRIS facility RELAP5 sensitivity analyses onthe containment system for design review. SIET 01 526 RT 09Rev.0., ENEA NNFISS-LP2-017, 2010.

[13] R. Ferri and P. Meloni, Approach for a correct simulation ofthe SPES3-IRIS Emergency Heat Removal System with theRELAP5/MOD3 Code. SIET 01 745 RT 11 Rev.0. Piacenza,Italy, 2011.

[14] RELAP5 code manual. NUREG/CR-5535/Rev.1 Idaho Nation-al Engineering Laboratory (USA), 2001.

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