iaea international collaborative standard problemon

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Fourth Workshop for the ICSP on Integral Water Cooled Reactor Designs, Pisa 25-28 February 2013, Italy

IAEA

International Collaborative Standard Problem on

Integral PWR Design Natural Circulation Flow Stability and

Thermo-hydraulic Coupling of Containment and

Primary System during Accidents

OPEN OPEN OPEN OPEN CalculationCalculationCalculationCalculation ResultsResultsResultsResults

FulvioFulvioFulvioFulvio MascariMascariMascariMascari, Giuseppe , Giuseppe , Giuseppe , Giuseppe VellaVellaVellaVella

Dipartimento Energia, Ingegneria dell’Informazione e Modelli Matematici(DEIM)

Università degli Studi di Palermo

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oContents


2

�TRACE REACTOR SYSTEM ANALYSIS CODE

�OSU MASLWR VS TRACE MODEL DESCRIPTION

�TEST2 ANALYSIS

�TEST3 ANALYSIS

�LEASSON LEARNED

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oTRACE REACTOR SYSTEM ANALYSIS CODE

� The U.S. Nuclear Regulatory Commission (USNRC) is in the process of developing a modern code for reactor analysis.

� It is an evolutionary code that merges RAMONA, RELAP5, TRAC-PWR and TRAC-BWR into a single code.

� The consolidated code is called the TRAC/RELAP Advanced Computational Engine or TRACE.


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� TRACE is a component-oriented code designed to analyze reactor transients and accidents up to the point of fuel failure.

� It is a finite-volume, two-fluid, compressible flow code with 3-D capability.

� It can model heat structures and control systems that interact with the component models and the fluid solution.

� TRACE can be run in a coupled mode with the PARCS three dimensional reactor kinetics code.

� TRACE can be run in parallel.

� TRACE has been coupled to CONTAIN through its exterior communications interface (ECI).

� TRACE has been coupled to as user-friendly front end, SNAP (Symbolic Nuclear Analysis Package), that supports input model development and accepts existing RELAP5 and TRAC-P input models.

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oTRACE FIELD EQUATIONS

5


•Mixture mass conservation equation:

0)]1([])1([ =−+⋅∇+−+∂∂

αραρρααρ llvvlv vvt

rr

•Vapor mass conservation equation:

vvvv vt

Γ=⋅∇+∂∂

)()( αραρr

•Liquid momentum conservation equation:

gvvc

vvvvvvc

pvvt

vll

l

wlv

l

condlvlv

l

i

l

lll rrrrrrrrrrrr

+−

+−−Γ

−−−−

+∇−=∇⋅+∂∂

||)1(

)()1(

||)()1(

1

ραραραρ

•Gas momentum conservation equation:

gvvc

vvvvvvc

pvvt

vvv

v

wvlv

v

Boiling

lvlv

v

i

v

vvv rrrrrrrrrrrr

++−Γ

−−−+∇−=∇⋅+∂

∂||)(||)(

1

αραραρρ

•Mixture energy conservation equation:

dlvwllvlllvvvllvv qqvvpveveeet

++−+⋅∇−=−+⋅∇+−+∂∂

])1([])1([])1([(rrrr

αααραραραρ

•Vapor energy conservation equation:

vvivdvwvvvvvvv hqqqvpt

pveet

Γ++++⋅∇−∂∂

−=⋅∇+∂∂

)()()(rr

αα

αραρ

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oTRACE FIELD EQUATIONS

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TRACE/SNAP environment architecture

SNAP System

Model database

RELAP5 ASCII

Input

TRAC-P ASCII

Input

TRAC-B ASCII

Input

SNAP

TRACE Input

Processing

Computational

Engine

Other support

Applications

3D Neutron

kinetics

Platform Independent

Binary File

Interprocess Message Passing

Service

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oOSU-MASLWR TRACE MODEL

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OSU-MASLWR VS TRACE MODEL

Primary System

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Core:

One thermal hydraulic region

thermally coupled with one

equivalent active heat structure

simulating the 56 electric heaters

Helical Coil

Steam Generator

Thick Baffle Plate

RPV is divided in two slice

hydraulic regions

PRZ:

divided in two hydraulic

regions to allow natural

circulation convection

phenomena

UP:

UP is divided in two

thermal hydraulic regions

connected to the PRZ.

TEE components are used

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Primary System

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Lower core flow plate

FDP-131: primary volumetric flow rate

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Primary System

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Parameters OSU-MASLWR

facility

TRACE

model

Error (m)

inch m m

Vent line elevation from the hydraulic bottom 174.44 4.4308 4.3616 0.07

Blow-down line elevation from the hydraulic bottom 53.25 1.3526 1.2931 0.06

Sump line elevation from the hydraulic bottom 29 0.7366 0.7020 0.03

Core heaters length 23.5 0.5969 - -

Total core heaters length (56 heaters) 1316 33.4264 33.4264 0.00

Non active core heaters length - 0.1401 - -

Total non active core heaters length - 7.8456 7.8456 0.00

PRZ heaters length - 0.2032 - -

Total PRZ heaters length (3 heaters) - 0.6096 0.6096 0.00

Lower shell section length 27 0.6858 0.6716 0.01

Coil section length (a) 49.25 1.2510 1.2510 0.00

Coil section length (b) 41.25 1.0478 1.0478 0.00

Steam drum section length 12 0.3048 0.3048 0.00

Steam line inlet position in the steam drum 11.75 0.2985 0.3048 0.01

Average position of the outlet coils in the steam

drum

4.38 0.1113 0.1113 0.00

Flange length 4.631 0.1176-

-

Total flange length-

0.23530.2352574

0.00

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Primary System heat structures

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Heat losses

core power

Mass flow

Over-estimation of the direct heat exchange

between Hot and Cold Region

Inlet core temperature increase

Direct heat exchange between Hot

and Cold Region

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oOSU MASLWR - Secondary System

� Steam generators.

• Helical coil, once through heat exchangers.

• Located within the pressure vessel in the annular space between the hot leg riser and the inside surface of the pressure vessel.


� Steam produced in the steam generators is vented to the atmosphere.

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oOSU MASLWR - Secondary System

� Steam generator consists of 3 separate parallel sections.

• Outer coil and middle coils consist of 5 tubes each. Inner coil consists of 4 tubes.

• Common inlet header to ensure pressure equilibrium.


Inner Coils

Middle Coils

Outer Coils

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SG COILS (three equivalent group of pipe)

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Prim

ary

sid

e v

olu

me

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FW lines

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Feed water lines

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SG COILS

� SG coils, are modeled with three different “equivalent” oblique group of pipes in order to simulate the three separate parallel helical coils.

� The equivalent group of pipes simulating the outer coils characterizes only four helical coils because, as it is described in the information’s disclosed to the ICSP participants, one of the outer coil is plugged.

� In order to simulate the metal mass of this helical coil a passive heat structure is modeled.

� Previous analyses, based on the TRACE simulation of the OSU-MASLWR-002 test, showed that the instabilities of the superheat condition of the fluid at the outlet of the SG are also related to the equivalent SG model. Since in theses analyses a model with one equivalent vertical group of pipes shows a more stable fluid temperature at the SG outlet, this model is used as reference for the ICSP test 2 and 3. A sensitivity analyses with three different equivalent oblique group of pipe is considered for the ICSP test 3

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SG COILS (1 equivalent group of pipe)

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Primary and secondary System

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Parameters OSU-MASWR Facility

ID (m) Thickness (m) OD (m) Insulation (m) Total thickness (m)

RPV external shell 0.2921 0.03175 0.3556 0.102 0.13375

HL lower shell 0.1971 0.00305 0.2032 -

HL upper shell 0.1023 0.00602 0.11434 -

Core heater rods - - 0.0125 -

PRZ heater rods - - 0.016 -

SG coils 0.0126 0.00165 0.0159

Steam line 0.03504 0.00356 0.04216 - -

Feed water lines 0.0094 0.00165 0.0127 - -

ParametersTRACE Model

ID (m) Thickness (m) OD (m) Insulation (m) Total thickness (m)

RPV external shell 0.2921 0.03175 0.3556 0.102 0.13375

HL lower shell 0.1971 0.00305 0.2032 -

HL upper shell 0.1023 0.00602 0.11434 -

Core heater rods - - 0.0125 -

PRZ heater rods - - 0.016 -

SG coils 0.0126 0.00165 0.0159

Steam line 0.03504 0.00356 0.04216 0.055 0.05856

Feed water lines 0.0094 - - - -

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oOSU MASLWR - Containment

• One vessel models the suppression pool volume, vapor bubble volume and the condensation surface inside of the containment vessel.

• The second vessel models the heat capacity of the water pool within which the containment vessel is held.

• Two tanks are separated by a plate of 0.04 m thick stainless steel.

� Models the heat transfer between the containment vessel and the surrounding vessel pool.


� The MASLWR containment vessel and the surrounding containment pool are modelled in the OSU test facility as two separate vessels.

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Containment Structure

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The HPC is modeled with one

equivalent group of pipe.

HPC

CPV

Heat transfer plate

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Containment Structure-Sensitivity Study

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The HPC is modeled with two

different pipes, connected by

single junctions, in order to allow

possible natural circulation

/convection phenomena inside the

containment.

HPC

CPV

Heat transfer plate

FOR THE SIMULATION OF THE ICSP

TEST 2 (one sensitivity study)

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Containment Structures

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Parameters OSU-MASWR Facility

ID (m) Thicknes

s (m)

OD (m) Insulation

(m)

Total

thickness

(m)

L (m)

HPC lower external

shell 0.26162 0.00419 0.27 0.102 0.10619 3.87

HPC upper cylindrical

shell 0.49128 0.00476 0.508 0.102 0.10676 1.21

CPV external shell 0.7493 0.00635 0.762 0.508 0.51435 7.15

Thikness

(m) Wide (m) - - - L (m)

Heat transfer plate 0.0381 0.168 - - - 5.59

Parameters OSU-MASLWR TRACE Model

ID (m) Thicknes

s (m)

OD (m) Insulation

(m)

Total

thickness

(m)

L (m)

HPC lower external

shell 0.26162 0.00419 0.27 0.102 0.106 3.87

HPC upper cylindrical

shell 0.49128 0.00476 0.508 0.102 0.10676 1.21

CPV external shell 7.15

Thikness

(m)

Wide (m)

- - -

L(m)

Heat transfer plate 0.0381 0.168 - - - 5.59

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oOSU MASLWR – ADS LINES


� The containment vessel is connected to the reactor pressure vessel by six independent lines.

• Two Automatic Depressurization System (ADS) lines.

• Two vent lines.

• Two sump recirculation lines.

• Flow controlled by an independent automatically operated valve.

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ADS LINES

25


In order to simulate the

ICSP test 2, the ADS lines

are modeled separately

in order to correctly

simulate the different

ADS valve actions

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ADS LINES

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OSU_MASLWR Facility

Line Tot lenght Lenght inside HPC delta Z

Vent line A 2.1 0.22 0

Vent line B 2.43 0.22 0

Sump Line A 3.18 0.43 0.21

Sump line B 3.26 0.43 0.21

OSU-MASLWR TRACE Model

Line Tot lenght Lenght inside HPC delta Z

Vent line A 2.10 0.22 0

Vent line B 2.43 0.22 0

Sump Line A 3.20 0.43 0.21

Sump line B 3.26 0.43 0.21

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PD CALIBRATION

�The value of roughness used in the hydraulic component is 5.0E-6 m.

�In order to estimate the k loss coefficient different options have been used. �For an abrupt expansion the Borda-Carnot loss coefficient

has been used:

27


2

1

1

−=

+j

j

A

AK

�For an abrupt contraction a table for

= +

j

j

A

AKK

1

has been used

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PD CALIBRATIONConsidering the mass flow rate of the OSU-MASLWR-002 [core power

80kW – 160 kW ] a sensitivity analysis of the core pressure drop has

been performed in order to have a comparable mass flow rate during its

simulation.

28


The resulting k coefficients

in the core region have

been used for the

simulation of the

ICSP test 1.

This is only a preliminary

analysis.

More Detail analysis is

required for the pressure

drop evaluation.

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OSU MASLWR- TEST FACILITY PROCESS

AND INSTRUMENTATION DIAGRAM


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oTRACE NODALIZATION MEASUREMENT POINTSTRACE NODALIZATION MEASUREMENT POINTSTRACE NODALIZATION MEASUREMENT POINTSTRACE NODALIZATION MEASUREMENT POINTS

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oTRACE NODALIZATION MEASUREMENT POINTSTRACE NODALIZATION MEASUREMENT POINTSTRACE NODALIZATION MEASUREMENT POINTSTRACE NODALIZATION MEASUREMENT POINTS

31


Facility instrumentation TRACE model measurement points

PT 301 1325 cell 2

TF 121, 122, 123, 124 51 cell 1

TF 106 21 cell 2

FDP 131 111 edge 1

TF 111 141 cell 2

TF 131, 133, 134 91 cell 1

DP 101 [RV 101-102] cb22 [1 cell 1 - 21 cell 2]

DP 102 [RV102- 103] cb 23 [21 cell 2- 21 cell 5]

DP 103 [RV 103 104] cb24 [21 cell 5 - 21 cell 8]

DP 104 [RV 104 108] cb 25 [21 cell 8 - 141 cell 2]

DP 105 [RV 105 108] cb55 [141 cell 2 - 101 cell 1]

DP 106 [RV 101 105] cb56 [101 cell 1 - 1 cell 1]

LDP 301 cb12

LDP 106 cb18

FCM 511 1071 edge 5

FCM 521 1061 edge 3

FCM 531 1051 edge 2

PT 511 1071 cell 5

PT 521 1061 cell 3

PT 531 1051 cell 2

TF 611, 612, 613, 614, 615 771 cell 1

TF 621, 622, 623, 624, 625 621 cell 1

TF 631, 632, 633, 634 431 cell 1

FVM 602 T 1021 cell 20

FVM 602 P 1021 cell 20

Secondary steam superheat cb30

Facility instrumentation TRACE model measurement points

FMM-501 1315 edge 1

TLN 501 1315 cell 1

PCS-106 A Flow 1585 edge 2

PCS-106 B Flow 961 edge 2

PCS-108 A Flow 1425 edge 2

PCS-108 B Flow 1001 edge 2

Total primary mass Cb 21

Void Fraction (Core Outlet) 21 cell 2

Void Fraction (Upper Plenum Bottom)

141 cell 1

Primary Void Fraction (SG Inlet)

151 cell 3

Primary Void Fraction (SG outlet)

861 cell 1

Heat Transfer (Core Rod)

905

Core power Heat structure 915

Heat Transfer (SG - Primary to Secondary)

Heat strctures 781(single coil)-441

Heat structures 781, 791, 801 (three equivalent coil)

441

Heat Transfer (Across Chimney - Hot to Cold Leg)

Heat strctures 831+821+823

Heat Losses Cb2

TF 811, 821, 831, 841, 851,861 1595 cell 9, 18, 24, 30, 36,

38

TF 812, 822, 832, 842, 852, 862

1615 A9, 18,24,30,36,38

R02

TF 813, 823, 833, 843, 853, 863

1615 A9, 18,24,30,36,38

R03

TF 814, 824, 834, 844, 854, 864

1615 A9, 18,24,30,36,38

R04

TF 815, 825, 835, 845, 855, 865

1605 cell 14, 23, 29, 35, 31,

43

PT 801 1595 cell 1

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oICSP TEST 2

�In order to improve the results of the TRACE ICSP test 2 calculated data, few modifications have been implemented in the input deck. �An increase of the heat losses;

�A better fitting of the SG secondary side outlet pressure, that is considered as a BIC

�The control of the SG outlet temperature during the steady state phase has been implemented as well.

�The SG outlet pressure, the SG inlet pressure, the SG inlet temperature and the SG mass flow rate are imposed as BIC. Considering the availability of the experimental data a revision of these BIC has been implemented during the OPEN case.

32


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oICSP TEST2 ANALYSES PERFORMED

33


BL

IND

PH

AS

E

ID

Calculation

Variation from reference

calculation

Target of the

sensitivity

analyses

Results of the

sensitivity analyses

REF2

BLIND

Reference BLIND PHASE

calculation

REF It is not considered the delay of the

logic

There isn’t sensible

difference with the

results of the REF2

case considering a

contemporary action

of the valve 106 A

and B, 108 A and B

when the difference of

pressure between the

RPV and the HPC is

0.034 Pa

SEN1 Change the control of the FW mass

flow rate, during the steady state

phase, in order to have an hotter

primary side condition with respect

to the ICSP specification

Show the effect

of the initial

condition on the

cycling phase

characterizing

the transient

An increase of the

cycling region has

been predicted by the

code

SEN2 Change the control of the FW mass

flow rate, during the steady state

phase, in order to have a colder

primary side condition with respect

to the ICSP specification

Show the effect

of the initial

condition on the

cycling phase

characterizing

the transient

A decrease of the

cycling region has

been predicted by the

code

SEN4 Increase of the heat losses of the

facility

Show the effect

of the heat losses

in the transient

A general reduction of

the cycling phase is

predicted by the code.

The primary system

shows a faster

depressurization as it

is expected.

SEN5 Decrease of the k coefficient of the

PCS 106 A

Show the effect

of the k

coefficient in the

transient

A variation of the

HPC pressure

behavior is observed

SEN6 Increase of the k coefficient of the

PCS 106 A

Show the effect

of the k

coefficient in the

transient

A variation of the

HPC pressure

behavior is observed

2C Divide the HPC in two thermal

hydraulic regions

Allow the

potential natural

circulation

convetion

phenomena

The thermal

stratification in the

HPC is influenced

OP

EN

PH

AS

E OPEN Reference OPEN PHASE

calculation

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oINITIAL CONDITION FOR THE ICSP TEST INITIAL CONDITION FOR THE ICSP TEST INITIAL CONDITION FOR THE ICSP TEST INITIAL CONDITION FOR THE ICSP TEST 2222

� In order to reach the BIC of the second ICSP test an arbitrary pre-test phase is conducted during the simulation.

� At the end of this pre-test phase, SOT, the BIC of the test are stable for 10 minutes prior to the loss of feed water event.

� The comparison of the initial condition reached by the code and the initial condition provided in the ICSP test plan are reported in the following table

34


Parameter MASLWR Unit Experimental Value

Steady-State Value from Code

Pressurizer pressure PT-301 MPa(a) 8.72 8.72

Pressurizer level LDP-301 m 0.36 0.34

Power to core heater rods (average)

KW-101/102 kW 298 298

Feedwater temperature TF-501 ºC 21.39 21.39

Steam temperature FVM-602-T ºC 205.38 200.4

Steam pressure FVM-602-P MPa(a) 1.411 1.414

Ambient air temperature

(Average)

ºC 24.89 24.85

HPC pressure PT-801 MPa(a) 0.1268 0.1264

HPC water temperature

(Average)

TF-811 ºC 27 26.85

HPC water level LDP-801 m 2.82 2.81

CPV water temperature TF-815 °C 300

Primary flow at core outlet FDP-131 kg/s 1.79

Primary coolant temperature at core inlet

TF- 121/122/

123/124

ºC 215 213

Primary coolant temperature at core outlet

TF-106 ºC 251.52 250.29

Feedwater flow FMM-501 kg/s Oscillating between

0.1 and 0.115

Steam flow FVM-602-M kg/s 0.1085

Primary coolant subcooling at core outlet

ºC 49

Total heat loss through primary system

kW About 3

Heat transfer through SG kW 293688.47

Maximum surface temperature of core heater rods

ºC Outer surface: 339

Location from the SG secondary inlet to reach

- saturation

- superheat

m Saturation : pipe 241

super heat: pipe 401

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FACILITY CONFIGURATION BEFORE

THE SOT OF THE TEST 2

35


System Facility

Operati

on

TRACE Model

Operation

Note

Core Heaters ON ON

PRZ Heaters ON ON

It is defined a table in order to control

the primary pressure

Independent variable = PRZ pressure

Dependent variable = PRZ heater

power

In order to

maintain the

primary pressure

set-point

Containment

Heaters

OFF OFF -

Feed water ON ON

It is defined a table in order to control

the outlet SG temperature

Independent variable = outlet SG

temperature Dependent variable =

feed water mass flow rate

In order to

remove the net

primary power

[primary power

less ambient

losses]

Main feed

water pump

ON

Charging

pump

OFF - -

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BOUNDARY CONDITION OF THE TRACE MODEL

DURING THE PRE-TEST PHASE OF THE ICSP TEST 2

36


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DURING THE PRE-TEST PHASE OF THE ICSP TEST 2

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oTEST TEST TEST TEST 2 2 2 2 PROCEDUREPROCEDUREPROCEDUREPROCEDURE

� The test 2 involves a loss of FW transient with subsequent automatic depressurization system actuation and long term cooling.

38


Time Facility Operation

0 (SOT) Start of simulation – steady state

(start of data collection)

De-energize PZR heaters

Once the transient has begun, the

pressurizer heaters are manually

deenergized.

Event 1 Stop MFP

Shut HPC vent valve SV – 800

Event 2 PZR pressure (PT-301) reaches 9.064 MPa(a) (1300 psig)

Enter decay power mode

~ 30 s

Event 3 Open ADS vent valve (PCS-106A) Major procedural change was that the

blowdown began 18 seconds after the

decay power was initiated at 1300 psig

instead of waiting until the pressure had

risen to 1350 psig.

Event 4 Different actions take place following the condition reported in the table 3-4.

Record opening and closing times for PCS-106A

Event 5 Start long-term cooling when pressure difference between primary system and

HPC (PT-301 minus PT-801) becomes less than 5 psi (0.034 MPa)

Open and remain open of PCS-106A and PCS-106B

Open and remain open of PCS-108A and PCS-108B

Event 6 End of test when one of the following conditions is reached:

- PZR pressure ≤ 0.135 MPa(a) (5 psig)

- Primary coolant temperature (TF-132) ≤ 35 ºC (95 ºF)

- 24 hours have elapsed

PT 801 indicating Pressure PCS 106 A SV-800250 psig SHUT SHUT

275 psig SHUT OPEN

200 psig OPEN SHUT

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FACILITY CONFIGURATION DURING THE

ICSP TEST 2

39


System Facility

Operation

TRACE model

Operation

Note

Core Heaters ON Following the ICSP

set point are

turned in decay

mode

PRZ Heaters ON� OFF Following the ICSP

setpoint is OFF

In order to prevent their

uncovered when the

reduction of the inventory

takes place

Containment

Heaters

OFF OFF

Feed water OFF OFF

Main feed

water pump

OFF

Charging

pump

OFF - -

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BOUNDARY CONDITION OF THE TRACE MODEL BOUNDARY CONDITION OF THE TRACE MODEL BOUNDARY CONDITION OF THE TRACE MODEL BOUNDARY CONDITION OF THE TRACE MODEL

DURING THE SIMULATION OF THE ICSP TEST DURING THE SIMULATION OF THE ICSP TEST DURING THE SIMULATION OF THE ICSP TEST DURING THE SIMULATION OF THE ICSP TEST 2222

40


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ICSP TEST 2

EVENT SEQUENCE

41


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oANALYSES OF THE ICSP TEST 2

�At the SOT a At the SOT a At the SOT a At the SOT a loss of feed water loss of feed water loss of feed water loss of feed water event takes placeevent takes placeevent takes placeevent takes place

�Since the energy removing capacity of the secondary Since the energy removing capacity of the secondary Since the energy removing capacity of the secondary Since the energy removing capacity of the secondary side tends to zero a primary pressure increase takes side tends to zero a primary pressure increase takes side tends to zero a primary pressure increase takes side tends to zero a primary pressure increase takes place. place. place. place.

�When the primary pressure reaches the value of When the primary pressure reaches the value of When the primary pressure reaches the value of When the primary pressure reaches the value of 9.064 9.064 9.064 9.064 MPaMPaMPaMPa the core heaters are turned in the core heaters are turned in the core heaters are turned in the core heaters are turned in decay decay decay decay modemodemodemode following the experimental data disclosed in following the experimental data disclosed in following the experimental data disclosed in following the experimental data disclosed in the blind ICSP phase specification the blind ICSP phase specification the blind ICSP phase specification the blind ICSP phase specification

((((BLIND: BLIND: BLIND: BLIND: 26 s - OPEN:42s after the SOT).).).).

�The valve PCS The valve PCS The valve PCS The valve PCS 106 106 106 106 A opens A opens A opens A opens (BLIND: 44 s - OPEN: 59 s after the SOT) and a and a and a and a bowdownbowdownbowdownbowdown takes place. takes place. takes place. takes place.

�The primary and HPC pressure starts a The primary and HPC pressure starts a The primary and HPC pressure starts a The primary and HPC pressure starts a process of process of process of process of equalizationequalizationequalizationequalization

43


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�Chocked flow phenomena Chocked flow phenomena Chocked flow phenomena Chocked flow phenomena takes place in the vent line Atakes place in the vent line Atakes place in the vent line Atakes place in the vent line A

�A rapid increase of the HPC pressure takes place. The A rapid increase of the HPC pressure takes place. The A rapid increase of the HPC pressure takes place. The A rapid increase of the HPC pressure takes place. The volume of the HPC is filled with steam condensing in the volume of the HPC is filled with steam condensing in the volume of the HPC is filled with steam condensing in the volume of the HPC is filled with steam condensing in the containment wall transferring energy to the CPVcontainment wall transferring energy to the CPVcontainment wall transferring energy to the CPVcontainment wall transferring energy to the CPV

�At BLIND: At BLIND: At BLIND: At BLIND: 125 125 125 125 s s s s –––– OPEN OPEN OPEN OPEN 134 134 134 134 s s s s after the SOT the valve after the SOT the valve after the SOT the valve after the SOT the valve PCS PCS PCS PCS 106 106 106 106 A, starts to A, starts to A, starts to A, starts to cyclingcyclingcyclingcycling following the logic actuation following the logic actuation following the logic actuation following the logic actuation of the table of the table of the table of the table 3333----4444. . . . InfactInfactInfactInfact ,,,,

between between between between BLIND: BLIND: BLIND: BLIND: 125125125125----4062 4062 4062 4062 s s s s –––– OPEN OPEN OPEN OPEN 134134134134----4039 4039 4039 4039 ssss, the , the , the , the

HPC pressure oscillates but never reach the HPC pressure oscillates but never reach the HPC pressure oscillates but never reach the HPC pressure oscillates but never reach the setpointsetpointsetpointsetpoint of of of of

275 275 275 275 psig.psig.psig.psig.

44


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ANALYSES OF THE ICSP TEST 2

Long term phase

� BLIND: BLIND: BLIND: BLIND: 4062 4062 4062 4062 s s s s ---- OPEN :OPEN :OPEN :OPEN :4039 4039 4039 4039 s after s after s after s after the SOT the pressure the SOT the pressure the SOT the pressure the SOT the pressure differences between the primary side and the HPC is less than differences between the primary side and the HPC is less than differences between the primary side and the HPC is less than differences between the primary side and the HPC is less than 0.034 0.034 0.034 0.034 MPaMPaMPaMPa, therefore the valve PCS , therefore the valve PCS , therefore the valve PCS , therefore the valve PCS 106 106 106 106 A stays permanently open.A stays permanently open.A stays permanently open.A stays permanently open.

� The valves PCS The valves PCS The valves PCS The valves PCS 106 106 106 106 B (BLIND B (BLIND B (BLIND B (BLIND 4152415241524152ssss---- OPEN OPEN OPEN OPEN 4129412941294129s after the SOT), s after the SOT), s after the SOT), s after the SOT), PCS PCS PCS PCS 108 108 108 108 A (BLIND A (BLIND A (BLIND A (BLIND 4154 4154 4154 4154 ssss----OPEN OPEN OPEN OPEN 4131413141314131s after the SOT) and B s after the SOT) and B s after the SOT) and B s after the SOT) and B (BLIND:(BLIND:(BLIND:(BLIND:4155415541554155s s s s ---- OPEN OPEN OPEN OPEN 4132413241324132s after the SOT) s after the SOT) s after the SOT) s after the SOT) stay permanently open stay permanently open stay permanently open stay permanently open permitting the permitting the permitting the permitting the refill of the primary side and the long term cooling refill of the primary side and the long term cooling refill of the primary side and the long term cooling refill of the primary side and the long term cooling phenomenology typical of the MASLWR designphenomenology typical of the MASLWR designphenomenology typical of the MASLWR designphenomenology typical of the MASLWR design

� During the long term cooling the During the long term cooling the During the long term cooling the During the long term cooling the vapor produced in the core goes in vapor produced in the core goes in vapor produced in the core goes in vapor produced in the core goes in the upper part of the facility and through the vent valve goes to the the upper part of the facility and through the vent valve goes to the the upper part of the facility and through the vent valve goes to the the upper part of the facility and through the vent valve goes to the HPC where it is condensed. HPC where it is condensed. HPC where it is condensed. HPC where it is condensed. At this point through the sump line the At this point through the sump line the At this point through the sump line the At this point through the sump line the fluid goes to the core again. fluid goes to the core again. fluid goes to the core again. fluid goes to the core again.

� At the end of the test At the end of the test At the end of the test At the end of the test (15814 s after the SOT) the primary pressure the primary pressure the primary pressure the primary pressure is at about is at about is at about is at about BLIND: BLIND: BLIND: BLIND: 0.6 0.6 0.6 0.6 MpaMpaMpaMpa----OPEN:OPEN:OPEN:OPEN:0.52 0.52 0.52 0.52 MpaMpaMpaMpa....

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LONG TERM COOLING TYPICAL OF THE MASLWR

46


Loss of feed water

When Primary P = 9.064

MPa:

Core decay mode

PCS 106 A open

Start of the Blowdown

When the pressure differences between

the RPV and HPS is less than 0.034

PCS 106 A and B and PCS 108 A nad B

stay permanently open

During the long term cooling the vapor

produced in the core goes in the upper

part of the facility and through the vent

valve goes to the HPC where it is

condensed. At this point through the

sump line the fluid go to the core again.

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Blowdown; Break Flow; Cycling Phase.

47


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�The primary pressure behaviour is well predicted by the TRACE code.

�Four different phases could be identify:

�Primary pressure peak phase, �Blowdown phase, �Valve cycling phase and �Long term cooling phase.

�The The The The open calculation results show a more accurate open calculation results show a more accurate open calculation results show a more accurate open calculation results show a more accurate primary pressure primary pressure primary pressure primary pressure behaviorbehaviorbehaviorbehavior prediction; this is related prediction; this is related prediction; this is related prediction; this is related to an increase of the heat losses of the RPV TRACE to an increase of the heat losses of the RPV TRACE to an increase of the heat losses of the RPV TRACE to an increase of the heat losses of the RPV TRACE modelmodelmodelmodel

48


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49


� The oscillation of the primary pressure

is well predicted by the TRACE code

and its length is in general depended

from

� the steady state conditions before

the SOT (for example the way to

control the feed water mass flow

rate before the SOT can influence

the fluid condition of the facility

before the SOT) and

� the heat losses of the facility

as it is shown from the sensitivity

analyses performed in the BLIND

phase of the ICSP.

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50


PCS106 A

PCS106 B

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51


PCS108 A

PCS108 B

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�TTTThe expected behavior of the vent and sump recirculation valves are predicted by the code.

�The behavior of the PCS 106 A, is characterized by an oscillating mass flow rate due to the valve cycling and a long term cooling mass flow rate behavior.

�The PCS 106 B is characterized by a first mass flow ratepeak, when the valves is opened, and a long termcooling phase mass flow rate; no oscillation are presentfor these valves.

�The PCS 108A/B are characterized by a first mass flow rate direction change with consequent mass flow rate peak and an long term cooling phase mass flow rate behavior

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Natural Circulation Phenomena

53


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55

The core outlet and the The core outlet and the The core outlet and the The core outlet and the average inlet temperature, average inlet temperature, average inlet temperature, average inlet temperature, are predicted by the code. are predicted by the code. are predicted by the code. are predicted by the code.

A decrease of the inlet core A decrease of the inlet core A decrease of the inlet core A decrease of the inlet core temperature is temperature is temperature is temperature is experimentally observed experimentally observed experimentally observed experimentally observed when the refill of the core when the refill of the core when the refill of the core when the refill of the core takes place. takes place. takes place. takes place.

During the simulation the During the simulation the During the simulation the During the simulation the decrease of the inlet decrease of the inlet decrease of the inlet decrease of the inlet temperature is not observed temperature is not observed temperature is not observed temperature is not observed and, as it is observed by the and, as it is observed by the and, as it is observed by the and, as it is observed by the analysis of the delta T core, a analysis of the delta T core, a analysis of the delta T core, a analysis of the delta T core, a difference of temperature is difference of temperature is difference of temperature is difference of temperature is always present though minor always present though minor always present though minor always present though minor from a quantitative point of from a quantitative point of from a quantitative point of from a quantitative point of view.view.view.view.

This could be related to the This could be related to the This could be related to the This could be related to the mono dimensional model of mono dimensional model of mono dimensional model of mono dimensional model of the downthe downthe downthe down----comer causing a comer causing a comer causing a comer causing a general mixing of the water in general mixing of the water in general mixing of the water in general mixing of the water in the volumesthe volumesthe volumesthe volumes. A fine three. A fine three. A fine three. A fine three----dimensional model of the dimensional model of the dimensional model of the dimensional model of the entire RPV could improve the entire RPV could improve the entire RPV could improve the entire RPV could improve the quantitative prediction of quantitative prediction of quantitative prediction of quantitative prediction of these parameters.these parameters.these parameters.these parameters.


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56


As it is expected the primary

temperature behavior is

dependent from the heat

losses of the facility

(BLIND SENSITIVITY ANALYSYS)

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57


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58


In relation to the RPV and PRZ In relation to the RPV and PRZ In relation to the RPV and PRZ In relation to the RPV and PRZ level, the results of the calculated level, the results of the calculated level, the results of the calculated level, the results of the calculated data show a general agreement data show a general agreement data show a general agreement data show a general agreement with the experimental data. with the experimental data. with the experimental data. with the experimental data.

The core, as in the experimental The core, as in the experimental The core, as in the experimental The core, as in the experimental data, data, data, data, is never uncoveredis never uncoveredis never uncoveredis never uncovered. . . .

The oscillation phase and the refill The oscillation phase and the refill The oscillation phase and the refill The oscillation phase and the refill phase phase phase phase are are are are predicted by the code. In predicted by the code. In predicted by the code. In predicted by the code. In both the simulations, both the simulations, both the simulations, both the simulations, BLIND and BLIND and BLIND and BLIND and OPEN, an underestimation of the OPEN, an underestimation of the OPEN, an underestimation of the OPEN, an underestimation of the RPV refill level rise is observedRPV refill level rise is observedRPV refill level rise is observedRPV refill level rise is observed, , , , therefore an underestimation of the therefore an underestimation of the therefore an underestimation of the therefore an underestimation of the long term core cooling phase RPV long term core cooling phase RPV long term core cooling phase RPV long term core cooling phase RPV level is observed.level is observed.level is observed.level is observed.

PRZ level

RPV level

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59


As it is expected the primary level behavior is dependent

from the heat losses of the facility

(BLIND SENSITIVITY ANALYSES)

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Thermo-fluid dynamics and pressure drops in various

geometrical configurations

60


�Cycling behavior

�Long term behavior

The analyses of the

BLIND/OPEN pressure

drop calculated data

show a general

underestimation in

comparison with the

experimental data.

More instrumentation

information’s are

necessary in order to

characterize these

differences.

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SECONDARY SIDE BEHAVIOR

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HPC, CPV and HTP behavior

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63


� The HPC pressure behaviour is characterized by different phases:

� a first pressure increase, � an oscillation phase, � and a long term cooling phase.

� The results of the BLIND calculated data show that the HPC pressure behavior and its different phases are predicted by the code.

� As in the experimental data the HPC pressure oscillates between the setpoint values .

� The HPC pressure long term cooling phase is in general overestimated in comparison with the experimental.

� A better quantitative prediction of the long term cooling phase is observed during the OPEN calculation, though and underestimation is observed in the last part of the transient. This is related to the better quantitative RPV pressure prediction of the OPEN calculations.

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64


It is to underline that, as it is

shown from the BLIND sensitivity

calculations, the slope of the HPC

pressure increase is related to the

PCS 106 A valve k loss coefficient.

Considering the RPV/HPC coupling, it is

to underline that the length of the HPC

pressure oscillation is in general

depended from the steady state

conditions before the SOT and the heat

losses of the facility as it is shown from

the sensitivity analyses performed in

the BLIND phase of the ICSP.

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65


� The first rapid increase of

level and the decrease of the

HPC level slope are predicted

by the simulations.

� When the sump recirculation

valves open, the decrease of

the HPC level is well

predicted by the TRACE code

as the long term steady state

level phase.

� In general during the

simulations, though the long

term level is in a quantitative

agreement with the

experimental data, it is

underestimated the HPC

level increase.

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66


From the BLIND calculated data

it is observed that the maximum

level reached by the HPC level is

dependent by the PCS 106 A k

loss coefficient

The slope of the HPC level increase

is in general depended from the

heat losses of the facility.

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� The TF 811 and 821 are the lower thermocouples.

� The TF 811 thermal behaviour is not predicted by the code. This is related to the mono dimensional model of the containment. In particular in the experimental data is observed a general mixing of the primary vapour with the HPC water, then a rapid increase of the HPC water temperature.

� The calculated TF 821 temperature increases but with delay and a different behaviour in comparison with the experimental data.

� The TF 831, 841, 851, 861, are qualitatively but not quantitatively predicted by the code. A general overestimation of the calculated data is observed. This is could be related to the position of the thermocouples; in fact they are located very close to the heat transfer plate, therefore they could not represent the bulk water temperature; the temperature calculated by the code is the bulk temperature related to the nodalizationvolume. It is underline that the rapid increase of the HPC temperature is well predicted by the TRACE code.

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71


In relation to the TF 891, 892, 893, 894, the comparison with the

experimental data show that there is an agreement with the experimental

data but more investigation need these parameters.

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�Thermal stratification Thermal stratification Thermal stratification Thermal stratification in the HPC and in the CPV is in the HPC and in the CPV is in the HPC and in the CPV is in the HPC and in the CPV is observed. The strong thermal stratification observed observed. The strong thermal stratification observed observed. The strong thermal stratification observed observed. The strong thermal stratification observed in the CPV could be related to in the CPV could be related to in the CPV could be related to in the CPV could be related to nodalizationnodalizationnodalizationnodalization option.option.option.option.

The effect of the nodalization strategy used to model large tanks, where possible natural/circulation

convection phenomena could take place, is characterized; the nodalization strategy could

influence the entity of the thermal stratification that could be present in the system

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73


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oICSP TEST 2 PHENOMENA

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oINITIAL CONDITION FOR THE ICSP TEST INITIAL CONDITION FOR THE ICSP TEST INITIAL CONDITION FOR THE ICSP TEST INITIAL CONDITION FOR THE ICSP TEST 3333

� In order to reach the BIC of the first ICSP test an arbitrary pre-test phase is conducted during the simulation

� At the end of this pre-test phase, SOT, the BIC of the test are stable for 10 minutes prior to the first mass reduction.

� The comparison of the initial condition reached by the code and the initial condition provided in the ICSP test plan are reported in the following table

Parameter MASLWR Unit Experimental Value

Steady-State Value from Code

Pressurizer pressure PT-301 MPa(a) 8.72 8.72

Pressurizer level LDP-301 m 0.3574 0.36

Power to core heater rods KW-101/102 kW 40 40

Feedwater temperature

(Average)

TF-501 ºC 31.49 31.49

Steam temperature FVM-602-T ºC 205.44 223.49

Steam pressure FVM-602-P MPa(a) 1.446 1.446

Ambient air temperature ºC 22 22

Primary flow at core outlet FDP-131 kg/s 0.646

Primary coolant temperature at core inlet

TF- 121/122/

123/124

ºC 250 250

Primary coolant temperature at core outlet

TF-106 ºC 263 262.56

Feedwater flow FMM-501 kg/s - 0.0117

Steam flow FVM-602-M kg/s 0.0117

Primary coolant subcooling at core outlet

ºC 38.5

Total heat loss through primary system

kW About 8

Heat transfer through SG kW 33183.711

Maximum surface temperature of core heater rods

ºC Outer surface: 280

Location from the SG secondary inlet to reach

- saturation

- superheat

m Saturation : Cell 201

Superheat: Cell 211


76

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FACILITY CONFIGURATION BEFORE

THE SOT OF THE TEST 3

77


System Facility

Operation

TRACE Model

Operation

Note

Core Heaters ON ON

PRZ Heaters ON ON

It is defined a table in order to control the

primary pressure

Independent variable = PRZ pressure

Dependent variable = PRZ heater power

In order to maintain

the primary

pressure set-point

Containment

Heaters

OFF OFF -

Feed water ON ON

It is defined a table in order to control the

secondary side steam super heat value

Independent variable = secondary side

steam super heat

Dependent variable = feed water mass

flow rate

In order to remove

the net primary

power [primary

power less ambient

losses]

Main feed

water pump

ON

Charging

pump

OFF - -

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At the end of the Steady State Phase

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At the end of the Steady State Phase

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oTEST TEST TEST TEST 3 3 3 3 PROCEDUREPROCEDUREPROCEDUREPROCEDURE

� The ICSP test 3 investigated the primary and secondary side thermal hydraulic behavior for a variety of core power levels and FW flow rate. The test stepped power level incrementally up to about 300 kW, varying FW flow rate at each power level. During this test seven different core powers were used.

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FACILITY CONFIGURATION DURING THE

ICSP TEST 3

81


System Facility

Operation

TRACE model

Operation

Note

Core Heaters ON ON

PRZ Heaters ON ON In order to control the

primary pressure

Containment

Heaters

OFF OFF

Feed water ON ON

( fixed as experimental

data)

In order to remove the net

primary power [core power

less ambient losses].

Charging

pump

OFF

Main feed

water pump

ON - -

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oICSP TEST 3

�In order to improve the results of the TRACE ICSP test 3 calculated data, few modifications have been implemented in the input deck. �An increase of the heat losses and

�an increase of the SG coil surface heat transfer area have been implemented.

� It is to underline that in order to have a better fitting of the RPV mass flow rate a Reynolds number - dependent loss coefficient could be necessary. Since this option is not available in the TRACE code version used for this ICSP (TRACEV5-patch1), a fictitious valve with flow area dependent from the core power has been implemented at the core entrance.

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oICSP TEST3 ANALYSES PERFORMED

83


ID

Calculation

Variation from

reference

calculation

Target of the

sensitivity

analyses

Results of the sensitivity

analyses

BL

IND

PH

AS

E

REF

BLIND

Reference

BLIND PHASE

calculation

SM Increase the

surface multiplier

of the equivalent

SG helical coil

heat structure

Increase the

primary/secondary

heat transfer

An increase of the primary

secondary heat transfer is

predicted by the code. This

effect increases with the

increase of the power. A general

colder primary system is

observed in particular in the last

part of the transient.

HL Increase the heat

losses of the

TRACE model

Decrease the

energy transferred

to the secondary

side

A general colder primary system

is observed

3T The SG is

modeld with 3

equivalent group

of pipes, one of

each bank.

Characterize the

facility with a

group of pipe for

each tube bank

A more detailed analyses is

obtained. More oscillation are

predicted in the secondary side

OP

EN

PH

AS

E

Open Reference

OPEN PHASE

Calculation

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Thermo-fluid dynamics and pressure drops in

various geometrical configurations

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The analyses of the

BLIND/OPEN

pressure drop

calculated data

show a general

underestimation in

comparison with the

experimental data.

More

instrumentation

information’s are

necessary in order

to characterize

these differences

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Natural circulation/heat transfer in

covered core

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covered core

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covered core

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The primary

system is

subcooled for each

step during the

BLIND and OPEN

phase simulations

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Heat transfer in SG/super heating in

secondary side

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ICSP3 Calculated data

Direct heat exchange

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oHeat transfer in SG

Super heating in secondary side

BLIND Sensitivity Analysis (SG with three equivalent group of pipe)

90


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oICSP3 BLIND Sensitivity Calculated Data

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Heat Losses

effect

SM

effect

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oICSP3 CODE PHENOMENA PREDICTION

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oLeasson Learned

� The expected phenomena are predicted by the TRACE code.

� RPV Natural circulation is predicted by the code� The RPV/containment coupling is predicted by the code (long term cooling

phenomenology typical of the MASLWR design)� The SG coil behavior:

� The subcooled, saturated and superheated regions are predicted by the code

� The superheating at the SG exit is predicted by the code

� More investigation’s are needed for a quantitative assessment

� The results of the calculated data show a strong user effect

� Way of reaching the BIC,� K loss coefficient of the vent valve� Nodalization strategy for the simulation of large pool� Nodalization strategy for the simulation of helical coil SG (different system

behavior if the system is modeld with one equivalnet helical coil or threedifferent equivalent helical coils)

� The graphical user interfaces is a mature tool for the analyses of the calculateddata. This is a way of reducing the user effect. Usefull application are the visulization of selected calcuated data and the temperature profile visualization.

�

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oLeasson Learned

� Considering� The general importance of heat losses calibration for the simulation of

experimental test facility

� The general importance of pressure drop calibration for the simulationexperimental test facility

� The results of the calculated data showing the influenze of the heat losses

� One issue is the quantitative validation of the code for the heat transfer between the primary and secondary side in presence of helical coil steamgenerator

� The general results of the primary side parameters

� The results of the comparison between the experimental and the calculatedpressure drop

� The importance of the pressure drop in natural circulation regime

It is fundamental for the use of best estimate thermal hydraulic system code for the analyses of small modular nuclear reactor a

� detailed characterization of the experimental test facilities: heat lossescharacterization at different primary temperatures; pressure dropcharacterization at different mass flow rates

� A detailed characterization of the facilities instrumentation.

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