UNIVERSITÀ DI PISA DIPARTIMENTO DI INGEGNERIA MECCANICA, NUCLEARE E DELLA PRODUZIONE VIA DIOTISALVI...

UNIVERSITÀ DI PISAUNIVERSITÀ DI PISADIPARTIMENTO DI INGEGNERIA MECCANICA,DIPARTIMENTO DI INGEGNERIA MECCANICA,

NUCLEARE E DELLA PRODUZIONENUCLEARE E DELLA PRODUZIONEVIA DIOTISALVI 2, 56100 PISAVIA DIOTISALVI 2, 56100 PISA

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Atucha-2 PHWR three Atucha-2 PHWR three dimensional neutron kinetics dimensional neutron kinetics coupled thermal-hydraulics coupled thermal-hydraulics

modelling and analyses by the modelling and analyses by the RELAP5-3D©RELAP5-3D©

C. Parisi, C. Parisi, A. Del Nevo,A. Del Nevo, O. Mazzantini, F. O. Mazzantini, F. D’Auria, K. IvanovD’Auria, K. Ivanov

RELAP5-3D User SeminarIdaho University Campus, Idaho Falls, USA

18-20 November 2008

RELAP5-3D User Seminar – Idaho University Campus, Idaho Falls, USA – November 18-20, 2008 2

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Outline Introduction

Atucha II PHWR Features

280 channels TH model

HELIOS Cross-Sections Libraries

3D NK - TH model

Sample results

Conclusions


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radoIntroduction

Argentinean electric utility “Nucleoelectrica Argentina – Societad Anonima” (NA-SA) signed an agreement with the San Piero a Grado Nuclear Research Group (GRNSPG) of the University of Pisa (UNIPI) in 2007 for the development of advanced simulation models for the Atucha-II NPP

GRNSPG/UNIPI developed Thermal-hydraulics, Neutronics, CFD and Structural Mechanics models for the safety analysis of the plant

Currently GRNSPG/UNIPI is also assisting NA-SA in the development of the Chapter 15 of the FSAR

Best-Estimate Plus Uncertainty (BEPU) method pursued for licensing calculation development of a BE RELAP5-3D model for licensing analyses


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Atucha II PHWR Features Atucha-II is a 692 MWe Siemens designed PHWR under construction in

Lima, Argentina Constructions started in 1981, suspended in 1994 Constructions resumed in 2005, first criticality scheduled for 2010 Heavy water cooled, heavy water moderated PWR Unique features:

Primary circuit based on the Konvoi-PWR design Circuit for moderator cooling / FW pre-heating Natural Uranium fuel Vertical Fuel Channels Large RPV (7.3 meter internal diam.)


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Atucha II PHWR Features Primary circuit characteristics & configuration

2 U-Tubes SG, 2 MCP Primary side pressure: 11.5 MPa Primary side temperatures: 278 °C at RPV inlet, 313.3°C at RPV outlet Total thermal power transferred to the steam water cycle : 2174 MW Average Moderator Temperature: 170 °C 4 U-Tubes HX for Moderator cooling / FW pre-heating

Moderator Cooling Circuit

Primary Circuit


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Atucha II PHWR Features Fuel placed in 451 vertical fuel channel (FC) 37 Natural Uranium Fuel rods per each FC On-line refueling Active Core Height: 5.3 m Oblique CRs

CR layout

Fuel Element

RPV Layout


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Atucha II PHWR Features Emergency Boron Injection System designed to act during RIA

(e.g., LBLOCA) To counteract positive reactivity excursion due to the reactor positive

void coefficient

4 Lances inject high pressure solution of boric acid into the moderator tank System reaction time reduced by NA-SA to roughly 0.5 secs.

Boron Injection

Lance (1 of 4)


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Rationale for the Nodalization Structure

Nodalization is the result of a brainstorming process where the computational resources available and the experience of the user play a major role consistently with the objectives of the analyses

Selected code was RELAP5-3D© developed for industrial applications in US, independent from the code(s) used by the regulator

Key role of:

Maximum allowed number of nodes,

Maximum allocable computer-code memory

Typicality of the accident scenarios to be analyzed

DEGB LBLOCA – Initial Reactivity Excursion and Recovery

LBLOCA and other transients

User in supplying unavailable information

Providing suitable qualification


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Rationale for the Nodalization Structure

“280 channels nodalization” consistent with the typicality of the accident scenarios to be analyzed (e.g. DEGB LBLOCA – Initial Reactivity Excursion and Recovery)

Computer resources not sufficient to implement all CNA-2 ECCS and Logics

“60 channels nodalization” consistent with the typicality of the accident scenario (e.g. LBLOCA and other transients)

Code computer resources saturated by implementation of suitable ECCS and Logics, so: “280 channels nodalization” for 3D NK – TH analyses “60 channels nodalization” for 0D NK – TH analyses


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50°

CL axisHL axis

CL1 HL1

CL2HL2

DC Nodalization & RPV Symmetry

Due to the legs geometry not all the coolant coming from a loop exits from

the same loop. A mixing (between inlet and outlet) has to be taken into

account


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DC Nodalization (Hydraulics)

6 vertical (downward oriented) pipesaxially subdivided in 25 volumes

joined by cross-flow (multiple) junctions (component no. 7 in the left figure)

6 branches represent the upper part, two of them linked to the CL

DC-UP bypass connection


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LP Nodalization

Three layers:

1) Bottom part – horizontally oriented (red): Level-1 (L1)2) Bottom part up to the channel inlet – vertically oriented (green): Level-2 (L2)3) Channel inlet up to the lower face of core plate – vertically oriented (blue): Level-3 (L3)


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LP Nodalization

LP grid nodalization approach Five rings are identified containing an

‘entire’ number of boxes

1

2

3

4

5Withoutchannel inlets!

CL1 HL1

CL2HL2


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LP NodalizationLP grid nodalization approach

36 sectors (amplitude of each sector is 10° = “maximum common divisor” for

90°, 40° and 50°) divide the boxes into 200 parts (sub-box) represented by

200 ‘branches’


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LP NodalizationBottom partBottom part

5 radial rings (according to LP plate subdivision)6 azimuthal parts (according to DC subdivision)

25 horizontal ‘branches’ constitute the bottom LP

The external ring is connected to DC pipes (green circles)

Each hor. branch is connected to the vert. branches forming the LP

grid (red circles)


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Core channels Nodalization

Five throttle types

Green zone 1Blue zone 2Red zone 3Black zone 4Light blue zone 5

Considering

65 Boxes

36 Radial sector

5 Rings

1 Max power channel

280 equivalent channels


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UP Nodalization

Four layers:1) First horizontal part connected to the coolant channel outlets (blue) 2) First vertical part up to the HL axis (orange)3) Second horizontal part along the HL (green)4) Second vertical part to account for the nearly semispherical shape (yellow)


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UP Nodalization

The three different layers modelled by several branches

E.g., the first layer – horizontal25 ‘branches’ connected to the 280 equivalent core channel (red circles)


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RPV Nodalization

Not all channelsrepresented!


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LOOP Nodalization (including SG)

‘Standard’ nodalization technique

General rules followed:• 1 junction only connected to a pipe• Ratio length of two consecutive nodes stays within 0.5 – 2.0• Junction at inlet and outlet of nodes only• SG modeled till the isolation valves

Pump homologous curves taken from NA-SA nodalization

2 loops modeled1 loop represented


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Moderator system4 loops modeled – 1 loop represented

Heat exchangersPrimary side of

moderator cooler

Safety injection

Moderator pump

Moderatordowncomer

Safety injection port

Pump homologous curves given by NA-SA


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Neutron XSec Libraries model - Generation

ENDF/B-VI NJOYNJOYMultiG XSec (47 Groups)

HELIOSHELIOSv. 1.9v. 1.9

* NEM-Cross Section Table Input * * T Fuel T Mod. Rho Cool. CXe 3 4 6 0 * ******* X-Section set # 1 * * Group No. 1 * *************** Diffusion Coefficient Table * .5570000E+03 .8500000E+03 .1030000E+04 .5570000E+03 .7000000E+03 .8560000E+03 .1060000E+04 .1000000E+02 .1000000E+03 .3000000E+03 .5000000E+03 .7440000E+03 .9980000E+03 .1161020E+01 .1161020E+01 .1161000E+01 .1161440E+01 .1161430E+01 .1161420E+01 .1160100E+01 .1160100E+01 .1160090E+01 .1157710E+01 .1157680E+01 .1157680E+01 .1159020E+01 .1159020E+01 .1159010E+01 .1159440E+01 .1159420E+01 .1159410E+01 .1158080E+01 .1158060E+01 .1158060E+01 .1155670E+01 .1155650E+01 .1155640E+01 .1153360E+01 .1153330E+01 .1153300E+01 .1153740E+01 .1153710E+01 .1153700E+01 .1152390E+01 .1152360E+01 .1152340E+01 .1149940E+01 .1149910E+01 .1149890E+01 .1146530E+01 .1146480E+01 .1146460E+01 .1146920E+01 .1146850E+01 .1146830E+01 .1145540E+01 .1145490E+01 .1145470E+01 .1143070E+01 .1143020E+01 .1142980E+01 .1137150E+01 .1137100E+01 .1137090E+01 .1137520E+01 .1137460E+01 .1137460E+01 .1136130E+01 .1136080E+01 .1136050E+01 .1133630E+01 .1133580E+01 .1133550E+01 .1126540E+01 .1126500E+01 .1126480E+01 .1126880E+01 .1126840E+01 .1126800E+01 .1125490E+01 .1125440E+01 .1125400E+01 .1122970E+01 .1122890E+01 .1122850E+01 * *************** Total Absorption X-Section Table

XSecs LibrariesXSecs Libraries(2 Groups)(2 Groups)

2D Transport Calculations


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Neutron XSec Libraries Code

Advanced lattice physics code HELIOSHELIOS used to calculate the cross section sets

HELIOSHELIOS is a neutron and gamma transport code for lattice burnup, in general two-dimensional geometry

Developed by STUDSVIKSTUDSVIK®® Scandpower Scandpower

One of the best features of this code is the complete geometric flexibility Cartesian, Hexagonal, Cylindrical,…

HELIOSHELIOS can calculate almost any two-dimensional geometry, it can generate the cross sections for most of the current nuclear reactor applications Successfully applied to PWR, BWR, WWER, CANDU, AGR, RBMKPWR, BWR, WWER, CANDU, AGR, RBMK


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Neutron XSec Libraries model

Channel-by-channel burnup distribution supplied by NA-SA

4510 burnup values reduced to 780 by using 1/6th core pseudo-symmetry


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For every composition a cross section set is generated

Each Cross Section set contains tables for:

Fast and Thermal Diffusion Coefficients

Fast and Thermal Capture Cross Sections

Fast and Thermal Fission Cross Sections

Fast and Thermal Nu-Fission Cross Sections

Removal Cross Sections (Group 1 2)

Inverse Neutron Velocities

Assembly Discontinuity Factors (ADFs)

Photoneutron effect (supplied by NA-SA) to be taken into account directly in NESTLE input


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Neutron XSec Libraries model Several HELIOSHELIOS input decks developed:

Fuel Channel (hexagonal lattice) Fuel Channel + Moderator CR absorbers (black & grey CR, upper & lower part) Reflector: Radial, Bottom, and Top

Fuel Channel Fuel Channel & ReflectorFuel Channel & CR


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Interpolation in Five-Dimensional TablesInterpolation in Five-Dimensional Tables

For CNA-II core model FiveFive Independent Parameters will be

used:

1) Fuel Temperature (Doppler Feedback)

2) Coolant Density (Void Effect)

3) Coolant Temperature

4) Moderator Temperature

5) Moderator Boron Concentration (Emergency System)


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Cross Section ModellingATUCHACROSS.exe

(FORTRAN 90 program)

ReferenceCross Section

Values

CROSS SECTION

LIBRARIES(nemtab, nemtabr_1,

nemtabr_2, nemtabr_3, nemtabr_4)

Cross-SectionVariation

Coefficients

5D LINEAR INTERPOLATION

ROUTINE(LINT5D)

LEAST SQUAREMETHOD

(MC)

Σref

Coolant

ModeratorB

FuelT

ModeratorT

CoolantT


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Final Version of the ATUCHACROSS program

5000 lines Fortran program

Automatically perform ad-hoc interpolations,

for several zones of the reactor core

Variation coefficient calculation

NESTLE input writing

Cross Section Modelling

Σref

Coolant

ModeratorB

FuelT

ModeratorT

CoolantT

CR information(Type, angles, number)

NESTLE INPUT


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3D NK – TH coupled model 3D NK nodes obtaining “weighted” feedback from TH model

NESTLE sending back power distribution to FA heat structures

Power

NESTLENESTLE

Fuel Channel

TH model

Moderator

TH model

Coolant Density

Coolant Temperatur

eModerator

Temperature

Boron Concentrati

on

Fuel Temperatur

e

RELAP5-3DRELAP5-3D


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3D Neutron Kinetic model NESTLE 3D NK model characteristics:

Hexagonal lattice

27.24 cm pitch

10 axial layers for active core: 53.07 cm

1 layer for the Bottom Reflector: 48.2 cm

1 layer for the Top Reflector: 34.4 cm

535 X 12 nodes = 6420 NK nodes

Feedback from RELAP5-3D(c) TH model

Hydraulic zones

Fuel Channels (coolant density, coolant temperature)

Moderator Zones (moderator temperature, boron conc.)

Heat structure zones

Fuel Channels (fuel temperature)

All CR type simulated by an ad-hoc representation

Upper & Lower absorber


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18 Control Rods inserted diagonally (17-25°) Black CR = Hafnium

absorber Grey CR = Steel

absorber Each CR has upper

and lower section with different materials/sections

CR arranged in 4 groups G10, G20, G30,

S10 = Safety & regulation

Shut-off = Shutdown CR


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66 44 18 60 54 25 50

440

439

178

597

10

09

08

07

06

05

04

03

02

01

535

244

243

492

20

201

596

CR modelling Four Cross Sections Libraries calculated for CR modelling CR XSec corrections due to the 3D geometry effects introduced

using 3D MCNP5 Monte Carlo Simulations

66 44 18 60 54 25 50

440

439

178

597

10

09

08

07

06

05

04

03

02

01

535

244

243

492

20

201

596

CR and Fuel Channels Section NESTLE modelling


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3D NK – TH coupled model – Fuel Channels

Atucha II NPP 280 channel280 channel RELAP5-3D TH model used # of TH channels modeled & coupled according to:

Hydraulic characteristics (throttled type/un-throttled)

Romboidal sub-plena belonging

Power distribution

Transient type

Code resources1

CL1 HL1

CL2HL2

1CL1 HL1

CL2HL2

01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

BGBFBEBDBCBBBABLAKAHAGAFAEADACABAAALLKLHLGLFLELDLCLBLA

2 2 1

1

1 2 1

1

1

1

2 1 1

1

1

1 1 1

2 2

1 1 1 22 2 1

3 6 2

2 12

21 1 2 362 2 2

2 2 1 13 3 2 23 3 3 3

2 1 1

1 1 1 2 2 2 3

3 3 2 23 3 3 3

1

1 1 1 2 2 3 3 3 3

6 2 2 24 3 3 34 4 4 46 3 3 31 1 2 2

3 2 2 14 4 3 34 4 4 4

1

1 1 2 2 3 3 3 4 4

3 3 3 24 4 4 44 4 4 4

3 6 1

1 2 2 3 3 3 4

4 4 4 34 4 4 44 4

1 1 1

1 1 2 6 3 3 4

4 3 3 25 4 4 44 4 5 5

2 1

1 1 2 2 3 3 4 4

3 3 3 25 4 4 44 5 5 5

2 1

1 2 2 3 3 3 4 4

4 3 3 25 5 4 44 5 5 5

2 2 1

1 2 2 3 3 4 4

4 3 3 35 5 4 44 4 5 5

2 1 1

1 2 2 3 3 3 4

4 3 3 25 4 4 44 4 5 53 3 4 41 1 1 2

6 2 1 14 4 3 34 4 4 44 4 4 41 6 3 3

3 2 2 14 4 3 34 4 4 43 4 4 41 2 3 3

2 2 1 13 3 3 34 4 4 4

1

1 2 2 3 3 3 3 4 4

6 2 2 14 3 3 34 4 4 46 3 3 31 2 2 2

2 1 1 13 3 3 23 3 3 3

1 1

1 1 2 2 2 3 3 3

2 2 2 1

1

1 1 2 2 2 2 3 3 3

2 2 2 12 6 3 3

1

1 1 2 2 2

111

1

1 112 1 2 2 2 2 2

1 11

12

1 1

1 2 2 2 2 1

1 1

1 2 1

6

3 3 3 3

2

11

2

1 1 2 2

451 FA simulated by

3D NK NESTLE code

280 FA simulated

by RELAP5


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3D NK – TH coupled model – Fuel Channels

280 RELAP5 Fuel Channels coupled with 6420 NESTLE neutronic nodes

Feedbacks for Radial, Top and Bottom Reflector coming also from neighbouring fuel channels

RELAP5-3D / NESTLE coupling Map – Fuel Channels


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3D NK – TH coupled model – 3D Moderator tank

Moderator Model using RELAP5-3D - 3D components possibility to simulate with high degree of realism the boron clouds

calculated by CFD simulation of asymmetric transients Very sophisticated mapping scheme resulted from the use of Cylindrical 3D

TH Components coupled with Hexagonal NK cells

• 6 radial sectors6 radial sectors

• 1+ 10 + 1 = 12 axial layers for 1+ 10 + 1 = 12 axial layers for Bottom Reflector, Core Active zone, Bottom Reflector, Core Active zone, Top reflectorTop reflector

• 16 azimuthal sectors16 azimuthal sectors3D Moderator Tank – NESTLE mesh overlay


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Modelling the boron emergency injection system

Boron Injection Clouds calculated by a previous CFD CFXTM code calculation reconstructed by ad-hoc TMDPJUN components in the 3D Moderator Tank

Injection ZonesInjection Zones

Comparison CFD – RELAP5-3D Comparison CFD – RELAP5-3D injected mass of boroninjected mass of boron

RELAP5-3D Mass of boron RELAP5-3D Mass of boron distribution in different layersdistribution in different layers


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“280 Channels” Nodalization Resources

Number of Hydraulic Nodes: 5,744 Number of Meshes for Heat Conduction: 67,640 Number of Junctions: 6,987 Number of Materials: 9 Number of Control Variables: 950 Number of Trips: 200 Number of TMDPVOL: 13 Number of NK nodes: 6420 Total Number of input deck lines: 117,000 Typical CPU for running 1 sec of SS (max time step 0.02 s,

on Pentium-IV 3.6 GHz): 850 s


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3D NK Coupled TH SS Results

Core SS conditions:Hot Full Power: 2.160 GWNominal values for Fuel, Coolant and Moderator

Temperatures distributionCR in (NA-SA configuration)

G10: 94% in

G20: 67% in

G30:24.5% in

S10: 4.29% in

Shut-Off (S20 & S30): All Rods Out

Boron Concentration: 0.05 ppm


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SS – Radial Power Keff= 0.99550 Fxy = 1.38

MaximumMaximum

Min= 1.01 MWMin= 1.01 MW

Max = 6.65 MWMax = 6.65 MWMinimum


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SS – Radial PowerRadial Power : Spatial Form Function


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SS Normalized Reactor Axial Power

Axial Power Distribution

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 100 200 300 400 500 600

Distance from the Bottom of Active Fuel (cm)

No

rma

lize

d P

ow

er

BAF TAF


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Fuel Channels Mass FlowMass Flow per Assembly [Kg/s]


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SS Coupled Codes TH Parameters

All the main TH parameters converged to SS reference valuesE.g., moderator Tank temperature distribution

Bottom & Top Reflector

Active Core

120

130

140

150

160

170

180

190

200

210

220

0 1 2 3 4 5 6 7

Multi-D Component Radial Sector

Tem

pe

ratu

re (

°C)

Lev0

Lev1

Lev2

Lev3

Lev4

Lev5

Lev6

Lev7

Lev8

Lev9

Lev10

Lev11


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LBLOCA 0.1 A in CL2 (reference DBA for Atucha-2) Actuation of

Scram by all CRs : +0.07 sEmergency Boron Injection System : + 0.63 s

MCP1 & 2 rundown : +0.07 sCR completely inserted : +3.64 sEnd of Boron Injection in moderator tank : +3.91 sNo Safety threshold exceeded

LBLOCA 0.1A in CL2 – Sample Results


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LBLOCA 0.1A in CL2 – Sample Results

0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Time (s)

0

.5

1

1.5

2

2.5

3x 10 9

Po

we

r (W

)

WinGraf 4.1 - 02-26-2008

XXX CNA2_01LBLOCA rkotpow0

XX X

X

X

XX

XX X X X X X X X X

Reactor PowerReactor Power

Pressure Trends in UP and Pressure Trends in UP and PRZPRZ

0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Time (s)

280.0

290.0

300.0

310.0

320.0

330.0

340.0

350.0

Tem

pe

ratu

re (

°C)

WinGraf 4.1 - 02-26-2008

XXX CNA2_01LBLOCA httemp250100209

XX X X X X X X X X X X X X X X

X

YYY CNA2_01LBLOCA httemp250100409

YY

Y Y YY

YY

YY

Y Y Y Y Y Y

Y

ZZZ CNA2_01LBLOCA httemp250100609

ZZ

Z Z Z ZZ

ZZ

ZZ Z Z Z Z

Z

VVV CNA2_01LBLOCA httemp250100809V V V V V V

VV

V V V V V VV

V

JJJ CNA2_01LBLOCA httemp250101009J J J J J J J J J J J J J J

J

HHH CNA2_01LBLOCA httemp272100209

H HH

H HH H H H H H H H

H

H

### CNA2_01LBLOCA httemp272100409

# ##

##

##

# # # # # #

#

OOO CNA2_01LBLOCA httemp272100609

OOOO

OO

O OO

O O O

OAAA CNA2_01LBLOCA httemp272100809

A A AA

A AA A A A A

A

A

BBB CNA2_01LBLOCA httemp272101009

B B B B B B B B B B B

B

Fuel Clad Temp. in Central and Hot ChannelFuel Clad Temp. in Central and Hot Channel

0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Time (s)

8.50

9.00

9.50

10.00

10.50

11.00

11.50

12.00

Pre

ss

ure

(M

Pa

)

WinGraf 4.1 - 02-26-2008

XXX CNA2_01LBLOCA p773010000X XX

XX X X X X X X X

XX

XX

X

YYY CNA2_01LBLOCA p652010000

Y YY

YY Y

YY

YY

YY

YY

YY

Y

ZZZ CNA2_01LBLOCA p692308010

ZZ

ZZ Z Z

ZZ

ZZ

ZZ

ZZ

Z

Z

0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Time (s)

-.10

0

.10

.20

.30

.40

.50

.60

.70

Vo

id F

rac

tio

n

WinGraf 4.1 - 02-26-2008

XXX CNA2_01LBLOCA voidg250040000

X X X X X X X X X X X X X X X X X

YYY CNA2_01LBLOCA voidg250080000

Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y

ZZZ CNA2_01LBLOCA voidg250120000

Z

ZZ Z

Z Z ZZ

ZZ

ZZ Z Z Z Z

VVV CNA2_01LBLOCA voidg272040000

V V V V V V V V V V V V V V V V

JJJ CNA2_01LBLOCA voidg272080000

J J J J J J J J J J J J J J J

HHH CNA2_01LBLOCA voidg272120000

H H HH H

HH

HH

H H H H H H

Void Fraction in Central and Hot Void Fraction in Central and Hot

ChannelChannel


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MCP Shaft seizure – Sample Results

MCP2 Shaft seizure in 1 s MCP1 continues operation CRs scram: +0.16 s CRs completely inserted: +3.73 s No Safety threshold exceeded0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Time (s)

0

.25

.5

.75

1

1.25

1.5

1.75

2

2.25

2.5x 10 9

Po

we

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WinGraf 4.1 - 02-26-2008

XXX MCP_Shaft_Seizure rkotpow0

X XX

X

X

X

X

X

X

XX

X X X X X X

Reactor PowerReactor Power

Void Fraction in Central & Hot Void Fraction in Central & Hot ChannelChannel

0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Time (s)

280.0

290.0

300.0

310.0

320.0

330.0

340.0

350.0

360.0

370.0

Tem

pe

ratu

re (

°C)

WinGraf 4.1 - 02-26-2008

XXX MCP_Shaft_Seizure httemp250100209

X X X XX X X X X X X

XX X X X

X

YYY MCP_Shaft_Seizure httemp250100409

Y YY

YY

Y Y Y YY

YY

YY

Y Y

Y

ZZZ MCP_Shaft_Seizure httemp250100609

ZZ

ZZ

Z Z Z Z Z ZZ

ZZ

ZZ

Z

VVV MCP_Shaft_Seizure httemp250100809

VV V V V V V V V V V V V

V

V

V

JJJ MCP_Shaft_Seizure httemp250101009

J J J J J J J J J J J J J J

J

HHH MCP_Shaft_Seizure httemp272100209

HH

H H H H HH

HH H H H

H

H

### MCP_Shaft_Seizure httemp272100409

##

# # # # ##

##

## #

#

OOO MCP_Shaft_Seizure httemp272100609

OOO O O O O O O OO

O

O

AAA MCP_Shaft_Seizure httemp272100809

A A A A A A A A A A AA

A

BBB MCP_Shaft_Seizure httemp272101009

B B B B B B B B B B B

B

0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Tim e (s )

-.10

0

.10

.20

.30

.40

.50

.60

Voi

d F

rac

tion

W inGraf 4 .1 - 02-26-2008

XXX MCP_Shaft_Seizure voidg250040000

X X X X X X X X X X X X X X X X X

YYY MCP_Shaft_Seizure voidg250080000

Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y

ZZZ MCP_Shaft_Seizure voidg250120000

Z

Z

Z

Z

Z

Z

Z

Z ZZ

Z

Z

Z

ZZ

Z

VVV MCP_Shaft_Seizure voidg272040000

V V V V V V V V V V V V V V V V

JJJ MCP_Shaft_Seizure voidg272080000

J J J J J J J J J J J J J J J

HHH MCP_Shaft_Seizure voidg272120000

H

H

H

H

H

HH

H

H

H

H

H

H

H

H

Fuel Clad Temp. in Central and Hot ChannelFuel Clad Temp. in Central and Hot Channel


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FC Blockage (BDBA) – Sample Results

Hot channel (6.63 MW) total blockage in 0.2 s No scram signal actuated Severe Fuel Assembly damage

0 .25 .50 .75 1.00 1.25 1.50 1.75 2.00 2.25 2.50

Time (s)

-5.0

0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

Ma

ss

Flo

w R

ate

(K

g/s

)

WinGraf 4.1 - 01-27-2008

XXX CNA2_FC_BLOCKAGE mflowj272010000

X X X X X X X X X X X X X X X X X X X X

0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Time (s)

200

400

600

800

1000

1200

1400

1600

Fu

el

Cla

d T

em

pe

ratu

re (

°C)

WinGraf 4.1 - 01-27-2008

XXX CNA2_FC_BLOCKAGE httemp272100209

X X X X X XX

XX

XX

XX

XX

X

X

YYY CNA2_FC_BLOCKAGE httemp272100409

Y Y Y Y YY

YY

YY

YY

YY

YY

YZZZ CNA2_FC_BLOCKAGE httemp272100609

Z Z

ZZ

ZZ

ZZ

ZZ

ZZ

ZZ

Z

ZVVV CNA2_FC_BLOCKAGE httemp272100809

VV

V V VV

VV

VV

VV

VV

V

V

JJJ CNA2_FC_BLOCKAGE httemp272101009

J J JJ J J J

JJ

JJ

J J J

J

Fuel Clad Temp. in Blocked ChannelFuel Clad Temp. in Blocked Channel

Blocked Channel PowerBlocked Channel Power

6.00E+06

6.10E+06

6.20E+06

6.30E+06

6.40E+06

6.50E+06

6.60E+06

6.70E+06

6.80E+06

0 1 2 3 4 5 6 7 8 9 10

Time (s)

Ass

embl

y P

ow

er (

W)

Blocked Channel Mass FlowBlocked Channel Mass Flow


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radoConclusions

GRNSPG/UNIPI developed for Argentinean electric utility NA-SA sophisticated RELAP5-3D models for Atucha II NPP

3D NK TH “280 channel nodalization” was presented 3D NK TH model set-up required strong interactions with other technology

fields (e.g., CFD, neutron XSecs generation) RELAP5-3D models calculations will constitute the Chapter 15 of the FSAR

for the Atucha II licensing RELAP5-3D demonstrated to be a very sophisticated tool, allowing a detailed

modelling of all relevant phenomena & peculiarities of the Atucha II design Key points for the code improvement were identified and suggested to INL.

E.g.: Increase of the allowable Trip cards Increase the number of 3D Volumes per Multi-D component On-line Cross Section libraries interpolation Automatic Calculation of Reactivity components (e.g., Doppler reactivity, coolant

temp. reactivity,..)

Further works are ongoing at GRNSPG/UNIPI in order to: Complete models qualification Extend the model to a full RPV 3D TH representation, including the simulation of

all 451 FC Complete simulation of Logics

UNIVERSITÀ DI PISA DIPARTIMENTO DI INGEGNERIA MECCANICA, NUCLEARE E DELLA PRODUZIONE VIA DIOTISALVI...

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