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Analysis of a Natural Circulation Transient at the VISTA Facility. Young-Jong Chung Korea Atomic Energy Research Institute. IAEA’s 4rd Research Coordination Meeting on the CRP on Natural Circulation Phenomena, Modeling, and Reliability of Passive Systems that Utilize Natural Circulation

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analysis of a natural circulation transient at the vista facility

Analysis of a Natural Circulation Transient at the VISTA Facility

Young-Jong Chung

Korea Atomic Energy Research Institute

IAEA’s 4rd Research Coordination Meeting on the CRP on Natural Circulation Phenomena, Modeling, and Reliability of Passive Systems that Utilize Natural Circulation

IAEA/Vienna, Austria, 10-14 Sept. 2007

contents
CONTENTS
  • INTRODUCTION
    • SMART Plant
    • VISTA Experimental Facility
  • ANALYSIS CODE
    • MARS code
    • TASS/SMR code
  • INITIAL and BOUNDARY CONDITIONS
  • RESULTS and DISCUSSIONS
  • SUMMARY
introduction

CEDM

MCP

Annular Cover

Pressurizer

Steam Generator

Reactor Vessel

Core

Side Screen

Displacer

INTRODUCTION
  • SMART (System-integrated Modular Advanced ReacTor) :
  • SMART plant is designed to supply an electricity and portable water
    • Maximum thermal power : 330 MWt
    • Portable water production : 40,000 tons/day
    • Electricity generation : ~90 MWe
  • Major components
    • Pump Type : Canned motor MCPs
      • Eliminates pump seal leak SBLOCA
    • SG Type : Helically coiled
      • Reduce possibility of SGTR acc.
    • PZR : A passive type with a large volume
      • The system pressure is self-controlled by N2 gas
      • Remove active component (spray and heater)
introduction1
INTRODUCTION
  • SAFETY SYSTEM
    • Passive residual heat removal system
    • Safety injection system
    • Over pressure protection system (POSRV)
    • Shutdown cooling system
introduction2
INTRODUCTION

PRHRS

  • Consist of Hx, compensating tank, RWT,

check and isolation valve

  • For normal operating condition;

This system is isolated from the secondary sys.

  • For accident condition;

Close MFIV and MSIV

Open PRHRS isolation valves

Established a natural circulation flow by gravity

  • Characteristics

Remove decay heat for 3days without operator

action

  • In order to verify the performance and the safety of the SMART plant,

the VISTA experimental facility is constructed

introduction vista facility
INTRODUCTION – VISTA Facility
  • VISTA Facility
    • Design to test system behavior of the integral reactor, SMART
    • Design for full pressure and

full temperature operation

    • Primary components are simplified

to be a loop type

    • Secondary and PRHR systems have

a single train

    • Major components
      • Vessel
      • 1 SG cassette,
      • 1 MCP
      • 1 train of PRHRS
slide7

Pressurizer

Gas

Cylinder

CEDM

MCP

PZR

Steam

Generator

SG

Reactor

Vessel

Reactor

Vessel

Core

Shielding

INTRODUCTION : SMART vs VISTA

MCP

slide8

VISTA Test

  • Overall Thermal-hydraulic Tests
    • Main components characteristics (pump, valve, heat exchanger)
    • Heat transfer at heater rod, PRHR Hx, Helical SG
    • System behavior during power change
  • Performance Tests
    • Reactor shutdown operation
    • Start-up, power change and MCP transient operations
    • PRHRS natural circulation operations
  • Transient and Accident Tests
    • Increase and decrease of feedwater flow
    • Increase steam flow
    • Power increase transient
natural circulation analysis code
NATURAL CIRCULATION ANALYSIS CODE
  • MARS 3.0 code
    • 1-D and 3-D system analysis code for thermal hydraulic analysis of the light water reactor transients
    • Developed at the KAERI by consolidating and restructuring the RELAP5/MOD3.2 and COBRA-TF codes
    • SMART specific models
      • Helically coiled SG
      • Pressurizer with non-condensable gas
    • Performed verification and validation using
      • Comparison of RELAP5/MOD3 results
      • OECD collaborative works such as SETH, PKL, BEMUSE, TMI-2
      • Data of VISTA experiment
natural circulation analysis code1
NATURAL CIRCULATION ANALYSIS CODE
  • Heat transfer correlation for natural circulation

(MARS code)

    • For vertical region (Churchill-Chu)
    • For horizontal region (McAdam)
      • For energy down-flow
      • For energy up-flow
natural circulation analysis code2
NATURAL CIRCULATION ANALYSIS CODE
  • Nodalization of MARS 3.0
natural circulation analysis code3
NATURAL CIRCULATION ANALYSIS CODE
  • TASS/SMR code
    • 1-D system analysis code for thermal hydraulic analysis of an integral reactor, SMART
      • Developed by KAERI
    • Basic conservation equation : mixture mass, liquid mass, non-condensable gas mass, mixture energy, steam energy, mixture momentum
      • The code incorporates slip effects between the phases by using empirical correlations
    • SMART specific models are included

Vertical Region

Horizontal Region

natural circulation analysis code4
NATURAL CIRCULATION ANALYSIS CODE
  • Nodalization of TASS/SMR
natural circulation analysis code5
NATURAL CIRCULATION ANALYSIS CODE
  • Summary of input model
    • Volume and Junctions
      • RCS : 0.13 m3
      • secondary system : 0.035 m3
      • ECT tank : 9 m3
      • 1-dimensional 233 nodes, 252 junctions – MARS code

117 nodes, 125 junctions – TASS/SMR code

    • Heat structure of the primary system
      • Heater rods
      • SG helical tubes
      • Wall heat structure and heat loss – MARS code

No wall heat structure excluding heat loss – TASS/SMR code

    • Pipe heat structure of the secondary system
      • PRHR heat exchanger tubes
      • Not model other structure
experiment results vista nc
Experiment Results – VISTA NC
  • Power changeswith constant FW flow
  • System behaviors are nearly the same
  • From these results,
  • effect of initial power is small for NC
experiment results vista nc1
Experiment Results – VISTA NC
  • Repetition test performs to enhance a reliability of the experiment
  • System behaviors show nearly the same results
  • From these results,
  • obtains a reliability of the NC test
  • at the VISTA facility
results and discussions

그림 3-1). VISTA 증기발생기 설계

Primary inlet

Steam outlet

FW inlet

Primary outlet

RESULTS and DISCUSSIONS

Boundary Condition

+ For the 100% operation, HT at active = 688.3, HT at inactive=10.4, heat loss at primary loop=16.8

Total power = 715.5

+ For the NC test, the heater power is zero

+ Initial power of MARS has the same value with the exp.

+ Initial power of TASS/SMR is smaller value => doesn’t model heat loss to the atm.

heat transfer at SG inactive

results and discussions1

ECT

Cooling water inlet

RESULTS and DISCUSSIONS

Boundary Condition

  • Cooling water temperature at ECT inlet
  • + Hx is cooled by chilled water in the CWS
  • + Cooling of chilled water is used by an air cooler
results and discussions2
RESULTS and DISCUSSIONS
  • Secondary Natural Circulation
  • +NC flow decrease 10% of initial flow early stage
  • +NC loop is formed within a few minutes
  • +Cal. results are predicted well the exp. result
results and discussions3
RESULTS and DISCUSSIONS

Forced circulation flow

Natural circulation flow

  • Primary Natural Circulation Flow
  • + Pri. NC flow fails to measure at the exp.
  • + NC flow of two codes predict nearly a same value
  • + Flow rate decrease 9% of initial flow early stage
  • + the flow decreases gradually to 2%
results and discussions4

Primary inlet

Steam outlet

FW inlet

Primary outlet

RESULTS and DISCUSSIONS
  • Primary Pressure
  • +Primary pr. becomes to decrease with transient
  • +Primary pr. depends on coolant temperature under NC
  • +Calculated depressurization rate is higher than the exp. pressure at the early stage
  • => final pr. is lower than the exp.
results and discussions5
RESULTS and DISCUSSIONS

SG Steam Pressure

+ From experiment,

Sec. pr. increases after it decreases

+Overall pressure is predicted well by codes

+Two codes doesn’t predict decrease at beginning of transient

+Calculated min. pr. is initial pressure

max. pr. is higher than exp. pressure

two codes over-predicts peak pr.

=> to find discrepancy

results and discussions6

Primary inlet

Steam outlet

FW inlet

Primary outlet

RESULTS and DISCUSSIONS
  • Primary temperature
  • +Two codes predict well overall trend
  • => NC HT model of helical tube
  • and bundle
results and discussions7

Primary inlet

Steam outlet

FW inlet

Primary outlet

RESULTS and DISCUSSIONS
  • SG Inlet and Outlet Temperature
  • + From exp., Sec. temp. is higher than Pri. Temp.
  • => Steam temp. affects on heat capacity of steam pipe wall
  • + SG inlet temp. is predicted reasonably
  • + Code doesn’t predict steam temp.
  • => the codes should be modeled the heat structure of steam pipe
results and discussions8
RESULTS and DISCUSSIONS

Hx Inlet and Outlet Fluid Temperature (Tube side)

+ Steam temp. is a saturated steam and liquid temp. is a subcooled liquid

+ Steam temp. is predicted well by two codes

+ Liquid temp. is slightly higher than the exp.

=> the codes seem to under predict heat transfer at the heat exchanger

results and discussions9
RESULTS and DISCUSSIONS

Surface temperature in the Hx tube

+Surface temperature in the upper part is always above 100 ℃ (≈106 ℃)

=> local boiling occurs at the upper part

+The lower part maintains a sub-cooled liquid condition

+Calculated temp. at the lower part is over-predicted

since the cal. heat transfer in the Hx is smaller than the exp.

results and discussions10
RESULTS and DISCUSSIONS

Liquid temperature in the ECT

+ The overall fluid temp. in the ECT is lower than the sat. temp

+ Fluid temp. in the upper part maintains a constant value and the lower part increase with time

+ Cal. Liquid temp. in the upper partis nearly same with exp. and the lower part is slightly higher

summary
The natural circulation test at the VISTA facility is performed to find thermal hydraulic characteristics in the PRHRS of SMART

The PRHRS removes well the primary heat source as long as the Hx is submerged the water in the ECT.

Natural circulation flow rate is around 10% of the initial flow for the integral reactor

The local boiling is occurred at the top of the heat exchanger bundle

Natural circulation of the VISTA facility depend on

Heat loss to the atmosphere at the reactor vessel and connected pipes

Latent heat in the reactor vessel

Friction and form loss of the geometry

Heat transfer at the SG and the heat exchanger

SUMMARY

From Experiment

summary1
The realistic calculations is performed to find analysis capability of the TASS/SMR and MARS codes

The model of the heat loss and heat capacity for the system are important to predict well the natural circulation

From the code calculation results

Two codes calculate reasonably the natural circulation at the integral reactor

It is important to model properly the boundary condition such as heat loss, heat capacity of the structure

Tow codes over-predicts depressurization rate of the primary pressure

Under-predicts heat transfer slightly at the SG and the heat exchanger

SUMMARY

From Calculation

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