Diapositiva 1

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DIPARTIMENTO DI INGEGNERIA MECCANICA, NUCLEARE E
DELLA PRODUZIONE UNIVERSITA' DI PISA 56100 PISA
-ITALY
NATURAL CIRCULATION AND BORON
DILUTION PROCESS IN PWR
F. DAuria, G. M. Galassi

IAEA 2nd CRP MEETING NATURAL CIRCULATION IN
WATER-COOLED NUCLEAR POWER PLANTS Corvallis,
Oregon (US), Aug. 29 Sept 2, 2005
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• NOMENCLATURE BACKGROUND
• B) THE NPP INPUT DECK
• C) THE PREDICTED NC SCENARIO
• The Boron-Dilution Map
• D) THE PKL-III NC EXPERIMENT
• The Scaling Issue
• The Boron Dilution Transport
• E) THE PREDICTABILITY OF BORON PHENOMENA
• F) THE SBLOCA BORON SCENARIO

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BORON DILUTION The process where a local decrease
in boron concentration in PS occurs with
(nearly) constant average boron concentration
DE-BORATION The process where a net loss of
boron from PS occurs that implies a decrease in
average boron concentration Consequently, the
following definitions can be introduced BORATION
(the opposite of de-boration) BORON
CONCENTRATION RECOVERY (the opposite of boron
dilution) DE-BORATION RATE (the rate of
de-boration) DILUTION RATE (the rate of boron
dilution)
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BORON TRANSPORT The movement of diluted boron
plugs in the primary loop (this occurs at
a system level and is affected by integral
phenomena like NC, SG-heat transfer a system
code is needed for the investigation) BORON
MIXING The process when volumes of fluid with
different boron concentration, temperature and
void fraction come into contact (this occurs at a
local level a CFD code is needed for the
investigation) Boron Dilution,
De-boration, Mixing Transport occur
simultaneously in case of selected
Boron Relevant Accidents (BRA)
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THE STUDY HAS BEEN CONDUCTED BY A QUALIFIED
SYS-TH CODE The phenomena BORON DILUTION,
DE-BORATION AND BORON TRANSPORT are calculated,
together with the effect of DILUTED VOLUME OF
WATER upon NK reactivity. The main assumptions
are FULL MIXING in the LP of the RPV and use of
POINT NK in the core (including the
boron-feedback).
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• THE QUALIFICATION LEVEL
• THE ADOPTED CODE IS QUALIFIED FOR THE SELECTED TH
  TRANSIENTS.
• THE ADOPTED NPP NODALISATION (INCLUDING BIC) IS
  QUALIFIED (COMPARISON WITH SIEMENS RESULTS,
  ETC.).
• THE ADOPTED CODE-NODALISATION IS QUALIFIED FOR
  BORON DILUTION, DE-BORATION AND BORON TRANSPORT
  (COMPARISON WITH AVAILABLE PKL TESTS).
• THE CODE-USERS ARE (PRESUMED TO BE) QUALIFIED.
• THE FULL MIXING IN LP AND CORE ( PARTIAL
  MIXING IN DC) CONSTITUTES AN UNQUALIFIED
  SIMPLIFYING ASSUMPTION.
• THE 0-D NK FEEDBACK IS AFFECTED BY THE SELECTED
  REACTIVITY FEEDBACK.
• THEREFORE, WEAK POINTS FOR THE ANALYSIS ARE
  THE RPV MIXING AND THE NK
  FEEDBACK.

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Initial Fine-UT nodalisations PS SG
pressure
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Initial Fine-UT nodalisations PS mass
inventory
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Initial Fine-UT nodalisations Core inlet
flow-rate
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Initial Fine-UT nodalisations Core inlet
flow-rate - detail
Fine
Initial
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Initial Fine-UT nodalisations HL liquid
velocity
Reflux Condensation start
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Initial Fine-UT nodalisations HL steam
velocity
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Initial Fine-UT nodalisations Boron in LS
LS ALWAYS FULL OF LIQUID
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THE BORON-DILUTION MAP
Quantity affected by time span at each PS MI
Boron dilution rate (R5 units)
Boron dilution rate gt 0 at high PS MI values
PS Mass Inventory (-)
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THE SCALING ISSUE
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THE SCALING ISSUE
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PWR Residual mass
PKL III Residual mass
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THE SCALING ISSUE
THE DATA BASE FOR DERIVING THE FLOW MAP
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THE SCALING ISSUE
PKL DATA SHOW EXCELLENT NC PERFORMANCE
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THE BORON DILUTION AND TRANSPORT HYSTERESIS
BETWEEN DRAINING FILLING CYCLES
PS DRAINING
PS FILLING
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THE BORON DILUTION AND TRANSPORT THE BORON
DILUTION RATE VS PS MI MEASURED IN PKL EXPERIMENT
AND
CALCULATED (BY RELAP5) IN NPP CONDITIONS
DATA 2005
NPP CALCULATION 2004
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THE PREDICTABILITY OF BORON PHENOMENA RELAP5
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TEST F1.2 (AVERAGE) BORON CONCENTRATION IN LS
3 OF 3
COMPARISON EXP (RED) / CALC (BLACK)
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TESTS E2.2 F1.1 BORON CONCENTRATION IN LOOPS
COMPARISON EXP (BLU) / CALC (BLACK)
CONCLUSION FROM THE APPLICATION OF CATHARE TO
BORON TRANSPORT EXPERIMENTS RESULTING
PREDICTION ACCURACY IS ACCEPTABLE
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FOUR LOOP PWR SEARCH FOR THE WORST RPV-LP
BREAK
RANGE FOR INVESTIGATION
20-40 CM2 BREAK IN LP WITHIN THE CRITICAL RANGE
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FOUR LOOP PWR RPV-LP BREAK (DBA CONDITIONS)
PS
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FOUR LOOP PWR RPV-LP BREAK (DBA CONDITIONS)
Loops w HPIS
Loops w/o HPIS
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FOUR LOOP PWR RPV-LP BREAK (DBA CONDITIONS)
Nominal power
Boron diluted plug in core
NC restart
CHF
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CONCLUSIONS

• THE BORON DILUTION PROCESS IS STRICTLY CONNECTED
  WITH NC.
• 2FNC CAUSES BORON DILUTION. THE 2FNC SCENARIO IS
  IDEAL TO INVESTIGATE THE BORON DILUTION AND THE
  SYSTEM BORON TRANSPORT PROCESSES.
• NC RESTART (SYSTEM RE-FILLING) CAUSES DILUTED
  WATER PLUG TO REACH THE CORE. CL AND RPV MIXING
  HAVE THE POTENTIAL TO MITIGATE THE RELATED
  CONSEQUENCES.
• CURRENT SYSTEM CODES APPEAR QUALIFIED TO PREDICT
  THE BORON DILUTION AND THE SYSTEM BORON TRANSPORT
  PROCESSES.
• ltQUALIFIEDgt CODE APPLICATION TO SBLOCA SHOWS
  RECRITICALITY IN SELECTED DBA CONDITION

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