First safety approach of the DHR system of XT-ADS

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First safety approach of the DHR system of XT-ADS

• B. Arien

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General purpose

• Main objective identification of the possible
  failure modes of the DHR system and its
  weaknesses, its limits
• Methodological approach master logic diagram
  (MLD) method
• Accidents into consideration
• Loss of heat sink (LOHS)
• Loss of flow (LOF)
• Combination of LOF and LOHS
• Protected and unprotected cases

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Main design assumptions

• Primary system
• 2 groups pump-HX (2 pumps, 4 HXs)
• Emergency electrical supply to pumps
• Free convection if total loss of pumps
• Secondary system
• 2 independent loops
• Emergency electrical supply to pumps
• Possibility of natural circulation to be
  considered
• Tertiary system no design information, supposed
  to work in natural circulation and is treated as
  a whole
• Vault system (RVACS) no design information,
  supposed to work in natural circulation mode and
  treated as a whole

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XT-ADS Sketch of the Secondary System and DHR
System (Proposal)
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SCK?CENs proposal
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MLD procedure

• For each accident type
• Step 1 identification of the failure modes that
  initiate the accident
• Step 2 development of a MLD for the protected
  case
• Step 3 development of a MLD for the unprotected
  case

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MLD procedure

• Symbols
• DHR system fulfills its function (
  .false.)
• may contribute to DHR system
  failure (.true.)
• question related to any
  unresolved problem

Accident initiating event
Failure in DHR system
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LOHS step 1
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(No Transcript)
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LOHS step 2
Failure of core cooling under protected LOHS
conditions
If single secondary pump failure
If total secondary pump failure
If tertiary cooling system unavailable
If depressur. in 1 SCS loop
If depressur. in whole SCS
If pipe break in 1 SCS loop
If pipe breaks in whole SCS
If partial HX blockage (water side)
Failure of tertiary cooling system
Vault System failure
SCS pipe breaks caused by external accident
Vault System failure
Vault System failure
Over- pressure in SCS
Safety valve failures
Vault System failure
Failure of emergency electrical supply to
secondary pumps
Failure of SCS pressurization
Vault System failure
Failure of electrical supply to secondary pumps
Free convection fails to take place in the
secondary system
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LOHS step 3
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LOF step 1
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(No Transcript)
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LOF step 2
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LOF step 3
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LOFLOHS step 1
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(No Transcript)
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LOFLOHS step 2
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LOFLOHS step 3
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Problems to be solved

• Q1 is the DHR possible with the SCS working in
  free convection mode?
• Q2 is the DHR possible when the SCS is at
  atmospheric pressure?
• Q3 can the nominal power be evacuated with the
  SCS working in free convection mode?
• Q4 is the DHR possible with the primary system
  working in free convection mode and with the
  presence of a core bypass?
• Q5 can the nominal power be evacuated when only
  one pump-HX group is operating in the primary
  system?
• Q6 can the nominal power be evacuated with the
  primary system working in free convection mode ?
• Q7 can the nominal power be evacuated with the
  primary system working in free convection mode
  and with the presence of a core bypass?
• Q8 is the DHR possible with the primary,
  secondary and tertiary circuits working in free
  convection mode?
• Q9 is the DHR possible via the VS with the
  primary system working in free convection mode
  and with a total blockage of the PHXs?
• Q10 can the nominal power be evacuated with the
  primary, secondary and tertiary circuits working
  in free convection mode?

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Cut sets for protected LOF
Failure of core cooling under protected LOF
conditions

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Cut sets for unprotected LOF
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Cut sets for protected LOHS
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Cut sets for unprotected LOHS (a)
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Cut sets for unprotected LOHS (b)
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Cut sets for protected LOFLOHS
Failure of core cooling under protected LOFLOHS
conditions

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Cut sets for unprotected LOFLOHS
Failure of core cooling under unprotected
LOFLOHS conditions

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Conclusions and future work

• A qualitative analysis was performed
• to provide first indications on the DHR
  performance
• to guide the future work
• Some unresolved questions require a quantitative
  analysis
• Design needs to be completed
• Choice of the SCS (Ansaldo or SCK?CEN)
• RELAP (or TRAC) model has to be developed for the
  simulation of the whole system in most of the
  transients
• CFD model of the primary system has to be
  developed
• Free convection simulation
• Calibration of the RELAP model
• Reassessment of the DHR system behaviour in
  accidental situations