1DM1 – WP1.5 meeting Stockholm, May 22-23, 2007
First safety approach of the DHR system of XT-ADS
B. Arien
2DM1 – WP1.5 meeting Stockholm, May 22-23, 2007
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
3DM1 – WP1.5 meeting Stockholm, May 22-23, 2007
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
EUROTRANS-DM1: T1.2.2 meeting, February 28, 2007
XT-ADS
Sketch of the Secondary System and DHR System
(Proposal)
Suppression Tank
PHX
Steam Separator
Air Condenser
Chimney
Fan
Louver
IsolationValve
IsolationValve
Safety Relief Valve
From second PHX
To second PHX
Pump
Check Valve
SCKCEN’s proposal
6DM1 – WP1.5 meeting Stockholm, May 22-23, 2007
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
7DM1 – WP1.5 meeting Stockholm, May 22-23, 2007
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
OK
unsuccess
yes
question
?no
Qi
LOHS accident
Secondary pump failure
Pipe break in SCS
Depressurization in SCS
Tertiary cooling system failure
HX blockage (secondary side)
Blockage by
debris
Partial blockage
HX blockage (primary side)
Accompanied by LOF
LBE freezing
in HX
Blockage by
debris
LOF&LOHS
LOHS: step 1
Failure of core cooling in LOHS conditions
Protected accident
Unprotected accident
Failure of core cooling under protected LOHS conditions
A
Failure of core cooling under unprotected LOHS conditions
Accelerator shutdown
failure
B
LOHS: step 2
Failure of tertiary cooling system
Failure of core cooling under protected LOHS conditionsA
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)
OK
OK
OK
OK
Vault System failure
Failure of SCS pressurization
Vault System failure
OK
yes
DHR possible at atm. p in SCS
?
no
Q2
Failure of electrical supply to secondary
pumps
Vault System failure
Failure of emergency electrical supply to secondary
pumps
Free convection fails to take place in the secondary system
yes
DHR possible by free convection
in SCS
?no
Q1
unsuccess
SCS pipe breaks caused
by external accident
Vault System failure
Vault System failure
Over- pressure in SCS
Safety valve
failures
LOHS: step 3
Failure of core cooling under unprotected LOHS conditionsB
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
Failure of SCS pressurization
Failure of pressurization in 1 SCS loop
Debris formation
in SCS
Single secondary
pump failure
Q3
Failure of emergency electrical supply to secondary
pumps
Failure of electrical supply to secondary
pumps Free convection fails to take place in the secondary system
yes
Nominal power can be removed by free convection in SCS
?no
Q3
unsuccess
SCS pipe breaks caused by
external accident
Over- pressure in SCS
Safety valve
failures
Single pipe
break in SCS
Over- pressure in 1 SCS
loop
Safety valve failure
LOF accident
Primary pump failure
HX blockage (primary side)
Accompanied by LOF
LBE freezing
in HX
Blockage by
debris
LOF&LOHS
Accidental core bypass
LOF: step 1
Failure of core cooling under LOF conditions
Protected accident
Unprotected accident
Failure of core cooling under protected LOF conditions
C
Failure of core cooling under unprotected LOF conditions
Accelerator shutdown
failure
D
Failure of core cooling under protected LOF conditionsC
Primary pumps fail to stop
If single primary pump failure
OK
If total primary pump failure
OK
If accidental core bypass
yes
DHR possible in free convection mode and
with core bypass
?no
Q4
unsuccess
Core bypass formation
Free convection fails to take place
LOF: step 2
Failure of core cooling under unprotected LOF conditionsD
If single primary pump failure
Single primary pump failure
If total primary pump failure
no
OK yes
Nominal power can be evacuated when 1 group is operating
?
Q5
unsuccess
Failure of electrical supply to primary pumps
Failure of emergency electrical supply to primary pumps
Nominal power can be evacuated in free
convection mode
yes?
no
Q6
unsuccess
OK
If accidental core bypass
Primary pumps fail to stop
yes
Nominal power can be evacuated in free convection mode and with core bypass
?no
Q7
unsuccess
Core bypass formation
Free convection fails to take place
LOF: step 3
LOF&LOHS accident
Common cause failure generating LOF and LOHS
HX blockage (primary side)
Freezing induced by LOF
LBE freezing in HX
Blockage by
debris
Partial blockage
Independent combinations of LOF and LOHS
Dependent combinations of LOF and LOHS
LOF&LOHS: step 1
Failure of core cooling under LOF&LOHS conditions
Protected accident
Unprotected accident
Failure of core cooling under protected LOF&LOHS conditions
E
Failure of core cooling under unprotected LOF&LOHS conditions
Accelerator shutdown
failure
F
Failure of core cooling under protected LOF&LOHS conditionsE
Independent combinations of LOF and LOHS
LOHS induced by LOF: HX blockage (primary side)
Partial HX blockage by debris
OK
Total HX blockage by LBE freezing
Station black-out
Common cause failure for LOF and LOHS
Vault System failure
Overcooling
Vault System failure
Total primary pump failure
Failure of electrical supply to primary pumps
Failure of emergency electrical supply to
primary pumps
yes
DHR possible via VS in ‘degraded’ free convection mode
?no
Q9
unsuccess
DHR possible by total free
convection in the primary,
secondary and tertiary systems
Q8
yes
?no
Free convection fails to take place in the secondary
system
unsuccess
Failure of emergency electrical supply
LOF&LOHS: step 2
Failure of core cooling under unprotected LOF&LOHS conditionsF
Independent combinations of LOF and LOHS
Common cause for LOF and LOHS
LOHS induced by LOF: HX blockage (primary side)
Partial HX blockage by debris
Total HX blockage by LBE freezing
OvercoolingTotal primary pump failure
Failure of electrical supply to
primary pumps
Failure of emergency
electrical supply to primary pumps
Debris formation in
primary system
Station black-out
Nominal power can be evacuated by
total free convection in the primary, secondary and
tertiary systems
Q10
yes
?nounsuccess
Free convection fails to take place in the secondary system
Failure of emergency electrical supply
LOF&LOHS: step 3
20DM1 – WP1.5 meeting Stockholm, May 22-23, 2007
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?
21DM1 – WP1.5 meeting Stockholm, May 22-23, 2007
Cut sets for protected LOF
DHR possible in free convection mode and
with core bypass
?
Q4
Failure of core cooling under protected LOF
conditions
:
Core bypass formation
Primary pumps fail to stopand if Q4 true
Core bypass formation
if Q4 false
22DM1 – WP1.5 meeting Stockholm, May 22-23, 2007
Cut sets for unprotected LOF
Nominal power can be evacuated in free
convection mode
?
Q6
Failure of core cooling under protected LOF
conditions
:
Single primary pump failure and
Accelerator shutdown failure
if Q5 false
Failure of electrical supply to
primary pumps
Failure of emergency
electrical supply to primary pumps
and andAccelerator
shutdown failure if Q6 false
Core bypass formation
Primary pumps fail to stopand and
Accelerator shutdown failure
if Q7 true
Core bypass formation and
Accelerator shutdown failure if Q7 false
Nominal power can be evacuated when 1 group is operating
?
Q5Nominal power can be
evacuated in free convection mode and with core bypass
?
Q7
23DM1 – WP1.5 meeting Stockholm, May 22-23, 2007
Cut sets for protected LOHS
if Q1 true
Failure of core cooling under
protected LOHS conditions
:
Failure of tertiary cooling system
Vault System failure
and
if Q2 falseandFailure of SCS pressurization
Vault System failure
DHR possible at atm. p
?
Q2
Vault System failure
and and andFailure of electrical supply to secondary
pumps
Failure of emergency
electrical supply to secondary
pumps
Free convection fails to take place in the secondary
system
Vault System failure
and andFailure of electrical supply to secondary
pumps
Failure of emergency
electrical supply to secondary
pumps
if Q1 false
DHR possible by free convection
in SCS
?
Q1
SCS pipe breaks caused by external
accident
Vault System failure
and
Overpressure in SCS
Vault System failure
andSafety valve
failuresand
24DM1 – WP1.5 meeting Stockholm, May 22-23, 2007
Cut sets for unprotected LOHS (a)
Failure of core cooling under
unprotected LOHS conditions
:
if Q3 true
and and andFree convection
fails to take place in the secondary
system
Failure of electrical supply
to secondary pumps
Failure of emergency electrical supply to secondary
pumps
Accelerator shutdown
failure
SCS pipe breaks caused by external accident
and Accelerator shutdown failure
andFailure of SCS pressurization
Accelerator shutdown failure
andAccelerator
shutdown failureDebris formation
in SCS
Failure of tertiary cooling system
Accelerator shutdown failure
and
Depressur. of 1 SCS loop
Accelerator shutdown failure
and
Single pipe break in SCS
Accelerator shutdown failure
and
Single secondary pump failure
Accelerator shutdown failure
and andFree convection fails to take
place in the secondary system
Nominal power can be removed by free convection in SCS
?
Q3
Overpressure in 1 SCS loop
andAccelerator
shutdown failureSafety valve
failureand
Overpressure in SCS
andAccelerator
shutdown failureSafety valve
failuresand
25DM1 – WP1.5 meeting Stockholm, May 22-23, 2007
Cut sets for unprotected LOHS (b)
Failure of core cooling under
unprotected LOHS conditions
:
if Q3 false
and andFailure of electrical
supply to secondary pumps
Failure of emergency electrical supply to secondary pumps
Accelerator shutdown
failure
SCS pipe breaks caused by external accident
and Accelerator shutdown failure
andFailure of SCS pressurization
Accelerator shutdown failure
andAccelerator
shutdown failureDebris formation
in SCS
Failure of tertiary cooling system
Accelerator shutdown failure
and
Depressur. of 1 SCS loop
Accelerator shutdown failure
and
Single pipe break in SCS
Accelerator shutdown failure
and
Single secondary pump failure
Accelerator shutdown failure
and
Nominal power can be removed by free convection in SCS
?
Q3
Overpressure in 1 SCS loop
andAccelerator
shutdown failureSafety valve
failureand
Overpressure in SCS
andAccelerator
shutdown failureSafety valve
failuresand
26DM1 – WP1.5 meeting Stockholm, May 22-23, 2007
Cut sets for protected LOF&LOHS
Failure of core cooling under
protected LOF&LOHS conditions
:
DHR possible via VS in ‘degraded’ free convection mode
?
Q9
Independent combinations of LOF and LOHS
Station black-out
Vault System failure
andFailure of
emergency electrical supply
Free convection fails to take place in the secondary system
and and if Q8 true
Station black-out
Vault System failure
andFailure of
emergency electrical supply
and if Q8 false
Failure of electrical supply to
primary pumps
Failure of emergency
electrical supply to primary pumps
and and andOvercoolingVault System
failure if Q9 true
Failure of electrical supply to
primary pumps
Failure of emergency
electrical supply to primary pumps
and and Overcooling if Q9 true
DHR possible by total free
convection in the primary,
secondary and tertiary systems
Q8
?
27DM1 – WP1.5 meeting Stockholm, May 22-23, 2007
Cut sets for unprotected LOF&LOHS
Failure of core cooling under unprotected LOF&LOHS conditions
:Failure of electrical supply to
primary pumps
Failure of emergency
electrical supply to primary pumps
and and andOvercoolingAccelerator
shutdown failure
Debris formation in
primary system
Accelerator shutdown failure
and
Independent combinations of LOF and LOHS
Accelerator shutdown failureand
Station black-out
andAccelerator shutdown
failure
Failure of emergency electrical supply
and if Q10 false
if Q10 trueStation black-out
andAccelerator shutdown
failure
Failure of emergency electrical supply
and Free convection fails to take place in the secondary
system
and
Nominal power can be evacuated by
total free convection in the primary, secondary and
tertiary systems
Q10
?
28DM1 – WP1.5 meeting Stockholm, May 22-23, 2007
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 SCKCEN)
• 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