DM1 – WP1.5 meeting Stockholm, May 22-23, 2007 1 First safety approach of the DHR system of XT-ADS...

1DM1 – WP1.5 meeting Stockholm, May 22-23, 2007

First safety approach of the DHR system of XT-ADS

B. Arien


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


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


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


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


OK

yes

DHR possible at atm. p in SCS

?

no

Q2

Failure of electrical supply to secondary

pumps


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



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


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


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


Failure of core cooling under protected LOF conditions

C

Failure of core cooling under unprotected LOF conditions


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


Free convection fails to take place

LOF: step 3

LOF&LOHS accident

Common cause failure generating LOF and LOHS


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


Failure of core cooling under protected LOF&LOHS conditions

E

Failure of core cooling under unprotected LOF&LOHS conditions


failure

F

Failure of core cooling under protected LOF&LOHS conditionsE


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


Overcooling


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


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



LOF&LOHS: step 3


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?


Cut sets for protected LOF

DHR possible in free convection mode and

with core bypass

?

Q4

Failure of core cooling under protected LOF

conditions

:


Primary pumps fail to stopand if Q4 true


if Q4 false


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


primary pumps



and andAccelerator

shutdown failure if Q6 false


Primary pumps fail to stopand and


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


Cut sets for protected LOHS

if Q1 true

Failure of core cooling under

protected LOHS conditions

:



and

if Q2 falseandFailure of SCS pressurization


DHR possible at atm. p

?

Q2


and and andFailure of electrical supply to secondary

pumps


electrical supply to secondary

pumps

Free convection fails to take place in the secondary

system


and andFailure of electrical supply to secondary

pumps


electrical supply to secondary

pumps

if Q1 false

DHR possible by free convection

in SCS

?

Q1

SCS pipe breaks caused by external

accident


and

Overpressure in SCS


andSafety valve

failuresand


Cut sets for unprotected LOHS (a)


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


pumps


failure

SCS pipe breaks caused by external accident

and Accelerator shutdown failure

andFailure of SCS pressurization


andAccelerator

shutdown failureDebris formation

in SCS



and

Depressur. of 1 SCS loop


and

Single pipe break in SCS


and

Single secondary pump failure


and andFree convection fails to take

place in the secondary system


?

Q3

Overpressure in 1 SCS loop

andAccelerator

shutdown failureSafety valve

failureand

Overpressure in SCS

andAccelerator


failuresand


Cut sets for unprotected LOHS (b)


unprotected LOHS conditions

:

if Q3 false

and andFailure of electrical

supply to secondary pumps

Failure of emergency electrical supply to secondary pumps


failure

SCS pipe breaks caused by external accident

and Accelerator shutdown failure

andFailure of SCS pressurization


andAccelerator

shutdown failureDebris formation

in SCS



and

Depressur. of 1 SCS loop


and

Single pipe break in SCS


and

Single secondary pump failure


and


?

Q3

Overpressure in 1 SCS loop

andAccelerator


failureand

Overpressure in SCS

andAccelerator


failuresand


Cut sets for protected LOF&LOHS


protected LOF&LOHS conditions

:

DHR possible via VS in ‘degraded’ free convection mode

?

Q9


Station black-out


andFailure of

emergency electrical supply


and and if Q8 true

Station black-out


andFailure of

emergency electrical supply

and if Q8 false


primary pumps



and and andOvercoolingVault System

failure if Q9 true


primary pumps



and and Overcooling if Q9 true

DHR possible by total free

convection in the primary,

secondary and tertiary systems

Q8

?


Cut sets for unprotected LOF&LOHS

Failure of core cooling under unprotected LOF&LOHS conditions

:Failure of electrical supply to

primary pumps



and and andOvercoolingAccelerator

shutdown failure

Debris formation in

primary system


and


Accelerator shutdown failureand

Station black-out

andAccelerator shutdown

failure


and if Q10 false

if Q10 trueStation black-out

andAccelerator shutdown

failure


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

?


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

Date post:	15-Dec-2015
Category:	Documents
Upload:	carlton-nickel
View:	212 times
Download:	0 times

DM1 – WP1.5 meeting Stockholm, May 22-23, 2007 1 First safety approach of the DHR system of XT-ADS...

Documents