ERMSAR 2012, Cologne March 21 – 23, 2012 ESTIMATION OF THERMAL-HYDRAULIC LOADING FOR VVER-1000 UNDER SEVERE ACCIDENT SCENARIO Barun Chatterjee 1, Deb Mukhopadhyay

ERMSAR 2012, Cologne March 21 – 23, 2012

ESTIMATION OF THERMAL-HYDRAULIC LOADING FOR VVER-1000 UNDER SEVERE ACCIDENT

SCENARIO

Barun Chatterjee1, Deb Mukhopadhyay1, Hemant G. Lele1, Pavlin Groudev2

1BARC, Mumbai (India)

2INRNE, Sofia (Bulgaria)


Study Objective

2

Structural components like SG tubes, RCP seals, hot leg, Pressuriser Surge line and RPV, Different valves of VVER1000 are likely to experience high temperature and pressure under postulated severe accident conditions arising from SBO ( a high pressure event among severe accident scenarios)

These loading may fail the components

These failure estimation will alter the course of the accident

* System depressurisation followed by less inventory/steam available for

hydrogen

generation * converting the possibility of high pressure melt ejection into a low pressure

melt ejection scenario in the Containment. The change in scenario will alter the load on the ultimate barrier

As severe accident analysis are based on realistic models, hence a realistic predictions will help to plan SAMG for Core and containment in a better way


VVER-1000 (V320) RCS Layout

3

Hot legSurge

Line

Pump Seal

SG tubes

RPV


Station Black Out (SBO) ANALYSIS

4

Following assumptions have been made for SBO simulation

1. Transient is initiated with Station Blackout

2. MCPs and turbine trip at 0.0 s due to SBO

3. Reactor trips at 1.6 s. due to loss of power

4. Feed pumps trip at 5 s due to turbine trip.

5. Pumped Safety Injection systems are assumed to be not available due to SBO


COMPUTER CODE ASTECV1.3rev3p1 AND VVER1000 -PLANT MODEL

5

BRU-K

PRZ Relief Valves

To Loop 2, 3, 4 4

SRG_LINE

ULEGP1 (Pump)

Lower Plenum

Reactor Vessel

Baffle

1 2 3 4 5

Lower Plenum

Reactor Vessel

Baffle

1 2 3 4 5

15 Grid Spacers

Lower Plate grid

DOWNCO1

UPPLE1

UPPLE2

HL1

PRZ

SG1

- HCOL

SG1

- CCOL

SG1_SEC

SG1_TUB

Safety valves SG-PSDs -

BRU-A

Upp_cor

INRJ7

Loop1j1

Loop1j2

Loop1j3

Loop1j5

Loop1j7

Loop1j8

Main steam Header

Main Steam Line From 2, 3, 4

From Loop 2, 3, 4

Parameters Design Value

Steady State value

Reactor Power (MW) 3000.0 3000.0

RCS Pressure (Mpa) 15.7 15.5

SG Pressure (MPa) 6.27 6.26

Coolant Temperature at reactor inlet (K)

562.0 562.3

Coolant Temperature at reactor outlet (K)

593.0 592.4

Coolant Flow per loop (kg/s)

4400.0 4387.0

Feed flow per SG (kg/s) 408.0 408.34

Initial Inventory

RCS Inventory (t.) 245.5

UO2 inventory in core (t.) 73.12

Zr inventory in core (t.) 21.6

B4C inventory in core (kg) 369.8

Total Steel Inventory (t.) 263.0

Decay Heat End of life


REACTOR BEHAVIOUR UNDER SBO

EVENT Time (s)

SBO 0.0

MCP #1,2,3,4 trip 0.0

Turbine trips 0.0

Reactor trips 1.6

Feed pumps stop 5.0

Beginning of oxidation

14,114.0

Start of FPs release 17,660.0

Total core uncovery 25,116.0

First corium slump in vessel lower

head

25,595.0

Lower head vessel failure

48,678.06

0 10000 20000 30000 40000 500004

6

8

10

12

14

16

18

20

Pre

ss

ure

(M

Pa

)

Time (s)

RCS Pressure SG Pressure

SG Boil Off

RCS Pressurisation

Chattering of PRZ Relief Valve

• SG Boil off

• SG Inventory depletion

• Loss of SG as a Heat Sink

• RCS Pressurisation

• Opening of PRZ relief valve

• RCS Boil off

• RCS Inventory Loss

• Core Heat up and Degradaton

• Vessel Failure


ASSESSMENT OF RCS AND SURGE LINE PIPE INTEGRITY

7

Material of construction of Reactor Coolant System and Surge line for VVER-1000 (V320) is 10 GN2 MFA steel (Dn-350)

High Temperature creep model for this material is not available in Open Literature,

Hence high temperature creep model for SS316 [R. M. Goldhoff ] for temperature range of 700-1089 K has been used for assessment

Ref. 1. F. R . Larsen and J. Miller, “a time temperature relationship for rupture and creep stress, Transaction of the ASME, July 1952, pp 765-775.

2. R. M. Goldhoff, “A Comparison of Parameter Methods for Extrapolating High Temperature Data”, ASME Journal of Basic Engineering, 1959, pp. 629-643.

ERMSAR 2012, Cologne March 21 – 23, 2012 8

The creep rupture time correlation for SS316 material is given as follows

ASSESSMENT OF RCS AND SURGE LINE PIPE INTEGRITY

ERMSAR 2012, Cologne March 21 – 23, 2012 9

0 10000 20000 30000 40000 50000

500

600

700

800

900

1000

1100

1200

1300

T

emp

erat

ure

(K

)

Time (s)

Upper Plenum Hot Leg Surge Line SG Tube Pump seal Vessel

Vessel Failure

Cre

ep c

orr

elat

ion

ran

ge

Component Temperatures under SBO


ASSESSMENT OF RCS AND SURGE LINE INTEGRITY

10

700 800 900 1000 1100 1200 1300 1400 1500 1600 17001E-9

1E-6

1E-3

1

1000

1000000

1E9

1E12

316 SS

Time t

o Rup

ture (

hr)

Temperature (K) Fig. 4: Variation of Rupture Time as function of Temperature

Surge Line

Time Required to Rupture Once the Component remains at a sustained high temperature :

Hot Leg : 22000 hrs[850 mm, 22 ksi (153 MPa)]

Surge Line : 0.11 hrs. (360 s)[400 mm, 14.8 ksi (108 MPa)]

Surge line fails after 360 s once it attains and remained at a Temperature higher than 1089 K :

Hot Leg


Conclusion

11

Analysis shows failure of Surge line (35,360 s) prior to Reactor

Vessel rupture from lower plenum creep (48,678 s)

SG tubes, hot leg, pump seal are unlikely to fail by thermal creep as

they remain at a lower temperature

Surge line rupture prior to vessel rupture at a high pressure event will

turn the event into a low pressure event

This situation will cause less severity to the containment as high

pressure melt ejection from lower head will not take place


Comparison between ASTECV1 and ASTECV2

EVENT Time (s) ASTECV1.3rev3p1

Time (s)ASTECV2.0r2p1

SBO 0.0 0.0

MCP #1,2,3,4 trip 0.0 0.0

Turbine, Reactor , Feed pumps trip 0.0, 1.6 s, 5.0 0.0, 1.6 s, 5.0

Beginning of oxidation 14,114.0 13,058.5

Start of FPs release 17,660.0 14,679.6

Total core uncovery 25,116.0 16,617.9

First corium slump in vessel lower head 25,595.0 16,516.5

Vessel failure 48,678.0 25,099.8

12

Large Discrepancy

In code (V1 –V

2) predictions CORE DEGRADATION ASTECV1 ASTECV2

Corium mass in the lower head (te) 32.9 24.9

H2 mass produced during the in-vessel phase (kg) 742 304

Aerosols mass produced during the in-vessel phase (kg) 885.8 382.5

Aerosols mass in containment at vessel failure (kg) 252.5 11.6



13

0 5000 10000 15000 20000 25000 300004

6

8

10

12

14

16

18

20

Pre

ssu

re (

MP

a)Time (s)

RCS PressureSG Pressure

ASTECV1 ASTECV2



14

0 10000 20000 30000 40000 50000

0

50000

100000

150000

200000

250000

Inve

nto

ry (

kg)

Time (s)

Liquid Inventory Vapour Inventory

0 5000 10000 15000 20000 25000

0

50000

100000

150000

200000

250000

Inv

en

tory

(k

g)

Time (s)

Vapour Inventory Liquid Inventory

ASTECV1 ASTECV2



15

ASTECV1 ASTECV2

Voided core

Voided core

No radial spread

radial spread(Magma

model)



16

0 5000 10000 15000 20000 25000 30000

500

600

700

800

900

1000

1100

1200

1300

Tem

pera

ture

(K)

Time (s)

Upper Plenum Hot Leg Surge Line

SG Tube Pump Seal Vessel

0 10000 20000 30000 40000 50000

500

600

700

800

900

1000

1100

1200

1300

Tem

per

atu

re (

K)

Time (s)

Upper Plenum Hot Leg Surge Line SG Tube Pump seal Vessel

Vessel Failure

Cre

ep c

orr

elat

ion

ran

ge

Component Temperatures under SBO

ASTECV1ASTECV2

Cre

ep C

orre

latio

n R

ange



17

700 800 900 1000 1100 1200 1300 1400 1500 1600 17001E-9

1E-6

1E-3

1

1000

1000000

1E9

1E12

316 SS

Time t

o Rup

ture (

hr)


Surge Line

700 800 900 1000 1100 1200 1300 1400 1500 1600 17001E-9

1E-6

1E-3

1

1000

1000000

1E9

1E12

316 SS

Time t

o Rup

ture (

hr)


Surge Line

ASTECV1 ASTECV2

Surge Line Failure Time : 0.11 hrs

Surge Line Failure Time : 80 hrs


Conclusion

18

In both versions of ASTEC, loss of RCS and SG inventory are comparable.

Core heat up and material relocation is faster in case of ASTECV2, hence a

large extent of anomalies are observed in core degradations parameters like

hydrogen, corium relocated mass and aerosol generation AGAINST V1

predictions

In case of ASTECV1, The surge line failure was predicted before vessel

failure. But in case of ASTECV2, there was no surge line failure prior to

vessel failure.Suggestion to SARNET:

Benchmark exercise among SARNET partners is strongly suggested for VVER-1000 SBO case to eliminate user effect, as the SA analyses are used for SAMG verification and Level-2 calculations.


Thank You

19

Documents

ERMSAR 2012, Cologne March 21 – 23, 2012 ESTIMATION OF THERMAL-HYDRAULIC LOADING FOR VVER-1000 UNDER SEVERE ACCIDENT SCENARIO Barun Chatterjee 1, Deb Mukhopadhyay