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Safety studies for MYRRHA

B. Arien, S. Heusdains, H. Aït Abderrahimon behalf of the MYRRHA Team and Support

IP-Eurotrans Workshop DM1-WP1.5 Brussels, March 17, 2006

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Contents

• 3 topics Enhancement of free convection LBE freezing in heat exchangers TH modelling of the spallation loop with

RELAP

• Future work

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Enhancement of free convection

• Unprotected total LOF and LOH accidents are beyond MYRRHA Draft_2 design

• 2 possible ways to improve natural circulation: by increasing the H between core and HXs by reducing the pressure losses

• First investigations with a simplified model loop model simulating the pool type system SITHER code provided with a free convection module

(SITHER-FC) results are indicative

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Reminder (PDS-XADS) : TH analysis results for

unprotected accidents (I)

Transient Fuel Clad LBE Water

LOF Partial (1 EHX check valve failed)

OK OK OK OK

LOF Partial (1 pump trip):

OK OK OK OK LOF Total (4 pumps trip):

OK T > 700°C after 7 s

OK OK TOP (410 pcm) OK OK OK OK LOH Partial (1 SCS failed):

OK OK OK OK LOH Total (2 SCS failed):

OK T > 700°C after 9 min

OK Boiling after 20 min

Partial LOF + Partial LOH

OK OK OK OK Total LOF + Total LOH

Melting after 20 min

T > 700°C after 5 s

OK Boiling after 1 min

Overcooling OK OK Freezing after 14 min in PHX

5 min in EHX

OK

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Reminder (PDS-XADS): TH analysis results for unprotected accidents

(II)

Transient Fuel Clad LBE Water

SA blockage (2.5%) OK Failure OK Spurious beam start-up OK OK OK

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Enhancement of free convection: strategy of computation

Start from SITHER-FC as originally developed for preliminary studies in the MYRRHA project free parameters

Calibrate SITHER-FC (free parameters) from Draft_2 design and results obtained with RELAP

2 possible options for the HXs in emergency: Emergency HXs (draft_2 design): EHX Primary HXs: PHX

Effect of H increase (H: difference of elevation between core and HXs)

Effect of pressure loss reduction over the core Note: spallation loop behaviour in transient conditions not

taken into account in the present study (very conservative)

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G: mass flow rate C: inertial coefficient pF: friction pressure losses (=f(G)) pP: pump pressure head 0 in fc mode pB: “buoyancy” pressure

BPF pΔpΔpΔtGC

HΔTΔgρβpΔ B

Momentum equation in the loop model:

• mass conservation• momentum conservation• energy conservation (core , HXs, pipes)

Enhancement of free convection: simplified loop model

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Enhancement of free convection: SITHER calibration – unprotected LOF

case

200

400

600

800

1000

1200

1400

0 300 600 900 1200 1500t(s)

T cl (

°C)

RELAP

SITHER

1600

1700

1800

1900

2000

2100

2200

2300

2400

0 300 600 900 1200 1500t(s)

T f (°

C)

RELAP

SITHER

max. fuel temperature max. clad temperature

core mass flow rate temperatures in EHX

0

500

1000

1500

2000

2500

0 300 600 900 1200 1500t (s)

G (k

g/s)

RELAP

SITHER

100

300

500

700

900

1100

0 300 600 900 1200 1500t (s)

T EH

X (°C

) EHX outlet RELAPEHX inlet RELAPEHX outlet SITHEREHX inlet SITHER

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Enhancement of free convection: effect of H increase

200

300

400

500

600

0 300 600 900 1200 1500t (s)

T cl (°

C)

PHX: high core position

PHX: low core positionEHX: high core position

EHX: low core position

200

400

600

800

1000

1200

1400

1600

1800

2000

0 300 600 900 1200 1500t (s)

T f (°C

)

PHX: high core position

PHX: low core positionEHX: high core positionEHX: low core position

1600

1800

2000

2200

2400

0 300 600 900 1200 1500t (s)

T f (°C

)

PHX: high core positionPHX: low core positionEHX: high core positionEHX: low core position

max. fuel temperature - PLOF max. clad temperature - PLOF

max. fuel temperature - ULOF max. clad temperature - ULOF

200

400

600

800

1000

1200

1400

1600

0 300 600 900 1200 1500t (s)

T cl (°

C)

PHX: high core positionPHX: low core positionEHX: high core positionEHX: low core position

PHX EHX

high core 0.81 1.67

low core 3.0 4.0

H (m)

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Enhancement of free convection: effect of pF

reduction

1500

1800

2100

2400

0 300 600 900 1200 1500t (s)

T f (°

C)

100% Dpcore

50% Dpcore

25% Dpcore

200

500

800

1100

1400

0 300 600 900 1200 1500t (s)

T cl (

°C)

100% Dpcore

50% Dpcore

25% Dpcore

1500

1800

2100

2400

0 300 600 900 1200 1500t (s)

T f (°

C)

100% Dpcore

50% Dpcore

25% Dpcore

max. fuel temperature - ULOF max. clad temperature - ULOF

200

400

600

800

1000

1200

1400

0 300 600 900 1200 1500t (s)

T cl (

°C)

100% Dpcore

50% Dpcore

25% Dpcore

EHX

PHX

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Enhancement of free convection: conclusions

• Effect of H increase: Even with large H emergency EHXs are not able to

keep core integrity in case of unprotected LOF accident (EHXs are not designed to evacuate nominal power)

Use of PHXs in emergency situations allows to mitigate strongly the unprotected LOF effects

• Effect of pcore reduction:relatively small benefit

• Behaviour of spallation loop should be taken into account

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LBE freezing in heat exchangers

• LBE freezing in HXs can occur with overcooling in secondary circuit

• In extreme conditions plugging could occur• If total plugging possibility of LOF & LOH • Difficulty to recover the normal operation in

case of plugging

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LBE freezing in heat exchangers: HX types

Option 1: pressurized water Option 2: boiling water

lead-bismuth

water

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LBE freezing in heat exchangers: model (I)

liquid LBE

solid LBE

water tube

0drdTkrdr

dr1

ff TThφ wewe TThφ

• Code WALEBI (LBE/water HX) updated for freezing

• Purely thermal model• Mechanical effects are

not taken into account (conservative)

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LBE freezing in heat exchangers: model (II)

0

1

2

3

4

5

6

7

8

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1r

f(r)

q

q1

q2

0

1

2

3

4

5

6

7

8

9

10

1 1.1 1.2 1.3 1.4r

f(r)

q

q2

q1

Option 1 Option 2

θ)ρ(f

f

wfTTTTθ

f(r): function depending on geometry and thermophysical properties of the materials

T liquid LBE temperature

wT water temperature

fT freezing temperature

r: frozen layer position (normalized to the inner/outer tube radius)

r solution of

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LBE freezing in heat exchangers: results (I)

liquid LBE

frozen LBE

LBE

water

water

water

LBE

Option 1

Option 2

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LBE freezing in heat exchangers: results (II)

0.0

0.2

0.4

0.6

0.8

1.0

0 20 40 60 80 100 120 140 160Tw (°C)

s

Frozen layer thickness

Option 1 Option 2

s: frozen layer thickness normalized to the inner/outer clad radius

Tw: water inlet temperature

Total freezing

0.0

0.1

0.2

0.3

0.4

0 20 40 60 80 100 120 140 160Tw (°C)

s

Total freezing

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LBE freezing in heat exchangers: conclusions

• Risk of tube plugging seems negligible• Freezing is less important with option 2

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TH modelling of the spallation loop: general sketch

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TH modelling of the spallation loop: RELAP model

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TH modelling of the spallation loop : results

100.81

0

20

40

60

80

100

120

140

0 1000 2000 3000 4000 5000 6000t(s)

Mas

s flo

w ra

te (k

g/s)

0

0.5

1

1.5

2

2.5

0 1000 2000 3000 4000 5000 6000t (s)

L

(m)

Mass flow rate Difference of free surface levels

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Future work

• Input from and interaction with designers (WP1.1, WP1.2, WP1.4) are imperative

• TH modelling of XT-ADS with RELAP• CFD simulation of XT-ADS primary system with

FINE\HEXA (SCKCEN) and CFX (NRG): forced convection and free convection

• Optimization of the emergency cooling system• …