gas plenum in xt-ads fuel rod

IP-Eurotrans DM1-WP1.5 meeting, Lyon, October 10-11, 2006 1

Gas Plenum in XT-ADS Fuel Rod

V. Sobolev, B. Arien

SCK·CEN, Boeretang 200, Mol, Belgium


1. Introduction

• During the DM1 Meeting in MOL it was required to adapt the gas plenum of XT-ADS fuel rod to assure the cladding withstand during 30 minutes at ULOF conditions at 100 % FG release.

• The recommended values for acceptable cladding temperatures and pressures were presented at the same meeting by D. Struwe and W. Pfrang (see next slide).


1. Introduction

Best estimate values from the CIEMAT creep experiment with T91 steel (D. Struwe, W. Pfrang, Mol, 20-21 June

2006)

Gas plenum pressure 5 MPa 10 MPa

Clad failure time Mid-wall clad temperature

10 000 h 955 K 920 K

1 000 h 985 K 955 K

10 h 1065 K 1030 K

1 h 1115 K 1070 K

30 min 1125 K 1080 K

2 min 1180 K 1135 K


2. XT-ADS fuel pin schematics

(pre-design of June 2006)

Top-cap

600100 100300 (?) 2020

1200 (?)

6.55

Bottom-cap

Lower reflector-insulatorOD=5.40 ID=1.50

Fuel pellet

OD=5.40 ID=1.60

Gas plenum

60

Spring

Upper reflector-insulatorOD=5.40 ID=1.50

Cladding OD=6.55 ID=5.60

Support Spring chamber


2. XT-ADS fuel pin: Equivalent gas chart

Gas plenum Lower reflector

V5 V4 V1 V2 V3

Fuel column Spring chamber Upper reflector

0

50 0

0 010 0

( ) ( )He void ii

p pN V T V T

R T R T

Filling

gas:

Hot stand-by:0 0

00

( )

( ) ( )hot He hot void

hoti hot void hot

i

R T N T V Tp p

V T T V T


3. Pressure within fuel pin

0.02 at/fisKr 0.01 at/fisHe

Operation at nominal power:

In LMFBR:

0 0( ) 0

50 0( )

01 ( )

( )1

( ) irr

void HMnom Bu Xe Xe Kr Kr He He

voidi i nom

i i nom

V T RT Bu mp p

p V TV TT

T

0.23 at/fisXe

, ,... [0;1] i T Bu - released fraction of the i-th gas


4. Operation conditions

• Hottest fuel column: <ql> = 201 W/cm, Kaxial hot = 1.257

• Filling gas pressure: 0.2 MPa (He at STP)

• Coolant:

Tinlet = 603.15 K (330 °C)

Nominal operation:Tcore = 90 K x Kcore rad =

= 90 K x 1.375 = 123.75 K (°C)

ULOF: T=472.25 K (°C) determined by natural

convection (Hcore-HX = 2 m; 60 % core resistance).


5. Temperature field in the hottest pin

600

800

1000

1200

1400

1600

0.0 0.1 0.2 0.3 0.4 0.5 0.6

Axial co-ordinate (m)

Tem

pera

ture

(K

)

pellet centre

pellet surface

pellet mean

clad inner

clad outer

coolant

Nominal operation at BOL (FEMAXI-5.1- mod.SCK; EFR TC )


5. Temperature field in the hottest pin

ULOF at BOL (FEMAXI-5.1- mod.SCK)

600

800

1000

1200

1400

1600

1800

0.0 0.1 0.2 0.3 0.4 0.5 0.6


Tem

pera

ture

(K

)

pellet centre

pellet surface

pellet mean

clad inner

clad outer

coolant


6. Free volumes and pressure within XT-ADS pin

Pressure and free volumes (cm³) within the main segments of the hottest fuel rod

Segment Gas plenum* Lowerreflector

Fuelcolumn

Upperreflector

Springchamber** Total Pressure

Index 1 2 3 4 5 void (MPa)

Cold conditions: Ti = 291.15 K 6.237 0.350 2.243 0.350 1.318 10.50 0.20

Hot stand-by: Ti = 603.15 K 6.286 0.353 2.265 0.353 1.328 10.59 0.41

Nominal regime (BOL) 6.286 0.353 2.116 0.349 1.332 10.44 0.47

ULOF (BOL)100%FGR (EOL)

6.286 0.353 2.064 0.361 1.347 10.410.517.5

The max. clad temperature at ULOF is 1117 K (844 °C) without clad corrosion, and the allowed pressure (Table on Slide 3, D. Struwe) is lower than 7.5 MPa.

Clad corrosion will create more severe situation (see next slide).


7. Temperatures of clad with corrosion layer at

ULOF

600

700

800

900

1000

1100

1200

0.0 0.1 0.2 0.3 0.4 0.5 0.6


Tem

pera

ture

(K

)

clad inner

clad mean

oxide-metal

clad outer

coolant

orr ~85 µm


8. Updated XT-ADS rod design (proposal)

Top-cap


60060 60580 2020

1400

6.55

Bottom-cap


Fuel pellet OD=5.40 ID=1.60

Gas plenum

60

Spring



Top-cap


60060 60580 2020

1400

6.55

Bottom-cap


Fuel pellet OD=5.40 ID=1.60

Gas plenum

60

Spring




8. Updated XT-ADS rod design (proposal)

SegmentGas

plenumLower

reflectorFuel

columnUpper

reflectorSpring

chamberTotal Pressure

Index 1 2 3 4 5 void (MPa)

Length (mm) 580 60 600 100 60 - -

Nominal regime: BOL EOL*

12.1512.15

0.210.21

2.031.63

0.210.21

1.331.33

15.9315.54

0.4523.94

ULOF at EOL with 100 % FGR

12.15 0.21 1.70 0.22 1.35 15.63 4.77

It has been postulated that the maximum thickness of the corrosion layer is 10 % of the initial clad thickness, i.e. 47.5 microns


ConclusionsConclusions

In order to assure the 30-minute cladding resistance of the hottest XT-ADS fuel rod under ULOF conditions, the gas plenum should be increased.

Clad corrosion can play a critical role. Taking into account a large uncertainly in the cladding corrosion, it is proposed to postulate at this stage of design that corrosion is limited to 10 % of the clad thickness.

The updated pin design with a larger gas plenum (580 mm) is proposed as a possible solution.


Transient analysisTransient analysis

Transient (protected or unprotected)

Comment Code

LOF First estimation SITHER - RELAP

LOH Needs HX and SCS design RELAP

LOF&LOH idem RELAP

TOPNeeds reactivity feedback coefficients

SITHER

overcooling Still to be done RELAP

SA blockage Still to be done SITHER


Unprotected LOFUnprotected LOF

Unprotected LOF - maximum fuel temperature

1200

1400

1600

1800

2000

2200

0 300 600 900 1200t (s)

T f (°

C)

XT-ADS

MYRRHA

Unprotected LOF - maximum clad temperature

200

400

600

800

1000

1200

1400

0 300 600 900 1200t (s)

T cl (

°C)

XT-ADS

MYRRHA

• core inlet T: 330°C

• H core-HX: 2m

• pcore: 0.1 MPa = 60% ptot

Note: ULOF becomes very unlikely is spallation loop pump and PHXs are

supplied by the same electrical circuit

gas plenum in xt-ads fuel rod

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