state scientific and technical center on nuclear and radiation safety

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State Scientific and Technical Center on Nuclear and Radiation Safety

THE THERMAL-MECHANICAL BEHAVIOR OF FUEL PINS DURING POWER'S

MANEUVERING REGIME AT STATIONARY CORE LOADING ON 2ND UNIT OF KHNPP

M. Ieremenko, Y.Ovdiyenko, V.Khalimonchuk

17th SYMPOSIUM of AER on VVER Reactor Physics and Reactor Safety, September 24-29, 2007, Yalta, Crimea, Ukraine

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THE THERMAL-MECHANICAL BEHAVIOR OF FUEL PINS DURING POWER'S MANEUVERING REGIME AT STATIONARY CORE LOADING ON 2ND UNIT OF KHNPP


Goal•M. Ieremenko, Y.Ovdiyenko, V.Khalimonchuk ASSESSMENT OF THE THERMAL-MECHANICAL BEHAVIOR OF FUEL PINS DURING POWER'S MANEUVERING REGIME ON 2ND UNIT OF KHNPP. 16th Symposium of AER on VVER Reactor Physics and Reactor Safety, 25-29 September 2006, Bratislava, Slovakia.

•It should be noted that the experiment on maneuvering is carried out during campaign №2, in which there is not a high-burnt fuel.

•As example of core with hihg-burnup fuel all calculations for design cycle #7 was repeated. It is the design variant of the campaign and reactor core containes the high burnup fuel and there is very high probability to reach interaction between the cladding of a fuel rod and uranium pellet.

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Loading schedule of the unit during power maneuvering

The main macro-characteristics of the reactor core (Kq, Kv) during power maneuvering are obtained by the DYN3D code (FZR, Germany). The simulation of these transient regimes was fulfilled for two moments of campaign - 100 fpd, 160 fpd and for two types of regulation. In the first type (#1) is using boron in the moderator and group of CR №10 for maintaining axial offset. For the second regime (#2) the central rod is dropped. The second regime is characterized by lower change of concentration of boric acid and higher change of the fuel rod power. In the moment of campaign 100 fpd was planned to perform 4 cycles of power's maneuvering, in the moment of campaign 160 fpd - 6 cycles of power's maneuvering.

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Development of the schedule of control rod’s movement for the reactor power’s decrease or increase was based on following requirements defined by normative documents:

•minimal deformation of axial power distribution (offset)•for allowable peaking factors and fuel rod's linear power•compliance for “frame” safety parameters (efficiency of emergency protection system without most effective rod, rate of positive reactivity’s insertion and efficiency of ejected control rod) for any transient’s condition•compliance for allowable rate of reactor power’s change•parameter’s keeping accuracy and acceptance of boron acid concentration change’s rate from the point of view of equipment’s and technological system’s functioning

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2100

2300

2500

2700

2900

3100

0 10 20 30 40 50

DYN3D modelling

time, h

React

or

pow

er,

MW

Fig. 1 – Change of reactor power

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0

100

200

300

0 10 20 30 40 50

Central rod, regime #2Central rod, regime #1WG #10, regimes #1 and #2

time, h

CR

pos

ition

, cm

Change of control rod’s position. Moment of campaign 100 FPD

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4.0

4.2

4.4

4.6

0 10 20 30 40 50

regime #2regime #1

time, h

boro

n ac

id c

once

ntra

tion,

g/k

g

Change of boron acid concentration . Moment of campaign 100 FPD

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-0.050

-0.025

0

0.025

0.050

0 10 20 30 40 50

regime #2regime #1

time, h

axia

l off

set

Change of axial offset. Moment of campaign 100 FPD

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1.2

1.3

1.4

1.5

1.6

1.7

0 5 10 15 20 25

Ko, regime #2Kr, regime #2Kv, regime #2Kq, regime #2Ko, regime #1Kr, regime #1Kv, regime #1Kq, regime #1

time,h

Peaki

ng

fact

ors

Change of peaking factors. Moment of campaign 100 FPD

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2.9

3.0

3.1

3.2

3.3

0 10 20 30 40 50

regime #2regime #1

time, h

boro

n ac

id c

once

ntra

tion,

g/k

g

Change of boron acid concentration. Moment of campaign 160 FPD

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-0.050

-0.025

0

0.025

0.050

0 10 20 30 40 50

regime #2regime #1

time, h

axia

l off

set

Change of axial offset. Moment of campaign 160 FPD

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1.2

1.3

1.4

1.5

1.6

1.7

0 5 10 15 20 25

Ko, regime #2Kr, regime #2Kv, regime #2Kq, regime #2Ko, regime #1Kr, regime #1Kv, regime #1Kq, regime #1

time,h

Pea

king

fac

tors

Change of peaking factors. Moment of campaign 160 FPD

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Common model of thermal-mechanical calculation

NESSEL

Service moduleDYN3D DERAB

TRANSURANUS

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Results of calculations a thermal-mechanical behaviour of fuel pins. Campaign №7

For the following thermal-mechanical analysis were selected 4 types of fuel rods:

1. Fuel rod with the maximal burnup level;2. Fuel rod with the maximal power;3. Fuel rod with the maximal change linear and average power concerning a beginning of power’s maneuvering regime;4. Fuel rod with the maximal change linear and average power concerning a previous step of power’s maneuvering regime.

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Most critical fuel pins during different regimes of regulation

Regime100fpd_#1_C7 100fpd_#2_C7 160fpd_#1_C7 160fpd_#2_C7

#FA #FP Value #FA #FP Value #FA #FP Value #FA #FP ValueFuel rod with the maximal burnup level,МW*Days/kgU

57 322 48.7 57 322 48.7 57 322 50.9 57 322 50.9

Fuel rod with the maximal power Ql, W/cm 17 39 238.0 17 39 283.9 17 272 282.9 17 272 283.8Fuel rod with the maximal change of average powerconcerning a beginning of power’s maneuvering regimedQl, W/cm

36 46 1.0 94 292 2.3 2 306 1.3 94 292 2.6

Fuel rod with the maximal change of linear powerconcerning a beginning of power’s maneuvering regimedql, W/cm

24 37 8.4 17 9 5.8 9 282 8.6 9 10 6.1

Fuel rod with the maximal change of average powerconcerning a previous step of power’s maneuveringregime dQl, W/cm

112 10 9.3 82 57 70.2 133 8 9.1 82 57 72.7

Fuel rod with the maximal change of linear powerconcerning a previous step of power’s maneuveringregime dql, W/cm

106 18 39.3 82 57 76.0 31 14 48.7 82 57 77.1

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0

0.2

0.4

0.6

0.8

1.0

0 10000 20000 30000

Clad Outer Surface

Time ( h )

H

eat F

lux

(W/m

m2 )

IDN=217 L= 7

Heat flux on clad outer surface FP № 57, FA № 82, control 160fpd_#2_C7.

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0.3

0.4

0.5

0.6

27000 27200

Clad Outer Surface

Time ( h )

H

eat Flu

x (W

/mm

2 )

IDN=217 L= 7

Heat flux on clad outer surface FP №57, FA № 82, control 160fpd_#2_C7. Control area.

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0

15

30

45

60

75

0 10000 20000 30000

Time ( h )

G

ap W

idth

(M

icro

n)

IDN=221 L= 7

Gap between cladding and fuel pellet. FP № 57, FA № 82, control 160fpd_#2_C7.

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0

0.25

0.50

0.75

1.00

1.25

0 10000 20000 30000

Clad Outer Surface

Time ( h )

H

eat F

lux

(W/m

m2 )

IDN=217 L= 7

Heat flux on clad outer surface FP № 322, FA № 57, control 160fpd_#2_C7.

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0.55

0.60

0.65

26900 27000 27100 27200

Clad Outer Surface

Time ( h )

H

ea

t F

lux

(W/m

m2 )

IDN=217 L= 7

Heat flux on clad outer surface FP № 322, FA № 57, control 160fpd_#2_C7. Control area.

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0

20

40

60

0 10000 20000 30000

Time ( h )

G

ap W

idth

(M

icro

n)

IDN=221 L= 7

Gap between cladding and fuel pellet. FP № 322, FA № 57, control 160fpd_#2_C7.

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-100

-75

-50

-25

0

25

0 10000 20000 30000

Tangential

Time ( h )

Ave

r. S

tres

s in

Cla

d (M

Pa)

IDN=202 L=16

Average tangential stress in cladding. FP № 57, FA № 82, control 160fpd_#2_C7

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-120

-90

-60

-30

0

30

0 10000 20000 30000

Tangential

Time ( h )

Ave

r. S

tres

s in

Cla

d (M

Pa)

IDN=202 L= 7

Average tangential stress in cladding. FP № 322, FA № 57, control 160fpd_#2_C7.

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Conclusions

•In the design variant of the campaign a reactor core containes the high burnup fuel and interaction between the cladding of a fuel rod and uranium pellet was reached.•It is possible to mark a more loaded regime of fuel pins operations during a regime of regulation with additional inserted central rod. On the other hand, this regime is characterized by lower change of boric acid density in moderator, that is favorably reflected in economic indexes of unit operation.•For regime of regulation with additional inserted central rod for core with the high burnup fuel is possible to recommend not to use the high burnup FAs in central place of core.

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reactor powers

reactor safety

vver reactor physics

powers maneuvering regime

reactor core kq

reactor core containes

fuel rod power

cycles of powers maneuvering