Abstract - Podolsk€¦ · given unit will move forward in each year, from February to May, from May to August, etc, ... The figures 4 to 7 show the most important characteristic

15m CYCLE OPTION FOR NPP PAKS OPERATION

Imre NEMES

MVM Paks NPP Ltd.

Paks, PO. BOX. 71. H-7031

Hungary

[email protected]

Abstract

There is an investigation started at Paks NPP to establish a 15-month operation of VVER-440

Units. Paks NPP has 4 units of VVER-440s, operating at uprated power to 500 MWe.

Operation scheme is prepared to make a plan of 15m operation of four units. The plan may

result that in each year would be necessary only 3 outages of 4 operating units.

A series of neutronphysical and hydraulic calculation is treated to find the appropriate

assembly enrichment and pin enrichment arrangement matches to reactor power and cycle

length. The selected enrichment is 4.7%, the transient and equilibrium fuel cycle plan of 15m

cycle of 1485 MWth units is prepared. The necessary safety evaluation in progress, Paks is

planning to introduce new fuel and 15m cycles from 2015.

1. Actual status and motivation

Paks NPP has 4 units of VVER-440s, all of them produce uprated power at about 500 MWe.

Units are operated in 12-month cycle. Actually we use 4.2% enriched fuel ( MSZ

production), containing 3 Gd-dopted fuel rods. The same enrichment is used for fixed fuels

and followers, cycles need 84 fresh assemblies per cycle. Follower are applied for 4 years,

fixed fuels partially 4 and 5 cycles. The maximum burnup of assembly is around 50

MWd/kgU.

In the last years Paks investigated the possibilities of using higher enriched fuel. Several

options has been examined, 12, 15 and 18-moths cycle lengths as well. Some results of these

investigations were published at AER symposium and working group meetings. From the

examined versions the 15-month cycle option seemed to be the most perspective.

2. 15m operation plan of Paks Units

Suppose that refueling outages of 4 Paks units are arranged according to Fig. 1. : the 1st

refueling in February, the 2nd

in May, the 3rd

in August, the 4th

in November. Then, if we can

evaluate cycles having 415-420 fpd. cycle length, the following will happen : outages of a

given unit will move forward in each year, from February to May, from May to August, etc,

and one of the unit will over jump the next year.

In order to examine the period of this kind of cycles, look at Fig. 2. The order of outages

within the year actually at Paks : Unit 1, Unit 4, Unit 2, Unit 3. Having 15m cycle length

the Paks operation will form a 5-year period, 4 of this 5 years we may have only 3 outages

per year.

Fig. 1.

Additionally, we can arrange maintenance such, that long outages are planned for those years,

when only 3 units are stopped, and in the 5th

year we may have only short outages. This

yields that we will have a stationary production-maintenance rate in each year.

Fig. 2.

3. Standpoints of fuel selection

To evaluate 15m cycle Paks wants to use 2nd

generation fuel. Paks as well as other VVER

utilities has wide range of experiences using this fuel version and in parallel with cycle

elongation Paks does not plan significant changes in fuel.

To be able to operate on 1485 MWth, we need a flat pin power and outlet temperature field

within the assembly, and in the whole core as well. During preliminary investigation several

option of pin and Gd pin arrangement has been examined, part of these were also published at

AER meetings. The investigation has been treated using :

HELIOS code for the pin power distribution investigation ( 16 different version)

The selected variants were analyzed using VERONA-TH hydraulics ( 8 different

version)

For the selected versions few group cross sections were generated and the equilibrium

cycles were planned. ( 4 different version)

In the final decision other specific aspects also were taken into account. (Due to state

prescription, Paks have a large reserve of fresh fuel assemblies, which are actually 4.2%

enriched. During and after the transient to 15m cycles, it is necessary to make the plan of

mixed cores, with the application of 4.2% and higher enriched. It was necessary to select

such fuel which is “compatible” to use mixed with the presently used 4.2 enriched fuel. )

4. Fuel enrichment for 15m cycles

In the 2nd

step the selected fuel has 4.7% avg. enrichment. The enrichment distribution is

given on Fig.3.

The figures 4 to 7 show the most important characteristic of this fuel calculated by HELIOS

code supposing infinite lattice of assemblies (white boundary condition). The maximum of k-

infinite is lower, then the k-inf of 3.82% enriched fuel. The maximum pin power is low

enough and even effectively decrease with burnup. The pin power of Gd-pins all time

remains under the average. The subchanel outlet temperature is still acceptable even in

extreme assembly condition. To calculate this, the VERONA TH model was used.

5. The cycles

In order to understand requirement related cycle length, look at real operating plan of Paks on

Fig. 8. There are units to have 420 fpd cycle length in sequence, others only 415 fpd. So the

requirements for the reload features can be summarized as follows :

Cycle plans should make possible to plan cycles with length of 415 fpd and even

lower, as well as 420 fpd and even higher.

Cycle plans should make possible to use reserved 4.2% enriched fuel.

To fulfill these requirements 2 different equilibrium cycle were planned. A “maximal” cycle

with 425 fpd (423+2 ) length, and “minimal” one, having 413+2 fpd. length. Both cycles

have use a mixture of 4.2% enriched ( actually used ) and 4.7% enriched assemblies, 102

fresh assemblies per cycle. The most important features of these as follows :

“Maximum cycle” :

“Minimum cycle” :

The real cycle will be evaluated between these two variants : different number of applied 4.2

and 4.7 % enriched fuel makes possible to vary the cycle length.

Figures 9 and 10 shows the loadings of “minimal” and “maximal” cycle. Figures 11 to 16

show the most important features a “maximal” cycle. It can be seen, that all investigated

limit can be satisfied. The “minimal” cycle characteristics as well as transient cycles are very

similar.

6. Transient to 15m and after

At Paks NPP a project is working on transient evaluation to 15m cycles. Safety analysis of

new cycles in progress in Russian and Hungarian institutes. According to plan the transient

cycles will start in 2015, from that date the units will operate in 15m cycles. (see Fig.8)

Between 2015 and 2020 Paks is planning to use the mixture of 4.2 and 4.7% enriched, 2nd

generation fuel. The cycles need all together 102 fresh fuel assemblies / 15m cycle. This

plan can be safely evaluated, nevertheless the fuel application is clearly not optimal. In

parallel with the evaluation of 15m cycles a next step of fuel modernization can be prepared.

Using more developed geometry differing from 2nd

generation fuel, a more optimal, 90

assembly/ cycle fuel application can be achieved.

Fig. 3. Enrichment distribution of calculated

Figure 4.

K-inf related to previous fuels

1

1.05

1.1

1.15

1.2

1.25

1.3

0 5000 10000 15000 20000

Burnup (MWd/TU)

k-i

nf

3.8

4.2

4.7

Figure 5.

Fig. 6.

Kk-max

1

1.02

1.04

1.06

1.08

1.1

0 5000 10000 15000 20000 25000 30000 35000 40000

Burnup (MWd/tU)

Kk

Kk of Gd-pin

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

0 5000 10000 15000 20000 25000 30000 35000 40000

Burnup (MWd/tU)

Kk

Fig 7.

Fig. 8.

15m cycle operation plan of Paks

316,6

316,8

317

317,2

317,4

317,6

317,8

318

0 5 10 15 20

Tsub

-max(C)

Burnup (Gwnap/tU)

Fig 9.

Loading of “minimal” cycle

1014,1015 : 4.2 % , 1035, 1036 : 4.7%

1 3 1015

2 3 1035

3 2 1014

4 2 1015

5 3 1014

6 2 1035

7 3 1015

8 2 1035

9 1 1035

10 3 1015

11 1 1035

12 3 1035

13 3 1035

14 1 1035

15 3 1035

16 2 1035

17 2 1035

18 1 1035

19 4 1035

20 3 1035

21 1 1035

22 3 1035

23 3 1035

24 2 1035

25 2 1035

26 1 1035

27 4 1035

28 3 1035

29 3 1035

30 2 1015

31 2 1035

32 3 1035

33 1 1015

34 1 1014

35 1 1035

36 3 1014

37 2 1014

38 3 1014

39 1 1035

40 1 1014

41 4 1035

42 3 1014

43 2 1035

44 3 1035

45 1 1035

46 2 1014

47 4 1035

48 2 1014

49 2 1035

50 1 1015

51 1 1014

52 4 1035

53 2 1035

54 1 1035

55 1 1014

56 4 1035

57 1 1035

58 2 1035

59 4 1035

Time= 0.00 eff.day

Power= 1485.000 MW

Tin.= 267.000°C

Mod.Flow= 30000.0 t/h

Cb= 7.294 g/kg

Reactivity= 0.0026 %

h6 pos.= 212.000 cm

2 -Ass.pos. 3 - kor [year] 1015 - típus

Results of C-PORCA Calculations

Unit=4 Cycle=39

code info: /4/39/102min/c/0/-/-

Paraméter Maximum Limit(Abs-MF) Mérn. fak torSzektor Pozíció Pálca számSzint

Kazetta telj. [MW] 5.68 6.22 0.36 1 11 --- ---

Kaz.k iégés [MWnap/kgU] 48.75 51.10 2.90 1 59 --- ---

Pálcateljesítmény [kW] 48.79 51.40 5.60 1 11 5 ---

Pálca k iégés [MWnap/kgU] 51.94 54.75 5.25 1 19 112 ---

Szubcsatorna hőmérsék let [°C] 317.44 319.64 6.90 1 11 94 ---

Lineáris hőteljesítmény [W/cm] 236.72 286.60 38.40 1 45 3 22

Lokális k iégés [MWnap/kgU] 58.78 62.90 7.10 1 19 121 18

Fig. 10.

Loading of “maximal” cycle

1014,1015 : 4.2 % , 1035, 1036 : 4.7%

1 3 1036

2 3 1035

3 2 1014

4 2 1036

5 3 1035

6 2 1035

7 3 1036

8 2 1035

9 1 1035

10 3 1036

11 1 1035

12 3 1014

13 3 1035

14 1 1035

15 3 1035

16 2 1035

17 2 1035

18 1 1035

19 4 1035

20 3 1014

21 1 1035

22 3 1035

23 3 1035

24 2 1035

25 2 1035

26 1 1035

27 4 1035

28 3 1035

29 3 1035

30 2 1036

31 2 1035

32 3 1035

33 1 1036

34 1 1014

35 1 1035

36 3 1035

37 2 1035

38 3 1035

39 1 1035

40 1 1035

41 4 1035

42 3 1035

43 2 1035

44 3 1035

45 1 1035

46 2 1014

47 4 1035

48 2 1035

49 2 1035

50 1 1036

51 1 1035

52 4 1035

53 2 1035

54 1 1035

55 1 1014

56 4 1035

57 1 1035

58 2 1035

59 4 1035

Time= 0.00 eff.day

Power= 1485.000 MW

Tin.= 267.000°C


Cb= 7.269 g/kg


h6 pos.= 212.000 cm

2 -Ass.pos. 3 - kor [year] 1036 - típus


Unit=4 Cycle=36

code info: /4/36/102max/c/0/-/-


Kazetta telj. [MW] 5.80 6.22 0.36 1 11 --- ---







Fig. 11.

Max. subchanel temperatures and max. pin power at BOC “maximal” cycle

1298.030.96

2308.238.58

3314.644.92

4308.943.50

5309.139.39

6312.743.29

7301.434.59

8314.144.99

9314.245.61

10291.724.87

11318.249.80

12309.639.79

13307.437.57

14317.147.77

15309.239.62

16315.346.44

17312.543.20

18308.439.77

19283.615.11

20307.637.57

21316.647.84

22307.537.62

23307.537.36

24314.645.56

25313.544.22

26312.944.32

27290.121.04

28306.836.83

29306.736.69

30309.544.04

31315.646.78

32308.438.46

33310.345.25

34306.136.80

35316.947.52

36309.139.47

37315.246.20

38309.239.28

39314.946.15

40308.539.96

41284.916.55

42307.237.29

43313.043.62

44307.337.17

45314.745.97

46305.035.41

47286.918.23

48314.044.95

49312.843.47

50310.044.93

51308.740.08

52286.918.30

53312.543.19

54313.244.54

55307.137.67

56285.116.79

57309.040.41

58298.129.20

59284.215.70

Time= 0.00 eff.day

Power= 1485.000 MW

Tin.= 267.000°C


Cb= 7.269 g/kg


h6 pos.= 212.000 cm

2 -Ass.pos.298.0 - tsk iNOM_km [°C] 31.0 - ppowNOM_km [kW]


Unit=4 Cycle=36

code info: /4/36/102max/c/0/-/-


Kazetta telj. [MW] 5.80 6.22 0.36 1 11 --- ---







Fig. 12. Boric acid letdown curve. Full power, “maximal” cycle

Fig. 13. Max. subchanel temperature and the limit. Full power, “maximal” cycle

Cycle Data Calculated by C-PORCA Unit=4 Cycle=36

(«)/4/36/102max/c cb_crit

teff [FPD]

420400380360340320300280260240220200180160140120100806040200

[g/k

g]

7

6

5

4

3

2

1

0


(«)/4/36/102max/c Tsub_max («)/4/36/102max/c Tsub_lim

teff [FPD]

420400380360340320300280260240220200180160140120100806040200

[°C

]

322

321

320

319

318

317

316

315

314

313

Fig. 14. Max. pin power and the limit. Full power, “maximal” cycle

Fig. 15. . Max. linear heat rate and the limit. Full power, “maximal” cycle


(«)/4/36/102max/c Pin_pow_max («)/4/36/102max/c Pin_pow_lim

teff [FPD]

420400380360340320300280260240220200180160140120100806040200

[kW

]

51

50

49

48

47


(«)/4/36/102max/c Lhr_max («)/4/36/102max/c Lhr_lim

teff [FPD]

420400380360340320300280260240220200180160140120100806040200

[W/c

m]

280

270

260

250

240

230

220

210

200

190

180

170

160

Fig. 16. Maximal assembly and pin burnup. EOC, “maximal” cycle

147.9850.66

248.8651.91

329.3233.80

435.4138.57

546.2350.56

634.9337.45

748.8452.06

831.2135.52

917.1119.58

1044.2749.45

1118.8320.23

1240.3847.34

1348.2551.66

1418.3819.55

1545.9050.44

1631.6336.00

1735.0637.76

1814.0917.92

1951.7957.96

2043.7548.49

2118.2819.71

2247.6051.37

2349.8452.59

2433.9236.84

2534.1537.34

2616.6619.55

2750.2957.61

2848.9351.42

2949.0251.98

3035.5937.86

3131.6935.65

3247.0851.15

3318.9220.89

3412.2516.66

3518.3019.50

3646.3650.84

3731.7636.16

3843.3248.22

3918.7920.37

4014.5718.72

4151.3758.62

4249.2152.27

4334.7736.75

4449.1652.51

4518.7820.35

4625.4932.48

4752.0559.14

4833.3136.84

4935.5837.91

5019.0320.85

5114.6818.79

5251.7559.06

5334.7837.07

5417.1119.71

5512.7017.02

5652.6659.00

5714.5318.18

5827.5632.50

5953.1958.66

Time= 425.00 eff.day

Power= 1485.000 MW

Tin.= 267.000°C


Cb= -0.002 g/kg


h6 pos.= 250.000 cm

2 -Ass.pos. 48.0 - bukaz [MWd/kgU] 50.7 - bupal_km [MWd/kgU]


Unit=4 Cycle=36

code info: /4/36/102max/c/eoc/-/-


Kazetta telj. [MW] 5.51 6.22 0.36 1 39 --- ---







Documents

Abstract - Podolsk€¦ · given unit will move forward in each year, from February to May, from May to August, etc, ... The figures 4 to 7 show the most important characteristic