22.08.2015   Natural circulation data and methods for advanced water cooled nuclear power plant designs

Results related to a UTSG PWR

A NC study was conducted utilizing a nodalisation for the PWR-1 in Table II, suitable for the Relap5/mod3.2.2, Ref. [14]. ‘Quasi’ steady-state thermalhydraulic NPP conditions are obtained at the end of transient calculations. The aim is to derive mutual relationships between significant NC parameters and to search for realistic boundary conditions allowing the maximum core power in NC. Use is also made of the NCFM derived above. Relevant results are given in Figs 7 and 8 and in Table VI.

image077

FIG. 7. Study of NC in PWR-1: ‘quasi’ steady NC conditions relevant for calculating the maximum removable thermal power in the NPP and in the ITF.

 

image078

FIG. 8. Study of NC in PWR-1: core flowrate versus core power at different pressure and

temperature related boundary conditions.

 

TABLE VI. REMOVABLE POWER BY NATURAL CIRCULATION IN PWR-1

No.

ID.

P

MW/%

G

(Kg/s)/%

SG PRE MPa

RM

KgE5/%

PS PRE MPa

UP

T/Tsat

K

UP Void

G/P

Kg/sMW

RM/V

Kg/m3

1#

KK01

1876/100

9037/100

6.1

1.08/100

15.6

598/618

0.

4.82

647

2Л

KK01

56/3.0

520/5.8

8.1*

1.08/100

13.6

577/608

0.

9.28

647

3

KK01

376/20

930/10.3

6.0*

1.08/100

15.4

615/617

0.

2.47

647

4

KN03

469/25

1016/11.2

6.0*

1.07/99.1

16.2

620/620

0.10

2.17

641

5

KN04

563/30

1140/12.6

6.0*

1.01/94.0

16.2

620/620

0.21

2.02

605

6

KN05

938/50

1370/15.1

6.0*

0.92/85.0

16.2

620/620

0.47

1.46

550

7

KN07

1032/55

1396/15.4

6.0*

0.90/83.3

16.2

620/620

0.48

1.35

539

8

KN08

1126/60

1428/15.8

6.0*

0.89/82.9

16.2

620/620

0.49

1.27

536

9

KN09

1219/65

1450/16.0

6.0*

0.88/82.0

16.2

620/620

0.51

1.19

529

10§

KN10

1313/70

1490/16.4

6.0*

0.87/80.8

16.2

620/620

0.62

1.13

523

11

KL10

1032/55

1396/15.4

3.5*

0.99/91.4

16.2

620/620

0.44

1.35

592

12

KL10

1313/70

1650/18.3

3.5*

0.95/88.2

16.2

620/620

0.49

1.26

571

13§

KL12

1500/80

1492/16.5

3.5*

0.91/84.6

16.2

620/620

0.60

0.99

547

14§

KL11

1688/90

1523/16.8

3.5*

0.87/80.4

16.2

620/620

0.77

0.90

520

15

LL11

1032/55

1365/15.1

3.5**

1.01/93.9

16.2

620/620

0.31

1.32

608

16§

LL11

1688/90

1525/16.9

3.5**

0.93/86.3

16.2

620/620

0.57

0.90

556

17

LL12

1500/80

1380/15.3

3.5**

0.96/88.8

16.2

620/620

0.49

0.92

575

18

LL13

1032/55

1300/14.4

2.5**

1.04/96.3

16.2

620/620

0.20

1.26

623

19

LL13

1500/80

1750/19.4

2.5**

1.00/92.3

16.2

620/620

0.48

1.17

597

20

LL14

1688/90

1460/16.2

2.5**

0.97/89.4

16.2

620/620

0.50

0.87

578

21 §

LL15

1876/100

1587/17.5

2.5**

0.94/86.6

16.2

620/620

0.63

0.85

560

22

HL15

1032/55

1290/14.3

2.5**

1.09/101.

18.5

631/633

0.01

1.25

652

23 §

HL15

1876/100

1630/18.1

2.5**

0.97/89.3

18.5

633/633

0.58

0.87

578

24

HL16

1032/55

1295/14.3

2.5+

1.09/101.

18.5

594/633

0.

1.25

652

25§

HL16

1876/100

1630/18.1

2.5+

0.99/91.4

18.5

633/633

0.50

0.87

590

Nomenclature

ID Calculation identification §

Dryout occurrence

G

Core flowrate

#

Nominal working conditions for the current system

P

Core Power

Л

Reference NC result

PRE

Pressure

*

Feedwater temperature same as in nominal condition

PS

Primary System

**

Feedwater temperature set at 363 K

RM

Mass Inventory in PS

+

Feedwater temperature set at 333 K

T

Fluid Temperature

+

Feedwater flowrate set at 1.3 times the equilibrium value

Tsat

Saturation temperature

UP

Upper Plenum

Void

Void fraction.

All the reported data relate to conditions where core power equals SG removed power. This is also valid when dryout situations occur and testifies of the small excursion of rod surface temperature. The excursion is actually limited to a few tens of Kelvin and is stable as a function of time. The main comments to the achieved results are:

• SPNC can be obtained up to about 20% core power, thus confirming the results related to ITF in Table V.

• TPNC allows removal of up to about 70% core power assuming nominal system conditions, again confirming the results related to ITF.

• Lowering SG pressure and increasing primary system pressure bring to increases in the NC thermal power removal capabilities. More than 90% core power can be removed in NC with SG pressure as low as 2.5 MPa.

• Dryout occurrences are undesirable. However, temperature excursions of rod surfaces are limited in space and do not affect the ‘stable and steady’ NC scenario.

• The NCFM obtained from the analysis of experimental NC scenarios at low core power values has been used as reference for high power NC scenarios. The information in Fig. 7, mainly the values of G/P and RM/V when dryout occur, shows that the NCFM (G/P versus RM/V) can be adopted also for high core power values. Dryout occurs with G/P close to unity (Kg/s/MW) or below this threshold. Lower values of G/P at dryout are experienced at higher core power.