LEADER Project

Analysis of Representative DBC Events of the ETDR with RELAP5 and CATHARE

Giacomino Bandini - ENEA/BolognaGenevieve Geffraye – CEA/Grenoble

LEADER 4th WP5 MeetingKarlsruhe, 22 November 2012

2

Outline

Analyzed DBC Transients at EOC ALFRED Modeling Transient Results Conclusions

3

Analyzed Transients

TRANSIENT Initiating Event (t = 0 s) Reactor scram and threshold

Primary pump trip

MHX FW trip

MSIV closure

DHR startup

TD-1: Spurious reactor trip Reactor scram 0 s, Spurious trip No No No No

TD-3: Loss of AC power Station blackout

0 s, CR magnet de-energization

0 s 0 s 0 s DHR-1 at 1 s (4 IC loops)

TD-7: Loss of all primary pumps All primary pump coastdown

3 s, ΔT hot FA = 120% nominal

0 s 3 s 3 s DHR-1 at 4 s (3 IC loops)

TO-1: Reduction of FW temperature

FW temperature from 335 °C down to 300 °C in 1 s

2 s, Low FW temperature

No 2 s 2 s DHR-1 at 3 s (4 IC loops)

TO-4: Increase of FW flowrate

20% increase in FW flowrate in 25 s

No, No scram threshold reached

No No No No

Main events and reactor scram threshold

4

RELAP5 Modeling

Feedwater

Steam

521- 8

531- 8

551- 8 561-8

151-

8

Feedwater

Steam

521- 8

531- 8

551- 8 561-8

151-

8

841 - 4

851 - 8441 -8

801 - 4

811-4831 - 4

815

401 - 8

841 - 4

-

801 - 4

811-4831 - 4

815

841 - 4

-

801 - 4

811-4831 - 4

815

611 - 8

841 - 4

-

801 - 4

811-4831 - 4

815

611 -

711 -

731-

741- 4

751 - 8

761- 4

621- 4

641 - 4

771

781 - 8

601- 4

661 - 4

611 -

711 - 8

731- 8

741- 4

751 -

761- 4

621- 4

641 - 4

771 -8

781 -

601- 4

661 - 4

611 -

711 -

731-

741- 4

751 -

761- 4

621- 4

641 - 4

771 -

781 -

711 -

731-

741- 4

751 -

761- 4

621- 4

641 - 4

771 -

781

601- 4

661 - 4

841 - 8

-

801 - 4

811-4831 - 4

815

841 -

-

801 - 8

811-8831 - 8

815

611 -

841 -

-

801 -

811-831 -

411 -8

611 -

711 -

731-

741- 4

751 -

761- 4

621- 4

641 - 4

771

781

711 -

731-

741- 4

751 -

761- 4

621- 4

641 - 4

771 -

781 -

601- 8

661 - 8

611 -

711 -

731-

741- 8

751 -

761- 8

621- 8

641 - 8

841 - 4

851 - 8441 -8

801 - 4

811-4831 - 4

815

401 - 8

841 - 4

-

801 - 4

811-4831 - 4

815

841 - 4

-

801 - 4

811-4831 - 4

815

611 - 8

841 - 4

-

801 - 4

811-4831 - 4

815

611 -

711 -

731-

741- 4

751 - 8

761- 4

621- 4

641 - 4

771

781 - 8

601- 4

661 - 4

611 -

711 - 8

731- 8

741- 4

751 -

761- 4

621- 4

641 - 4

771 -8

781 -

601- 4

661 - 4

611 -

711 -

731-

741- 4

751 -

761- 4

621- 4

641 - 4

771 -

781 -

711 -

731-

741- 4

751 -

761- 4

621- 4

641 - 4

771 -

781

601- 4

661 - 4

841 - 8

-

801 - 4

811-4831 - 4

815

841 -

-

801 - 8

811-8831 - 8

815

611 -

841 -

-

801 -

811-831 -

411 -8

611 -

711 -

731-

741- 4

751 -

761- 4

621- 4

641 - 4

771

781

711 -

731-

741- 4

751 -

761- 4

621- 4

641 - 4

771 -

781 -

601- 8

661 - 8

611 -

711 -

731-

741- 8

751 -

761- 8

621- 8

641 - 8

ALFRED Nodalization scheme with RELAP5

8 MHXs

8 Secondary loops Primary circuit

8 IC loops

Steam line

Feedwater line

100

101102109

110

115

060061-8 070

050

020

200 151-8

121-8

131-8

141-8

220

230

210

100

101102109

110

115

060061-8 070

050

020

200 151-8

121-8

131-8

141-8

220

230

210

100

101102109

110

180

060061-8 070

050

020

200 151-8

121-8

131-8

141-8

220

230

210

Feedwater

Steam

521- 8

531- 8

551- 8 561-8

151-

8

Feedwater

Steam

521- 8

531- 8

551- 8 561-8

151-

8

841 - 4

851 - 8441 -8

801 - 4

811-4831 - 4

815

401 - 8

841 - 4

-

801 - 4

811-4831 - 4

815

841 - 4

-

801 - 4

811-4831 - 4

815

611 - 8

841 - 4

-

801 - 4

811-4831 - 4

815

611 -

711 -

731-

741- 4

751 - 8

761- 4

621- 4

641 - 4

771

781 - 8

601- 4

661 - 4

611 -

711 - 8

731- 8

741- 4

751 -

761- 4

621- 4

641 - 4

771 -8

781 -

601- 4

661 - 4

611 -

711 -

731-

741- 4

751 -

761- 4

621- 4

641 - 4

771 -

781 -

711 -

731-

741- 4

751 -

761- 4

621- 4

641 - 4

771 -

781

601- 4

661 - 4

841 - 8

-

801 - 4

811-4831 - 4

815

841 -

-

801 - 8

811-8831 - 8

815

611 -

841 -

-

801 -

811-831 -

411 -8

611 -

711 -

731-

741- 4

751 -

761- 4

621- 4

641 - 4

771

781

711 -

731-

741- 4

751 -

761- 4

621- 4

641 - 4

771 -

781 -

5

CATHARE Modeling

ALFRED Nodalization scheme with CATHARE

Primary circuit

2 Secondary loops (weight 4)

2 IC loops (weight 4)

6

TD-1: Spurious reactor trip (1/3)(RELAP5 – CATHARE Comparison)

Total reactivity and feedbacks

ASSUMPTIONS: Reactor scram at t = 0 s Reactivity insertion of at least 8000 pcm in 1 s Secondary circuits are available constant feedwater flowrate

RELAP5 CATHARE

7

TD-1: Spurious reactor trip (2/3)(RELAP5 – CATHARE Comparison)

Core and MHX powers

RELAP5 CATHARE

Core decay power level in CATHARE is much higher than the one in RELAP5 in the initial phase of the transient

Power removal by secondary circuits reduces with reducing primary temperatures

8

TD-1: Spurious reactor trip (2/2)(RELAP5 – CATHARE Comparison)

Core temperatures (inlet, max outlet and max clad)

RELAP5 CATHARE

Initial temperature gradient on the fuel rod clad is about -10 °C/s No risk for lead freezing since the feedwater temperature (335 °C) is above the

solidification point of lead (327 °C)

9

TD-3: Loss of AC power (1/4)(RELAP5 – CATHARE Comparison)

Active core flowrate

ASSUMPTIONS: At t = 0 s Reactor scram, primary pump coastdown, feedwater and turbine trip At t = 1 s DHR-1 system activation (4 IC loops)

RELAP5 CATHARE

10

TD-3: Loss of AC power (2/4)(RELAP5 – CATHARE Comparison)

Core temperatures Core temperatures

Active core flowrate Active core flowrate

11

TD-3: Loss of AC power (3/4)(RELAP5 – CATHARE Comparison)

Core decay, MHX and IC powers Core decay, MHX and IC powers

Primary lead temperatures Primary lead temperatures

12

TD-3: Loss of AC power (4/4)(RELAP5 – CATHARE Comparison)

MAIN RESULTS: No initial core flowrate undershoot No significant clad temperature peak in the

initial phase of the transient After the initial transient the natural circulation in the primary circuit stabilizes

around 1-2% of nominal value Initial primary temperature decrease is over predicted by RELAP5 with respect to

CATHARE due to differences in core decay power and steam release through safety relief valves

Primary temperature reduction in the long term is faster in RELAP5 calculation due to lack of mixing in the cold pool cold lead at the MHX outlet flows towards core inlet without mixing in the cold pool above MHX outlet (different behavior in CATHARE with similar modeling)

Risk of freezing at MHX outlet is predicted by RELAP5 after about 2 hours, much earlier than with CATHARE

Similar DHR power removal (about 7 MW with 4 IC loops) is obtained by nearly halving the actual heat transfer surface of IC in CATHARE (much larger htc for steam condensation on the inner tube side)

13

TD-7: Loss of primary pumps (1/3)(RELAP5 – CATHARE Comparison)

Total reactivity and feedbacks

RELAP5 CATHARE

ASSUMPTIONS: At t = 0 s All Primary pump coastdown Reactor scram at t = 3 s on second scram

threshold (Hot FA ΔT > 1.2 nominal value) At t = 4 s DHR-1 system activation (3 IC loops)

14

TD-7: Loss of primary pumps (2/3)(RELAP5 – CATHARE Comparison)

Core temperatures Core temperatures

Active core flowrate Active core flowrate

15

TD-7: Loss of primary pumps (3/3)(RELAP5 – CATHARE Comparison)

Core decay, MHX and IC powers Core decay, MHX and IC powers

Primary lead temperatures Primary lead temperatures

16

TO-1: FW temp. reduction (1/3) (RELAP5 – CATHARE Comparison)

Primary lead temperature

ASSUMPTIONS: Loss of one preheater (FW temperature from 335 °C down to 300 °C in 1 s) +

primary pump coastdown reactor scram at t = 2 s on low FW temperature 4 IC loops in service for decay heat removal

RELAP5 CATHARE

17

TO-1: FW temp. reduction (2/3) (RELAP5 – CATHARE Comparison)

Primary lead temperatures Primary lead temperatures

Core decay, MHX and IC powers Core decay, MHX and IC powers

18

TO-1: FW temp. reduction (3/3) (RELAP5 – CATHARE Comparison)

MAIN RESULTS: No risk of lead freezing in the initial phase of the transient due to prompt reactor

scram Primary temperature reduction in the long term is faster in RELAP5 calculation due

to lack of mixing in the cold pool cold lead at the MHX outlet flows towards core inlet without mixing in the cold pool above MHX outlet (different behavior in CATHARE with similar modeling)

Risk of freezing at MHX outlet is predicted by RELAP5 after about 3 hours, much earlier than with CATHARE

19

TO-1: FW flowrate +20% (1/3) (RELAP5 – CATHARE Comparison)

Core and MHX powers Core and MHX powers

Primary lead temperatures Primary lead temperatures

20

TO-1: FW flowrate +20% (2/3) (RELAP5 – CATHARE Comparison)

Core temperatures Core temperatures

Total reactivity and feedbacks Total reactivity and feedbacks

21

TO-1: FW flowrate +20% (3/3) (RELAP5 – CATHARE Comparison)

ASSUMPTIONS: Feedwater flowrate +20% in 25 s

MAIN RESULTS: No significant perturbations on both primary and secondary sides The system reaches a new steady-state condition in about 10 minutes without

exceeding reactor scram set-points The increase in power removal by secondary side is larger with RELAP5 with

respect to CATHARE higher perturbation on primary side with RELAP5

22

Conclusions

In all analyzed DBC accidental transients, the protection system by reactor scram and by the prompt start-up of the DHR-1 for core decay heat removal is able to bring the plant in safe conditions in the short and long term

The core temperatures always remains well below the safety limits No significant vessel wall temperature increase is predicted The time to reach lead freezing at MHX outlet after start-up of DHR-1

system strongly depends on the assumptions taken on cold pool mixing but in any case there is large grace time for countermeasures by operator actions