Nathlia N. Arajo, Maritza R. Gual & Marcos C. Maturana Brazil - - PowerPoint PPT Presentation

Nathália N. Araújo, Maritza R. Gual & Marcos C. Maturana Brazil

Technical Meeting on the Phenomenology, Simulation and Modelling of Accidents in Spent Fuel Pools 2-5 September 2019, Vienna, Austria

Sum umma mary ry

• PROBABILISTIC SAFETY ASSESSMENT (PSA)
• DESCRIPTION OF THE SFP COOLING SYSTEMS

(SFPCS)

• EVENT SEQUENCES
• SPF MODELING WITH MELCOR
• RESULTS OF THE SIMULATIONS
• CONCLUSIONS AND FUTURE WORK

Probabilistic Safety Assessment (PSA)

• Selection of the most frequent accident sequences

through PSA level 1

• Preparation of an SFP model in MELCOR
• Support the calculation of frequency and release of

radioactive material – PSA level 2 – with the accident simulation results

PSA Levels At each level the risk associated with the indicated event is analyzed.

SFP COOLING SYSTEMS (SFPCS)

FUEL BUILDING (FB)

CONTROL ROOM (CR)

Compartment FSP-I Compartment FSP-II Compartment FSP-III B1 B2 B3 B4 T2 T3 P1 P2 S1

FE

Cleaning and Purification System (CPS) T1

FE

Safety Water Cooling System (SWCS) Drainage System (DS) S3

V34

Transfer Channel (TC)

V47 V36 V62 V65 V72 V22 V23 V27 V25 V35 V28 V31 V57 V71 V70 V52 V56 V4 V5 V7 V9 V11 V64 V10 V14 V17 V63 V44 V38 V76 V45 V75 V40 V73 V46 V74 V53

Sampling System (SS)

V51 V37

S2

SFPCS OPERATIONAL MODES

Operational Mode Cooled Compartments Description B FSP-II Normal operation. Circulation by pump B3. Cooling by the heat exchanger T2. B. B.1 Degraded operation. Circulation by pump B3. Cooling by the heat exchanger T3. B. B.2 Degraded operation. Circulation by pump B4. Cooling by the heat exchanger T2. B. B.3 Degraded operation. Circulation by pump B4. Cooling by the heat exchanger T3.

EVENT SEQUENCES TO BE CONSIDERED IN PSA LEVEL 2

• PSA Level 1 results:

– Failure to open valves for redundant circuit: first three cases; – CCF of B3 and B4 to start: fourth case (3.43E-6 / yr); – One pump unavailable due to testing and maintenance and standby pump failure to start: fifth and sixth cases (5.00E-7 and 4.70E-7 / yr);

• The set of abnormal conditions

identified in the PSA Level 1 will be considered for the spent fuel pool accidents in PSA Level 2.

SHUTDOWN PSA LEVEL 1 TOP 3 SFP FUEL DAMAGE FREQUENCY CUTSETS

Cutset Number Event Description Event Probability Frequency (yr) 1 Plant is shutdown based on annual availability 8.22E-2 8.56E-6 Shutdown Phase II, III, IV duration 7.33E-1 Loss of SFPCS 1.00 Flag: Spent fuel elements in FSP-II. 1.00 Manual Valve _036_ Failure to Open 1.42E-4 2 Plant is shutdown based on annual availability 8.22E-2 8.56E-6 Shutdown Phase II, III, IV duration 7.33E-1 Loss of SFPCS 1.00 Flag: Spent fuel elements in FSP-II. 1.00 Manual Valve _034_ Failure to Open 1.42E-4 3 Plant is shutdown based on annual availability 8.22E-2 3.66E-6 Shutdown Phase II, III, IV duration 7.33E-1 Loss of SFPCS 1.00 Flag: Spent fuel elements in FSP-II. 1.00 Check Valve _032_ Failure to Open 6.07E-5

MELCOR SFP MODELING

• MELCOR 2.2.9541

– SFP – PWR – 3 rings × 12 axial levels (6 for active fuel) – 21 fuel assemblies with UO2 ~5% fuel rods – 48 MW (NPP) ~ time decay heat of 5 days

MELCOR SFP MODELING

MELCOR RESULTS

MELCOR RESULTS

MELCOR RESULTS

CON ONCL CLUSIONS USIONS & FU FUTURE URE WOR ORK

• The Shutdown PSA Level 1 of a reference NPP

was analysed and a set of accident sequences was selected;

• A MELCOR model for SFP was obtained;
• A

better understand

• f

the LOFA physical phenomena was reached;

• The SFP accidents evaluation will be based on the

results of these simulations;

• Improvement of MELCOR model of the SFP;
• The resulting MELCOR model will be useful for the

calculation Large Early Release Frequency (LERF)

• f the reference NPP

.

Thank You!