HTGR simulations in PSI using MELCOR 2.2

WIR SCHAFFEN WISSEN HEUTE FÜR MORGEN Jamo Kalilainen :: Paul Schee Institut HTGR simulations in PSI using MELCOR 2.2 10 th Meeting of the Euopean MELCOR Use Goup (EMUG), 25 27 Apil, Zage, Coatia

Intoduction Since the code vesion 2.1, MELCOR includes seveal featues fo modeling of accident scenaios in High Tempeatue Gas cooled Reactos (HTGRs) Models fo oth pismatic lock and the pele ed fueled HTGR designs. In the pevious investigation, Coson (2010) conducted an extensive study on Pessuized and De pessuized Loss of Foced Cooling accidents in the South Afican PBMR 400 design using the MELCOR 2.1 code Also, a pevious modified vesion of the MELCOR code has een used fo example, on an ai ingess accident analysis of a pele ed eacto (Meill, 2010). Page 2

Intoduction We have used MELCOR 2.2 code to simulate Pessuized and De pessuized loss of foced flow accidents (PLOFC/DLOFC) in the HTR PM HTR PM is a 250 MWth twin unit, modula pele ed eacto, cuently eing uild in Shandong povince, China Pictue: http://www.wold nuclea news.og/ Pictue: IAEA I3 TM 50156 Pictue: https://nucleasteet.com/ Page 3

Intoduction We have used MELCOR 2.2 code to simulate Pessuized and De pessuized loss of foced flow accidents (PLOFC/DLOFC) in the HTR PM The input was pepaed with the help of the old open liteatue HTGR wok pefomed on MELCOR and an open liteatue desciption of the HTR PM pele ed coe, side and ottom eflectos, intenal caon stuctues, eacto pessue vessel and the esidual heat emoval system. Some input, like the eacto powe distiution and decay heat otained fom pevious PSI HTGR wok Page 4

MELCOR model of the HTR-PM 2.25 m 11 m Following Coson and Zheng et al., Heat tansfe coefficient at pele suface set to: Gaphite eflecto 1.5 m Pele ed coe 2.5 m C a o n i c k Most of the infomation on HTR PM geomety + mateial popeties Zheng et al., Ann. Nucl. Enegy 36 (2009) Side and ottom/top eflectos poous With coolant channels, contol ods Page 5

MELCOR model of the HTR-PM 4.25 m (estimate) 2.85 m (Zheng et al., 2009) 2.65 m (estimate) Size of the RPV otained fom Zheng et al. Othe distances estimated fom vaious HTR PM open liteatue souces Radiation heat tansfe fom the caon ick to RHRS Gaphite eflecto Pele ed coe C a o n i c k He He Ai Coe ael (Stainless steel) RPV (stainless steel, thickness 131 cm) Wate cooling panel (RHRS) T = 70 C Page 6

Relative powe MELCOR model of the HTR-PM: Powe distiution The powe distiution of the coe was otained fom the Sepent 2, a 3D continuous enegy Monte Calo code calculation of the HTR PM, pefomed as a pat of pevious MSc wok in PSI 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 2 4 6 8 10 12 Distance fom the ottom of the coe [m] Relative powe 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 0 0.5 1 1.5 Distance fom the cente of the coe [m] Page 7

MELCOR model of the HTR-PM: Decay heat Decay powe also otained fom a Sepent 2 simulation Aveage flux ove the whole lifetime of a pele in coe Bunup: 90 MWd/kg HM Compaed to one used y Zheng et al. 1 h: ~72 % 10 h: ~75 % 100 h: ~80 % Decay heat used in the MELCOR simulation Zheng et al., Ann Nucl Enegy 36 (2009) Page 8

Results: Nomal opeation He C a o n i c k In nomal opeation: He mass flow ate 96 kg/s He pessue in pimay loop 7 Mpa He tempeatue: T in : 523 K T out = 1022 K He Page 9

Results: Nomal opeation Melgen flag: EXEC_SS Heat capacities in COR and HS educed with a facto of 0.01 Steady state eached in appox. 5000 s. Gaphite eflecto C a o n i c k In nomal opeation: He mass flow ate 96 kg/s He pessue in pimay loop 7 Mpa He tempeatue: T in : 523 K T out = 1022 K Side eflecto gaphite tempeatue: T max 620 K Aveage fuel element tempeatue in the pele ed Page 10

Results: PLOFC accident Pessuized Loss of foced cooling (PLOFC) accident Helium flop disupted (e.g. He lowe failue) Pimay cicuit kept intact Gaphite eflecto Pele ed coe C a o n i c k In PLOFC: He flow ate educed to 0 kg/s in 30 s He pessue in the pimay loop 7 Mpa He Page 11

Results: PLOFC accident Pessuized Loss of foced cooling (PLOFC) accident Helium flow ate educed to 0 in 30 s. Max. fuel tempeatue at appox. 145000 s T max 1342 K, Height 9 m High density of the high pessue He Buoyancy lifts high tempeatue He up in the coe Natual ciculation estalished in the pele ed Page 12

Results: DLOFC accident De pessuized Loss of foced cooling (DLOFC) accident Beak in the pimay cicuit Gaphite eflecto Pele ed coe C a o n i c k In DLOFC: Pessue deceased to 0.1 Mpa in appox. 20 s. He flow simultaneously deceased to 0 kg/s Page 13

Results: DLOFC accident De pessuized Loss of foced cooling (DLOFC) accident Pessue deceased to 0.1 Mpa in appox. 20s. Max. fuel tempeatue appox. at 570000 s T max 1732 K, Height 6.5 m Low density of He in low pessue: No significant convection Heat tansfe mainly y conduction and adiation Page 14

Results: Compaison with a efeence Compaison to analysis y Zheng et al., Ann Nucl Enegy 36 (2009) Zheng et al. simulated P/DLOFC in HTR PM using a THERMIX code Themohydaulics steady state and tansient code fo pele ed eacto pimay cicuit, including a neuton point kinetics and gaphite coosion models Max fuel tempeatue DLOFC: 1458 C (MELCOR), 1492 C (Zheng et al.) Max fuel tempeatue PLOFC: 1069 C (MELCOR), 1134 C (Zheng et al.) Maximum fuel tempeatue fom the MELCOR simulation Maximum fuel tempeatues Zheng et al., Ann Nucl Enegy 36 (2009) Page 15

Results: Compaison with a efeence Compaison to analysis y INET (Zheng et al., Ann Nucl Enegy 36 (2009) Max fuel tempeatue DLOFC: 1458 C (MELCOR), 1492 C (Zheng et al.) Max fuel tempeatue PLOFC: 1069 C (MELCOR), 1134 C (Zheng et al.) The maximum fuel tempeatues quite close in DLOFC, with PLOFC the fast incease and cooling (at 10 h) missing in MELCOR esult Could e patly due to the lowe decay heat Slow heating peiod to each T max much longe in MELCOR Page 16

Results: heat tansfe to the wate panel Cuently, heat tansfe though conduction fom coe ael to RPV is not consideed in the simulations Impotant accoding to Zheng et al. Conduction added in a vey ecent simulation to DLOFC case Max. tempeatue of the fuel deceased only appox. 10 K > no significant diffeence on the esults Page 17

Results: heat tansfe to the wate panel Cuently, heat tansfe though conduction fom coe ael to RPV is not consideed in the simulations Impotant accoding to Zheng et al. Conduction added in a vey ecent simulation to DLOFC case Max. tempeatue of the fuel deceased only appox. 10 K > no significant diffeence on the esults Also, due to insufficient data the ottom and top eflecto models lack detail in cuent model Could have an effect on the esults To e impoved in the futue Page 18

Conclusions and futue wok MELCOR model of an HTR PM was developed Mainly open souce liteatue was used fo the geomety details > uncetainties emain Powe distiution and decay heat otained fom pevious simulations of the HTR PM in PSI Two accident scenaios, PLOFC and DLOFC wee investigated Maximum fuel tempeatues emained elow the pele fuel safety limit of 1600 C. Fuel tempeatue changes slowly compaed to the efeence simulation y Zheng et al.. Futue wok: Impovement of the eacto geomety (especially coe ael and RHRS placement) MELCOR code also includes models fo fission poduct elease fom the fuel elements duing nomal opeation and in accident conditions of the HTGR In the futue wok, also the study of FP elease and tanspot duing diffeent accident scenaios is envisioned Page 19

Wi schaffen Wissen heute fü mogen Thank you! Page 20