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Nagoya University  Tomohiro ENDO, Shunsuke SATO, Akio YAMAMOTO

Estimation of average burnup of damaged fuels loaded in F ukushima D ai -I chi R eactors by using the 134 Cs/ 137 Cs ratio method. Nagoya University  Tomohiro ENDO, Shunsuke SATO, Akio YAMAMOTO. Question.

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Nagoya University  Tomohiro ENDO, Shunsuke SATO, Akio YAMAMOTO

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  1. Estimationofaverageburnupofdamagedfuelsloadedin Fukushima Dai-Ichi Reactorsbyusingthe134Cs/137Cs ratio method Nagoya UniversityTomohiro ENDO, Shunsuke SATO, Akio YAMAMOTO Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  2. Question • Why is radioactivity ratio, derived fromFukushima Dai-ichi NPPs accident,134Cs : 137Cs = 1 : 1 as of Mar. 11th, 2011? Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  3. Contents • 134Cs/137Cs ratio method • Numerical analysis • Analysis of actually measured 134Cs/137Cs ratio • contaminated soils within the range of 100km from the 1F NPPs • Discussion Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  4. Overview of 1F NPPs accident • Station blackout accompanied with loss of cooling capability and loss of ultimate heat sink due to excessive tsunami (~15m) caused by M9.0 earthquake at 14:46 Mar. 11th, 2011 • Severe core damage in units 1-3, confinement capabilities (RPV, CV) are partially damaged • Release of radioactive nuclides to environment • Atmosphere : 131I=130~160 [PBq], 137Cs=11~15 [PBq] • Ocean : 131I=11 [PBq], 137Cs=4 [PBq] [1] 原子力安全・保安院, (平成23年6月6日) [2] 原安全委員会, 第64回原子力安全委員会資料第3号(平成23年8月24日) [3] H. Kawamura, et al., JNST, 48[11], p.1349–1356 (2011) Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  5. Purpose of this presentation • Estimation of burnup of damaged fuels by using 134Cs/137Cs ratio method • Effectiveness of estimated burnup • Health effects due to released radioactive nuclides from 1F NPPs • Isotopic composition depends on fuel burnup • Especially important for unsurveyed isotopes • Burnup credit for criticality safety for discharging process of fuel-debris Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  6. 134Cs/137Cs ratio method • Radioactivity ratio of 134Cs/137Cs corresponds to fuel burnup • Convert measured 134Cs/137Cs ratio to burnup measured ratio estimated burnup Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  7. Production and depletion equation for 134Cs and 137Cs fission … 137Cs 133Cs 134Cs decay 30 year 2 year capture Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  8. Analytical solution 134Cs/137Cs ratio • Rigorously, microscopic reaction rates and fission yield depend on fuel burnup • Numerical solution can be solved by • Bateman’s method • Matrix exponential method Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  9. Modeling of numerical analysis • Detail information are classified due to proprietary data • U, Pu, and Gd enrichment/content splittingin UO2 and MOX assemblies • Fuel loading pattern • Power, void, and temperature histories • Simple model in the present research • Pin cell geometry • Assembly average values of 235U, Pu • Typical core-averaged power, void, temp. Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  10. Loaded fuels and core averaged specific power input [4] TEPCO homepage, http://aoisora.org/genpatu/2011/tepco_data/20110409151130/atomfuel01-j.html [5] TEPCO homepage, http://www.tepco.co.jp/nu/f1-np/intro/outline/outline-j.html • MOX is ~10-years storage fuels and loaded in this cycle for the first time Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  11. Dimensions & compositions of fuels only assembly average values are published fuel rod information is sufficient to carry out pin-cell calc. [6] http://www.nsc.go.jp/shinsashishin/pdf/1/ho007.pdf [7] http://www.pref.fukushima.jp/nuclear/info/pdf_files/100714-2.pdf Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  12. Other input conditions • Void fraction (VF) of coolant : 40% • Temperature • Fuel：900 [K] • Cladding: 600 [K] • Moderator：560 [K] • These values are typical BWR core parameters Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  13. Comparison of 134Cs/137Cs ratio among various calculation codes • Deterministic code • SRAC2006/PIJ (Collision probability method) • SCALE6.0/TRITON (Discrete ordinate method) • Monte Carlo code • MVP-BURN • total number of histories: 5000×80 for each burnup step • With same nuclear data library: ENDF-B/VII.0 • SRAC2006/PIJ : 107 energy groups • SCALE6.0/TRITON : 238 energy groups • MVP-BURN : continuous energy Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  14. Calculation scheme of SCALE6.0/TRIRON • Deterministic code for neutron transport and depletion calculations Resonance Calculation 2-D discrete ordinate method for neutron transport calculation Fuel depletion and decay calculation Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  15. Numerical results of 134Cs/137Cs ratio among calculation codes • 99(B) fuel, VF=40%, 25 [MW/tHM] 0.02 Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  16. Void fraction and nuclear data library effects for 134Cs/137Cs ratio • SRAC2006/PIJ • Void Fraction (VF) • 0% for lower part • 40% for average • 70% for upper part • Nuclear data library • JENDL-4.0 • ENDF-B/VII.0 Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  17. Lib. Dif. 0.05 VF. Dif. 0.3 Numerical results of 134Cs/137Cs ratio for different VF & nuclear data library • 99(B) fuel, 25 [MW/tHM] Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  18. Comparison of 134Cs/137Cs ratio among fuel type • Depends on specific power • Difference between UO2 and MOX ←UO2, 25 [MW/tHM] ←others Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  19. Estimation formula for fuel burnup • SRAC2006/PIJ with JENDL-4.0 • Weighting 134Cs & 137Cs by tHM for each cores Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  20. Contamination densities of 134Cs &137Cs • Contaminated soils within the range of 100 km from the Fukushima Dai-ichi NPPs 134Cs 137Cs ÷ [8] http://www.mext.go.jp/b_menu/shingi/chousa/gijyutu/017/shiryo/__icsFiles/afieldfile/2011/09/02/1310688_2.pdf Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  21. Frequency distribution of 134Cs/137Cs • Estimated burnup : 17.2±1.5 [GWd/tHM] 0.996±0.07 [9] http://www.mext.go.jp/b_menu/shingi/chousa/gijyutu/017/shiryo/__icsFiles/afieldfile/2011/09/02/1310688_1.pdf Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  22. Plant data at 14:00 Mar. 11th (1F#3) • Alarm recording data includes numerical summaries of BWR plant process computer burnup data [10] http://www.tepco.co.jp/nu/fukushima-np/plant-data/f1_3_Keihou3.pdf Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  23. Discussion • Core burnup by plant process computer • Estimated burnup(17.2±1.5 [GWd/tHM]) is nearly equal to but slightly lower than core-averaged value • Possible causes • Postulated core meltdown process • Once-burned fuel *Hard to read due to low quality of published pdf file Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  24. Postulated core meltdown process • Damages of Fuel Assemblies (FAs) progressed from center to peripheral region • FAs loaded in peripheral region are typically 4th - and/or 5th-burned fuel • Averaged burnup of damaged fuel would be lower than that of core averaged value upper lower center [11] 東京電力株式会社福島第一原子力発電所の事故に係る1号機、2号機、3号機の炉心の状態に関する評価 報告書, JNES-RE-2011-0002 Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  25. Once-burned fuel • once-burned FAs, which have relatively high power density due to burnout of burnable poison, may be highly damaged due to higher decay heat. Infinite neutron multiplication factor Burnup [GWd/tHM] ~10 [GWd/tHM]for 1 cycle(1 year) Nov. 17th, 2011, 2011 Symposium on Nuclear Data [12] CASMO-4/SIMULATE-3 コードシステムによるBWR実機炉心解析に関する報告書, JNES/SAE05-029

  26. Conclusion • In the present research, estimated burnup is 17.2±1.5 [GWd/tHM] by using 134Cs/137Cs ratio method for contaminated soils • VF effect in depletion calculation has a major impact on 134Cs/137Cs ratio • More precise evaluation requires more detail information about fuel assemblies’ data loaded in 1F NPPs: • histories and distributions of the specific power and the void fraction are strongly desired. Nov. 17th, 2011, 2011 Symposium on Nuclear Data

  27. Thank you for your attention We sincerely thank all of researchers that are involved in the measurement and analysis of radiation dose and radioactive-contamination map project supported by MEXT Nov. 17th, 2011, 2011 Symposium on Nuclear Data

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