Estimation of average burnup of damaged fuels loaded in Fukushima Dai-Ichi Reactors by using the 134Cs/137Cs ratio method

1
Estimation of average burnup of damaged fuels
loaded in Fukushima Dai-Ichi Reactors by using
the 134Cs/137Cs ratio method

• Nagoya University?Tomohiro ENDO, Shunsuke SATO,
  Akio YAMAMOTO

2
Question

• Why is radioactivity ratio, derived
  fromFukushima Dai-ichi NPPs accident, 134Cs
  137Cs 1 1 as of Mar. 11th, 2011?

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

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 1446 Mar. 11th, 2011
• Severe core damage in units 1-3, confinement
  capabilities (RPV, CV) are partially damaged
• Release of radioactive nuclides to environment
• Atmosphere 131I130160 PBq, 137Cs1115
  PBq
• Ocean 131I11 PBq, 137Cs4 PBq

1 ????????, (??23?6?6?) 2 ??????,
?64????????????3? (??23?8?24?) 3 H. Kawamura,
et al., JNST, 4811, p.13491356 (2011)
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

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
7
Production and depletion equation for 134Cs and
137Cs
fission
133Cs
134Cs
137Cs

decay
2 year
30 year
capture
8
Analytical solution 134Cs/137Cs ratio

• Rigorously, microscopic reaction rates and
  fission yield depend on fuel burnup
• Numerical solution can be solved by
• Batemans method
• Matrix exponential method

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.

10
Loaded fuels and core averaged specific power
input
4 TEPCO homepage, http//aoisora.org/genpatu/201
1/tepco_data/20110409151130/atomfuel01-j.html 5
TEPCO homepage, http//www.tepco.co.jp/nu/f1-np/in
tro/outline/outline-j.html

• MOX is 10-years storage fuels and loaded in this
  cycle for the first time

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
12
Other input conditions

• Void fraction (VF) of coolant 40
• Temperature
• Fuel900 K
• Cladding 600 K
• Moderator560 K
• These values are typical BWR core parameters

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 500080 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

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
15
Numerical results of 134Cs/137Cs ratio among
calculation codes

• 9?9(B) fuel, VF40, 25 MW/tHM

0.02
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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

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Numerical results of 134Cs/137Cs ratio for
different VF nuclear data library

• 9?9(B) fuel, 25 MW/tHM

18
Comparison of 134Cs/137Cs ratio among fuel type

• Depends on specific power
• Difference between UO2 and MOX

?UO2, 25 MW/tHM
?others
19
Estimation formula for fuel burnup

• SRAC2006/PIJ with JENDL-4.0
• Weighting 134Cs 137Cs by tHM for each cores

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/gij
yutu/017/shiryo/__icsFiles/afieldfile/2011/09/02/1
310688_2.pdf
21
Frequency distribution of 134Cs/137Cs
0.9960.07

• Estimated burnup 17.21.5 GWd/tHM

9 http//www.mext.go.jp/b_menu/shingi/chousa/gij
yutu/017/shiryo/__icsFiles/afieldfile/2011/09/02/1
310688_1.pdf
22
Plant data at 1400 Mar. 11th (1F3)

• 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
23
Discussion

• Core burnup by plant process computer
• Estimated burnup(17.21.5 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
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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 ????????????????????????1???2???3????????????
?? ???, JNES-RE-2011-0002
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)
12 CASMO-4/SIMULATE-3 ??????????BWR?????????????
, JNES/SAE05-029
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Conclusion

• In the present research, estimated burnup is
  17.21.5 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.

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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