- Heat generated by decay (beta, gamma) of Fission products and Minor actinides - more than 1,000 fission products. U-235 thermal pulse[r]
(1)1 Nuclear Fission
(2)
2 2
4
c
Z Z e E
R R
Fissile : U-235, U-233, Pu-239 U-235 + n ⇒ fission Fertile : Th-232, U-238
Natural abundancy
Uranium : 0.72% U-235, rem U-238 Thorium : 100% Th-232
233 233
(22.3 ) (27 )
232 233
Th n Th m Pa d U
239 239
(23.5 ) (2.36 )
238 239
U n U m Np d Pu
(3)ref) D.G.Madland, Nuclear Physics A 772(2006) 113-137
(4)2.4367 0.14 ( )
v E MeV
2.8807 0.14 ( )
v E MeV
(5)4
Average total prompt fission neutron energy
(6)Maxwllian spectrum E T/ M
E Ee
Watt spectrum /
sinh
E a
E e bE
Madland and Nix spectrum
Prompt neutron spectrum
(7) 0.4865sinh 2 E
P E E e
Flux distribution
flux = speed x number density
n
E
E P E
m
6
(8)Fission products : ~ 1,000 nuclides
Mass distribution of fission products
Mass number (A)
(9)103 39Y
102
Y
103
Zr 103Nb 103Mo 103Tc 103Ru 10345Rh
102
Zr 102Nb 102Mo 102Tc 102Ru
101
Zr 101Nb 101Mo 101Tc 101Ru
0.08% 0.26% (8%) 101 Y 0.40% 100
Zr 100Nb 100Mo
100
Y
0.13%
0.54% 1.62% 0.72% 0.07%
2.08% 0.39% 0.32%
2.64% 1.88% 0.15%
5.24% 0.23s
(4.9%)
(1.9%)
(0.9%)
1.3s 1.5s 67.5s 54.2s 39.3d
0.30s 2.9s 21.3s 11.3m 5.28s
0.45s 2.3s 7.1s 14.6m 14.2m
735ms 7.1s 1.5s
5.80% 0.99% 0.01% n fission yield
- direct yield
- accumulated yield
8
(10)(11)(12)(13)12
Gamma rays from fission
(14)(15)(16)(17)16
(18)Fission products are neutron-rich, under going beta decay
e
n p e
~1/3 energy is carried by beta ray(electron) remaining energy by neutrino
Delayed emission
beta spectrum
(19)139 2.28s Xe
138 2.28 n s Xe (90%)
branch ratio : 10%
fission yield: ~1% 95 Rb fission yield: ~0.8% 139 I 95 0.3775s Sr
94 0.3775 n s Sr (91.37%)
branch ratio : 8.73%
fission yield : ~2%
normailized to per per fission
branch ratio : 2.52%
6.83MeV
2.78MeV
(76.3m)
3.887MeV
0.282MeV
(4.75x1010y)
(stable) 2.55MeV
branch ratio : 97.48%
18
(20)Delayed neutron is important - to control chain reaction - power rise : fast component
- power down : slow component
Delayed neutron group
~200 delayed neutron precursors for analysis
- merge to groups
(21)20
(22)average ~500 keV
(23)22
Decay heat
- Heat generated by decay (beta, gamma) of Fission products and Minor actinides - more than 1,000 fission products
U-235 thermal pulse
(24)(25)24
Decay heat
Important nuclides for decay heat
Ni-68~71, Cu-69~71, Zn-70~71, Kr-97, Rb-89~91,-93, Sr-93~95, Y-94~95, Kr-97, Cs-138~141, Ba-141~145, La-142~145, Ce-145~148, Pr-146~149,-151,
Nd-149,-151,-153~155, Pm-152~157, Sm-157,-158, Eu-158, etc
i i i
h t EN t
b t t h t
i i i j j i
N t N N f t Concentration of F.P nuclides decay chain equation
beta(gamma) heating
burst function
(26)(27)26
Beta decay heat depends on irradiation time
(28)(29)28
(30)Decay heat power
- Heat generated by decay (beta, gamma)
- Too many fission products ( ~ 1,000 nuclides)
ANSI/ANS-5.1 : decay heat power standards 1971 :
1979 :
1994 : 23 group model 2015:
(31)ANSI/ANS-5.1-2005
ORIGEN-S [ENDF/B-6 library, ORNL/TM-2003/118]
ref) Gauld, 2006.
(32) Decay heat data is important for safety analysis
such as LOCA Important for LWR
- U-235 thermal
- U-238 fast
(33)Fission product average energy : ~98 MeV, Z : ~38, N:~56
Stopping range of MeV beta in UO2 : ~ 0.08cm Stopping range of F.P in UO2 : ~9m
gamma attenuation : MeV in UO2 : 0.77/cm = half intensity 0.9cm in water : 0.0707/cm = half intensity 9.8 cm
can damage fuel, cladding
fission neutron mean free path : MeV in UO2 : ~ 1.9cm thermal energy in UO2: ~0.072 cm
in water : ~ 1.87cm in water: ~0.66cm
some times important (gamma redistribution)
U‐235 Pu‐239
kinetic energy of fission fragments : 169.13 MeV 175.55 MeV kinetic energy of prompt neutrons : 4.92 MeV 6.07 MeV kinetic energy of delayed neutrons : 0.0074 MeV 0.003 MeV
Prompt gamma : 6.60 MeV 6.74 MeV
Delayed gamma : 6.33 MeV 5.17 MeV
Delayed beta : 6.50 MeV 5.31 MeV
‐‐‐‐‐‐‐‐‐‐‐‐‐recoverable energy 193.48 MeV 198.84 MeV
Neutrinos : 8.75 MeV 7.14 MeV
‐‐‐‐‐‐‐‐‐‐‐‐‐‐total fission energy 202.23 MeV 210 MeV Number of neutrons per fission 2.44 2.88
average energy of neutron 4.84 MeV 6.13 MeV Number of photons per fission 6.53 6.78
average energy of photon 0.97 MeV 0.95 MeV
32