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- Heat generated by decay (beta, gamma) of Fission products and Minor actinides - more than 1,000 fission products. U-235 thermal pulse[r]

1 Nuclear Fission

Jonghwa Chang

jhchang@kaeri.re.kr

Natural abundancy Uranium : 0.72% U-235, rem U-238 Thorium : 100% Th-232

ref) D.G.Madland, Nuclear Physics A 772(2006) 113-137 2

Fission process

Fission products : ~ 1,000 nuclides

Mass distribution of fission products

Mass number (A)

- direct yield

- accumulated yield

8

Decay chain

Kinetic energy of fission product

10

Gamma rays from fission

ref) T.E Valentine, ORN:/TM-1999/3000

Prompt gamma

14

Prompt fission energy (n + FP + )

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

decay scheme

2.28s Xe

 

 138 2.28

branch ratio : 97.48%



18

Delayed neutron emission

Delayed neutron is important

- to control chain reaction

- power rise : fast component

- power down : slow component

Six group delayed neutron parameters

average ~500 keV

Spectrum of delayed neutron

Decay heat

- Heat generated by decay (beta, gamma) of Fission products and Minor actinides

- more than 1,000 fission products

U-235 thermal pulse

ref) M Fleming, CCFE-R(15)28, 2015

Evolution of decay heat production

Decay heat burst function

Short half life FP decays (equillibrium)

Beta decay heat after 100,000 s irradiation

28Gamma decay heat

Decay heat power

- Too many fission products ( ~ 1,000 nuclides)

ANSI/ANS-5.1 : decay heat power standards

ref) Gauld, 2006.

30

 Decay heat data is

important for safety

Fission product average energy : ~98 MeV, Z : ~38, N:~56

Stopping range of 1 MeV beta in UO2 : ~ 0.08cm

Stopping range of F.P in UO2 : ~9m

gamma attenuation : 1 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 : 1 MeV in UO2 : ~ 1.9cm thermal energy in UO2: ~0.072 cm

Delayed gamma : 6.33 MeV 5.17 MeV

‐‐‐‐‐‐‐‐‐‐‐‐‐ recoverable energy 193.48 MeV 198.84 MeV

‐‐‐‐‐‐‐‐‐‐‐‐‐‐ total fission energy 202.23 MeV 210 MeV

Number of neutrons per fission 2.44 2.88average energy of neutron 4.84 MeV 6.13 MeVNumber of photons per fission 6.53 6.78average energy of photon 0.97 MeV 0.95 MeV

32

Summary of fission power