Presentation on theme: "Wir schaffen Wissen – heute für morgen Fast Reactor Physics Konstantin Mikityuk, FAST reactors PSI Thorium Energy Conference."— Presentation transcript:
Wir schaffen Wissen – heute für morgen Fast Reactor Physics Konstantin Mikityuk, FAST reactors PSI Thorium Energy Conference 2013 CERN Globe of Science and Innovation Geneva, Switzerland, October 27-31, 2013
2 Outline. Fast reactors: breeding. Fast reactors: past and future. Fast reactors: few R&D projects in Europe. Fast reactors: could Th become a fuel? Sustainability Safety Proliferation resistance Radiotoxicity and decay heat Summary: advantages and disadvantages of Th for FR
3 Fast reactors: breeding.
4 Fast critical reactor A fast neutron critical reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons. Such a reactor needs no neutron moderator, but must use fuel that is relatively rich in fissile material when compared to that required for a thermal reactor. SFR PWR
5 Breeding U 93 Np 94 Pu 91 Pa 90 Th β–β– β–β– β–β– β–β– Thorium fuel cycle Uranium fuel cycle (n, γ ) fertile fissile 23.5 m 2.35 d 22 m 27 d A production of new fissile isotopes in the nuclear reactor is a kind of transmutation called a breeding and non-fissile isotopes (U-238 and Th-232), which give birth to the new fissile isotopes, are called fertile.
6 Neutron balance in a critical reactor A_fissile P=A_fissile + A_fertile + A_parasitic + LR P=A + LR k eff = Production rate / (Absorption rate + Leakage Rate) = 1 A_fissile =1+BR+L – Number of n’s emitted per neutron absorbed in fissile fuel BR – Breeding Ratio: Number of fissile nuclei created per fissile nucleon destroyed L – Number of neutrons lost per neutron absorbed in fissile fuel
7 Breeding: for main fissiles Average number of fission neutrons emitted per neutron absorbed as a function of absorbed neutron’s energy for three fissile isotopes Best for breeding
8 Breeding Burning of Pu-239 and U-233 in a fast neutron spectrum (>10 5 eV) provides the highest number of fission neutrons per neutron absorbed in fuel. The extra neutrons can be absorbed by fertile isotopes with a rate which is equal or even higher than the fissile burning rate. The fast neutron spectrum reactor with BR>1 is called a breeder and with BR=1—an iso-breeder. Fast neutron spectrum allows to efficiently “burn” fertile U-238 or Th-232— via transmutation to fissile Pu-239 or U-233.
9 Fast reactors: past and future.
10 First "nuclear" electricity – fast reactor. In 1949 EBR-I – Experimental Breeder Reactor I – was designed at Argonne National Laboratory. In 1951 the world’s first electricity was generated from nuclear fission in the fast-spectrum breeder reactor with plutonium fuel cooled by a liquid sodium. First “nuclear” electricity : four 200-watt light bulbs. Courtesy of ANL.
11 Fast reactors: 1946 – 2013 MWth Hg NaK Na LBE
12 The Generation IV International Forum (GIF) is a cooperative international endeavor organized to carry out the R&D needed to establish the feasibility and performance capabilities of the next generation nuclear energy systems. Argentina, Brazil, Canada, France, Japan, Korea, South Africa, the UK and the US signed the GIF Charter in July 2001, Switzerland in 2002, Euratom in 2003, China and Russia both in Six nuclear energy systems were selected for further development: 4.Very-high-temperature reactor (VHTR) 5.Supercritical-water-cooled reactor (SWCR) 6.Molten salt reactor (MSR) 1.Gas-cooled fast reactor (GFR) 2.Sodium-cooled fast reactor (SFR) 3.Lead-cooled fast reactor (LFR)
19 Sustainability. Depleted U stock Spent fuel cooling Fuel fabrication Fast reactors Geologic repository Separation of elements U-dep Ac AcO 2 + FP FP + losses “Ac” = “actinides”, i.e. U + Np + Pu + Am + Cm +... “FP” = fission products AcO 2 (According to calculations) fast reactors can operate in an equilibrium closed U- Pu fuel cycle with BR=1 (amount of fissile produced = amount of fissile consumed) fed by only depleted (or natural) uranium
U 93 Np 94 Pu 95 Am 96 Cm FP – – –14 6 – –84 12 –62 10 –6 410 – –2 3 – –4 21 – –5 –8 –844 –1 –142 –1000 (Cm) (Am) (Pu) (Np) (U) 242 m feed fuel 6.75 d 2.1 d 87.7 y 23.5 m 2.35 d 7 min 14.3 y 4.98 h 26 min 18.1 y 16 h 163 d –1 (n,2n) β–β– (n, γ ) β+β+ fission M mass number α EQL-U: mass balance in SFR (simplified model)
21 Sustainability. Could the same reactors operate in an equilibrium closed Th-U fuel cycle? (According to calculations) the answer is yes, but since no U-233 (main fissile isotope for this cycle) is available, we face a problem Th disadvantage : How to start thorium fast reactor? What fissile material to use? Plutonium? Uranium-235? Uranium-233 generated somewhere else?
22 EQL-Th: mass balance in SFR (simplified model) U 93 Np 94 Pu 91 Pa 90 Th –35 feed fuel m h d h 4 27 d 955 – – y 234 – – – d – d 238 –4 1 1 – y y FP –5 –2 –957 –0 –35 –999 (Pu) (Np) (U) (Pa) (Th) Th advantage : very low amount of minor actinides Th disadvantage : production of U-232—precursor of gamma emitters
23 EQL-U and EQL-Th fuel compositions in SFR (%wt)
24 EQL-U and EQL-Th neutron balance k-inf = k-inf = Blue bars are isotope-wise contributions to absorption (sum up to 1) Red bars are isotope-wise contributions to production (sum up to k-inf) Th disadvantage : lower k-infinity
25 Safety. We look at just two reactivity effects: Doppler effect and (sodium) void effect having in mind other reactivity effects (less fuel type dependent) Thermal expansion effects (not considered) Void reactivity effect
26 EQL-U and EQL-Th fuel reactivity effects in SFR Th advantage : stronger Doppler and weaker void effects Infinite medium (no leakage component) Doppler (Nominal → 3100 K) Void (Nominal → 0 g/cm 3 ) Isotope-wise decomposition:
27 EQL-U and EQL-Th fuel reactivity effects in SFR Why void effect is weaker in case of EQL-Th? Sodium removal leads to spectral hardening—shift to the right Pu-239: grows quicker U-233: grows slower
28 Proliferation resistance U 93 Np 94 Pu 91 Pa 90 Th β–β– β–β– β–β– β–β– Thorium fuel cycle Uranium fuel cycle (n, γ ) fertile fissile 23.5 m 2.35 d Th disadvantage: fissile precursor has higher half life, potential to be separated 22 m 27 d Th advantage: misuse of U-233 is protected by presence of U β–β– 231
29 EQL-U and EQL-Th fuel RT and DH (no FP) Th advantage : Radiotoxicity and decay heat of EQL fuel are lower for ~10000y
31 Summary... Th disadvantages Past and current fast reactors were/are based on U-Pu cycle. Operational experience with thorium-uranium fuel is low. Experience in fuel manufacturing and reprocessing is lower for Th-U fuel compared to U-Pu. Fissile fuel for Th-U cycle (U-233) is not available. U-232—precursor of hard gamma emitters—is produced in Th-U cycle (n2n reaction is higher in fast spectrum). k-infinity of equilibrium fuel is lower for Th-U cycle compared to U-Pu one. This means that to reach iso-breeding the blankets of fertile material can be required. Fissile precursor of U-233 (Pa-233) has higher half life (compared to Np-239)—potential to be separated and decayed to pure U-233.
32 Summary... Th advantages Calculational analysis with state-of-the-art codes shows that fast reactor can operate as an iso-breeder in Th-U cycle closed on all actinides. There is very low amount of minor actinides in EQL-Th fuel cycle. Doppler effect is stronger and void effect is weaker in EQL-Th fuel compared to EQL-U. Misuse of U-233 is protected by presence of U-232 (predecessor of hard gamma emitters). Radiotoxicity and decay heat of EQL-Th fuel are lower during the first years of cooling compared to the EQL-U fuel.