Minor actinide burning in a CANDU thorium reactor

Abstract

Nuclear waste actinides can be used as a booster fissile fuel material in form of mixed fuel with thorium in a CANDU reactor in order to assure the initial criticality at startup. Two different fuel compositions have been found useful to provide sufficient reactor criticality over a long operation period: 1) 95% thoria (ThO2)+5% minor actinides MAO2 and 2) 90% ThO2+5% MAO2+5% UO2. The latter allows a higher degree of nuclear safeguarding through denaturing the new 233U fuel with 238U. The temporal variation of the criticality k∞ and the burn-up values of the reactor have been calculated by full power operation for a period of 10 years. The criticality starts by k∞>1.3 for both fuel compositions. A sharp decrease of the criticality has been observed in the first year as a consequence of rapid plutonium burnout in the actinide fuel. The criticality becomes quasi constant after the 2nd year and remains close to k∞ = ∼1.06 for ∼10 years. After the 2nd year, the CANDU reactor begins to operate practically as a thorium burner. Very high burn up could be achieved with the same fuel material (up to 200000 MW.D/MT), provided that the fuel rod claddings would be replaced periodically (after every 50000 or 100000 MW.D/MT). The reactor criticality can be maintained until a great fraction of the thorium fuel is burnt up. This would reduce fuel fabrication costs and nuclear waste mass for final disposal per unit energy drastically.

Large-scale energy production with thorium in a typical heavy-water reactor using high-grade plutonium as driver fuel

“…[12][13][14][15][16][17][18][19][20][21] In a series of systematic studies conducted with the SCALE5 code package, 22 the utilization potential of HG-Pu, reactor-grade plutonium (RG-Pu), and minor actinides (MA) as mixed with thorium in CANDU reactors has been investigated. [23][24][25][26] These generic studies had been performed with the help of the SCALE5 code 22 in 1-D cylindrical geometry and S 8 -P 3 approximation using 238 groups' neutron cross sections of the ENDF-V data library under consideration of the transmutation and radioactive decay of all actinide isotopes. The incremental time duration for each successive burn step has been taken as Δt = 30 days to be close to the half-life time of 233 Pa with T 1/2 = 27 days, the precursor of 233 U. Axial neutron leakage was approximated with a buckling factor.…”

“…52 Figure 6 shows the pertinent transmutation reactions observable in a nuclear reactor. 23,24,43 The temporal variation of actinide isotope densities until EOL for the mixed fuel composition 6% HG-PuO 2 + 94% ThO 2 is depicted in Figure 7, averaged over the core. The driving main initial fissile isotope 239 Pu is depleted continuously.…”

“…High neutron economy of heavy‐water–moderated Canada Deuterium Uranium (CANDU) reactors promises to be an attractive option for the exploitation of rich world thorium reserves, which was subject of different work . In a series of systematic studies conducted with the SCALE5 code package, the utilization potential of HG‐Pu, reactor‐grade plutonium (RG‐Pu), and minor actinides (MA) as mixed with thorium in CANDU reactors has been investigated . These generic studies had been performed with the help of the SCALE5 code in 1‐D cylindrical geometry and S 8 ‐P 3 approximation using 238 groups' neutron cross sections of the ENDF‐V data library under consideration of the transmutation and radioactive decay of all actinide isotopes.…”

Utilization of nuclear waste plutonium and thorium mixed fuel in candu reactors

“…In the course of reactor operation, actinide isotopes undergo several transmutation processes through neutron interaction Nuclear waste plutonium and thorium S. Şahin, B. Şarer and Y. Çelik and radioactive decay, as depicted in Figure 7 [11,12,15]. Time evolution of actinide isotope densities until EOL for mode ② is shown in Figure 8, averaged over the core.…”

“…Recently, a number of studies have been conducted to search the possibility of further exploitation of these precious RG-Pu and MA in heavy water or graphite moderated nuclear reactors, having a better neutron economy than LWRs. Previous work has investigated intensively the utilization potential of RG-Pu and MA in the form of a mixed ThO 2 /PuO 2 fuel in CANDU reactors and fixed bed nuclear reactors [10][11][12][13][14][15][16][17][18]. These studies have been conducted under consideration of the transmutation and radioactive decay of all heavy metal isotopes with high precision in S 8 -P 3 energy groups using 238 neutron groups.…”