Effective Application of Partitioning and Transmutation Technologies to Geologic Disposal Joonhong Ahn Department of Nuclear Engineering University of California, Berkeley Tetsuo Ikegami O-arai Engineering Center, Japan Nuclear Cycle Development Institute, Japan November 9-11, th Information Exchange Meeting, OECD/NEA Las Vegas, Nevada

Background Effects of P/T on safety of a geologic repository have been measured by –the radiological exposure dose rate, which is insensitive to P/T application due to solubility-limit mechanisms –the radio-toxicity of solidified HLW, which does not indicate repository performance. Performance of geologic repositories assessed by considering canister-multiplicity shows that –initial mass loading of toxic radionuclides and canister-array configuration in the repository affect repository performance, and –environmental impact, if it is measured as radiotoxicity of radionuclides existing in the environment, can be reduced by reducing the initial mass loadings of radionuclides in a waste canister.

Objectives of the present study To develop models for evaluation of environmental impact as functions of –repository-configuration parameters, –radionuclide-mobility parameters, and –waste-package parameters. To investigate quantitative relationships, for LWR and for FBR –between the capacity and environmental impact of the repository, and –between the initial mass loadings of radionuclides in waste canisters and environmental impact of the repository.

Environmental Impact from nuclide i Radionuclide mass: M i (t) repository Uncontaminated groundwater Environmental Impact, Contaminated groundwater NyNy NｘNｘ Mass loading in a canister P i is the ratio of the peak mass in the environment to the total initial loading in the repository, of radionuclide i.

Mass of Np-237 in Environment Peak

Mass of Cs-135 in Environment Rp=1.3 ep=0.5 K = 48 e=0.3 S=0.905 m2 D=10 m V=4.525 m3 L=0.98 m V=1 m/yr TL=10,000 yr h.l. = 2.3E6 yr Mo=3.48 mol/can Peak

Formulas for Factor P i P i is a function of: –canister-array configuration, such as N x, –repository design, such as engineered-barrier dimensions, –radionuclide-transport parameters, such as groundwater velocity, solubilities, diffusion coefficients and retardation factors of radionuclides, –waste-package parameters, such as package failure time, initial mass loadings of radionuclides, waste-matrix dissolution time. Two analytical formulas have been derived: –for congruent-release radionuclides, and –for solubility-limited release radionuclides.

Waste conditioning model to determine initial mass loading in waste package the waste composition In a canister Canister dimensions Radiation conditions the radionuclide composition vector from separation process Number of canisters Repository conditions Storage conditions Materials conditions Repository performance

HLW Glass Mass: canister Composition vector: Solidification of HLW (r = HLW loading fraction) Solidified Waste Mass:

Standard form of LP problem Linear Programming (LP) Model where c = row vector of coefficients of objective function, x = column vector of independent variables, A = matrix of coefficients of constraint inequalities, b = column vector of RHS of constraint inequalities. Objective function Constraints LP model for optimizing HLW conditioning - For objective function: c = [1, 0], x = [M W, M G ] T - For constraints: A and b are determined based on regulations/specifications imposed on solidified HLW products.

Canistered waste weight ≤ 500 [kg] Canistered waste fill height ≤ volume of an empty canister V can = 0.15 m 3 Canistered waste heat generation ≤ 2300 [W/canister] MoO 3 content ≤ 2 wt% Na 2 O content ≤ 10 wt% HLW loading ≤ 25 wt% Considered Constraints for JNC-HLW

Filled canister weight Filled HLW glass volume (Approximate) HLW loading limit Heat generation Mo-limit Na-limit (1) (2) (6) (4) (5) (3) Summary of Constraints

M G [kg] M W [kg] (Heat) (Filled waste volume) (Filled canister weight) (25 wt% waste loading) (Mo- limit ) (Na- limit ) (1) (3) (2) (6) (4) (5) Graphical representation of optimum

Composition Vector of HLW Glass Product: = composition vector of HLW before vitrification (known) = composition vector of glass frit before vitrification (known) r = HLW waste loading fraction (determined by LP model) where For r = 0.25 Canisters produced from 1 MTU of PWR-Spent Fuel = The amount of HLW from 1 MTU of PWR-spent fuel [kg] The amount of HLW loaded into a canister [kg] = HLW Glass Compositions & Number of Canisters per ton

PWR vs FBR PWR –0.79 canister/MT –11.7 GWd-e/canister –1420 GWy for 40,000- canister repository FBR –1.25 canister/MT –21.3 GWd-e/canister –2590 GWy for 40,000- canister repository

Environmental impact from 40,000 canister repository (LWR)

Environmental impact from 40,000 canister repository (FBR)

Initial mass loading vs. EI

EI from Repository LWR only –1.7E8 m 3 /GWy LWR + P/T that reduces Np+Am by a factor of 200 –4.0E6 m 3 /GWy FBR –4.4E6 m 3 /GWy

Toxicity of depleted uranium and mill tailings 1GWyr(e), LWR, Thermal efficiency 0.325; Capacity factor 0.8; 33GWday/ton; 27.4 ton of 3.3% enriched U fuel; Reprocessing; 26 ton of recovered U returned to enrichment; Depleted U from enrichment contains 0.3% of U-235; Mill tailings contain all decay daughters of uranium isotopes that were in secular equilibria in the ore and 7% of U isotopes; 181 tons of natural uranium in the ore.

EI from Repository + Depleted Uranium LWR only 1.7E8 m 3 /GWy + 1.0E10 m 3 /GWy = +1.0E10 m 3 /GWy LWR + P/T that reduces Np+Am by a factor of E6 m 3 /GWy + 1.0E10 m 3 /GWy = +1.0E10 m 3 /GWy FBR that consumes 1 ton of DU/GWy 4.4E6 m 3 /GWy – 5.3E7 m 3 /GWy = – 4.9E7 m 3 /GWy

Summary If a P/T system is applied to the LWR system to reduce the environmental impact from the repository, the target nuclide would be Np-237 and Am-241. The reduction of these nuclides would be meaningful until the environmental impact of Np-237 is reduced to the level of environmental impacts of dominating FP nuclides, such as I-129 and Cs-135. The repository filled with 40,000 HLW canisters from FBR operation would result in the environmental impact smaller than that from the LWR repository by a factor of 20. If compared on a per GWyear basis, the advantage of FBR is even greater (a factor of 40). Because the dominating radionuclides are FP nuclides, P/T application for a FBR system to reduce actinides is not attractive. The possibility of decreasing the environmental impact from the entire cycle, including legacy depleted uranium, by the FBR system has been indicated. On the other hand, with the LWR + P/T system, depleted uranium will continue to be generated and dominate the environmental impact.