Effective Application of Partitioning and Transmutation Technologies to Geologic Disposal

Effective Application of Partitioning and Transmutation Technologies to

Geologic Disposal

Joonhong AhnDepartment of Nuclear Engineering

University of California, Berkeley Tetsuo Ikegami

O-arai Engineering Center, Japan Nuclear Cycle Development Institute, Japan

November 9-11, 20048-th Information Exchange Meeting, OECD/NEA

Las Vegas, Nevada

Background• Effects of P/T on safety of a geologic repository have be

en 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 conf

iguration in the repository affect repository performance, and – environmental impact, if it is measured as radiotoxicity of radionu

clides 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: Mi(t)

repository

Uncontaminated groundwater

Environmental Impact,

Contaminated groundwater

Ny

Nｘ

310 3

/s 1000 g kg /molm -water kg-nuclide

g/mol 3.7 10 Bq/Ci MPC Ci mi A

ii i

NC

M

ˆ oiMMass loading in a canister

ˆi ix i

oy iMI N N C P

Pi is the ratio of the peak mass in the environment to the total initialloading in the repository, of radionuclide i.

Mass of Np-237 in Environment

1.E-4

1.E-3

1.E-2

1.E-1

1.E+0

1.E-1 1.E+0 1.E+1 1.E+2 1.E+3

Normalized time

Nor

mal

ized

mas

s of

Np-

237

in e

nviro

nmen

t

Nx=10

Nx=100

Nx=1

Initial mass loading per canister = 3.9 molPeak

Mass of Cs-135 in Environment

1.E-5

1.E-4

1.E-3

1.E-2

1.E-1

1.E+0

1.E+1

1.E+2

1.E+3

1.E+0 1.E+2 1.E+4 1.E+6

time, year

Mas

s in

env

ironm

ent,

mol

Nx=1

Nx=10

Nx=200 Rp=1.3ep=0.5K = 48e=0.3S=0.905 m2D=10 mV=4.525 m3L=0.98 mV=1 m/yrTL=10,000 yrh.l. = 2.3E6 yrMo=3.48 mol/can

Peak

Formulas for Factor Pi

• Pi is a function of:– canister-array configuration,

• such as Nx,– 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 radionuclidecomposition vector

from separation process Number of canisters

Repository conditions

Storage conditions

Materials conditions

Repository performance

HLW Glass

Mass: Mass:

canister

GWS MMM

Composition vector:

Composition vector: Composition vector:

Solidification of HLW

Wn Gn

(1 )S W Gr r n n n(r = HLW loading fraction)

Solidified Waste

Mass:

WM GM

Standard form of LP problem

Linear Programming (LP) Model

0xbAxcx

andtosubject

fMaximize ,

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 = [MW, MG]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 Vcan = 0.15 m3

Canistered waste heat generation ≤ 2300 [W/canister]

MoO3 content ≤ 2 wt%

Na2O 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

kgMM GW 400

073

GW MM

][3.238 kgMW

0544.0 GW MM

0417.0 GW MM

4.547508.1 GW MM

(1)

(2)

(6)

(4)

(5)

(3)

Summary of Constraints

MG [kg]

MW [kg]

200

400

200 400

400 GW MM

600

600

800

800

(Heat)

(Filled waste volume)

(Filled canister weight)

(25 wt% waste loading)GW MM 333.0

(Mo- limit )GW MM 544.0

(Na- limit )GW MM 417.0

kgMMax W 0.99%)0.25( wt

4.547508.1 GW MM

3.238WM

(1)

(3)

(2)

(6)

(4)

(5)

Graphical representation of optimum

Composition Vector of HLW Glass Product:

GWWG NrNrN

)1(

WN

= composition vector of HLW before vitrification (known)

GN

= composition vector of glass frit before vitrification (known)

r = HLW waste loading fraction (determined by LP model)

where

GWWG NNN

75.025.0 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]

78.12 [ ] 0.79 [Can/MT]99.0 [ ]

kgkg

=

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 repositoryLWR (mol/canister) FBR (mol/canister) Nuclide

Lumped Lumped Am 243 4.35E-1 3.04E-3 Pu 239 1.55E-2 4.51E-1 1.93E-1 1.96E-1 Pu 241 3.67E-3 1.20E-2 Am 241 9.27E-1 7.23E-3 Np 237 2.04E+0 2.97E+0 1.12E-3 2.04E-2 I 129 1.28E+0 2.58E+0

Cs 135 2.64E+0 1.39E+1 Tc 99 7.06E+0 1.05E+1

Environmental impact from 40,000 canister repository (LWR)

1.E+07

1.E+08

1.E+09

1.E+10

1.E+11

1.E+12

1 10 100 1000

Number of canisters connected in a row, Nx

Env

ironm

enta

l im

pact

, m3 , f

rom

repo

sito

ry

Np-237

Pu-239

Tc-99

I-129

Cs-135

after reduction ofAm and Np by 1/100

Environmental impact from 40,000 canister repository (FBR)

1.E+07

1.E+08

1.E+09

1.E+10

1.E+11

1.E+12

1 10 100 1000

Number of canisters connected in a row, Nx

Env

ironm

enta

l im

pact

, m3 , f

rom

repo

sito

ry

Np-237

Pu-239

Tc-99

I-129

Cs-135after reduction of

Am and Np by 1/100 and Pu by 1/10

Initial mass loading vs. EI

1.E+8

1.E+9

1.E+10

1.E+11

1.E+12

1.E-3 1.E-2 1.E-1 1.E+0 1.E+1Initial mass loading per canister, Mol

Env

ironm

enta

l im

pact

, m3 , f

rom

rep

osito

ry Np-237

Pu-239

40,000 canisters of HLWin a repository

Initial loading in a canisterfrom LWR spent fuel

Initial loading after reductionof Am and Np by a factor of100 from LWR canister

Initial loading in a canisterfrom FBR spent fuel

Initial loading after reductionof Am and Np by a factor of100 and Pu by a factor of 10from a FBR canister

EI from Repository

• LWR only– 1.7E8 m3/GWy

• LWR + P/T that reduces Np+Am by a factor of 200– 4.0E6 m3/GWy

• FBR– 4.4E6 m3/GWy

Toxicity of depleted uranium and mill tailings

1.E+4

1.E+5

1.E+6

1.E+7

1.E+8

1.E+9

1.E+10

1.E+11

1.E+2 1.E+3 1.E+4 1.E+5 1.E+6 1.E+7 1.E+8Time, year

Toxic

ity (m

3 -wat

er) p

er G

Wy

Total

Pb210Po210Ra226

Th230

Ac227

Pa231

U238

Ra223

U235

Bi210

Th227

U234

Depleted U

1.E+4

1.E+5

1.E+6

1.E+7

1.E+8

1.E+9

1.E+10

1.E+11

1.E+2 1.E+3 1.E+4 1.E+5 1.E+6 1.E+7 1.E+8Time, year

Toxic

ity (m3 -w

ater

) per

GW

y Total

Pb210Po210

Ra226Th230

Ac227

Pa231

U238, U234

Ra223

U235

Bi210

Th227

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 only1.7E8 m3/GWy + 1.0E10 m3/GWy = +1.0E10 m3/GWy

• LWR + P/T that reduces Np+Am by a factor of 2004.0E6 m3/GWy + 1.0E10 m3/GWy = +1.0E10 m3/GWy

• FBR that consumes 1 ton of DU/GWy4.4E6 m3/GWy – 5.3E7 m3/GWy = – 4.9E7 m3/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.