Thermodynamic performance of a gas core fission reactor

418

Journal of Nuclear Materials 130 (I 985) 4 I8425 North-Holland, Amsterdam

THERMODYNAMIC

PERFORMANCE

W. BOERSMA-KLEIN, FOM-Institute

OF A GAS CORE FISSION

F. KELLING,

for Atomic

REACTOR

J. KISTEMAKER

and Molecular

Physics,

Kruislaan

407,

1098 SJ Amsterdam,

The Netherlands

and R.J. HEIJBOER Westerduinweg

nr. 3, 1755 LE Petten, The Netherlands

In this work we investigated the thermodynamic behaviour of fission products and plutonium as obtained in a gas core fission reactor with graphite walls and operated at 1200 MW thermal power. Equilibrium compositions of the system U-C-F-Pu-fission products were calculated for pressures of 0.1 MPa and 2.5 MPa and temperatures of 1300 K to 10000 K. We found that the reactor can be operated at a pressure of 2.5 MPa and a wall temperature of 2500 K without condensation of any component; no carbides are formed. The main plutonium compound is PuF4 which, from thermodynamic point of view, can be recycled with UF4.

1. INTRODUCTION

the corresponding

The basic principles of a gas core fission

and operating

reactor,

conditions

build-up

of gra-

formed,

fluorine

the fuel composition

lation possibilities,

phite and using uranium fluoride as a fuel were treated previously 1,2,3 . It is shown that such

positions

a reactor,

2. FUEL COMPOSITION

based on an energy

MWth, can be operated

hold up of 0.6 ton uranium

UF4 and 30% CF43. Briefly,

lindrical diameter

(30% enriched).

of a cy-

by a layer of graphite

100 cm thick, which acts as moderator is divided

the two end sections ed by cooling pressurized

the temperature

rods of carbon,

helium

rises in the center

In

is regulat-

In the middle

is applied;

the tempe-

to about 25000 K, but

the wall has to be kept at 2500 K. Because

of

the high temperature

there

is a plasma,

in the middle

section

from which energy can be extracted

by means of electromagnetic

mainly on the inventory

of the fission

and the relative

the thermodynamic

abundances

ducts which are formed

perfor-

reactor described

of the fission

to operating

times of

50 hours till IO years and the inventory fission

products

by applying nuclear

data required

computer

about

program.

for the calculation

were based on the reactor

as calculated

temperature

The

of the neu-

for this type of reThe effective

actor by v. Dam and Hoogenboom5. neutron

of the

up to 200 hours were calculated

the "ORIGEN"4

tron spectrum

pro-

in our system. The fuel

corresponding

in the thermal region was

1300 K.

The cross sections uranium,

plutonium

of the main isotopes of

and neptunium

were calculated

the code FOUR ACES and using the da-

ta files ENDF/BIV

products,

the isotope

B.V.

OF THE FISSION

above, we needed data about the fuel composition

ourselves

0022-3 115/85/$03.30 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)

AND INVENTORY

mance of the gas core fission

by applying

induction.

In the present work we concentrated

com-

of 10000 K.

PRODUCTS

fuel composition

through which

is circulated.

section only wall cooling rature

reflector.

into three sections.

with its recircu-

up to temperatures

composition

having a length of 24 m, a

of 3 m surrounded

The cylinder

The

of 70%

which are

and the equilibrium

In order to analyze

from a point of view

the reactor consists

vessel,

of

of 2.5 MPa and a

in the reactor consists

of construction,

of 1200

at a wall temperature

about 2500 K, at a pressure

gaseous mixture

production

compounds

and ENDF/BV.

species the nuclear

For the rest of data were ob-

419

W. Boersma-Klein et al. /A gas core fission reactor

tained from the LWR library of the ter program ditions

and corrected

for the operating

Table

con-

of the gas core reactor.

In the calculations computer

program

operating keeping

performed

of the gas core reactor by

the inventory

of the fissile components

performed

with different

amounts

In these preliminary

assumed

computations

that the feed consists

this latter va-

from various

points of

view, we could draw some conclusions bulk composition thermodynamic composition

it was

of uranium en-

riched from 35% to 90%. Although lue is not practical

were

of feed and

calculations

about the

total

665

Np total

21

1

Pu total

28

20

Am total

2

4

Cm total

3

7

U

described

tonium and neptunium

together

below. This

non-proliferation.

I.

requires

able in this reactor.

a factor ten more material

was about 4-7% of

these isotopes

the total amount of heavy metals.

In Fig. 1 we

tonium while

give the inventory

and plutonium

is about 67-82%

obtained

of the uranium

as a function

of operation

PUCK', PUCK', which

aspect

%

is a

an operation

is about

15-30% of the total plu-

in the gas core fission

products

obtained

in Table

II.

In Table III

0.23 0.24 0.021 0.0046

Uranium

YEARS

235 gU/s (35%U235) g IJ/s(~O%U~~~) gU/s(90%U235i gU/s (3O%U

and plutonium

235 Feed: 0.021 gU/s (90%U235i Drain: O.O046gU/s(3O%U

FIGURE 1 isotope vector as a function

Feed: 0.23gU/s Drain: 0.24gU/s

of operational

recycling

after

compounds,

YEARS

time

it

with

we give their

U 238

Feed: -'Drain: Feed: -(Drain:

reactor

time of 200 hours, together

their assumed most stable fluorine given

than avail-

In a LWR the amount of

The amount of fission

It has

isotopes

from a point of view of

YEARS

__

time.

that the main plutonium

are Pu238,

very favourable

A bomb of this composition

the amount of plu-

is given in Table

In all of the calculations

isotopes

549

of the fuel to be used in the

calculations

to be remarked

Feed: 0.23 (35% LJ3$' Drain: 0.24 g U s (30% u23 6 )

Feed: 0.021 (90% uj3u5js Drain: 0.0046 u/s (30% u2 ! 5)

the

conditions

Herefore

I. Fuel composition (Kg) after 5 years of operation at constant reactivity 1200 MWth. Initial inventory: 600 Kg U (30% U235)

with the ORIGEN

it was aimed to simulate

and of U235 constant.

drain.

ORIGENcompu-

is

total thermal

decay power and their radioactivi-

ty up to a periode of one year. From the fission

products

we selected

some

typical ones with regard to their volatility relative abundances. refreshment

Different

of the fission

their concentration

of one of the

products.

Thermal decay power KW

-~ Radioactivity MCurie

initial

7.27x 104

5240

IO min

2.27~

lo4

2370

I day

0.25~

lo4

520

after a time of

Therefore

must remain small and they

hardly will have any influence economy

and

from a LWR the

time of the fuel is only determined

by the danger of condensation fluorides

Table III. Thermal decay power and radioactivity of the fission products extracted from the reactor after an operation time of 200 hours; total amount of fission products 1.05~ 104 g,

on the neutron

in this type of reactor.

1 year Table

II.

Inventory

Element

Atomic weight

of the most abundant quantity of fission products in grams

fission

products

in case of a refreshment

For the element _I b oiling ’ point vapour pressure in Kelvin at2500 Kin Torr

Br

79.9

8

330

Kr

83.7

147

120

1.7

time of 200 hours

For the molecule moleboiling point cule in Kelvin

gas

Br2

330

gas

Kr

120

Rb

85.5

137

960

gas

RbF

1700

Sr

87.6

579

1650

gas

SrF2

2760

Y

88.9

252

3000

N IO

yF3

1660

Zr

91.2

1320

4600

1om2

ZrF4

1179*

Nb

92.9

15

4950

1o-5

NbF5

500

MO

96.0

880

4900

1O-3

MoF4

?

Tc

99.0

163

5150

1o-3

?

?

Ru

101.7

664

4200

1oe2

RuF5

520 _-

Sn

118.7

9

2550

102

SnF4

1000

Sb

121.8

8

1950

103

SbF3,5

500

Te

127.6

240

I260

high

TeF4

660

J

126.9

232

457

gas

J2

457

Xe

131.3

1620

166

gas

Xe

166

cs

132.9

513

960

high

CaF

Ba

137.4

742

1910

high

BaF2

2410

La

138.9

446

3700

-2

LaF3

‘..2500

Ce

140.1

1190

3450

-1

CeF3

2570

1520

Pr

140.9

287

3450

- 20

?

?

Nd

144.3

764

3450

N IO

NdF3

2570

Pm

145.0

63

3200

- 50

?

?

Total production * Sublimation

1.05. IO4 grams

point

421

W. Boersma-Klein et al. / A gas core fission reactor given elsewhere7.

3. EQUILIBRIUMCOMPOSITIONS The method equilibrium nimization system

applied

compositions method.

cal potentials

is the free energy mi-

as a function

Eriksson's

compositions

of the in-

the equilibrium

"SOLGASMIX"6

used. Two sets of calculations 1) Equilibrium

of the chemi-

and the mole fractions

species. To calculate

compositions

of the

The total free energy of the

is expressed

dividual

for the computation

program was

were performed:

in the temperature

range 1300 K to 4500 K. 2) Equilibrium

compositions

Equilibrium

nium, plutonium

and neptunium,

those given in Table thermodynamic

tunium fluorides

the corresponding

to those obtained 1) Equilibrium range

compositions

in the temperature

pressures

compositions

were calculated

for

200 hours, as given

it

compositions,

and several condensed

dynamic

The thermo-

data used for these calculations

are

investigated

of certain

the possibi-

species. There-

of the equilibrium

we considered

consisted

time of

II.

we included

fore in the calculations

with

viz. solid carbon.

thermodynamic

products correspond

in Table

tures up to 2400 K and 2800 K respectively

the reactor wall,

of simplicity of plutonium

after a refreshment

was assumed

that the gas is in equilibrium

and nep-

compounds.

lity of condensation

of 0.1 MPa and 2.5 MPa. For tempera-

were

were those of plutonium

In our calculations

1300 K to 4500 K.

Equilibrium

of plutonium

abundances

considered

and its fluorine

of ura-

considered

and for purposes

we added the relative and neptunium;

for

I. Because of the similar

properties

The amounts of fission

range 4500 K to 10000 K.

were calculated

of about 27% CF4, 68%

UF4 and 5% PuF4 and NpF4. The amounts

properties in the temperature

compositions

a gas phase composition

one gaseous mixture

phases. The total system of 52 species,

as given

below.

2.5 MPa

2cioo

3000 Temperature K

FIGURE 2 Equilibrium composition of the system U-C-F-Pu-fission products. "PuF3' and "PuF4" refer to the sum of the plutonium and neptunium compounds. ----- condensed species; gas species.

422

W. Boersma-Klein et al. / A gas core fission reactor

P = 2.5 MPa 0.8 0.6 .k 0.4 ti / z 0.2 IL w

s z

0.1-

4500

6000

8000 Temperature

to000

K

P= 2.5 MPa

0.008-

g 0.006.2 Lk 0.004W z ZE

0002-

Temperature

Equilibrium

composition

K

FIGURE 3 of the system U-C-F at high temperatures

423

W.Boersmu-Klein et al. / A gas core fission reactor

Gaseous

mixture

UF,

:

n=O-6;

CF,,

:

n= 1-4;

LaF,:

n= O-3;

consisting C

:

n

'ZF2n' SrF, :

data used in these calculations

of: n= l-5;

ble IV.

n= l-3;

cluded

n= O-2;

UF,

:

CF,

:

BaF,:

n= O-2;

PuF,

:

n= 0,3,4,6;

ZrF,:

n= 0,4;

LaC,

:

n=2.

F

n= 1,2;

:

Pure eventually

condensed

number of condensed

compositions

as ob-

species

we present

moles of component

not given. The relative ponents occuring the equilibrium total pressure

:

n= l-5;

at total pressures for a pres-

abundance

not given. Only

is taken into considera-

tion. of 0.1 MPa all the processes

and ionization

lower temperatures;

are shifted

dissociations

to

of CF4 and UF4

i, divii.

than 0.01 are of the com-

in minor amounts, compositions

n= l-2.

gas, no solid phase,

of dissociation

the

ded by the total number of moles of component smaller

Fn n

sure of 2.5 MPa are given in Fig. 3. Mole frac-

of the condensed

mole fractions

n=O-5;

were performed

For a pressure

The mole fractions

UF+: n C :

tions smaller than O.OOOl'are

in Fig. 2.

Actually

n=l-4;

Calculations

of 2.5 MPa are given

refer to the pure components;

are given in Taspecies were in-

of 0.1 and 2.5 MPa; results obtained

UC2' U2C3, LaC2, PuF4, PuF3, Pu equilibrium

n=O-6;

C2F2n' F-, C-, e-;

UF4, UF3, LaF3, SrF2, BaF2, ZrF4, C, UC,

The resulting

gaseous

in the calculations:

n=l-3;

phases:

tained for a total pressure

The following

as well as

corresponding

1

P~2.5

“E

MPa

0

3

0.8

to a

of 0.1 MPa are given elsewhere7.

As it can be seen from Fig. 2, condensation

of

SrF2, BaF2, LaF3, UF4, PuF3 occurs below a temperature

of about

2200 K at a pressure

MPa. At a pressure

of 0.1 MPa condensation

curs below a temperature

2) Equilibrium

of 2.5

of about

compositions

oc-

1900 K.

is j

in the temperature

o.2L 2

range 4500 K to 10000 K. Equilibrium

compositions

were calculated

initial gas phase composition UF4 and 30% CF4. Sources Table

consisting

Number density of temperature

IV. Sources of thermodynamic

Component UF,: n-1-6 UF;: n= O-5 UF,: n= l-6

data used for the calculations range 4500 K to 10000 K

Thermodynamic

property

Heat of formation

8

UF,: n=O-6 UF;: n=O-5

Difference

between

heat of forlo

FIGURE 4 of uranium atoms as a function

of the equilibrium

Component

at 298 K

mation at 298 K and 0 K

8 10 K(x103)

for an of 70%

of the thermodynamic

the temperature

4 6 Temperature

Thermodynamic '1 I

compositions

in

property

Free energy function'

C-F compounds

Standard

C-, F-, e-

mationl'

free energy of for-

424

W. Boersma-Klein et al. /A gas core fission reactor

start at temperatures pectively,

while

of 1600 K and 2400 K res-

ionization

of UF, components

Actually

we are investigating

tions which

starts at a temperature

of 4300 K. In Fig. 4 we

interested

give the number density

of the uranium atoms as

CF4 and the fission

a function

of temperature.

we accounted presented

In these calculations

for dissociation

in figures

and ionization

as

2 and 3 above.

mainly

tal fluorides separation fluoride

in the possibility products

of uranium

In Table composition

partial

of the fuel for different

most critical

conditions

pressure

It has to be emphasized

that

and relative

these values are the result of preliminary

cal-

vapour

which were performed

in order to get

about the performance

type of reactor. dynamic

from plutonium

is required.

I and Fig. 1 we give the isotopic

some estimates

fluoride

In this case no

are based on a refreshment

time of 200 hours limited by the maximum

of feed and drain.

culations

to separate

from the heavy me-

by centrifugation.

Our calculations 4. DISCUSSION

the unit opera-

should be used in the cycle. We are

Nevertheless,

calculations,

of this

for the thermo-

which were the main pur-

pose of our work, they are satisfactory. over, they give us the possibility

more detail the fuel cycle connected type of reactor.

More-

to study in

of SrF2. This compound

plutonium where7.

is the

from a point of view of volatility abundance.

pressures

the fission

allowed

Detailed

figures about

and the partial pressures

product

fluorides

tri and tetra fluorides

At a wall temperature

still a factor

are givenelse-

of 2500 K we are

five below the vapour

SrF2. Therefore

temperature

at a total pressure

of

and of uranium and

pressure of

excursions

of 200 K

of 2.5 MPa are allowed.

to this

In Fig. 5 we give a block dia-

5. CONCLUSIONS We have demonstrated

gram of such a fuel cycle.

sures of the fission

(2)

in a gas-core-fission

that the partial

product-fluorine reactor

pres-

compounds

(with a hold-up of

70% UF4 and 30% CF4), after 200 hours operation at 1200 MW thermal

8 5 30 TJ* ,I

L Reprocessing t Feed

Separator

sures. Therefore, products

ZLZ .&z Purifier

mation

fission produ;ts

CF,

I

J

(2)

1.51

x IO-~

moles/set

U CFL

FIGURE 5 Block diagram of a gas fuel cycle.

No foroccurs. beha-

with the in-

ones and with Sr, Ba, Zr compounds, formation

either of

these components. fluorine

compound

with UF4. No condensation

ly five main species exist,

about65%

is

and recycled

will occur. At a pres-

sure of 2.5 MPa and a temperature

the whole mixture

formed

point of view, thiscom-

pound can easily be reprocessed

actinides

3.45 x 10-3moles/sec

compounds

we don't expect any carbide

PuF4. From thermodynamic

(11 UFL+CFL+

carbides

of the thermodynamic

viour of other rare-earth

pres-

of fission

inside the reactor.

of uranium and lanthanum

From the similarity

The plutonium

7I Make- up CFL

no condensation

is expected

vestigated

PI Waste

power at 2.5 MPa and 2500

Kelvin are below their correspondingvapour

of 10000 K on-

viz. C,F,U,U+,e-;

is practically

dissociated

and

of the original IAraniumatoms are ionized.

W. Boersma-Klein et al. /A gas core fission reactor

425

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