Design Study of Pb-Bi- and NaK-Cooled Small Deep Sea Fast Reactors

Akira Otsubo and Minoru Takahashi

N1-18, Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology

2-12-1 O-okayama, Meguro-ku, Tokyo 152-8550, JapanTel: 81-3-5734-2957, Fax: 81-3-5734-2957,

E-mail: mtakahas@nr.titech.ac.jp

Abstract – The liquid lead-bismuth eutectic (Pb-Bi) has good compatibility with water, which is different from sodium.

It is expected that the Pb-Bi could be used as a coolant of the deep sea fast reactor (DSFR).

Physics analysis of the Pb-Bi-cooled small reactor cores with and without inner control rods was performed. The coolant of Pb-Bi seems to be good as well as NaK for DSFR

301010.10.010.0011W

10W

100W

1kW

10kW

100kW

1MW

10MW

100MW

TERM(YEAR)

Fixed Pointlong termcontinuousobservation

Medium-sizedsubmersible

Small deep sea submersible

Remotely operated vehicle

Sea bottomphotographing

Mother ship of submersibleSea bottom oil exploitation

Large scale fixedpoint continuousobservation

Mineralsourcemining

Fig. 1 Demand of electric power for activities in the sea

Nuclear powerHeat engine

Storage battery RI

RI & Heat engine

0.001 0.01 0.1 1 3010

Fuel cell

1W

10W

100W

1kW

10kW

100kW

1MW

10MW

TERM(YEAR)

DSFR

Fig. 2 Supply of electric power

Fig. 3 Schematic of the deep sea fast reactor (DSFR)

Fig.4 Structure of DSFR with power of 40kWe

Fig. 5 DSFR with power of 200kWe

Item NaK Pb-BiWeight 64 t 67.5 t

S.S.corrosion Twice as high as in sodium

Higher than in NaK

Coolant & sea water reaction

Violent reaction.

No reaction(right)

several hundreds kW15th from the bottom

Core immersion accident

Re liner in cladding required

No liner required

Neutron economy

Good Excellent

Coolant freezing at the sea lowest temp. of 2ºC

No freezing due to melting point of -12ºC

Freezing. Heating with NaK reactor required

Table 1Comparison ofNaK- & Pb-Bi-cooled 200kWeDSFRs used in the 6km-deep sea

Fig. 7 Sea bottom base using acoustic tomography system

Fig. 8 Sea bottom observation base with AUVs

AbsorberReflector

Core

Control Drum

AbsorberReflector

CoreCont. Rod

Control Drum

(a) Reactor without control rods inside core

(b) Reactor with control rods inside core

Fig.10 Schematics of Pb-Bi-cooled and NaK-cooled reactors

(a) Reactor without control rods inside core

(b) Reactor with control rods inside core

Fig. 11 Analytical systems of Pb-Bi-cooled and NaK-cooled reactors

Without inner cont. rods

With innercont. rods

FuelNitride fuel UN-PuN UNPu fraction 50wt.% 0wt.%

Enrich. of U235 20% 20-60%Enrich. of N15 100% 100%

Fuel pel. Outer diameter 5.56mm 5.56mmSmear density 85% 85%

Fuel pin cladding

Material SUS316 SUS316Outer diameter 6.5mm 6.5mmThickness 0.47mm 0.47mm

Re liner in cladding Exist. or not Exist. or notFuel pin pitch 7.3mm 6.5, 7.3mmAxial reflector Be，SUS316 Be, cladding,

coolantCore radius 10.5-14.5 cm 20.0cm

Table 2 Analytical parameters

10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 14.0 14.5

0.860.880.900.920.940.960.981.001.021.041.061.081.101.121.141.16

Keff

Radius cm

NaK SUS NaK SUS Re liner PbBi SUS NaK Be NaK Be Re liner PbBi Be

Fig. 12 Dependence of effective multiplication factor Keffon core radius in the reactor without control rodsinside core

15 20 25 30 35 40 45 50 55 60 65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

1.25

1.30

Keff

U235%

PbBi Pi:7.3mm NaK ditto. NaK ditto. Re liner PbBi Pi:6.5mm NaK ditto. NaK ditto. Re liner

Fig. 13 Dependence of Keff on enrichment of U235

in the reactor with control rods inside core

0 1000 2000 3000 4000 5000 6000

0.970.980.991.001.011.021.031.041.051.061.071.081.091.101.111.121.13

Keff

Days

PbBi NaK

Fig. 14 Change in Keff with burn-up in the reawithout control rods inside core

300 400 500 600 7000

2

4

6

8

10

12

14

16

18

20

22

24

Thermal efficiency %

Temperature C

Fig. 15 Thermal efficiency and turbine inlet temperature

V. CONCLUSIONS

Development of two types of small reactors is desired. One is the NaK-cooled reactor for about 40 kWe and the other is the Pb-Bi-cooled reactor of a few hundreds kilowatts to a few megawatts to a few megawatts used as the DSFR.