Survey of Space Nuclear Power Options

Dr. Andrew KadakAnd Peter Yarsky

MIT12.11.03

Dec 10th and 11th , 2003 MIT 22.033 / 22.902, Mission to Mars

Introduction

The goal of current work at MIT is to identify potential Power Conversion Options with use of an Ultra High Power Density Core (UHPDC) that will be scalable to achieve requirements for a plethora of exploration missions, eventually meeting the needs for a manned mission to Mars


The MIT - UHPDC

•Ultra High Power Density Core– Fast spectrum– Tightly coupled / leakage controlled– Reactor Grade Plutonium (PuC)

•~60% Pu239 / ~20% Pu240– Honey Comb Fuel Nb cladding– 20 cm x 20 cm x 20 cm– 10 – 11 MWth (liquid metal)

UHPDC Core Layout


Outline

•Power Conversion

–Thermophotovoltaics (st)

–Thermionics (st)

–Brayton Cycle (dy)

–Rankine Cycle (dy)


Thermophotovoltaics (TPV)

1. LM transfers the heat from the core to the internal radiator

2. All power is radiated towards TPV collector

3. TPV collectors generate DC from thermal radiation

4. Unconverted heat is dissipated via the external radiator


TPV Challenges

•TPV efficiency decreases with higher cell temperature

•The temperature of external radiator is the coldest the TPV cells can be (900 K)

• It is unlikely that TPV Power Conversion will be scalable.


Thermionic Converters (TIC)

• TIC Benefits

– Single or Dual Layered Concepts

– Static and Direct

– 12-15% efficiency for TH ~1200 K

– 25% or higher efficiency for TH ~2200 K

– Temperature of heat rejection is ~ 750 K

• TIC Challenges

– Direct Contact with the Fuel


Conceptual Unit Cell


TIC Comparison

•Low Temperature Single– 1200 K emitter / 750 K collector– 12% efficiency / 400 kWe

•High Temperature Dual– 2200 K emitter / 750 K collector– 25% efficiency / 900 kWe

•High Temperature Single– 2200 K emitter / 1200 K collector– 12% efficiency / 2500 kWe


Argon Brayton Cycle


Low Med High

T1 (low) 400 K 473 K 533 K

T2 665 K 780 K 890 K

T3 (high) 1200 K 1400 K 1600 K

T4 830 K 970 K 1100 K

Net Work 300 kW 560 kW 950 kW

Efficiency 0.20 0.19 0.20

Mass Flow Rate 5.5 kg/s 9.1 kg/s 13 kg/s

Reactor Power 1.5 MW 3.0 MW 4.9 MW

Pressure Ratio 3.18 3.13 3.18

Comparisons


Sodium Rankine Cycle

• Sodium because:

– 2100 R (1167 K) saturation temperature

at 15.4 psia (1.05 atm)

– Neutronic Inertness

– Heat Removal Properties (UHPDC)

– Saturation Curves are steep (scalability)

– Little Pumping Power Required

– Phase Transition (maximal radiator usage)


Results for 1200 K

Turbine Efficiency 0.95 0.9 0.85

Cycle Efficiency 11% 11% 11%

Turbine Work [MW] 1.18 MW 1.15 MW 1.14 MW

Turbine Outlet Pressure [psia]

4.0 3.7 3.2

ComparisonsT(hot) T(rej) Work Efficiency

TIC 1 (low T) 1200 K 750 K 0.4 MW 12%2 (high T) 2200 K 750 K 0.9 MW 25%1 (high T) 2200 K 1200 K 2.5 MW 12%

Ar Brayton 1600 K 850 K 0.95 MW 20%Na Rankine low T 1200 K 1000 K 1.1 MW 11%

high T 1500 K 1300 K 3.4 MW 13%TPV (MSFR) 1400 K 900 K 4 MW 40% **


Conclusions

• Dynamic PCU technology is more

effective and scalable than Static

(Sodium Rankine in particular)

• Static direct energy conversion

is still attractive from a

reliability standpoint (TIC in

particular)


BONUS SLIDES

•Slides in case we need clarification


Single Layer Concept1. LM flows through UHPDC2. LM heats the emitter3. Electrons flow towards

collector4. Collector is in direct

contact with external radiator


HEU alternative

•Less Reactive Fuel– Larger Core

•More Fuel Mass•More shielding Required

•No Fertile-Fissile Species (240Pu)– Larger Reactivity Swing

•More demand on Control Devices

•Work Still in Progress on CBA

Survey of Space Nuclear Power Options

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