Nuclear Reactors for The Moon and Mars

Martian Surface Reactor Group

December 3, 2004

Massachusetts Institute of Technology

Nuclear Engineering Department

M artian

S urface

R eactor Group

OVERVIEW

• Need for Nuclear Power

• Fission 101

• Project Description

• Description and Analysis of the MSR Systems

– Core

– Power Conversion Unit (PCU)

– Radiator

– Shielding

• Conclusion



MSR Group, 12/3/2004

Slide 2

Motivation for MSR

NASA Concept Exploration and Refinement Study

Surface Power

Lunar Surface Power Options

Chemical

Fission Reactor

Solar

Fission Reactor + Solar

Radioisotope +

Solar

Martian Surface Power

Options

- Solar power becomes much less feasible

- Mars further from Sun

(45% less power)

- Day/night cycle

- Dust storms

- Too-short Lifetime for

Martian missions

- Nuclear Power dominates curve for Martian missions.

Duration of use


Nuclear Engineering Department –


Slide 3

Need for Nuclear Power

Comparison of Solar and Nuclear Power on the Moon

2.5E+04

2.0E+04

1.5E+04

1.0E+04

5.0E+03

0.0E+00

0 50 100 150

Power (kWe)

200 250

Solar

Reactor




Slide 4

Fission 101




Slide 5

MSR Mission

• Nuclear Power for the Martian Surface

– Test on Lunar Surface

• Design Criteria

– 100kWe

– 5 EFPY

– Works on the Moon and Mars




Slide 6

Decision Goals

• Litmus Test

– Works on Moon and

Mars

– 100 kWe

– 5 EFPY

– Obeys Environmental

Regulations

• Extent-To-Which Test

– Small Mass and Size

– Controllable

– Launchable/Accident

Safe

– High Reliability and

Limited Maintenance

– Scalability




Slide 7

MSR System Overview

• Core (54%)

– Nuclear Components, Heat

• Power Conversion Unit (17%)

– Electricity, Heat Exchange

• Radiator (4%)

– Waste Heat Rejection

• Shielding (25%)

– Radiation Protection

• Total Mass ~8MT




Slide 8

CORE




Slide 9

Core – Goals and Components

• Goals

– 1.2 MWth

– 1800K

• Components

– Spectrum

– Reactivity Control

Mechanism

– Reflector

– Coolant System

– Encapsulating Vessel

– Fuel Type/Enrichment




Slide 10

Core - Design Choices Overview

Design Choice

Fast Spectrum, High Temp

UN Fuel, 33 w / o enriched

Lithium Coolant

Reason

High Power Density

High Temperature/Breeding

Power Conversion

Re Cladding/Internal Structure Physical Properties

Zr

3

Si

2

Reflector material Neutron “Mirror”

Rotating Drums Autonomous Control

Hafnium Core Vessel

Tricusp Fuel Configuration

Accident Scenario

Superior Heat Transfer




Slide 11

Core - Pin Geometry

• Fuel pins are the same size as the heat pipes and arranged in tricusp design.

• Temperature variation 1800-1890K

Fuel Pin

Heatpipe



Tricusp Material


Slide 12

Core – Design Advantages

• UN fuel, Ta absorber, Re

Clad/Structure high melting point, heat transfer, neutronics performance, and limited corrosion

• Heat pipes pumps not required, excellent heat transfer, small system mass

• Li working fluid operates at high temperatures necessary for power conversion unit

(1800K)




Slide 13

Core – Dimensions and Control

• Reflector controls neutron leakage

• Small core, total mass ~4.3 MT

42 cm

89 cm

Reflector

Core

Fuel Pin

10 cm

Reflector

Fuel

10 cm

Reflector




Slide 14

Core - Composition

Material Purpose

7

Li

15

N

Coolant

Fuel Compound

Nat

Nb Heatpipe

181

Ta Poison

Nat

Re Cladding/Structure

235

U Fissile Fuel

238

U Fertile Fuel

Volume Fraction

0.073

0.353

0.076

0.038

0.110

0.117

0.233




Slide 15

Core - Power Peaking

Peaking Factor, F(r)

1.4

1.2

1

0 .8

0 .6

0 .4

0 .2

0

- 2 2 - 2 0 - 18 - 16 - 14 - 12 - 10 - 8 - 6 - 4 - 2 0 2 4 6 8 10 12 14 16 18 2 0 2 2

RPPR

Drums In

Core Radius (cm)



1 .

31 RPPF

Drums Out



1 .

24




Slide 16

Operation over Lifetime

Reactivity over Lifetime

BOL k eff

: 0.975 – 1.027

 k eff

= 0.052

EOL k eff

: 0.989 – 1.044

 k eff

= 0.055

1.08

1.06

1.04

1.02

1.00

0.98

0.96

0.94

0 1 2 3

Years of Operation

4 5 6




Slide 17

Launch Accident Analysis

• Worst Case Scenario:

– Oceanic splashdown assuming

• Non-deformed core

• All heat pipes breached and flooded




Slide 18

Launch Accident Results

• Inadvertent criticality will not occur in any conceivable splashdown scenario

Water

Wet Sand

Reflectors Stowed

K eff

=0.970

K eff

=0.974



Reflectors Detached

K eff

=0.953

K eff

=0.965


Slide 19

Core Summary

• UN fuel, Re clad/structure, Hf vessel, Zr

3

Si

2 reflector

• Relatively flat fuel pin temperature profile 1800-1890K

• 5+ EFPY of 1.2 MW th

, ~100 kW e, at 1800K

• Autonomous control by rotating drums over entire lifetime

• Subcritical for worst-case accident scenario

• Mass : ~4MT




Slide 20

PCU




Slide 21

PCU – Mission Statement

Goals:

– Remove thermal energy from the core

– Produce at least 100kWe

– Deliver remaining thermal energy to the radiator

– Convert electricity to a transmittable form

Components:

– Heat Removal from Core

– Power Conversion/Transmission System

– Heat Exchanger/Interface with Radiator




Slide 22

PCU – Design Choices

• Heat Transfer from Core

– Heat Pipes

• Power Conversion System

– Cesium Thermionics

• Power Transmission

Reactor

– DC-to-AC conversion

– 22 AWG Cu wire transmission bus

• Heat Exchanger to Radiator

– Annular Heat Pipes




Slide 23

PCU – Heat Extraction from Core

• How Heat Pipes Work

– Isothermal heat transfer

– Capillary action

– Self-contained system

• Heat Pipes from Core:

– 127 heat pipes

– 1 meter long

– 1 cm diameter

– Niobium wall & wick

– Pressurized Li working fluid, 1800K




Slide 24

PCU – Heat Pipes (2)



• Possible Limits to Flow

– Entrainment

– Sonic Limit

– Boiling

– Freezing

– Capillary

• Capillary force limits flow:

Q m ax



 l

 l

L K A w

2

1 r e

 l l



 l g l sin ( )

 l


Slide 25

PCU - Thermionics

• Thermionic Power Conversion Unit

– Mass: 240 kg

– Efficiency: 10%+

• 1.2MWt -> 125kWe

– Power density:

10W/cm 2

– Surface area per heat pipe:

100 cm 2




Slide 26

PCU - Thermionics Issues &

Solutions

– Creep at high temp

• Set spacing at 0.13 mm

• Used ceramic spacers

– Cs -> Ba conversion due to fast neutron flux

Cs

133

( n ,



)



Cs

134 

Ba

134  

• 0.01% conversion expected over lifetime

– Collector back current

• T

E

= 1800K, T

C

= 950K




Slide 27

PCU – Thermionics Design




Slide 28

PCU – Power Transmission

– D-to-A converter:

• 25 x 5kVA units

• 360kg total

• Small

– Transmission Lines:

• AC transmission

• 25 x 22 AWG Cu wire bus

• 500kg/km total

• Transformers increase voltage to 10,000V

– ~1.4MT total for conversion/transmission system




Slide 29

PCU – Heat Exchanger to Radiator

• Heat Pipe Heat Exchanger




Slide 30

PCU – Failure Analysis

• Very robust system

– Large design margins in all components

– Failure of multiple parts still allows for ~90% power generation & full heat extraction from core

• No possibility of single-point failure

– Each component has at least 25 separate, redundant pieces

• Maximum power loss due to one failure: 3%

• Maximum cooling loss due to one failure: 1%




Slide 31

Radiator




Slide 32

Objective

• Dissipate excess heat from a power plant located on the surface of the Moon or Mars.



Q

 σεA



T s

4 

T

4








Slide 33

Environment

• Moon

– 1/6 Earth gravity

– No atmosphere

– 1360 W/m 2 solar flux

• Mars

– 1/3 Earth gravity

– 1% atmospheric pressure

– 590 W/m 2 solar flux




Slide 34

Radiator – Design Choices

• Evolved from previous designs for space fission systems:

– SNAP-2/10A

– SAFE-400

– SP-100

• Radiates thermal energy into space via finned heat pipes




Slide 35

Component Design

• Heat pipes

– Carbon-Carbon shell

– Nb-1Zr wick

– Potassium fluid

• Panel

– Carbon-Carbon composite

– SiC coating

Thermal Radiation

5 mm

Heat Pipe

Vapor

Channel

Exterior of Panel

3 mm




Slide 36

Component Design (2)

• Supports

– Titanium beams

• 8 radial beams

• 1 spreader bar per radial beam

Support

Anchor 6.54°

– 3 rectangular strips form circles inside the cone

Core

1.5 m

Radiator

Panel

1.25 m

Strips




Slide 37

Structural Design

• Dimensions

– Conical shell around the core

– Height 3.34 m

– Diameter 4.8 m

– Area 41.5 m 2

2.97 m

0.918 m

Radiator

Panel

2.34 m

• Mass

– Panel 360 kg

– Heat pipes 155 kg

– Supports 50 kg

– Total: 565 kg

Heat Pipe



0.60 m

Core & Shield

0.5 m 0.5 m

2.4 m


Slide 38

Shielding




Slide 39

Radiation Interactions with Matter

• Charged Particles ( α, β)

– Easily attenuated

– Will not get past core reflector

• Neutrons

– Most biologically hazardous

– Interacts with target nuclei

– Low Z material needed

•

Gamma Rays (Photons)

– High Energy (2MeV)

– Hardest to attenuate

– Interacts with orbital electrons and nuclei

– High Z materials needed




Slide 40

Shielding - Design Concept

• Natural dose rate on Moon &

Mars is ~14 times higher than on Earth

•

Goal:

– Reduce dose rate due to reactor to between

0.6 - 5.6 mrem/hr

• 2mrem/hr

– ALARA

• Neutrons and gamma rays emitted, requiring two different modes of attenuation




Slide 41

Shielding - Constraints

• Weight limited by landing module (~2 MT)

• Temperature limited by material properties (1800K)




Slide 42

Shielding - Design Choices

Neutron shielding Gamma shielding boron carbide (B

4

C) shell (yellow) Tungsten (W) shell (gray)

40 cm 12 cm

• Total mass is 1.97 MT

• Separate reactor from habitat

– Dose rate decreases as

1/r 2 for r >> 50cm

- For r ~ 50 cm, dose rate decreases as 1/r




Slide 43

Shielding - Dose w/o shielding

• Near core, dose rates can be very high

• Most important components are gamma and neutron radiation




Slide 44

Shielding - Neutrons

• Boron Carbide (B

4

C) was chosen as the neutron shielding material after ruling out several options

Material Reason for Rejection

H

2

O

Li

LiH

B

B

4

CAl

Too heavy

Too reactive

Melting point of 953 K

Brittle; would not tolerate launch well

Possible; heavy, needs comparison w/ other options




Slide 45

Shielding - Neutrons (3)

• One disadvantage: Boron will be consumed over time

20

18

10

8

6

4

2

0

16

14

12

Dose after 5 years of operation

Dose at 0 years of operation

5 10 15 20 25 50 75 100 125 150 175 200 225 250 meters




Slide 46

Shielding - Gammas

• Tungsten (W) was chosen as the gamma shielding material after ruling out several options

Material Reason for Rejection

Z < 72 Too small density and/or mass attenuation coefficient

Unstable nuclei Z > 83

Pb, Bi

Re, Ir

Os

Hf, Ta

Not as good as tungsten, and have low melting points

Difficult to obtain in large quantities

Reactive

Smaller mass attenuation coefficients than alternatives




Slide 47

Shielding - Design



• Two pieces, each covering 40º of reactor radial surface

• Two layers: 40 cm B

4

C

(yellow) on inside, 12 cm

W (gray) outside

• Scalable

– at 200 kW(e) mass is

2.19 metric tons

– at 50 kW(e), mass is

1.78 metric tons


Slide 48

Shielding - Design (2)

• For mission parameters, pieces of shield will move

– Moves once to align shield with habitat

– May move again to protect crew who need to enter otherwise unshielded zones




Slide 49

Shielding - Design (3)

• Using a shadow shield requires implementation of exclusion zones:

•

Unshielded Side:

– 32 rem/hr - 14 m

– 2.0 mrem/hr - 1008 m

– 0.6 mrem/hr - 1841 m

•

Shielded Side:

– 32 rem/hr - inside shield

– 400 mrem/hr – at shield boundary

– 2.0 mrem/hr - 11 m

– 0.6 mrem/hr - 20 m


Nuclear Engineering Department core


Slide 50

MSR Assembly Sketch




Slide 51

MSR Mass

Component

Core

PCU

Radiator

Shielding

Total

Bottom Line: ~82g/We

Mass (kg)

4310

1385

565

1975

8245




Slide 52

Mass Reduction and Power Gain

• Move reactor 2km away from people

– Gain 500kg from extra transmission lines

– Loose almost 2MT of shielding

Bottom Line: ~60g/We

• Use ISRU plant as a thermal sink

– Gain potentially 900kWth

– Gain mass of heat pipes to transport heat to ISRU

(depends on the distance of reactor from plant)

– Loose 515kg of Radiator Mass




Slide 53

MSR Mission Plan

• Build and Launch

– Prove Technology on Earth

• Earth Testing

– Ensure the system will function for ≥ 5EFPY

• Lunar / Martian Landing and Testing

– Post Landing Diagnostics

• Startup

• Shutdown




Slide 54

MSR

Group

Expanding Frontiers with Nuclear Technology

“The fascination generated by further exploration will inspire…and create a new generation of innovators and pioneers.”

~President George W. Bush




Slide 55

Additional Slides




Slide 56

Future Work – Core

• Investigate further the feasibility of plate fuel element design

• Optimize tricusp core configuration

• Examine long-term effects of high radiation environment on chosen materials




Slide 57

PCU – Decision Methodology

Brayton Sterling

Small Mass and Size (Cost) - 1.35

Actual PCU

Outlet Temperature

Peripheral Systems (i.e. Heat Exchangers, A to D converter)

Launchable/Accident Safe - 1.13

Robust to forces of launch

Fits in rocket

Controllable - 1.14

High Reliability and Limited Maintenance - 1.00

Moving Parts

Radiation Resistant

Single Point Failure

Proven System

Inlet Temperature

Total



1

3

2

2

3

1

2

3

2

1

3

1

Thermionics

3

3

2

3

3

1

1

2

1

2

3

23.77

2

3

2

2

3

26.55


Slide 58

3

1

3

2

1

28.51

PCU – Future Work

• Improving Thermionic Efficiency

• Material studies in high radiation environment

• Scalability to 200kWe and up

• Using ISRU as thermal heat sink




Slide 59

Radiator Future Work

• Analysis of transients

• Model heat pipe operation

• Conditions at landing site

• Manufacturing




Slide 60

Analysis

• Models

– Isothermal

– Linear Condenser

80

70

60

50

40

30

20

10

0

700 800

Radiating Area needed to Reject 900 kW

900 1000 1100

Radiator Temperature (K)

1200 1300 1400



• Comparative Area

– Moon 39.5 m 2

– Mars 39 m 2


Slide 61

Shielding - Future Work

• Shielding using extraterrestrial surface material:

– On moon, select craters that are navigable and of appropriate size

– Incorporate precision landing capability

– On Mars, specify a burial technique as craters are less prevalent

• Specify geometry dependent upon mission parameters

– Shielding modularity, adaptability, etc.




Slide 62

Shielding - Alternative Designs

• Three layer shield

– W (thick layer) inside,

B

4

C middle, W (thin layer) outside

– Thin W layer will stop secondary radiation in

B

4

C shield

– Putting thick W layer inside reduces overall mass




Slide 63

Shielding -Alternative Designs (2)

-The Moon and Mars have very similar attenuation coefficients for surface material

-Would require moving 32 metric tons of rock before reactor is started




Slide 64

MRS Design Advantages

• Robustness

• Redundancy

• Scalability




Slide 65

MSR Cost

• Rhenium Procurement and Manufacture

• Nitrogen-15 Enrichment

• Halfnium Procurement




Slide 66

Nuclear Reactors for The Moon and Mars

CORE

PCU

Radiator

Shielding

MSR

Group

Additional Slides

Related documents

Products

Support

Nuclear Reactors for The Moon and Mars

CORE

PCU

Radiator

Shielding

MSR

Group

Additional Slides

Related documents

Add this document to collection(s)

Add this document to saved

Suggest us how to improve StudyLib