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SNAP (SYSTEMS FOR NUCLEAR AUXILIARY POWER)

TECHNICAL BRIEFS

PART 8, AEROSPACE SAFETY

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ATOMICS INTERJiIATIONAL A DIVISION OF NORTH AMERICAN AVIATION, INC.

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

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LEGAL NOTICE

This report was prepared as on account of Government sponsored work. Neither the United States, nor the Commission, nor any person acting on behalf of the Commission:

A. Mokes any warranty or representation, express or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this report, or that the use of any information, apparatus, method, or process disclosed in this report may not infringe privately owned rights; or

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NAA-SR-MEMO-8215 PARTS

32 PAGES

SNAP (SYSTEMS FOR NUCLEAR AUXILIARY POWER)

TECHNICAL BRIEFS

PART 8, AEROSPACE SAFETY

ATOMICS INTER^TIONAL A DIVISION OF NORTH AMERICAN AVIATION, INC. P.O. BOX 309 CANOGA PARK, CALIFORNIA

CONTRACT: AT(ll-l)-GEN-8 FEBRUARY 21, 1963

millerc

Text Box

BLANK

CONTENTS

Pag

Introduction 1

Objectives of the AI Aerospace Safety P r o g r a m 3

Bas i s for Selection of Cur ren t P r o g r a m 4

Technical Descr ipt ion of P r o g r a m 5

A. Assembly, Handling, and Packaging of APU at

Santa Susana 6

B. Transpor ta t ion of APU from Santa Susana 6

C. Assembly and Handling at Launch Site 6

D. Pre launch Operat ions 7

E. Launch and Orbit Injection 7

F . Orbital Operat ions 7

G. Orbital Reentry 7

Cur ren t P r o g r a m 9

Technical Status 16

A. Cr i t ica l Configuration Tes t s 16

B. Mechanical and Thermochemica l Effects 16

C. Reactor Trans ien t Tes t s 17

D. F i s s ion Product Release Studies 19

E. End-of-Life Shutdown Devices 19

F . Reactor Reentry Separation and Fuel Element Ejection 20

G. Fuel Element Burnup and F i s s ion Product Dispersa l 21

Future Space Miss ions 23

P r o g r a m Schedule 24

Appendix. . 27

A. Aerospace Safety P r o g r a m Budget 27

B. Bibliography 28

NAA-SR-MEMO-8215 iii

TABLES

Page

I. Mechanical and Thermochemica l Effects — Phase 1 12

FIGURES

1. Water Immers ion Cr i t i ca l Machine 10

2. Shipping Sleeve Configuration 11

3. SNAPTRAN Reactor Schematic 13

4. Flight Test Reactor Model 15

5. Aerospace Safety P r o g r a m Schedule 25

NAA-SR-MEMO-8215 iv

I. INTRODUCTION

The Division of Reactor Development of the AEC establ ished the Aerospace

Nuclear Safety P r o g r a m two y e a r s ago under the Ass i s tan t Di rec tor for Nuclear

Safety. The Aerospace Nuclear Safety P r o g r a m was es tabl ished to provide an

independent a s s e s s m e n t of the nuclear safety aspec ts associa ted with the space

uses of nuclear pow^er.

With respec t to nuclear aiixiliary pow^er and specifically with respec t to the

SNAP lOA, 2, and 8 projec ts (for which AI i s the sys tem p r ime cont rac tor ) ,

the re a r e th ree separa te p r ime con t rac to r s par t ic ipat ing in the P r o g r a m , In

addition to AI, the unique capabil i t ies of the Sandia Corporat ion and the Phil l ips

Pe t ro l eum Company a r e being uti l ized in the a r e a s of nuclear excurs ion exper i ­

mentat ion, a tmospher ic r een t ry experimentat ion, and abor t - s imula t ion to p r o ­

vide a comprehensive Aerospace Nuclear Safety P r o g r a m ,

In addition to the t e s t s , exper iments , and analyses per formed in the AI

Aerospace Safety P r o g r a m , the AI P r o g r a m also provides technical l iaison with

the other AEC con t rac to r s , guidance to the con t rac to r s and the AEC on safety

c r i t e r i a , r eac to r and special tes t ha rdware for the safety exper iments , and the

communication channel for information flow betw^een the total Aerospace Nuclear

Safety P r o g r a m and the SNAP lOA, 2, and 8 p ro jec t s . It is in this manner that

the p r o g r a m s of Phi l l ips , Sandia, and AI a r e compiled into an integrated p r o ­

g r a m which will provide an a s su rance that the safety r equ i rement s have been

met for each r eac to r sys tem. In al l cases , how^ever, the responsibi l i ty for the

safety of the specific SNAP projec ts r e s t s with the AEC and i ts p r ime cont rac tor .

The respons ib i l i t ies of Phil l ips Pe t ro l eum Co, within the Aerospace Nuclear

Safety P r o g r a m lie in the a r e a of r eac to r excurs ion tes t and ana lys i s . The ob­

jec t ives of this tes t p r o g r a m a r e to de te rmine and demons t ra te the consequences

of nuc lear accidents and to provide exper imenta l information regarding the cha r ­

a c t e r i s t i c s of SNAP r e a c t o r s of impor tance in evaluating and predict ing the r e a c ­

to r behavior with r e spec t to Nuclear Safety.

Sandia Corporat ion provides ground and flight tes t and analysis assoc ia ted

with abor t accidents and reen t ry . The objectives of this p r o g r a m a r e to d e t e r ­

mine and demons t ra te the behavior of the r eac to r in the abort and r een t ry en­

vi ronment and to provide exper imenta l information n e c e s s a r y for predict ing the

consequences of these environments on nuclear safety.

NAA-SR-MEMO-8215 1

The p r o g r a m s of Sandia and Phi l l ips , therefore , provide special ized exper i ­

mentat ion and analyses in support of the genera l and m o r e comprehensive A e r o ­

space Safety P r o g r a m .

NAA-SR-MEMO-8215 2

II. OBJECTIVES OF THEAI AEROSPACE SAFETY PROGRAM

A portion of the overa l l AEC Aerospace Nuclear Safety P r o g r a m has been

es tabl ished at Atomics Internat ional , The AI p r o g r a m i s assoc ia ted w^ith, but

independent of, the SNAP 2, lOA, and 8 p ro jec t s . Its p r i m a r y function is to

provide an a s s e s s m e n t of the safety assoc ia ted with the SNAP 2, lOA, and 8

nuclear sy s t ems . The objectives of this p r o g r a m a re to demons t ra te , through

analyses and exper iments , that SNAP r e a c t o r s mee t the specified safety c r i ­

t e r i a as es tabl ished by the project organizat ions and to verify that these safety

c r i t e r i a a r e adequate to provide the safety r equ i r emen t s consis tent with the use

of each SNAP sys tem. These objectives encompass al l SNAP uses from feas i ­

bility demonst ra t ion flights through the operat ional phases and embody all safety

considera t ions throughout the factory-to-f l ight and eventual d isposal sequence.

To accompl ish these objectives, the Aerospace Safety P r o g r a m provides

for a review^ of the specified safety c r i t e r i a , the sys tem designs, and the p r o ­

posed p rocedu re s . The r e su l t s of this independent review a r e given to the

affected project along with any appropr ia te conclusions or recommendat ions for

modification to the safety c r i t e r i a , sys tem design, or proposed p r o c e d u r e s .

A r e a s of uncer ta inty not covered by the reac to r sys tem development plan a r e

highlighted. Analyses , exper iments , and suitable r eac to r or sys tem t e s t s a r e

then perforined within the Aerospace Safety P r o g r a m to invest igate these a r e a s

of uncer ta inty. The purpose of these act ivi t ies is to a sce r t a in that the designs

and p rocedures a r e consis tent with the specified safety c r i t e r i a .

The Aerospace Safety review covers not only the proposed reac to r p r o g r a m

but a lso invest igates other future mis s ions and applications and a t tempts to eval ­

uate potential safety c r i t e r i a which may apply to these future u se s of the r eac to r

systein. In i ts test ing, exper imenta l , and analys is p rog ram. Aerospace Safety

•will develop safety fea tures and p rocedures n e c e s s a r y for advanced sys tem

applications and /o r potential m i s s i o n s .

During and after each phase of the exper imenta l , test ing, and analysis p r o ­

gram, the safety c r i t e r i a a r e reviewed. As a resu l t of this review, comments

and recommendat ions a r e made to the Pro jec t .

NAA-SR-MEMO-8215 3

III. BASIS FOR SELECTION OF CURRENT PROGRAM

The cu r ren t Safety P r o g r a m resul ted from a review of the p resen t SNAP lOA

and SNAP 2 flight tes t p r o g r a m s , the projected SNAP 8 flight t es t p rog ram, and

the future operat ional uses of SNAP reac to r sy s t ems . Considerat ion w^as given

to var ious launch s i tes , va r ious means of t ranspor ta t ion , possible launch

vehic les , and future space m i s s i o n s . The p re sen t Aerospace Safety P r o g r a m ,

while dealing most ly v/ith the SNAP lOA/2 reac to r sys tem, w^as formulated to

include in i t s future planning the SNAP 8 r eac to r and operat ional uses of SNAP

2/lOA and 8 for communicat ion sa te l l i tes , manned space s tat ions, deep space

probes , and lunar b a s e s .

In genera l , it w^as foiind that the development plans for the SNAP lOA and 2

r e a c t o r s and thei r assoc ia ted sys tems adequately covered the safety objectives

of the flight t es t p r o g r a m . Fo r backup data, it was felt that a demonst ra t ion of

the impact per formance of the sys tem and an exper imenta l verif icat ion of the

shipping sleeve and void-f i l ler block nuclear design was des i rab le .

NAA-SR-MEMO-8215 4

IV. TECHNICAL DESCRIPTION OF PROGRAM

The exper iments , t e s t s , and analyses to be per formed under the Aerospace

Safety P r o g r a m were der ived to obtain data on potential haza rds and to demon­

s t ra te the inherent safety of the SNAP s y s t e m s . A brief descr ip t ion of the

SNAP lOA, 2, and 8 r e a c t o r s is included he re for the purpose of famil iar izat ion.

The SNAP lOA, 2, and 8 r e a c t o r s have cer ta in common fea tures . They

incorpora te a hydride alloy of fully enriched uranivim-zirconium as fuel and

mode ra to r in a core which is sufficiently compact to allow control to be ex­

clusively provided by manipulation of external beryl l ium re f lec to rs . This

r e su l t s in a considerable simplification of core design and a m o r e uniform power

dis tr ibut ion.

The p r i m a r y heat t r ans fe r medium in these r e a c t o r s is NaK, In SNAP lOA,

a 500-w e lec t r i ca l design, the NaK is c i rcula ted by an e lec t romagnet ic pump to

t he rmoe lec t r i c e lements mounted in a c o n v e r t e r - r a d i a t o r s t ruc tu re . This s y s ­

t em is designed for operat ion without the p resence of an act ive control sys tem.

In SNAP 2, a 3-kw^ e lec t r i ca l design, the NaK is pumped into a m e r c u r y

boi ler . The m e r c u r y vapor dr ives a two-s tage turbine , an a l t e rna to r ro tor ,

and the m e r c u r y pump. All the rotating components of the power conversion

sys tem a r e mounted on a single shaft. In the SNAP 8 sys tem, a somewhat

l a r g e r co re , sma l l e r fuel element d iameter and higher operating t empera tu re

pe rmi t s a power rating of 60 kwe.

The core configurations for SNAP 2 and lOA a r e identical . The concent ra -22 3

tion of hydrogen in the fuel is 6.5 x 10 a t o m s / c m . Each fuel element is

1.212 in. in d iamete r and 12.25 in. in length. The fuel is canned in Hastel loy-N,

the in te r ior surface of which is coated to min imize hydrogen loss . Th i r ty - seven

e lements a r e a r r anged on 1.260-in. cen te r s in a hexagonal a r r a y . The core

vesse l cons is t s of a cyl indrical shell of 0.031-in. -thick 316 s ta in less s teel .

Beryl l ium inse r t s fill the volume between the fuel and the core vesse l .

The SNAP 8 fuel loading cons is t s of 211 fuel e lements , each ^^0.6 in. in

d iameter and 18 in. in length. The overal l dimensions of the hexagonal a r r a y

a r e slightly l a r g e r than those of the SNAP 2/lOA a r r a y ,

A m o r e detailed descr ip t ion of each of the SNAP nuclear sys t ems is p r e s ­

ented in the respec t ive technical brief.

NAA-SR-MEMO-8215 5

The formulation of the test ing p r o g r a m resul ted from a detailed analys is

of the sequence of events , s tar t ing at the t ime the r eac to r is f i r s t a potential

c r i t i ca l m a s s , and ending after it has r een te red from orbit and been reduced

to a noncr i t ica l m a s s . During the various handling and operat ional sequences ,

accidents can be postulated to occur , from which it is possible to formulate a

t es t p r o g r a m to de te rmine the consequences of these acc idents . The following

pa rag raphs p resen t a brief d iscuss ion of the handling and operational sequence,

A m o r e detai led d iscuss ion can be found in the technical brief entitled "Flight

Tes t Safety P r o g r a m . "

A. ASSEMBLY, HANDLING, AND PACKAGING OF APU AT SANTA SUSANA

In this operat ion, the r eac to r will be loaded with fuel and brought to c r i t i -

cality in the Acceptance Tes t Faci l i ty at Santa Susana. A nuclear accident can

be postulated due to operat ional malfunctions. The r eac to r will then be packaged

for shipment to the launch si te . During the subsequent handling and packaging

p rocedure , it can be postulated that the APU can be dropped or in some w ay

damaged. Since the shipping sleeve •will be in place and v/ater w^ill be excluded

from the a r e a , no nuclear accident w^ill occur.

B. TRANSPORTATION OF APU FROM SANTA SUSANA

After packaging in an appropr ia te container , the APU will be mounted on a

t r u c k - t r a i l e r and shipped to the launch s i te . The t ranspor ta t ion will be made

by convoy ear ly in the morning when min imum traffic conditions exist . During

the t r ip , accidents such a s a coll ision with a speeding gasoline t ruck , etc . can

be postulated. Since the r eac to r will have the shipping sleeve instal led and will

be packaged in a double-walled container , no nuclear accident is postulated.

C. ASSEMBLY AND HANDLING AT LAUNCH SITE

After the APU a r r i v e s at the launch si te , it will be unpacked and inspected

for t ranspor ta t ion damage. Non-nuclear t e s t s will then be per formed. While

at the a s sembly building, the shipping sleeve will be removed and the Be re f lec ­

to r s instal led. The Be re f lec tors contain keyed void filler blocks, lockout pin,

etc. that prevent the control d rums from rotat ing. During these opera t ions ,

the APU might be t r anspor ted to other faci l i t ies for further non-nuclear tes t ing.

No nuclear accident is postulated, since all operat ions a r e per formed in facil i t ies

where water is excluded.

NAA-SR-MEMO-8215 6

D. PRELAUNCH OPERATIONS

After the APU a r r i v e s at the launch pad, a s e r i e s of mating t e s t s with the

vehicle will be per formed. During these prelaunch t e s t s , the launch vehicle

is fueled and could produce f i re , explosion, or other chemical in te rac t ions .

During such an accident , the APU could fall to the pad -where it could be engulfed

in the deluge water . A nuclear accident would possibly occur under such con­

dit ions. P r i o r to the fueling operat ion, however, the pad a r e a would be evacuated

and a nuclear accident -would not resul t in a harmful dose to personnel .

E. LAUNCH AND ORBIT INJECTION

P r i o r to launch, while the vehicle is being fueled, accidents s imi la r to those

postulated in the prelaunch operat ions can be postulated. In addition, p r io r to

the final fueling, the void fi l ler blocks will have been removed, thus the reac to r

would be in a m o r e reac t ive configuration.

During the launch and orbit injection, a vehicle abort is possible at any point.

Should this happen, the point in the t ra jec tory where the abor t occurs will d e t e r ­

mine the approximate point of impact and the velocity at impact . During a n e a r -

ground abor t , the APU could fall to the launch pad intact and be engulfed in the

deluge wate r , resul t ing in a nuclear excursion. At abor t s occurr ing a t higher

a l t i tudes , the resul t ing impact would be at a t e rmina l velocity,

F . ORBITAL OPERATIONS

After a safe orbit is achieved, the r eac to r will be s ta r ted up. Fo r the

initial R & D flights, the objective is to achieve an orbit of sufficient duration

so as to prec lude the possibi l i ty of a highly radioact ive r e a c t o r reenter ing and

falling in a populated a r e a . An accident condition could resul t if the end-of-life

shutdo-wn device failed and the r eac to r continued operat ion (at some reduced

power level) for hundreds or even thousands of y e a r s , thus not permit t ing the

inventory of fission products to decay to a safe level .

G. ORBITAL REENTRY

After the orbit of the APU degenera tes to a low alt i tude, the r eac to r will

r een te r the e a r t h ' s a tmosphe re . As previously stated, the objective of the

f i r s t R & D flight s e r i e s is to achieve a long-lived orbit . Thus, when the sys tem

r e e n t e r s , t he re will be only a h a r m l e s s amount of radioactivi ty remaining.

NAA-SR-MEMO-8215 7

For operat ional sy s t ems , it is possible that a low or shor t - l ived orbit would

be requi red . Fo r such a case , the r eac to r , upon reen t ry , -would have a high

radioactivi ty level and could p resen t a se r ious hazard problem if allo-wed to

r een te r intact. Consequently, it is des i rab le to have the sys tem designed such

that, under r een t ry conditions, the reac tor -would d i sa s semble , fuel e lements

would be ejected, and the e lements would burn up with subsequent d i spe r sa l of

the f ission products in the upper a tmosphere .

' •

NAA-SR-MEMO-8215 8

V. CURRENT PROGRAM

The p resen t AI Aerospace Safety P r o g r a m is divided into seven projec ts

which cover the fac to ry- to -d i sposa l sequence. These projects a r e entitled,

Cr i t ica l Configuration Tes t s , Mechanical and Thermochemica l Effects, Reactor

Trans ien t s and Excurs ion Tes t s , F i ss ion Product Release Studies, Reactor

End-of-Life Shutdown Devices, Reactor Separation and Fuel Element Ejection,

and Fuel Element Burnup and F i s s ion Product D i spe r sa l .

The Cr i t ica l Configuration Tes ts project i s designed to invest igate the a r e a s

assoc ia ted with the t ranspor ta t ion , assembly , and handling phases . The project

i s determining the react iv i ty of the SNAP r e a c t o r s -when they a r e subjected to

var ious w a t e r - i m m e r s i o n configurations (see F igure 1) and demonstra t ing that

the shipping sleeve (see F igure 2) and fil ler block designs a r e adequate to p r e ­

vent c r i t ica l i ty upon -water i m m e r s i o n and subsequent flooding of the core . The

cur ren t s e r i e s of t e s t s will a lso a s s i s t in developing the ability to analyze a gen­

e ra l poison-void shipping sleeve design without the necess i ty of performing

exper iments to evaluate each new^ design.

While the r eac to r i s enroute and pr ior to the actual launch, var ious acc i ­

dents have been postulated. Potent ial accidents such as impacts , chemical

in te rac t ions , f i r es , and explosions could occur . The Mechanical and The rmo­

chemical Effects project has conducted and is continuing to conduct severa l

s e r i e s of t e s t s to evaluate the possible effects of these mechanica l and t h e r m o ­

chemical changes on the SNAP sys tem. Fu l l - sca l e mockup r e a c t o r s and sys ­

t e m s have been and a r e being subjected to conditions s imi la r to those which

would occur in the var ious postulated accidents . The data (see Table I) obtained

from these t e s t s will pe rmi t an analysis of these potential h a z a r d s .

The Reactor Trans ien t and Excurs ion Tes ts project and the F i s s ion Product

Release Studies project a r e studying, by exper imenta l and analyt ical m e a n s , the

nuclear behavior of the SNAP sys tems under var ious accident conditions. Two

SNAPTRAN r e a c t o r s have been designed and a r e being fabricated for t es t pur ­

poses (see F igure 3). These r e a c t o r s will be used to de te rmine the response

cha rac t e r i s t i c s of the SNAP r e a c t o r s to varying react ivi ty inse r t ions . The in­

herent shutdown mechan i sms , such as the prompt negative t empera tu re coeffi­

cient and hydrogen r e l ea se from the fuel modera to r ma te r i a l , will be evaluated.

These shutdown mechan i sms -will be further demons t ra ted by observing the

NAA-SR-MEMO-8215 9

1-21-63 7611-1827A

Figure 1. Water Immers ion Cri t ica l Machine

NAA-SR-MEMO-8215 10

1-21-63 7611-1824A

Figure 2. Shipping Sleeve Configuration

NAA-SR-MEMO-8215 11

TABLE I

MECHANICAL AND THERMOCHEMICAL E F F E C T S - PHASE I

Tes t No.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Type

LOX s p r a y

LOX-NaK in te rac t ion

N a K - H 2 0 in te rac t ion

F i r e t e s t

Explosion

Drop t e s t

Drop t e s t

Drop t e s t

Impact

Impact

Impact

Impact

Impact

Impact

Envi ronment

LOX vapor

LOX vapor

Water tank

3700°F - 2 sec 1500°F - 15 min

250 lb TNT

100 ft tower head

100 ft tower ta i l

100 ft tower side

560 f t / s e c - concre te head

750 f t / s e c - concre te head

580 f t / s ec - wa te r head

594 f t / s ec - wa te r ta i l

560 f t / s e c - wa te r side

750 f t / s e c - wa te r head

Configuration

Reac to r ve s se l

Reac tor ve s se l

Reac to r v e s s e l

Reac tor and ref lec tor

Reac tor and ref lec tor

Full APU

Full APU

Full APU

Reac tor and ref lector

Reac to r , ref lec tor and shield

Reac tor and ref lec tor

Reactor and ref lector

Reactor and ref lector

Reac to r , ref lec tor and shield

Status

Completed

Completed

Completed

Completed

Completed

Completed

Completed

Completed

Completed

Deleted

Completed

Completed

Completed

Completed

Resul ts

No dannage

No interact ion

Violent reac t ion , t e s t tank des t royed - incomplete

Reflector ejected

Reflector ejected

Drums severed , ref lec tor ejected

Drums severed , ref lec tor ejected

Drunns severed , ref lec tor ejected

Complete des t ruc t ion

Test model to be used for soil impact

Drums severed , re f lec tor ejected, top cover removed

Drums seve red , ref lec tor e jected, pa r t i a l core d i sa s sembly

Drums severed , re f lec tor ejected

Velocity was only 428 f t / s e c , shield and conver te r e jected, core remained intact

2-20-63 7611-1023A

I in

1

OO

o I

00 ro t—'

POSITION INDICATOR SWITCHES

LEVEL SENSING UNIT-

HYDROGEN TRANSDUCERS

NITROGEN EXHAUST

DRUM ASSY DRUM COUNTERWEIGHT.

ROTATING DEVICE

PIUOTJi SHOCK MOUNTS

11-6-62

UPPER DRUM SHAFT BEARING

COOUNG FINS

STATIONARY REFLECTOR BLOCK

DRUM COUNTERWEIGHT

Figure 3 . SNAPTRAN Reactor Schematic

LEVELING DEVICE

MOTOR & BRAKE

7562-0079

r e sponses of the r eac to r to react ivi ty inser t ions la rge enough to cause an i r r e ­

vers ib le r eac to r shutdown. After a postulated excurs ion, the amount of fission

product r e l ease will govern the potential hazard . The F i s s ion Product Release

Studies project i s investigating the fractional r e l e a se of radioact ive m a t e r i a l

f rom u ran ium-z i r con ium hydride fuel. A s e r i e s of r e l ease t e s t s has been con­

ducted at the NRTS to obtain re l iable data with respec t to this potential hazard .

The Reactor End-of-Life Shutdown Devices project has been studying v a r i ­

ous mechanica l and chemical methods of rel iably reducing the r eac to r to a sub-

c r i t i ca l s ta te . Should the r eac to r enter the a tmosphere st i l l intact, the r e su l t s

obtained from the Reactor Separation and Fuel Element Ejection and Fuel E l e ­

ment Burnup and F i s s ion Product Dispersa l projec ts would come into play.

Under the fo rmer project , the mode of breakup of the r eac to r and i t s assoc ia ted

s t ruc tu re , when it is subjected to reen t ry heating, a r e being invest igated. The

pr inciples of aerodynamic and thermodynamic theory, along with available ex­

per imenta l data, a r e being used in this study. Later in the p rogram, flight

t e s t s using r eac to r models (see F igure 4) -will be conducted to provide further

data for the study. Under the la t te r project , the behavior of the fuel e lements

following thei r ejection from the reac to r is being studied. An analyt ical model

of the ablation p r o c e s s i s being developed to a s s i s t in this a r ea . A s e r i e s of

a r c - j e t t e s t s has been conducted (and m o r e a r e planned) to inc rease the knowl­

edge of fuel e lement ablation phenomena. E lements filled with f lare m a t e r i a l

will be r e l eased into the upper a tmosphere to de te rmine the ra te of ablation

under actual r een t ry conditions. Ways of enhancing the fuel burnup and the sub­

sequent d i spe r sa l of the fuel m a t e r i a l will be studied. This project will provide

the data n e c e s s a r y to es tabl ish the fuel element r e l ea se al t i tudes which a r e n e c e s ­

sa ry to insure upper a tmospher ic d i spe r sa l of the fission products .

NAA-SR-MEMO-8215 14

11-28-62 F igure 4 . Flight Test Reactor Model

NAA-SR-MEMO-8215 15

7611-1122

VI. TECHNICAL STATUS

A. CRITICAL CONFIGURATION TESTS

Exper iments to de te rmine the react ivi ty assoc ia ted with water immers ion

and flooding of SNAP 2, lOA, and 8 r e a c t o r s have been per formed using the

c r i t i ca l a s sembly machine shown in Figure 1. This machine contains a r e m o v e -

able water ref lector which is physically separa ted into th ree regions sur round­

ing the r eac to r co re . Each region may be remotely filled -with or emptied of

water .

Initial t e s t s have been per formed which m e a s u r e d the react ivi ty worth of

-water flooding and i m m e r s i o n for a SNAP 2/lOA core . The nuclear design of

shipping s leeves to insure subcr i t ical i ty \inder conditions of water flooding and

immers ion has been determined. Figure 2 sho-ws the final configuration for the

shipping s leeve.

Beryl l ium and void fil ler blocks have been tes ted to demons t ra te that a

subcr i t ica l configuration re su l t s from wate r immers ion . The p r o g r a m for

developing the ability to analyze general poison-void sleeve designs has s ta r ted .

A s imi l a r p r o g r a m is underway for the SNAP 8 r eac to r .

B. MECHANICAL AND THERMOCHEMICAL EFFECTS

During the fac tory- to -orb i t sequence, the SNAP r e a c t o r s and thei r re la ted

sys tems will be subjected to var ious handling, t ranspor ta t ion , and launch con­

dit ions. As a resu l t of these conditions, potential accidents have been postu­

lated. In o rde r to provide adequate nuclear safeguards , the potential haza rds

that could resu l t from the postulated accidents mus t be analyzed. A s e r i e s of

t e s t s has been completed whereby ful l-scale mockup r e a c t o r s and sys tems were

subjected to conditions s imi la r to those which would occur in the various postu­

lated acc idents . These Phase I t e s t s were conducted at Holloman Air Force

Base . The re su l t s a r e summar ized in Table I. These t e s t s uti l ized reac to r

models which were designed and fabricated as requi red by the conditions of each

tes t . Tes t s -were conducted which simulated the f i re , explosion, and impact

environments expected during abor t s . The design of four r eac to r models to be

used for additional Phase II impact t es t s during FY 63 has been completed and

fabrication has s ta r ted . Phase II of the ground tes t s e r i e s has been initiated

and will be completed during FY 64. During FY 64, six t es t models will be

NAA-SR-MEMO-8215 16

fabricated for ground t e s t s . The specific t e s t s with emphas is on the SNAP 2

r eac to r will be de te rmined after thorough analys is of the Phase I and II tes t

r e su l t s .

Analysis of the r e su l t s of the Phase I ground tes t s e r i e s has es tabl ished

that the r eac to r is vir tual ly unaffected by f i re , explosion, the rmochemica l

envi ronments , or impacts (at l e s s than t e rmina l velocity on concre te) . A

detailed repor t is in the final s tages of p repara t ion descr ibing the per formance

and re su l t s of the Phase I t e s t s . The Phase II and Phase III t e s t s will be com­

pleted during FY 63 and FY 64. This will provide fur ther detail with r ega rd to

the effects of possible hazardous environments on the SNAP lOA and SNAP 2

r eac to r sy s t ems . Analyses effort will be expended concurrent ly to investigate

the r e su l t s of each of the Phase II and Phase III t e s t s . FY 64 will a lso include

the p re l imina ry analys is and tes t effort to de te rmine the mos t appropr ia te new

designs for operat ional SNAP r e a c t o r s . A s e r i e s of t e s t s simulating the SNAP 8

r eac to r will be conducted -when the flight design becomes finalized.

C. REACTOR TRANSIENT TESTS

The ability to predic t the consequences of r eac to r nuclear excurs ions de ­

pends on an understanding of the role of each of the shutdown mechan i sms on

the te rmina t ion of the t rans ien t . Fo r SNAP r e a c t o r s , t he re a r e two such

mechan i sms . The f i r s t is the prompt (fuel) negative t empe ra tu r e coefficient,

compr i sed of an axial expansion contribution and a spec t ra l (neutron t h e r m a l i -

zation) contribution. The second is the rapid evolution of hydrogen gas from

the z i rconium hydride fuel at high t e m p e r a t u r e s , insofar as it produces loss of

modera to r and /o r severe p r e s s u r e gradients a c r o s s the core -which cause core

d i sassembly .

At p resen t , very l i t t le exper imenta l data is available to quantitatively

evaluate each of the above effects over the t empera tu re range of in te res t

(100°F < T < 3400° F) , except at the lower end of the sca le . A p re l imina ry study

of hydrogen diffusion r a t e s at t e m p e r a t u r e s approaching 2200° F was conducted

by means of e l ec t r i ca l heating of fuel samples . The re su l t s have been repor ted

in NAA-SR-7398 and NAA-SR-7736. The appara tus employed was not capable of

rapid enough heating to explore the region above this t e m p e r a t u r e , i. e. , all the

NAA-SR-MEMO-8215 17

hydrogen -was dr iven out of the fuel during the t ime ('^0.5 sec) of the t rans ien t .

These exper iments -will be continued in FY 64 with a somewhat m o r e e laborate

sw^itching a r r a n g e m e n t and po-wer supply to achieve an order -of -magni tude in­

c r e a s e in heating ra t e . Also, additional ins t rumentat ion will be provided to

m e a s u r e the coefficient of expansion of the fuel during the t rans ien t .

Still m o r e rapid heating ra t e s can be achieved with capsule exper iments in

the TREAT reac to r . Such exper iments have the additional vir tue of heating the 235 fuel in p rec i se ly the same manner (fissioning of U ) as in the SNAP reac to r .

A few p re l imina ry exper iments of this type have been per formed in the KEWB

reac to r , but the integrated neutron flux in the KEWB pulse is not sufficient to

meet the r equ i remen t s of the t e s t s . A s e r i e s of exper iments in the TREAT

r e a c t o r is therefore planned for FY 64.

The shock wave and par t ic le veloci t ies in SNAP fuel have been measu red ,

a s they a r e important to a descr ipt ion of r eac to r d i sassembly .

The value of the prompt (fuel) t empe ra tu r e coefficient in SNAP r e a c t o r s has

not been accura te ly m e a s u r e d due to operat ional safety l imitat ions on the types

of exper iments that can be per formed in existing faci l i t ies . The SNAPTRAN

s e r i e s of t rans ien t exper imen t s , to be conducted at the NRTS in Idaho, will not

be const ra ined in the same manne r . An integral m e a s u r e m e n t of the prompt

coefficient, as a function of t e m p e r a t u r e , will therefore be performed. Ad­

ditionally, each of the SNAPTRAN tes t s e r i e s will be t e rmina ted by a des t ruct ive

t rans ien t . The f i r s t such t rans ien t will be a h igh-react iv i ty input (^^$5) ex­

curs ion to demons t ra te the adequacy of the previously developed calculat ional

model in giving the c o r r e c t energy r e l ease . Due to the na ture of the des t ruc t ive

exper iment , l i t t le in the way of an understanding of the phenomena can be ex­

pected. This mus t come from the other exper iments previously descr ibed.

Accura te in ternal core ins t rumenta t ion is essent ia l to a meaningful

SNAPTRAN project . To this end, an ins t rumented fuel e lement has been de ­

signed which provides fuel t e m p e r a t u r e and hydrogen p r e s s u r e information.

These ins t rumented e lements will be employed in the nondestruct ive exper iments .

The f i r s t and second SNAPTRAN r e a c t o r s (SNAPTRAN-2/lOA-1 and -2)

(see F igure 3) a r e be ry l l ium-re f lec ted SNAP 2/lOA reac to r c o r e s . The thi rd

and fourth (-3 and -4) a r e wa te r - r e f l ec ted a s semb l i e s for investigating.

NAA-SR-MEMO-8215 18

respect ive ly , the possibi l i ty of achieving a s teady-s ta te mode of operat ion in

water and the consequences of rapid water immers ion . The reac t iv i t ies a s ­

sociated with water immers ion have been m e a s u r e d by the Cri t ical Configuration

Tes t project .

The fifth SNAPTRAN reac to r (SNAPTRAN-8-5) is to consis t of a be ry l l ium-

reflected SNAP 8 r eac to r .

The schedule shown in F igure 5 indicates -when design, fabricat ion, tes t ing,

and des t ruc t ion of each of the SNAPTRAN r e a c t o r s a r e planned. At p resen t , the

-1 and -2 r e a c t o r s a r e being assembled at Atomics Internat ional . Test ing of the

f i rs t r eac to r at the NRTS will begin in Apri l .

An extensive analyt ical effort is being conducted concurrent ly with the t e s t ­

ing p r o g r a m s . By maintaining a close re la t ionship between exper iment and

ana lys i s , each -will provide information of value to the other, to the benefit of

the project . For the SNAPTRAN prog ram, rapid yet thorough data analys is

will be provided by a digital computer code present ly being developed.

D. FISSION PRODUCT RELEASE STUDIES

Radioactive contamination following a nuclear excurs ion is a function not

only of the energy r e l ea se but of the species and fractions of fission products

r e l eased from the fuel. An exper imenta l project to study these p roper t i e s at

high t e m p e r a t u r e s has recent ly been completed. Radiochemical ana lyses of the

fuel and of var ious tes t appara tus components a r e now being performed. Ad­

ditional data will become available and be analyzed as a resu l t of the Reactor

Trans ien t and Excurs ion Tes t s project .

E. END-OF-LIFE SHUTDOWN DEVICES

T^vo approaches to end-of-life shutdown devices have been studied. Both

suffer from the disadvantages of d ispers ing fuel in space. A m o r e sat isfactory

solution to the problem would be an int r ins ic shutdown mechan ism not requir ing

disruption of the fuel e lement a r r a y . This p r o g r a m is cur rent ly being reevaluated

to a s s e s s the possibi l i ty of a more sat isfactory approach. Fu ture direct ion of

the work will depend upon the r e su l t s of this reevaluation.

NAA-SR-MEMO-8215 19

F. REACTOR REENTRY SEPARATION AND FUEL ELEMENT EJECTION

Before a SNAP reac to r is placed into orbit for a prolonged period of op­

erat ion, the consequences of its r e tu rn to ear th mus t be considered. To combat

the potential haza rds -which could resu l t from such an occur rence , knowledge of

the mel t down and d i spers ion sequence of the r eac to r during the reen t ry phase

is requi red . Extensive analyt ical and exper imenta l projec ts a r e needed to

de te rmine these c h a r a c t e r i s t i c s . Such projec ts a r e present ly in p r o g r e s s .

Of p r i m a r y significance to these projec ts is the development of accura te

aerodynamic heating calculat ions. To date, the original work, completed some

2 to 3 y e a r s ago, has been much improved, but continued effort is requi red

during the coming fiscal y e a r s .

Studies accompl ished up to this t ime include calculat ions of local heating

r a t e s on reac to r and vehicle components and of heat t r ans fe r within the com­

ponents. Ho-wever, only one vehicle atti tude has been considered. Additional

studies a r e requi red which will include other a t t i tudes . These -will be com­

pleted during the r ema inde r of this fiscal yea r and during FY 64. Exper iments

will a lso be per formed during this period to m e a s u r e actual local heating r a t e s .

It has been de te rmined that the NaK in the coolant sys tem will be liquid

while the r e a c t o r is in orbit , even -without heat from radioact ive decay p r o c e s s e s

The effect of the coolant on the mode of r eac to r breakup has yet to be determined

Extensive effort has gone into the determinat ion of the c ha r a c t e r i s t i c s of

orbi ta l decay and vehicle motion. The mos t significant requ i rement of this

study is the determinat ion of a p roper drag coefficient. This will r equ i re in­

c r e a s e d study and exper iments during FY 64. Effort to date has es tabl ished

the expected l i fe t imes as a function of al t i tudes utilizing three values for the

drag coefficient. Considerable refinement of this effort will be accomplished

during the r emainder of this fiscal year and during FY 64.

Orbital per turba t ions which the vehicle may undergo due to the oblateness

of the ear th and a tmosphe re , with r e spec t to vehicle al t i tudes and osci l la t ions ,

will be investigated during the coming year . To date, a computer code has

been es tabl ished for the calculat ions of satel l i te t r a j ec to r i e s during reen t ry

considering an oblate, rotating ear th . A detailed study of the osci l lat ions

c rea ted by the aerodynamic and gravi tat ional forces acting on the vehicle during

reen t ry is cur ren t ly in p r o g r e s s . This study will be continued through FY 64.

NAA-SR-MEMO-8215 20

The vehicle att i tude angle, as a function of t ime , cannot be predicted for

the en t i re r een t ry per iod on the bas i s of the available information on the s t r u c ­

ture and aerodynamic heating in tens i t ies . The analyses to date have been made

for the postulated case of ze ro angle of at tack. Fu r the r ana lyses for other

angles mus t be made in the remaining months of FY 63 and during FY 64 to

further our abi l i t ies in these a r e a s .

The exper imenta l effort requi red to de te rmine r eac to r separat ion and fuel

e lement ejection cha rac t e r i s t i c s during reen t ry includes the demonstra t ion

flight t e s t s . The design and fabrication of the r eac to r models for the r eac to r

flight demonst ra t ion (RFD-1) have been completed. (See F igure 4. ) The f l a r e -

fuel e lements to be included as a par t of the t e s t flight a r e '~50% complete. The

final planning and engineering efforts have not yet been initiated for the two

demonst ra t ion flights during FY 64.

G. FUEL ELEMENT BURNUP AND FISSION PRODUCT DISPERSAL

The radiological hazard assoc ia ted with a SNAP sys tem reenter ing the

a tmosphere is p r ima r i l y contained in the fuel e lements r e l eased from the r e a c ­

tor following breakup. There fo re , special emphasis must be given to the

sequence of events that the fuel e lements undergo once they a r e r e l eased to the

a tmosphere during reen t ry .

Again, exper imenta l and analyt ical pro jec ts a r e requi red to de te rmine that

sequence of events . The objective of the project is to complete an analys is of

fuel element ablation under the conditions of r een t ry to f i rmly es tabl ish the

r e su l t s of r e l ea se of the e lements .

Some qualitative t e s t s for the determinat ion of the the rmochemica l behavior

of the fuel ma te r i a l during reen t ry have been completed during FY 63. Ad­

ditional quantitative t e s t s a r e requi red during the remaining portion of FY 63

and during FY 64 to definitely es tabl ish these behavioral c h a r a c t e r i s t i c s .

Fuel e lement ablation cha r a c t e r i s t i c s have been investigated for th ree

postulated r e l ea se a l t i tudes . Supporting calculat ions of heat r a t e s and drag

coefficients were completed to supplement these invest igat ions. Additional

ana lyses a r e requi red based on the f i rm expected r e l ea se al t i tude. This will

be accompl ished as soon as the base data a r e made avai lable .

NAA-SR-MEMO-8215 21

Ablation analyses to date have been based on th ree a s sumed modes of fuel

element motion. The study of the tumbling of fuel e lements will be extended to

es tabl ish a meaningful foundation for the ablation ana lyses .

P r e l im ina ry a r c - j e t t e s t s have been completed to es tabl ish p roper testing

p rocedures and to give qualitative indications of fuel element ablation c h a r a c t e r ­

i s t i c s . Additional t e s t s will be accomplished this f iscal year and during FY 64.

The information gained will a l so be applied to establishing a descr ipt ion of the

p rope r t i e s of fuel m a t e r i a l s . A l i t e ra tu re search has been completed and

enthalpy c h a r a c t e r i s t i c s has been establ ished. Emiss iv i t i e s , oxidation effects,

v iscosi ty , and surface tension m e a s u r e m e n t t e s t s will be init iated and continued

throughout FY 64. The effect of the cladding on fuel e lements ablation will a lso

be investigated.

Analysis and exper imenta l work is planned to allow conclusions to be

es tabl ished regarding par t ic le breakup during reen t ry . A study has been com­

pleted which sho-ws that l i t t le radioactivity is removed if a l l the gaseous and

volatile fission products a r e s t r ipped out of the fuel. Extended studies of

par t ic le fallout w^ill be made during FY 64 utilizing, newer t ra jec tory data and

par t ic le generat ion r a t e s .

NAA-SR-MEMO-8215 22

VII. FUTURE SPACE MISSIONS

To date, the Aerospace Safety P r o g r a m has been geared to provide adequate

nuclear safeguards for the ent i re Flight Tes t P r o g r a m and operat ional systenas.

As our technology advances and manned space flight activity i n c r e a s e s , r e ­

quiring advanced nuclear po-wer sys t ems , it will become neces sa ry to expand

the scope of the Aerospace Safety P r o g r a m . Studies and exper imenta l act ivi t ies

must continue to be per formed to ensure that our as t ronau ts -will not be subjected

to undue nuclear haza rds while they a r e completing thei r space mi s s ions . As

m o r e pow^erful r e a c t o r s a r e developed for these m i s s i o n s , the Aerospace Safety

P r o g r a m naust provide, with a high degree of confidence, the nuclear safe­

guards n e c e s s a r y to ensure that these mis s ions a r e completed safely. Special

emphas is will be given to the p rob lems assoc ia ted with manned space explora­

tion, space s ta t ions , and lunar bases -which uti l ize nuc lear power sou rce s .

NAA-SR-MEMO-8215 23

VIII. PROGRAM SCHEDULE

The planned act ivi t ies of the Aerospace Safety P r o g r a m through fiscal year

1970 a r e shown in F igure 5. The P r o g r a m has been planned to es tabl i sh that

adequate safety considera t ions a r e an inherent pa r t of the sequence of events

which occur from the loading of the r eac to r w^ith fuel through eventual d isposal

for SNAP lOA, 2, and 8 reac to r s y s t e m s . Other advanced reac to r sys t ems

w^hich will come into existance as a pa r t of the communicat ions sa te l l i t es , space

s ta t ions , p lanetary b a s e s , and other advanced concepts will be s imi la r ly inves ­

tigated and defined.

The schedule of effort for the Aerospace Safety P r o g r a m act ivi t ies mus t n e c ­

e s s a r i l y be flexible to absorb per turba t ions in the requ i red work c rea ted by s igni­

ficant design changes and by the r e su l t s of tes ts and analyses per formed within

the p r o g r a m itself. In al l ins tances , the determinat ion of possible haza rds

resul t ing from nuclear excurs ions , r eac to r h is tory during reen t ry , and fuel

e lement h i s to ry after r e l e a s e to the a tmosphere will be s imultaneously pursued.

This effort will f i r s t be d i rec ted to the SNAP 2/lOA configuration, then to SNAP 8

and subsequently to the advanced r e a c t o r s that will be developed for space . The

specific aspec ts of each sys tem w^hich must be analyzed and descr ibed will be

de te rmined by the individual r eac to r sys t ems and their appl icat ions . The Aero ­

space Safety P r o g r a m is therefore an a l l - inc lus ive and dynamic p r o g r a m , e s t ab ­

lished to ensure that al l phases of SNAP safety a r e invest igated and verified from

the p resen t s tages of development through the continuing phases of operat ional

SNAP s y s t e m s .

NAA-SR-MEMO-8215 24

I

to k

O 00

U i

Reactor Trans ien t Studies

SNAPTRAN-2/10A -1 (Be-ref lected) -2 (Be-reflected) -3 (H2O-immersed) -4 (H20-ref lected)

-8 -5 (Be-ref lected) -8 -6 (H20-ref lected)

Advanced Reactor Designs

E l e c t r i c a l Heating Exper iments

TREAT Capsule Exper iments

Disassembly Exper iments (with HE)

F i ss ion Product Release Studies

Simulated Reentry Conditions

Advanced Fuel Composit ions

Cr i t ica l Configuration Studies

Unusual Configurations

SNAP 2/lOA

SNAP 8

Advanced Designs

SNAP 2/lOA Sleeve Evaluation

SNAP 8 Sleeve Evaluation

End-of-Life Shutdown

SNAP lOA

SNAP 2

SNAP 8

Advanced Designs

Fiscal Year

1964 1965 1966 1967 1968 1969 1970

Figure 5. Aerospace Safety P r o g r a m Schedule (Sheet 1 of 2)

I I

1^ W

I

00

t—'

Reactor Separat ion

SNAP lOA

SNAP 2

SNAP 8

Communicat ions Satel l i tes

Space Stations

P lane ta ry Bases

Advanced Power Systems

Fuel Burnup

SNAP 2/lOA

SNAP 8

Advanced Fuels Composition

Mechanical and Thermochemica l Effects

SNAP lOA

SNAP 2

SNAP 8

Advanced Systems

Lunar Impact

Reactor Maintenance, Recovery, and Refueling in Space

Fiscal Year

1964 1965 1966 1967 1968 1969 1970

Figure 5. (Sheet 2 of 2)

APPENDIX A

AEROSPACE SAFETY PROGRAM BUDGET

Pro jec t Engineering

Cr i t ica l Configurations Tests

Mechanical and Thermochemica l Effects

Reactor and Excurs ion Tests

F i s s ion Product Release Studies

End-of-Life Shutdown Devices

Reactor Reent ry Separat ion and Fue l Element Ejection

Fue l Element Burnup and F i s s ion Product D i spe r sa l

Total

FY 1963 (000)

110

141

249

2,046

168

100

325

111

3,250

FY 1964 (000)

113

106

453

1,573

-

175

467

563

3,450

FY 1965 (000)

170

250

550

2,500

200

200

550

580

5,000

NAA-SR-MEMO-8215 27

APPENDIX B

BIBLIOGRAPHY

1. "Pu l se Heating of Modified Zirconium Uranium Hydride," NAA-SR-7736, i ssued F e b r u a r y 14, 1963

2. " P r e l i m i n a r y SNAP l O A - F l i g h t Test Safety Report ," NAA-SR-6684, i ssued F e b r u a r y 26, 1962

3. "Proposed Test P r o g r a m for S T E E R - 1 , " NAA-SR-MEMO-7466, i ssued September 18, 1962

4. "Pu l se Heating of Zirconium Uranium Hydr ides ," NAA-SR-MEMO-7398, i ssued December 30, 1962

5. "Quar te r ly Technical P r o g r e s s Repor t , Ju ly-September 1962," NAA-SR-7797, to be i ssued

6. "Quar te r ly Technical P r o g r e s s Report , Oc tober -December 1962," NAA-SR-8097, to be i ssued

7. "SNAP Cri t ica l Assembly-4B (SCA-4B) Water I m m e r s i o n Summary Hazards Repor t and Operat ions Manual ," NAA-SR-MEMO-6877 (Rev 1), i ssued March 1, 1962.

NAA-SR-MEMO-8215 28