The results of the analysis of the S-2 and S-4B components, although incomplete, indicate that many Saturn 5 components and subsystems, e.g., pumps, valves, etc., can be radiation hardened to meet NRV requirements by material substitution and minor design modifications. Results of these analyses include  (1) recommended radiation tolerance limits for over 100 material applications; (2) design data which describes the components of each system; (3) presentation of radiation hardening examples of systems; and (4) designing radiation effects tests to supply data for selecting materials

Cheever, P. R.

Greenhow, W. A.

English

NASA Technical Reports Server

RADIATION HARDENING OF COMPONENTS AND SYSTEMS
FOR NUCLKAR ROCKET VEHICLE APPLICATIONS*
William A. Greenhow and Paul R. Cheerer
GENERAL DYNAMICS
Convair Aerospace Division
Fort Worth Operation
INTRODUCTION
The Nuclear Rocket Vehicle (NRV) is an
advanced space vehicle employing the NERVA
engine and liquid hydrogen as fuel. _ne
final design and ultimate selection of
NRV components and systems will evolve
from various technical approaches pre-
sented below.
TECHNICAL APPROACHES
As shown in Figure I, the various pro-
cedures which can be employed in the
development of NRV components and systems
include: (i) experimental, (2) shielding,
(3) research, (4) analytical, and (5)
radiation hardening. Since all of the
procedures may be employed before the NRV
is a reality, the merits of each are
briefly reviewed here.
Experimental
Candidate "off-the-shelf" components,
such as transducers, will be tested in a
combined nuclear and simulated space
environment to determine the best designs
for various applications and establish
their safe operating limits. This approach
is very costly but results in a high con-
fidence level since the component is re-
quired to operate before, during, and after
irradiation.
Shieldin_
The shielding approach is an extension
of the experimental approach in that
shielding is employed to attenuate the
nuclear radiation to levels below the
components recommended radlation tolerance
if the component cannot be relocated in a
lower radiation environment. Because of
the weight penalty, the use of shields
must be m_nlmized.
*Work performed under Contract NAS8-25848
with MSFC, Dr. R. L. Gause, Contracting
Officer's Representative.
Research
In some instances, materials and com-
ponents unique to the NRV, e.g., reactor
components, must be designed and developed.
Preliminary design data, which are obtained
from radiation effects tests conducted on
materials and subassemblies, are integrated
into prototype systems which are proof
tested and modified, as required, prior to
incorporating them into the NRV preliminary
design.
Analyt ic al
This technique, which is described later,
requires detailed analysis of component
drawings and specifications as well as
establishing radiationtolerance limits
for each material application. Since many
NRV components are located in areas in
which the predicted nuclear environment is
considerably below the recommended radia-
tion tolerance for each material contained
in the component or system under considera-
tion, their usage can be justified on the
basis of this analysis.
I
i
........................................................ j
l:Jgure ! EVOLUTION OF RADIATION RESISTANT CO_4PONENTS AND SYSTEI_4S
471
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Radiation Hardenin_
The analytical procedures provide the
basis for radiation hardening studies.
Those components and systems which contain
radiation sensitive materials are hardened
by: (I) material replacement, i.e.,
radiation stable materials are substituted
for materials with low radiation tolerance;
(2) system design modifications; or (3) re-
design of functional roles of components.
The modified or redesigned system is then
irradiated to verify its performance in a
simulated NRV environment.
RADIATION HARDENING
Analytical and radiation hardening pro-
cedures are being employed by General
Dynamics for analyzing the mechanical
components of the S-II and S-IVB stages of
the Saturn V vehicle to determine those
which might be considered suitable, or
which might require modification to a
sufficient level of radiation hardness,
for NRV applications. The technical
approach is best visualized through the
following steps:
I.
2.
S-II and S-lVB drawings and specifi-
cations were examined to identify the
and determine their locations and
applications.
Recommended radiation tolerance limits
were established for each material and
application on the basis of previous
test experience.
3.
.
5.
Each major component and subsystem
was carefully analyzed, and the radia-
tion tolerance of the basic "as de-
signed" system was assessed.
Assuming the system to be located in
a reasonable position on the NRV, the
recon_nended radiation tolerance limits
were compared to the predicted nuclear
environment for missions requiring i0
hours of engine operation. (Radiation
levels are based on ANSC nuclear flux
data for the NERVA full-flow engine.)*
If the radiation tolerance of the
basic system was less than the pre-
dicted environment, recommendations
were made to radiation harden it in a
multistep procedure in which (i) mat-
erials with low radiation resistance
were replaced by materials having
greater stability in a nuclear environ-
ment and yet can satisfy the require-
ments of the particular application,
or (2) vulnerable components which
limit its usage were replaced, or (3)
a system redesign was suggested to
overcome the deficiency.
. Radiation effects test programs were
designed to test modified components
and systems as well as to obtain
materials data for components critical
to the mission whenever sufficient in-
formation was not available.
A review of stages S-II and S-IVB
drawings and specifications indicated that
33 different radiation sensitive materials
were employed in over I00 types of appli-
cations. Recon_nended radiation tolerances
were established for each material appli-
cation on the basis of previous radiation
effects tests performed at General Dynamics
and other test facilities. Table i, which
presents the recommended radiation toler-
ances for Buna N and the criteria employed
in establishing these limits, is typical
of data resulting from this analysis. In
this example, the recommended limits are
conservative. A high confidence level is
required for the mission, and component
designers must be alerted to potential
problems which might result from indis-
criminate usage or failure to adequately
specify materials. This conservatism re-
sults from:
l° Basing recommended limits on radiation
damage to the least radiation stable
chemical formulation of the particular
class or type of material.
2. Criteria established for mechanical
properties limits. These limits cor-
respond to radiation exposures beyond
which the degradation might compromise
the functional performance of the
material as used.
3. Not taking advantage of improved per-
formance wh_h might result from operat-
ing in the space environment where
oxygen is excluded unless adequate test
data are available from tests conducted
in a vacuum.
*NERVA Reference Data (Full-Flow) Engine,
Aerojet Nuclear Systems Company Report
SI30-CP-090290-FI-PREL, April 1970.
472
Table I
RECOMMENDEDRADIATIONTOLERANCES FOR BUNA N
Application
Hoses
Gaskets and Seals
Sealants
Packing
Grommets
Recommended
Tolerance
ergs/gin(C)
I x 108
I x 109
8 x 109
I x I0 I0 )
I x i0 I0 I
Basis for
Recommendation
Hose Tests
25_ Decrease in Elon-
gation
Absolute Elongation
> 30%
Physical Deterioration
Material applications were arranged into
four classes according to their recommended
limits. Figure 2 shows the unattenuated
full-flow engine gamma dose rates as well
as the regions in which each class of
material applications may be safely em-
ployed, assuming a 10-hr engine operation.
As illustrated in Figure 2, components for
a specific subsystem can be distributed
from one end of the vehicle to the other,
thus permitting use of materials from each
class.
Table 2 summarizes the stage S-ll and
S-IVB systems investigated; however, it
should be noted that electrical and/or
electronic components were only evaluated
if they were an integral part of a mechani-
cal component, e.g., a solenoid within
the actuator of a valve would be analyzed,
but switching relays would not be examined.
The principles of radiation hardening
can be illustrated with the 17-in. rotary
shutoff valve (P/N 138025A) designed by
the Whitaker Corporation for potential
application as the LH 2 tank shutoff valve.
The valve, which was initially designed as
the LOX valve for stage S-IC of the Saturn
V, was radiation hardened by the Whitaker
Corporation. The modified valve assembly,
which is comprised of three major sub-
assemblies (the actuator and the upstream
and downstream shell assemblies), is a
spring-opened, pneumatically closed,
spherical rotary shutoff valve intended for
LH 2 service in a radiation field. The
473
I_°FIx io6_ PNIIMATICONTI_OI
i. 5 1 _01°61200 '_,x ,
=_ ASS_ _e [TOLERANCE<I x 108 ergslgm (C)]
EQUIPMENT
'_ 400 CLASS Tll [TOLERANCE >-I x 108 ergslgm (C}]
_ _i_-,,__ -- /_REPRESSURIZATION
._CLASS I_e[Tolerance _>I x 109 ergslgm (Cll
I x_10 9
UN_D _..._CLASS I lTolerance->I x 1010 ergslgm (C)IFULL FLOW
O
GAMMA DOSE / \ °Material ClassificationBased Upon 10 Hour
RATES
(ergslgm(C)-HR)_ Engine Operation
Figure 2 ASSUMED LOCATIONS OF PRESSURIZATION
SYSTEM COMPONENTS
Table2 SYSTEMS ANALYZED
I SATURNV j
I I
{ STAGES'"I I STAGES-IVBI
• PROPELLANT FEED • HYDRAULIC
• PROPELLANT MANAGEMENT • PROPULSION
• PRESSURIZATION • ENGINE
• LEAK DETECTION & PURGE • AUXILIARY PROPULSION
• PROPULSION • STRUCTURES
• AUXILIARY PROPULSION • SUPPORT
• CONDITIONING • THERMO-CONDIT_ONING
• ENGINE ACTUATION • DESTRUCT
• REQUIREMENT
110h @ 9 x IO7 ergslg(C)-h)
• BASIC
(Teflonas Seals,Rings)
• MODIFIED
(Composite,Narmco 1343)
GAMMA DOSE [ergs/g(C)l
ip5 ip6 1o7 ip8 1o9
IRm
Figure 3 RADIATION TOLERANCE OF 1/-INCH VALVE
valve, which has a nominal line size of 17
inches, would be flange-mounted between
the LH 2 tank and the suction side of each
engine turbo pump on the NRV where it
would be subjected to an integrated ex- ,
r" ....... _'r'_'"_'_-'-_-.) ' u A _._ _;L_l_t_ )
over a vehicle life requiring I0 hours of
engine operation.
Radiation hardening of the valve for
operation in the LH 2 environment was
achieved primarily by replacement of the
radiation sensitive materials Teflon and
Rulon (reinforced PTFE). Replacement
materials were (I) Kynar (vinylidene fluo-
ride resin), (2) a composite seal of Kynar,
glass, and TFE Teflon fibers, and (3) a
polyurethane elastomer (NARMCO 7343). As
shown in Figure 3, the valve assembly has
been radiation hardened by material sub-
sti_ution such that its recommended radia-
tion t_lerance has been increased from
7 x i0 u, as limited by Teflon TFE, to
I x 109 ergs/gm(C), which is slightly
higher than the predicted exposure of 8 x
I0 _ ergs/gm(C). The modified valve assem-
bly is scheduled for testing later this
year in a nuclear radiation environment
with LH 2 flow, using the Ground Test Reac-
tor (GTR) at the Fort Worth operation of
the Convair Aerospace Division of General
Dynamics.
In the radiation hardening analysis of
S-If and S-IVB components, radiation
sensitive material applications were iden-
tified and classified into two categories:
critical and non-critical. In a critical
application the mission would be compromised
if the material properties degraded below
the requirements ot the particular applica-
tion. If material substitution increases
the recommended radiation tolerance to a
value in excess of the predicted environ-
ment, it was recommended; otherwise, minor
design modifications were suggested. The
results of these analyses are typified by
the data presented in Table 3.
SUMMARY
The results of the analysis of the S-II
and S-IVB components, although incomplete,
indicate that many Saturn V components and
subsystems, e.g., pumps, valves, etc., can
be radiation hardened to meet NRV require-
ments by material substitution and minor
design modifications. Results of these
analyses include: (i) recommended radia-
tion tolerance limits for over i00 material
applications, (2) design data which des-
cribes the components of each system which
can be employed on the NRV and the modifi-
cations necessary to radiation harden
other components, (3) presentation of
radiation hardening examples of systems
which will provide guidance to component
designers, and (4) designing radiation
effects tests to supply data for selecting
materials with confidence.
474
Table 3 RADIATION HARDENING SUMMARY
COMPONENT
HOSE
ASSEMBLY
VALVE
ASSEMBLY
APPLICATION
HOSE
SEAL
SEAL
SEAL
SLEEVE
GROMMET
ELEC. INSULATION
MATERIAL
TEFLON TFE
BUNA N
TEFLONFEP
KEL-F
TEFLONTFE
TEFLON FEP
SILICONE RUBBER
CRIT.
APPLIC.
YES
YES
YES
NO
NO
NO
YES
GAMMA ENVIRONMENT
[ergs/gm (C)]
PREDICTED
1 x 109
1 x 109
1.5 x 109
1.5 x 109
RECOMMENDED
3 x 106
1 x 109
1 x 108
1 x 109
1 x I0 8'
1 x 108
1 x 109
RECOMMENDATION
WELD METAL
• TUBING AND
ELIMINATESEALS
REPLACEW ITHKYNAR
REPLACE W ITHMYLAR
475


Radiation hardening of components and systems for nuclear rocket vehicle applications

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