ML20246J466
| ML20246J466 | |
| Person / Time | |
|---|---|
| Site: | 07100666 |
| Issue date: | 08/25/1989 |
| From: | Lowman R NAVY, DEPT. OF, NAVAL SEA SYSTEMS COMMAND |
| To: | NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| References | |
| 11-00989, 11-989, NUDOCS 8909050159 | |
| Download: ML20246J466 (87) | |
Text
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e fpg DEPARTMENT OF THE NAW l j NAVAL SEA SYSTEMS COMMAND DETACHMENT
- RADIOLOGICAL AFFAIRS SUPPORT OFFICE (RASol YoRKToWN. VA 23691 5098 5104/0464A Ser 11/ n 2 5 AUG 1983' 0 9 8 9 US Nuclear Regulatory Commission 1/-06d Division of Fuel Cycle'and Material Safety 1
Material Licensing Branch j
Washington, DC 20555 Gentlemen:
Evaluation and registration of a sealed tube neutron generator for ' use 'as an explosives detector is requested.
Enclosure (1) is the technical data supporting the application.
Questions or comments should be directed to Mr. William J.
Morris, (804) 887-4692.
Sincer ly, R. W. LOWMAN By Direction
Enclosure:
(1) NAVEODTECHCEN Indian Head Registration Application for a Sealed Tube Neutron Generater of 1 Nov 88, with Revisions (2 copies)
Copy to:
COMNAVSEASYSCOM (06GN)
NAVEODTECHCEN Indian Head l
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1 DRAFT 3.8' GENERAL H
This islan. application for a radiation safety evaluation and registration of a device which'contains by-product material.
This application was developed using the format suggested by USNRC.
Regulatory. Quide 19.10 dated March 1987. The application sections -
that. f ollow respond - to section 3.9 of the_ guide.
3.1
SUMMARY
DATA-'
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f 13.1 ~ 1 Date of' Application-November 1, 1988 3.1.2
.Acclicant-
'NAVEODTECHCEN Indian Head, MD 28640.
3 The ' applicant is NAVE 0DTECHCEN. The manufacturer and
-distributor of the device that is tosbe registered is consolidated Controls Corporation,- Advanced Systems Division.
3.1.3' Device'Tyne 1
The device that is to be evaluated is commonly referred to-by the industry as a ' neutron generator.' The particular neutron generator that-is being offered for evaluation and registration is a Sealed Tube: Neutron Generator known by the acronym (STNG) which describes its design characteristics.
-3.1.4
-Model
'The device, model number CCC STNG, serial number C-03,.
offered-for evaluation and registration is an experimental device.
Each copy is individually made and is constructed to improve the operating characteristics of formerly produced copies.
Copies are identified serially for ease of assessing experimental progress.
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s 3.1.5 Other Companies Involved At this time, no other companies areiknown to be involved ~
in the manufacture of.STNG type devices of the kind being_ produced
' by Consolidated Controls Corporation (CCC). However,.the-manufacture of neutron generators that use the same principle to
' produce neutrons (D-T reaction) is not.new. Such devices have been used over.the'past enree decades.
3.1.6 Radioactive Bource Model Destination T'ae. radioactive sounce is'a sealed tube (custom made) which.
contains tritium used as the target material.
1
' 3.1.7 Radionueltdes and Maximum Activity 1
The amount of tritium varies with changes in the design of.
each STNG. At'least-400 m1111 curies and no more than one Curie are used per unit.'
3.1.8 Leak Test Frecuency The STNG is a sealed unit that has been evacuated to a vacuum of 10-9 Torr.
If the unit leaks, the vacuum 1s lost and the device will no longer produce neutrons.
3.1.0 Pesnoteal Use' Codes It is proposed, at this time, that the STNG be possessed and used only under a specific'11 cense. Principle use code *H*
. lfsted in Appendix C of the Regulatory Guide, most closely describes the STNG.
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- 3.1.16 Custom Device The'STNG is"a fast neutron source for associated particle, y
neutron-time.of flight spectroscopy and inslastic gamma ray j
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Its intended use is within a system used to'
.l determine the contents of inaccessible. spaces.
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3.1.11 Custom User The.only user will be the Naval Explosive Ordnance' Disposal
... Technology Center. Therefore, the STNG is virtually a custom j
device.
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SUMMARY
DESCRIPTION 3.2.1 Written Description The Sealed-Tube Neutron Generator (STNG) is shown schematically in Fig. 1.
The STNG envelope is seamless tubing of 304L stainless steel welded to a ceramic high voltage insulator.
The overall length is approximately 10 inches and the external diam 2ter is 3 inches (C-series) or 2.75 inches (B-series).
Further physical details are contained in Section 3.3.2.
The basic design of the neutron generator is similar to that described by Reifenschweiler,(8.88 in that a
getter-controllable mixture of deuterium and tritium gases provides a self-loading target for the T(d,n)He* reaction. The innovations in the STNG used for neutron diagnostic probe application are:
(1) the inclusion of an internal a-detector to supply time and direction information by the associated-parti;1e technique and (2) provision for focusing the ion beam on the target to insure a
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" point-source" of 14-MeV neutrons.
The STNG operates in the following way (refer to Fig.1).
The gas pressure of the D-T mixture in the tube is set to about 10-8 Torr by adjusting the heating current through the getter.
Approximately 3KV DC is then applied to the ion source which generates an internal plasma of predominantly molecular ions of deuterium and tritium.
The ions are extracted by a potential of 10-20KV between the ion source and the focus electrode.
The ion source-electrode geometry of the extraction alsh provides an The ions in electrostatic lens to focus the D-T ions into a spot.
the beam are increased in energy to about 120KV by an additional accelerating electrode at a potential of about 100 KV.
The geometric arrangement of the accelerating and focus electrodes creates a weak electrostatic 1cns for a final 1-2 mm diameter focus of the D-T beam on the internal target.
An equilibrium fraction 4
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interactions with subsequent accelerated ions in the beam. In this way the D-T target is continually repleni3hed.
A Faraday cage at -200 V around the target has the dual purpose of suppressing secondary electrons streaming back to the ion source and reducing ambiguity in the apparent target current (i.e.,
target current can be interpreted as positive ions arriving rather than electrons leaving).
The geometry of the target is arranged (at 45' to the beam) so that the alpha particles (Hed) generated in the T(d,n)He4 reaction can exit the surface and be detected by a zine sulfide (ZnS) scintillator.
Because the 14 MeV neutrons and 3.7 MeV alpha particles leave the T (d, n) He* interaction site at approximately 180* to each other to conserve energy and momentum, the alpha detection yields both time and direction information on the subsequent trajectory of the neutrons as they leave the STNG.
The 14-MeV neutrons travel with a velocity vs = 5 cm/ns (1 ns = 10-8 sec).
If, for example, an unknown obj.ect of interest were located about 30 cm from the tritium target in the STNG, as shown in Figure 2, the 14-MeV neutrons would enter the object about 6 ns af ter emission.
Some of these neutrons would be inelastically scattered in the object to product gamma rays.
Some would be elastica 11y scattered, a few might produce (n,p),
( n, cr ) or some other nuclear reaction, and the remainder would be transmitted through the object without any interaction.
The inelastic-gamma rays (gamma rays from inelastic scattering events) travel with a velocity of aboit 30 cm/ns.
If, for example, a gamma-ray detector were located 30 cm from the target object (as shown in Figure 2),
then some of the inelastic-gamma rays would be detected by this detector about 1 ns after production in the unknown material.
These inelastic-gamma rays would be detected about 6+
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Nast The inelastic gamma rays are correlated with a specific associated alpha particle by a Time-To-Pulse-Height converter (TPHC), as illustrated in Figure 3.
The outputs of the alpha detector and gamma-ray detector are analyzed by a Constant Fraction Discriminator (CFD) to determine their respective occurrence times.
The output of the alpha CFD is used to " start" the TPHC and the output of the gamma-ray CFD is used to "stop" the TPHC.
The output signal amplitude of the TPHC is proportional to the difference in time between the " start" and "stop" signals.
The TPHC output is displayed on a multichannel analyzer (MCA) as a graph of the number of counts per unit time versus time.
If, as illustrated in Figure 3, intervening material is placed between the target object and the sealed-tube neutron generator (STNG), the timing spectrum (illustrated in Figure 3) will consist of two peaks superimposed upon a small background from random events that are not correlated in time with the alpha detector signal.
The first peak will be from the intervening material and the second peak from the target object.
The inelastic-gamma rays produced in an object have an energy spectrum that is characteristic of the elements in the object.
The time that the inelastic-garaa rays are detected can be used to select those inelastic-gamma rays produced in a specific object at a particular distance from the STNG.
This was shown in Figure 3.
This selected time signal can be used to trigger a linear gate thus allowing the chosen gamma ray to pass into a MCA that measures its energy.
This arrangement is illustrated in i
In Figure 4, ' he selected time is a window with a width, t
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A T, that encloses the timing peak associated with the intervening material.
The single channel analyzer (SCA) is set for this window (i.e.,
from ti to ti + 6 T).
The output from the SCA turns the linear gate on for a time long enough to permit the inelastic garma-ray pulse from the detector to pass through the gate.
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energies of the selected inelastic-gamma rays are analyzed by the MCA to produce an energy spectrum as shown in Figure 4.
The peaks (i.e.,
photopeaks) -in this spectrum are characteristic of the elements in the material.
The relative magnitudes of the photopeaks in this spectrum are related to the abundance of the elements in the material.
The above discussion describes how the fast-neutron system illustrated in Figure 4 can spatially resolve the inelastic-gamma rays produced in two or more objects that are located along the axis of the 14-MeV neutron " beam".
This spatial resolution is thres-dimensional, determined by the orientation (0,4) of the neutron " beam" and the distance from the STNG (i.e., R = tv = 5t; where t is the TPHC time in nanoseconds and R is in cm).
This system is also capable of resolving the energy of the inelastic-gamma rays.
The combination provides four-dimensional (E, R,0,$,)
resolution of the inelastic-gamma rays produced by the 14-MeV neutron "'
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The energies of the inelastic-gamma rays can be analyzed
.etermine the elements from which they were produced.
Consequently, the system illustrated in Figure 4 is capable of a four-dimensional resolution of the distribution of the elements in objects placed in the neutron " beam".
3.2.1.1 Radiological Safety Considerations The STNG is a source of neutrons when activated and emits no radiation when turned off.
Thetubeisenclosedo$l a 1/8 inch lead shield to absorb
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As shown in -
Figure 5, a screen surrounds the accessible area of the STNG at a distance of 7 inches from the target so that access to the source of neutrons is not possible unless the' device is dismantled.
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relationship on the inverse square Computations based between neutron flux and distance from a point radiation source show that an unshielded STNG in continuous operation at its maximum
'. -. -neutrons per second does not' exceed the NRC design rate'of 10 tor 40 hours4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br /> exposure (8) at a permissible occupational dose level distance of 2.8 m (9 f t).
At 8.9 m (29 ft) the exposure level will
- However, not exceed that which is approved for the general public.
any operational system can be designed with appropriate shielding.
of polyethylene reduces the dose from 14-MeV About 33 cm (13 in) neutrons by a factor of 10H).
Thus, an operating STNG with.o0ut 30 cm (1 ft) of shielding would meet occupational dose level
. standards at a distance of 90 en (3 ft) and general public standards at 3 m (10 ft).
Capture gamma ' rays from 14-MeV interactions within the shielding material are expected to contribute less than 10 percent to the overall dose.
From the radiological health point of view, it is clear that shielding can be provided that will allow the STNG to operate safely in almost any environment.
The amount of radioactive tritium gas (400 mci) in the STNG is approximately 50 times less than the content of commercially-available, self-illuminated
" EXIT" signs.
Furthermore, since the STNG is a mechanically strong, vacuum-sealed the tritium gas is not considered to be a safety hazard.
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Very~ ~1ittle radioactivity will be induced by fast or exposed to the STNG thermal neutron capture reactions in objects The f ast-neutron flux at a range for the order of several minutes.
of 25 cm (10 in) (inspection distance) is 1.3x108 n/sec/cm2 The elements is on capture cross section for 14-MeV neutrons in most the order of a few millibarns(88 A typical example is a material 13
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j rp v with a 5 mb cross section and an. induced radioactivity having a half-life in the 5-10' min range.
An object of this material weighing 11.3 kg (25 lb)-exposed to-the STNG at a distance of 25 cm (10 in) for 1 min would have an induced activity of a total of about 2 nanocuries (about 75 dps) in the entire object.
This amount of activity is at the limits of detectability.
No damage to photographic film, magnetic tape, electronics or other materials would be expected.
3.2.2 Drawina Figure 6 shows the STNG as mounted for stationary use.
.The horizontal tube is the recoil alpha particle detector.
The fluorinert chamber surrounds the upper body of the STNG and the high voltage leads into the STNG itself.
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SEALED TUBE NEUTRON GENERATOR Figure 6.
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p 3.3 DETAILS ON CONSTRUCTION AND USE 3.3.1 Conditions of Use The STNG will. operate in any normal' range of environmental conditions. The environmental limitations on system operations would be set by the _ ancillary equipment such as detectors and electronics rather than the STNG itself.
Previous experience indicates-that an approximate tube lifetime may be 500 hours0.00579 days <br />0.139 hours <br />8.267196e-4 weeks <br />1.9025e-4 months <br /> at.an output of 5 x 108 neutrons /sec. and.200 hours0.00231 days <br />0.0556 hours <br />3.306878e-4 weeks <br />7.61e-5 months <br /> at the design-maximum of 10' neutrons /sec.
These expectations are extrapolations of experience, not the result of lifetime tests.
3.3.2 Details of construction The construction of the STNG envelope is shown in Figure 7.
All welds, brazes and seals which are necessary to produce a vacuum tight enclosure are indicated on the figure and explained in the legend.
The letter A in the legend indicates "TIG" welds which are tungsten inert gas welds, also called "heliare" welds, which are carried out in an argon atmosphere.
The metal envelope is seamless tubing of 304L stainless steel, 0.065 inches thickness.
STNGs designated as B-Series are 2.75" external diameter; those STNGS designated as C-series are 3.00" external diameter.
The ceramic insulator is composed of aluminum oxide and is supplied by the Alberox Corporation.
A complete parts list for STNG assembly is contained in Table 1.
All materials within the envelope are 30 stainless steel with the exception of the ion source -which is 1045 steel, the magnets which are indox 5 and the D-T target which is a layer of titanium and silver on an oxygen free hard copper (OPHC) post.
d STNGs normally also have an internal foil of aluminum between the target and the alpha detector window.
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Table 1.
STNG PARTS LIST Quantity Eart Name
.1 Alberox A1203 100 kV body 1.
.Alberox Ion source header 1
Alberox Target header 1
304 S.S. envelope 1
,304 S.S. window nipple (large) 1.
1 304 S.S. adaptor weld ring (large) 1 304 S.S. adaptor ring Alberox to envelope
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Outer veld ring 1
1045 carbon steel ion source chambers 1
304 S.S. ion source aperture 1
304 S.S. ion source anode I.
1 OTHC anode lead i
1 OTHC tree cross 1
304 S.S. output electrode 1
304 S.S. input electrode funnel 1
304 S.S. electrode collar 1
304 S.S. focus output aperture 1
304 S.S. accelerator output electrode 1
304 S.S. accelerator clamp ring l
1 304 S.S. retaining ring 1
304 S.S. x-ray deflection cone (large) 304 S.S. foil retaining ring (large) 1 Steel getter mount 1
1 CHFC target 1
SAES getter ST171/LH1/4-7/200 3 or 5 0FHC 1/2 tubing (tree) 1 Tritium capsules 4
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1 Glass capsule - large dia..
C S.S.'2-56 x 1/8 set screws 6
S.S. 1-72 x 1/4 binding head screws 4
S.S. 4-40 x 5/16 binding head screws 1/4 oz.
Silver solder 1
1/2 x 1 x 2 magnet blank 1
1/8 x 1 x 2 magnet blank 1-Foil A1 59.7% 0.0008 mm x 160 mm x 160 mm 1
Foil Al.65 u 1
304 envelope raw material 1
Faraday cage 1
Faraday cage aperture 1
Faraday cage support 1
Fluorinert chamber flange 1
Fluorinert clamp ring 1
Fluorinert adaptor ring 2
Fluorinert "O" rings 6
4-40 socket head screws 7 lbs Fluorinert 1
Plastic chamber 1
Anode lead heat sink 2
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.The procedures followed, and parts used in constructing a STNG are shown in Table 2, STNG Aceembly-Work Breakdown Schedule on the following pages.
As shown on this table, leak tests are carried out at 6 test points in the assembly process (Tasks 2.5,
- 4. 3, 5. 6, 6. 3, 12. 3 and 14.1) to insure the vacuum integrity of the STNG when fully assembled. The final operational test of the STNG, Step 16.3 is also a leak test in that the tube will not function if it leaks.
3.3.3 Labelina Each STNG is given a serial numl?er when being assembled.
After assembly, a label showing the serial number is attached so as to be readily visible when the STNG is in use.
See Item A in l
Figure 8.
- Also, each STNG device will be affixed with a l
yellow / magenta label which ready " Caution - Radioactive Material" l
and the universal radiation symbol.
See Itea B on Figure 8.
Four (4) such inbels will be affixed to each STNG.
3.3.4 Testine of Prototvoes Upon completion of steps identified in Table 2, the STNG is removed and tested.
This test provides assurance,that the STNG will perform as previously anticipated.
3.3.5 Ouality control As the items listed on Table 1 are received from the supplier, they are visually inspected to insure that their quality is consistent with that normally obtained. Assembly procedures are then followed extremely closely in order that the resultant STNG will meet high quality and performance standards.
Table 2 details the procedures always followed.
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STNG ASSEMBLY - VORK BREAKDOWN SCHEDULE Task'per STNG Materials l'.0 - Initiate Assembly 1.1 - Remove parts from inventory
- 1.2 - Order rep 1. parts for inventory 1.3 - Receive / inspect rep 1. parts Locating fixture Copper heat sink 2.0 - Assemble Ion source (1) Ion source header 2.1 - Machine and clean 2 magnets (1) Ion source chamber 2.2 - Clean ion source parts (1) s.s. anode ring 12.3 - Assemble / braze anode (1) copper anode lead 2.4 - Assemble ion socree (1) s.s. aperture (1) 1/2" x 1" dia magnet (1) 1/8"x1" dia magnet-Silver solder & flux 2.5 - Leak check (Test Points)
-3.0 - Test ion source output 4.0 - Alberox insulstor assembly 4.1 - Leak check insulator (1) Tested ion source 4.2 - Weld ion source (1) Alberox assy.
Locating Fixture Argon purge 4.3 - Leak check (Test Points) 4.4 - Clean, assemble, set gap, and install focus electrode
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5.0 - Envelope Assembly (1) 304 envelope 5.1 - Braze nipple to envelope, fit (1) 304 nipple foil holder, and clean Silver solder & flux (1) 304 envelope s
5.2 - Wnld insulator adaptor ring to (1) 304 envelope envelope (1) 304 adaptor ring l
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Task Per STNG-Materials 5.3 - Send envelope to machinist 5.4 - Oxidize envelope Kiln 5.5 - Weld window ring to adaptor ring (1) window ring (1) adaptor ring 5.6 - Leak' check'(Test Points)
Leak check fixture 6.0 - STNG body assembly 6.1 - Clean and install accelerating (1) Alberox asy. (4.4) electrode, clamp ring, screws, and (1) Accel, electrode snap ring (1) clamp ring 6.2
' Veld insulator to envelope 6.3 -' Leak check (Test points) 7.0 - QC check and HV condition insulator 7.1 - Set up on cryopump test stand. Air beam check, Da beam check, Da ion source firing 8.0 - D /T: tree (1) OTHC cross 8.1 - Make tree 3-5 OTHC 1/2 x 6 tubes 8.2 - Make capsule supports 114 copper wire Silver solder & flux 9.0 - Getter assembly 0FHC.032 sheet 9.1 - Make and_ clean getter mount and Silver solder 1115-shield
$10 copper wire 10.0 - Header assembly (1) Alberox large header 10.1 - Drill and weld ground lead (1) Faraday cage assy.
10.2 - Clean, fit, and weld Taraday cage (1) Target parts (1) SAES getter 10.3 - Install target (1) 4-40x1/2 s.s. screw 10.4 - Assemble Faraday weld lead (3) 4-40 s.s. nuts 10.5 - Install getter assembly 22
--____-______s
gf '? -
)-
'.}
l 7tble 2'(cont.)
Task Per STNG Materials 11.0 - Add alpha scintillator (1) IT&T window Argon
'11.1 - Clean, prepare purge, and weld
(
12.0 - Veld header to STNG 12.1_ - Cut and install alpha foil in Foil punch holder and install Foil Foil holder 12.2 - Set up, purge, and weld header to i-STNG t
12.3 - Leak test-(Test Points)
I 13.0 - Add D /T: tree to STNG 13.1 - Braze tree to STNG and add D /T:
ampoules, and braze end caps 13.2 - Cryopump mount and leak check 14.0 - Vacuum bake-out and pinch-off 14.1 - Leak check while hot (Test Points) j l
14.2
. Repairs (if necessary) 15.0-AddfluorinertH.V.insulatoh
~
l 16.0 - D-T tests 1
16.1 - Attach electrodes to ion source and focus electrode 16.2 - Mount tube on test stand 23
~
red
)
J
\\
~*
Table 2 (cont.)
Task Per Stne' Materials L
16.3 - D-T' testing 17.0 - Redesignof ancillary parts, e.g.,
'fluorinert cans, bottom connectors,.
etc., as' required by application.
l l:;
m see
,e 24 x=-__-
saw:2
[C66Z!I
~*
)
.u l
MODEL NO SER NO E6fRE DAT E BJi?.E INPUT VOLT AGE M VAC 50/60 Hz ADD L INF Item A Mmmm:
==-
V TERTA Item B l
Figure 8.
25
__4 o
3.3.6 Radiation Profiles Figures 9 and 10 show isodose contours at one, two and three meters from the STNG during normal operating rates of 106 neutrons per second (Figure 9) and 107 neutrons per second (Figure 10),
i 3.3.7 Installation The Sealed Tube Neutron Generator would normally be used in a fixed vertical position.
However, it is light enough and small enough to be mounted on a moving platform if desired.
Section 3.2.1.1, Radiological Safety Considerations discusses the shielding of the STNG and level of radiation encountered in the surrounding areas.
As pointed out in that section, the device is to be used only by a trained operator with a surrounding safety zone.
If the STNG is a replacement unit, the user would be expected to install the STNG following instructions provided by the manufacturer.
3.3.8 Radiological Safety Instructions Radiological Safety Instructions are contained as an integral part of the Single Pixel Explosive Detection Operator's Manual and are attached as A and B.
Two basic considerations are essential to the safe j
handling and operation of the STNG.
First, operation depends on the productions of high energy neutrons which can penetrate several inches of solid materials and which produce biological damage with significant exposure.
Second, neutron production results from the interaction of deute~rium (H-2) on a tritium (H-3) target.
Tritium is a radioactive form of hydrogen and, therefore, care is needed in handling devices in which it is contained.
)
26
. OPE NAL 150 DOSE LINES FOR THE STNG y,
]
-1 tsst
'4..
NEUTRON GENERATOR E
e+
g#
e' 4
3 Meters 10-11 ER/hr.
3-4 mR/hr.
~
1.5-2 mR/hr.
6 OPERATIONAL OUTPUT:
(4n 1.5 x 10 n/sec.)
DOSE RATE:
10-11 mR/hr. @
1 METER 3-4 mR/hr. @ 2 METERS 1.5-2 mR/hr. @
3 METERS NOTE: All Neutrons are Monoenergetic.
Figure 9.
27
e RADIATION PROFILES
'h,f /
~~
OPERA.fNAL IS0 DOSE LINES FOR THE STNG I
2 NEUTRON GENERATOR.
1 4
f 4s
. d' d'
d
}
- 3 Meters
[.
15-20 mR/hr.
I 4-5 mR/hr.
]
2.5-3 mR/hr.
l !
OPERATIONAL' OUTPUT:
(4n 1 x 10 n/sec.)
DOSE RATE:
15-20 mR/hr. @
1 METER i
1 4-5 mR/hr. @ 2 METERS 2.5-3 mR/hr. @ 3 METERS NOTE: All Neutrons are Monoenergetic.
Figure 10.
28 1
.i
.c 3.3.8.1 External Radiation
' Measurements made immediately.next to the STNG indicate
.that *high radiation"- as defined by Title 10 Code of Federal Regulations, part 20 is produced at' approximate contact with the device when it is operating.
Exposure to high radiation dose rates can be hazardous. The precautions listed below should be taken to j
prevent exposure in excess of the limits detailed in le CFR 20.201 for radiation workers.
j
- a. A restricted area' boundary shall be established at a perimeter where the radiation level is less than 2 mrem / hour,
- b. The operstor:will remain outside the restricted area boundary during operation.
- e. 0perators will wear neutron sensitive thermoluminescent' l
dosimeters.
3.3.8.2 Radioactive Contamination
- a. The user will not be allowed to open the sealed tube containing the target.
- b. In case of a rupture or leak of the STNG, evacuate area and ensure adequate ventilation (one change'of room air) before approaching the STNG.. Place the STNG in a strong air tight container. Tritium will desorb from the target and readily diffuse through plastic in a short period of time.
R) 29
' sesses Using rubber gloves, seal the STNG in a plastic bag and dispose of as regulations require.
Access to area should be restricted until a check for contamination is made.
3.3.8.3 Electrical AC Power.
The basic AC power for the STNG is 110V, 60 cycle,. single phase.
Normal precautions should be taken.
High Voltage.
The primary high voltage supply for the STNG is a. 100 KV,
i.e.
Spellman Model UHR100P100/SS.
Overall precautions for operation of the HV supply are included in the vendor's manual.
The STNG control system also includes a floating 30KV an? SKV power which supply the focus electrode of the STNG and the -ion source respectively. These power supplies should be turned off or disconnected and grounded before any manipulation of the HV cables or work'on the STNG.
3.3.8.4 Mechanical Shielding Material such as lead blocks, paraffin blocks or metal cages need to be handled with care.
The STNG may possibly be used with a positioning system.
Assembly and disassembly of the position system presents similar mechanical safety hazards.
If the positioning system is powered, this requires caution to be sure no body parts get pinched or jammed while the positioning system is in powered motion.
3.3.8.5 chimical Fluorinert. ~In general, the FC-77 Fluorinert insulating fluid used to surround the STNG high voltage terminal is relatively safe and is not flammable.
However, according to the manuf acturer, some toxic by-products may form on its decomposition.
The STNG should be in a vertical position at all times to avoid loss of fluorinert.
See Figure 6.
30
+,
~3.3.9' Documentation Accompanying the Device In addition to the radiological safety instructions, complete operating instructions and major component manuals will be supplied with each STNG and associated electronic components.
3.3.16 Servicing Other than checking the fluorinert insulating fluid level, there is no servicing possible.
3.3.11 Radioactive Leak Testing STNG 1eakage from the outside atmosphere will raise the' internal _ gas pressure and render the device inoperative.
Therefore, each instance of successful STNG operation may be considered a negative result leak test because if leakage had occurred the tube would not function.
Leak testing by operation is,
advised whenever a period of six months has elapsed to insure that
'the STNG.is functional. Mandatory leak testing is not required since the device contains no radioisotope other than Hydrogen-3.
3.3.12 Safety Analysis The STNG is a device that has a low potential for exposing individuals to unacceptable levels of either external ionizing or radioactive contamination. This statement is based on the following facts:
- a. Only 400 mil 11 curies of Hydrogen-3 are contained in the STN0;
- b. The Hydrogen-3 is contained in a sealed, steel container that was evacuated to a high vacuum prior to Hydrogen-3 introduction and remains at a vacuum with respect to atmosphere pressure after loading; i
- c. Sufficient warning against tampering with the device is given in 3.3.10;
- d. Isodose profiles are supplied with each device to J
indicate the exposure one may be subjected to at various distances from the device during operations. See Figures 9 and 10; i
- e. Section 3.3.8.1 contains specific warnings with respect to exposure to external radiation; and R) 31 1
]
i ifi
' released as a gas immediately upon rupture. The tritium gas will-h rapidly diffuse into the surrounding air space and be removed by
[
ventilation or inhalation by individuals.in the area. An individual _ exposed to a 100 millicurie release in a 10'X10'X10'
,~
unventilated room (6).would inhale the entire volume of air in the room in 2'1/4 hours and all of the released tritium. This would t
result in an internal dose of 20 rem (7).
An accidental dose of this magnitude is unlikely as the following safety precautions will
~
be used to mitigate the effects of a rupture.
I
- g. Safety Precautions:
i:
- a. The STNG will be~used in ventilated areas
- b. When the STNG fails to operate the area will be evaluated and adequently ventilated (one change of.
-room air)'before approaching.the STNG.
e i
4 R) 32
REFERENCE LIST t
d 1.
Reifenschweiler, 0..
- A High Output Sealed-off Neutron Tube with High Reallability and Long Life,* Nat. Bur. Standards Spec.
Publ. 312, Vol-II,.(June 1969) 00S.
2.
' Reif enschweiler, 0.,'
- Sealed-of f Neutron Tube: The Underlying Research Work,' Phillips Res. Rpts. 16, (1961) 401-418.
'3.
United States Nuclear Regulatory Commission Rules.and Regulations. Title 10,-Chapter 1, code of Federal Regulations-Energy. Part 20: Standards for Protection Against Radiation. September 1,1978. pp 20-1 thru 20-21.
4..
Profio, A. Edward, " Radiation Shielding and Dosimetry," John Wiley & Sons, New York, (1979).
i S.
.Peto, 0..
Z. M111gy and I. Hynyada, Journal of Nuclear Energy, (1967) Vol. 21, pp 797-801.
~6.
National Council on Radiation Protection and Measurements (NCRP) Report No. 72, Radiation Protection and Measurements for
. Low-Voltage Neutron Generators.
7.
NCRP Report No.-65, Management of Persons Accidentally Contaminated with Radionuclides.
t R) 33
- esst \\..
A'ITACIMNT A 1
,o.
g '.
-]
ij vg 1
i APPENDIX C l
l I
RADIOLOGICAL SAFETY CONSIDERATIONS j
The transportable, single-pixel, explosive-detection system (TSPEDS) does not use radioactive material as its source of
]
neutrons and therefore constitutes no significant safety problem when turned off.
The sealed-tube neutron generator (STNG) in 4
TSPEDS utilizes the T(d,n)He fusion reaction to produce 14-MeV 7
neutrons at a designed rate of 10 /sec.
The STNG operates at 100 kV accelerating voltage and contains a
low-pressure (5x10-5 Torr) mixture of deuterium 'and tritium gases (400 uCi tritium).
Radiological safety considerations with regard to fast-neutron generation in this instrument are based on Nuclear Regulatory Commission standards.
The specific sections of interest in
" Units of Radiation Dose,"
reference 1 are:
(1) Section 20.4 2
which indicates that approximately 1.4x107 14-MeV neutrons /cm
" Exposure of produce a dose of 1 rem; (2) Section 20.101 individuals to radiation in restricted areas," which gives a permissible whole-body dose of 5 rem per year; and (3) Section
" Permissible levels of radiation in unrestricted area,"
20.10 which allows a yearly whole-body dose of 0.5 rem for the general public.
Computations based on the inverse square relationship between neutron flux and distance from a point radiation.. source show that an unshielded STNG in continuous operation meets the occupational siafety specification at a distance of 2.8 m (9 feet) and general public safety at 8.9 m (29 feet).
- However, the TSPEDS system has been designed with appropriate supplementary shielding.
The-TSPEDS includes shielding fabricated from paraffin and metal.
It is seen from the data in Figure C1 that about 33 cm (13 inches) of polyethylene reduces the dose from 14-MeV neutrons by a factor of 10.
Thus an operating STNG with A-1 f
1
L"# F l O*,*
..e i
about 30 cm (1 f oot) of shielding would meet occupational radiation saf ety standards at a distance of 90 cm (3 feet) and general public standards at 3 m (10 feet).
Capture gamma rays from 14-MeV interactions within the shielding material are expected to l
contribute less than 10 percent to the overall dose. From the radiological health point of view it is clear that shielding can be provideL that will allow the STNG to operate safely in almost any environment.
The amount of radioactive tritium gas (400 mC1) in the STNG is approximately 50 times less than the content of commerically-available, self-illuminated
- EXIT
- signs.
Furthermore, since the STNG is a mechanically strong, vacuum-sealed system, the tritium gas is not considered to be a safety hazard.
However, in the event of a rupture of the STNG, tritium gar will very rapidly diffuse into the surrounding air space and expose any In order to personnel in the area to potential contamination.
mitigate the effects of a rupture the STNG will be used only in ventilated areas.
If the STNG fails to operate, the area will be i-immediately evacuated and one change of room air will be completed before approaching the STNG.
Very little radioactivity will be induced by f ast or thermal neutron capture reactions in objects exposed to the STNG for the order of several minutes. The fast-neutron flux at a range of 25 cm {10 inches) (inspection distance] is 1.3x103 n/sec/cm2.
It is seen f rom Figure C2 that the capture cross section for 14-MeV neutrons in most elements is the order of a few millibarns.
j Consider a typical example of a material with a 5 mb cross section and an induced radioactivity having a half-life in the S-10 min range.
If an object of this material weighing 11.3 kg (25 lb.)
were exposed to the STNG at a distance of 25 cm (10 inches) for 1 min, the neutron flux would induce a total of about 2 nanocuries (about 75 dps) of radioactivity in the entire object. This amount of activity is at the limits of detectability and is not a health hazard.
q
'l e
i R) A-2 I
,s.,e2
- 3. v. 3 it E66Z
/
.,g I\\
14 MeV l
i I
i a'
i4_Mey Incident neutron 3
energy a
i.
a I
o 10
l
\\
x N
" l
.,, Con.r...,Nrs i
a e5* Concrets or NTE j
e 7f..Concrew or NTS
\\
o F. Polyveylone or weier
\\ 's o 45~', Poire$ylene or water g\\
C 77, Polyethylene or water 1 in, of polyethylene = 1.21 h of water
'sq
= 1.00 h of concrets ig-
= 1.54 'an. of Nevede Test Siw soil (100% wtureted)
= 1.8$ of Nevada Test a
Sete soil (Arms 7) 1 I
I I
I O
2 4
6 8
10 Thicknas of polyettrylene (in.)
l (f) 14 MeV FlkureC1. Neutron dose transmission in i
f polyethylene for 3-4-MeV neutrons (Proflo, 1979).8 i
s l
i 8A.
Edward Proflo, Radiation Shielding and Dosimetry, John Wiley &
Sons, New York,1979.
l A-3 i
- ?,{
I
[~
oo so-r..n w 60-40-ao-th An e
=
la1-s.
.n f 4 -,
,.ar 2-
'J
.n
.m m-
.co es-os-(
s..
04-
.s.n
.cn
~/ Ii i
i as so se es o 'A'4'A k k' k' k's Nadron matar of syyst sudas-Figure C2. Radiative capture cross sections for 14-MeV neutrons as a
'~
function of neutron number of the target nucleus (Peto et al,1967).8 sG. Peto, 2.
Millgy and I.
Hynyadi, Journal of Nuclear Energy, 1967 Vol. 21, pp 797-801.
A-4
sua dfj>N) I k
d i
REFERENCES 1
8 United States Nuclear Regulatory Commission Rules and Regulations.
Title 10. Chapter 1, Code of Federal-Regulations-Energy.
Part 20:
Standards for Protection Against Radiation, September 1, 1978, pp 20-1 through 20-21.
- 8Profio, A.
Edward, Radiation Shielding and Dosimetry, John Miley and Sons, New York, 1979.
- 8Peto, G.,
Z. Miligy and, I. Hynyadi, Journal of Nuclear Energy, 1967, Vol. 21, pp 797-801.
l l
l l-l A-5 l
i 3
ATTACHVINT B 8.0
. SAFETY 8.1 Radiation 8.1.1 General
-Two basic consideration are essential to the saf e handling and operation of the system.' First, system operation depends on-the production of high energy neutrons which can penetrate several inches of solid materials and which produce biological damage with significant exposure.. Second, neutron production results from the-interaction of deuterium (H-2) on a tritium (H-3) target.
Tritium is a radioactive f orm of hydrogen and, theref ore, care is needed in
[
handling devices in which it is contained.
l; 8.1.2 External Radiation i
1:
Measurements made immediately next.to the STNG indicate trhat *high radiation
- as defined by Title 10 Code of Federal Regulations, Part 20 is produced at approximate contact with the I
device when it,is operating.. Exposure to high radiation dose rates can be hazardous.. The precautions listed below should be taken to b
prevent ~ exposure in excess of the limits detailed in le CFR 20.201.
y d
8.1.3 Radioactive Contamination The STNG must not be opened except as specifically approved q
in an NRC license or NRMP.
I Each STNG contains 400 to 600 millicuries of tritium.
This o
amount is considered as moderately hazardous.
As.a radioactive isotope of hydrogen, it readily exchanges with the stable hydrogen that is a component of body water. Tritium enters the body through the skin as well as through the breathing process.
Sealed inside it the STNG it is harmless. Tritium may be released if the STNG is opened under non-controlled conditions. Should the STNG rupture or leak, certain precautions are required to minimize exposure to i
personnel. These precautions are listed below:
d a
'8.1.4 Precautions The following steps should be taken to insure against excessive exposure to neutron radiation during the om ration of the STNG.
- \\
I!
- a. A restricted area boundary shall be established at a perimeter where the radiation level is less than 2 mrem / hour.
- b. The operator will remain outside the restricted area boundary during operation.
f R) B-1
9:
t..
,g
- c. Operat, b will wear neutron sensitive thermolouminescent-dosemeters.
w..'< l-:
or 3+ 5ei'i - noint. Fea ': a c t i ^ n W. tory and $pecial Protecton l If decomposition occurs, in the absence of adequate ventilation, an air supplied r.sentra o-rhn n d ba vnrn.
- 8. Precivtionary Information FC-77 is not expected to present a hazard wr.en used w r. t h good i n d t. r t r i a l hyg e;'-
pr v t ic e:: und..r the f c.1 '. 3 w : n g cone::.one. "re only in area with rufficient local exhau : vontalat.en to :.aintain airborne concentration at :eccgn: red h'alth and scfo*y 2*.vels. A v o :, r' p r c.l o ng ed breath:ng of vap:rs. Do not breathw ~.orral deco::.por t : on productr. Avc:d eye ccntact; w e r. : rafcty glacrer. ? ne: emoke when using the product. Local exhaust ventilation with a minimum capture velocity of 50 linear feet ;er minute should be provided for applications at or above the boiling point. If interfering air currents are present, minimum j capture velocity should be at least 100 linear feet per minute. B-S [.- LRAFT 3.81 GENERALL This 1s-an application for a radiation safety evaluation I and registration of a device which contains by-product asterial. This application was' developed using the. format suggested by USNRC Regulatory Guide 10.10 dated March 1987. The application sections that follow respond to section 3.0 of the guide. 3.1
SUMMARY
DATA f
3.1.1 Date of Aeolication November 1,'1988 3.1.2 Aeolicant l
NAVEODTECHCEN Indian Head, MD 28648 The applicant is NAVE 0DTECHCEN. The manufacturer and distributor of the device.that is to be registered is Consolidated Controls Corporation, Advanced Systems Division.
3.1.3 Device Type The device that is to be evaluated is commonly referred to by the industry as a
- neutron generator.' The particular neutron generator that is being offered for evaluation and registrationLis a Sealed Tube Neutron Generator known by the acronym (STNG) which-describes its design characteristics.
4 3.1.4 Model The' device, model number CCC STNG, serial number C-03, 6
offered for evaluation and registration is an experimental device.
Each copy is individually made and is constructed to improve the operating characteristics of formerly produced copies.
Copies are identified serially for ease'of assessing experimental progress.
R) 1 L-.___._.___.______.___._____
L l
L
~3.1.5 Other Companies Involved At'this time, no other companies are kncwn to be involved
-in the. manufacture of STNG type devices.of the kind being produced by Consolidated Controls Corporation.(CCC). !*owever, the manufacture of neutron generators that use the same principle to produce neutrons (D-T reaction) is not new. 'Such devices have been used over the past three decades.
3.1.0
. Radioactive' Source Model Destination
.The radioactive source is a sealet. tube-(custom made)'which contains tritium used as the target material.
t 3.1.7' Radionue11 der and Maximum Activity The amount of tritium varies with changes in the desagn of each STNG. At least 400 m1111 curies and no more than one Curie are used per. unit.
3.1.8-Leak Test Frecuency The STNG is a sealed unst that has been evacuated to a
. vacuum of 18-9 Torr.
If the unit leaks, the vacuum as lost and the device will no longer produce neutrons.
3.1 '. 9 Posnoical Use Codes It is proposed, at this time, that the STNG be possessed and used only under a specific license. Principle use code
- H*
listed in Appendix C of the Regulatory Guide, most closely describes the STNG.
i R) 2 i
_r_____________________
'j
3 i:
- s, t ')
'3.1.10.. Cus' tom Device u
=The STNG is a: fast' neutron source for assoca't particle ~.
a neutron time of flight spectroscopy and.inelastle gamma ray
. spectroscopy.
Its intended use is within'a system used to determine the contents of inaccessible spaces.
3.1.11-Custom Usg The only user will be the' Naval Explosive Ordnance Disposal tf Technology Center; Therefore, the STNG is virtually a custom
' device.
I l'
i i
61 i
R) 3 i
I.
L.. _ _ _ _ _ _ _ _ _ _ _.. _ _ _..._
8
^
5 3.2.
SUMMARY
DESCRIPTION
-3.2.1 Written Description The Sealed-Tube Neutron Generator (STNG) is shown schematically in Fig. 1.
The STNG envelope is seamless tubing of 304L stainless _ steel welded to a ceramic high voltage insulator.
The overall length is approximately 10 inches and the external diameter is 3 inches (C-series) or 2.75 inches (B-series).
Further.
physical-details are contained in Section 3.3.2.
The basic design of the neutron generator is similar to
~
that_ described by Reifenschwei2er,Oa8) in that a
getter--
contro11able' mixture of deuterium and. tritium gases provides a self-loading target for the T(d,n)He# reaction. The innovations in the-STNG used'for neutron diagnostic probe-application are:
(1) the inclusion of an internal a-detector to supply time.and direction information by the associated-particle technique and (2) provision. ' for focusing the ion beam on the target to insure a
'il
" point-source" of 14-MeV neutrons.
.~i1 The STNG operates in the following way (refer to Fig.1).
The gas pressure of the D-T mixture in the tube is set to about 10-8 Torr by adjusting the heating current through the getter.
Approximately 3KV DC is then applied to the ion source which generates an internal plasma of predominantly molecular ions of deuterium and tritium.
The ions are extracted by a potential of 10-20KV between the ion source and the focus electrode.
The ion source-electrode geometry of the extraction als6 provides an electrostatic lens to focus the D-T ions into a spot.
The ions in the beam are increased in energy to about 120KV by an additional l
accelerating electrode at a potential of about 100 KV.
The geometric arrangement of the accelerating and focus electrodes creates a weak electrostatic lens for a final 1-2 mm diameter focus of the D-T beam on the internal target.
An equilibrium fraction 4
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of the accelerated ions are implanted in the surface of the target and serve as the D-T source for T(d,n)He*
interactions with subsequent accelerated ions in the beam. In this way the D-T target is continually replenished.
A.' Faraday cage at -200 V around the target has the dual purpose of suppressing secondary electrons q
streaming back to the ion source and reducing ambiguity in the apparent target current (i.e.,
target current can be interpreted as positive ions arriving rather than electrons leaving).'
The geometry of the target 'is arranged (at 45' to the beam) so that the alpha particles (He*) generated in the T(d,n)He* reaction can exit k
the surface and be detected by a zine sulfide (Zns) scintillator.
Because the 14'MeV neutrons and 3.7 MeV alpha particles leave the T(d,n)He*. interaction site at approximately 180* to each other to conserve energy and momentum, the alpha detection yields both time and direction information on ' the subsequent trajectory of the neutrons as they leave the STNG.
r-The 14-MeV neutrons travel with a velocity v. = 5 cm/ns (1 ns = 10-8 sec).
If, for example, an unknown object of interest were located about 30 cm from the tritium target in the STNG, as shown in Figure 2, the 14-MeV neutrons would enter the object about 6 ns af ter emission.
Some of these neutrons would be inelastically scattered in the object to product gamma rays.
Some would be elastica 11y scattered, a few might produce (n,p),
(n,a) or some other nuclear reaction, and the remainder would be transmitted through the object without any interaction.
The inelastic-gamma j
rays (gamma rays from inelastic scattering events) travel with a velocity of abodt 30 cm/ns.
If, for example, a gamma-ray detector were located 30 cm from the target object (as shown in Fig ~ure 2),
then some of the inelastic-gamma rays would be detected by this detector about i ns after production in the unknown material.
These belastic-gamma rays would be detected about 6+ 1 = 7 ns after the time the 14-MeV neutrons that produced them were emitted from the tritium target.
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The inelastic gamma rays are correlated with a specific associated - alpha particle by a Time-To-Pulse-Height converter (TPHC),. as illustrated in Figure 3.
The output.s of the alpha detector and gamma-ray detector'are analyzed by a Constant Fraction Discriminator (CFD) to determine their respective occurrence times.
The output of'the alpha CFD is used to " start" the TPHC and the output of the gamma-ray CFD is used to "stop" the TPHC.
The output-signal amplitude of the TPHC is proportional to the difference in time between the " start" and "stop" signals.
The TPHC output is displayed on a multichannel analyzer (MCA),as a graph of the number of counts per unit time versus time.
If, as illustrated in Tigure 3, intervening material is placed between the target object and the' sealed-tube neutron generator (STNG), the timing spectrum (illustrated in Figure 3) will consist of two peaks superimposed upon a small background from random events that are not correlated in time with the alpha detector signal.
The first peak will be from the intervening material and the second peak from the target object.
The inelastic-gamma rays produced in an object have an energy ' spectrum that is characteristic of the elements in the object.
The time that the inelastic-gamma rays are detected can
. be used to calect those inelastic-gamma rays produced in a specific object at a particular distance from the STNG.
This was shown in Figure 3.
This selected time signal can be used to trigger a linear gate thus allowing the chosen gamma ray to pass into a MCA that measures its energy.
This arrangement is illustrated in
~'
~ Figure 4.-
In Figure 4, the selected time is a window with a width, A T, that encloses the timing peak associated with the intervening material. The single channel analyzer (SCA) is set for this window (i.e.,
from ti to tt + A T).
The output from the SCA turns the linear gate on for a time long enough to permit the inelastic gamma-ray pulse from the detector to pass through the gate.
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s energies of the selected inelastic-gamma rays are analyzed by the MCA to produce an energy spectrum as shown in Figure 4.
The peaks (i.e.,
photopeaks) in this spectrum are characteristic of the elements in the material.
The relative magnitudes of the photopeaks in this spectrum are related to the abundance of the elements in the material.
The above discussion describes how the fast-neutron system illustrated in Figure 4 can spatially resolve the inelastic-gamma rays produced in two or more objects that are located along the axis of the 14-MeV neutron " beam".
This spatial resolution is three-dimensional, determined by the orientation (0,4) of the neutron " beam" and the distance from the STNG (i.e.,
R = tv = 5t; where t is the TPHC time in nanoseconds and R is in cm)., Tnis system is also capable of resolving the energy of the inelastic-gamma rays.
The combination provides four-dimensional (E, R,0,&,)
resolution of the inelastic-gamma rays produced by the 14-MeV neutron " beam".
The energies of the inelastic-gamma rays can be analyzed to determine the elements from which they were produced.
Consequently, the system illustrated in Figure 4 is capable of a four-dimensional resolution of the distribution of the elements in objects placed in the neutron " beam".
3.2.1.1 Radiological Safety Considerations The STNG is a source of neutrons when activated and emits no radiation when turned off.
The ube is enclosed on a 1/8 inch lead shield to absorb x-rays produced when the STNG internal be'am is on.
As shown in -
Figure 5, a screen surrounds the accessible area of the STNG at a distance of 7 inches from the target so that access to the source of neutrons is not possible unless the device is dismantled.
The STNG is intended for use only by a trained operator and is to be 11
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STNG in vertical position m
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i operated with a - surrounding safety zone so that inadvertent exposure to the neutron beam is not possible.
relationship on the inverse square Computations. based between neutron flux and distance from a point radiation source show that an unshielded STNG in continuous operation at its maximum design rate of 10' neutrons per second does not exceed the NRC tor 40 hours4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br /> exposurets) at a permissible occupational dose level distance of 2.8 m (9 f t). At 8.9 m (29 ft) the exposure level will
- However, not exceed that which is approved for the general public.
any operational system can be designed with appropriate shielding.
About 33 cm (13 in) of polyethylene reduces the dose from 14-MeV neutrons by a factor of 10(4).
Thus, an operating STNG with about 30 cm (1 ft) of shielding would meet occupational dose level standards at a distance of 90 cm (3 ft) and general public standards at 3 m (10 ft).
Capture gamma rays from 14-MeV interactions within the shielding material are expected to contribute less than 10 percent to the overall dose.
From the it is clear that shielding can radiological health point of view, be provided that will allow the STNG to operate safely in almost any environment.
The amount of radioactive tritium gas (400 mci) in the STNG is approximately 50 times less than the content of commercially-available, self-illuminated
" EXIT" signs.
Furthermore, since the STNG is a mechanically strong, vacuum-sealed system, the tritium gas is not considered to be a safety hazard.
~
Very' little radioactivity will be induced by fast or exposed to the STNG thermal neutron capture reactions in objects The f ast-neutron flux at a range for the order of several minutes.
of 25 cm (10 in) [ inspection distance) is 1.3x108 n/sec/cm*.
The elements is on section for 14-MeV neutrons in most capture cross the order of a f ew millibarns(8).
A typical example is a material 13
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1withla.5 mb cross section and.an induced radioactivity ~ having a
' half-life in. the s 5-10 min range.-
An" object. of.: this material
> weighing.11.3 kg (25::1b). exposed to the - STNG at 'a distance of ~ 25 cm'(10 in) for 1 min would have an induced activity of a total of about. 2 nanocuries -(about 75 dps).in ' the entire object.
.-This amount of activity is at the limits of detectability.
No damage-to photographic' film, magnetic tape, electronics or other materials lwould be expected.
3.2.2 Drawina Figure 6 shows..the STNG as mounted for stationary-'use.
The horizontal tube is the recoil alpha particle detector.-- The fluorinert chamber surrounds the upper body of the STNG and the l
. high voltage leads into-the STNG itself.
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SEALED TUBE NEUTRON GENERATOR Figure 6.
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-DETAILS ON CONSTRUCTION AND USE 3.3.1 Conditions of Use The STNG will operate in any normal range of environmental conditions. The environmental limitations on system operations would be set by the ancillary equipment such as detectors and electronics rather than the STNG itself.
Prcvious experience indicates that an approximate tube lifetime may ba 500 hours0.00579 days <br />0.139 hours <br />8.267196e-4 weeks <br />1.9025e-4 months <br /> at an output of 5 x 10' neutrons /sec. and 200 hours0.00231 days <br />0.0556 hours <br />3.306878e-4 weeks <br />7.61e-5 months <br /> at the design maximum of 10' neutrons /sec.
These expectations are extrapolations of experience, not the result of lifetime tests.
~3.3.2 Details of Construction The construction of the STNG envelope is shown in Figure 7.
All welds, brazes and seals which are necessary to produce a vacuum tight enclosure are indicated on the figure and explained-in the legend.
The letter A in the legend indicates "TIG" welds which are tungsten inert gas welds, also called "heliarc" welds, which are carried out in an argon atmosphere.
The metal envelope is seamless tubing of 304L stainless steel, 0.065 inches thickness.
STNGs designated as B-Series are 2.75" external diameter; those STNGS designated as C-series are 3.00" external diameter.
The ceramic insulator is composed of aluminum oxide and is supplied by the Alberox Corporation.
A complete parts list for STNG assembly is contained in Table 1.
All materials within the envelope are 30k stainless steel with the exception of the ion source -which is 1045 steel, the magnets which are indox 5 and the D-T target which is a layer of titanium and silver on an oxygen free hard copper (OFHC) post.
STNGs normally also have an internal foil of aluminum between the target and the alpha detector window.
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4 Table 1.
STNG PARTS LIST Ouantity Part Name 1
Alberox A1203 100 kV body 1-Alberox Ion source header 1
Alberox Target header 1
304 S.S. envelope 1
304 S.S. window nipple (large) 1 304 S.S. adaptor weld ring (large) 1 304 S.S. adaptor ring Alberox to envelope
[
1 P11 face plate assembly 1
Outer veld ring I
1045 carbon steel ion source chambers 1
304 S.S. ion source aperture m
1 304 S.S. ion source anode t
1 0FHC anode lead
]
1 0FHC tree cross
(,
1 304 S.S. output electrode l
1 304 S.G. input electrode funnel 1
304 S.S. electrode collar 1
304 S.S. focus output aperture 1
304 S.S. accelerator output electrode 1
304 S.S. accelerator clamp ring 1
304 S.S. retaining ring 1
304 S.S. x-ray deflection cone (large) 304 S.S. foil retaining ring (large) l 1
1 Steel. getter mount 1
OHFC target i.
1 SAES getter ST171/LH1/4-7/200 l
3 or 5 OTHC 1/2 tubing (tree) f 1
Tritium capsules 4
Deuterium capsules 18
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Ouantity Part Name 4
Glass capsules - small dia.
1 Glass capsule - large dia..
5 S.S. 2-56 x 1/8 set screws
.6 S.S. 1-72 x 1/4 binding head screws 4
S.S. 4-40 x 5/16 binding head screws 1/4 oz.
Silver solder 1
1/2 x 1 x 2 magnet blank 1
1/8 x 1 x 2 magnet blank 1
Foil A1 99.7% 0.0008 mm x 160 mm x 160 mm i
Foil Al.65 u 1
304 envelope raw material 1
Faraday cage 1
Faraday cage aperture 1
Faraday cage support 1
Fluorinert chamber flange 1
Fluorinert clamp ring i
Fluorinert adaptor ring 2
Fluorinert "O" rings 6
4-40 socket head screws 7 lbs Fluorinert 1
Plastic chamber 1
Anode lead heat sink 2
Ion source connectors s
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The procedures followed, and parts used in constructing-a STNG are shown in Table 2, STNG Assembly-Work Breakdown Schedule on the following pages.
As shown on this table, leak tests are carried out at 6 test points in the assembly process (Tasks 2.5, 4.3, 5.6, 6. 3, 12. 3 and 14.1) to insure the vacuum integrity of the STNG when fully assembled. The final operational test of the STNG, Step 16.3 is also a leak test in that the tube will not function if it leaks.
3.3.3 Labeline Each STNG is given a serial number when being assembled.
After assembly, a label showing the serial number is attached so as to be readily visible when the STNG is in use.
See Item A in Figure 6.
- Also, each STNG device will be affixed with a
yellow / magenta label which reads " Caution - Radioactive Material" and the universal radiation symbol.
See Item B on Figure 8.
Four (4).such-labels will be affixed to each STNG.
3.3.4 Testino of Prototvoes Upon completion of steps identified in Table 2, the STNG is removed and tested.
This test provides assurance,that the STNG will perform as previously anticipated.
3.3.5 Ouality control As the items listed on Table 1 are received from the supplier, they are visually inspected to insure that their quality is consistent with that normally obtained. Assembly procedures are then followed extremely closely in order that the resultant STNG will meet high quality and performance standards.
Table 2 details the procedures always followed.
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a Table 2.
j STNG ASSEMBLY - VORK BREAKDOWN SCHEDULE Task per STNG' Materials 1.0 - Initiate Assembly 1.1-- Remove parts from inventory 1.2 - Order' rep 1. Parts for inventory 1.3 - Receive / inspect rep 1. parts o
Locating fixture Copper heat sink 2.0 - Assemble Ion source (1) Ion source header 2.1 - Machine and clean 2 magnets (1) Ion source chambar 2.2 --Clean ion source parts (1) s.s. anode ring.
~2.3 - Assemble /brare anode (1) copper anode lead 2.4 - Assemble ion source (1) s.s. aperture (1) 1/2" x 1" dia magnet 3
(1) 1/8"x1" dia magnet Silver solder & flux 2.5 - Leak check (Test. Points) 3.0 - Test ion source output r
4.0 - Alberox insulator assembly 4.1 - Leak check insulator (1) Tested ion source 4.2 - Veld ion source (1) Alberox assy.
Locating Fixture Argon purge 4.3 - Leak check (Test Points) 4.4 - Clean, assemble, set gap, and install focus electrode
~
~
5.0 - Envelope Assembly (1) 304 envelope 5.1 - Braze nipple to envelope, fit (1) 304 nipple foil holder, and clean Silver solder & flux (1) 304 envelope 5.2 - Weld insulator adaptor ring to (1) 304 envelope envelope (1) 304 adaptor ring 21
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Table 2 (cont.)
i' Ac i
Task'Per STNG Materials 5.3 - Send envelope to machinist
[
-5.4 - Oxidize envelope Kiln 5.5 - Veld window ring to adaptor ring (1) window ring (1) adap';or ring 5.6 - Leak check (Test Points)
Leak check fixture 6.0 - STNG body assembly 6.1 - Clean and install' accelerating (1)'Alberox asy. (4.4).
electrode, clamp ring, screws, and (1) Accel. electrode snap ring (1) clamp ring 6.2 - Weld insulator to envelope 6.3 - Leak check (Test points) 7.0 - QC check and HV condition insulator 7.1 - Set up on cryopump test stand. Air beam check,'D: beam check, Da ion source.
firing 8.0 - D:/T tree (1) OFHC cross 8.1 - Make tree 3-5 OFHC 1/2 x 6 tubes 8.2 - Make capsule supports
- 14 copper wire Silver solder & flux 9.0 - Getter assembly OTHC.032 sheet 9.1 - Make and, clean getter mount and Silver solder 1115-
~
shield 110 copper wire 10.0 - Header assembly (1) Alberox large header 10.1 - Drill and weld ground lead (1) Faraday cage assy.
10.2 - Clean, fit, and weld Taraday cage (1) Target parts (1) SAES getter s.
10.3 -Install target (1) 4-40x1/2 s.s. screw 10.4 - Assemble Faraday weld lead (3) 4-40 s.s. nuts 10.5 - Install getter assembly 22
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Table 2 (cont.)
.i
. Task Per STNG Naterials 11.0 - Add-alpha scintillator
- (1) 1T&T window Argon 11.1'- Clean, prepare purge, and weld 12.0 - Veld header to STNG R1,.1 - Cut and install alpha foil in Toil punch 2
holder and-install Toil Toil holder 12.2 - Set up, purge, and weld header to STNG 12.3 - Leak test-(Test Points) 13.0 - Add D /T tree to STNG 13.1 - Braze tree to STNG and add Dz/T
. ampoules, and. braze end caps 13.2 - Cryopump mount and leak check 14.0 - Vacuum bake-out and pinch-off 14.1 - Leak check while hot (Test Points) l l
14.2 - Repairs (if necessary) 15.0 <- Add fluorinert H.V. insulator
'16.0 - D-T tests l
16.1 - Attach electrodes to ion source and focus electrode 16.2 - Mount tube on test stand l
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= Task Per Stna.
' Mat'erials h
16.3
-D-T' testing
-17.0 --Redesign of ancillary parts, e.g.,
fluorinert cans, bottom connectors, etc.,'as required by application 1
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Item B Figure 8.
25
- 4)..
o 3.3.6 Radiation Profiles Figures 9 and 10 show isodose contours at one, two and three meters from the STNG during normal operating rates of 105 neutrons per second'(Figure 9) and 107 neutrons per second (Figure j
10).
3.3.7 Installation The Sealed Tube Neutron Generator would normally be used in a fixed vertical position.
However, it is light enough and small enough to be mounted on a moving platform if desired.
Section 3.2.1.1, Radiological Safety Considerations discusses the shielding of the STNG and level of radiation encountered in the surrounding areas.
As pointed out in that section, the device is to be-used only by a trained operator with a surrounding' safety zone.
If the STNG is a replacement unit, the user would be expected to install the STNG following instruction,.s provided by the l
manufacturer.
i 3.3.8 Radiological Safety Instructions Radiological Safety Instructions are contained as an 1
integral part of the Single Pixel Explosive Detection Operator's
[.
Manual and are attached as A and B.
i Two basic considerations are essential to the safe handling and operation of the STNG.
First, operation depends on the production of high energy neutrons which can penetrate several inches of solid materials and which produce biological damage with significant exposure.
Second, neutron production results f rom the interaction of deute'ium (H-2) on a tritium (H-3) target.
Tritium l
r is a radioactive form of hydrogen and, therefore, care is needed in handling devices in which it is contained.
26
OPERA NAL 150 DOSE LINES FOR THE SING w,
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),
NEUTRON GENERATOR N
1 +*~eM 4
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-.3 Meters -
10-11 mR/hr.
3-4 mR/hr.
l l-
/
1.5-2 mR/hr.
6 l
OPERATIONAL OUTPUT:
(4n 1.5 x 10 n/sec.)
DOSE RATE:
10-11 mR/hr. @ 1 METER q
3-4 mR/hr. @ 2 METERS 1.5-2 mR/hr. @ 3 METERS NOTE: All Neutrons are Monoenergetic.
Figure 9.
27 i
L 1
._____________-_____-a
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- A-O RADIATION PROFILES
.g OPERAUJNAL ISODOSE LINES FOR THE STNG J.
NEUTRON CENERATOR l
)
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b'
~$
-.3 Meters --
15-20 mR/hr.
4-5 mR/hr.
2.5-3 mR/hr.
OPERATIONAL OUTPUT:
(4n 1 x 10 n/sec.)
DOSE RATE:
1$-20 mR/hr. (c 1 METER 4-5 mR/hr. @ 2 METERS 2.5-3 mR/hr. @
l' METERS NOTE: All Neutrons are Monoenergetic.
Figure 10.
28
i:
3.3.8.1 External-Radiation Measurements made immediately next to the STNG: Indicate
..that,*high radiation
- as defined by Title 10 Code'of Federal' Regulations, part 20 is produced at approximate contact with the device when it is operating. Exposure to high radiation dose rates can be hazardous; -The precautions listed'below should be taken to.
prevent exposure in excess of the limits detailed in 10 CFR 20.201 fop-radiation. workers.
a..A restricted area boundary shall-be established at a perimeter where the radiation level.is less than 2 mrem / hour.
i b.' The operator will remain outside the restricted area
, boundary during operation.
- c. Operators will wear-neutron sensitive thermoluminescent dosimeters.
3.3.8.2 Radioactive Contamination-
- a. The user will not be allowed to open the sealed tube containing the, target.
b.-In case of a rupture or leak of the STNG, evacuate area and ensure adequate ventilation (one change of room air) before approaching the STNG.
Place the STNG in a strong air tight.
container. Tritium will desorb from the target and readily diffuse through plastic.in a short period of time.
s R) 29
Q j
.Using rubber gloves, seal the STNG in a plastic bag and dispose of as regulations require.
Access to area should be restricted until a check for contamination is made.
3.3.8.3 Electrical AC Power.
The basic AC power for the STNG is 110V, 60 cycle, single phase.
Normal precautions should be taken.
High Voltage.
The primary high voltage supply for the STNG is a 100KV, i.e.
Spellman Model UHR100P100/SS.
Overall precautions for operation of the HV supply are included in the vendor's manual.
The STNG control system also includes a floating 30KV an? SKV power which supply the focus electrode of the STNG and the ion source respectively. These power supplies should be turned off or disconnected and grounded before any manipulation of the HV cables or work ~on the STNG.
3.3.8.4 Mechanical Shielding Material such as lead blocks, paraffin blocks or metal cages need to be handled with care.
The STNG may possibly be used with a positioning system.
Assembly and disassembly of the position system presents similar mechanical safety hazards.
If the positioning system is powered, this requires caution to be sure no body parts get pinched or jammed while the positioning system is in powered motion.
3.3.8.5 Chimical_
Fluorinert. ~In general, the FC-77 Fluorinert insulating
~
fluid used to surround the STNG high voltage terminal is relatively safe and is not flammable. However, according to the manuf acturer, some toxic by-products may form on its decomposition.
The STNG should be in a vertical position at all times to avoid loss of fluorinert.
See Figure 6.
30
s'
.3.3.0-Documentation Accompanying the Device _
In addition to ti.e radiological safety instructions, complete operating instructions and major component manuals will be supplied with each STNG and associated electronic components.
3.3,10 Servicing Other than checking the fluorinert insulating fluid level, there is no servicing possible.
'3.3.11 Radioactive Leak Testing o
i STNG 1eakage from the outside atmosphere will raise the
.'I internal gas pressure and render the device inoperative.
Therefore, each instance of successful STNG operation may be considered a negative result leak test because if leakage had occurred the tube would not function. Leak testing by operation is adviand whenever a period of six months has elapsed to insure that the STNG is functional. Mandatory leak testing is not required since.the device contains no radioisotope 6 other than Hydrogen-3.
-3.3.12 Bafety Analysis The STNG is a device that has a. low potential for exposing individuals to unacceptable levels of either external ionizing or radioactive contamination. This statement is based on the following facts:
- a. Only 400 mil 11 curies of Hydrogen-3 are contained in the STNG:
- b. The Hydrogen-3 is contained in a sealed, steel container that was evacuated to a high vacuum prior to Hydrogen-3 introduction and remains at a vacuum with respect to atmosphere pressure after loading; I
- c. Suf f scient warning against tampering with the device is given in 3.3.10; i
- d. Isodose profiles are supplied with each device to indicate the exposure one may be subjected to at various distances from the device during operations. See Figures 9 and 10;
- e. Section 3.3.8.1 contains specific warnings with respect to exposure to external radiation; and R) 31
l e
- f. In case of tritium tube rupture tritium would be released as a gas immediately upon rupture. The tritium gas v.111 rapidly diffuse into.the surrounding air space and be removed by l
ventilation or inhalation by individuals in the area. - An individual exposed to a 100 millicurie release.in a 10'X10'X10' unventilated. room (6) would inhale the entire volume of air in the l'
room in 2'1/4 hourt and all of the released tritium.
This would result in an internal. Jase of 20 rem (7). An accidental dose of this magnitude is unlikely as the following safety precautions will:
be used.to mitigate the effecte.of a rupture.
- g. Safety Precautions:
- a. The'STNG will be used in ventilated areas
- b. When the STNG fails.to operate the area will be evaluated and adequently' ventilated tone change of Poom air) before approaching the STNO.
l.
R) 32 i
L____________.____
pur.
1 REFERENCE LIST 1.
Reifenschweiler, 0., *A High Output Sealed-off Neutron Tube with High Realfability and Long Life,' Nat. Bur. Standards Spec.
Publ. 312, Vol II, (aune 1969) 905.
2.
Reifenschweiler, 0.,
- Sealed-off Neutron Tube:
The Underlying Research Work,* Phillips Res. Rpts. 16, (1961) 401-418.
3.
United States Nuclear Regulatory Concission Rules and Regulations. Title 10, Chapter 1. Code of Federal Regulations-Energy.
Part 20: Standards for Protection Against Radiation, Septenber 1, 1972. pp 20-1 thru 20-21.
4.
Profio, A. Edward, " Radiation Shielding and Dostmetry,' John Wiley & Sons, New York, (1079).
S.
Peto.
O., 2. M111gy and I. Hynyada, Journal of Nuclear Energy, (1967) Vol. 21, pp 797-801.
6.
National Council on Radiation Protection and Measurements (NCRP) Report No. 72, Radiation Protection and Measurements for Low-Voltage Neutron Generators.
7.
NCRP Report No. 6S, Management of Persons Accidentally Contaminated with Radionuclides.
R) 33 L___________--
h j
f APPENDIX C RADIOLOGICAL SAFETY CONSIDERATIONS The-transportable, single-pixel, explosive-detection system (TSPEDS) does not use radioactive material as its source of neutrons and therefore constitutes no significant safety problem when turned off.
The sealed-tube neutron generator (STNG) in l
4 TSPEDS utilizes the T(d,n)He fusion reaction to produce 14-MeV 7
neutrons at a designed rate of 10 /sec.
The STNG operates at 10 0 kV accelerating voltage and contains a
low-pressure (5x10-5 Torr) mixture of deuterium
~and tritium gases (400 mci tritium).
Radiological-safety considerations with regard to fast-neutron generation in this instrument are based on Nuclear Regulatory Commission standards.
The specific sections of interest in
" Units of Radiation Dose,"
reference 1 are:
(1) Section 20.4 2
which indicates that approximately 1.4x107 14-MeV neutrons /cm
" Exposure of produce a dose of 1 rem; (2) Section 20.101 individuals to radiation in restricted areas," which gives a permissible whole-body dose of 5 rem per year; and (3) Section
" Permissible levels of radiation in unrestricted area,"
20.10 which allows a yearly whole-body dose of 0.5 rem for the general public.
Computations based on the inverse square relationship between neutron flux and distance from a point radiation, source show that an unshielded STNG in continuous operation meets the occupational safety specification at a i:listance of 2.8 m (9 feet) and general public safety at 8.9 m (29 feet).
- However, the TSPEDS system has been designed with appropriate supplementary shielding.
The-TSPEDS includes shielding fabricated from paraffin and metal.
It is seen from the data in Figure C1 that about 33 cm (13 inches) of polyethylene reduces the dose from 14-MeV neutrons by a factor of 10.
Thus an operating STNG with A-1
_____.____________j
.Y '
about 30 cm.(l' foot) of shielding would meet occupational radiation
. safety standards at a distance of 90 cm (3 feet) and general public standards at 3' m (10 ieet).. Capture gamma rays from 14-MeV interactions within the shielding material are expected to contribute less than le percent to the overall dose. From the radiological health point of view it is clear that shielding can be provided that will allow the STNG to operate safely in almost any environment.
' The' amount of radioactive tritium gas (400 m01) in the STNG is approximately 50 times less than the content of-commerically-available, self-illuminated *EX1T* signs.
Furthermore', since the STNG is a mechanically strong, vacuum-sealed system, the tritium gas is not considered to be a safety hazard.
However, in the event of a rupture of the STNG, tritium gas will very rapidly diffuse into the surrounding air. space and expose any personnel in the area to potential contamination.
In order to mitigate the effects.of a rupture the STNG will be used only in ventilated areas. :If the STNG fails to operate, the area will be L
immediately evacuated'and one change of room air will be completed before approaching the STNG.
i Very little radioactivity will be induced by f ast or thermal neutron capture reactions in objects exposed to the STNG for the l
order of several minutes. The fast-neutron flux at a range of 25 cm (10 inches)-(inspection distance) is 1.3x103 n/sec/cm2.
It j
is seen from Figure C2 that the capture cross section for 14-MeV j
neutrons in most elements is the order of a few millibarns.
Consider a typical example of.a material with a S mb cross section j
and an induced radioactivity having a half-life in the S-10 min range..If an object of this material weighing 11.3 kg (2S lb.)
were exposed to the STNG at a distance of 25 cm (10 inches) for 1 min, the neutron flux would induce a total of about 2 nanocuries (about 75 dps) of radioactivity in the entire object. This amount of activity is at.the limits of detectability and is not a health hazard.
T l.
R) A-2 l
' emeen g l
i 14 MeV I
i i
1 14-uev Incident neutron
- aerty.
a
=
t
}
4 i
e D
1 C*'
l
\\
4,N 3
" l
. r, -., m a 49, Canerves or NTS j
e ir..c-== - m N
o r, Pidyseylone or water
\\ \\
o 45*, Polyemynene or water
$ 7r, Poireshylene or water
%g 1 in, of poWylene = 1.21 in of wenst
= 1.00 Irt of concrets
= 1.54 in. of Nevsde ID*3 Test Site soll (100% sturated)
= 1.85 of Nerede Test W>
SJu soil (Ares 7) 1 I
I I
I o
2 4
s s
to ThidJnsus of polyemytene (in.)
(f) 14 MeV FlhureC1. Neutron dose transmission in polyethylene for 14-MeV neutrons (Proflo, 1979).8 8A.
Edward Proflo, Radiation Shielding and Dosimetry. John Wiley &
l Sons, New York,1979.
A-3
....1
. +
5,?
5'~
hi l
co ao-
- r. a w 60 -
40 -
ac -
n,.,.*
=
fal-
't
.n 1 *
,b
.Pr j't
? ".e.
- a Va.
.a
.m m
w -
04-04-y s.
94 -
W
.n.
-l..o=i
.i
.i.
.i.
o 'E'a's 4 k'k'k's u nren www er w t nawa.
w Figure C2. Radiative capture cross sections for 14-MeV neutrons as a function of neutron number of the target nucleus (Peto et al,1967).8
- G.
Peto.
2.
M111gy and I.
Hynyadi, Journal of Nuclear Energy, 1967, Vol. 21, pp 797-801.
A-4
i.
". C' }
g f.),,tP/
-d J
REFERENCES SUnited States Nuclea.r Regulatory Commission Rules and Regulations.
Title 10. Chapter 1, code of Federal Regulations-Energy.
Part 20:
Standards for Protection Against Radiation, September 1, 1970, pp 20-1 through 20-21.
8Profio, A. Edward, Radiation Shielding and Dosimetry, John Wiley and Sons, New York, 1979.
- sPeto, G.,
Z. Miligy and, I.
Hynyadi, Journal of Nuclear Energy, 1967, Vol. 21, pp 797-801.
=*
4 A-5
.f
- i.
ATTACHMENT B' i-
'8.0 SAFETY 8.1 Radiation
'B.1.1 General Two basic consideration are essential to the safe handling
~
and operation of the system. First, system operation depends on the production of high energy neutrons which can penetrate several inches of solid materials and which produce biological damage with
{
significant exposure.
Second, neutron production results from the
,3 interaction of deuterium (H-2) on a tritium (H-3) target. Tritium
.Q is a radioactive form of hydrogen and, theref ore, care is needed in h
handling devices in which it is contained.
G 8.1.2 External Radiation n
Measurements made immediately next to the STNG indicate 1
trhat *high radiation
- as defined by Title le Code of Federal Regulations, Part 28 is produced at approximate contact with the device when it is operating. Exposure to high radiation dose rates 6
can be hazardous. The precautions listed below should be taken to prevent exposure'in excess of the limits detailed in le CFR 20.201.
h l
B.1.3 Radioactive Contamination l
The STNG must.not be opened except as specifically approved in an NRC license or NRMP.
l Each STNG contains 400 to 600 mil 11 curies of tritium. This amount is considered as moderately hazardous. As a radioactive isotope of hydrogen, it readily exchanges with the stable hydrogen that.is a component of body water. Tritium enters the body through the skin as well as through the breathing process. Sealed inside i
the STNG it is harmless. Tritium may be released if the STNG is opened under non-controlled conditions.
Should the STNG rupture or leak, certain precautions are required to minimize exposure to personnel. These precautions are listed below:
8.1.4 Precautions The following steps should be taken to insure against j
excessive exposure to neutron radiation during the operation of the STNG.
- a. A restricted area boundary shall be established at a l.
perimeter where the radiation level is less than 2 mrem / hour,
- b. The operator will remain outside the restricted area boundary during operation R) B-1
.e l
, d.
- c. Operat h will wear neutron sensitive
- thermolouminescent-dosemeters.
'^
w a;< V tegt ec.drJmea
- Should the STNG vupture or= leak, seal;it in & ph.;ta: L ;, u 1..s
.nik..
Restrict access to the area until it can be checked
- s.....
for contamination.
Prior to use.~of the STNG, the Radiation Safety Officer will' train operators.in radiation safety precautions'and relevant Naval and NRC regulations and requirements.
,h l
l l-1 i
i l
l
'. l R) B-2
__.___.___..__._.__m_
c
.,8.2 Electrical 8.2.1 AC Power.
The basic AC power for the SPEDS is 110V, 60 cycle, single phase.
Normal precautions should be taken.
8.2.2 DC Power.
Most DC power to the nuclear electronics is supplied by' the ORTEC Hodel' 402D power supplies in the ORTEC Hodel 4001A' BIN.
Precautions are included in the vendor's manuals relating to the use of these DC systems (Part No.
)
8.2.3 High Voltage.
The primary high voltage supply for the STNG is a 100KV, Spellman Model UHR100P100/SS (Part No.
).
Overall precautions for operation of the HV supply are included in the vendor's manual.
The STNG control system also includes a floating 30KV and SKV power which supply the focus electrode of the STNG and the ion source respectively.
These supplies should be turned off-or disconnected and grounded before any manipulation of the HV cables or work on the STNG.
8.3 Hechanical 8.3.1 Shielding Material.
The gamma-ray detectors are " shadow shielded" with lead blocks.
In specific applications, additional lead bricks may be required.
In general the safety hazard involved is physically jamming fingers or dropping the lead during assembly or rearrangement.
Work cautiously and keep the problem in mind.
8.3.2 Positioning system.
Assembly and disassembly of the position system presents similar mechanical safety hazards to those described above in 8.'3.1.
.In addition the positioning system is powered.
This requires caution to be sure' no body parts get pinched or jammed while the positi.oning system is in powered motion.
8.4 Chemical 8.4.1 Fluorinert.
In general the FC-77 Fluorinert insulating R) B-3
)
I o' i
fluid used to surround the STNG is relatively safe and is not flammable.
However, according to.the manufacturer some toxic by--
l products may form on its decomposition.
A copy of the_ relevant
.section~of The Material Safety Data Sheet is attached.
8.5 Explosives i
8.5.1 It is assumed that the operators of the SPEDS are thoroughly trained by NAVEODTECHCEN with regard to the safety hazards associated with handling and measurements on explosives..
No discussion of that subject will be included in this manual.
I i,
l 8
l
+
c B-4
3' h,03 c 77 r.unervre-o-d a r om,n..e 14-2.g
.._ m,
/
-fWeafheibsrs%ste N
Effd&Mt FC-77 is'not expected to produ. significant arritation of the eyes on contact.
After FC-77 has been an use, contaminants may be introduced that may cause 2--i+n+4nn nr tw.
ayr -
r sm contact FC-77 is not expected to cause irritation of the skin after limited, direct contcet. After FC-77 has been in use, contaminants may be introduced that may e n o r. o ireitation en the y tr i n.
traatm The hazards associated with vapors of FC-77 are expected to be low. Above the boiling point small amounts of toxic decomposition products which may include i
hydrogen fluoride (HF) and perfluoroisobutylene (pFIB) may occur.
Hydrogen fluoride (HF) has an American Conference of Government Industrial Hygienists' (ACGIH) threshold limit value of 3 parts per million parts of air of flucirde as
=
I an eight hour time-weighted average, perfluoroisobutylene (pFIB) has a 3M recommended exposure guideline of 0.01 parts per million parts of air as a ceilino value.
'1 FYJrstm FC-77 is expected to be practically non-toxic by ingestion.
After FC-77 has been in use, contaminants may be introduced that are toxic by ingestion, sonesi.d rrst A d EYE CONTACT:
Flush with plenty of water. Call a physician.
SM!N CONTACT:
Wash affected area with soap and water.
!SHALATION:
If exposed to decomposition products, remove person to froth air.
Call a physician.
phyr.ician or poison Contro: C o r. e r with detailed dercriptic n.
!NGECTION:
Cal; a In~';en nor r-5' n meter s'
th? cnnte-nator' 1:c r: e dure r e u c r-
- 6. ReactMty Data h>=t.tm.
t j stat >.
Statatny Candrtsons To Awnd NA Matenats To Avoid hcompetitulity Finaly d i v i d e.d ertiva - es t il r. nit n's and nikalina enrth
- ^*A'e l May occur p l Wai Not occur Candstons To Avond tson NA anaroout om~.s Prodxts Thermal decomp. may produce trace amounts of HF and in some cases pFIB. Trace decoen. nt 200 C and increased decomo. with increased rurface temos.
- 7. Special Protection inf armstion Skin Protecten Eye Protecam FA#s.+U. 0 3 A e e a 'rt NDnn recifirad 8: r O ~ T: t e wi n e r a t p *- s..
Vantdaten I.nce c.xhau-t raccemande.d fo-ta-ne.
> or at beitin-noint. Foa sactinn o.
Respectory end Specaal Protecten If decomposition occurs, in the absence of adequate ventilation, an air supplied i
reenirA*e-rhnm a ba wnrn.
S. Pro X utionairy Information FC-77 is not expected t c-present a hazard wr.en used w.th good i n c t.r t r i a l hyg:.ce p n c t i c et: und.r the fci;> wing c one:.
one. Ure only
.n arenc with rufficient locci exhauct ventil a t r.c.n t o
.a :, n t a :. n airborne concentration at recognired h m1th and st.fety I.vels. Avo:.d prc. longed breath:.ng of v a p:.r e.
- o not brea-he
- .ormal deco..por
- ::on produc*s. Ave d eye ccntact; w e :. r r :< f c t y glac:er.
E' nt; e nc4:e when ustng the product. I.ocal exhaust ventilation w :. t h a minimum capture I velccity of 50 linear feet per minute chould be provided for applications at or
' ebove the boiling point. If interfering air currents are present, minimum l capture velocity should be at least 100 linear feet per minute.
l
@-3
__