Seal system with integral detector

There is disclosed a seal system for materials where security is of the essence, such as nuclear materials, which is tamper-indicating, which indicates changes in environmental conditions that evidence attempts to by-pass the seal, which is unique and cost effective, said seal system comprised of a seal where an optical signal is transmitted through a loop, with a detector to read said signal, and one or more additional detectors designed to detect environmental changes, these detectors being operatively associated with the seal so that detection of a break in the optical signal or detection of environmental changes will cause an observable change in the seal.

This invention relates to seal systems, and more particularly to seal 
systems intended to detect and indicate unauthorized attempts to obtain 
access to valuable material, such as nuclear material. 
A seal, as herein understood, has a body or housing which closes a loop. 
The loop secures the sealed item in such a way that it must be removed in 
order to use, move or have access to the sealed item. For example, a valve 
may be sealed by a wire loop closed by pressing the ends of the wire into 
a small piece of lead. To increase security the body or housing may be 
provided with a unique identification in order to make it more difficult 
for an unauthorized person to simply remove and replace the seal without 
detection. Thus, the simple wire seal described above may have a symbol 
embossed into the lead body. 
Such a seal must have certain physical properties: (1) the housing and loop 
must be tamper-indicating, i.e., attempts to defeat the seal must be 
obvious to an inspector; (2) the identification of the seal must be 
unique, i.e., it should not be possible to remove and replace the seal 
with a duplicate, except at an excessive cost; and (3) the cost of the 
seal and the effort to inspect it must be reasonable for the application. 
As the security of the item to be sealed becomes more important more effort 
must be put into insuring that the seal is both tamper-indicating and 
unique, necessarily increasing the cost of the seal. In applications such 
as the protection of nuclear materials seal manufacturers must go to 
elaborate lengths to insure that their seals have good tamper-indicating 
qualities and are sufficiently unique since it must be assumed that 
persons attempting to obtain undetected access to nuclear materials will 
be willing to go to great expense and effort to defeat the seals. 
Typical seals which have been developed for nuclear security applications 
are of the type wherein an optical signal is transmitted through a loop 
comprising a fiber optics cable, closing said loop serving to secure the 
item to be sealed, and the transmitted signal is detected by an optical 
detector so that attempts to open or tamper with the loop will cause a 
change in the optical signal to be detected. Detection of such a change in 
the optical signal causes an observable change in the state of the seal 
which cannot easily be reversed by unauthorized persons. Typically such a 
seal might have a visual display which changes periodically in accordance 
with an arbitrary pseudorandom pattern known only to authorized persons. 
This pattern would be changed in response to an unauthorized attempt to 
obtain access to the secured item and could not be restored by 
unauthorized persons. Housings for such seals may be made 
tamper-indicating by any of a number of well known techniques; for 
example, the seal housing may be pressurized and a pressure sensor used to 
detect any attempts to open the housing. In general, such seals and 
methods for insuring that they are tamper-indicating are well known and a 
further discussion of them is not believed necessary to an understanding 
of the present invention. 
When items such as nuclear material are to be sealed the possibility that 
attempts to bypass the seal, such as by penetrating the vessel containing 
the nuclear material, must be considered. For this reason seals should be 
coupled with various types and combinations of detectors, such as 
vibration, motion or radiation detectors. Incorporating such detectors 
into seal systems will permit detection of attempts to bypass the seal. Of 
course, the detectors must have essentially the same properties of 
tamper-indication, uniqueness and cost-effectiveness as the seal in order 
to form an effective seal system. It is easy to see that a complete seal 
system designed to secure items such as nuclear materials may prove to be 
highly complex and expensive. 
Thus, it is an object of the present invention to provide a single 
apparatus which forms an effective seal system. 
It is a further object of the present invention to provide such a seal 
system while minimizing the cost of insuring that the seal system is 
tamper-indicating and unique. 
BRIEF SUMMARY OF THE INVENTION 
The disadvantages of the prior art are overcome and the above objects are 
achieved by means of a seal system comprising a seal of the type wherein 
an optical signal, which may be pulsed, is transmitted through a loop 
comprising a fiber optics cable, closing said loop serving to secure the 
item to be sealed. The transmitted signal is detected by an optical 
detector so that attempts to open or tamper with said loop which cause 
changes in said signal will be detected and will cause an observable 
change in the state of the seal. The seal system also comprises a second 
detector, such as a motion, vibration or radiation detector, for detecting 
significant changes in the local environment which might indicate an 
attempt to gain access to or tamper with the sealed item, the detector 
being operatively associated with the seal so that detection of such 
environmental changes will also cause an observable change in the state of 
the seal. 
Preferably such a seal system would have the signal from the detector 
interrupt or interfere with the optical signal, causing the seal to react 
essentially as though the loop were opened or tampered with. 
Thus, it may be seen that the seal system of the present invention 
advantageously provides a system wherein a single inspection will reveal 
both if the seal has been opened or tampered with and if attempts to 
bypass the seal have been made. 
It is a further advantage of the present invention that the seal and the 
second detector may share unique circuitry, and may share, or use an 
identical tamper-indicating housing, thereby reducing the cost of the seal 
system. 
Other objects and advantages of the present invention will become apparent 
to those skilled in the art from consideration of the attached drawings 
and the detailed description set forth below.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
Turning to FIG. 1, there is shown a seal system 10 in accordance with the 
subject invention. Tamper-indicating housing 12 contains electronics which 
transmit optical signals through fiber optics cable 14 to detector housing 
20 which may be substantially identical to housing 12. Housing 20 contains 
electronics which detect and retransmit the optical signals back to 
housing 12. (By optical signals herein is meant electromagnetic signals, 
normally in the visible spectrum, but which may range into the ultraviolet 
or infrared.) 
The electronics in housing 12 are designed to detect any changes in the 
retransmitted signal such as changes caused by opening the loop comprising 
fiber optics cables 14 and 16, or by attempts to tamper with seal system 
10. Suitable electronics for the generation and detection of optical 
signals are taught in U.S. Pat. No. 4,292,628 to Sadler for a "Fibre Optic 
Security System", issued Sep. 29, 1981, which is hereby incorporated by 
reference. 
If such a change in the optical signal, which may be continuous, pulsed or 
otherwise modulated, is detected, display 18 on housing 12 is changed so 
that evidence of attempts to gain unauthorized access to the sealed item 
will be readily observable to inspectors. 
Typically display 18 will be a visual display, such as a light emitting 
diode display, which changes periodically according to an arbitrary, 
pseudorandom pattern based on information stored in the electronics in 
housing 12. Detection of a change in the optical signal causes destruction 
of this information, so that the display pattern cannot be restored by 
unauthorized persons. 
Turning to FIG. 2, a logic diagram showing the logic circuitry in 
tamper-indicating housing 20 is shown. The optical signal from fiber 
optics cable 14 is detected by optical detector 30. In response to the 
optical signal, detector 30 generates a logical signal which passes 
through "AND gate" 32 and triggers optical generator 60 to retransmit the 
optical signal over fiber optics cable 16. Gate 32 is enabled by the 
absence of output from either of the detectors connected to "AND gate" 32. 
In the embodiment shown, a radiation detector 50, to detect changes in 
background radiation, and a load cell 40, to detect movement, are used. 
However, other combinations of detectors are within the contemplation of 
the present invention, their choice depending upon the particular 
application. Logic box 51 is placed between radiation detector 50 and "AND 
gate" 32 while logic box 41 is placed between load cell 40 and "AND gate" 
32. 
Any change in the background radiation and/or the weight sensed by load 
cell 40 will cause the output of the corresponding detector to change, 
disabling "AND gate" 32 and interrupting the optical signal just as though 
the loop comprising cables 14 and 16 had been opened. Thus, the same 
electronic circuitry is used to insure uniqueness for the environmental 
detectors and the seal which comprise the seal system. 
Circuitry to produce a signal which will disable "AND gate" 32 whenever the 
environmental property being monitored exceeds a threshold level is 
incorporated with detectors 40 and 50. These thresholds may be fixed, as 
for load cell 40, or may be based on an average of the level over a 
preselected preceding period of time, as for radiation detector 50, to 
allow for slow changes in the normal levels or drift in the detector. 
It should be noted that each of the subsystems described above, the optical 
detector, "AND gate", optical generator, and the various environmental 
detectors and incorporated circuitry, are well known and numerous 
particular designs for carrying out their functions are known to those 
skilled in the art. Further, the embodiments described above are given by 
way of illustration only, and numerous other embodiments within the 
contemplation of the present invention will be apparent to those skilled 
in the art. In particular, it will be apparent that all the electronics 
and logic may be contained in a single tamper-indicating housing to form a 
seal system or conversely, that one or more detectors in separate housings 
may be inserted into the fiber optic loop. Thus, the limits of the present 
invention are to be found only in the claims set forth below.