Publications

Abstract not provided.

Procedures to predict the reliability of electrical circuits are discussed. Three cases are introduced and discussed. In Case 1, an analyst predicts the probability of any failure in the intended relations between circuit inputs and circuit outputs. In Case 2, an analyst predicts the probability that specified unintended outputs would occur. In Case 3, an analyst considers coupling between circuits. Logic models are given for the three cases, and sources of failure probabilities of components are mentioned. Methods of analysis are given, software tools are mentioned, and recommendations for presentation and review of results are discussed.

Abstract not provided.

Abuse tests were conducted on the lead-acid batteries used to power electrical testers used at the Department of Energy's Pantex Plant. Batteries were subjected to short circuits, crushes, penetrations, and drops. None of the observed responses would be a threat to nuclear explosive safety in a bay or cell at Pantex. Temperatures, currents, and damage were measured and recorded during the tests.

The current that flows between the electrical test equipment and the nuclear explosive must be limited to safe levels during electrical tests conducted on nuclear explosives at the DOE Pantex facility. The safest way to limit the current is to use batteries that can provide only acceptably low current into a short circuit; unfortunately this is not always possible. When it is not possible, current limiters, along with other design features, are used to limit the current. Three types of current limiters, the fuse blower, the resistor limiter, and the MOSFET-pass-transistor limiters, are used extensively in Pantex test equipment. Detailed failure mode and effects analyses were conducted on these limiters. Two other types of limiters were also analyzed. It was found that there is no best type of limiter that should be used in all applications. The fuse blower has advantages when many circuits must be monitored, a low insertion voltage drop is important, and size and weight must be kept low. However, this limiter has many failure modes that can lead to the loss of over current protection. The resistor limiter is simple and inexpensive, but is normally usable only on circuits for which the nominal current is less than a few tens of milliamperes. The MOSFET limiter can be used on high current circuits, but it has a number of single point failure modes that can lead to a loss of protective action. Because bad component placement or poor wire routing can defeat any limiter, placement and routing must be designed carefully and documented thoroughly.

Electrical discharges from a lightning simulator were directed at Mk12 aeroshells. Buckling of the aluminum substrate was observed after some 100-kA shots, and severe damage consisting of tearing of the aluminum and the production of inward flying aluminum shrapnel was observed after some 200-kA peak-current shots. Some shots resulted in severe damage to both the aluminum and the carbon-phenolic ablative material. It is reasonable to conclude from the experimental results that a lightning stroke with very high-peak current could, by itself, produce an opening in an Mk12 aeroshell. Because the aeroshell is part of the nuclear explosive safety exclusion region for the Mk12/W62 nuclear weapon, an opening would significantly reduce the assured safety of the weapon. It is unlikely that the observed interaction between lightning and the aeroshells would have been predicted by any form of computer simulation.

Silicon power diodes, transistors, thyristors and other devices can be damaged by elevated temperatures, temperature cycling, and radiation. In this paper we discuss the vulnerability of devices that integrate bipolar and MOSFET (metal-oxide-semiconductor-field-effect transistor) devices onto a single chip. Such devices offer the advantages of good current carrying capability that is characteristic of bipolar structures and high impedance control nodes that are characteristic of MOSFET devices. Devices located near a space-based fission power source will be subjected to high temperatures, temperature cycling, naturally occurring radiation, radiation from the reactor; and these devices may be subjected to radiation from or caused by weapons used to attack the power source. Damaging radiation includes electrons and protons trapped in naturally occurring radiation belts, electrons pumped into these belts as a result of nuclear explosions, cosmic rays, neutrons from the reactor, and high energy photons (gamma rays and x-rays). 3 refs., 2 figs.

This paper reports the changes caused by fast neutrons and 200 MeV protons in the electrical properties of high electron mobility transistors (HEMT). A larger gate voltage was required after irradiation with neutron fluences in the 1E14 to 2E15 n/cm{sup 2} range and 200 MeV proton fluences in the 1E14 to 1E15 p/cm{sup 2} range than was required prior to irradiation to obtain the same value of I{sub ds}. The increase in gate voltage required to compensate for a fluence of 1E15 protons/cm{sup 2} was up to four times as great as that required to compensate for the same fluence of neutrons. All devices showed microwave gain (s21) after exposure to 6E14 particles/cm{sup 2} if the gate bias was adjusted to maintain the pre-irradiation value of I{sub ds}. Gamma irradiation at 5E7 rads(GaAs) had no detectable effect on the devices. 8 refs., 6 figs., 1 tab.