The main point to emphasize is that a nuclear consequence occurs only if an accident occurs. It is because of the ‘if statement that only a probabilistic approach makes sense. The first step is that NASA describes the launch vehicle and accidents which may occur. The analysis then presumes that an accident has occurred. Then one estimates the effect (e.g. blast overpressure, high velocity fragment, flames) of that accident on the nuclear system. The response of the system to the accident is the heart of the analysis. In the case of RTGs, the DOE has an extensive database that has grown during more than 25 years of research, development, testing and evaluation (RDT&E). Proposed reactor systems will require similar safety verification testing and analysis activities. Where the system response indicates the release of nuclear material, a pathways- and-consequence analysis (atmospheric dispersion and deposition) is performed. Finally, the risk is the product of the probability and the consequences. Implementing the Process The Galileo and Ulysses EIS (Tier-1) Both the Galileo and Ulysses missions were scheduled for launch, in May/June 1986, aboard the Space Shuttle—both using the Centaur G-prime upper stage for injection into a transplanetary trajectory. Both missions were to fly to Jupiter. The Galileo mission was to fly to Jupiter, inject a probe into Jupiter’s atmosphere, and the main spacecraft was to orbit the planet for about two years to study Jupiter’s major moons and electromagnetic environment. The Ulysses mission was to swing by Jupiter and gain sufficient kinetic energy to move out of the ecliptic plane and study the polar regions of the Sun. In the wake of the Challenger accident, NASA cancelled the Centaur G-prime. Both missions were redesigned to use the inertial upper stage—a less energetic booster than the Centaur but also less likely to contribute to accident environments. The mission redesign, a major federal action, prompted the need for an EIS. It should also be recognized that neither Galileo nor Ulysses had a completed EIS at the time of their inceptions. Both programs were started in the FY78/FY79 timeframe. On the one hand, NASA regulations were still being written at that time; on the other hand, both programs suffered continual major changes. Galileo changed upper stages three times: from the Centaur, to the three-stage IUS, back to the Centaur. Similarly, Ulysses not only changed upper stages, but the USA modified its level of participation when NASA cancelled the ISPM program in which a Ulysses companion spacecraft was to be built. So at the time of the Galileo mission redesign, NASA had published a draft EIS for Galileo but the NEPA process was not complete. A tiering approach (Fig. 4) was adopted for several reasons: (1) Detailed safety and environmental analyses were under way, but were not yet completed. Enough general data were on hand from previous missions and from ‘quick look’ assessments to support overall program-level decisionmaking. (2) There were no immediate environmental impacts of the mission redesign; the only significant impacts could be expected from the launch of the missions. (3) The decision making associated with the redesign would not preclude or obviate a future decision to delay or cancel the missions.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==