NUCLEAR SAFETY
Understanding the Challenge

In a nuclear safety test in the mid-1980s, bundles of non-nuclear fuel rods were heated until they melted to determine safe temperature limits.

ORNL has influenced nuclear safety in numerous ways. It trained more than 900 engineers in reactor design and safe operation. The Laboratory published the journal Nuclear Safety for more than 30 years. Since the 1960s ORNL has had a major impact on nuclear criticality safety—using industrial controls to protect against potential consequences of an unintentional, uncontrolled chain reaction during uranium or plutonium processing, storage, or transport. ORNL researchers provided the basis for several criticality safety standards and administered the international group approving this guidance.

In the late 1960s ORNL researchers led by Grady Whitman began studying whether steel walls of reactor pressure vessels exposed to high temperatures and embrittling radiation could withstand the water pressures of reactor operation without cracking. Having conducted research for more than three decades on thermal shock, fracture mechanics, and radiation embrittlement, ORNL became the world leader in producing data that have provided a basis for licensing and operation of light-water-reactor (LWR) pressure vessels.

ORNL research showing that zirconium-alloy fuel cladding became brittle under simulated accident conditions led to new regulations limiting LWR power levels. These results, reported by ORNL experts during national safety hearings, led to tighter requirements to lower the probability that reactor cores would overheat if emergency cooling water were lost. ORNL fission-product-release studies also provided a basis for safety regulations.

When a loss-of-coolant accident occurred in 1979 at the Three Mile Island power plant, ORNL researchers assisted the Nuclear Regulatory Commission in ascertaining causes and consequences of the accident and discovered that less radioactive gas was released than expected. As a result of the accident, ORNL and NRC staff developed the Sequence Coding and Search System, which captures information on nuclear power plant operations for inclusion in a database. The system has been used for numerous safety studies, regulatory actions, and risk assessments.

ORNL researchers developed accident models for NRC that prompted improvements in advanced boiling-water-reactor designs. They also have helped establish regulatory guides for digital instrumentation and control systems in nuclear plants.

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