Darrell Dunn

Current NRC Perspectives Concerning Primary Water Stress Corrosion Cracking

Materials currently used in nuclear power plants are reliable and are generally resistant to environmental degradation. However, occurrences of environmental degradation have been observed as the current fleet of reactors ages. Primary water stress corrosion cracking (PWSCC) is of particular interest to the US Nuclear Regulatory Commission (NRC). This paper provides a historical assessment of operating experience associated with PWSCC and welding issues associated with PWSCC resistant materials. The paper also considers the regulatory issues associated with PWSCC, especially those associated with gaps in the understanding of the behavior of PWSCC resistant material under actual reactor conditions.

Effect of Residual Stress on Crack Growth Specimens Fabricated From Weld Metal

Slitting method residual stress measurements (Hill Engineering and UC Davis) and finite element weld simulation (US Nuclear Regulatory Commission) have been conducted in order to evaluate both the residual stress intensity factor and residual stress profiles for two compact tension coupon blanks. The two compact tension coupon blanks were provided by Argonne National Lab (ANL) and are similar to coupons used in ongoing stress corrosion cracking (SCC) studies in weld metal. The experimental data and finite element results are in reasonable agreement, showing similar trends in calculated residual stress profiles. Results from the work document the effect of specimen size and location on residual stress profiles, and could be used to determine the degree to which residual stresses affect crack growth measurements made in similar coupons.© 2011 ASME

Containment Liner Corrosion

Of the 104 currently operating nuclear power plants in the U.S, there are 66 plants that have containment buildings constructed with an inner steel liner plate in contact with a thick concrete shell. The steel liner is nominally 6 to 10 mm [0.25 to 0.375 in] thick and is designed in conjunction with the concrete containment building to function as an essentially leak tight barrier against the release of radiation under accident conditions. Corrosion of the containment liner has been observed and corrosion penetration of the liner associated with foreign materials embedded in the concrete from original construction has occurred in a few U.S. plants. This paper reviews plant operating experience, evaluates factors that can affect containment liner corrosion susceptibility, and discusses the mechanisms for through-wall corrosion initiated at the concrete/liner interface.

Severe Transportation Accidents: Impacts of Severe Fires on Radioactive Material Transportation

In 2007, a severe transportation accident occurred in Oakland, California in what is commonly known as the “MacArthur Maze” section of Interstate 580 (I-580). The accident involved a tractor trailer carrying gasoline that impacted an overpass support column and burst into flames. The subsequent fire burned for over 2 hours and led to the collapse of the overpass due to the loss of strength in the structural steel that supported the overpass. The US Nuclear Regulatory Commission (NRC) studied this accident to examine any potential regulatory implications related to the safe transport of radioactive materials, including spent nuclear fuel. This paper will discuss the details of the NRC’s MacArthur Maze fire investigation.