The American Nuclear Society (ANS) recently revised the standard ANS-2.21: Criteria for Assessing Atmospheric Effects on the Ultimate Heat Sink (UHS). This standard establishes criteria for the selection and use of meteorological data and identifies supporting hydrologic information to determine whether the design water temperature and cooling capacity requirements for the UHS at a nuclear generating facility are adequately established.

The standard also describes atmospheric effects that need to be considered when designing UHSs for safety-related systems at nuclear power plants such that cooling capacity requirements are met during a licensing-basis event. It applies to the design of the UHS cooling system at existing plants that utilize external water or air sources and includes both open-cycle (rivers, lakes, oceans, atmosphere) and closed-cycle (cooling ponds, spray ponds, cooling towers — wet or dry) UHS systems. It also applies to new nuclear plants that rely on similar external UHS cooling systems.

The document applies to cooling systems that are part of the UHS complex that reject heat to external water or air resources and involve meteorological elements in the design and operation of a UHS. Accident scenarios and assumptions for UHS designs that are not directly related to design meteorological input variables are not covered.

Nuclear power plant operators, designers and nuclear vendors/consultants will benefit from an awareness of the inherent limitations of meteorological data collection, as well as potential data resources described in this revision. The appendices provide examples of applying deterministic and risk-informed, performance-based approaches to developing input data for UHS performance modeling; examples of adjusting data for representativeness and gap filling; and a listing of additional online resources for meteorological data that will evolve with advances in monitoring technology.

To contact the author of this article, email