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Conference Spotlight
Nuclear Energy Conference & Expo (NECX)
September 8–11, 2025
Atlanta, GA|Atlanta Marriott Marquis
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The Standards Committee is responsible for the development and maintenance of voluntary consensus standards that address the design, analysis, and operation of components, systems, and facilities related to the application of nuclear science and technology. Find out What’s New, check out the Standards Store, or Get Involved today!
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Deep Space: The new frontier of radiation controls
In commercial nuclear power, there has always been a deliberate tension between the regulator and the utility owner. The regulator fundamentally exists to protect the worker, and the utility, to make a profit. It is a win-win balance.
From the U.S. nuclear industry has emerged a brilliantly successful occupational nuclear safety record—largely the result of an ALARA (as low as reasonably achievable) process that has driven exposure rates down to what only a decade ago would have been considered unthinkable. In the U.S. nuclear industry, the system has accomplished an excellent, nearly seamless process that succeeds to the benefit of both employee and utility owner.
Mark T. Leonard
Nuclear Technology | Volume 62 | Number 1 | July 1983 | Pages 31-42
Technical Paper | Nuclear Safety | doi.org/10.13182/NT83-A33229
Articles are hosted by Taylor and Francis Online.
Upper head injection (UHI) is an emergency core coolant (ECC) system design that injects subcooled water into the upper head of the reactor vessel in a pressurized water reactor. An analysis has been performed that investigates the effects of UHI on small-break transient behavior. The analysis consists of several RELAP5/MOD1 computer code calculations, which have been compared to experimental data from a series of small break loss-of-coolant accident simulations, performed in the Semiscale Mod-2A system. Small-break transient phenomena were calculated not to be significantly affected by the introduction of subcooled liquid into the vessel upper head. Nonequilibrium effects were minimal and limited to the period of ECC injection. The analysis covered a range of small-break sizes, and the severity of the transients (in terms of minimum core coolant level) was calculated to be a maximum (with or without UHI) for a cold leg break size of ∼5.0% of the cold flow area. For all break sizes, UHI was calculated to increase the margin against core uncovery. The calculated hydraulic phenomena and specific fluid conditions were generally in good agreement with data. The calculated relative magnitudes of important phenomena were preserved over the break size spectrum.
