Real-Time Modelling of HFIR Accident Releases

Abstract

A multitude of variables affect an accurate determination of exposure risk to the public following an accidental release of fission products from a nuclear installation. A rapid estimate of fuel damage, expected mitigating equipment availability, and short- and long-term meteorological forecasts are necessary for emergency response personnel to mitigate the consequences of an accidental release most effectively. Critical analogue and digital plant parameters are monitored, displayed, and archived at the High Flux Isotope Reactor (HFIR) through a suite of programmes developed by the Instrumentation and Controls Division of the Oak Ridge National Laboratory. By providing distribution of low-level formatted plant data across a wide area network, these programmes allow tremendous flexibility in the development of end-user applications. An Excel spreadsheet has been developed at ORNL that interacts with the HFIR on-line monitoring system (i.e. using Excel's Dynamic Data Exchange function) to import real-time plant and meteorological variables and create a time history of the pertinent variables necessary for emergency response personnel in off-site decision-making support. The spreadsheet imports raw data in the form of noble gas, iodine and particulate releases, and/or radiation levels, as well as real-time meteorology, stack flow rate, and water PH and from this estimates a core damage fraction as well as expected release rates for the duration of the accident. These estimates are based upon release studies performed using precomputed results from a TRENDS model developed in support of the HFIR FSAR. Through these estimates, the HFIR Accident Release (HAR) spreadsheet allows the results of off-line sophisticated modelling to be used automatically to generate real-time input decks from measured and inferred releases for use in the RASCAL emergency management dose consequence code. The use of this spreadsheet is expected to (1) improve real-time decision making support, especially in the event of an accidental release occurring during the evening hours when many trained technical personnel may be off-site, and (2) provide a readily formatted, archived, time-history of HFIR accident releases for post event evaluations. An accident simulation that makes online use of the HFIR Monitoring System and HAR spreadsheet is presented along with discussion of how these results would be used by emergency response personnel during an accidental release at the HFIR.