ANSTO has welcomed an independent study of its HIFAR reactor that found the plant safety status has been shown to be generally good with no evidence of major safety-related problems from its operation.
The Department of Industry, Science and Tourism, following a recommendation of the Research Reactor Review in 1993, commissioned the study, a Probabilistic Safety Assessment (PSA). Carried out over some 18 months by a United States consultancy, PLG, the PSA was the most extensive ever conducted on a research reactor. The study considered the likelihood of events that could lead to damage to HIFAR's fuel or to its cooling circuit.
The Probabilistic Safety Assessment established seven benchmarks for HIFAR to allow comparison with a modern research reactor. These were expressed as the number of times certain events may acceptably occur in every 10,000 years. Two benchmarks were primary safety objectives, the remainder secondary safety objectives.
The primary objectives correspond to the capacity to withstand postulated scenarios that could lead to fuel overheating and that may have potential for impact on the environment. The secondary safety objectives apply to the capacity to withstand postulated scenarios that, if they were to occur, have a much lower potential for impact on the environment.
HIFAR met the first primary safety objective comfortably. PLG noted that, "By meeting the first objective one can conclude that HIFAR is adequately designed and operated to prevent the fuel in the reactor and No.1 Storage Block from overheating."
The second objective considered the capacity to withstand an earthquake of a severity that would occur once or less often than once in every 10,000 years in the Sydney area. With the current level of information and assumptions, this objective was considered to be exceeded, because there are no accurate data available on the severity of such earthquakes. As a result, the standard practice in PSAs of using very pessimistic assumptions, when applicable data are unavailable was used to calculate HIFARs performance.
ANSTO notes that an earthquake of the intensity assumed, with a likelihood of occurrence no more than once in 10,000 years has never been recorded in Sydney and would cause much more serious damage to other buildings and structures in the Sydney region, if it did occur.
ANSTO supports the comment by PLG that, "when specific pessimistic assumptions are found to significantly impact the analysis results, they are and should be carefully re-evaluated, justified by more detailed analysis, to yield a more realistic estimate of the risk."
PLG specifically recommended additional study of the potential effects of earthquakes. The Department of Industry, Science and Tourism has commissioned further study into the earthquake question. However, ANSTO has already begun preparations to enhance the protection of the relevant equipment, the primary cooling pipework.
This new pipework protection system will prevent loss of cooling to the reactor core, even if an extreme earthquake were to occur, and effectively remove the concern over fuel damage during seismic events.
Of the five secondary safety objectives, three were regarded as met; the remaining two were not, also because of the lack of data on both large earthquakes and incidents during flask movements. The scenario tested in the flask movement assessment was the potential to damage fuel from dropping of the fuel transport flask, either within the reactor building or outside.
As there has never been such an occurrence in the 40 years of HIFAR's operation, no data were available for HIFAR. Very pessimistic assumptions were therefore made. ANSTO, in conjunction with independent consultants, has subsequently confirmed that, with current operations, there is no possibility that dropping of fuel flasks will cause fuel melting or damage.
This further analysis has also confirmed that any radioactive release from damaged fuel in the flask would be insignificant. The PSA also recommended a number of changes to design or procedures. All have been
implemented.
"Compared to the internationally recommended and normally used Level 1 PSA for research reactors, HIFAR has done well", ANSTOs Chief Executive, Professor Helen Garnett, said.
"ANSTO is confident that the additional measures adopted and the further analysis will show the HIFAR reactor fully complies with the required benchmarks", she said.
The study was overseen and reviewed by a Technical Review Committee appointed by the Department.
ANSTO wishes to thank the members of the Committee for their contributions: Emeritus Professor Ian Polmear, formerly Chairman Department of Materials Engineering and Deputy Vice Chancellor of Monash University (Chair); Professor Rob Melchers, Head, Department of Civil, Surveying and Environmental Engineering, University of Newcastle; Dr Derek Mullins, Leader, Major Hazards Policy Unit, NSW Department of Urban Affairs and Planning; Dr Garry Smith, Principal Environmental Scientist, Sutherland Shire Council; and Dr Ron Cameron, Director, Safety, ANSTO.
ANSTO wishes to thank the members of the Committee for their contributions: Emeritus Professor Ian Polmear, formerly Chairman Department of Materials Engineering and Deputy Vice Chancellor of Monash University (Chair); Professor Rob Melchers, Head, Department of Civil, Surveying and Environmental Engineering, University of Newcastle; Dr Derek Mullins, Leader, Major Hazards Policy Unit, NSW Department of Urban Affairs and Planning; Dr Garry Smith, Principal Environmental Scientist, Sutherland Shire Council; and Dr Ron Cameron, Director, Safety, ANSTO.