Agenda - 02-02-1999 - 9e1 - Laserfiche WebLink

Browse Search

8 concentrated almost entirely on a postulated condition of instantaneous, complete loss of water from a pool. Such a condition is unrealistic in any scenario which preserves the configuration of the spent fuel racks. If water is lost by drainage or evaporation and no makeup occurs, then complete loss of water will always be preceded by partial uncovering of the fuel. If makeup is considered, the water level could fall, rise or remain static for long periods. 33. Partial uncovering of the fuel will often. be a more severe condition than complete loss of water because, during partial uncovering, convective heat loss is suppressed by the residual water at the base of the fuel assemblies. As a result, longer-discharged fuel with a lower heat output may undergo a runaway steam-zirconium reaction during partial uncovering while it would not undergo a runaway air-zirconium reaction if the pool were instantaneously emptied. 34. I am aware of only one instance in which reports produced by or for the NRC address the hazard posed by partial uncovering, namely in a report prepared for the NRC by Sandia Laboratories and published in 1979.23 Part of this report did address a situation of partial uncovering, but used a crude heat transfer model and neglected to consider the onset of asteam-zirconium reaction. Nevertheless, the report found (page 76) that "......an incomplete drainage can potentially cause a more severe heatup problem than a complete drainage, if the residual water remains near-the baseplates". A portion of the 1979 Sandia report is provided here as Attachment E. An internal NRC memo mentions the consideration of partial uncovering in the 1979 Sandia report.24. Otherwise, it appears that the NRC has ignored the hazard posed by partial uncovering. This hazard was not reflected in the regulatory analysis whereby the NRC purportedly resolved Generic Issue 82.25 35. In a situation of falling water level, a fuel assembly might first undergo a runaway steam-zirconium reaction, then switch to anair-zirconium reaction as water falls below the base of the rack and convective air flow is established. In this manner, a runaway alr- zirconium reaction could occur in a fuel assembly that is too long-discharged (and therefore produces too little heat) to suffer such a reaction in the event of instantaneous, complete loss of water. Conversely, a rising water level could precipitate a runaway steam-zirconium reaction in a fuel assembly that had previously been completely uncovered but had not necessarily suffered a runaway air-zirconium reaction while in that condition. The latter point is highly significant in the context of emergency measures to recover control of a pool which has experienced water loss. Inappropriate addition of water to a pool could exacerbate the accident. 36. The NRC's failure to consider partial uncovering of fuel should be borne in mind when one reviews NRC-sponsored reports that purport to address the hazard posed by water loss from a fuel pool. This hazard should be re-analyzed through detailed J Travis et al, A Safety and Regulatory Assessment of Generic BWR and PWR Permanently Shutdown Nuclear Power Plants, NUREG/CR-6451, August 1997. ~ 23 Allan S Benjamin et al, Spent Fuel Heatup Following Loss of Water During Storage, NUREG/CR-0649, March 1979. ~ 24 Internal NRC Memorandum from J T Han to M Silberberg, "Response to a NRR request to review SNL studies regarding spent fuel heatup and burning following loss of water in storage pool", 21 May 1984. ~ 25 E D Throm, op cit