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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 a steam- 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 3 5 . In a situation of falling water level , a fuel assembly might first undergo a runaway steam-zirconium reaction, then switch to an air-zirconium reaction as water falls below the base of the rack and convective air flow is established . In this manner, a runaway air- 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-zirconiurfi 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.