Work supported by the Air Force Office of Scientific Research under Grant AFOSR-69-1625.

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recommended to switch back and forth between intermittent and dc operation.In the intermittent mode, the lamp is operated for only a short time, nt, typically 20 X 0.01 sec = 0.2 second for the results in Table II. We found that the light output is the same and so is the stability if n and t are changed within limits to maintain the product constant. For example, if instead of twenty 15-msec pulses, sixty 5-msec pulses are used, output signal is nearly the same value and stability is constant. For short ON-times of less than 2 msec, time delay problems in lamp response and power supply responses can lower reproducibility. In our case, a 4-15 msec ON-time per period proved to be the most appropriate.Measurement Conditions. It is important when making measurements with the hollow cathode lamps to operate under experimental conditions so that sufficient photons are incident on the photomultiplier cathode during the measurement period (12). For example, if a relative standard deviation of 0.1 % is desired for each integration of n pulses, then 10s photon counts must be obtained for the selected hollow cathode time. Thus, the optical throughput and the product nt must be sufficient to provide the required number of photons for the desired precision.

This report provides the results of work carried out in support of the U.S. Nuclear Regulatory Commission Accident Management Research Program to develop a technical basis for evaluating the effectiveness and feasibility of current and proposed strategies for boiling water reactor (BWR) severe accident managemenl First. the findings of an assessment of the current status of accident management strategies for the mitigation of in-vessel events for BWR severe accident sequences are described. This includes a review of the BWR Owners' Group Emergency Procedure Guidelines (EPGs) to detennine the extent to which they currently address the characteristic events of an unmitigated severe accident and to provide the basis for 111 recommendations for enhancement of accident management procedures. Second. where considered necessary. new candidate accident management strategies are proposed for mitigation of the late-phase (after core damage has occurred) events. Finally. recommendations are made for consideration of additional strategies where warranted. and two of the four candidate strategies identified by this effort are assessed in detail: (1) preparation of a boron solution for reactor vessel refill should control blade damage occur during a period of temporary core dryout and (2) containment flooding to maintain the core debris within the reactor vessel if the injection systems cannot be restored.