Development of Transient Criteria

The criteria for abnormal transients to ensure the fuel integrity are very important. They limit the maximum allowable coolant temperature and the choice of the fuel cladding material to be used at high temperature. So, to maximize the economical potential of the Super LWR, and minimize the research and development efforts, the criteria need to be rationalized based on detailed fuel rod analyses. 

In the following, the FEMAXI-6 code [35], described in Sect. 2.7.2 is used with the same models for the fuel rod analyses. 

Cladding Material Stainless steel Zircaloy 2 Zircaloy 4 

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In this paper we discuss three issues related to our ability to exploit the undoubted attractions of the EQCM technique (a) the extent of mobile species uptake as a function of solution concentration (b) the use of transient measurements to obtain (additional) selectivity and (c) the need to establish that the criteria are satisfied for the Sauerbrey equation (equation [1]) to be used to convert measured frequency changes to mass changes. Of these, (a) and (c) have been demonstrated (see previous paragraph) to be directly relevant to QCM-based biosensors. The concept of using transient measurements in this context has not yet been explored, but is a natural development. 

Given the DSM-IV criteria, evaluating a patient in one office visit will not be sufficient to diagnose PTSD. Continuity of care is essential in determining whether patients have PTSD. Most distress symptoms are transient. To make the diagnosis, primary care physicians should document an accumulation of symptoms, a lack of improvement or a deterioration of the patient s condition and the persistence or development of a functional disability during several office visits over 3 weeks (30). 

However, such conservative criteria severely limited the plant operability during anticipated transients. In order to maximize the economical potential of the Super LWR and Super FR, and minimize the R D efforts, the criteria were rationalized based on detailed fuel analyses. The FEMAXI-6 code [31] for LWR fuel analyses was used for the study. The principle of rationalization of the criteria for anticipated transients of Super LWR was developed [32, 33]. The design and integrity analysis of the Super LWR fuel rods is summarized in ref. [34]. 

The principle of rationalization of the criteria for abnormal transients of the Super LWR was developed. Detailed fuel analyses showed that allowable limits to the maximum fuel rod power and maximum cladding temperature can be determined to ensure the fuel integrity for abnormal transients of the Super LWR. 

The safety principle and safety system design are described in Sects. 6.2 and 6.3, respectively. Then, the deterministic approach to the Super LWR safety is described in Sects. 6.4-6.7 these describe safety analysis methods, selection and classification of abnormal events, the criteria for safety analyses, and the results of safety analyses. In addition, development of a transient subcharmel analysis code and its application to the flow decreasing events are described in Sect. 6.8. Based on the safety system design and the deterministic safety analyses, level-1 probabilistic safety assessment (PSA), which is also called level-1 probabilistic risk assessment (PRA), is presented. 

The ESDs were then translated into associated event trees. A generic event tree was developed for all initiators not involving LOCA. The generic transient event tree for each category of the transient initiators and loss of offsite power were specialized by the impact of the initiators on the safety and support systems, from the success criteria of the mitigating systems, and the initiator-specific human actions which were modeled in the fault trees. 

The criteria used to select the core and coolant designs were developed with emphasis on safety and assurance of technical feasibility. The operating and transient design criteria mostly concern fuel performance. 

For the transient relaxation of X to the non-equilibrium stationary state AG is not a valid criterion of irreversibility or spontaneous reaction. We shall develop necessary and sufEcient thermodynamic criteria for such cases. 

The restart criteria require that transient and accident analyses include the assumption that mitigating systems are not actuated until the most conservative setpoint is reached. The Action Plans discuss setpoints and the time delays allowed for scram. In responding to the staff s inquiry, WSRC has indicated that worst-case setpoints are assumed for the analyses and, in particular, for the scram or the actuation of the Supplementary Shutdown System (SSS). WSRC further assured the staff that it has prepared specific calculations containing tables for all trip setpoints used for its analyses and that WSRC is currently developing a setpoint methodology document. Determination of setpoints is an open item. 

The change of cross flow within a subassembly may occur during transients. The MCST may change from the result of the single-channel calculation. A transient subchannel analysis code was developed and the safety analysis of a Super LWR was carried out [70]. The temperature rises from the steady state value are about 20°C at the abnormal transients and about 130°C at accidents. The maximum values still stay below the MCST criteria for transients and accidents. The development and application of the transient subchannel analysis code are sununarized in Sect. 6.8. 

Since the Super LWR is presently in the concept development phase, the safety criteria cannot be determined based on experiments. The principle for the safety criteria and tentative values for the safety analyses have been determined [4-6]. The requirements for abnormal transients are the same as those of LWRs no systematic fuel rod damage and no pressure boundary damage. The requirements for accidents are no excessive core damage and no pressure boundary damage, which also correspond with LWRs. The safety criteria described below are determined for concept development. Experiments will be necessary for assessing their validity. 

The fuel rod cladding material of the Super LWR is being developed and tested. For fuel rod design of the Super LWR in the cmicept development phase, typical austenitic stainless steels or Ni-alloys are applied as described in Chap. 2. The principle of the safety criteria for fuel rod integrity is shown in Table 6.6. Since heat transfer deterioration is a much milder phenomenon than boiling transition, the minimum deterioration heat flux ratio was eliminated from the transient criterion related to fuel rod heat-up [7]. The types of abnormalities are separated into loss of cooling and overpower . 

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