[en] The purpose of this investigation was to perform an analytical evaluation of a postulated loss of coolant incident in a large pressurized water reactor. A coupled thermal and stress finite element analysis of a fuel rod subjected to a hypothetical blowdown transient was carried out. The effect of two gap conditions and two initial stress states on the response of the fuel rod was studied. Both one-dimensional and three-dimensional models were investigated. To study the heat transfer in the gap region one assumes a conductive mode of heat transfer in the gap characterized by an equivalent thermal conductivity, which is dependent on the current gap width. Accordingly, coupled analysis procedure and computational scheme were established. A mesh generation computer program was developed for the three-dimensional model. The mesh program can be used, with minor modification, to include any degree of ovalization of the clad

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[en] RELAP4/MOD7, a best estimate computer code for the calculation of thermal and hydraulic phenomena in a nuclear reactor or related system, is the latest version in the RELAP4 code development series. This paper evaluates the capability of RELAP4/MOD7 to calculate refill/reflood phenomena. This evaluation uses the data of International Standard Problem 10, which is based on West Germany's KWU PKL refill/reflood experiment K9A. The PKL test facility represents a typical West German four-loop, 1300 MW pressurized water reactor (PWR) in reduced scale while maintaining prototypical volume-to-power ratio. The PKL facility was designed to specifically simulate the refill/reflood phase of a hypothetical loss-of-coolant accident

[en] RELAP4 is a thermal-hydraulic code which predicts the transient response of a nuclear power plant subjected to postulated accidents such as a loss of coolant (LOCA). When loss of coolant occurs, the Emergency Core Cooling System (ECCS) will respond automatically and the cold water from accumulators and high and low head pumps is injected into the reactor core. The ECC bypass model currently used in RELAP4 is a conservative approach which removes the total amount of injected water (up to the end of bypass) from the reactor coolant system and replaces it with saturated steam. A new model, which is consistent with the current model yet gives a better prediction of ECC water distribution, is presented in this paper. This model, which calculates the distribution of ECC water in the reactor coolant system, only removes the amount remaining

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[en] The induction of P450 4A enzymes by peroxisome proliferators (PPs) and fatty acids is mediated by the peroxisome proliferator activated receptor α (PPARα) that binds to response elements in target genes as a heterodimer with the retinoid X receptor (RXR). The consensus sequence recognized by PPAR/RXR heterodimers, contains an imperfect direct repeat of two nuclear receptor binding motifs separated by a single nucleotide. This repeat is preceded by a conserved A/T rich sequence that is required for function. In mice, chronic exposure to PPs results in PPARα mediated liver hypertrophy, hyperplasia and carcinogenesis accompanied by a proliferation of peroxisomes. In contrast, humans exhibit a reduced sensitivity to PP pathogenesis. This could reflect >10-fold lower PPARα levels relative to mice as well as differences in targeted genes. In order to identify PPAR responsive human genes, the human hepatoma cell line, HepG2, was engineered to express increased levels of PPARα. Several genes encoding rate-limiting enzymes and branch points in ketone body formation are regulated by PPARα in these cells. In contrast, significant induction by PP is not evident for peroxisomal fatty acid oxidation that is associated with peroxisome proliferation in mice. Human P450 4A11 is not expressed in dividing cultures of cells with enhanced PPARα levels, but it is expressed in confluent cultures expressing elevated amounts of PPARα

[en] Fixed in-core instruments (ICIs) allow the core power distribution to be measured on a continuous basis and provide information which is used as input to on-line surveillance and monitoring systems. The use of fixed in-core detectors provides a more accurate assessment of the status of the core power distribution than that which may be inferred by the indirect measurement from ex-core based systems. The higher accuracy translates into a reduction of uncertainties and conservatism which are applied to measured parameters which are monitored to comply with Technical Specifications. Consequently, the higher accuracy results in an effective gain in margin to the licensed thermal limits. The thermal margin gain can be translated into higher allowable power peaks, wider operating spaces or additional flexibility in fuel management

[en] Various patterns of In-Core Instruments (ICIs) have been selected and evaluated for the purpose of reducing the number of installed ICIs. The objective of the investigation has been to satisfy the limits in measurement uncertainty and synthesis uncertainties in existing Topical Reports. The analysis results indicate that a significantly reduced number of ICIs is sufficient to meet the licensed uncertainty limits. The analysis also demonstrates that fuel misloading can be detected with a significantly reduced number of ICIs. This investigation demonstrates that a relatively small number of ICIs, appropriately located, and sophisticated software are sufficient to satisfy requirements placed by Licensing Authorities on core power monitoring and surveillance systems. This work shows consistent results with those described in Reference 1