Hidetoshi Karasawa

MAT, a novel, open cycle gas turbine for power augmentation

Abstract A Moisture Air Turbine (MAT) cycle is proposed for improving the characteristics of land-based gas turbines by injecting atomized water through an inlet into a compressor. Compressor work of isentropic compression for moist air mixtures with phase change is theoretically considered, which has revealed that water evaporation may reduce compressor work. An experiment using a 15 MW class axial flow load compressor has also verified the theory. Realistic cycle model calculations predict that a 10% power increment by a ratio of 1% water to compressor intake air is expected and also that the amount of water consumption is much less than that of conventional inlet air cooling systems, used for heat rejection at the cooling tower. In addition, thermal efficiency is anticipated to be improved mainly due to the reduction of compressor work. Contrary to the conventional evaporative cooler, a MAT cycle could provide power output at a desired value within its capability regardless of ambient humidity condition.

Analysis of Core Degradation and Fission Products Release in Phebus FPT1 Test at IRSN by Detailed Severe Accidents Analysis Code, IMPACT/SAMPSON

The Phebus FPT1 test at IRSN, selected to be ISP-46, has been analyzed by the IMPACT/SAMPSON code, a detailed severe accidents (SAs) analysis code for an LWR. The results for the Bundle phase, involving an examination of bundle degradation and fission products release during SA conditions, were reported. Conclusions obtained from the analyses are as follows: (1) Temperature changes of fuel, cladding, and control rod were well predicted until about 12,000 s when almost all thermocouples measuring them failed. (2) Accumulated hydrogen generation due to Zr/steam reaction differed only about 3% from the test result. (3) Overall, good agreement was obtained for the fuel relocation and an accumulation of debris just below original spacer position was well predicted in the analysis. (4) Analysis of enhanced diffusion due to degraded fuel by Lewis et al.s method enabled simulation of release behaviors of Xe, Cs, I, and Te within the uncertainties in the test when the effective surface to volume ratio was changed in the evaluation of the UO2 oxidation. (5) Diffusion analysis through single-crystal grain could trace the release behavior of Mo, Sb, Tc, Ru, and Ba observed in the Phebus FPT1 test after optimizing their diffusion coefficients with the effective surface to volume ratio determined above.

Behavior of Nitrogen Compounds in Radiation Field and Nuclear Reactor Systems

Formation of nitrogen compounds in N2-H2O systems under radiation was studied. A reaction scheme with 24 species and 73 reactions was proposed. Two trigger reactions for nitrogen atom generation: N2 → 2N (g-value of 1.6 μmol per 1 kJ absorbed energy in N2 molecules), and N2+H2O*→NH2+NO (κ=3.0×109 S−1·M−1 at 298 K with activation energy of 34.4kJ/mol) were included. Calculated results with the reaction scheme agreed within an error factor of two with ammonium formation rates from an aqueous solution with dissolved nitrogen and hydrogen gasses under γ-irradiation at temperatures of 288~473 K. The reaction scheme was also verified with BWR plant observations on nitric acid formation from in-leaked air under hydrogen water chemistry and ammonium injection tests.

Hydrogen management and overpressure protection of the containment for future boiling water reactors

New design and evaluation method for hydrogen management of containment atmosphere have been developed for application in the future boiling water reactor (BWR). These are intended as a part of consideration of severe accidents in the course of design so as to assure a high level of confidence that a large release of radioactivity to the environment that may result in unacceptable social consequences can reasonably be avoided. Emphasis on hydrogen management and protection against overpressure failure is based on the insights from probabilistic safety assessments (PSAs) that late phase overpressure (and associated leakage) and molten corium concrete reaction (MCCI) need attention to ensure that containment remains intact, in case energetic challenges to the containment such as DCH (direct containment heating) or FCI (fuel coolant interactions) are practically eliminated by design or resolved from risk standpoint of view. The authors studied the use of palladium-coated tantalum for hydrogen removal from containment atmosphere in order to avoid pressurization of the containment with small free volume by non-condensable gas and steam. Its effectiveness for ABWR (advanced boiling water reactor) containment was evaluated using laboratory test data. Although further experimental studies are necessary to confirm its effectiveness in real accident conditions, the design is a promising option and one that could be backfitted upon necessity to existing plants for which pressure retaining capability cannot be altered. Also new evaluation method for flammability control under severe accident conditions was developed. This method employes a realistic assessment of the amount of oxygen and hydrogen gases generated by radiolytic decomposition of water under severe accident conditions and their subsequent transport from water to containment atmosphere.

Hydrazine and Hydrogen Co-injection to Mitigate Stress Corrosion Cracking of Structural Materials in Boiling Water Reactors, (III): Effects of Adding Hydrazine on Zircaloy-2 Corrosion

The effects of hydrazine on the corrosion of Zircaloy-2 were examined in supercritical water. Hydrazine could be used as a reducing agent to control the corrosive environment for the coolant of boiling water reactors (BWRs). Before the corrosion test, the applicability of supercritical water for corrosion testing of zirconium alloys was studied. Supercritical water was found to be a useful solvent for testing corrosion based on the following facts: (1) the weight gain of Zircaloy-2 in supercritical water followed the same cubic law with the activation energy of 133 kJ/mol as that in water and steam did, and (2) the weight gain in supercritical water at 723 K and 24.5 MPa was more than 8 times greater than that in water at 561 K and 7.8 MPa depending on immersion time. The corrosion tests in supercritical water at 723 K and 24.5 MPa under γ-irradiation for 1,000 h were conducted to study the effects of adding nitrogen and ammonia on the corrosion of Zircaloy-2. Nitrogen and ammonia are decomposed products of hydrazine. The measured weight gain, oxide film thickness, and amount of hydrogen pick-up had slight differences between cases with and without the additives. Based on these data, it was concluded adding hydrazine to the coolant has little influence on the corrosion of Zircaloy-2 used in BWR cores.

Radiation induced decomposition of nitrogen

Abstract The radiolysis of nitrogen in N 2 -O 2 -H 2 O and N 2 -H 2 -H 2 O systems was examined to obtain the G -values of radiolytic decomposition products of nitrogen in the gas and liquid phases. The main product was nitric acid in the N 2 -O 2 -H 2 O system, and ammonia in the N 2 -H 2 -H 2 O system. Nitrogen molecules decomposed radiolytically into nitrogen atoms via ionic and excitative processes with the respective G -values of 5.6 and 2.4. In the 100% liquid system, nitrogen atoms were formed only by the excitative process because charge transfer from nitrogen ions to water tookplace. In the N 2 -O 2 -H 2 O system, all nitric acid was formed by oxidation of nitrogen atoms. In the N 2 -H 2 -H 2 O system, nitrogen atoms reacting with hydrogen were responsible for forming about 30% of the ammonia produced. About 70% of the ammonia was produced by reaction of nitrogen molecules with hydrogen atoms.