Sustainability and Efficiency Improvements of Gas-Cooled High Temperature Reactors

摘要: The work presented in this thesis covers three fundamental aspects of High Temperature Reactor (HTR) performance, namely fuel testing under irradiation for maximized safety and sustainability, architecture improved economy a novel Balance Plant concept to enable future high-tech process heat applications with minimized RD negative Doppler coefficient; high quality elements low power density. All together, these features keep the core temperature within safe boundaries minimise fission product release, even case severe accidents. Very (VHTR) was selected by Generation IV International Forum as one six most promising nuclear reactor concepts based on following criteria: economy, reliability, proliferation resistance physical protection. VHTR is same initial HTR. However, it aims at offering better higher outlet (and thus efficiency) discharge burn-up sustainability). inherent HTR have been demonstrated small pebble-bed reactors practice, but be replicated industrially relevant size power. While an increase density (in order helium coolant temperature) would attractive regard efficiency possible applications, leads temperatures therefore failure probability. consists 6 cm diameter spheres (pebbles) that form randomly packed porous bed, which cooled pressure helium. These pebbles contain thousands 1 mm particles baked into graphite matrix. particles, turn, consist kernel successive coatings pyrocarbon silicon carbide layers. coating layers are designed products build up during operation reactor. Like energy sources, feasibility performance key improvements requires experimental verification view qualification licensing. For fuel, required test string comprises amongst others burn-ups gas release measurements. To end, HFR-EU1 Flux Petten (2006-2010) explored potential existing German (3 produced AVR research centre Julich) newly Chinese (2 INET use HTR-10 China). five were irradiated 445 days separately controlled capsules, while monitored gamma spectrometry enabling evaluation characteristic over birth fraction, indicative health fuel. In none pebbles, abnormally increased observed indicating all approx. 45,000 coated had remained intact. results cover first 332 irradiation. dedicated particularly burn-up, HFR-EU1bis, performed between 2004 2005, investigated extremely steady-state conditions. comparison both experiments confirms plays decisive part integrity. peak can lowered so-called “wallpaper fuel”, arranged spherical shell pebble. This wallpaper also enhances neutronic through neutron resulting reduced fissile material and/or enrichment needs or providing achieve burn-up. quantify improvements, calculations using Monte Carlo transport depletion codes MCNP/MCB (to assess conversion ratio, coefficient reactivity multiplication) PANTHERMIX (for cycle steady state conditions loss accident calculations). Based conditions, particle fractions (with CRYSTAL code) cost determined: Wallpaper type impacts positively reduces need production minor actinides, facilitating reprocessing reducing cost. Safety being operation. parallel, expected fraction 85% its in-core lifetime, and, concomitantly release. long term, very version believed suitable co-generation heat. Its exergy large-scale hydrogen other applications: It meant supply (> 850?C) thermochemical processes. Although has far not disappeared, recent years tendency international projects goes back lower (“HTR” instead “VHTR”) mainly reasons. two main driver countries dropped from their priority list, due economic corrosion issues. second > 950?C require totally new materials construction standards delaying effective future. third reason market shown (steam < 600?C) already so big investment longer term receives priority. addition, tend reach objectives much earlier, approach developed: plant run acceptably compression pump system acting booster. Thus, could limited section conventional external circuit, avoiding constraints related combination separation avoid massive R&D requirements materials, components uncertain outcome, unnecessarily delay introduction otherwise concept. Additionally, improves capability deliver narrow window (50 – 100 K) typically cycles specific end-user applications.