Effect of packing fraction variations on the multiplication factor in pebble-bed nuclear reactors
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L. Snoj
Abstract
The effect of fuel element packing density on the effective multiplication factor, keff, in a typical pebble-bed reactor (PBR) is studied using MCNP and WIMS computer codes. It is observed that at normal operating conditions keff increases with packing density. Increase in packing density of 1% results in approximately 0.0015 increase in keff. A negative temperature effect is observed at all feasible packing densities. The effect of secondary coolant (water) ingress in the core at accidental conditions is studied at various packing densities. The effect of effective water density on keff depends on packing fraction, fuel enrichment and fuel-to-graphite ratio. It is strongly positive in highly enriched fuel at low water density regardless of packing fraction. For fuel enrichment 8% and normal packing density, a maximum positive effect of approximately +0.10 on keff is observed at a water density of ∼0.1 g/cm3. The positive effect is reduced at low enrichments. Above a water density of 0.5 g/cm3, the effect on keff becomes negative regardless of enrichment and packing density.
Kurzfassung
Der Einfluss der Brennelementpackungsdichte auf den effektiven Multiplikationsfaktor keff in einem typischen Kugelhaufenreaktor wurde mit Hilfe der Rechencodes MCNP und WIMS untersucht. Dabei wurde beobachtet, dass bei normalen Betriebsbedingungen keff mit der Packungsdichte wächst. Ein Anstieg der Packungsdichte von 1% hat einen Anstieg von keff um etwa 0,0015 zur Folge. Ein negativer Temperatureffekt wurde bei allen möglichen Packungsdichten beobachtet, der Effekt des Zuflusses von Sekundär-Kühlmittel (Wasser) in den Kern unter Unfallbedingungen wurde bei verschiedenen Packungsdichten untersucht. Der Einfluss der effektiven Wasserdichte auf keff hängt von der Packdichte, der Brennstoffanreicherung und dem Brennstoff-Graphit-Verhältnis ab. Der Effekt ist stark positiv bei hoch angereichertem Brennstoff und niedriger Wasserdichte unabhängig von der Packungsdichte. Für 8% angereicherten Brennstoff und normale Packungsdichte wurde ein maximal positiver Effekt von ca. +0.10 auf keff bei einer Wasserdichte von ca. 0.1 g/cm3 beobachtet. Dieser positive Effekt reduziert sich bei niedrigeren Anreicherungen, oberhalb einer Wasserdichte von 0.5 g/cm3 wird der Einfluss auf keff negativ, unabhängig von Anreicherungsgrad und Packungsdichte.
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© 2006, Carl Hanser Verlag, München
Artikel in diesem Heft
- Contents/Inhalt
- Contents
- Summaries/Kurzfassungen
- Summaries
- Technical Contributions/Fachbeiträge
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- Determination of the exposure build-up factor in a slab using the LTSN method
- Lumped parameters analysis of the IAEA research reactor benchmark problem
- Assessment of the look-up table using the tubular and bundle CHF data and modification of the bundle correction factor
- A finite element model for static strength analysis of CANDU fuel bundle
- Effect of packing fraction variations on the multiplication factor in pebble-bed nuclear reactors
- Design of a dry cask storage system for spent LWR fuels: radiation protection, subcriticality, and heat removal aspects
- Radiological and thermal characteristics of CASTOR RBMK-1500 and CONSTOR RBMK-1500 casks for spent nuclear fuel storage at Ignalina Nuclear Power Plant
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Artikel in diesem Heft
- Contents/Inhalt
- Contents
- Summaries/Kurzfassungen
- Summaries
- Technical Contributions/Fachbeiträge
- The multipurpose thermalhydraulic test facility TOPFLOW: an overview on experimental capabilities, instrumentation and results
- Uncertainty in cross-section calculations for reactions induced by neutrons with energy above 0.1 MeV
- Determination of the exposure build-up factor in a slab using the LTSN method
- Lumped parameters analysis of the IAEA research reactor benchmark problem
- Assessment of the look-up table using the tubular and bundle CHF data and modification of the bundle correction factor
- A finite element model for static strength analysis of CANDU fuel bundle
- Effect of packing fraction variations on the multiplication factor in pebble-bed nuclear reactors
- Design of a dry cask storage system for spent LWR fuels: radiation protection, subcriticality, and heat removal aspects
- Radiological and thermal characteristics of CASTOR RBMK-1500 and CONSTOR RBMK-1500 casks for spent nuclear fuel storage at Ignalina Nuclear Power Plant
- Analyses of severe accident scenarios in RBMK-1500
