TY  - JOUR
AU  - Moormann, R.
TI  - Fission Product Transport and Source Terms in HTRs: Experience from AVR Pebble Bed Reactor
JO  - Science and technology of nuclear installations
PB  - Hindawi Publishing Corporation
M1  - PreJuSER-136055
SP  - 597491
N1  - Record converted from JUWEL: 18.07.2013
AB  - Fission products deposited in the coolant circuit outside of the active core play 
AB  - a dominant role in source term estimations for advanced small pebble bed HTRs, particularly in design basis accidents (DBA). The deposited fission products may be released in depressurization accidents because present pebble bed HTR concepts abstain from a gas tight containment. Contamination of the circuit also hinders maintenance work. Experiments, performed  from 1972 to 88 on the AVR, an experimental 
AB  -  pebble bed HTR, allow for a deeper insight into fission product transport  behavior. The activity deposition per coolant pass was lower than expected and was influenced by fission product chemistry and by presence of
AB  -   carbonaceous dust. The latter lead also to inconsistencies between Cs plate out experiments in laboratory and in AVR. The deposition  behavior of Ag was in line with present models. Dust as activity carrier is of safety relevance because of its mobility and of its sorption capability for fission products.  All metal surfaces in pebble 
AB  -   bed reactors were covered by a carbonaceous dust layer. Dust in AVR was produced by abrasion in amounts of about 5 kg/y. Additional dust sources in AVR were ours oil ingress and peeling of fuel element
AB  -    surfaces due to an air ingress. Dust has a size of about 1 μm, consists mainly of graphite, is partly remobilized 
AB  -    by flow perturbations, and deposits with time constants of 1 to 2 h ours. In future reactors, an efficient filtering via a gas tight containment is required because accidents with fast depressurizations induce 
AB  -     dust mobilization. Enhanced core temperatures in normal operation as in AVR and broken fuel pebbles have to be considered, as inflammable dust concentrations in the gas phase.
LB  - PUB:(DE-HGF)16
DO  - DOI:10.1155/2008/597491
UR  - https://juser.fz-juelich.de/record/136055
ER  -