System and safety studies of accelerator driven transmutation ... - SKB

Carl-Magnus Persson et al.
5 CONCLUSIONS
Approximate values of the kinetic parameters for Yalina and Yalina Booster, calculated
from ENDF/B-VI, are summarized in Table V. Since the studied configuration of Yalina
Booster is closer to criticality than Yalina, the uncertainty of the values are lower. At deep
subcriticalities, the fundamental decay mode is dominating during a very short time period. In
Yalina, the injection and adjustment periods take approximately 5 ms and the delayed
neutrons start to influence the pulse after approximately 7 ms. However, in the Monte Carlo
simulation of the PNS experiment in Yalina, the delayed neutrons were excluded, but the
count rate after such long time is low.
Concerning the neutron mean generation time, the value is considerably lower for Yalina
Booster than for Yalina, but still higher than for a fast system. A typical value for a fast
system is on the microsecond-scale; for MASURCA, used in the MUSE-program, the mean
generation time is 0.58 µs [3]. This shows that the fission chain generation process in Yalina
Booster is mainly driven by fissions induced in the thermal zone. Monte Carlo simulations
have shown that the effective multiplication constant for the fast zone by itself is
approximately 0.60 and for the thermal zone 0.95.
The effective delayed neutron fraction is somewhat lower for Yalina Booster than for
Yalina. This is expected since the softer spectrum of the delayed neutrons, in comparison with
the fission neutron spectrum, results in a higher fission probability in a thermal reactor and
the opposite in a fast reactor.
In a near future, PNS experiments will be performed at the Yalina Booster facility and
the values of the kinetic parameters will be verified.
Table V. Summary of the quantitative values of the kinetic parameters for Yalina
and Yalina Booster as evaluated from ENDF/B-VI.
Parameter Yalina Yalina Booster
keff 0.92 0.982
α -700 s -1 -469 s -1
Λ 140 µs 56 µs
βeff 790 pcm 760 pcm
6 ACKNOWLEDGEMENTS
The program of experimental investigations at the Yalina facility has been realized within
the framework of the ISTC Project #B-070, and the construction of the Yalina Booster facility
has been done within the framework of the Belarus State Scientific Program “Instruments for
Scientific Research”. The realization of the experiments and simulations has also been
financially supported by SKB AB (Swedish Nuclear Fuel and Waste Management Co) and
SKI (Swedish Nuclear Power Inspectorate). The authors would like to thank R. Klein
Meulekamp for calculations of effective delayed neutron fractions and for useful discussions.
ICENES’2005, Brussels, Belgium, 2005 8/9