ORNL-4191 - the Molten Salt Energy Technologies Web Site

Work related to the Molten-Salt Breeder Reactor
was initiated during this period. Studies were
made of the problems related to the removal of
the noble gases from the circulating salt to help
identify the equipment and systems required to
keep the '35Xe poison fraction and the fission
product afterheat to an acceptable level. Preparations
were begun for operation of a small out-ofpile
loop in which a molten salt will be circulated
through a graphite fuel cell and for operation of an
isothermal MSRE-scale loop with sodium fluoroborate.
The major effort of the program at this time is
to help establish the feasibility of improved
concepts and to define problem areas. Since the
production of suitable and reliable salt pumps is
one of the longest lead-time items for molten-salt
reactors, a major emphasis is being placed on this
program.
Some of the work related to problems of the
Dunlap Scott
graphite and other sinks in the MSRR. The sink
terms considered are:
1. Decay
2. Eurnup - takes place in the graphite and in the
fuel salt passlrig through the core.
3. Migration to graphite - these gases ultimately
decay or are burned up.
4. Migration to circulating bubbles ...- these gases
are stripped from the fuel loop to go to the
off-gas system.
Two source terns are considered: generation
directly from fission, which is assuined to occur
only in the core, and generation from decay of the
precursor, which OCCUKS throughout the fuel loop.
The model is based on conventional iiiass transfer
concepts, Some degree of success has beeil ex-
perienced with similar models developed for the
MSKE, for example:
MSBR but actually performed on the MSRE is 1. Xenon-135 poison fraction calculations. The
discussed in the MSRE section of this report.
The other work is described below.
7.1 NOBL E-GAS AVlQR Ira THE MSBR
R. J. Ked1
In the MSBR conceptual designs, the graphite
in the reactor core is unclad and in intimate
contact with fuel salt. Noble gases generated by
fission and any gaseous compounds can diifuse
from the salt into the porous structure of the
graphite, where they will serve as heat sources
and nuclear poisons.
A steady-state analytical model was developed
to compute the migration of noble gases to the
90
steady-state model is developed in ORNL-4069.
Results of the time-dependent form of the model
are summarized in OKNL-TM-1796.
2. A model was developed t~ compute the con-
centrations of daughters of very short-lived
noble gases in graphite (QRNL-TM-1810).
Computed concentrations check very well with
measured values.
With this model, steady-state l3 5Xe poisoning
calculations have been made for the MSBR [556
Mw (thermal) fueled with 233U and moderated with
unclad graphite) to show the influence of various
design parameters involved. The reactor con-
sidered here is essentially that described in
ORNL-3996 [P. FZ. Kasten ef a]., Design Studies
of 1000-Mw (e) Molten-Salt Breeder Reactors], with
specific design parameters as listed in 'Table 7.1.