Reacteur BR1 - Première operation de recuit

Followlng a sIx years' perlod of operatlon at a maximum
power of M- MW, the BRl reactor was annealed In order to release the
Wigner energy stored in the crystalline lattice of lts moderating graphite
. When the annealing was performed, the maximum energy was of the
order of 90 cal/g . None of the usual annealing procedures I.e. the
nuclear heating or the fIow of hot air in the plle, was used but a new
process, the internal electrical heating, had to be developed for that
purpose ; moreover, the fuel elements were unloaded from the reactor
before the annealing • The report describes in a detailed manner the
new System which was used and States the advantages of unioading the
ura niurn .
The studies and simulations done before the annealing, the
methods used for measuring the energy of the graphite, and an estimate
of the cost of the material are d‘scussed in a first part, which also
includes a descr’ptlon of the material, the procedures established in
order to guarantee the safety of the operation, and the doses integrated
by the workers during the doublé handling of the 28 tons of irradiated
uranium Included in the core •
In a second part, the chronology of the annealing and its
results are descr'bed and Illustrated ; they can be summarlzed as fotlows
r a maximum temperature voluntarily limited at 398*C, more than
300*C foi 26 hours *n the central part of the plle where the remainlng
energy as measured after the annealing has dropped from 90 cal/g down
to less than 2 cal/g.