atw 2018-04v6
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<strong>atw</strong> Vol. 63 (<strong>2018</strong>) | Issue 4 ı April<br />
DECOMMISSIONING AND WASTE MANAGEMENT 242<br />
1 Introduction<br />
The ENEA RB3 (Reattore Bologna 3)<br />
reactor was a 100 Wth research installation<br />
owned and operated by ENEA<br />
in its center of Montecuccolino, near<br />
Bologna, from 1971 to 1989. It consisted<br />
of a cylindrical aluminium vessel,<br />
about 4.3 m high and 2.9 m in diameter,<br />
which could host various types of<br />
fuel elements suspended from the top<br />
of a special adjustable rack, and submerged<br />
into heavy water serving both<br />
as moderator and coolant. Principal<br />
aim of the reactor was to provide<br />
neutronics data for the CIRENE NPP, a<br />
SGHWR that was being designed, and<br />
then partially built in Latina, starting<br />
from 1979. The specific RB3 core, surrounded<br />
by a graphite reflector and<br />
housed inside a concrete biological<br />
shielding, allowed to test easily very<br />
different fuel element configurations<br />
by changing their pitches and by<br />
regulating the heavy water level inside<br />
the vessel. The reactor design, similar<br />
to that of the ZED-II Canadian<br />
research facility, was originally developed<br />
by CEA for its Aquilon facility in<br />
Saclay in 1956; in fact, through a<br />
special arrangement between ENEA<br />
and CEA, parts of the Aquilon facility<br />
were ultimately donated to ENEA at<br />
the end of the 60s for the construction<br />
of RB3. In 1989, after more than 18<br />
years of operation, the RB3 reactor<br />
was shut down, and in the late 2010,<br />
after waiting for the entry into force of<br />
Legislative Decree (L.D.) 230/1995<br />
[1], which introduced new laws for<br />
the decommissioning of NPPs, ENEA<br />
received by ministerial decree the<br />
authorization to its dismantling, with<br />
the aim of reaching the “green field”<br />
status and with the unconditional<br />
release of its building, including the<br />
reactor concrete biological shielding,<br />
which is actually owned by the<br />
University of Bologna. In fact the site<br />
of Montecuccolino, some 3.5 km to<br />
the South of downtown Bologna,<br />
hosted three research reactors: RB1,<br />
owned and operated by the University<br />
of Bologna, RB2, owned and operated<br />
by AGIP Nucleare, and RB3, owned<br />
and operated by ENEA. RB1 and RB2<br />
were decommissioned up to the green<br />
field status well before the entry into<br />
force of L.D. 230/1995.<br />
Figure 1 shows an aerial view of<br />
the Montecuccolino research center,<br />
with the area hosting RB3 contoured<br />
in red. Figure 2 shows a plan of the<br />
main reactor hall, with in red the<br />
area once occupied by the reactor<br />
vessel, surrounded by the hectagonal<br />
graphite reflector and encased within<br />
a thick concrete biological shielding.<br />
Figure 3 shows a vertical section of<br />
the RB3 building; the lowermost floor<br />
hosted 4 large tanks for a total of<br />
20,000 L (in red) for the storage of the<br />
heavy water which was daily pumped<br />
up into the vessel to reach criticality<br />
and then drained after the conclusion<br />
of the experiments. Three floors are<br />
present in the building: floor +6.0 m<br />
corresponding to the ground level,<br />
floor +0.0 m, corresponding to the<br />
level of the reactor vessel, and floor<br />
-3.0 m, with the heavy water storage<br />
tanks, heating and cooling systems,<br />
and other auxiliaries. The control<br />
| | Fig. 2.<br />
Plan of main hall of RB3.<br />
room was located at floor +0.0 m.<br />
While allowed to operate up to 100<br />
Wth, operations at RB3 were always<br />
conducted at 50 Wth.<br />
Between 1991 and 1992, all the<br />
fuel elements used at RB3 were either<br />
restituted at their owner (JRC Euratom<br />
Ispra) or sent to the ENEA Research<br />
Center of Saluggia or to the fuel fabrication<br />
plant of Fabbricazioni Nucleari<br />
at Bosco Marengo. Between 1992 and<br />
1993 all the heavy water was transferred<br />
to the ENEA Research Center of<br />
Borgo Sabotino, and before the end of<br />
1997 all the sealed radioactive sources<br />
used at the plant were disposed of.<br />
2 Regulatory Requirements<br />
and Classification<br />
of Components and<br />
Materials<br />
In the late 2010, ENEA received, by<br />
decree of the Italian Ministry of<br />
Economic Development, the authorization<br />
[2] to proceed with the dismantling<br />
of RB3; included in the<br />
| | Fig. 1.<br />
Aerial view of the Montecuccolino site; the RB3 building is inside the red square.<br />
| | Fig. 3.<br />
Section of the RB3 building.<br />
Decommissioning and Waste Management<br />
The Decommissioning of the ENEA RB3 Research Reactor in Montecuccolino ı F. Rocchi, C. M. Castellani, A. Compagno, I. Vilardi, R. Lorenzelli and A. Rizzo