RRFM 2009 Transactions - European Nuclear Society

PARTIAL DISMANTLING OF RESEARCH REACTOR-SOFIA PRIOR
ITS REFURBISHMENT INTO LOW POWER REACTOR
T.G.APOSTOLOV, E.I.ANASTASOVA, V.D.ANASTASSOV, A.D.MLADENOV
Institute for Nuclear Research and Nuclear Energy/Bulgarian Academy of Sciences
72, Tzarigradsko chausse blvd., 1784 Sofia - Bulgaria
ABSTRACT
The strategy for the Research Reactor IRT-Sofia, after decision of the Government
for its refurbishment, is a partial dismantling of the old systems and equipment.
Removal of the reactor core and replacement of old equipment will not pose any
significant problems for dismantling. For most efficient use of resources there is a
need for implementation of the engineering project, “Plan for partial dismantling of
equipment of the IRT-Sofia as a part of its refurbishment and conversion into low
power RR”, which has been already prepared.
Key words: partial dismantling, decontamination, reactor equipment, radioactive wastes
The IRT-Sofia research reactor was designed and constructed in the period
from 1958 to 1961. First criticality was reached in September 1961 and the
research reactor (RR) was in operation for 28 years, until July 1989. The reactor
was started up 4189 times, and it was in operation 24623 hours altogether, at
different power levels (by 2 MW) requested by the users at regular weekly
meetings. It was shut down in 1999 after the Council of Ministers of the
Republic of Bulgaria decision.
The IRT-Sofia is a pool type reactor, cooled and moderated with light water.
The core contains up to 48 fuel and graphite assemblies. There are 14, 15 or 16
fuel rods per assembly. The fuel rods are of the EK-10 type (10% enrichment)
and C-36 (36% enrichment). The reflector includes 13 graphite blocks.
The principal areas of reactor usage ranged from basic and applied
research, to technological and commercial applications. Moreover, it was an
important place for university and post graduate education and training.
To carry out the resolution # 552 of the Council of Ministers of the Republic
of Bulgaria from 2001 for refurbishment and partial dismantling of the
Research reactor IRT-Sofia during its conversion into a low-power reactor, a
Plan for the partial dismantling of the RR has been developed, according to
IAEA Safety Guides [1] and [2]. We are going to carry out this plan in the near
feature.
The partial dismantling activities are part of the overall process of IRT-Sofia Research
Reactor refurbishment. The final state of the IRT-Sofia after the partial dismantling will be the
initial state of mounting the IRT-Sofia new systems and equipment. The criteria that should
be taken into account are the following:
1. Ensuring full technological possibility for mounting of the new systems and
equipment in the reactor pool, the shaft for SNF repository and the primary
circulation loop.
2. Removal of the dismantled equipment from the mounting sites (Reactor hall and
the rooms inside it).
3. Ensuring surface contamination levels and effective dose rate (EFD) below the
admissible values according to the Norms of Radiation Protection (NRP) -2004.
The detailed plan for partial dismantling is intended to describe in detail the succession
of procedures related to the dismantling of the equipment of the Research reactor IRT-Sofia
that is not going to be used for the purposes of its refurbishment into a low-power reactor,
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