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the mechanisms involved in these two processes.
A mechanistic understanding applied to models for
these phenomena improves our ability to explain
results to regulatory agencies, and justifies application
of these results to ranges outside the tested
conditions (e.g., extrapolation to a wider selection
of materials and to larger-scale experiments and
containment conditions).
The specific technical objectives for BIP-2 are:
• to obtain a more detailed and mechanistic understanding
of iodine adsorption and desorption on
containment surfaces by means of new experiments
with well-characterised containment paint
constituents and novel instrumentation (spectroscopic
methods);
• to obtain a more detailed and mechanistic understanding
of organic iodide formation by means of
new experiments with well-characterised containment
paint and paint constituents and novel
instrumentation;
• to develop a common understanding on how to
extrapolate confidently from small-scale studies
to reactor-scale conditions.
The BSAF
The Benchmark Study of the Accident at the
Fukushima Daiichi Nuclear Power Station (BSAF)
was established among eight NEA member countries
as a new joint research project in 2012. The BSAF is
intended to improve severe accident (SA) codes, and
to analyse accident progression and current core status
in detail for preparation of fuel debris removal as
a part of the R&D projects for the mid- to long-term
response for decommissioning Fukushima Daiichi
units 1 to 4.
The project is hosted by the Japan Atomic Energy
Agency (JAEA), the operating agent, in collaboration
with other Japanese institutions such as the Institute
of Applied Energy (IAE), the Japan Nuclear Energy
Safety Organisation (JNES) and the Central Research
Institute of Electric Power Industry (CRIEPI), and is
supported by the Tokyo Electric Power Company
(TEPCO) and other Japanese industry partners. The
project brings together international experts to
advance the understanding of the phenomena of
severe accident behaviour specific to the Fukushima
Daiichi nuclear power plant accident while also
improving the methods and codes for modelling
such behaviour. A phased approach will be applied in
the NEA benchmark exercise. The range of analysis
for this first phase will include: conducting a full
scope analysis of Fukushima Daiichi units 1 to 3
using currently available SA integral codes, using a
time span for analysis of accident events of about
six days from the occurrence of the earthquake (or
reactor scram), and analysing in full a number of
key phenomena including, but not limited to, initial
transient from rated condition to core heat-up, core
heat-up, core melt, release of fission products (FPs)
from fuel, behaviour of core internals (core shroud),
core status including debris behaviour, molten
debris-coolant interaction in the lower plenum (if
necessary) and FP transfer.
The first phase of this project is scheduled to run
from November 2012 to March 2014.
The Cabri Water Loop Project
The Cabri Water Loop Project, which began in 2000,
is investigating the ability of high burn-up fuel to
withstand the sharp power peaks that can occur in
power reactors due to postulated rapid reactivity
insertions in the core (RIA accidents). The project
participants, from 13 member countries, intend to
determine the limits for fuel failure and the potential
consequences of possible ejection of fuel into the
coolant environment. Different cladding materials
and fuel types are being studied. Project execution
involves substantial facility modifications and
upgrades, and consists of 12 experiments with fuel
retrieved from power reactors and refabricated to
suitable length. The experimental work is being carried
out at the Institut de radioprotection et de sûreté
nucléaire (IRSN) in Cadarache, France, where the Cabri
reactor is located. Programme execution can, however,
involve laboratories in participating organisations,
for instance, in relation to fuel fabrication and
characterisation and instrumentation.
IRSN, Cadarache, France
Cabri reactor with water loop scheme.
Two tests (still using the sodium loop) were
carried out with high burn-up fuel cladded with
zirconium-niobium material. Fuel that had been in
service in Spanish and French reactors, respectively
with ZIRLO and M5 cladding, and with burn-up in
excess of 70 MWd/kg, was subjected to a ~100 cal/g
energy injection during the transients. No fuel failure
was registered.
The assessment process of the refurbishment
works conducted over the last few years on the Cabri
research reactor was completed and an authorisation
to refuel the CABRI core was received from the
French nuclear regulatory authority in March 2012.
The Cabri tests are being complemented by additional
reactivity-initiated accident (RIA) tests performed
in Japan. These tests, which constitute the
in-kind contribution from the Japan Atomic Energy
Agency (JAEA) for its participation in the project, will
be carried out under both cold and hot coolant conditions,
and with both BWR and PWR fuel.
NEA Annual Report 2012
35