Second quarter of 2001
leaks on fuel assemblies at Cattenom
WISE-Paris, 31 May 2001
An "unprecedented" number
of "leaking faults" of nuclear fuel was noted on 15 March 2001
at Cattenom, by the operating company, Électricité de
France (EDF). During the shutdown for the ten-yearly visit of reactor
3, the user company noted leaks in not less than "28 assemblies,
comprising 26 of the third cycle and 2 of the second cycle"
(1), which included, "on average, 3
damaged rods", representing a total of 92 damaged cladings (2).
Up to "18 rods" showing transverse cracks were found in one assembly,
which is nearly as twice many as the "5 to 10 cracks of clads"
usually counted "in the total number of reactors" every year.
Located in Lorraine, near Moselle,
within a stone's throw of the German and the Luxembourg borders, the
Cattenom site is composed of four 1300MW reactors. The core of each
of the reactors is made up of 193 assemblies, each composed of 264 steel
claddings, or rods, which contain the fuel in the form of uranium oxide
pastilles. The leaking is due to cracks in the claddings, which constitute
the first of the three containment barriers, fundamental for the reactor
safety (the second and third barriers are respectively the reactor vessel
and (biological) containment).
Last year EDF detected "an increase
in the radioactivity of the water of the reactor's primary coolant circuit"
(3) and, suspecting a leaking, prepared
itself to "manage the problem" but only when it shut it down
on January 27 2001- without anticipating it. But given the "unusual"
number of "assemblies concerned", it suggested to classify
the incident at level 1 on the INES scale (International Nuclear Event
Scale, graduated from 0 to 7). The reactor, which was scheduled to restart
at the latest in the beginning of May 2001, has not been restarted yet.
According to EDF, the claddings had
never presented such -transverse and longitudinal- cracks, the length
of which reached 1 cm and a half. One of the rods was found to be "broken",
but the fuel pastilles were not released, assured the communication
office of the Cattenom site.
The origin of this exceptional phenomenon
has not been established with certainty. The first hypothesis is that
of a quality failure of the claddings, based on a recent precedent:
in August 2000, a fuel cladding was found broken at the level of reactor
2 of the Nogent-sur-Seine site.
The investigation revealed sometime
later a problem of quality control concerning a certain number of rods
at the Paimboeuf factory (4), only admitted
a long time afterwards by Framatome, parent company of the claddings
manufacturer, CEZUS (Compagnie Européenne de Zirconium).
However, the Safety Authority (Direction
de la sûreté des installations nucléaires (DSIN))
affirms that "the assemblies in question are old, (...) in their
third processing cycle" (5) and sees
no relationship with the CEZUS case.
Asked to comment on this matter,
Framatome, whose group provided the assemblies in question from the
Pierrelatte, Dessel and Romans factories, says that "given the fact
that the incident took place in the reactor and during the exploitation
phase... once the assemblies are delivered" the supplier "doesn't
have to comment" (6).
EDF's first investigations tended
towards another track. The concerned assemblies are spread "homogeneously"
and EDF has not established a cause and effect relationship between
the core loading and the leaking. Yet, Mr. Dominique Minière,
Director of the Cattenom site, put forward the theory according to which
the cause of the leaking is linked to "fretting and vibrations in
the lower grid", adding that they expected "a four to six-month
inquiry" and that "several causes may be combined, for example
damaged grids" (7).
The first elements of the inquiry
have shown in fact "leaking problems... due to vibration phenomena",
but the origin of the vibrations remains unknown. EDF suspects these
vibrations of having induced "more sustained fretting" between
the claddings and the springs that maintain them, resulting in term
in their cracking.
According to the position expressed
by the DSIN in April 2001 (8), the reactor
will not be allowed to restart until the vibration phenomenon is clarified.
EDF nevertheless sent "a technical proposal" to the Safety Authority,
in which it suggests to replace the damaged assemblies and restart the
reactor "under reinforced observation", given the fact that the
"immediate cause" is now fully established.
Besides, the exploiting company will
continue to study the origin of the vibration phenomenon and submit
the results of its studies to the Nuclear Protection and Safety Institute
(Institut de protection et de sûreté nucléaire (IPSN))
which is charged by the Safety Authority to check whether they are "coherent"
(9). According to the Cattenom site, "part
of these investigations" cannot be undertaken "unless the reactor
As of June 6, EDF had "a one-month
delay on the schedule" for maintenance works and replacing of the
damaged assemblies, knowing that the average cost per day for the shutdown
of a reactor, either programmed or not, is estimated by EDF at 1 million
It is not the only problem the electrician
is experiencing. In fact, on 12 March 2001, EDF informed the safety
authority, that it detected a manufacturing anomaly on the emergency
coolant circuit valves of 12 reactors (1,300 MW units), of which Cattenom's
reactors (10), which may affect their operating
in emergency situations.
In the case of important leakage
from the primary circuit, and once the water reserves of the PTR reservoir
are exhausted, the emergency coolant circuit permits to recover the
water that flows into the sumps (11) within
the reactor containment and to reinject it into the primary circuit.
EDF proposed to modify the valves
on the five sites concerned by the anomaly. According to the DSIN, the
new system is being put in place and the operation is almost completed
The Safety authority reclassified
this generic incident at level 2 on the INES scale, on 27 April 2001.
- This reactor is exploited within the framework
of extended campaigns (GEMMES) of 18 months per cycle. The loading
is programmed for one-third of the core at a time
- Unless specified otherwise, EDF's statements were
made by the Press office of the Cattenom site, on 17, 28 and 31 May
2001, during telephone conversations
- See the Safety authority's 19 March 2001 communiqué
on the official site (http://www.asn.gouv.fr/)
- See "The
Cezus affair: A flaw in the quality control of nuclear fuel",
WISE-Paris, 20 December 2000
- Mr. Alain Delmestre, DSIN, telephone conversation,
2 May 2001
- Framatome, Press service, telephone conversation,
17 May 2001
- Cited by WOXX, published on 20 April 2001
- According to Nucleaonics Week, "EDF, Framatome
still in the dark about cause of Cattenom leakers", 3 May2001
- Mr. Thomas Maurin, DSIN, personal conversation,
31 May 2001
- The other reactors being those of Belleville, Golfech,
Nogent and Penly
- PTR reservoir, among other functions, stores the
water necessary to the fuel handling pools. Sumps collect the water
leaking from the primary circuit which is used to cool the core