AREVA’s Flamanville nuclear rector – safety hazards revealed

EDF engineers had concluded by 2007 that the entire core of the reactor should be reconfigured.
Safety Fears Raised at French Reactor, NYTimes.com, By PATRICIA BRETT July 26, 2010 “……….among the leaked documents, one dated February 2007 — just before the construction of the Flamanville plant was approved — reported that technical studies by EDF had shown that the EPR’s original core design had failed to meet safety criteria for a control rod ejection accident at high power

Control rods, as the name suggests, regulate the nuclear reaction in the reactor vessel, and a control rod ejection accident has a domino effect, causing parts of the reactor to overheat. In a bad enough case, that will break the cladding covering the radioactive fuel rods, causing them to release radioactivity, with potentially disastrous consequences.

One of the safety requirements for the EPR is that no more than 10 percent of the rods should break during an accident. But simulations reported in the February 2007 document were described as “particularly unfavorable,” pointing to “very significantly higher” damage levels of 20 to 30 percent.

According to the documents, EDF engineers had concluded by 2007 that the entire core of the reactor should be reconfigured. Also, as a temporary fix, the EPR’s operational flexibility should be abandoned “until after licensing, and the implementation of new changes in the methodology or the safety criteria so as to ease the operating constraints,” according to a May 2007 document.

Leaked EDF technical documents dating from 2007 and 2009 repeatedly argued the case for the A.S.N. to ease its safety criteria in this domain. …..

According to a leaked document dating from April 2004, EDF has tried to find a safer cladding material. However, all alternative materials examined so far have failed to meet expectations, Ms. Cadet-Mercier said. Several other “remedy” materials are still under study, she added.

Radiation, especially in accident conditions, can cause equipment to malfunction. Equipment required to ensure reactor safety must be qualified to keep working under accident conditions involving the breaking of 10 percent of the fuel rods. But according to an April 2009 document, some equipment used in the EPR design would fail if 1 percent of the rods were to break, leaving the plant vulnerable in an accident.

If a control rod ejection accident happened at low power, the EPR’s automatic shutdown mechanism could fail to operate, it indicated…..

Both EDF and the security regulator insist that safety is a top priority. Yet Mr. Wack acknowledged that the use of mixed oxide, or MOX, fuel — a blend of plutonium and uranium oxides, for which the EPR reactor is designed — is intrinsically more risky than the uranium oxide fuel used in most nuclear plants. Because it is more highly radiated, it is more complicated to use, store, transport and manage in case of an accident, he said.

“In case of a burst fuel rod cladding, the released fission products will be more difficult to manage, more numerous,” he said………….

EDF papers dating from 2007 pinpointed MOX fuel use as partially responsible for poor safety test results relating to reactor operations in both high-power and very low-power conditions. Operations in those conditions would not be allowed unless EDF could demonstrate that the safety criteria were met, Mr. Wack said.

Special Report – Energy – Safety Fears Raised at French Reactor – NYTimes.com