Superphénix (Part 3)

This post is the final of three parts on the history of France’s fast breeder Superphenix reactor, now in the fifteenth year of its decommissioning phase (see Part 1 & Part 2). What follows is a translation of a blog post at GEN4 - Les 4 Vérités du Nucléaire.

This post goes into some detail about the ongoing problems with decommissioning of this reactor that had its life cut short in 1998 after numerous technical problems, dangerous incidents, and political conflict over national energy policy.

The story of the Superphenix is relevant today because the promise of fast breeder reactors and the closed fuel cycle is always being reborn, like a mythical, amnesiac Phoenix itself. Promoters hope the present generation has missed the lessons of all the dangerous mishaps, wasted national treasure, and ongoing decommissioning dilemmas related to fast breeder reactors.

The Union of Concerned Scientists has pointed out that the main flaw with fast breeder technology is that it makes an unreasonable bet that future generations will be able to manage the waste products, which are still substantial, regardless of what is said about the reactors’ ability to “burn them up.” For the UCS, the problem is that this technology does… “not satisfy the fundamental ethical principle for the disposal of nuclear waste: intergenerational equity.”

If a nation one hundred years from now could not or did not want to maintain its fast breeder reactors, the promised closed fuel cycle would no longer exist. The country would suddenly have a massive waste and decommissioning problem to deal with. This could be horrific enough for a future society ravaged by war, environmental damage or economic decline, but the story of the Superphenix illustrates that it’s enough of a nightmare when it happens just a few years after the reactor goes on line, and the society that manages the decommissioning is the same relatively competent and prosperous society that built it.

Translation of a blog post at GEN4 - Les 4 Vérités du Nucléaire,

August 2013

Superphenix : 15 years after its “shutdown,” has the risk posed by sodium really been eliminated?

The fire reported last night in the former Superphenix reactor occurred in heating ducts meant, according to l’ASN, to recover 5,000 tons of sodium which was used to cool the core of the fast breeder reactor that was shut down in 1998. You may wonder what is going on with this damn sodium at Creys-Malville, 15 years later? Here are some  answers.

August 8, 2013, fire breaks out in the facility for recovering sodium.

Last night around 19:00, the ASN (1) Rhone-Alps division announced that a fire had affected the installation holding sodium at the site of the decommissioning of the Superphenix fast breeder reactor (2). The primary circuit of the reactor was slowed in 1998 after numerous technical and financial problems led to its closure.

The fire would have been delicate to handle because sodium fires are particularly devious, corrosive and toxic, so much so that a specialized sodium fire response course was created at Cadarache in the 1970s, requiring 250 hours of training for firefighters. 

The important question: solid or liquid sodium?

We already discussed this question in relation to a fire at the Monju (Japan) fast breeder reactor in May 2013. In that case also it was very difficult to have a precise idea of the gravity of the fire because the information available about such fires, regardless of the country providing it, is always fragmentary and incomplete (3).

It is necessary to keep in mind that sodium, in order to circulate in the pipes, must be kept heated to its melting point of 100° C. If the sodium solidifies or gels, it stops circulating (4) and makes it very difficult to restart circulation. It is impossible to drain the sodium if it is not in a liquid state, and so it must be constantly heated to its melting point (5).

In 2006, EDF (Electricité de France) (6) announced that the drainage of the sodium cooling circuit would be complete in 2013 and all risk from it would be eliminated. Today this doesn’t seem to be the case. The fire seems to have been limited to a piece of equipment designed to heat and reheat the sodium so that it can be isolated in small quantities, deactivated and placed in thousands of concrete blocks (7). However, Le Monde Diplomatique reports that the operations are not going well – obviously not, according to the plan of 2006.

Sodium still stored in liquid state 15 years after the supposed “shutdown” of the installation?

In this article that deserves a more detailed analysis, the journalist points out notably that sodium is still stored in liquid form in its primary containment which has a temperature of 180° C. In order deactivate it without causing a fire, EDF collects it in small amounts (150 kg?). An article appeared in Le Canard enchaîné in August 2011 stating that 5,000 tons of sodium were still being heated at that time. The article noted the irony that the operation consumes vast quantities of electricity.

Sodium, a doubly dangerous metal

Beyond the non-negligible chemical risks that it presents, the sodium that is stored now in ad hoc containment is radioactive after having flowed some eleven years in the primary circuit of the reactor. Why? Simply because of the same phenomenon of neutron activation that creates new isotopes and new elements in the presence of nuclear fission. It is thus that the stable isotope Fe-54 gains a neutron and becomes radioactive Fe-55. Likewise for Cobalt, Chrome, Silver, Nickel, and Manganese which are used in various parts which come into contact with the reactor core. Some of the cooling water used in light water reactors becomes Carbon-14 (8) and Tritium (H-3) (9).

Radioactive sodium is formed by the activation of the stable isotope Na-23 + neutron = Na-24, an isotope which decays quickly (half life: 5 hours) to Mg-24, a stable element. Thus the radioactivity of sodium is almost completely gone in two or three days. But it’s not so simple. Actually, during the cooling process, other elements, highly radioactive ones, are created and mixed into the liquid sodium (10).

The fuel, 15 tons of Plutonium-239, still stored in proximity to the sodium hazard

We must remember that 15 tons of Plutonium-239, placed in the SPX reactor in 1984 are still kept in close proximity to the turbine building where the “de-sodiumization” process is carried out. Knowing that this quantity of Pu-239 could, in the case of a fire or explosion, spread a billion lethal doses (11), we can say this is like storing explosives and matches side by side.

Notes:

(1)        Rhône-Alpes regional office of the French regulatory agency Autorité de Sureté Nucléaire.

(2)        Decommissioning is an unfortunate neologism. Demolition would have been sufficient, but the connotations might be critically important.

(3)        Since the 1950s there have been nine nuclear installations of this type and they have all had accidents or fires.

(4)        That is, if the temperature goes below 97° C.

(5)        The enormous thermal constraints linked to the phase change would break a part of the sodium circuits.

(6)        As operator of the site, EDF was found to be responsible for the decommissioning.

(7)        There are to be 38,000 containers holding 5,500 tons of sodium, so 150 kg of sodium per container.

(8)        O-13 gains 1 neutron to become N-14 (stable) which gains a neutron (cool double effect!) to become C-14, emitting one proton.

(9)        Lithium-6 + Neutron => Lithium-7 => Helium-4 + Helium-3 or again by ternary fission of boric acid used often in reactors.

(10)     The metal coolant strains the metal circuits and ends up incorporating their active elements: Fe-56, Co-60...

(11) Lethal dose of  Pu-239: 50 micrograms.