31 mars 2013
Suite à des travaux sur l’alternateur du réacteur n° 1, la chute du rotor de 500 tonnes a entrainé la perte de toutes les alimentations électriques de ce réacteur, à 7h50. L’accident a entrainé la mort d’une personne et quatre travailleurs ont été grièvement blessés. A 10h33, le plan d’urgence a été enclenché.
Type : PWR - Puissance n° 1 : 842 MW ; n° 2 : 993 MW - Première divergence n° 1 : 08/1974 ; n° 2 : 12/1978
Available in english only.
La réalité est bien loin du communiqué rassurant émis le 1er avril : "Les deux réacteurs sont en condition d’arrêt stable et il n’y a aucun danger pour la population".
Les générateurs diesels de secours ont démarré et alimenté plusieurs éléments, dont des disjoncteurs et des pompes. Le réacteur n° 1 est entré en mode dégradé. Un circuit vital pour le réacteur a été perdu durant 3 min et 50 secondes alors que le cœur était critique.
Le réacteur n° 2 s’est arrêté à son tour et l’injection d’urgence d’eau de secours a été enclenchée. L’alimentation du réacteur était effectuée par les lignes électriques extérieures et, suite à l’explosion d’un disjoncteur dans une zone protégée, le plan d’urgence a été enclenché à 10 h 33.
Les barres de contrôle ont été insérées correctement durant l’arrêt et le cœur est refroidi par convection naturelle (Les pompes auraient donc été inactives à ce moment là). Il n’y pas de fuite connue entre le circuit primaire et le circuit secondaire.
A 18h21, une seule voie d’alimentation électrique aurait été touchée par les dommages.
Le réacteur n°1 a pour sa part retrouvé sa puissance de 100 % le 19 août après une succession de problèmes depuis le 5 août lors des tentatives de redémarrages.
Plus d’infos et des photos ici :
https://enformable.com/2013/05/healthy-discussion-of-the-arkansas-nuclear-one-accident/
Informations complémentaires de la NRC suite à l’accident du 31 mars 2013 :
L’unité 2 qui fonctionnait à pleine puissance et qui a perdu subitement son alimentation est restée 4 minutes sans aucune alimentation électrique.
L’unité 1 en cours de travaux a été privée de courant durant six jours.
Sur l’origine de l’accident, la grue de transport du rotor était inadaptée et les contrôles réalisés par l’exploitant insuffisants. Suite à une visite post-accident, la NRC avait déclaré qu’il n’y avait aucun problème de sûreté sur les réacteurs.
En février 2014, suite à des réexamens, la NRC a reclassé le problème survenu sur le réacteur n° 1 en haute menace de sûreté et le n° 2 en menace de sûreté importante.
En septembre 2013, le "US Department of Labor’s Occupational Safety and Health Administration" a déterminé 26 violations de sécurité. Un certain nombre d’entreprises impliquées dans le remplacement du rotor ont été condamnées à 175 000 dollars d’amende.
A noter que le 9 décembre 2013, le transformateur auxiliaire du réacteur n° 2 a pris feu et a explosé. Le réacteur s’est à nouveau retrouvé sans alimentation électrique.
Pour en savoir plus, voir : https://www.sortirdunucleaire.org/Etats-Unis-Arkansas-explosion
Unsuitable crane led to Arkansas accident
25 June 2014
The US Nuclear Regulatory Commission (NRC) has revealed the cause of a fatal industrial accident that took place during refurbishment work last year at Entergy’s Arkansas Nuclear One plant. In a letter to the utility, it said that an inappropriate lift assembly had been used.
Unit 1 of the two-unit plant was taken offline in early 2013 for refuelling and refurbishment work which required the removal of the generator stator. In late-March, the gantry used to remove this from the turbine hall collapsed, sending the 525-tonne component crashing through a hole in the floor to a heavy transport vehicle below. One contractor was killed and eight other workers were injured.
The dropped stator ruptured a water pipe in the transport vehicle bay, causing flooding in unit 1. Certain electrical systems shared by both reactors were damaged and unit 2 automatically shut down. Unit 2 remained without power for some four minutes, with normal grid power supply restored after about ten hours. Unit 1 was without offsite power for six days.
The NRC has now concluded that Entergy "approved a design for the temporary hoisting assembly that was not supported by detailed drawings, specifications, evaluations and/or certifications." In addition, Entergy failed to review associated calculations to ensure that the assembly was designed to support the projected load. It also failed to carry out a load test on the lifting assembly in all configurations for which it would be used.
It also determined that Entergy "did not ensure adequate supervisory and management oversight of the contractors and other supplemental personnel involved with the stator lift, and this contributed to the event."
The NRC inspected the Arkansas Nuclear One plant immediately after the accident and said it had no safety concerns about the plant. However, after a follow-up inspection this February, it determined a "high safety significance" finding related to the accident for unit 1 and one with "substantial safety significance" for unit 2. At Entergy’s request, a regulatory conference was held on 1 May to discuss these findings.
The NRC has informed Entergy that both findings have now been classified as being of "substantial safety significance."
Last September, the US Department of Labor’s Occupational Safety and Health Administration cited 26 safety violations against a number of companies involved in the stator replacement and issued fines totalling $175,000.
Researched and written by World Nuclear News
https://www.world-nuclear-news.org/RS-Unsuitable-crane-lead-to-Arkansas-accident-2506144.html
Facility : ARKANSAS NUCLEAR - State : AR - Unit : [1] [2]
RX Type : [1] B&W-L-LP,[2] CE
Event Date : 03/31/2013 - Event Time : 10:33
Emergency Class : UNUSUAL EVENT
10 CFR Section : 50.72(a) (1) (i) - EMERGENCY DECLARED
50.72(b)(2)(iv)(B) - RPS ACTUATION - CRITICAL
Réacteur 1 Initial PWR : 0 % Current PWR : 0 % Réacteur 2 Initial PWR :100 % Current PWR : 0%
NOTIFICATION OF UNUSUAL EVENT DECLARED DUE TO A BREAKER EXPLOSION IN THE PROTECTED AREA
"At 0750 [CDT] on 3/31/2013, during movement of the Unit 1 Main Turbine Generator Stator ( 500 tons), the Unit 1 turbine temporary lift device failed. This caused a loss of all off site power on Unit 1. The ANO Unit 1 #1 and #2 EDG [Emergency Diesel Generator] have started and are supplying A-3 4160V switchgear and A-4 4160V switchgear. P-4A Service Water pump and P-4C Service Water pump has been verified running. Unit 1 has entered [procedures] 1202.007 - Degraded Power, 1203.028 - Loss of Decay Heat, and 1203.050 - Spent Fuel Emergencies. Unit 1 is in MODE 6.
"ANO-1 entered TS 3.8.2 A, ’One Required Offsite Circuit Inoperable’. All required actions are complete. The event caused a loss of decay heat removal on ANO Unit 1 which was restored in 3 minutes and 50 seconds.
"Unit 2 tripped and is in MODE 3. Emergency Feed Water was initiated on Unit 2 and Unit 2 was in [Technical Specification] 3.0.3 from 0817 [CDT] to 0848 [CDT] due to Emergency Feedwater. Unit 2 is being powered by off-site. Unit 2 Startup 3 [transformer] lock out at 0921 [CDT]. [Bus] 2A1 is on Start up 2 [transformer] and [bus] 2A3 is on #2 EDG.
"10CFR50.72 (b)(3)(iv)(A) - 4-hr. notification due to the ES [Engineered Safeguard Feature] actuation on both Unit 1 and Unit 2. 10CFR50 72 (b)(2)(iv)(B) - 4-hr. notification due to RPS [Reactor Protection System] actuation on Unit 2. 10CFR50.72 (b)(2)(xi) - 4-hr. notification due to Government Notification. 29CFR1904.39a - [OSHA] 8-hr. notification due to death on site.
"At 1033 [CDT] on 3/31/2013, Unit 2 entered a Notification of Unusual Event based on EAL HU4 due to damage in 2A1 switchgear. Notification of the NUE will be made lAW Emergency Plan requirements. Follow-up notifications will be made as appropriate."
At this time, the full extent of structural damage on Unit 1 is not known. There was one known fatality and 4 known serious injuries to workers. The local coroner is on site for the fatality and the injured personnel have been transported offsite to local hospitals. Investigation into the cause of the failure and extent of damage is ongoing.
On Unit 2, all rods inserted during the trip. The core is being cooled via natural circulation. Decay heat is being removed via steam dumps to atmosphere. There is no known primary to secondary leakage.
The licensee has notified the State of Arkansas, local authorities, OSHA and the NRC Resident Inspector.
Notified DHS SWO, DHS NICC, FEMA and Nuclear NSSA (via email).
* * * UPDATE FROM DAVID THOMPSON TO HOWIE CROUCH AT 1934 EDT ON 3/31/13 * * *
The licensee terminated the NOUE at 1821 CDT. The basis for termination was that the affected bus (2A2) is de-energized and no other equipment on Unit 2 was damaged.
The licensee has notified the state and local authorities and will be notifying the NRC Resident Inspector.
Notified R4DO (Pick), NRR EO (Howe), IRD (Gott), DHS SWO, DHS NICC, FEMA and Nuclear SSA (via email).
* * * UPDATE FROM STEVE COFFMAN TO HOWIE CROUCH AT 1054 EDT ON 4/2/13 * * *
The licensee made the following edits to the third paragraph of their original report (edits in quotes) :
Unit 2 tripped and is in MODE 3. Emergency Feed Water initiated on Unit 2. Unit 2 was in [Technical Specification] 3.0.3 from 0817 [CDT] to 0848 [CDT] due to Emergency Feedwater "being procedurally overridden." Unit 2 "was initially" being powered by off-site. Unit 2 Startup 3 Lock out occurred at 0921. 2A1 is now on Startup 2, and "2A4" is on #2 EDG.
Notified R4DO (Kellar) via email.
https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2013/20130401en.html
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