Experience feedback: methodology & recent events. Kiev March 22, 2017

Transcription

1 Experience feedback: methodology & recent events Kiev March 22, 2017

2 Nuclear safety stakeholders in France Technical safety organization Regulatory body Others Licensee Kiev March 22, 2016 International conference 2 / 27

3 2 kinds of operational events Safety Significant Events SSE 900/year events that have to be reported to the nuclear safety authority (ASN) and for which a specific analysis has to be provided. Events of Interest for Safety /year whose immediate importance does not justify an individual analysis and reporting to the ASN but which can be of interest by its repetitive character and could be a sign of a problem that requires an in-depth analysis. The ASN issued a guideline defining criteria and mode of reporting of SSE. Criteria characterizing EIS have been defined by the operator. Kiev March 22, 2016 International conference 3 / 27

4 Significant events notification process 1 The licensee notifies by fax within 48 hours the occurrence of an SSE 2 The licensee writes and sends within 2 months a report for this SSE Kiev March 22, 2016 International conference 4 / 27

5 Improper actuation of a safety injection pump during a periodic test Output of the operating domain (P,T) Specified by the tech. Spec. due to an overcooling of the primary circuit Loss of heat sink caused by massive influx of vegetable matter (Cruas, 2009) or icing of protective grid at pumping station (Chooz, 2010) Emergency shutdown due to a malevolent act causing a turbine trip (strike context) 3 Non compliance with tech. Spec. 4 External hazard 2 Actuation of safety system 5 Malvolent act 1 Emergency shutdown SSE Emergency shutdown (manual) due to the loss of main electrical line caused by a fire 6 Unit fallback according to tech. Spec. 10 Other events 7 Multiple failure 9 Design 8 Affecting main primary or secondary circuit Equipment(s) required in a defined state unavailable (pumps of the steam generator emergency feedwater system (EFWS)) default in preparing a fire permit Breaking default of valve screws qualified for earthquake Thickness below the required value on a pipe Common cause failure on Emergency Diesel Generators due to a default of the bearings Kiev March 22, 2016 International conference 5 / 27

6 SSE report content Scenario Initial state and sequence of events Cause analysis Direct and in-depth causes Defense in-depth lines Lines not respected/respected Consequences assessment Effective and potential consequences Corrective actions Actions of treatment Action to avoid the occurrence of the same event Kiev March 22, 2016 International conference 6 / 27

7 Screening of SSE by IRSN Actions taken by IRSN within a week after receiving the first information by fax Checking the content of the fax report (if the given information are complete and correct) by the engineer in charge of the NPP safety assessment Immediate exchanges between the licensee and IRSN as soon as the fax is received Updating the IRSN database dedicated to SSE (SAPIDE). A first ( precursor ) meeting is held to select outstanding events (200/year) and events that could be precursor of core damage (15-20/year). If necessary, a PSA study is initiated Kiev March 22, 2016 International conference 7 / 27

8 Screening of SSE by IRSN Actions taken by IRSN after receiving the detailed report : Complete the updating of the IRSN s NPP events database (SAPIDE). The engineer in charge of the site safety assessment carries out the first level analysis of the event. Every Friday, all the operational events whose reports were received during the week, are reviewed during a second level SSE treatment meeting in presence of engineers in charge of the site safety assessment and several experts Kiev March 22, 2016 International conference 8 / 27

9 Output of this screening process SSEs for in depth analysis, SSEs to be declared to the IRS, SSEs to be discussed with the operator during technical meetings dedicated to experience feedback (4/year), SSEs for generic investigation (several SSEs of the same kind). All relevant knowledge is stored by IRSN in a dedicated database called SAPIDE. Kiev March 22, 2016 International conference 9 / 27

10 IRSN also works on international incidents and on French events with lower safety significance but that are still useful to detect trends in the NPP fleet (socalled weak signals). IRSN uses safety performance indicators to provide an updated view of the safety of the French NPP fleet. All this work is used: to enhance the safety of the fleet through technical reports to the ASN containing recommendations for safety improvement based on the knowledge gained from experience feedback, to inform the public through an annual report. Kiev March 22, 2016 International conference 10 / 27

11 Anomalies in the manufacture of steam generators in the EDF fleet 11 / 11 Kiev March 22, 2016 International conference 11 / 27

12 Nuclear pressure vessels: Requirements Reactor pressure vessel / steam generators: 2 nd containment barrier Their failure is not postulated in the safety demonstration High quality in design, manufacturing and in-service tracking in particular: Specific design rules and calculations with the most penalizing stresses resulting of operating conditions and accident situations High level of manufacturing quality: proven techniques (intrinsic quality) and advanced controls (guarantee of absence of defects) Hydro pressure test prior to reactor commissioning In-service checks: decennial hydro pressure test and non-destructive testing to verify the maintenance of integrity over time Kiev March 22, 2016 International conference 12 / 27

13 Questions Anomaly in the chemical composition of the steel: carbon content locally in excess of the target value Attributed to the technique of forging (full ingots of high tonnage) Impact: alteration of the local mechanical properties of steel Reduction of fracture toughness: resistance to propagation of possible defects in steel Questions: Carbon content? Location (extension, depth)? Is the equipment fit for duty? Kiev March 22, 2016 International conference 13 / 27

14 Location of the zone with an excess of carbon Kiev March 22, 2016 International conference 14 / 27

15 Fast fracture risk analysis Stresses Most penalizing thermal shocks? Review of thermohydraulical solicitations for the location concerned by the anomaly Depending on location: Hot thermal shocks Cold thermal shocks Defects State of health of the equipment? Review of end-ofproduction checks On site non destructive techniques Study on the basis of the postulated reference defect Material Mechanical properties of the steel? Mechanical testing impossible Measurements of the carbon ratio on the outer surface Tests on sacrificial mockups Kiev March 22, 2016 International conference 15 / 27

16 Sample cold thermal shock Kiev March 22, 2016 International conference 16 / 27

17 Before break Steam generator Liquid water at 290 C Liquid water at 305 C Water emulsion steam Primary pump Primary Cirduit Temperature ( C) 290 Channel head Core RPV Time

18 After break Liquid water at 250 C Liquid water at 270 C Loss of primary coolant Lower pressure and temperature Reactor scram Safety injection Safety injection Steam Break Temperature ( C) 290 Break Time

19 After safety injection Liquid water at 10 C Liquid water at 170 C Liquid water at 180 C Steam Safety injection Break Temperature ( C) Time

20 Later Liquid water at 10 C Liquid water at 170 C Liquid water at 180 C Steam Safety injection Break Temperature ( C) Cold thermal shock Time

21 Sample hot thermal shock Kiev March 22, 2016 International conference 21 / 27

22 Steam Épingles generator GV en tubes équilibre (thermal thermique equilibrium with avec the le secondaire secondary side) 10 C 25 C 120 C RHRS Refoulement outflow Channel Fond head GV swept balayé by par le refoulement the outflow of the RHRS RHRS Aspiration inflow RRA Risk of hot thermal shock if a primary pump is inapropriately restarted Kiev March 22, 2016 International conference 22 / 27

23 IRSN s expertise About 15 experts mobilized (mechanics / materials / nondestructive testing / thermohydraulics) during one month Assistance of, BEL-V, the Belgian TSO, which is a member of the European ETSON 2 cases: Channel heads fabricated by Creusot Forge: max. carbon ratio 0.3 % Channel heads fabricated by JCFC: max. carbon ratio 0.4 % Kiev March 22, 2016 International conference 23 / 27

24 IRSN s opinion on the treatment of the anomaly (JCFC channel heads) Stresses Most penalizing thermal shocks? Improving transient characterization Adding additional transients Additionnal studies by EDF Defects State of health of the equipment? The control methods employed are able to detect a defect superior to those postulated Material Mechanical properties of the steel? Outer surface: 0,39 % Inner surface: 0,26 % Relevant values Conservative evaluation of mechanical properties Reinforcement of precautionary measures No defects detected during checks Test program on sacrificial mock-ups to be continued Kiev March 22, 2016 International conference 24 / 27

25 Sample precautionary measures Cooling rate for reactor shutdown (normal operations) : 28 C / hour 14 C / hour Disconnecting primary pumps when they are not needed Kiev March 22, 2016 International conference 25 / 27

26 Public awareness Assessment published on IRSN s website Presented to the press during a joint conference with ASN on 5 December 2016 Presented to the High Committee for Transparency and Information on Nuclear Safety (HCTISN) at its meeting on 6 December 2016 Moreover, in conjunction with the National Association of Local Information Commissions and Committees (ANCCLI) and ASN, a meeting has been organized in February 2017 to hold an exchange of views with civil society stakeholders More than 60 persons attended, representing 16 information commissions. Kiev March 22, 2016 International conference 26 / 27

27 Thank you for your attention Kiev March 22, 2016 International conference 27 / 27

28 Operational hazards Operational rigour Unavailibility of safety systems Cause of significant safety-related events Event seriousness State of safety barriers Radiological protection Radio active releases Number of automatic reactor trips Number of forced power reductions Number of loads on various safety systems Latency time of defaults Number of unexpected unavailibility of safety systems Number of waivers on Operating Technical Specifications (OTS) Distribution of RECUPERARE event types Average overrun time between the tolerance end date and the realization date of the periodic tests due to the non compliance of incidental or accidental procedures Detection time of fault according the dependency mode Detection time of fault according the detection mean (alarm or not) Detection time of fault depending on the procedures are erroneous or not linked to the non compliance of the OTS linked to unauthorized deviations from temperature and pressure requirements Number of failures of various safety systems caused by human Consumption leaks (L/h) Thank youerrorsfor your to precursor rate of attention emergency initiation times for unexpected unavailibility of safety systems situations Number of non-respect of the periodic tests frequency Number of periodic tests not in conformity with the rule Number of defaults discovered thanks to the periodic tests Number of safety significant events (SSE) involving equipment misalignment related to human error in administrative directives caused by erroneous procedures caused by maintenance involving the human factor caused by tests involving the human factor Number of significant safety events (SSE) caused by technical failures caused by organizational deficiencies caused by operation crew caused by programmable controllers events caused by maintenance crew caused by the testing department caused by the chemistry department considered outstanding (according to IRSN) Core damage probability increase related Number of events related to radioactive releases per year, uncontrolled or above limits fixed by Regulations Kiev March 22, 2016 International conference 28 / 11 events (per year and per unit) during the unit outage period Reactor coolant circuit contamination (MBq/t) Average flow rate of reactor coolant system Average flow rate of reactor/secondar y coolant leaks from the steam generators (L/h) Average leak rate from the containment converted to one P of 60 mbar (Nm 3 /h) Collective dose per unit outage (and per number of affected persons) Number of significant radiological events (SRE) related to contamination and radiation beyond authorized threshold Number of significant radiological events linked to access to controlled zones Safety performance indicators