Core Former Baffle Bolt Event Indian Point Unit 2 March 29, 2016

Transcription

1 Core Former Baffle Bolt Event Indian Point Unit 2 March 29, 2016 Workers identified aging degradation in more than 10 percent of the core baffle/former bolts. Rev. 1 March 30, 2016

2 The core baffle and former surrounds the nuclear fuel to direct cooling water entering the reactor vessel initially downward and then upward through the core.

3 Source: ML15337A264

4 This diagram looks sideways at a crosssection of the reactor vessel. Water enters the reactor vessel, flows downward outside the core baffles, and then passes upward through the reactor core. Source: ML15334A231

5 Source: ML15334A231

6 Source: ML15334A231

7 Core Baffle and Former Assembly

8 Looking down into the upper core barrel and then the core baffle and former assembly at Watts Bar Unit 2. Source: Tennessee Valley Authority

9 A closer look down into the upper core barrel and core baffle and former assembly of a pressurized water reactor.

10 Source: ML15334A231

11 Source: ML15334A231

12 Source: ML15334A231

13 Source: ML15337A264

14 The horizontal metal plates of the core former are bolted to the vertical metal plate of the core baffle to create the core baffle and former assembly. Source: ML15331A179

15 The core former is made from horizontal metal plates bolted to vertical metal plate called baffles on one side and to the vertical core barrel on the other side. Source: ML15331A179

16 The core baffle and former assembly, including the bolts, is first inspected after the reactor has operated for 20 to 40 effective full power years (EFPY) and then every 10 years thereafter. Source: ML15331A179

17 The various parts that are put together to make the reactor vessel and its internals.

18 Core Baffle and Former Assembly Bolt Issues 2010 Workers replaced 52 baffle-former bolts at DC Cook Unit 2 in Michigan 2009 Workers found degraded baffle-former bolts at Beznau in Switzerland 1999 Workers replaced 56 baffle-former bolts at Ginna in New York 1998 NRC warns U.S. owners about baffle-former bolt cracking identified in six French PWRs 1995 Workers replaced 3 baffle-former bolts at DC Cook Unit 1 in Michigan

19 Safety Concern: Coolable Geometry NRC s regulations require emergency core cooling systems be capable of maintaining a coolable geometry for the reactor core. If the baffle and former assembly do not remain intact, water can enter and leave the reactor vessel without passing through, and cooling, the core. Source: ML15334A231

20 Safety Concern: Loose Parts, Impingement, and Obstruction 2007 Workers plugged a steam generator tube on Millstone Unit 3 in Connecticut due to damage caused by impact from a foreign object Vibrations following power uprate cracked the steam dryer atop the reactor core of the Quad Cities Unit 1 reactor in Illinois. Impact markings on the impeller of recirculation pump 1B suggest that pieces from the broken dryer traveled through the pump NRC warned plant owners about fuel rods that were damaged by impingement from water jetting through gaps in the core baffles.

21 Safety Concern: Much Abridged Timeline to date : New York State submitted a Petition to Intervene in the proposed 20-year renewal of the operating license for Indian Point Units 2 and 3. The State contended: Entergy s License Renewal Application Does Not Include an Adequate Plan to Monitor and Manage the Effects of Aging Due to Embrittlement of the Reactor Pressure Vessels ( RPVs ) and the Associated Internals : Entergy amended its license renewal application to add a Reactor Vessel Internals Program to implement the MRP-227 guidelines developed by EPRI : NRC requires MRP-227 to be implemented for aging management of reactor vessel internals at PWRs already relicensed as well as those seeking renewal.

22 Unanswered Questions (so far) 1) What about the core former bolts on Indian Point Unit 3, a virtually identical reactor with nearly the same operating history? 2) Was degradation detected in the core former bolts during prior inspections? If not, why not? 3) Will all pieces of degraded bolts (e.g., missing bolt heads) be found and recovered? 4) If all missing pieces are not recovered, what damage could the pieces cause (e.g., interfering with control rod and valve movements, damage fuel rods and steam generator tubes, etc.)?