ML023580119
| ML023580119 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 03/14/2002 |
| From: | Karwoski K, Long S, Anthony Mendiola, Sheron B NRC/RGN-III |
| To: | |
| References | |
| Download: ML023580119 (15) | |
Text
UQJ8LIS UeiaJ EIO!PUOLAJ AuojL 6uo1l OAOIS PISQMJB>I ue)A 11I UOl6Oaj UOJe~qs UeliJ eu J nS
.0
- ..... SaOIIA I13V uo1Je 31un w w~oo S..............................
.suo!leo!IldL l NIS!1i
...... s nssl le !uqoe..L 55.....
S......
ess
-SiAeO le sn5e5s S..
.o..6.............
.0.....
.....u o i l, o n p o iJ
, U l zO0;z 'iv L qlowe VON39V peaH IlSSOA Jo138oea!
SSaE]-S!Ae1 6u!*aeiJ V1 SJOUO!SS!WWOO
'4.'
CD EL
) Q0-
STATUS AT DAVIS-BESSE Licensee Activities Shutdown in February 2002 Vessel head penetration nozzle inspections Inspection results Root cause team Region III Activities Augmented inspection team Confirmatory Action Letter AIT activities/issues TECHNICAL OBSERVATIONS Boric acid-like-material covering reactor pressure vessel head for several cycles 3 leaking vessel head penetration nozzles including nozzles 2 and 3 Two cavities - one near nozzle 2 and one near nozzle 3 Largest cavity - nozzle 3 Length: approximately 5-inches Width: approximately 4 to 5-inches at widest point Depth: approximately 6-inches Root cause investigation is on-going Either the deposits on the top of the head, the leaking penetration, or both could contribute to the degradation Boric acid may be a contributor HISTORICAL PERSPECTIVE Boric acid corrosion well documented Generic Letter 88-05, "Boric Acid Corrosion of Carbon Steel reactor Pressure Boundary Components in PWR Plants" Industry assessment of wastage at top of head as a result of a leaking nozzle - 1993 Water will flash to steam leaving dry boric acid crystals which have a slow corrosion rate Maximum wastage rate of 6.4 in3/yr RPV boric acid corrosion experience at Salem 2 3 feet by 5 feet by 1 foot high pile of boric acid crystals 9 corrosion pits ranging from 1 to 3 inches in diameter and to a depth of 0.4-inch CURRENT STATUS Monitoring results at Davis-Besse to assess generic implications RES Activities NRR and RES developing near-and long-term plan to address structural integrity, corrosion mechanism/mitigation, and NDE issues RES is also planning to look at thermal hydraulic response Developing models for assessing structural integrity of degraded area and repair proposals Preliminary calculations underway Reviewing boric acid operating history Supporting review of licensee and MRP activities RES staff member participating on AIT GENERIC TECHNICAL ACTIVITIES Issued letter to industry on March 11, 2002 documenting prior phone calls Requested justification for continued operation for plants that have not inspected Requested risk assessment Industry provided preliminary results on March 13, 2002 and will provide detailed results next week Visual exam of 100% of head?
If not 100%, can external corrosion be ruled out?
If UT or other approach used during most recent inspection was UT capable of detecting cavity?
Plans for Spring 02 outages?
Preparing Bulletin and associated Information Paper RISK IMPLICATIONS Rupture of the exposed clad area would create a medium LOCA Conditional probability of core damage for a medium LOCA is 7E-3 in Davis Besse IPE Conditional probability for large early release for medium LOCA core damage events is about 0.006 for large, dry containments in NUREG-1 150 PRAs Bottom line:
CDP appears to be about E-3; LERP appears to be about E-5.
COMMUNICATION ACTIVITIES Initiated daily status briefings between licensee, Region 3, and NRR Issued Preliminary Notification of Event Initiated Communication Plan Issued NRC Information Notice (IN-02-001 1)
Issued AIT Press release Initiated NRC website for public information Issued Confirmatory Action Letter Commissioner's TA Briefing CRGR Briefing for draft NRC Bulletin Public Meeting between NRC and Industry Representatives Public Meeting for NRC Stakeholders ACRS Subcommittee Briefing on Event 03/06/02 03/08/02 03/11/02 03/12/02 03/12/02 03/13/02 03/13/02 03/14/02 03/18/02 03/19/02 03/20/02 04/09/02 DAVIS-BESSE RPV HEAD
LU
- a.
cc ui (1)
U) w In I Cl)
DAVIS-BESSE NOZZLES 1 AND 2
L. 31ZZON 3SSE18-SlAva
DAVIS-BESSE NOZZLE 3
DAVIS-BESSE NOZZLE 3
DAVIS-BESSE NOZZLE 3 - VIEWS OF TOP OF RPV HEAD (Brown area is borated water at the bottom of the cavity)