ML20202J009
| ML20202J009 | |
| Person / Time | |
|---|---|
| Site: | Bellefonte  |
| Issue date: | 03/27/1986 |
| From: | Gridley R TENNESSEE VALLEY AUTHORITY |
| To: | Grace J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| REF-PT21-86, REF-PT21-86-121-000 PT21-86-121, PT21-86-121-000, NUDOCS 8604150509 | |
| Download: ML20202J009 (3) | |
Text
.
J t
e TENNESSEE VALLEY AUTHORITY 6N 157B Lookout Place e3; B
~
j ld. 3
~
March 27, 1986 I
I U.S. Nuclear Regulatory Comission i
Region II Attn:
Dr. J. Nelson Grace, Regional Administrator
{
101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323
Dear Dr. Grace:
i BELLEFONTE NUCLEAR PLANT UNITS 1 AND 2 - FAILURE OF MAIN STEAM LINES BECAUSE OF MAIN FEEDWATER OVERFILL - NCR BLN NEB 8004 - FINAL REPORT On March 19, 1980, Bruce Cochran, NRC-0IE Region II, was informed that the subject nonconformance was determined to be reportable in accordance with 10 CFR 50.55(e). Enclosed is our final. report. We consider 10 CFR Part 21 to be applicable to this nonconformance.
If you have any questions concerning this matter, please get in touch with R. H. Shell at FTS 858-2688.
f Very truly yours, TENNESSRE VALLEY AUTHORITY.
R. L. Gridley Manager of Licensing cc (Enclosure):
Mr. James Taylor, Director Office of Inspection and Enforcement U.S. Nuclear Regulatory Comission Washington, D.C.
20555 Records Center Institute of Nuclear Power Operations 1100 Circle 75 Parkway, Suite 1500 Atlanta, Georgia 30339 Babcock & Wilcox Company Attention:
Mr. H. B. Barkley i
3315 Old Forest Road P.O. Box 10935 Lynchburg, Virginia 24505-0935 1
1 8604150509 860327 PDR ADOCK 05000438-S PDR s
l
- An Equal Opportunity Employer
)
I gy
._._._.._....,m.
.~...,_ _
1 ENCLOSURE BELLEFONTE NUCLEAR PLANT UNITS 1 AND 2 FAILURE OF MAIN STEAM LINES BECAUSE OF MAIN FEEDWATER OVERFILL NCR BLN NEB 8004 10 CFR 50.55(e)
FINAL _ REPORT Description of DeficiencI A preliminary safety concern, PSC 35-79, was initiated within Babcock &
Wilcox Company (B&W), Lynchburg, Virginia, which presents the concern that a potential exists for overfilling steam generators by excessive addition of main feedwater (MFW) or auxiliary feedwater (AFW).
Excessive feedwater addition, as used here, is defined as a condition which would exist if feedwater (main or auxiliary) is continually added to the steam generators in an unplanned fashion at a rate greater than the core heat generation capability for converting it to steam. Overfill, the condition addressed in this preliminary safety concern, may be defined as a limiting case of excessive feedwater addition which allows liquid spillage 1
into the steam lines.
It is estimated that the time to overfill the integral economizer once-through steam generators (IEOTSG) provided on the Bellefonte Nuclear i
Plant (BLN) is approximately 2 to 4 minutes with MFW and between 7 to 15 minutes with AFW.
]
The cause of this nonconformance report (NCR) is that the main steam lines were not designed for the dynamic loads resulting from the overfilling of the steam generators, and there was no reliable steam generator overfill protection system.
In order to assess the root cause of the identified deficiency, TVA contacted B&W and requested that they provide an explanation of the design basis concepts that led to the deficiency.
B&W's response follows:
The original design of the BLN Integrated Control System (ICS) included nonsafety-grade features to prevent excessive carryover (the least case of overfill) from the steam generators to the turbine and steam lines. These features provide a backup defense, should potential control system failures lead to overfeeding the steam generators, and help provide reasonable assurance that' actual steam conditions will not exceed those presently used as the base Bellefonte steam line design. Should a steam line break occur, an analysis summarized in Section 15.1.5 of the BLN FSAR showed that safety requirements for the plant would be met.
This analysis was typical of those performed in the industry and accepted by the NRC in the 1970s. Specifically, Section 15.1.5.3.2 of the FSAR lists the variables for which parametric studies were done to identify worst case initial conditions for the steam line break analysis and states that steam generator inventory was considered to be at a worst case normal end-of-life condition of +5 percent. A higher steam generator inventory would result only from
r
& l 4
failures such as those addressed in the increase in feedwater flow accident analyzed in Section 15.1.2 of the FSAR.
It was not the design basis of the plant to consider simultaneous multiple accidents, multiple equipment failures, and spurious operator actions.
In this case, ACRS concerns developed in the late 1970s when operating experience showed excessive NFW to be more likely than other FSAR Chapter 15 accidents and when concern developed that NFW overfill events could lead to steam line break accidents.
B&W investigations of these concerns showed that a steam line break from an initial condition of an overfilled steam generator would produce unacceptable results. These concerns led to the addition of the safety-grade Overfill Protection System.
In summary, the root cause of NCR BLN NEB 8004 was a shortcoming in the originally established basis for the accident analysis performed for BLN.
Safety Tmplications Potential results of overfill could be:
1.
Steam line deformation and failure because of water accumulation.
2.
Steam generator blowdown because of steam line failure with the potential for core return to power from a safe shutdown condition, excessive steam-generator tube stress, exceeding reactor vessel NDT limits, or containment overpressurization.
These conditions could be adverse to the safe operation of the plant.
Corrective Action The corrective action for this NCP. undertaken by B&W is to provide a design for a safety-grade MFW overfill protection system for the steam generators.
i
^
B&W has proceeded to provide such a MFW overfill protection system via the BLN upgrade "Do It Now" (DIN) program, Item 702. This program is the TVA-instituted program to meet post-Three Mlle Island (TMI) upgrade requirements.
TVA has reviewed and approved B&W's FCP 177A, which implements the MFW overfill protection system. Construction of the system will be complete no later than six months before fuel loading of the unit the system serves.
1 TVA has reviewed and approved the analysis which shows that the main steamline piping can withstand the limited NFW overfill event that is postulated to occur with the overfill protection system in place. The analysis is i
acceptable, and TVA has completed the verification and approval of all six analysis probleas' associated with this item.
(problems N4-1(2)SM-A, -C,
-K,
-L,
-M, and -N are all complete.) A copy of the analysis has been sent to B&W for their information and~ review.
i Since this was a unique occurrence which is being corrected by the addition of a safety-grade overfill protection system, and since no other TVA plants are j
affected, no further action is required to prevent recurrence.
1
my-
--n-,+
,,__,.,,-v.me---y w ye.-w--
, e y v. w w w y -.,
y-w,+-,---
.,,my,--~-,-cew.+--,
, W n y-.4,,-3---y-,-,,--,+r=:
r y=
~~4we t-,-
+-
4-e,--