ML17158C016
| ML17158C016 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 03/24/1997 |
| From: | Poslusny C NRC (Affiliation Not Assigned) |
| To: | Byram R PENNSYLVANIA POWER & LIGHT CO. |
| References | |
| NUDOCS 9703270134 | |
| Download: ML17158C016 (8) | |
Text
March 24, 1997 Mr. Robert G.
Byram Senior Vice President-Nuclear Pennsylvania Power and Light Company 2 North Ninth Street Allentown, PA 18101
SUBJECT:
REVIEW OF PRELIMINARY ACCIDENT SEQUENCE PRECURSOR ANALYSIS OF EVENT AT SUSQUEHANNA STEAM ELECTRIC STATION, UNIT 1
Dear Hr. Byram:
Enclosed for your information is a copy of our resolution of your comments on the Preliminary Accident Sequence Precursor Analysis of the operational event at Susquehanna Steam Electric Station, Unit 1, reported in Licensee Event Report No. 387/95-013.
The enclosed document was prepared by our contractor at the Oak Ridge National Laboratory based on review and evaluation of your comments on the preliminary analysis and comments received from the NRC staff and from our independent contractor, Sandia National Laboratories.
Our review of your comments employed the criteria contained in the material which accompanied the pre1iminary analysis.
The results of this review indicate that this event is not a precursor for 1995.
Please contact me at (301) 415-1402 if you have any questions regarding the enclosure.
We recognize and appreciate the effort expended by you and your staff in reviewing and providing comments on the preliminary analysis.
Sincerely,.
Original signed by:
Chester
- Poslusny, Senior Project Manager Project Directorate I-2 Division of Reactor Projects
- I/II Office of Nuclear Reactor Regulation Docket No. 50-387
Enclosure:
As stated cc w/encl:
See next page DISTRIBUTION LDocLet~Fi 1 e PUBLIC PDI-2 Reading SVarga/JZwolinski JStolz CPoslusny OGC P>00 HO'Brien ACRS
- WPasciak, RGN-I PO'Rei lly NRC~CRYBNH OFFICE DATE PDI-2/ 8 CPoslusny:rb 9 59/97 PD MO'B z97 PDI JStolz L
DOCUMENT NAME:
SUPRECUR.GEN 9703270i34 970324 PDR ADQCK 05000387 8
)
I
pe REGS
~4
~o Cy J
C1O I
cO e
O
/J gO
++*++
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 March 24, 1997 Hr. Robert G.
Byram Senior Vice President-Nuclear Pennsylvania Power and Light Company 2 North Ninth Street Allentown, PA 18101
SUBJECT:
REVIEW OF PRELIMINARY ACCIDENT SEQUENCE PRECURSOR ANALYSIS OF EVENT AT SUSQUEHANNA STEAN ELECTRIC STATION, UNIT 1
Dear Hr. Byram:
Enclosed for your information is a copy of our resolution of your comments on the Preliminary Accident Sequence Precursor Analysis of'he operational event at Susquehanna Steam Electric Station, Unit 1, reported in Licensee Event Report No. 387/95-013.
The enclosed document was prepared by our contractor at the Oak Ridge National Laboratory based on review and evaluation of your comments on the preliminary analysis and comments received from the NRC staff and from our independent contractor, Sandia National Laboratories.
Our review of your comments employed the criteria contained in the material which accompanied the preliminary analysis.
The results of this review indicate that this event is not a precursor for 1995.
Please contact me at (301) 415-1402 if you have any questions regarding the enclosure.
We recognize and appreciate the effort expended by you and your.
staff in reviewing and providing comments on the preliminary analysis.
Sincerely, Docket No. 50-387
Enclosure:
As stated cc w/encl:
See next page Q.r 0+
Chester
- Poslusny, Senior Project Manager Project Directorate I-2 Division of Reactor Projects
- I/II Office of Nuclear Reactor Regulation-
I
Hr. Robert G.
Byram Pennsylvania Power 5 Light Company Susquehanna Steam Electric Station, Units 1 L 2 CC:
Jay Silberg, Esq.
Sh"w, Pittman, Potts 5 Trowbridge 2300 N Street N.W.
Washington, D.C.
20037 Bryan A. Snapp, Esq.
Assistant Corporate Counsel Pennsylvania Power 5 Light Company 2 North Ninth Street Allentown, Pennsylvania 18101 Hr. J.
H. Kenny Licensing Group Supervisor Pennsylvania Power 5 Light Company 2 North Ninth Street Allentown, Pennsylvania 18101 Hr. K. Jenison Senior Resident Inspector U. S. Nuclear Regulatory Commission P.O.
Box 35 Berwick, Pennsylvania 18603-0035 Hr. William P. Dornsife, Director Bureau of Radiation Protection Pennsylvania Department of Environmental Resources P. 0.
Box 8469 Harrisburg, Pennsylvania 17105-8469 Hr. Jesse C. Tilton, III Allegheny Elec. Cooperative, Inc.
212 Locust Street P.O.
Box 1266 Harrisburg, Pennsylvania 17108-1266 Regional Administrator, Region I U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, Pennsylvania 19406 Hr. George Kuczynski Plant Hanager Susquehanna Steam Electric Station Pennsylvania Power and Light Company Box 467 Berwick, Pennsylvania 18603 Hr. Herbert D. Woodeshick Special Office of the President Pennsylvania Power and Light Company Rural Route 1,
Box 1797 Berwick, Pennsylvania 18603 George T. Jones Vice President-Nuclear Operations Pennsylvania Power and Light Company 2 North Ninth Street Allentown, Pennsylvania 18101 Dr. Judith Johnsrud National Energy Committee Sierra Club 433 Orlando Avenue State College, PA 16803 Chairman Board of Supervisors 738 East Third Street
- Berwick, PA 18603
t
Resolution ofLicensee Comments on the Analysis for Susquehanna 1 (LER 387/95-013)
Reference R.
J. Byram (Pennsylvania Power & Light Company) letter to the U.S. Nuclear Regulatory Commission, "Review ofHPCI Thermal Overpressure Precursor Analysis," PLA4497, September 6, 1996.
Note:
The PP&L comments in the reference given above referred both to the analysis of 1995 thermally-induced pressure locking (theimal overpressure) event (LER 387/95-013) and the analyses of several 1982-83 precursors being performed by Sandia National Laboratories.
The responses provided herein are applicable to comments on the analysis of the 1995 event.
PP&L comments concerned the models used to assess the HPCI injection valve unavailability and the assumptions made in the analysis concerning the inoperability ofthe valve once the thermal overpressurization occurred.
Background
During an outage in November, 1995, a modification to prevent thermally-induced pressure locking was performed on the HPCI and RCIC injection valves at Susquehanna
- 1. During disassembly ofthe HPCI injection valve, the followingdamage was observed:
the valve bonnet pressure seal segmented retaining ring was bent approximately 0.135 in., the pressure seal spacer ring was bent, and the packing follower flange was bent approximately 0.25 in. The damage was caused by pressure in the valve bonnet, which resulted in forces great enough to deform these components.
PP&L determined that valve damage was caused by thermally-induced pressure locking. The internal bonnet pressure required to cause the observed valve damage was estimated to have been between 3000-7000 psig, based on the material strengths of damaged and undamaged valve parts.
These pressures would prevent the HPCI injection valve from opening ifit had been demanded.
The valve was considered unavailable for an indeterminate amount oftime between April 1992 (when the valve was previously disassembled) and November 11, 1995. The HPCI injection valve was not challenged, except for testing with the unit shut down, during this time period.
The preliminary precursor analysis assumed that the HPCI system injection valve was unavailable due to pressure locking and valve damage once the overpressurization condition occurred.
Since the date when the valve damage occurred is unknown, the preliminary ASP analysis assumed the unavailability existed for one-half ofthe time since the valve was previously disassembled, or 22 months.
Comment 1 In the three comments provided in Part 11 to PP&L's letter (Specific Comments on the HPCI Event),
which addressed similar points in the Event Summary, Event Description, and Modeling Assumptions sections ofthe preliminary analysis, PP&L provided additional information concerning the HPCI valve thermal overpressurization that was developed afler LER 387/95-013 was submitted.
Engineering calculation EC-052-1029, which documented PP&L's analysis of the valve overpressurization, was also provided.
PP&L estimated that 2.60 ibm would have to leak out of the valve bonnet to fully depressurize the valve.
Using an assumption that the valve would leak at the manufacturer's leak rate acceptance
criterion (2 cdhrfin), PP&L estimated a maximum time to depressurize ofbetween 42 and 56 hours6.481481e-4 days <br />0.0156 hours <br />9.259259e-5 weeks <br />2.1308e-5 months <br />, depending on the leakage path.
Furthermore, PP&L noted that the HPCI system injection valve successfully passed inservice tests, including static diagnostic VOTES testing, during the two intervening refueling and inspection outages between April 1993 and November 1995.
PP&L hypothesized that the valve damage occurred following valve refurbishment in the Spring of 1992, when the valve would have been most leak-tight. Based on the calculated leakage rate, the successful tests aAer the 1992 outage, and the plant startup profile followingthe 1992 outage, PP&L estimated a maximum valve inoperability period ofeight days.
Response
1 The preliminary precursor analysis assumed the HPCI injection valve was inoperable once it was damaged by thermal overpressurization, independent ofvalve bonnet pressure.
Based on the reported results of VOTES testing during the two refueling outages following the 1992 valve refurbishment, the HPCI intr "'i"n valve appears to have been operable except during those time periods when the valve would have been subjected to increasing temperatures that could cause thermal overpressurization.
This occurs during plant startups, when feedwater temperature increases.
Such startups constitute a small &action ofthe operating profile.
Following a plant startup and HPCI valve thermal pressurization, valve leakage will subsequently deprcssurize the overpressurized bonnet. As described above, PP&L estimated depressurization times of 42 - 56 hours6.481481e-4 days <br />0.0156 hours <br />9.259259e-5 weeks <br />2.1308e-5 months <br />, based on an assumed leak rate of2 car per inch ofvalve diameter.
An alternate approach, which estimated the leak rate required to limitbonnet pressurization to 7000 psi, produced similar values.
Such depressurization times, combined with the relatively, few days during a calendar year during which the unit is increasing feedwater temperature (this occurs while increasing power), would result in the HPCI injection valve being unavailable for a small &action of time. For example, during the one-year period before the damaged valve was discovered, Susquehanna 1 increased power greater than 10% a day on 15 days, some ofwhich were contiguous.
Assuming that the HPCI injection valve bonnet was overpressurized for the entirety of the 15 days (this is conservative) plus 56 hours6.481481e-4 days <br />0.0156 hours <br />9.259259e-5 weeks <br />2.1308e-5 months <br /> for depressurization followingeach heatup results in an unavailability ofapproximately 1.3 months.
This event was initially selected for analysis because it involved a pressure-locking condition. If PP&L's estimated eight day inoperability is utilized in the analysis, the resulting increase in core damage probability is less than the ASP truncation value of 1.0E-6. IfHPCI is assumed to be unavailable for the 1.3 month period discussed in the previous paragraph, an increase in core damage probability of 2.8E-6, is estimated..
This latter unavailability estimate is considered a pessimistic upper bound.
A value between the two - less than one month and closer to the licensee's eight-day estimate - is probably more realistic.
Such low-probability, short-term, single-train unavailabilities are not considered risk significant and are typically not analyzed in the ASP program.
Therefore, this event has been removed Gom the set ofprecursors.
Comment 2 PP&L provided six comments in Part I to PP&L's letter (General Comments) related to the assumptions and data used in the ASP model of the HPCI valve thermal overpressurization event.
These comments concerned differe'nces between the ASP model and the model utilized in the Susquehanna Individual Plant Examination.
Response 2 As noted in the response to comment 1, based on additional information provided by PP&L, this event has been removed &om the set ofprecursors.
Because ofthis, PP&L's general comments concerning the ASP model for the event were not addressed at this time. These comments are being considered as part ofthe ASP model development process.
UTIL-2