ML20207M316
| ML20207M316 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 12/24/1986 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20207M277 | List: |
| References | |
| NUDOCS 8701130139 | |
| Download: ML20207M316 (3) | |
Text
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SAFETY EVAll'ATION BY THE OFFICE OF Nt' CLEAR REACTOR REGULATION RELATED TO HIGH ENERGY LINE BREAK IN THE ISOLATION CONDENSER DRYWELL PENETRATIONS GPU NUCLEAR CORPORATION OYSTER CREEK NUC!FAR GENEPATING STATION DOCKET NO. 50-219 1
1.0 BACKGROUND
In January, 1986, Niagara Vohawk Power Corporation (NMPC) notified NRC Region I of a potentially reportable condition involving a failure mode for the Nine Pile Point I containment penetrations. Loads calculated for the penetrations due to a postulated High Energy Line Preak (HELB) in the process piping within the penetrations were determined to exceed those for which the penetrations were designed. These higher loads resulted from use of a more accurate analysis model which included both pressure and momentum effects. GPU Nuclear (GPUN) became aware of the NMPC analysis and, in February 1986, voluntarily initiated an investigation of the Oyster Creek (OC) plant containment penetrations.
The evaluation of the 15 high energy lines which penetrate the drywell showed that 13 of the 15 peretrations could tolerate a HELB in their normal power operation alignment. The calculations for the two penetrations for the emergency condenser steam lines have not yet been verified; hcwever, this is i.
expected to be completed before the restart from the current Cycle 11 Refueling (Cycle 11R) outage. The two emergency condenser condensate return penetrations were found to have excessive stresses if a guillotine rupture of the process line within the penetration was to occur while the system was in operation.
The issue concerning the er:ergency condenser piping penetrations, because of I
their potential failure mode, was found by GPUN to be an unreviewed safety ouestion, because they are not fully in conformance with the updated Final Safety Analysis Report IFSAR) design criteria.
1 i
As a result of discussions with the staff concerning the isolation condenser piping centainment penetrations, the licensee would intend to coordinate finel resolution of the isolation condenser piping containment penetration issue with other issues related to the piping in the penetrations:
NUREG-0313, Revision 2, " Technical Report on Material Selection and Processing Guidelines i
for BWR Coolant Pressure Roundary Piping", and Systematic Evaluation Program (SEP) Topic III-5.B. " Pipe Break Outside Containment". The concern identified in NUREG-0313. Revision 2, is that the welds inside the penetrations cannot be inspected and the weldment is subject to IGSCC.
SEP Tepic 111-5.8 is concerned i
with the two series isolation valves outside containment which are located in each of two isolation condenser steam supply lines at the penetrations. Any i
modifications resulting frcm the resolution of these issues would be implemented
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as a single integral change for each isolation condenser penetration.
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. l The licensee has stated that a physical modification, if needed, could not be performed during the current refueling outage (cycle 11R) because of the '
time needed to complete the necessary evaluations and do the required support engineering.
The licensee has stated that his coal.is to have all Cycle I?R outage-relate'd 1
engineering released for construction six months prior (based on the current 4
schedule this is October 1, 1987) to the outaae in order that construction planning and material procurement can be finalized prior to the outage. This will assure full NRC review of any proposed modifications.
Sirce the resolution of the other issues would impact on the HELE issue, the staff felt that it was logical and would be expeditious to coordinate the j
resolution all the issues.
2.0 EVALUATION The purpose of this evaluation is to present the licensee's discussion and the staff's analysis to establish that the facility may safety operate for an additional cycle due to certain compensatory measures that are to be implemented.
This evaluation is based on material provided by the licensee in letters dated September 17, 1986 and November 25, 1986.
Independent fracture mechanics calculations performed by the staff have shown that, based on the ability te detect a leaking sub-critical crack, sufficient margins to prevent a pipe rupture exist. Therefore, the compensatory measures required of the licensee relate to augmented unidentified leak rate monitoring requirements. We have i
determined that the ability to detect a crack leaking at a 2 gallons per minute will assure that a leak would be detected well before unstable rupture of the piping could occur.
l Oyster Creek Technical Specifications (TS) reouire plant shutdown if the unidentified leak rate exceeds 5 gpm total or if an increase of 2 gpm or 4
greater is detected in a 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> period while operating at steady state power.
An existing administrative procedure requires corrective actions and an 3
investigation if the unidentified leakage rate exceeds 4 gpm. A leak rate flow integrator can measure a minimum of I gallon in a 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> period. This is t
considered sufficiently sensitive to assess an increase in unidentified leak t
rate. There is also a backup leak rate recorder in the control room which continuously records unidentified leak rate to the nearest 0.2 gpm.
In order to alleviate tbc concern of a postulated HELB in the condensate return line penetratiers. The licensee has committed to an additional restriction to be imposed during operation. Tbc action required by the additional restriction will be taken if unidentified leakage increases 2 gpm or more in a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period rather than the 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> period currently i
i in TS. This will ensure that corrective actions are initiated based on l
the investigation of slower developing increases in unidentified leak rate than currently required by the TS.
0
. Unidentified leak rate increases of 2 gpm or more above the baseline over a longer period, i.e., weeks or months, will be investigated to ascertain the source.
If an increase of 2 ppm or more is detected and investigation does not provide reasonable assurance of the absence of a through-wall pipe crack at either of the two condensate return line penetrations, then a plant shutdown will commence to identify the source of leakage.
In addition, the licensee has further committed to install thermocouples on the isolation condenser condensate return line piping both inside and outside containment prior to restart. A significant increase in the temperature differential above baseline (which would result from heatup of the in-contain-ment piping) would provide an indication this would confirm the leak location.
Coupled with indication of low Isolation Condenser System process f'ow this would confirm the leak location that a through-wall crack might e'
- t at the penetration.
3.0 CONCLUSION
S Eased on the factors discussed above, the staff concludes that the operation of the Oyster Creek Nuclear Generating Station for the interim period would be safe with the stated penetration not fully in conformance with the original FSAR design criteria and, considering the compensatory measures, would not present an endue risk to the public health and safety.
4.0 REFERENCES
1.
Letter from R. F. Wilson (GPUN1 to J.A. Zwolinski (NRC), Postulated High Eneroy Line Break Within Energency Condenser Penetrations, dated September 17, 1986.
2.
Letter from R. F. Wilson (GPUN) to J.A. Zwolinski INRC), Postulated High Energy Line Preak Within Energency Condenser Penetrtions, dated November 25, 1986.
Principal contributor:
H. Conrad Dated:
December 24, 1986 i
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