IR 05000259/1992036
| ML18036B044 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 10/29/1992 |
| From: | Crlenjak R, Mellen L NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | |
| Shared Package | |
| ML18036B043 | List: |
| References | |
| 50-259-92-36, 50-260-92-36, 50-296-92-36, NUDOCS 9211030136 | |
| Download: ML18036B044 (13) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION
REGION II
101 MARIETTASTREET, N.W.
ATLANTA,GEORGIA 30323 ENCLOSURE Report No.:
50-259/92-36, 50-260/92-36, AND 50-296/92-36 Licensee:
Tennessee Valley Authority 6N 38A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801 Docket Nos.
50-259, 50-260, 50-296 License Nos.
DPR-33, DPR-52, DPR-68 Facility Name:
Browns Ferry Units 1, 2,
and
Inspection Conducted:
October 19 - 23, 1992 Inspector:
. Mellen, Reactor Inspector Date Signed Approved by:
. L.
C engak, C ief Operational Programs Section Division of Reactor Safety Date Signed SUMMARY Scope:
This was a special announced inspection.
Its purpose was to verify the Browns Ferry Standby Gas Treatment System and Secondary Containment were technically adequate, appropriately tested, met Technical Specification requirements, Final Safety Analysis commitments, and the systems could perform their intended safeguard requirements.
This inspection also reviewed TVA's Secondary Containment breach philosophy.
Results:
The inspector found that Browns Ferry's Standby Gas Treatment System and Secondary Containment were technically adequate, met Technical Specification requirements, Final Safety Analysis commitments, and the systems could perform their intended safeguard requirements'he inspector also concluded that TVA's Secondary Containment breach philosophy was technically adequate and conservative.
The inspector noted that with the current main steam vault configuration, it would be inappropriate to test the standby gas treatment system at elevated main steam line temperatures due to concerns about the environmental qualification of the main steam valve vault high temperature t
trsp sensors.
PDR ADD + 921029 921103013
CK 05000259 PDR
,
REPORT DETAILS 1.
Persons Contacted Licensee Employees A. Brindle, System Engineer P.
Ebersole, Mechanical Engineer, Operations Procedures Group H. Goldmann, Principal Nuclear Engineer
- S. Kane, Licensing Engineer M. Morrison, Regulatory Licensing R.
Mundy, Principal Mechanical Engineer
- G. Pierce, Site Licensing Manager
- J. Rupert, Engineering and Modifications J. Scalice, Plant Manager S. Smith, Operations Procedures and Support Manager
- 0. Zeringue, Vice President Browns Ferry Operations Other licensee employees contacted included instructors, engineers, mechanics, technicians, operators, and office personnel.
NRC Representatives W. Beardon, Resident Inspector
- J. Hunday, Resident Inspector
- C. Patterson, Senior Resident Inspector 2.
- Attended Exit Interview Standby Gas Treatment System A.
Background The Standby Gas Treatment System was originally designed as a two train system with each train capable of removing 9000 CFM, with a single failure the system was capable of delivering 9000 CFM. It was designed to maintain a minimum of 0.25 inches of negative pressure in each reactor building zones and the common refueling zone.
In 1975 a third train was added and the system minimum capacity was raised to 12000 CFM after a single failure.
Based on discussions with licensee personnel and review of selected records, the inspector developed the following historical evolution from independent zonal isolation to the present.
During a surveillance on one reactor. building zone the normal reactor building Heating Ventilating and Airconditioning in the reactor building zone tripped and the surveillance failed.
After a root cause investigation, TVA determined that there was significant inter-zonal leakage between the units.
Following the discovery of the inter-zonal leakage between adjacent reactor building zones TVA worked on the seals between the zones, but was unsuccessful in isolating a single zone and drawing 0.25 inches of negative pressure.
TVA decided to test the three reactor building zones
and the common refueling zone as a single entity.
This was accomplished by isolating the normal ventilation to all four zones and measuring the pressure in each zone.
In 1989, in response to NRC Information Notice 88-76, RECENT DISCOVERY OF A PHENOMENON NOT PREVIOUSLY CONSIDERED IN THE DESIGN OF SECONDARY CONTAINMENT PRESSURE CONTROL, TVA verified the location of the pressure sensing instruments used during the verification of Secondary Containment were located in accordance with the enclosed suggestions.
One sensor was situated as high as practical in each of the three reactor building zones, and three sensors were situated as high as practical on the refueling floor in each unit.
TVA reviewed their process of bypassing the temperature sensors in the main steam vault and determined the temperature would exceed the environmental qualification values.
The Secondary Containment integrity test has not been performed since the environmental qualification criterion applied to Browns Ferry.
TVA was still evaluating the effects of the elevated temperature on the environmental qualification of the main steam vault equipment.
With the relatively low air volume in the main steam vault, approximately 25,000 cubic feet; the low heat capacity, approximately 0.2 BTUs per pound; and the low air density of approximately 13 cubic feet per pound under these conditions, a
small amount of added heat will cause a rapid change in temperature.
TVA estimated that the main steam vault temperature would reach 200 degrees fahrenheit in 6 to 10 minutes.
The total time normal ventilation is isolated during this test is approximately four hours.
TVA successfully completed the most recent Secondary Containment surveillance O-SI-4.7.C, SECONDARY CONTAINMENT INTEGRITY TEST, on February 10, 1991.
This surveillance test used the aforementioned sensor locations and was completed with normal ventilation isolated.
The unit was shutdown during this test, therefor, the main steam vault high temperature trip sensors were not bypassed.
TVA is currently reviewing several options regarding the main steam vault temperature during the test.
These include: using the new drywell coolers for main steam vault cooling during the test or pending the outcome of the environmental qualification review using an alternative to using jumpers to bypass the main steam vault high temperature trip sensors.
During the reconstruction effort for unit three TVA initially decided to isolate the unit three reactor building from the other two reactor building zones and the common refueling zone.
Among other problems TVA determined that this would involve the administrative control of approximately 1100 valves along with approximately 15,000 feet of piping and duct work.
This was
considered possible, but difficult to implement due to the number of items that would require administrative control and the manpower required for the zonal boundary upgrade.
Technical Specifications Requirements Technical Specification section 3.7/4.7.B, Standby Gas Treatment System, describes the Standby Gas Treatment system limiting conditions for operation and the surveillance requirements.
Technical Specification section 3.7/4.7.C, Secondary Containment, describes the Secondary Containment Integrity and its'ssociated limiting conditions for operation and the surveillance requirements.
Section 4.7.C. l.a stated that Secondary Containment must be capable of maintaining 1/4 inch of water vacuum under calm wind conditions with a system leakage of not more than 12,000 CFN, shall be demonstrated each refueling prior to the refueling outage.
The bases section for 4.7.B/4.7.C, Standby Gas Treatment System and Secondary Containment, stated in part "Initiating reactor building isolation and operation of the Standby Gas Treatment System to maintain at least a 1/4 inch of water vacuum within the Secondary Containment provides an adequate test of the operation of the reactor building isolation valves, leak tightness of the reactor building and performance of the Standby Gas Treatment System.
.
.
. performing these tests prior to refueling will demonstrate Secondary Containment capability prior to the time the primary containment is opened for refueling."
The inspector reviewed the most recent surveillance test to ensure compliance with applicable portions of Technical Specification and applied the Technical Specification criteria to determine the actual measured leakage at 0.25 inches of negative pressure.
The inspector corrected the Standby Gas Treatment flow for any of the tests where the minimum pressure was above 0.25 inches of negative pressure.
July 1987 O-SI-4.7.C test resulted in 10,762 CFN 8 0.29 inches of negative pressure.
Correcting the results to 0.25 inches of negative pressure yielded approximately 9995 CFN.
2.
3.
4, April 1988 O-SI-4.7.C test resulted in 7,994 CFM 8 0.29 inches of negative pressure.
This test was later determined to be invalid because of interference from main control room Heating Ventilating and Airconditioning.
December 1988 O-SI-4.7.C test resulted in 10,767 CFM 8 0.25 inches of negative pressure.
January 5,
1991 O-SI-4.7.C test resulted in 10,822 CFN 8 0.25 inches of negative pressure.
Although the test passed the licensee made leak repairs and performed another test (February 10, 1991).
5.
February 9,
1991 test O-TI-235, Secondary Containment Zonal Integrity Test, Revision 0.
This test was designed to test the boundary between unit two and unit three.
There were many problems encountered during the test and the results were inconclusive.
6.
February 10, 1991 O-SI-4.7.C test resulted in 10,135 CFM 8 0.305 inches of negative pressure.
Correcting the results to 0.25 inches of negative pressure yielded approximately 9175 CFM.
All of the above tests were conducted assuming 0.7 flow coefficient for all leakage.
This coefficient was based on a
square edged orifice and Reynolds Number of approximately 40 which resulted in the most conservative point on the applicable diameter ratio (8) curve.
In all cases the flow numbers calculated were very conservative.
The tests reviewed met all applicable portions of Technical Specification sections 3.7/4.7.B and 3.7/4.7.C.
The inspector concluded the licensee's current configuration conforms with the existing Technical Specifications.
FSAR Commitments The FSAR states
"The safety objective of the Secondary Containment System is to limit the release of radioactivity to the environs after an accident so that the resulting exposures are kept to a
practical minimum and are within the guideline values given in published regulations (10 CFR 20 and
CFR 100 as applicable)
.
. The Secondary Containment System provides primary containment when any of the three Primary Containment Systems are open such as during refueling and maintenance."
Section 5.3.3.2 states
"The reactor building is divided into four ventilation zones which may be isolated independently of each other.
The refueling room which is common to the three units forms the refueling zone.
Individual units below the refueling floor form the other three reactor zones.
The four-zone ventilation system provides increased capability for localizing the consequences of an accident or radioactive release such that the effect will be localized in one zone while maintaining the ability to isolate the entire Reactor Building if necessary.
With one or more zones isolated, normal operations may be continued in the unaffected zones.
If the internal zone boundaries should fail, the entire Reactor Building would still meet the requirements of Secondary Containment by assuring filtered elevated release.
The zone system is not an engineered safeguard, and failure of the zone system would not in any way prevent isolation or reduce the capacity of the Secondary Containment System."
The inspector reviewed several completed tests and discussed FSAR section 5.3.3.2 with the project engineer and system engineer.
The inspector determined that TVA met the inter-zonal isolation described in this section and it was possible to conduct normal operations in one zone while localizing the consequences of an accident or radioactive release in another zone.
In the event that inter-zonal isolation was not available the portions that were considered engineered safeguards, the entire Secondary Containment boundary, would be available and could perform its function.
The inspector reviewed the design criteria BFN-50-7064C, Secondary Containment, and discussed the isolation of individual reactor building zones or the common refueling zone following an event with radiological consequences.
The discussion centered on the effects of this event at the site boundary.
The flow from standby gas treatment is such that the flow would be primarily through the zone exiting through the Standby Gas Treatment System.
In the event there were interactions with the non-isolated zones, there are radiation monitors on these zones that would isolate the zone on receipt of a high radiation signal.
The effect would be a
further isolated zone with no additional adverse radiological consequences.
The Secondary Containment would continue to function as the system that isolated, contained, and assured a
filtered and controlled elevated release, as designed.
The inspector concluded the licensee's current configuration conforms with the existing FSAR.
Additional Communication Between Secondary Containment Zones The inspector reviewed Design Change Notice S17557B which delineated the licensee's plan to combine the Secondary Containment zones.
There was approximately 170 feet of suction losses between units
and 2 and an additional 170 feet more between unit 2 and 3.
This arrangement caused unit 3 to be maintained at a less negative pressure than unit 2, which would be at a less negative pressure than unit l. If a leak in unit 1 were of sufficient size it could prevent either unit 2 or 3 from reaching the required negative pressure.
With an opening of at least 22.5 square feet the pressure difference between the zones would be less than 0.001 inches of water 9 2000 CFH.
To accomplish this the equipment hatch blowout panels would be left open between the refueling floor and the individual reactor compartments.
Operation of unit 1 or 3 above 211 degrees fahrenheit would not be permitted until the operator dose calculations were revised to include units 1 or 3, The inspector reviewed the calculation, verified the assumptions, and determined that from a Secondary Containment boundary standpoint these actions were conservativ Total Allowable Breach Margin The inspector reviewed O-TI-237, Secondary Containment Penetration Breach Analysis, which contained the instructions for determining total allowable Secondary Containment breach margin.
This technical instruction used the values determined in O-SI-4.7.C, SECONDARY CONTAINMENT INTEGRITY TEST.
The calculation resulted in the total number of square inches that could breach the Secondary Containment and two trains of Standby Gas Treatment System would maintain the pressure at or below 0.25 inches of negative pressure.
The calculation is extremely conservative, in that it does not consider the effects of anything other that a breach with the characteristics of a square edged orifice (the most conservative geometry).
Additional conservatism in the, calculation included only the Technical Specification flow value was used, only two of the three Standby Gas Treatment System trains were included in the test data, and no credit was taken for test pressures that exceeded 0.25 inches of negative pressure.
In a meeting with NRR, the Vice President
- Browns Ferry Operations stated that TVA did not intend to use more than
% of the calculated value.
The inspector considered the use of this test method both conservative and appropriate.
The licensee has proposed the use of the total available breach margin wherever required on the Secondary Containment boundary in Design Change Notice S17557B.
0-TI-237 contained the detailed instruction for determining breach margin.
The inspector reviewed the design change notice and 0-TI-237 determined that the assignment of allowable leakage to a particular unit was primarily for book keeping purposes.
From a system performance perspective it did not matter which unit the leakage was on as long as did not exceed the total allowable leakage.
The inspector concluded this was an appropriate disposition of the total breach margin.
Emergency Operating Instructions As described in section 2.D TVA has proposed creating a large opening between each of the four zones to ensure an equal pressure distribution.
This would in effect reduce the pressure drop from unit three to the Standby Gas Treatment System fans and equalize the pressure between the four zones.
The inspector reviewed applicable Emergency Operating Instructions and Abnormal Operating Instructions to ensure the inter-zonal communications would not effect the implementation of the procedures.
TVA also reviewed the applicable emergency procedures.
Both the inspector and the licensee concurred that there will be some additional communications between the zones, however, the procedure network will bound any of these conditions.
The most limiting of these appeared to be EOI-3, Secondary Containment Controls, path SC/R (secondary containment/radiation control).
If the radiation levels were high enough, this could result in an early shutdown of
the reactor.
The inspector reviewed this path and selected other paths and concluded this was within the current accident mitigation strategy.
G.
Conclusions The inspector concluded the Secondary Containment would still meet the requirements of assuring filtered elevated release if the individual zones were cross tied by removing the blowout panels on the equipment hatches.
Browns Ferry's Secondary Containment and Standby Gas Treatment Systems met Technical Specification requirements, Final Safety Analysis commitments, and the systems could perform their intended safeguard requirements.
The inspector further concluded that from a mathematical and engineering perspective the total breach margin could be used on either of the units.
Finally, the inspector concluded that with the current main steam vault configuration, it would be inappropriate to test the standby gas treatments system at elevated main steam line temperatures due to concerns about the environmental qualification of the main steam valve vault high temperature trip sensors.
Exit Interview The inspection scope and findings were summarized on October 23, 1992, with those persons indicated in paragraph 1.
The NRC described the areas inspected and discussed in detail the inspection findings.
No proprietary material is contained in this report.
No dissenting comments were received from the license ty