ML20248D277
| ML20248D277 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 09/18/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20248D272 | List: |
| References | |
| NUDOCS 8910040181 | |
| Download: ML20248D277 (6) | |
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ENCLOSURE 4 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO.171 TO FACILITY OPERATING LICENSE NO. DPR-33 AMENDMENT NO.173 TO FACILITY OPERATING LICENSE NO. DPR-52 AMENDMENT NO.142 TO FACILITY OPERATING LICENSE NO. DPR-68 TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT, UNITS 1, 2 AND 3 DOCKET NOS. 50-259, 50-260 AND 50-296
1.0 INTRODUCTION
By letter dated February 14, 1989, 1989, the Tennessee Valley Authority (TVA or the licenseeand as supplemented by) submitted a request for a temporary amendment to licenses DPR-33, DPR-52,.and DPR-68 to change the Browns Ferry' Nuclear (BFN) Technical Specification (TS) for Units 1, 2, and 3 relative to the Control Room Emergency Ventilation System (CREVS).
The proposed temporary TS change 265T would allow power operation and fuel movement during Unit 2 Fuel Cycle 6 and until just before startup for Unit 2 Cycle 7, with the CREVS not meeting its design basis (achieve control room pressurization with essentially zero unfiltered in-leakage).
2.0 BACKGROUND
Temporary TS change 245T addressed and justified allowing both trains of the CREVS to be inoperable (not meet design basis) during the Unit 2 Cycle 5 outage. All fuel had decayed for at least three years and had been removed to the fuel pool. The temporary change was granted on July 20, 1988 by the NRC on the basis that the radiological consequences due to postulated fuel handling accidents would be much less severe than normally predicted.
Temporary TS change 253T addressed and justified CREVS not being operable during Unit 2 Cycle 5 fuel loading and sub-critical functional testing opera-tions. This change allowed the reload of the Unit 2 core and it was approved by the NRC on October 3,1988.
The CREYS problem also has been identified by the licensee in Licensing Event Report 88-025.
The design baseline review program determined that unfiltered air from the control bay supply duct would leak into the control room.
The licensee's review of its own Conditions Adverse to Quality Reports revealed that non-safety related equipment associated with stack ventilation was also hbk**$lyK0500o239 1 69091s P
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' required to be operable during an emergency to avoid a ground level release from the standby gas treatment system.
This was reported in LER 88-039.
Conditions leading to both LERs were attributed to inadequate design and design reviews.
In the LERs TVA has committed to procedural improvements to minimize the occurrence of future design errors, completion of modification of the stack ventilation system prior to Unit 2 restart from the current outage and comple-tion of modifications of the CREVS prior to Unit 2 restart after the next outage (Cycle 7).
3.0
,P,R,0 POSED TS CHANGE Since the CREVS is common to all three units, its operability is required for the operation of any unit.
Therefore, the proposed technical specification changes apply to all three BFN units. These temporary changes would allow Unit 2 Cycle 6 operation and permit the subsequent defueling, refueling, and sub-critical functional testing activities required until just prior to startup for Unit 2 Cycle 7.
The BFN design of CREVS was addressed in TVA's Final Safety Analysis Report (FSAR) response to NRC question 10.2 and the Technical Specification Bases 3.7.E/4.7.E.
"The cor3 'l room emergency ventilation system is designed to automatically start up sn control room isolation and to maintain the control room pressure at a slight positive pressure so that all leakage should be out leakage." Also, ".... in emergencies, the makeup air to the control room will pass through at least three and possibly four air cleanup stages.
(The fourth stage is the optional high efficiency particulate absolute (HEPA) filter in the ventilation system inlet tower)." In their submittal TVA estimates that 2,750 cubic feet per minute (CFM) would bypass the CREVS (which contains three of the fourcleanupstages). Therefore, the conditions of providing filtered air are not being met.
However, control room pressurization can be accomplished and some of the pressurizing air (500 CFM per CREVS) is properly filtered to reduce radiation doses.
The proposed TS change would delete the current subscript and replace it with the folloving:
CREVS is considered inoperable only because it does not meet its design basis for essentially zero unfiltered in-leakage.
REACTOR POWER OPERATION and fuel movement are acceptable until just PRIOR TO RESTART for Unit 2 Cycle 7.
During Cycle 6, CREVS must be demonstrated to be functional by performing all applicable surveillance.
In the event that the applicable surveillance are not successfully performed, the actions required by the LCO's must be complied with.
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f4.,- :In addition, the following is proposed to be appended to the first paragraph of the Bases Section 3.7.E/4.7.E-for Units 1,'2 and 3:
During Cycle 6. CREVS has-been declared inoperable only because it does not meet its design basis for essentially zero unfiltered in-leakage.
Reactor power operation and fuel movement are acceptable until just prior to start-up for Unit 2 Cycle 7.
During Cycle 6 CREVS must be demonstrated to be-functional by performing all appli-cable surveillance.
In the. event that the applicable surveillance are not successfully. performed, the actions required by the LCO's must be complied with.
3.1> Discussion of Proposed Changes The changes remove constraints to plant operation until just prior to Unit 2 Fuel Cycle.7. -The staff has reviewed the current TS, surveillance requirements and concludes that these requirements can. still be met because the requirements do not-address duct leakage.
4.0 DISCUSSION OF JUSTIFICATION OF PROPOSED CHANGES During an August 11, 1988 meeting. TVA presented arguments to the NRC in favor of the proposed TS change (meeting summary dated August 19,1988).
TVA com-mitted to:
(1) Provide technical justification for one more cycle of operation in terms of worst case dose calculations for design basis accident cases.
(2) Commit to compensatory actions such as breathing apparatus to protect the operating staff.
L (3) Provide the NRC with a proposal for resolution of the CREYS design oroblem within 90 days after restart of Unit 2.
The.NRC, in turn, agreed to review TVA's proposed interim technical specifica-tion changes relative to CREVS.
The licensee's technical justification and proposed compensatory actions were provided in the February 14, 1989 submittal.
i TVA reviewed the BWR operating status and epplicable design bases events to determine which events had the potential for causing fuel damage and radio-1 l.
active release which could require the filtration provided by CREVS. The selected events are addressed briefly as follows:
' Loss of Fuel Pool Cooling The fuel pool cooling and cleanup system is supplemented by the residual heat removal (RHR) system.
The design includes a permanently installed crosstie.
The staff agrees with the licensee that fuel damage is essen-tially precluded by the availability of the RHR system as a backup.
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Control-Rod Drop ~and Main Steamline Break TVA' reevaluated the Control. Rod Drop and Main Steam 11ne Break. accidents to
' determine'the resulting doses to control room operator and technical support.
center (TSC) personnel. The results from both accidents confirmed that doses-were well within:10 CFR 50, Appendix A, General Design Criteria'19
- guidelines of 5 rem whole body or its equivalent to any part of the body
' (30 rem thyroid), even when the control room is not isolated and the nonnal. heating,' ventilation and air conditioning (HVAC) flow of unfil-
~tered outdoor air is supplied.
Based upon the above, the staff finds the dose: levels to-be' acceptable.
Fuel Handling' Accident This conservative reanalysis assumed.the dropped fuel bundle strikes additional bundles, fracturing'125 fuel' rods..The limiting case'is the fuel drop into the storage pool as described in FSAR Section 14.6.4.
With appropriate assumptions relative to-the CREVS, doses over 30. days to the control room operators and TSC personnel following the fuel handling accident were predicted to be 0.03 rem gamma (whole body), 0.26 rem beta
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_and:14 rem thyroid (inhalation). These results are-below the 5 rem whole body, or its equivalent to any part of the body (30 rem thyroid) !imits and are acceptable to~the staff.
Loss-of-Coolant : Accident (LOCA)
The design basis LOCA was reevaluated considering 2.750 CFM CREVS bypass air leakage.
Subsequent analysis was performed to determine the operator dose.
Stack releases were included but the dominant source was deter-mined to be reactor building exfiltration due to high winds concurrent with the LOCA.
The exfiltration was modeled as a puff release beginning at the time o_f caximum concentration in the Reactor Building.
The rate of exfiltration was calculated considering the pressure differential induced across the exterior walls and roof of the reactor building as a function of wind speed and direction. The worst case occurred with the secondary containment internal pressure at - 0.25" W.G. [ associated with only one of the three. Standby Gas Treatment Systems (SGTS) operational]. The bounding case projected 332.9 rem total without compensatory actions. With potas-
~ ium iodide (KI) tablets taken within thirty minutes as a proposed compen-s satory action, the control room operators and TSC personnel would have ample time to metabolize the KI tablets before thyroid limits would be exceeded.
Breathing apparatus is available but was not proposed because it could detract from critical communications among personnel during the emergency. The staff finds this acceptable.
4.1 Summary Discussion of Events The NRC staff has reviewed the cases submitted by TVA and has performed some independent analysis of the events. The NRC results are in general agreement with the TVA results. The staff reviewed the circumstances of the bounding event in accordance with Regulatory Guide 1.7, Section 2.3.4.2, and determined
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'g?, 3 the event to be too infrequent to be credible. TVA also considers it an unlikely event and further points out that the release.or infiltration j
could be detected at either of the two intakes and corrective action could be taken; 1.e.. ' shut down one ventilation, system and/or take KI per
-_ prepared instructions.
5.0 STAFF REVIEW 0F DRAWINGS AND FACILITY The NRC staff discussed with TVA the history of this design deficiency which has existed for over four years including the two temporary TS changes issued to TVA. The staff reviewed drawings and walked down the plant, and then agreed that the installed system was unable to achieve the design objectives.of zero unfiltered in-leakage during.certain postulated emergencies..TVA identified seven design considerations involved in resolving the deficiency. Briefly, the
. ducts are not leak proof..the roof would have to be strengthened to support the filters for 100% filtration and the CREVS is probably too small in capacity to achieve pressurization if the duct leakage is eliminated.
Significant modifications will be needed to correct these problems.
The NRC discussed with TVA whether modifications to the CREVS were required since the system satisfies all requirements except for-infiltration with unfiltered air and no credible event had been identified which would provide-undue exposure to personnel in the control room.
It was concluded that the BFN CREVS problem was a design problem which should be fixed to support the NUREG-0737,Section III.D.3.4 position on Control Room Habitability Require-ments:
Licensee (s) shall assure that control room operators will be adequately protected against the effects of accidental release of toxic and radio-active gases and that the nuclear power plant can be safely operated or shut down under design basis accident conditions.
Therefore, the staff has determined the following:
(1) The current surveillance requirements of the TS address the perfor-mance of individual filters and blowers but do not address the operability concerns related to in-leakage.
The licensee will be required to address this TS deficiency as a part of the redesign of the system and include in the TS a surveillance of in-leakage.
(2) As stated above, no credible combination of events was identified by the staff which resulted in a significant radiation dose to the control room operators or technical support center personnel.
The unique combination of events analyzed by the licensee were not considered credible by the staff.
(3) The staff believes.that the temporary TS change will not make the occurrence of an accident any more likely, the consequences of postulated accidents any more severe, or create the possibility of a new or different kind of accident from those previously evaluated.
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l (4) The staff believes that there is reasonable assurance that. doses to emergency personnel will be'little affected in the event of an accident. Temporary Change No. 265 T is acceptable based upon the licensee's comitments to modify the Standby Gas Treatment System as committed in LER 88-039 prior to startup.
6.0 ENVIRONMENTAL CONSIDERATION
Pursuant to 10 CFR 51.21, 51.32 and 51.35, an environmental assessment and finding of no significant impact have been prepared and published in the Federal Register on September 18,1989 (54 FR 38467).
Accordingly, based upon the environmental assessment, we have determined that the issuance of the amendment will not have a significant effect on the quality of the human environment.
7.0 CONCLUSION
The Commission issued a Consideration of Issuance of Amendment to Facility Operating License and Opportunity for Hearing which was published in the Federal Register (54 FR 15572) on April 18, 1989 and consulted with the State of Alabama. The licensee's letter of July 14, 1989 provided clarification that the projected radiation doses to control room operators and Technical Support Center personnel were within acceptable limits as defined in.10 CFR Part 50, Appendix A. General Design Criteria 19.
No requests for hearing were received and the State of Alabama did not have any comments.
The staff has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Comission's regulations, and the issuance of the amendments will not be inimical to the common defense and security nor to the health and safety of the public.
Principal Contributor:
J. Watt Dated: September 18, 1989
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