ML20129B505
| ML20129B505 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 10/18/1996 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20129B501 | List: |
| References | |
| NUDOCS 9610230029 | |
| Download: ML20129B505 (9) | |
Text
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UNITED STATES NUCLEAR REGULATORY COMMISSION f
WASHINGTON, D.C. 30886-0001
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.129 TO FACILITY OPERATING LICENSE NO. NPF-29 ENTERGY OPERATIONS. INC.. ET AL.
GRAND GULF NUCLEAR STATION. UNIT 1 DQCKET NO. 50-416
1.0 INTRODUCTION
By letter dated June 20, 1996, as supplemented by letter dated September 11, 1996, Entergy Operations, Inc. (the licensee) submitted a request for a change to Facility Operating License No. NPF-29 for the Grand Gulf Nuclear Station, Unit 1 (GGNS).
The proposed license condition to be added to the operating license would redefine the secondary containment boundary to allow the enclosure building to be inoperable and the standby gas treatment (SGT) system to not start automatically during fuel handling in the upcoming refueling Outage 8 (RF0 8) scheduled to begin on October 19, 1996. The license condition would state that the enclosure building may be inoperable during core alterations and movement of spent fuel that has decayed at least 12 days after the reactor was shut down for refueling during RF0 8 and the SGT system may be unable to automatically start or achieve and maintain the required vacuum, provided the following four prerequisites exist in the plant in the outage:
i a.
All dampers communicating between the auxiliary building and the enclosure building are closed.
b.
The access door between the auxiliary building and the enclosure building is closed, except when the access opening is being used for entry and exit.
c.
The SGT system is blocked from automatic initiation.
d.
The SGT system is available for manual initiation or the ac'tions of Limiting Conditions for Operation (LCO) 3.6.4.3 are complied with.
The proposed license condition is an exception to the following requirements in the Technical Specifications (TSs) for GGNS:
LCO 3.3.6.2, " Secondary Containment Isolation Instrumentation," which requires the fuel handling area ventilation and pool sweep exhaust radiation monitors which automatically start the SGT system on high-high radiation to be operable.
9610230029 961018 PDR ADOCK 05000416 p
. LCO 3.6.4.1, " Secondary Containment" which requires the enclosure building to be operable during core alterations and movement of spent fuel in the primary or secondary containment, and the capability of maintaining negative pressure when the SGT system is operating.
LCO 3.6.4.3, " Standby Gas Treatment (SGT) System," which requires the SGT system to be operable and automatically start on the signal from the secondary containment isolation instrumentation.
The proposed amendment is only applicable for the upcoming RF0 8.
It is to allow flexibility for the licensee to repair the roof of the enclosure building during RF0 8.
This amendment will allow the licensee to place the enclosure building in an inoperable status and the SGT system in a manual mode while spent fuel is being handled during refueling.
The letter of September 11, 1996, provided clarifying information that did not change the initial proposed no significant hazards consideration determination for the proposed amendment to the license.
2.0 BACKGROUND
The secondary containment, the SGT system, and the fuel handling accident are described in Section 6.2.2, Section 6.5.1, and Sections 15.7.4 and 15.7.6, respectively, of the Updated Final Safety Analysis Report (UFSAR) for GGNS.
In the letter of June 20, 1996, the licensee stated that its application was prompted by the need to repair the roof of the enclosure building.
The enclosure building is a metal-siding structure which completely surrounds the primary containment above the auxiliary building roof line.
The reactor vessel containing the core and the upper containment fuel racks are located in the primary containment. The spent fuel pool is located in the auxiliary building.
The licensee explained that, during a refueling outage, the primary containment is essentially part of the auxiliary building since the primary containment equipment hatch and the primary containment personnel airlocks are open.
For the fuel handling accident in the primary containment, leakage is from the primary containment to the auxiliary building. The enclosure building merely functions as a mixing volume for the source term released into the auxiliary building in the event of a fuel handling accident in the auxiliary building or in the primary containment.
The fuel handling area and the auxiliary building ventilation systems maintain the auxiliary building at a slightly negative pressure during normal operation. These non-safety systems assure that no ambient air escapes from the fuel-handling area during fuel handling operations without first being monitored and, if needed, treated for airborne radioactivity. Upon detection of high radioactivity, the SGT system is initiated and these ventilation systems are isolated.
l :
The SGT system maintains the enclosure building or secondary containment at a negative pressure and provides cleanup of the potentially contaminated I
^
secondary containment volume following a design basis accident.
Following SGT actuation, the system draws air from the auxiliary building, mixes this air with air drawn from the enclosure building, and returns the mixed air to the enclosure building. A portion of the mixed air is exhausted through a charcoal filter assembly to maintain the secondary containment boundary region at a negative pressure (no leakage from the enclosure building to the enviromment) and to filter the air.
4 The licensee explained that over the years as leaks have developed in the enclosure building roof the affected areas have been patched. As the roof has aged, the frequency of the leaks and thus the required repairs has increased.
Also, GGNS has experienced severe weather including significant hail storms, that have resulted in multiple leaks through the roof. The enclosure building i
has a metal decking roof which by design is sealed sufficiently to support the i
inleakage requirements of the secondary containment. To protect the metal decking and associated sealant (e.g., caulking), the roof decking was overlaid with approximately 2 inches of insulation, several layers of fiberglass felt, gravel, and asphalt.
It is this overlay which will be replaced in repairing the roof.
l The licensee stated that replacing the enclosure building roofing material is i
the best option for stopping the current leaks and precluding future degradation of the secondary containment boundary.
The enclosure building metal decking and associated sealant is by design sufficient to support the leaktightness requirements of the secondary containment.
i The licensee stated that, to date, the leakage has not adversely affected the function of any safety equipment within the enclosure building nor has the leakage adversely affected the ability of the enclosure building to perform its safety functions. However, the licensee stated that it is prudent to replace the portion of the enclosure building roofing material that overlays the secondary boundary to avoid any further adverse impacts to the roof including the metal decking and sealant.
In addition, the licensee stated in its submittal of June 20, 1996, that loads in excess of 1140 pounds (i.e., heavy loads) are prohibited from travelling 1
over spent fuel assemblies in the spent fuel pool or the fuel storage racks in j
the upper containment. Because without controls loads of less than i
1140 pounds (i.e., light loads) of sufficient impact energy could result in dose consequences exceeding the criteria of Standard Review Plan (SRP) 15.7.4 if dropped on irradiated fuel, the licensee identified the matter in Licensee Event Report (LER)-88/016-1, final report dated February 1,1989, and established administrative controls that involved height and weight limits on light loads carried near spent fuel to control the impact energy so that the dose criteria would not be exceeded. These controls included the use of the secondary containment of the enclosure building. These controls on light and heavy loads are not being changed by this proposed amendment, except for the j
i
4 effect of the work on the enclosure building roof which is discussed in the l
evaluation below, and would be in effect during refueling operations for i
RF0 8.
7 3.0 EVALUATION f
l Without the proposed change to the license, the enclosure building would be i
required to be operable during core alterations and movement of spent fuel in the primary and secondary containment and capable of maintaining negative pressure when the SGT system is operating. To provide flexibility to the 1
licensee in doing repairs to the enclosure building roof, the licensee is i
proposing to not require that the secondary containment is operable while l
l handling fuel if the spent fuel has decayed at least 12 days. Therefore, with j
the proposed change, the effect on the containment to hold up whatever radioactivity is released during an accident and the dose consequences of not j
j having the secondary containment are addressed in the following sections.
4 3.1 Containment Function The proposed change will redefine the secondary containment pressure boundary to allow the enclosure building to be inoperable during the upcoming refueling outage. The boundary would be moved from the enclosure building to the l
primary containment and auxiliary building by the actions to ensure the following l
The auxiliary building to enclosure building access door is closed, the SGT system dampers which communicate between the two buildings are 1
closed, and the SGT system will not automatically start.
l The licensee stated that auxiliary building to enclosure building access door would be opened and closed as needed for access to the enclosure building during the outage, but otherwise would be closed.
This door is normally locked closed and access to the enclosure building is controlled through security.
As a result, in the event of a fuel handling accident, an isolated low leakage l
boundary (consisting of the primary containment and the concrete auxiliary building surrounding the containment) would be established. The low leakage j
boundary is established by automatically shutting down the fuel handling area and the auxiliary building ventilation systems described in Section 2.0 above and by the three conditions above, which are three of the four prerequisites stipulated by the licensee in the proposed amendment to the license. The fourth prerequisite will ensure that the SGT system can be manually started, if the system is needed to reduce the consequences of a fuel handling accident.
The licensee stated that the proposed change is very conservative with respect to the postulated design-basis fuel handling accident because the change requires a period of greater than 12 days decay in the spent fuel, does not i
take credit for dose mitigation by associated engineered safety feature
l systems, and will establish in effect a low leakage boundary which will i
automatically isolate in the event of a fuel handling accident. Establishing the low leakage boundary requires that the SGT system does not start automatically for a fuel handling accident, but that the system be available i
for manual initiation if it is needed.
i Because the roof of the enclosure building needs to repaired, the pressure boundary of the enclosure building and its operability in the TSs may be affected during the work. The pressure boundary of the roof is the metal decking and sealant (e.g., caulking) and this supports the accident l
requirement for maintaining a partial vacuum in the secondary containment when the SGT system is operating. To protect the metal decking and associated sealant the roof decking was overlaid with approximately 2 inches of insulation, several layers of fiberglass felt, gravel, and asphalt.
It is this overlay tnat needs to be replaced.
Although the license does not expect the repair work to _ affect the metal decking and sealant which forms the secondary containment pressure boundary for the roof, this work could result in the secondary containment ceasing to be able to maintain a pressure boundary (i.e., becoming inoperable in terms of the TSs) if decking is removed to be repaired or replaced. With the overlay removed, the decking will be inspected for possible repair or replacement.
Some amount of work to the decking and sealant must be done because there is water leakage through the roof.
Because fuel handing during the outage requires the operability of the enclosure building (i.e., LCO 3.6.4.1 of the TSs), the licensee has proposed to not require this operability so that if the roof repairs do require repairs or replacement of the roof decking and sealant the fuel handling inside the primary containment does not have to stop. The licensee submitted the potential consequences of the postulated fuel handling accident to justify that the operability of the enclosure building was not required when fuel was being handled after 12 days of decay. To have acceptable dose consequences during a fuel handling accident with the secondary containment inoperable, the licensee has proposed to start the work after the spent fuel has decayed 12 days during the refueling outage. To further reduce these doses, the licensee has proposed to set up an isolable low leakage boundary formed of the primary containment and the auxiliary building that surrounds the primary containment.
The potential dose consequences are addressed in Section 3.2.
Setting up the SGT system not to automatically start up on a high-high radiation signal, as currently required, having certain doors and dampers closed, and having the fuel handling area and auxiliary building ventilation systems shut down will act to keep the radioactivity released during a fuel handling accident within the primary containment and auxiliary building.
Because the radioactivity released would eventually leak from the buildings without filtration if the SGT system is never started, the licensee intends to re-establish the secondary containment if decking has been removed, open the dampers to re-establish communication between the buildings, and then start
_ _ ~ _ _ - _ _ _ _
i j :
the SGT system to collect and filter the radioactivity. This would reduce the potential consequences for the postulated fuel handling accident from the i
values given in Section 3.2.
Therefore, the staff concludes that a reduced containment function will be provided for the fuel handling accident by the licensee. This containment function will be provided by the actions proposed to establisii an isolable low leakage boundary which would be formed by the primary containment and the i
auxiliary building.
3.2 Reanalysis of the postulated Fuel Handling Accident The proposed amendment required a reassessment of the radiological dose consequences of postulated fuel handling accidents at GGNS, based on the prerequisites of the proposed amendment. The licensee reanalyzed fuel handling accidents for GGNS and did not take credit for the active engineered safety feature systems (e.g., auxiliary building and enclosure building i
integrity, isolation of the containment and fuel handling area ventilation systems, and the SGT system), that are currently taken credit for in the UFSAR Chapter 15 analysis, to reduce the dose consequences of the analyzed events.
In performing the analysis, the licensee used the assumptions and methodology prescribed by Regulatory Guide (RG) 1.25, " Assumptions Used for Evaluating the Potential Radiological Consequences of a Fuel Handling Accident in the Fuel Handling and Storage Facility for Boiling and Pressurized Water Reactors."
A 12-day (288-hour) decay time and 23 feet of water coverage (LCOs 3.7.6 and
)
3.9.7 of the TSs) are assu'ned in the analysis.
No credit was taken for iodine removal by filtration by charcoal beds in the SGT system and no credit was taken for prompt radiation detection and isolation of containment building penetrations. The primary containment and the auxiliary building were assumed to be together because the primary containment equipment hatch and the primary containment personnel airlocks between the buildings would be open.
3 The licensee's analysis calculated the doses for the 0-2 hour period at the exclusion area boundary to be 0.13 rem to the whole body and 63 rem to the thyroid. These calculated doses are within the SRP 15.7.4 criteria of 6 rem to _the whole body and 75 rem to the thyroid. The thyroid dose to the control room personnel was calculated to be 16 rem and is within the dose acceptance criteria of General Design Criterion (GDC) 19 of Appendix A to 10 CFR Part 50.
The staff has completed its evaluation of the potential radiological dose consequences of a fuel handling accident (FHA) at GGNS based upon the prerequisites of the proposed amendment.
In its analysis, the staff also used the assumptions contained in RG 1.25 and the review procedures specified in SRP Section 15.7.4, " Radiological Consequences of Fuel Handling Accidents," of NUREG-0800.
The staff has computed offsite doses for GGNS using the assumptions described above and the Commission's ACTICODE computer code. The resulting doses in rem
i d
j calculated for the site exclusion area boundary and the control room are the i
i following:
Exclusion Area Boundary Dng SRP 15.7.4 limits j
Whole Body 0.2 6
l Thyroid 64 75 l
Control Room Operator D. gig GDC-19 Limits Whole Body
<0.1 5
Thyroid 14 30 The 30 rem thyroid dose for the GDC-19 limit is equivalent to 5 rem whole body
)
in accordance with SRP 6.4, " Control Room Habitability System."
i The staff's dose calculations were based on the assumptions listed in Table 1.
l The staff assumed an instantaneous puff release of noble gases and radiciodine from the gap and plenum of the broken fuel rods. These gas bubbles will pass through at least 23 feet of water covering the fuel before reaching the containment atmosphere. All airborne activity reaching the containment atmosphere is assumed to exhaust to the environment within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. The gap l
activity is assumed to have decayed for a period of 12 days (288 hours0.00333 days <br />0.08 hours <br />4.761905e-4 weeks <br />1.09584e-4 months <br />). All of the radioactive material released to the containment escapes the
]
containment within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.
i i
The proposed amendment leaves in effect a secondary boundary which will provide a low leakage boundary (consisting of the primary containment and the L
auxiliary building) by automatically isolating in the event of the design basis FHA and requires that the SGT system be available for manual initiation i
when needed. The provisions described in this safety evaluation provide reasonable assurance that the SGT system as a defense-in-depth measure can be reestablished quickly to limit releases much lower than was assumed in the dose calculations. The staff and the licensee have taken no credit for this secondary boundary.
Because the potential dose consequences are based on a minimum of 12 days of decay of the spent fuel being handled while the roof is being repaired, it is best to do the work while the plant is shutdown in a refueling outage. The potential dose consequences during refueling are within acceptable limits ar.d, therefore, it is not necessary to do the work while the fuel is in the reactor vessel with the head on the vessel, and no fuel handling being conducted.
3.3 Conclusion The staff has reviewed the licensee's proposal and performed an independent assessment of the radiological dose consequences from a FHA under the prerequisites for the proposed amendment.
The staff agrees that the repair work to the enclosure build roof is needed and should be done while the plant is shutdown during the upcoming RF0 8.
The staff concludes that a containment function will still be maintained during the repair work in that the secondary 4
. j containment will either never be affected by the repair work or will be returned to service in the aftermath of a FHA. The staff also concludes that the potential offsite radiological consequences associated with the postulated FHA are within the acceptance criteria set forth in 10 CFR Part 100 and the potential doses associated with this accident to the control room operators are within the criteria specified in GDC 19 of Appendix A to 10 CFR Part 50.
l Therefore, the staff concludes that the proposed amendment is acceptable.
4.0 STATE CONSULTATION
l In accordance with the Comission's regulations, the Mississippi State official was notified of the proposed issuance of the amendment. The State official had no comments.
5.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued ^ proposed finding that the amendment involves no significant hazards consi8a ation, and there has been no public comment on such finding (61 FR 37299).
Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
6.0 CONCLUSION
The Commission 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, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributors: John Minns Jack Donohew Date: October 18, 1996
b e TABLE 1 - ASSUMPTIONS USED FOR CALCULATING RADIOLOGICAL CONSE0VENCES Parameters Quantity Power Level (Mwt) 3993 Number of Fuel Rods Damaged (1 assembly plus 32 rods) 108 Total Number of Fuel Rods 60800 Shutdown time, hours 288 Power Peaking Factor
- 1.5 Fission Product Release Duration 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> Release Fractions
- Iodine 12%
Noble Gases 10%
Krypton Gas 30%
Iodine Forms
- Elemental 75%
Organic 25%
Core Fission Product Inventories per TID-14844 Recentor Point Variables **
Exclusion Area Boundary Atmospheric Relative Boundary, NyQ (sec/mP) 0-2 hours 1.5 E-3 i
Control Room Volume l
3 Atmospheric Relative Concentration, XyQ (sec/m )
3.29 E-4 Control Room Volume, cubic fept 2.53 E+5 Maximum Infiltration Rate, ft / min 600 Geometry Protection Factor 17.5 Iodine Protection Factor Not Used Note: Dose conversion factors from ICRP-30 were utilized for all calculations Regulatory Guide 1.25 Grand Gulf UFSAR, Table 15.2 l
l