ML17215A642
| ML17215A642 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 10/16/1984 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17215A641 | List: |
| References | |
| NUDOCS 8411140471 | |
| Download: ML17215A642 (14) | |
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0 UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO.
7 TO FACILITY OPERATING LICENSE NO. NPF-16 FLORIDA POWER AND LIGHT COMPANY, ET AL.
ST.
LUCIE PLANT, UNIT NO.
2 DOCKET NO. 50-389
1.0 INTRODUCTION
By letter dated March 13, 1984, Florida Power and Light Company (FP8L) submitted an application to increase the storage capacity of the spent fuel pool (SFP) by replacing the existing racks with new storage racks.
By letter dated August 29,
- 1984, FPKL provided additional clarification in response to the NRC staff's requests.
This is the first rerack for St. Lucie Plant, Unit No. 2.
The proposed amendment would authorize the licensee to increase the current capacity by installing high density racks to bring the capacity up to 1076 cells.
With the 300 presently available cells, St. Lucie 2 would lose the full core reserve storage capability after the second refueling in 1986.
With 675 cells, allowed by the current license, the reserve storage capability would be lost in 1992.
The new spent fuel storage racks would have a usable storage capacity of 1076 cells, extending the full core reserve storage capability until 1998 when a federal depository should be available for spent fuel [Nuclear Waste Policy Act of 1982, Section 302(a)(5)J.
2.0 DISCUSSION AND EVALUATION
- 2. 1 Criticality Considerations Florida Power and Light Company (FP&L) has requested approval to modify the spent fuel storage racks at St. Lucie 2.
At present, there is one spent fuel pool at St. Lucie 2 with existing racks that have a capacity of 300 storage cells.
FPSL contracted with Combustion Engineering (CE) for new spent fuel storage racks that allow for more dense storage of spent fuel.
These new racks will replace the existing racks and have a usable storage capacity of 1076 cells.
CE is responsible for the design and fabrication of the new spent fuel storage racks and providing engineering assistance in reviewing the spent fuel pool cooling system.
Ebasco Services, Inc. is responsible for reviewing building structural analysis and accident evaluation.
Region I of the two region spent fuel pool contains four 7xll modules and two 7x10 modules.. However, in order to achieve a sufficient center-to-center 84iii40471 84iOih PDR ADQCK 05000389 P
spacing between fuel assemblies, only one-half of these cells (224) will be available for fuel assembly storage.
The remaining unused cells will contain blocking devices to preclude fuel assembly storage.
Region I will, therefore, be a checkerboard configuration.
Fuel similar to the CE 14x14 or 16xl6 design with U-235 enrichments up to 4.5 weight percent may be stored in Region I.
Region II contains one Sx19 module and twelve Sxll modules.
Fuel is stored in three out of four locations with cell blocking devices in each unused cell.
Therefore, 852 cells will be available for storage.
Region II is used to store fuel that has experienced sufficient burnup such that storage in Region I is not required.
2.1.1 Analysis Methods The criticality aspects of the storage of the CE design fuel from St. Lucie
- Unit 2 in the spent fuel storage pool are analyzed using the DOT-2W two-dimensional discrete ordinates transport theory code with s order 6 for reactivity determination.
Four energy-group neutron cross 3ections are calculated by the CEPAK lattice code with correction factors to account for heterogeneous lattice effects calculated by the NUTEST two-dimensional integral transport theory code.
FPSL has provided qualification of the CE calculation model and methods used in spent fuel storage rack analyses.
Based on the results'f a series of UO critical experiments, a calculational uncertainty of 0.00714 at the 95/95 cohfidence level and a calculational bias of +.00138 were obtained.
In addition, calculations were performed to evaluate the effects of mechanical tolerances, off-center placement of fuel assemblies, and temperature changes on the rack reactivity.
These uncertainties, which are at least 95/95 confidence level, result in a value of 0.0184 for Region I and 0.0115 for Region II when combined statistically.
The overall uncertainties
- are, therefore, 0.024 and 0.017 for Regions I and II, respectively.
Section 4.3 of the St. Lucie 2
FSAR illustrates the good agreement obtained between measured plutonium isotopic concentrations and values predicted with CEPAK.
- 2. 1.2 Spent Fuel Storage Rack Analysis The spent fuel racks have a nominal center-to-center spacing between adjacent storage cells of 8.965 inches and a nominal stainless steel wall thickness of 0.135 inches.
The design analysis assumed a nominal pool temperature of 98.6'F and the storage cell arrays were assumed to be infinite in lateral extent and in length.
The cal,culated multiplication factor (K
) for the Region I checkerboard configuration is 0.942 including the pr5ffously mentioned uncertainties and calculational biases.
An enrichment of 4.5 weight percent U-235 was assumed f'r Region I.
For Region II, a family of curves of k versus burnup for a range of enrich-ments is generated.
These resulting vlBes of k f include the calculational uncertainties and biases (net value of +0.0172 if> f f) previously described.
The curves are then used to define the minimum burn3 for fuel of a given initial enrichment which will result in a k
of 0. 95 when Region II is ful'ly loaded with fuel assemblies of this tQ T.hese burnup/enrichment data points are then used to plot the curve of burnup versus initial fuel enrichment to be included in the St. Lucie 2 Technical Specifications.
Since these calculations assumed an assembly average
- burnup, a burnup bias of 1900 HWD/t)TU was applied to the figure to conservatively account for the most adverse axial burnup distribution.
- 2. 1.3 Abnormal'nd Accident Conditions Postulated accidents such as the dropping of a fuel assembly on top of the
- racks, dropping of other objects into the spent fuel pool, deformation and relative position of racks due to tornado or earthquake, and loss of one spent fuel pool-cooling pump were considered and do not violate our accept-ance criterion of 0.95.
For these accidents, the assumption is made that it is not necessary to assume concurrently two unlikely independent events to ensure protection against a criticality accident (double contingency principle).
Therefore, the assumption of the minimum boron concentration in the spent fuel pool required by the Technical Specifications (1720 ppm) ensures that k ff is no greater than 0.95 for these accidents.
- 2. 1. 4 Conc lus ions The staff concludes that the proposed storage racks meet the requirements of General Design-Criterion 62 as regards criticality. -This conclusion is based on the'following. considerations:
1.
Acceptable calculation methods that have been verified by comparison with experiment have been used.
2.
Conservative assumptions have been made about the enrichment of.the fuel to be stored and the pool conditions.
3.
Credible accidents have been considered.
4, 5.
Suitable uncertainties have been considered in arriving at the final value of the mu1 tip 1 icat ion factor.
The final effective multiplication factor value meets our acceptance criterion.
The staff has also concluded that the modifications to the St. Lucie 2 Technical Specifications are acceptable to allow operation with the proposed expansion of spent fidel pool storage capacity.
2.2 SPENT FUEL POOL COOLING AND MAKEUP The increase in the total decay heat load resulting from the expansion will amount to only a few percent of the total heat load due to the longer decay times of the oldest fuel assemblies.
The licensee therefore concluded that the existing spent fuel cooling capability could adequately remove the additional decay heat without exceeding the pool water temperature presented in Standard Review Plan Section 9.1.3.
Information was also provided to demonstrate that the available source of makeup water provides adequate
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assurance that the fuel would not become uncovered in the event all pool cooling was lost.
2.2.1 Spent Fuel Storage Pool The St. Lucie 2 spent fuel facility is housed in the Fuel Handling Building adjacent to the reactor Containment Building. It consists of the storage pool, the spent fuel cask loading pit and the transfer canal.
These three areas within tlie Fuel Handling Building are connected by waterproof gates that are normally closed except at those times when radioactive material is moved from one area to another, e.g.,
during refueling of the reactor and loading the spent fuel shipping cask.
The storage pool is L-shaped with the longest dimensions, 33' 46',
and contains water to a depth of 38'-6".
The storage pool, canal and pit are lined with stainless steel liner plates.
A leak detection system is provided on the concrete side of the liner to detect and col-lect any pool water that leaks through the liner plate welds.
The 23 feet of water above the top of the spent fuel assemblies acts as a transparent shielding and cooling medium.
2.2.2 Decay Heat Loads The licensee's'calculated spent fuel discharge heat load to the pool, which was determined in accordance with the Branch Technical Position ASB 9-2, "Residual Decay Energy for Light Water Reactors for Long Term Cooling",
and the Standard Review Plan Section 9.1.3,. "Spent Fuel Pool Cooling and Cleanup System",
indicates that the expected maximum normal heat load following the last refueling is 16.9 MBTU/Hr.
This heat load results in a maximum bulk pool temperature of less than 137'F.
The expected maximum abnormal heat load following a full core discharge is 31.7 MBTU/Hr.
This
" abnormal heat load results in a maximum bulk pool temperature of less than 150 F with both cooling trains operating.
Assuming the loss of all cooling, boiling would occur after 9.0 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> for the normal heat load condition and after 2.9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br /> for the maximum heat load condition.
This results in a boil off rate of 35.6 and 66.3 gpm, respectively.
This provides reasonable time to initiate makeup to the spent fuel pool.
2.2.3 Spent Fuel Pool Cooling System The cooling portion of the Fuel Pool System is a closed loop system consisting of two half-capacity fuel pool pumps and two full-capacity fuel pool heat
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exchangers, where the full capacity condition corresponds to the design condition of a full core placed in the spent fuel pool seven days after reactor
- shutdown, in addition to the decay heat from seven previous annual
- batches, the most recent of which has been cooling for 90 days.
The fuel pool water is drawn from the fuel pool near the surface as required and is circulated by fuel pool pumps through one of the fuel pool heat exchangers where heat is rejected to the Component Cooling Water System.
From the outlet of the fuel pool heat exchanger, the cooled fuel pool water is returned to the bottom of the fuel pool via a distribution header.
This spray header allows for overall pool circulation.
The cooling system is controlled manually from a local control panel.
Control room alarms for high fuel pool temperature, high and low water level in the fuel pool, low fuel pool pump discharge
- pressure, overload of fuel pool cooling and fuel pool purification pump motors and high radiation in the fuel pool area are provided to alert the operator to abnormal circumstances.
The major chemical concerns for the fuel pool are boron reactivity worth, radioactivity, and optical clarity.
Proper boron reactivity worth is maintained by adding water to the pool at the prescribed refueling concentration.
Soluble and insoluble radioactivity in the water is controlled by the fuel pool purifi-cation circuit while gaseous and airborne radioactivity is controlled by area ventilation systems.
The purification system is. normallv run on an intermittent basis as required to maintain the fuel pool water purity and clarity permitting underwater operations for discharge of spent fuel, bundle inspection and visual observation for these planned maneuvers.
Crud carried into the pool on spent fuel usually settles to the bottom of the pool and can be removed by the pool purification loop, or via special underwater vacuum cleaning equipment connected to an external filter.
With the exception of that time after fuel bundle movement when crud is sloughed off and clouds the water, optical clarity is maintained through purification system operation.
Various samples are taken periodically from local sample points off the purifi-cation loop (fuel pool filter inlet, filter outlet/fuel pool ion exchanger inlet and the ion exchanger outlet) to meet the chemistry objectives.
Wet chemistry techniques are used to analyze key parameters.
These parameters include pH, ammonia and lithium for monitoring proper system operating condition
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and for minimizing corrosion, boron for maintaining proper boron reactivity worth and chloride and fluoride for monitoring ion exchanger performance.
2.2.4 Storage Racks The spent fuel storage racks are fabricated with 304 stainless steel having a
maximum carbon content of 0.065K.
The racks are monolithic honeycomb structures with square fuel storage locations.
Each storage location is formed by welding stainless steel sections along the intersecting
- seams, permitting the assembled cavities to become the load bearing structure, as well as framing the storage cell enclosures.
Each module is free standing and seismically qualified without mechanical dependence on neighboring modules or pool walls.
This feature enables remote installation (or removal if required for pool maintenance) with minimal effort.
Reinforcing plates at the upper peripheral edges provide the required strength for handling.
Stainless steel
- bars, which are inserted horizontally through the rectangular slots in the lower region of the module, support the fuel assemblies.
These support bars, when welded in place, support an entire row of fuel assemblies.
Semicircular pass'ages at the bottom of every cell wall allow cooling water to flow to all cells.
The size of the openings precludes blockage by any crud accumulations.
Loading of the fuel racks is facilitated via a movable lead-in funnel assembly containing four lead-in devices.
The openings of the funnel assembly are symmetrical and the assembly sits on top of the rack module.
The module wall thickness is 0.135 inch 304 stainless steel.
The L-inserts are 0.188 inches thick.
L-inserts are used only in Region I and cell blocks are used in both Regions I and II.
The cell blocks for Region II are removable and are similar to those for Region I.
The nominal pitch of the spent fuel racks is uniform throughout the,19 modules to be contained in the spent fuel pool.
This pitch is 8.96 inches center-to-center in both horizontal directions.
Region I is located within 6 modules and comprises a total of 448 cells.
Region I is the high-enrichment, core off-load region.
The fuel assemblies are to be stored in every other location in a checkerboard configuration.
The checkerboard arrangement mades SO% of the Region I storage capacity initially avialable for storage of fuel with high fissile concentrations.
The unused cells are fitted with cell blocking devices to prevent inadvertent insertion of fuel into these locations.
Region I is designed for a total of 224 usable cells for enrichments up to and including 4.5 w/o U-235.
The cells in Region I contain an L-insert.
The L-shaped stainless inserts lock into the storage cell using a spring locking mechanism on the upper end.
This locking mechanism snaps into one of the holes in the four surrounding cell walls.
These L-shaped 304 stainless inserts are neutron absorbers.
Region II consists of a total of 1136 cells.
Within Region II, fuel assemblies are stored in 75% of the total cells for an initial available storage capacity of 852 cells.
Ce11 blocking devices are used to preclude placement of fuel
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assemblies into every fourth cell, which remains empty and provides a flux
'trap for reactivity control.
The spent fuel racks have been designed for direct bearing onto the spent fuel pool floor.
A 10" support plate under the peripheral cells provides the bearing surface for the racks.
Fuel rack module leveling is accomplished by placing 10" square stainless steel shims between the support plates and the fuel pool liner.
2.2.5 Makeup Water Redundant spent fuel pool water level and temperature devices alarm in the control room should a loss of fuel pool cooling occur.
Two permanent fuel
pool inventory makeup systems are provided.
The fuel pool purification pump draws water from the refueling water tank (Rl<T) at a flow capacity of 150 gpm.
In addition, the primary water pumps, with suction from the primary water
- tanks, provide makeup to the fuel pool at 100 gpm.
These makeup systems are designed as non-safety-related and designated nonseismic.
In addition to these permanent makeup systems, water inventory sources (e.g. city water storage tank, condensate storage tank, demineralized water tank, Steam Generator Blowdown System Monitor Tanks and St. Lucie Unit I primary water storage and refueling water storage tanks), in excess of three million gallons are available onsite which could be utilized for fuel pool makeup.
These additional water sources could supply fuel pool makeup for more than 40 days at the maximum water boil-off rate without any makeup to these sources.
A seismic Category I backup system is also available for fuel pool makeup.
A hose connection is provided on each seismic intake cooling water header.
A seismic standpipe is provided in the Fuel Handling Building from grade to the operating deck elevation.
The Intake Cooling Hater System via the hose connections can'rovide flow in excess of 61.6 gpm for an indefinite period of time.
The seismic standpipe backup system would introduce salt water to the fuel pool.
The salt water does not affect the integrity of the spent fuel pool leakage barrier.
The rate of corrosion of the stainless steel liner is dependent on the oxygen content of the water.
At boiling temperatures, the oxygen content of water is extremely low thereby greatly reducing the stress corrosion.
Sea water does not result in unacceptable corrosion of the Zircaloy-4 fuel cladding or structural components.
It is unlikely that any localized corro-sion cracking can result in a loss of structural integrity of these compo-nents.
Should sea water be introduced to the fuel pool, fuel elements would be inspected.
2.2.6 Conclusions I
Based the staff review of the proposed spent fuel pool expansion program for St. Lucie 2, the staff concludes the following:
1.
The. calculated maximum normal-and abnormal heat loads have been properly determined and are acceptable.
2.
The existing spent fuel pool cooling capability can maintain the fuel pool water temperature f'r the maximum normal and abnormal heat loads within the limits indicated in the criteria of SRP Section
- 9. 1.3.
3.
The design for the new storage racks provides adequate flow paths per-mitting sufficient flow for fuel cooling to preclude local boiling.
Therefore, the proposed spent fuel pool expansion is acceptable.
2.3 INSTALLATION OF RACKS AND LOAD HANDLING There is no spent fuel in the St. Lucie 2 spent fuel pool at the present time.
Therefore, no special administrative controls or procedures will be necessary to provide radiation protection.
Standard construction techniques and proce-dures will be utilizied during installation to ensure worker safety and compliance with guidelines from the manufacturer.
Based on the above, the staff concludes that the installation of the new racks will be accomplished with reasonable assurance that a load drop accident will not occur and, therefore, the installation of the new racks is acceptable in this regard.
2.4 STRUCTURAL DESIGN The structural aspects of the pr'oposed modification are based on a review per-formed by the staff's consultant, Franklin Research Center (FRC).
The FRC Technical Evalu'ation Report TER-C5506-528 is appended to this Safety Evaluation as an appendix.
2.4.1 Description of the Spent Fuel Pool and Racks Ihe high density rack modules for long term fuel storage
'are located in the spent fuel pool of the Fuel Handling Building.
The spent fuel pool is a steel lined reinforced concrete tank structure that provides space for spent fuel racks and the storage of spent fuel.
The spent fuel racks are fabricated from 304 stainless steel that is 0.135 inches thick.
Each cell is formed by welding along. the intersecting seams which enables the assembled cells to become a free-standing module that is seismically qualified without depending on neighboring modules or the fuel pool walls for support.
2.4.2 Applicable Codes, Standards and Specifications Load combinations and acceptance criteria were compared with those found in
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the "Staff Position for Review and Acceptance of Spent Fuel Storage and Handling Applications" dated April 14,
- 1978, and amended January 18, 1979.
The existing concrete pool structure was evaluated for the new loads in accordance with the requirements of NUREG-0800, Standard Review Plan Section 3.8.4 and the St. Lucie 2 FSAR.
2.4.3 Loads and Load Combinations Loads and load combinations for the racks and the pool structure were reviewed and found to be in agreement with the applicable portions of the NRC position and the SRP.
2.4.4 Seismic Loads Seismic loads for the rack design are based on the original design floor acceleration response spectra calculated for the plant at the licensin'g stage.
The seismic loads were applied to the model in all three orthogonal directions.
Damping values for the seismic analysis for the racks were taken as 2 percent for OBE and 4 percent for SSE.
Rack/fuel bundle inter-actions were considered in the structural analysis.
2.4.5 Design and Analysis Procedures a.
Design and Analysis of the Racks A non-linear time-history analysis of the rack module model was performed.'he model included mass,
- spring, damping, and gap elements and accounts for sliding, tipping and potential rack-to-rack interaction in order to determine stresses and strains within the racks.
A three dimensional finite element model was used to determine a final stress in the rack modules.
This finite element model was also used to generate an equivalent stiffness for the simplified two dimensional non-linear dynamic model.
Calculated stresses for the rack components were found to be well within allowable limits.
The racks were found to have adequate margins against tipping and impacting.
An analysis was conducted to assess the potential effects of a dropped fuel assembly on the racks and results were considered satisfactory.
An analysis was conducted to assess the potential effects of a stuck fuel assembly causing an uplift load on the racks and a corresponding downward load on the lifting device as well as a tension in the fuel assembly.
Resulting stresses were found to be within acceptance limits.
b.
Analysis of the Pool Structure The St. Lucie 2 fuel poolis a reinforced concrete structure.
The
- slab, beams and walls are reinforced to meet all FSAR criteria.
The existing structures were analyzed for the modified fuel rack seismic loads using a conventional lumped mass mathematical model.
A finite element model was used to calculate final stresses.
Original plant response spectra and damping values were used in consideration of the seismic loadings.
Design criteria, including loading combinations and allowable stresses, are in compliance with St. Lucie 2
FSAR Section 3.8.4.
Consequently, the existing spent fuel pool structure has been determined to safely support the loads generated by the new fuel racks.
2.4.6 Conclusion Based on the above, the staff concludes that the proposed rack installation will satisfy the requirements of 10 CFR Part 50, Appendix A (GDC 2, 4, 61 and 62),
as applicable to structures.
2.5 MATERIALS The proposed spent fuel storage racks are fabricated of Type 304 stainless steel with a maximum carbon content of 0.065%,
which is used for all structural components.
Each fuel assembly is stored. in an individual cell of square cross section, designed to accommodate storing both the 14xl4 design fuel from St. Lucie I and the 16x16 fuel from St; Lucie 2.
Criticality is.controlled by three methods used together:
stainless steel cell blocks prevent fuel element storage in one half of the cells in Region I and one fourth of the cells in Region II, limiting the'nitial capacity of the racks to 1076 fuel assemblies; "L" inserts of stainless steel are inserted into each cell in Region I to provide additional neutron absorption; and a technical specifica-tion amendment is proposed requiring a minimum of 1720 ppm boron as boric acid must be present in the spent fuel pool water.
Fuel assemblies with low burnup can be stored only in Region I.
The licensee has stated that the new storage racks will be fabricated in accordance with NRC regulations and regulatory guides for materials and quality assurance, the ASIDE Boiler and Pressure Vessel Code Section III-NP, and ASTM and ANSI standards.
2.5.1 Evaluation The modified spent fuel pool storage racks will be fabricated of materials possessing good compatibility with the borated water chemistry of the spent fuel pool.
The corrosion rate of Type 304 stainless steel in this water is low and unmeasurable.
No instances of corrosion of this material in spent fuel pools containing boric acid have been observed (Ref. I).
The Technical Specification requirement for a minimum of 1720 ppm boron as boric acid does not affect the compatibility of the materials with the environment, since a normal boron concentration of 2000 ppm as boric acid is used in many spent fuel pools at pressurized water reactor sites (Ref. 1).
The Codes and Standards used in fabricating and inspecting the proposed new fuel storage racks should ensure their integrity and minimize the likelihood that any stress corrosion cracking will occur during service.
2.5.2 Conclusion Based on the above, the staff concludes that the corrosion that will occur in the modified spent fuel pool will be of little significance during the remaining life of the unit.
Components of the spent fuel storage pool are constructed of alloys that are known to have a low galvanic differential potential and that have performed well in spent fuel pools at other pressurized water reactor sites where the water chemistry is maintained at comparable standards.
The staff finds that no, significant corrosion should occur in the proposed spent fuel storage racks for a period well in excess of the design life of the facility.
- Further, since there is no significant change in either the materials or water chemistry associated with this reracking amendment, the conclusions in the original SER are not changed by it.
Therefore, the staff.'concludes that the compatibility of the materials and coolant used in the spent fuel storage pool is adequate based on tests,
- data, and actual service experience in operating reactors and that the selection. of
.appropriate materials by the licensee meets the requirements of 10 CFR Part 50, Appendix A, Criterion 62, because of the capability to prevent criticality by maintaining structural integrity of components, and is acceptable.
2.5.3 References 1.
J.
R. Weeks, "Corrosion of Materials in Spent Fuel Storage Pools,"
BNL-NUREG-23021, July 1977.
2.6 SPENT FUEL POOL CLEANUP SYSTEM The clarity and purity of the water in the fuel pool, refueling cavity and refueling water tank are maintained by the purification portion of the fuel pool system.
The purification loop consists of a fuel pool purification pump, fuel pool filter, fuel pool purification pump suction strainer, fuel pool ion exchanger, fuel pool skimmer, fuel pool ion exchanger strainer, associated
- valves, and piping.
Purification is conducted on an intermittent basis as required by the fuel pool water conditions.
Most of the purification flow is drawn directly from the bottom of the fuel pool while a small frac-tion of the purification flow is drawn through the fuel pool skimmer to re-move surface debris.
During purification operations, the capability exists for taking suction at three different levels within the pool to prevent stratification.
A strainer is provided in the purification line to the fuel pool purification pump suction to remove particulate matter before the fuel pool water. is pumped through the fuel pool filter and the fuel pool ion ex-changer.
The fuel pool water is circulated by the fuel pool purification pump through the fuel pool filter, which removes particulates larger than five micron size, then through the fuel pool ion exchanger to remove ionic
- material, and finally through a "Y" type fuel pool strainer.
Connections to the refueling water tank provide makeup to the fuel pool through the purification loop.
In addition to purifying the fuel pool water, the refueling water tank and the refueling transfer canal are cleaned through connections to the purification loop.
The staff expects only a small increase in radioactivity and other contaminants to be released to the pool water as a result of the proposed modification and concludes that the spent fuel pool cleanup system is adequate for the proposed modifications and will continue to keep the concentrations of radioactivity and other contaminants in the pool water to acceptably low levels.
- 2. 7 OCCUPATIONAL RADIATION EXPOSURE The staff has reviewed the licensee's plan for the removal and disposal of the low density racks and the instal'lation of the high density racks with respect to occupational radiation exposure.
Since the SFP for St. Lucie 2 has never had spent fuel stored in it and is currently dry, clean and uncontaminated, there will be no additional radiation exposure to workers due to the SFP modification.
Therefore, the staff concludes that SFP modification exposure to workers is as low as is reasonably achievable (ALARA) and acceptable.
The staff has estimated the increment in onsite occupational dose resulting from the proposed increase in stored fuel assemblies at St. Lucie 2 on the basis of information supplied bg the licensee and by utilizing relevant assumptions for occupancy times and for dose rates in the spent fuel pool area from radionuclide concentrations in the SFP water.
The spent fuel assemblies themselves contribute a neg1igible amount to dose rates in the pool areas because of the depth of water shielding the fuel.
Hased on present and projected operations in the spent fuel pool area," the staff estimates that the proposed modification should add less than one percent to the total annual occupational radiation dose at the unit.
This small increase in radiation dose in the SFP area should not affect the licensee's ability to maintain individual occupational doses to ALARA levels and within the limits of 10 CFR Part 20.
Therefore, the staff concludes that storing additional fuel in the St. Lucie 2 SFP will not result in any significant increase in doses received by workers.
2.8 RADIOACTIVE WASTE TREATMENT St. Lucie 2 contains radioactive waste treatment systems designed to collect
- and process the gaseous, liquid, and solid wastes that might contain radio-active material.
The radioactive waste treatment systems were evaluated in the Safety Evaluation Report, dated October 1981, in support of the issuance of Operating License No.
NPF-16 and in supplements thereto.
There will be
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no change in the radioactive waste treatment systems or in the conclusions given regarding the evaluation of these systems because of the proposed spent fuel pool rerack.
2.8. 1 Conclusions The staff evaluation of the radiological considerations supports the conclusion that the proposed installation of new spent fuel storage racks at St. Lucie 2
is acceptable because the conclusions of the evaluation of the radioactive waste treatment
- systems, as found in the St. Lucie 2 Safety Evaluation Report, are unchanged by the installation of new spent fuel storage racks.
2.9 RADIOLOGICAL CONSEQUENCES OF ACCIDENTS INVOLVING POSTULATED MECHANICAL The staff has reviewed the FPSL submittal for the expansion of the storage capacity of the Spent Fuel Pool (SFP) at St. Lucie 2.
The review was conducted according to the guidance of Standard Review Plan 15.7.4, NUREG-0612, and NUREG-0554 with respect to accident assumptions.
2.9.1 Cask Drop Accident The SER Issued in October 1981 states "With respect to the fuel cask drop
- accident, the cask handling crane and the travel limit switch interlock circuitry are designed to preclude the spent fuel cask from traversing over the spent fuel pool.
The. maximum potential drop of a spent fuel cask is about 43 feet just outside the fuel handling building.
Accordingly, it was assumed that the cask becomes disengaged from the crane and falls 43 feet upon a [sic] unyielding surface, resulting in the damage of all ten irradiated fuel assemblies'nd the instantaneous release of the associated radioactivity to the atmosphere from ground level.
Our calculated doses are shown in Table 15.3."
Based on the licensee's March 13, 1984 submittal and the SER review, the staff concludes that the operating license SER cask drop evaluation remains unchanged.
2.9.2 Fuel Handling Accident For the fuel handling accident, it is assumed that a fuel assembly is dropped by the refueling crane into the reactor core or spent fuel pool.
The licensee has proposed to expand the storage capacity of the SFP from 300 spent fuel assemblies to 1076 assemblies that requires a re-evaluation of the fuel han'dling accident presented in the SER issued in October 1981.
The new high density racks will be installed prior to the first refueling outage; the spent fuel pool contains no spent fuel at this time.
The proposed spent fuel pool modification does not increase radiological consequences of fuel handling accidents considered in the staff SER of October 1981, since this accident would still result in, at most, release of the gap activity of one fuel assembly due to the limitation on available impact kinetic
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energy. "
2.9.3 Conclusion The above accident evaluations are based on the recommended design basis assumptions in Standard Review Plans 15.7.4 and l5.7.5 and Regulatory Guide 1.25.
However, the licensee is proposing to store extended burnup fuel (45,000 Mw-days/Metric ton) in the rerack spent fuel pool that may result in larger gap releases than were assumed in the analysis submitted.
Therefore, it is concluded that the licensee proceed with the SFP modification, and that a licensing condition be placed on the SFP so that the licensee cannot store extended burnup fuel (greater than 38,000 Mw-days/Metric ton) in the modified pool until a new analysis is submitted and approved that addresses the potential for larger gap releases for the extended burnup fuel.
3.0 Conclusions t
In conclusion, the staff finds the proposed changes to the St. Lucie 2 Technical Specifications to be acceptable
- and, based on the considerations discussed above, that (I) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed
- manner, and (2j such activities will be conducted in compliance with the Commission's regulations and the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Date:
October 16, 1984
Attachment:
Technical Evaluation Report prepared by Franklin Research Center Principal Contributors:
D. Sells, Project Manager L. Bell, Accident Evaluation Branch L. Kopp, Core Performance Branch J. Ridgely, Auxiliary Systems Branch
, J.
Nehemias Radiologica1 Assessment Branch M. Lamastra, Radiological Assessment Branch J.
Lee, Meteorology and Effluent Treatment Branch B. Turovlin, Chemical Engineering Branch S.
Kim, Structural and Geotechnical Engineering Branch