Text

Forwards Response to RAI Re Bulletin 96-04, Chemical, Galvanic or Other Reactions in Spent Fuel Storage & Transportation Casks.
	ML18066A908
Person / Time
Site:	Palisades
Issue date:	03/06/1997
From:	Bordine T; CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	; NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
	IEB-96-004, IEB-96-4, NUDOCS 9703120141
	Download: ML18066A908 (19)
	v • d • e

e.

consumers Power Thomas C. Bordlne Manager, licensing Palisades Nuclear Plant: 27780 Blue St~r Memorial Highway, Covert, Ml 49043

. March 6; 1997 U.S. Nuclear Regulatory C.ommissiori *

Document Control* Desk *

Washington 1 DC '2osss . *

.LICENSE DPR DOCKET 50-255 - AND DOCKET 72 PALISADES PLANT VSC-24 VENTILATED STORAGE CASK - REPLY TO REQUEST FOR INFORMATION

REGARDING RESPONSE TO NRC BULLETIN 9S-04, "CHEMICAL, GALVANIC, OR OTHER REACTIONS IN SPENT FUEL STORAGE AND T~NSPORTATION CASKS~

By.letter dated February 12, 1997, the NRC requested additional information regarding

*our November 12, 1996 response. to Bulletin 96-04, "Chemical, Galvanic, or Othe*r * .*

Reactions in Spent Fuel Storage and Transportation Casks." T~e attachment to this letter provides that .information.

The attachment also contains:: .1) a gen~ral description of the Palisades administrative controls used to .limit the drain down time during loading and the time to prevent boiling during unloading, including both the previously establisned and the newly developed

administrative controls; *and, 2) lists each of the individu_al requests for information 'and/*

provides the Consumers Power Company response. . . . \ *l 120019 9703120141 970306 POR AOOCK .

05000255 PDR G

. A CMS' ENER5Y COMPANY 111m11m111111m11m1mt111Dl~llllll~

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I I I t 1 1 *

SUMMARY

OF CQMMITMENTS This letter contains one new commitment and no revisions to existing commitments.

The new commitment is:

1. _The time limit to drain the Multi-Assembly Basket will be established using the linear equation from Section 1.2.10 of the Certificate of Compliance with an adjustment for spent fuel pool starting temperature.

Ys*CJ?~.

. . \ \ Thomas C. Berdine

~Manager, Licensing CC -Administrator, Region ill, USNRC Project Manager, NRR, USNRC NRC Resident lnspec.tor - Palisade_s Director, Office qt *Nuclear Material' Safety and Safeguards Attachment

e, -

ATTACHMENT CONSUME~S POWER COMPANY PALISADES PLANT DOCKET 50-255 DOCKET 72-7

. RESPONSE TO REQUEST FOR INFORMATION BY NRC LETTER (Dated February 12, 1997) .

CONCERNING NRC BULLETIN 96-04

16 pages

RESPONSE TO NRC BULLETIN 96-04 REQUEST FOR ADDITIONAL INFORMATION The Palisades response to the request for additional information (RAI) related to Bulletin 96-04 is sum!11arized below.

Background:

The NRC ~equ*est for additional information dated February 12, 1997, contains items which are directed toward both the Palisades response to the hydrogen ignition event and the conservative Palisades administrative controls previously implemented with regard to: *1) the drain down time limit requirement during loading of the MSB; and, 2)

. the time to prevent boiling in the. MSB requirement during *unloading. Those items are addressed in the general response helow. The Palisades response to the individual items in the February'12, 1997 RAI is addressed after the general response.

CPCo General Response:*

The Palisades administrative.controls related to the drain down time.limit during loading and the time to prevent boiling-requirement during*unloading, including both the

previously established and the newly developed administrative. controls, are summarized below.

L~adjng:

. 'During loadi°ng; the Multi-assembly Sealed Basket Transf~r Cask and the Multi~ .

Assembly Sealed Basket combination (MTC/MSB) js in a heat-up mode following removal from the .spent fuel pool. Certificate .of Co'mpliance No. 1007 (C bf C) req.uires the water inside the MSB to be drained within 47 hours5.439815e-4 days 0.0131 hours 7.771164e-5 weeks 1.78835e-5 months after th~ MSB, ..

.when loaded.with fuel producing 24 kW of heat, *is remove_d from thespent The C of C also allows the time limit for draining an MSB, when loaded with fuel producing less than 24 kW of heat,* to be determined by multiplying the 47 hour5.439815e-4 days 0.0131 hours 7.771164e-5 weeks 1.78835e-5 months limit for 24 kW by the ratio of 24 kW divided by the *actual heat load of the fuel to be loaded. The drain down time limit is necessary to provide added assurance'

that significant changes in moderator density cannot occur in order to support the double contingency *criteria for criticality safety during loading.

Early in 1993, Consumers Powers Company reviewed the Sierra Nuclear Corporation (SNC) heat-up calculation contained in SNC Analysis WEP 109.003.13 which established the heat-up rate of 3.0°F/hr that is used as the basis for the drain down time limit specified in Section 1.2.10 of the Page 1 of 16

Certificate of Compliance. That review indicated that, for Palisades, the calculation was nonconservative in the following areas:

The starting ambient spent fuel pool temperature of 70°F would not apply since the Palisades pool temperature could reach 100°F .

.* The original calculation assumed no material specific heat transfer coefficient for any of the MSB/MTC materials. This results in the generated heat being transferred through each material in the.t:ieat transfer path at an equal rate. At the time, this assumption was considered nonconservative by the Palisades staff.

These combined conditions were expected. by the Palisades staff to result in a calculated heat up rate and drain down time limit which would not be adequately conservative for Palisades.

In 1993, a more conservative analysis (EA.:FC-864-36) was performed by Consumers Power Company to. address the issue~ outlined above. The results_

indicated that with an assumed initial temperature of 100°F: 1) the water in the .

MSB, when loaded with a decay heat load of 24 KW, could be expected to boil after 20 hours2.314815e-4 days 0.00556 hours 3.306878e-5 weeks 7.61e-6 months following removal from thes spent fuel pool; and 2) the water in

the MSB,*when loaded with a 12 kW decay heat load, would be expected to boil

after 45 hours5.208333e-4 days 0.0125 hours 7.440476e-5 weeks 1.71225e-5 months following removal from* the spent fuel pool. As a result,

administrative controls we.re incorporated into the loading procedure to assure

that- the water inside the. MSB would be drained within the more conservative

.. -time iimit established in' Palisades calculation EA-FC-864.:-36. Ttlese controls were used during the loading of the first thirteen casks at Palisades.

'In 1997, we plan to load four (4) casks* at Palisades. They are expected to have heat loads of approximately 15 kW. A review of the drain down time limits a*ssociated with the higher heat loads indicated that the more conservative time limits imposed by Palisades in the. past are too restrictive in contingency situations and would require additional administrative controls such as: 1) temperature monitorin'g; and 2) recirculation of water thrm~gh the MSB to assure drain down prior to boiling of the water inside the MSB.

Therefore, we reviewed*

the measured heat up rates that we had recorded while loading the first thirteen casks.

Heat-up data from the first 13 cask loadings at Palisades indicate that the measured heat-up rates, when factored up by the ratio of the maximum allowable load (24 kW) to the actual cask heat loads, are less than the original SNC calculated (SNC Analysis WEP 109.003. 13) heat-up rate in all cases. The Page 2 of 16

average heat-up rate from the 13 loaded casks (factored up to 24 kW) is 2.18°F/hr and the maximum heat-up rate is 2.89°F/hr compared to the SNC calculated heat-up rate of 3°F/hr. This data substantiates that the heat-up rate used to support the time limit in the C of C is conservative.

On this basis, the original Palisades administrative controls used in the loading procedure established by EA-FC-864-36 will, at Palisades, be replaced with a time limit to drain using the linear equation from Section 1.2.1 O of the C of C with an adjustment for spent fuel pool starting temperature. Since the SNC calculation was done at 70°F .and the loading procedure limits the spent fuel pool temperature to 100°F, an adjustment of 10 hours1.157407e-4 days 0.00278 hours 1.653439e-5 weeks 3.805e-6 months [(100°F - 70°F)/3°F/hr]

would be required. This will result in an adjusted*drain down time of 37 hours4.282407e-4 days 0.0103 hours 6.117725e-5 weeks 1.40785e-5 months ~or

a heat load of 24 kW. The drain down time limit for an MSB, with a 15 kW heat

load would be determined on this basis to be equal to (37 hr x 24 kW/15 kW) or

.59 hours6.828704e-4 days 0.0164 hours 9.755291e-5 weeks 2.24495e-5 months . * * *-

Casks loaded at Palisades will be drained prior to the time limit allpwed by the*

C of C. Loaded casks *at Palisades are not planned to be returned to the .spent fuel pool .since such a move creates the unnecessary tasks and risks associated with the requirement to: 1) perfqrm the infrequent evolution for the movement a

heavy load over the spent fuel pool; 2) circulate water inside the cask to avoid boron depletion during cool down; and, 3) repeat deeontamination*adivities following removal from the spent fuel pool.

Before draining the MSB, water should remain in-the MSB long.enough to

. complete the hydro test which: is done after completion of the shield., lid weld_. A review of data associated with the loading of .the first 13 casks at Palisades indicates that the stileld lid weld is typically* complet~d within 18 hours2.083333e-4 days 0.005 hours 2.97619e-5 weeks 6.849e-6 months of removal from the spent fuel pool. Sufficient time does exist within the C of C requirements to complete the shield lid weld using either automatic or manual

. *. welding procedures or both. The average time to complete the weld and drain

. the 13 casks loaded at Palisades was 25.5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months with a maximum time of 35 hours4.050926e-4 days 0.00972 hours 5.787037e-5 weeks 1.33175e-5 months . Thus, the actual weld and drain down times indicate that drain down of the water inside of the MSB can be accomplished within the time limit specified by the C of C. -

In addition, the temperature of the water inside of the*MSB will be mo_nitored

during loading to provide historical data and a time for initiating expedited drain down should the water begin to approach boiling prior to the time limit required by Section 1.2.10 of the C of C after adjustment for starting pool temperature. In any event, drain down will always occur prior to the adjusted C of C drain down time limit.

Page 3 of 16

The dose records associated with each previous cask loading were also reviewed. This review indicates that the dose per loading for the initial two casks_was approximately 2 rem and was subsequently reduced for later casks to 200 mrem by following improved ALARA practices. -The contributors to the reduced dose were: 1) the loading of cooler fuel bundles along the periphery; 2) additional lead shielding; and, 3) the elimination of large holes in the shield lid support plate. The lead shielding placed on the lids during welding will significantly r~duce the dose during welding even after the water inside the MSB is drained. In summary, although we desire to keep water in the MSB as long as possible to reduce radiation dose to the welders, historical data indicates sufficient time is available to complete all welding prior to drain down; however,

if it is necessary.to drain down, it is*not*expected to increase the dose per cask

loading by more than 1O to 20 percent-which is within acceptable limits of the Palisades radiation protection program*.

-unloading:

The MTC/MSB enters a heat-up mode after the MSB *is transferred from the Ventilated Concrete Cask (VCC) to the MTC becaus*e the MTC is not intended to provide cooling for long term storage. The heat..:up mode continues to a steady state level in app~oximately 96 hours0.00111 days 0.0267 hours 1.587302e-4 weeks 3.6528e-5 months and remains there until reflooding occurs .

. Reflooding is init_iated after a 2 inch vent path is established following removal of the structural lid. Circulation of borated spent fuel pool water will then reduce .

the.MSB water temperature to less than 130°F, depending upon.heat load.

.Before returning the MTC/MSB to. the spent fuel p~ol, the stiielc;l-lid_ ~eld- must be .*

r~moved: The shield lid weld is removed in two steps. The initial cut Is made.to

a depth which does not break through the entire weld. This allows coolant circulation to continue ..during the initial cut. The coolant circulation is then * .

suspended for the finalcut since the circulating water, under a slight pressure*,

would exit during _the final cut through the breached areas of the shield lid weld

'-* and pose a personnel safety concern to the workers.

The su~pension of circulation for the final cut will cause the MTC/MSB to reenter the heat-up mode. -The water inside of the MSB will heat-up arid boil, and again pose a personnel safety concern to the workers if the final cut is not completed within a determined time li_mit. In order to: assure th~ safety of involved personnel, a time limit to prevent boiling is incorporated into the -unloading procedure .. This limit is presently based upon the conservative Palisades heat-up calculation contained in EA-FC-864-36. Engineering analysis EA-FC-864-36 indicates that the heat-up rate is 2.4°F/hr for an MSB with a 12 kW heat load.

Page 4 of 16

The corresponding time limit to prevent boiling is determined to be ({212°F -

130°F} / 2.4°F/hr) or 34 hours3.935185e-4 days 0.00944 hours 5.621693e-5 weeks 1.2937e-5 months .

Before loading additional casks, the time limit to prevent boiling and the heat-up rate presently in the unloading procedure will be replaced with values established using the heat-up rate which is the basis for the linear equation shown. in Section 1.2.1 O of the C of C. The time to boil for a heat load of 24 kW is [(212°F -130°F)/ 3°F/hr] or 27.hours. This approach when applied to the MSB-4 unloading activities would result iri a time limit to prevent boiling of (27 hours3.125e-4 days 0.0075 hours 4.464286e-5 weeks 1.02735e-5 months x 24 kW/9.38 kW) or 69 hours7.986111e-4 days 0.0192 hours 1.140873e-4 weeks 2.62545e-5 months .

The elapsed time for removing the shield lid .weld,* shim removal and movement of the MTC/MSB to the spent fuel pool was first estimated to be 1.6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months .

During the unloading mockup activities in preparation for the unloading *of MSB-4, the elapsed. time for this evaluation was found to be 26 hours3.009259e-4 days 0.00722 hours 4.298942e-5 weeks 9.893e-6 months under very extreme contingency conditions, (an unprepared operator, broken cutting to'!ls;

.cutting machine bearings in need of replacemen.t and jammed shims). The

jammed shims were caused-by mock-up fabrication activities and were .not a

.

. concern associated with t~e cask components or unloading practices.

Therefore, our experience shows that sufficient time is available to complete 'he

removal of the shield lid weld, remove the shims and move the MTC/MSB to the

spent fuel pool prior to boiling ~ even under. extreme .conditions. Corrective actions have been implemented to ~liminate the extreme contingencie*s

.observe~ d!-,Jring ~he unloading mock-up activities .

Criticality _during.unloading .was previously add~essed in EA:-SC~93~o"83-04*.

(submitted.to the'NRC on June 2, 1995) and is.summarized in this response*.

. Criticality concern~ with loading the VSC-24 were* ~nalyzed by considering a worst case scenario of 24 fresh assemblies at optimum moderation. A boron concentration of 2850 ppm provides enough negative reactivity to ensure keff < 0.98. Tc;1king credit for the soluble boron rn the water is acceptable because any dilution w~uld itself be an unexpected event. This, coupled with the accidental loading of fresh fuel assemblies, would represent simultaneous In unexpected events ... contrast, it is not applicable to consider the rnisloading

event during unloading since verification that loaded fuel meets C of C criteria (bt,1rnu~), enrichment' etc.) has been accomplished during loading before the cask

was initially drained-and again verified by temperature measurement of the air

. exiting the load~d VCCs. Therefore, the bounding criticality.analysis for the unloading event is as descriped in Section 6 of the VSC-24 SAR From a criticality view, boiling is* not a concern during unloading since any change from the analyzed optimum moderation density results in a reduction of the calculated Keff*

Page 5 of 16

e.

SNC letter (SNC 95048) dated January 31, 1995, to Consumers Power Company, confirmed that the design basis criticality analysis bounds the effects of water-to-steam flashing and localized or even general boiling. The analysis calculates ketr for optimum _moderator density. Any effects that would cause the optimum density to change (such as boiling) would result in reduction of ketr* *The steam density is so low that the basket has a ketr of only 0.43 in a pure unborated steam environment.

In s~mmary, unloading of the spent fuel assemblies from the MSB in accordance wi~h the unloading procedure, FHS-M-34, will meet the design base criteria of ketr

< 0.95 during entire.unloacjing process.

Page 6 of 16

SPECIFIC RESPONSE TO NRC BULLETIN 96-04 Reguest for Additional Information:

1. Submittal dated August 19, 1996, pages 15 and 16: Specify the cleanliness checks and controls that will be taken b_efore cask loading a.nd unloading to verify that the cask components are free of foreign materi?Jls.

CPCo Response:

The cleanliness checks and controls that will be taken before cask: loading and ..

unloading are described below: . *

Loadjng:

The following cleanliness checks and controls are implemented to verity that.the cask components are free offore!gn material prior to loading.

The cask components are cl~aned using a high pressure.potable water

spray; drained down and visually *inspected for cleanliness prior to

movement into the spent fuel* pool to verify that obvioµs foreign material is removed before pro~ed.ing. Foreign material includes, . but is.not limit~d

to dust, .dirt, rust, residue, and lubricants, In addition, all components and items including riggingare inspected to assure.no loo~e hardware such

- a$ nuts, bolts, Wire,"washers orweld scraps.are left on the.coryiponents*

. which may come off while over the fuel pool.- . .

A check for debris and sediment is performed when the MSB is fi.lled with borated water prior to loading. Provisions are included for recirculating *.

a the waterin the MSB through filter in order to remo.ve any debris and*

. sediment created during the filling process.

The external surface pf the MTC/MSB is again inspected for cleanliness

. and freedom from debris just before movement into the spent fuel pool.

Portions of the inspections pre completed while moving the MTC/MSB to the spent fuel pool in order to access the lower a.reas of the MTC. All items used over.the fuel pool or tilt pits receive a loose parts, debris, and cleanllnes~ insp'ection just prior to movement over the Debris Free Zone.

The inspection .is performed to verify that obvious foreign material is removed before proceeding.

Paget of 16

The general guidelin~s used to prevent the introduction of foreign material are described in loading procedure, FHS-M-32. Cleaning agents, decontamination solutions, lubricants, nondestructive examination material, etc., identified in the loading procedure and referenced procedures have been evaluated and found to be acceptable for use.

Alternate materials must be evaluated for compatibility with other materials prior to use.

Unloading:

The following cleanliness checks and controls are implemented to verify that the

. cask components are free of foreign material prior to unloading. *

The general guide lines used to prevent the introduction of foreign

material are described in unloading procedure, FHS-M-34. Cleaning agents, decontamination solutions, lubricants, nondestructive examination

materials, etc., identified in.the unloading procedure and referenced

-* procedures have been evaluated and found to be acceptable for use.

Alternate materials m1,Jst be ev~luated for compatibility with other

.materials pi"ior to use.

Debris barriers and vacuuming operations are utilized during drilling and cutting activities to minimize the introduction of foreign materials into t~e

MSe priqr to movement into the spent fuel pool.*

- All items used .over the fuel pool or tilt *pits receive a loose parts; ~ebris,

and cleanliness inspection just prior to movement over the D.ebris _Free

\.

Zone. The inspection is performed to verify that obvious foreign material is removed before proceeding.

Regues_t for Additional Information:

2. Submittal.dated August 19, .1996, pages 15 and 16: Provide.details for venting and monitoring the Multi-assembly sealed basket (MSB) during loading and

unloading. In particular:

.a. Discuss how the MSB air space will be vented and how the hydrogen gas*

concentration will* be monitored and measured.

b. Specify at which point during cask loading and unloading will venting and monitoring be initiated and terminated.

Page 8 of 16

c. Specify the maximum hydrogen gas concentration for which welding, cutting, grinding, or other activities where an ignition source is present

would be allowed.

CPCo Response:

The details for venting and monitoring the MSB during loading.and unloading

are described below.

Loading:

The spa.ce under the shield lid created during i.nitial water removal will be purged with .an inert gas (argon). The inert gas purge will be instituted through the, Swagelok in the shield lid during MTC/MSB movement from the spent fuel pool and subsequent decontamination activ_ities and will be maintained until the root pass of the shield lid is completed. The established vent path . for the gas purge

. is at the gap between the shield lid and the shell.

Combustible gases will be monitored and measured using twb instruments. One instrument will provide continuous monitoring of the air aroun_d.the MTC for* combustible gases and oxygen levels for the duration.

of all lid welding activities. A second instrum~nt will be used for initial

.meas_urfilrn':mts_of the air:at the gap between the shield lid and shell (vent

. .path) for combustible' gas*es whenever*.starting a new weld, new grinding area or other.hot work. Welding, grinding or other hot:work will not-be - ~

initiated unless combustible gases are less tha*n 1,0% of the Lower Explosive L,irT)it (LEL).. , .

In the event the checks reveal that 10%.of the LEL is exceeded all work ~ . ;,

will be stopped and the flow rate of the inerting gas purge will be increased for a short time and returned to normal flow followed by a check for combustible gases. This cycle will be repeated until .the gas concentration remains below 10% of the LEL at the normal inerting .gas purge rate. Work will be allowed to resume after the gas concentration is reguced to below 10% of the LEL.

Unloading:

The space under the shield lid will be purged with an inert gas (argon).

The inert gas purge will be instituted through the Swagelok in the shield lid after suspension of cooling and will be used for water removal during Page 9 of 16

water removal prior to starting the final cut on the shield lid weld to ensure the MSB water level remains below the cutting area. The purge will be maintained throughout the shield lid weld and shim removal process; then*

discontinued just prior to moving the MSB into the spent fuel pool. The established vent path for the gas* purge is at the gap between the shield lid and the shell that is created when the shield lid weld i~ breached.

combustible gases will be monitored and measured using two

.. *i~struments. One instru.ment will. provide co.ntinuous monitoring of the air arouncj the MTC for the duration of. all shield lid *weld removal activities. A second instrument will be used to perform initial measurements of the air at the gap between_the .shield lid and shell (vent path) for combustible gases whenever starting a new weld, new grinding area or other hot work.

Welding, grinding or other hot work, will not be initiated unless

. combustible* gases are iess than 10% of the Lower Explosive Limit (LEL).

In the event the checks re~~al that 10°/o of the LEL is exceeded all work . "

.. _will be stopped and the flow rate of the inerting gas purge will be

.

increased 'tor a short time and returned to normal flow followed by a check

for c.ombustible gases: This cycle will be repeated until the gas concentration remains below 10% of the LEL at the normal inerting gas purge rate. Work will be allowed to resume after the gas concentration is reduced to below 10% of the LEL. * * *

.. ~ -

Reguest for Additional lnf()rmation:

3. Submittal dated August 19, 1996, pages 14 and 15, and submittal dated *

'November 12, 1996, Attachment 2, pages 12 and 13: *For both loading and.

unloading, specify the frequency for sampling the MSB water boron

concentration, when the MSB is isolated from spent fuel pool water (e.g., when the shield lid is in place), and when the MSB water is in communication with spent fuel pool water. Justify that the sampling frequency is adequate, considering a boron depletion rate of 2* ppm/hr and. a higher depletion rate during cask cool-down events. * *

. CPCo Response:

The response will be provided in two (2) parts: 1) will address the f~equency for sampling the MSB water boron concentration, when the MSB is isolated from spent fuel pool water (e.g., when the shield lid is in place) for both loading and

Page 10 of 16

unloading, and 2.) will address the sampling frequency when the MSB water is in communication with spent fuel pool water. *

1. The frequency for sampling the MSB water boron concentration, when the MSB"is isolated from spent fuel pool water (e.g., when the shield lid is in place) for both loading and unloading.

Loading:

During.loading the MTC/MSB will be jn a heat up mode following

removal from the spent fuel pool. The cool-down event will not be

exper:i~nced because*the cask wlll not, as discussed ii"! the *General*

Response, be returned to the spent fuel pooL. Therefore*, only t~e 2 ppm/hr maximum boron depletion rate is applicable and

.bounding during* loading at Palisades.

Boron depletion is addressed using the related laboratory test r~sults. Arkar:isas N~clear One (ANO) lab testing indicates thatthe maxiniuni boron depletion rate is 2 pp(Tl/hr: SNC lab testing by * ,

NWT indicates that the actual depletion rate is much less. The

- spent fuel f:)ool boron conceritrat_ion administrative limit for dry fuel storage has been raised tc;> 3000 ppm. Therefore, even assuming t.he maximum-boron depletion rate from ANO testing, 75 hours8.680556e-4 days 0.0208 hours 1.240079e-4 weeks 2.85375e-5 months could elapse ~ef~re*the regulatory limit of2850 ppm WO!Jld be reached .. The.drain down time limit will not exceed 59 iiour_~ for the remaining "vSC-24 MS B's to be loaded. Therefore, verification that MSB boron concentration is greater* than 3000 ppm once the MTC/MSB is removed from the spent fuel pool will ensure that * *

.boron pepletion is not an issue since the water must be removed

from the MSB b~fore the boroh could deplete to the regulatory limit.

Steps have been added to the loading procedure to accordingly

. increase the administrative spent fuel pool boron concentration

limiffo 3000 ppm and to require a boron sample check of the 75.

gallons :removed from the MSB wh.en it is initially r.emoved .from. the spent fuel* pool. If the sample result is less than 3000 ppm, the

-- *-

spent tue.1 pool water will be recircula~ed back through the MSB until the MSB boron concentration has been raised to 3000 ppm.

The boron concentration measurements performed at ANO during loading of the first two casks showed no appreciable change with noted varicitions well within the accuracy of the measurements.

Page 11 of 16

Unloading:

During unloading the MTC/MSB will be in a heat up mode following removal from the ventilated concrete cask (VCC). The heat up **

mode will essentially exist during unloading as the cask will not be returned to th~ spentfuel pool until the shield lid can be removed and the fuel is ready to be unloaded. During reflood and recirculation cycles, cask cool-down will occur but the boron depletion is not a concern because the water inside the MSB is being replaced with 3000 pp_m borated sp~nt fuel pool water.

After the MSB is filled, borated water will be continuously circulated

through the MSB until just prior to fin~I breaching of the shield lid weld~* Boron .depletion is addressed using the related laboratory test result_s. ANO lab testing indicates that the maximum boron depletion rate is 2 ppm/hr. SNC lab testing by NWT indicates that *

., *the actual depletion rate* is much less. The spent fuel pool boron

- ... concentration administrative limit for dry fuel storage has been

raised to 3000 ppm. Therefore, even assuming the maximum boron depletion rate.from ANO testing, 75 hour8.680556e-4 days 0.0208 hours 1.240079e-4 weeks 2.85375e-5 months s* could elapse before the regul~tory limit of 2850 ppm would be reached ..

. The time limit to prevent .boiling varies between 27 hour3.125e-4 days 0.0075 hours 4.464286e-5 weeks 1.02735e-5 months s* for. the**24 kW desigri basis heat load and 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months for the cask with the minimum_heat load Which* was loaded at* Palisades. The.. minimum time limit to prevent boiling provides sufficient time for th~ finaL breaching cut on the shield lid weld; stiim removal and movement .

of the MTC/MSB to the spent fuel poof as described under the unloading General Response. The minimum time limit to prevent boiling exceeds the estimated elapsed time period as well as the very extreme contingency conditions experienced during *the unloading mockup activities. Therefore, sufficient time is available to effectively comple~e this evolution.

In the event that the time limit to prevent boiling or the time limit for boron depletion is reached and the shield lid weld removal and associated work are not completed, bo"rated spent _fuel pool water will be recirculated through the MSB to return the water inside the ..

MSB to the cooldown temperature of 120°F to.130°F and to ensure that the water inside the MSB contains 3000 ppm boron.

Recirculation will result in a new time limit to prevent boiling and. in a new time limit for boron depletion. This cycle can be repeated Page 12 of 16

until the shield lid is *completely breached, the shims are removed and the cask is ready to be returned to the spent fuel pool.

On this basis the frequency for sampling the MSB water concentration when th_e MSB is isolated from spent fuel pool water

for both loading and unloading, as indicated above, is considered

. to be adequate.

2. Th.e sampling frequency when the MSB water is. in communication with spent fuel pool water.

Loading/Unloading: *

The spent fuel.pool boron concentration limit has been increased to 3000 ppm .. Sampling to verify the boron concentration of the spent fuel pool. will be P,erformed within 4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months before the

. beginning of fuel loading or the reflooding for unloading.the MSB

- and every 48 ~*hours thereafter. The frequency for. sampling the boron concentration in the MSB water when the MSB is in . .

. communication with' spent fuel pool water complies with the C of C, section 1.2.6.. ..

Communication with spent.fuel pool water occ4rs.during reflood

.. . arid recircl!lation activiti,es _and boron depletion is not a concern a.s .

the water in.side the MSB is being replaced with 3000 ppm borateo*

. s"pent fuel pool water. . ,_ .* . .* . - .

Request for Additional Information:

.. 4.

Submittal dated November 12,

1996, Attachment 2, pa.ge 12: Specify how a

'boron concentration of 2850 ppm or more will be maintained in loading cases when the drain-down time exceeds 45 hours5.208333e-4 days 0.0125 hours 7.440476e-5 weeks 1.71225e-5 months .

The submittal states tha( the drain-down time during loading is 45 hours5.208333e-4 days 0.0125 hours 7.440476e-5 weeks 1.71225e-5 months or less.

Thus, with .an initial_ MSB boron concentration of 3000 ppm and a 2 ppm/hr boron depletion rate, boron depletion woulq not be a concern. However, Certificate of Compliance No. 1007 allows the time limit for draining the MSB to exceed 47 hours5.439815e-4 days 0.0131 hours 7.771164e-5 weeks 1.78835e-5 months when the total heat generated by the fuel assemblies is less than 24 kW.. .

Page 13 of 16

CPCo Response:

The boron concentration of 2850 ppm or more will be maintained during loading.

as described in the Palisades response to Item 3.

The anticipated heat load of the remaining casks to be loaded at Palisades is expected to be greater than 15kW. (The drain down time limit for a cask with a 15kW heat load is 59 hours6.828704e-4 days 0.0164 hours 9.755291e-5 weeks 2.24495e-5 months , as discussed in the General response section).

Because the heat 1o*ad for future casks is greater than 15kW the drain down time limit will be less than 59 hours6.828704e-4 days 0.0164 hours 9.755291e-5 weeks 2.24495e-5 months . Therefore, even assuming the maximum boron depletion rate from ANO testing (2 ppm/hr), 75 hours8.680556e-4 days 0.0208 hours 1.240079e-4 weeks 2.85375e-5 months has to elapse before the regulato,.Y limit of 2850 ppm could be reached. Consequently, maintenance o.f the boron fn the MSB water is not an issue since the water must be drained from

the MSB before the boron could deplete to the regulatory limit of 2850 ppm.

Request for Additional Information:

5. *Submittaidated August 19; 1996,* page.14, and submittal dated November 121 1996, Attachment 2, page 12: Specify f)ow a boron concentration bf 2850 ppm or

more will be maintained under a cool-down scenario (i.e., in th,ievent that the

- MSB is returned. to the spent fuel pool). * *. *

The labora.iory tests performed at Arkansas Nuclear One (ANO) indicated a higher boron depletion rate during: a cool<Jown even(** Thus, ANO modif{fJd its

operating pro*qedures to include increased monitoring (every 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months ) of the

boron in the MSB.

CPCo Response:

The laboratory tests performed at Arkansas Nu.clear *one indicated a higher boron depletion rate during a cool-down event which can only occur when the loaded cask is returned to the spent fuel pool. The following controls are in piace to _assure that the MSB is not returned to the spent fuel pool during loading and un_loading at Palisades.

-:* .... - ~ --

Loading:

The cool-down scenario could not occur at Palisades because the administrative controls in the loading procedure require that the cask be drained prior to reaching the C of C drain down time limit as described in the G~neral Response. This action satisfies Section 1.2.10 which page 14 of 16

requires the loaded MSB to be drained or returned to the pool within the *-*--~---~

drain down time limit.

Unloading:

During unloading, the cask will not be returned to the spent fuel pool until the shield lid can be removed and the fuel is ready to be unloaded. As described in response to Item 3, in the event that the time limit to prevent boiling *or the time limit for boron depletion *is reached and the work is not completed, borated spent fuel pool water will be recirculated through the MSB to return the water inside the MSB to the cooldown temperature and to ensure the water inside the MSB contains 3000 ppm boron.

Recircula~ion will result in a* new time*limit to prevent.boiling and a new

-time iimit fcir boron depletion.* This cycle can be repeated until the shield

_lid is- completely breached, the shims are removed and the cask is ready

_ to be. returned to the spent fuel pool.

Reguest for Additional Information:

6. Submittal dated November 12, 1996, Attachment 1, pages 7 and 8: Discuss the bases for the administrative drain:.down limits imposed 'during loading (45 hours5.208333e-4 days 0.0125 hours 7.440476e-5 weeks 1.71225e-5 months or less) *'and unloading *(38 to 75 hours8.680556e-4 days 0.0208 hours 1.240079e-4 weeks 2.85375e-5 months ). * -

Th_ese aclministrative limits do not* appear to be consistent with Certificate of

.Compliance No. 1007, which specifies that the time limit .for draining the A.'fSJ? be determined as follows:

-y hours = 47 hours5.439815e-4 days 0.0131 hours 7.771164e-5 weeks 1.78835e-5 months [(24 kW) I (x kW)],

where y is the time limit for draining the MSB and xis the* totalheat generated by

the assemblies loaded into_ the MSB.

CPCo Response:

- The newly develqped administrative controls implemented by Palisades for loading and unloading have be.en aiscussed in the General Resp~:mse and in response to the specific items of this request for additional information. The riew -

administrative controls ar~ summarized below for both loading and unloading:

page 15of16

Loading:

The time limit to drain will be established using the linear equation from Section 1.2.1 O of the C of C with an adjustment for spent fuel pool starting temperature. Drain down may be initiated prior to the C of C based time limit if indicated by actual measurements of the water inside the MSB.

The maximum drain down time limit will not exceed 59 hours6.828704e-4 days 0.0164 hours 9.755291e-5 weeks 2.24495e-5 months which will.

also assure that boron depletion time limit of 75 hours8.680556e-4 days 0.0208 hours 1.240079e-4 weeks 2.85375e-5 months is' not reached.

Thus, the MSB will be drained before the drain down time limit is reached and the ~sk will not be r~turned to the spent fuel pool.

Unloading:

The tim~ limit to prevent boiling when cooling is suspended for the final breaching of the.shield iid cut, will be replaced with a heatup rate base.d upon the. linear equation *shown in Section 1."2.1 a*of the C of C. .

Recirculation will be initiated* in the event. th.at the ~ime limit to prevent boiling or the tim.e limit for.boron depletion is reached before the shield lid.

is completely bre*ached, the shims .are removed and the cask is returned to the ~pent fuel pool for the removal of fueL R~circulation will establish a .

new time limit to prevent boiling and a new time limit for boron d,epletion .

. This cycle can be repeated until the work is complet~d and the cask is returned to the sp~nt fuel pool for the:.*removal of fuel. Th~ cask _will not . . * .

be ref urned fo the spent fuel *pool until the shield lid can be_.rempved and *

the .fuel is re~dy to be unloaded. *

The recirculation flow rate can be increased or decreas~d based upon actual te.mperature measurement of the water *inside the MSB.

The adjusted time limit to prevent boiling will continue to be coordinated with the boron depletion time to assure that both requirements are satisfied. *

The actions identified above for loading will be taken to assure that the

adminTStrative controls implemented at Palisades are aligned with the C of C .

drain down time li~it. The C of C drain down time limit to prevent' criticality does

not apply during unloading, however; an administrative time limit to prevent boiling will be established using the C of C, Section 1.2.10 heatup rate in order to eliminate a personnel safety concern.

page 16 of 16

ML18066A908

Text

SUMMARY

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