ML18065A928

Forwards & Discusses Rept of Review of Sfsp Safety Issues. Staff Concludes That Existing Structures,Sys & Components Re Storage of Irradiated Fuel Provide Adequate Protection. Review of Rept Requested for Applicability to Plant

ML18065A928
Person / Time
Site:	Palisades
Issue date:	09/26/1996
From:	Robert Schaaf NRC (Affiliation Not Assigned)
To:	Bordine T CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
References
TAC-M88094, NUDOCS 9609300274
Download: ML18065A928 (28)

Text

-

Mr." Thomas c( Bo.rdinAt Sep&er 26, 1996

., Manage.r, Licensing:**

Pali sades Pl ant 27780 Blue Star Memar~al High~a;*

5

.covert, MI

.~ ~90,43

SUBJECT:

RES.OLUHON OF.'.sP~NT, FUEL STd~AGE 'poqL* SAFETY ISSUES: ISSUANCE OF

~FINAL REPpRT, PApSADES PLANT (iTA~ ~-NO~~ M88094)

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Dear Mr. Bordirie:

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The Nuclear Regul~tory C~mmiss.ion staff retently comple.ted a detailed review of spent fuel storage p9ol safety"iss_ues.

The results of the staff's review are documented in.a report to the, Commission which is enclosed for your information.

Ih *the report, th~ staff concludes that eiisting structures, systems, and components relate.d,to the storage of irradiated fuel provide adequate protection of ~ubJl~ health and safetj..

~

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"i Notwithstanding this finding, t~e ~taff has also identifi~d certain design features that reduce the reliability of spent'fuel pool decay heat removal, increase the potential for loss of spent fuel coolant inventory, or increase the potential for consequential loss of essential safety functions at an operating reactor. The staff intends to conduct plant-specific regulatory analyses to evaluate potential safety enhancement backfits pursu.nt *to 10 CFR 50.109(a)(3) at a number of operating plants that possess one or.more of these design features.

• Although Palisades is not identified for a plant-specific safety enhancement *.

• *backfit analysis* by the staff, it is requested that you review th.e enclosed

• report for applicability to your facility and consider actions, as

• appropriate, r~lated to the desi~n of spent fuel pool decay heat removal systems at your facility.. This letter does not require any respons_e.

• If you have any q*uestions regarding this matter, ple~se* do not hesitate to contact me at 415:..1312.

• Sincerely;

• Original s.igned by:.

Robert G. Schaaf, Project Manager

---

'---:~=-=-:=-:---"-___,.,TI..,--~ Project Directorate II I -1

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93~85t~ 6~86a~ss Division of Reactor Projects - III/IV

.____~P'---______

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_.-J '----~ Office of Nuclear Reactor Regulation Docket N6. 50-255

Enclosure:

Memo to the Com'rnis~'ion, from J. Taylor, "Resol utfon of Spent Fuef s'torage Pool

- --------Act*io*n -pi-an--I-ssues-.,~l!...dated.-July-.26, _ 199_6 _.*

cc wt*nc1, ~** n~xt pag*

-JI\\& \\fU C!ENiER CO!JllV DISTRIBUTION:; S~J~ '.a.ttach~d 1 i st :"

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DOCUMENT NAME:., G :\\wi>ooc:s\\PALl~~DE\\PALB8094 :;sFP To receive 11 copy of thla docume?.t! lnjflcete In the box:.""C" = Copy without attachment/enclo ure "E" = Copy with attachment/enclosure "N" = No copy OFFICE PM:'PD31 NAME DATE

Mr. Thomas C. Bordine

--Consumers Power Company cc:

Mr. Thomas J. Palmisano Plant General Manager Palisades Plant 27780 Blue Star Memorial Highway

,Covert, Michigan 49043 Mr. Robert A. Fenech Vice President, Nuclear Operations

.Pa 1 i sades Pl ant 27780 Blue Star Memorial Highway Covert, Michigan 49043 M. 1. Miller, Esquire Sidley & Austin 54th Floor One First National Plaza Chicago; Illinois 60603 Mr. Thomas A. McNish Vice President & Secretary Consumers Power Company 212 West Michigan Avenue Jackson, Michigan 49201 Judd L. Bacon, Esquire Consumers Power Company 212 West Michigan Avenue Jackson, Michigan 49201 Regional Administrator, Region III U.S. Nuclear Regulatory Commission 801 Warrenville Road

,Lisle, Illinois 60532-4351 Jerry Sarno -

. Township Supervisor Covert Township 36197 M-140 Highway Covert, Michigan 49043

- *Office of the Governor Room *1 - Capitol Buildin~

lansing, Michigan 48913 U.S. Nuclear Regulatory Commission Resident Inspector's Office Palisades Plant 27782 Blue Star Memorial Highway Covert, Michigan 49043 Palisades Plant Drinking Water and Radiological Protection Division Michigan Department of Environmental Quality 3423 N. Martin Luther King Jr Blvd P. 0. Box 30630 CPH Mailroom Lansing, Michigan 48909-8130 Gerald Charnoff, Esquire Shaw, Pittman, Potts and Trowbridge 2300 N Street, N. W.

Washington DC 20037 Michigan Department of Attorney General Special Litigation Division 630 Law Building P.O. Box 30212 Lansing, Michigan 48909 Auguat 19916

DISTRIBUTION FOR LETTER FROM R. SCHAAF TOT. BORDINE DATED: September 26, 1996 w/encl:

~Phlet File, _cso..::2~_)s

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MEMORANDUM TO:

FROM:

I UNITED STATES N CLEAR REGULATORY COMMISST0N WASHINGTON, D.C. 20595 0001 July 26,)1996 Chairman Jackson.

ColTITlissioner Rogers ColllTlissioner Dicus ~ -

Executive Dire t for perations

SUBJECT:

James M. Taylcto"'---

~

RESOLUTION OF ENT FUEL STORAGE POOL ACTION PLAN ISSUES In a meeting with Chairman Jackson on February 1, 1996, regarding spent *fuel pool issues, the staff committed to prepare a course of action for resolving*

significant issues.developed through the staff's Task Action Plan for Spent Fuel Storage Pool Safety. The significant issues examined within the f~amework of that plan were the reliability of spent fuel pool.decay heat removal and the mafotenanc.e of an adequate spent fuel coolant inventory in the spent fuel pool.

The staff was *lso directed to identify plant-specific and generic.. areas for regulatory. analyses in support of further regulatory action; The staff has completed its review and evaluation of design features rel~ted to the spent fuel pool associated with each operating reactor. Details of the staff's review and ~valuation are presented in the attached report. *The* staff classified operating reactors on the basis of specific design features associated with the spent fuel pool in the following areas: coolant inventory control, cool~nt temperature control, *and fuel reactivity control~

• In comparing-design features with NRC design require~ents and guidance, the.

staff determined that design*features related to coolant inventory control and reactivity control were more consistent with NRC guidance than were design features associated with coolant temperature control. The staff concluded that coolant inventory".control design features were more consistent with present guidance because the staff had issued explicit guidance for prevention of coolant inventory loss in the form of design criteria before it issued most construction permits.for currently operating *reactors. These criteria are documented in plant specific AEC Design Criteria in each affected facility's safety analysis report; in the General Design Criteria of Append*ix A to 10 CFR Part 50, which became effective in 1971; and in Safety Guide 13 (now Regulatory.Guide 1.13), *spent 'Fuel Storage Facility Design Basis," which was issued in March' 1971. -_The staff concluded that reactivity control prov.is ions are consistent because nearly all operating reactors have incre*ased their spent fuel pool storage capacity since the NRC i~s~ed specific guidance for reactivity control, and-such increases involve design and analysis of new fuel storage racks for criticality prevention. Conversely, the NRC staff did not

.... tssue specific guid~n~.e _on_ the ~esign of s~ent fuel pool cooling sys.tems until the issuance of the Standard Review Plan (NUREG-:..75/087) :_fr1 1975, which was* -* * - -* -

CONTACT:

Steven Jones, NRR 415-2833 ENCLOSURE

• f The Convnissioners *~ -

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oA:...... ~

after the issuance of most construction i/ermits for currently operating reactors, and spent fuel storage capacity increases have seldom involved a

• sufficient increase in decay heat generation that an expanded cooling system was warranted.

The staff has found that existing structures, systems, and components related to storage of irradiated fuel provide adequate protection for public health and safety. Protection has been provided by seve.ral layers of defenses that perform accident prevention functions (e.g., quality cantrols on design.

construction, and operation), accident mitigation functions (e.g., multiple cooling systems and multiple makeup water paths), radiation protection functions, and emergency preparedness functions.

Design *features addressing each of these areas for spent fuel storage have been reviewed and approved by the staff.

In-addition, the limited risk analyses available for spent fuel storage suggest*that current design features and oper~ional constraints cause issues related to spent fuel pool storage to be a small.fraction of the overall risk associated with an operating light water reactor.

Notwithstanding this finding, the staff has reviewed each operating reactor**s spent fuel pool design to identify strengths and weaknesses, and to identify potential areas for: safety enhancements.

The staff-plan~ to address certain design features that reduce the reliability of spent fuel pool decay.heat removal, increase the potential for loss of spent fuel _coolant *inventory, or increase the potential for consequential loss of.essential safety functions at an operating reactor.

We intend to pursue regulato-ry analyses for safety enhancement backfits on a plant-specific basis pursuant to 10 CFR 50.109 at the small number of operating reactors possessing eic~~articular identified design feature.

The specific plans for* safety enhancement backfi t's and their b.as*es are.described in the attached report.

Because of the relathely low safety significance.of these issues, the staff

. recognizes that some, or all, of these potential enhaqcements.may not pass the backfi t tests.

T,he stafr"will provide the attached report to.the l ice11sees of all operating reactors.

The staff intends to r~quest that those li~nsees identified.in the report for plant-specific regulatory analysis verify Ue applicability of the*

.staff's findings and conclusion~. The staff w\\11 also request that licensee's.

provide,. on a voluntary basis; their perspective on the potential increase in the overall protection of public health and safety and information regarding the cost of potential modifications to address the design features identified in the staff.report. Staff reviews of potential plant-specific or generic backfits.will ~e appropriately coordinated with the CC11111ittee to Review generic Requirements (CRGR).

The staff also plans to address issues relating to the functional performance of spent fuel pool decay heat removal, as well as the operational aspects related to coolant inventory control and reactivity control, through expansion of the proposed, performance-based rule, "Shutdown Operations at Nuclear Power Plants" (10 CFR 50.67), to encompass fuel storage pool ~perations.

The Commissioners -----. __ Concurrent with the regulatory analyses lor the potent i a 1 safety enhancements, the staff will develop guidance for implementing the proposed rule for fuel

. storage pool operations at nuclear power plants.

The staff will also develop plans to improve existing guidance documents related to design reviews of spent fuel pool cooling systems.

In addition, the staff will issue an information notice as a mechanism for distributing information in areas where regulatory analyses do not support rulemaking or plant-specific backfits.

Attachment:

Plan for Resolving Spent Fuel Storage Pool Action Plan Issues

PLAN FOR RESOLVING SPENT FUEL STORAGE POOL ACTION PLAN ISSUES

1.0 INTRODUCTION

)

The NRC staff developed a~d ;mplemented a gener;c act;on plan for ensur;ng the safety of spent fuel storage pools in response to two postulated event.

sequences involving the spent fuel pool (SFP) at two separate plants. The principal safety concerns addressed by the action plan involve the potential for a sustained loss of SFP cool fog* and the potential for a.substantial loss of spent fuel coolant inventory that could expose irradiated fuel.

The first* postulated event sequence was reported to the"NRC staff in November 1992 by two engineers. who formerly*worked under contract.for the Pennsylvania Power and Light Company (PP&L).

In the report, the ~ngineers contended that the design of the Susquehanna station faHed to meet regulatory requirements with respect to susta;ned loss of the cooling.funct;on to the SFP that could.

result from a loss~of-coolant accident (LOCA) or a loss of offs;te power (LOOP).

The heat and water vapor added to the reactor bu;lding atmosphere by subsequent SFP bo;ling could cause fa;lure of acc;dent mitigation* or other safety equipment and an associated increase in the consequences of the in;tiating event.

Using probabilistic and deterministic methods, the staff evaluated these issues.as they related to Susquehanna and determined that public health and safety were adequately protected on*the basis of existing design features and operating practices at Susquehanna (see attached safety, evaluatio~ for additi6nal details): However, the staff~also concluded that~

broader evaluation.of the potential for this type of.event to occur.at other facilities was.Justified~

~he s~cond postulated event sequence was based on an.actual event that occ~rred at Dresden l, which is permanently shut down.

Thi1 plant ex~erienced containment flooding because of.freeze damage to the service water.system inside the containment building on January 25 1 1994.

Commonwealth Edison reported that the configuration of th~ spent fuel transfer system between the SFP-and the containment similarly threatened SFP coolant inventory control..

At Dresden Unit 1, portions* of the spent fuel transfer system piping inside*

the containment could have burs.t due to freezing at an elevation that would drain the spent fuel coolant to a level below the top of stored irradiated fuel in the SFP.

A s*ubstantial loss of SFP coolant inventory could lead to

~uch consequences as high local radiation levels due to loss of shielding,

. unmonitored release of radiolo~ically contaminated coolant~ and inadequate 0 cooling of stored fuel.

The staff concluded that the potential for*this type of event t~ occur at other facilities should be evaluated.

. : Finally, the action plan its.elf calle~ for a review of events related to wet stor_age of *:irradiated.fuel.

From this review and information from the.two postulated ~vent sequences that prompted developm~nt of the_ action plan. the

__ staff id.enlif..ied.are~~ to_*_ev~Juate for further regulatory action.-. Design information to support this evaluation was developed'through four onsite. --

assessme*nts, a safety analysis report review for several *operating reactors, and the staff's survey of refueling practices completed iri May 1996.,

ATTACHMENT

z Because the safety of fuel storage in the SFP is principally determined by coolant inventory, coolant temperature, a~d reactivity, the staff divided its evaluation into those areas. Coolant inventory affects the capability to cool the stored fuel, the degree of shielding provided for the operators, and the consequences of postulated fuel handling accidents. Coolant temperature affects operator performance during fuel handling, control of coolant chemistry and radionuclide concentr1tion, generation of thermal stress within structures, and environmental conditions surrounding the SFP.

Spent fuel storage pools are designed to maint1in a substantial reactivity margin to criticality under all postulated storage conditions.

In order for operators to. promptly identify unsuitable fuel storage conditions, the spent fuel storage facility must have an appropriate means to notify operators of changes to the conditions in the SFP.

2.0 REGULATORY FRAMEWORK FOR SPENT FUEL POOL STORAGE The NRC acceptance criteria for the design of *structures, *systems, and

• components related.to the SFP has evolved from case-by-case reviews for early plants to the present guidance of the Standard Review Plan (SRP) - NUREG-0800

- and regulatory guides, and the requirements of the General Design Criteria (GOC) of Appendh A to 10 CFR Part 50, as implemented by 10 CFR 50.34.

In addition, the increased *use of. high density sto.rage* *ra.cks to expand onsite irradiated fuel storage capability hu required nearly'.all operating reactor 1 icensees to *request 1 icense amendments related to fuel storage.

Consequently, the design*of certain structures, systems, and components related to the SFP may vary among a gr~up of plants, depending ~n th~ stage of'.

evolution of acceptance criteria developed by the staff and th~ deviatioris -

from thes*e criteria the staff found acceptable.

The Atomic Energy Commission (AEC) developed design criteria in the mid-60s that were used as guidance in evaluating plant' design. These criteria were continually revised so that a consistent basis for acceptable design practices for the SFP ~as not established~ As an example, Criterion 25 from a versiGn of the AEC design criteria;dated November 5, 1965~ stated:*

The.fuel handling and storage facilities must be designed to prevent criticality and to maintain adequate shielding* and cooling under all anticipated normal and abnormal conditions, and credible accident conditions.* Variables upon which the health and safety *of the

_public depend_ must be monitored. -

These AEC design criteria evolved into the GDC presented in Appendh A to 10 CFR Part 50, whkh the AEC hsued in 1971. Criterion 61 of the GDC requires, in part, that the fuel storage syste~ be designed with*a residual heat removal capability having reliability and testability that reflects the importance to safety of decay heat and other residual heat removal and *be designed to prevent significant reduction in coolant inventory under accident conditions. Criterion 62 provides requirements for prevention of criticality, and Criterion 63 specifies requirements for systems to monitor fu*el storage systems.

/

3

~~~~~In 1970, the AEC developed and began issujlng safety guides to make available specific methods acceptable to the staff for implementing regulations.

Regulatory Guide 1.13 (formerly Safety Guide 13), "Spent Fuel Storage Facility Design Basis,A was used as guidance in the licensing evaluation of many spent fuel storage facilities. Regulatory Guide 1.13 described an acceptable method of implementing General Design Criterion 61 in order to:

(l)

(2)

(3)

Prevent loss of water from the fuel pool that would uncover fuel.

Protect fuel from mechanical damage.

Provide the capability for limiting the potential offsite exposures*

~in the event of a significant release of radioactivity from the fuel.

Regulatory Guide 1.13 has no specific guidance for evaluating criticality preventiori measures or SFP cooling system design features.

The SRP gives specific acceptance criteria derived from applicable GOC and-.

other NRC regulations, and a method acceptable to the staff to demonstrat~

• complia~ce with those acceptance criteria for various structures, systems, and components at commercial light water reactors.

The SRP was first issued ln*

1975 as NUREG-75/087, and NUREG-0800 was issued in 1981.

The SRP is not ~

substitute for NRC regulations, and compliance is not a requirement.

How~~er, 10 CFR 50.34 requires applications*for light water re~ctor operating lice~~es:

and construction permits docketed after Hay 17, 1982, to include an evaluation

-of the facility against the SRP.

Although currently operating reactors all had construction permits before* 1982, the staff used the SRP in evaluating operating license aP.plications for facilities that began commercial operation after 1982.

Because compliance with* the* specific acceptance criteria *in the*

SRP is not a requirement, use of the* SRP in evaluating operating licerise applications does not mean that each reactor~beginning commercial 09erat.i.on satisfies each acceptance criterion in the SRP; Rather, the staff used.the*

SRP acceptance criteria as an aide in determining the**acceptability of a structure, system, or component.

Detailed NRC guidance for.evaluating the design of SFP storage facilities and the design of the SFP cool;ng and* cleanup system is in SRP Sections 9.1.2 and 9.1.3, respectively. The acceptance criteria in SRP Section 9.1.2 relate to the' SFP structural considerations for coolant inventory control, reactivity control *criteria, and monitoring* instrumentation.

The acceptance criteria in SRP Section 9.1.3 relate to the SFP cooling system considerations for coolant inventory control and coolant temperature control. Both SRP sections reference Regulatory Guide 1.13 for specHic criteria related to coolant

• inventory control *.. --

Because of the unlikely prospects for successful reprocessing of chil ian reactor fuel, the NRC developed Mu*lti-Plant Action (HPA) A-28, "Increase in*

Spent.fuel Pool Storage Capacity," to address continued on-site storage of spent fuel.

The staff developed a task action plan in the late 1970's to resolve HPA A-28.

This action plan resulted in the development of guidance to address the increased number of SFP modifications involving replacement of low

4 dens Hy fuel storage racks with high dens)ity fuerstorage radts*:--*ape-.:-ati~g-....... --

reactor licensees pursued these modifications because, at the time many operating reactor spent fuel storage areas were designed, offsite storage and reprocessing of spent fuel was expect~d to limit the need for ohsite storage.

On April 14, 1978, the NRC staff issued a letter to all power reactor licensees that forwarded the NRC guidance on SFP modifications.

The guidance, entitled "Review and Acceptance of Spent Fuel Storage and Handling Applications," gave (1) guidance on the type and extent of information needed by the NRC staff to perform the review of proposed modifications to an operating reactor spent fuel storage pool and (2) the acceptance criteria to be used by the NRC staff in authorizing such modifications. Thereview"areas addressed by this guidance inciuded prevention of criticality, prevention of mechanical damage to fuel, and adequacy of cooling for the increased fuel storage capac1ty.

The actions recommended to resolve the action plan issues for MPA A~28 were to

_revise the NUREG-75/087 version of SRP Section 9.1.3 and the 1975 version of Regulatory _Guide 1.13. Although revisions to Regulatory Guide 1.13 were developed that expanded the scope of the document to address SFP *cooling and rea~tivity control, the revised ver-sion was not issued for comment.

• Minor revisions to SRP Section 9.1.3 were incorporated in the NUREG-0800 versfon in 1981.

In 1977, the NRC initiated the Systematic.Evaluation Program (SEP) to review the designs of older operating buclear reactors. Although the staff originally planned to conduct the' SEP-in several phases, the SEP-was conducted in two phases.

The first phase involved identification of :issues-for which regulatory guidance and requirements had ch*anged enough s i nee 1 i tensing of the older plants to warrant a re-evaluation of those older operating reactors.

In*.

thj second phase, the staff re-evaluated 10 of the older operating reactors (7 of which are currently operating) against* the guidance and requirements existing at the time of the re-evaluation.

From_ the results -0f the second phase, the staff identified 27 issues, termed the SEP ~"lessons learned" issues, that involved some corrective action at one or more of the 10 reactors reviewed in the second phase of the SEP.

The staff concluded that these 27 issues would be generally applicable to other-older operating reactors that were not reviewed in the second phase of the SEP, and the staff proposed to include these issues in the Integrated Safety.Assessment Program (ISAP).

However, the ISAP was discontinued after reviews at two pilot plants.

• The SEP "lessons learned" issues were subsequently tracked as Generic Issue {GI) *156 until resolution of that GI in 1995.

Fuel storage was one of the issues identified in the first phase of the SEP.

The purpose of the fuel storage review in the second phase of the SEP was to ensure that new and irradiated fuel are stored safely with respect to criticality prevention; cooling capability, shielding, and structural capability. For the seven currently operating reactprs reviewed-in the secon4 phase of the SEP, the staff found that irradiated fuel was stored safely at those facilities on the basis of staff reviews conducted in the late 70s or -

early 80s that approved license amendments for increased spent fuel storage capacity. During the staff's review of the SEP program as part of our action

5

~~-p~-an for spent fuel _storage pool safety, t)~ staff determined that three of.

the seven license amendments for spent fuel storage capacity increases were approved on the basis of substantial hardware modification to the SFP cooling system.

Despite the hardware modifications necessary to satisfy the staff acceptance criteria at the time of the increase in spent fuel storage capacity, the staff did not identify the fuel storage issue as an SEP "lessons learned" issue.

3.0 PARAMETERS AFFECTING THE SAFE STORAGE OF IRRADIATED FUEL 3.1 Coolant Inventory The coolant inventory in the SFP protects the fuel cladding by cooling the fuel, protects operators by serving as shielding, decreases fission prodvct releases from postulated fuel han~ling events by retaining soluble and part~culate fission products,*and supports operation of forced cooling sy~tems by providing adequate net positive suction head.

Adequate cooli~g of the fuel and cladding is establi_shed by maintaining a coolant level above the top of the fuel (however, this condition does not ensu*re that the SFP structure and other non-fuel components 'Will not be degraded by high temperature). A water depth of several feet above the top of irradiated fuel assemblies stored in racks serves as acceptable shielding, but add_ition_al water depth is necessary to provide adequate shielding during movement of fuel assemblies above the storage racks and to maintain operator dose as low as ls reasonabl~ achievabie

{ALARA)..

Consequence analys*es for fuel hand.ling accidents.typically assume a*

water depth of 23 feet above the top of irradiated fuel. storage racks, and this value is specified as a ~inimum depth for fuel

~andling operations in the NRC's Standard Technical Specifications. Because cooling system suction connections to the SFP are typically located well above the top of stored fuel to prevent inadvertent drainage, a substantial depth of water above t~e top of fuel storage racks is necessary to provide adequate net positive suction head for forced cooling system pumps.

• ~*,;

Design features to reduce the potential for a loss of coolant inventory are common.

On the basis of the staff's design review, all operating reactors

• have a reinforced-concrete Sf P structure designed to retain their function following the design-basis seismic event (i.e., seismic Category I or Class 1) and a welded, corrosion-resistant.SFP liner. Only one operating reactor lacks leak detection channels positioned behind liner plate welds.to collect leakage and direct the leak.age to a point where it can easily be monitored. Nearly all operating reactors have passive features preventing draining or siphoning of the SFP to a coolant level below the top of stored, irradiated fuel.

Excluding paths used for irradiated f~el transfer, p~ssive features ~t nearly

_all operating reactors prevent draining or siphoning of -coolant to a level that-prov-ides inadequate shielding for fuel seated in _the sto!"age racks.

In the event that SFP coolant inventory decreases significantly, several.

indications are available to alert operators of that condition.

The primary indication is a low-level alarm. *A secondary indication of a loss of coolant level is provided by area radiation alarms.

These alarms indicate a loss of shielding that occurs when SFP coolant inventory is lost. Except for the SFP located inside the containment building, the area radiation alarms are set to J.i\\.

tt\\

~~

j,);_

. :;j.

6 alarm at a level low enough to detect a lpss of coolant inventory early enough to allow for recovery before radiation levels could make such a recovery difficult.

The staff noted five categories of operating reactors that warrant* further review based on specific design features that are contrary to guidance in Regulatory Guide 1.13. These categories are described in the next five sections.

3.1.1 Spent Fuel Pool Siphoning via Interfacing Systems The SFPs serving four operating reactors lack passive anti-siphon devices for piping systems that could, through improper operation of the system, reduce coolant invento-ry to a level that provides insufficient shielding and eventually exposes stored fuel.

These four operating reactors, all issued*

construction permits preceding the issuance of Safety Guide 13, have piping that penetrates the SFP liner several feet above the top of-stored fuel, but the piping extends nearly to the *bottom of the SFPs.

Because, for each of these reactors, this piping is connected to the SFP cooling and cleanup syste1r through a normally locked closed valve and lacks passive anti-siphon protection, mispositioning of the normally locked-closed valve coincident with a pipe break or refueling water transfer operation could reduce the SFP coolant inventory by siphon flow to a level below the top of the stored fuel.

This coniern il related to ~ 1988 event at San Onofre Unit 2, which involved a partial loss *of SFP coolant inventory due to an improper purification system*

alignment an~ inadequate anti-siphon pr6tection. *The NRC issued Informatiori Not i c*e 88-'65, "Inadvertent Ora*; n*ages of Spent Fuel Pools," to alert holders -of operating l i cens*es and construet ion penni ts of this event and similar system misalignments.

Al~hough the coolant inventory loss at San Onofre Unit 2 was not significant in this instance, the piping extended deep enough *in the pool that failure of operator action to halt the inventory loss would have been of..

concern.

Co~rective action for this event included removing the portion of piping that extended below the technical specification limit on SFP level and strengthening administrative controls on system alignment.

Reduction in coolant inventory to an extremely low level is unlikely because.

of the low probability of the necessary coincident events, the long time period necessary for significant inventory loss through small siphon lines, and the many opportunities afforded operators to identify the-inventory loss (e.g., SFP low-level alarm, SFP area high-radiation alarms, building sump high-level alarms, observed low level in SFP, and accumulation of water in unexpected locations).

However, the staff believes that a design modification to introduce passive anti-siphon protection for the SFP could be easily implemented at the plants currently lacking this protection.

Therefore, the staff will conduct a regulatory analysis to determine if such modifications are justified.

e e

7

~-.

-~3.1. 2 Spent Fuel Pool Drainage vi a the FJJel Transfer System The SFP-~-servi ngfi ve ope rat fng-reac-tors-t-onta-; n-f ue-l--tr~ns-fer--tubes-located at elevations below the top of fuel stored in the SFP racks. These five reactors also held construction permits preceding the issuance of Safety Guide 13.

During refueling periods when the blank flange on the containment side of the tr*ansfer tube is removed, improper operation of the spent fuel transfer system or the SFP cooling and cleanup system could lead.to a loss of coolant inventory from the SFP to the refueling cavity *inside the containment through the transfer tube.

This concern is related to a 1984 event at Haddam Neck, which, involved a manive loss *of water froin the reactor refueling* cavity inside the containment caused by a failed -refueling cavity seal. The spent fuel transfer tube at Haddam Neck, whidl separates the refueling cavity inside t_he contai.rmient from the SFP jn the fuel *handling building, enters the SFP at an elevation below the top of the stored fuel, and, had the transfer tube been open at the time of the refueling cavity seal failure, the water loss could have* uncovered fuel stored in th.e SFP. 'The NRC issued Information Notice 84-93, "Potential for Loss of Water frOlt the.Refueling Cavity," to ~lert holders of operating.

licenses and construction permits of this event and of similar, but less, severe, seal failures.

I,'

Since that event. the. licensee for Haddam Neck has installed a cofferdam to.

-

• prevent water loss throu~h _the transfer tube to such an extent that fueJ c~uld.

be uncovered and has al so improved the design of the refueling cavity. sea,l.

W_ith the e,xception of the. five operating.r:eactors with transfer tubes in their assochted SFPs, operating reactors have some type of weir that separates the f ue 1 trans fer arH* from the' storage area so that loss pf *cool ant inventory through the fuel transfer :~ystem to a level below the top of the _stored.fuel

. i s pr'evented ~by *design.

A review of refueling cavity sul failure potential by all operating-reactor licensees~ whi'ch was performed in response to NRC Bulletin 84-03,_ *Refueling Cavity Water Se.al," indicated.that refueling *cavity*seal failures.were more likely to occ*ur at Haddam Neck than at other* opera-ting reactors because of the

_unique_desig~ of the Haddam Neck refueling cavity.* The review also found that such fail~res would likely be less severe at other reactors than at Haddam Neck.

Other potential drainage paths (e.g., refueling cavity drains and systems.interfacing with the reactor coolant system) have a much lower maxtmum rate of water loss because of the smaller flow area. Therefore, similar.to the loss.of coohnt inventory scenario* by siphoning, water loss from the refueling cavity that exposes fuel in the SFP is unli~ely because of the low

-probability of water lo_ss_ from,the refueling cavity when the-transfer tube is.

• open, the long* time period necessary -for the inventory loss-, and ~he many. --..

opportunities for operators to identify the invent9ry. loss.

However, the staff conclude*s that the relative rarity of fuel tran'sfer systems lacking passive design features to prevent uncovery of stored fuel warrants a.. more _

deta;led review of the design features and administrative controls at the operating reacto~ that have this characteristic.

The staff will perform regulatory analyses at these five reactors to determine if *any safety enhancement backfits related to this design feature are justified under current guidance.

r~

~

~.-;:.

• ,:~

'.~7~

'ii

~

8 3.1.3 Spent Fuel Pool Drainage via Interjacing Systems Of the five operating reactors associated with SFPs containing.fuel transfer tubes at elevations below the top of the stored fuel, three have an interfacing system connected to the transfer tube. This interfacing system is designed to supply purified water from the SFP for reactor coolant pump seal injection during certain low-prob~bility events postulated to occur du~ing reactor operation. Administrative controls maintain the SFP inventory available to supply water to this interfacing sjstem during reactor operation.

The configuration of this system increases the potential for inadvertent drainage that uncovers fuel.. The configuration-introduces the potential.for improper alignment of the interfacing system or failure of.the piping for the interfacing system'so that coolant inventory is lost; the staff did not find this potential at any other operating reactor.

By design, *the system withdraws water from the SFP for reactor coolant pump seaJ inj~ction at a rate that would* leave insufficient water for sMelding over the stored fuel after*

72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> of operation.

The inadvertent drainage of the SFP to a level that -

would un.cover the stored. fuel is* an* unlikely event base.d on the long t.ime period r:iecessary for the inventory loss and the many opportunit,ie~ for operators*.to discover the inventory loss. However, the staff has concluded that a.safety enhancement modification to the SFP *may be justified to ensure that the fuel remains covered for any potential occurrence involving.,the interfacing system piping. Therefore, the staff w*i11 conduct a regulatory analysis to determine if such a ~odification is justified~

3.1. 4

• Absence. of a Direct.Low Level Al arm Abs~nce of a d~re~t SFP low level **alar.m could delay _operator identiflcation of a significant loss of SFP.coolant inventory. :The staff identified one operating reactor that do*es not have some type of SFP low-level alarm, but.

that reactor does have control room indication of SFP level and-the SFP is inside the contain~ent building. Add.tionally, six operating reactors ha~e only indirect indication and alarm for a *1ow SFP level. These-six r_eac~ors.

have low.:.level _alarms in the SFP.cooling system surge tanks and* low-discharge-pressure alarms.. for the SFP cooling system pumps.. Surge tanks -~re used ~o..

accommodate movement.of large objects, such as spent fuel storage* casks, __ into and out of *the SFP and thermal expansion or*contraction of the coolant without.

a large change in coolant level.

To accomplish this function, surge tanks are separated from. the SFP by a weir slightly below the normal SFP. water level, and the SFP cooling system pumps draw water from the surge tanks.

With continuous*operation of the SFP cooling system pumps, the surge tank low-level alarm is equivalent to the.SFP level alarm because the surge.tank would rapidly drain once the SFP level decreased below.the surge tank entry weir.

The SFP cooling system pump low-discharge-pressure alarms would alert the operators to a change.in the status of the cooling system pumps~ The staff.*

will perform regulatory analyses at these seven reactors to determine if any safety enhancement backfits to improve SFP level monitoring.capability are

• justified under current guidance.

I

9

____ 3.1.S Absence of Isolatfon Capability-fo9*Le*a1<:"ageCOTiictfon-System _____ - -*-**-*-* --****---

The absence of isolation capability for leakage identification systems could allow water to leak at a rate in excess of make-up capability for certain events that cause failure of the SFP liner. The staff identified four operating reactors with this charaiteristic, but this item was not included in our previous information collection efforts. However, the staff also has not collected the information necessary to evaluate makeup capability relative to credible leakage through the leakage detection channels.

To address this omission, the staff will examine previous licensing reviews to determine if the staff had previously evaluated makeup capability relative to credible coolant inventory loss through the leakage detection channels. *Because the four plants identified w.ith this characteristic were not evaluated for inventory control using the SRP guidance, the staff believes that the depth of revie~ for these plant~ would b~ indicative of the depth.of review at other operating reactors.

If this issue has not been previously addressed by the staff at the four operating reactors, the staff will initiate additional information collection activities for this design characteristic and conduct a regulatory analysis to determine if modification to the leakage detection system is justified.

3.2 !oolant Temperature Coolant temperature has a less direct effect on safe storage of i~radiated fue 1 than cool ant.inventory.. Cool ant temperature at the pool surface is*

limited by evaporative cooling from.the free surface of the pool to a value of about l00°C [212°F], and the design of the pool stor~ge racks ~rovides adequate natural circulation to maintain the coolant in a subcooled state at the fuel cladding surface assumfog the coolant inventory is at its normal level. Therefore, forced cooling is not required to protect the fuel cladding integrity when adequate water is supplied ~o makeup for coolant i.nventory loss.

The temperature of the SFP does have an effect on structural loadsr the operation of SFP purification systems, op~rator performance during fuel :

h~ndling~ and the environment around the SFP.

3.2.1. Structural Consid~rations The SFP structure is evaluated to ensure that its structural integrity and leak tightness are retained under various operating, accidental, and environmental loadings. -Th.e reinforced concrete SFP walls and floors are required to withstand the loadings without exceeding the corresponding allowables set forth in the American Concrete Institute Code requirements for Nuclear Structures (ACI 349) as modified by Regulatory Guide 1.142. Appendix A, '"Thermal Consideration,* of ACI 3~9 limits the long-term temperature.

• * - *-. -exposure of. conc.r.ete s_ur.face_s _to 1_~0 F, and short term exposures temperature (under accident condition~) to 350 F.

It permits long term-temperature exposures higher than 150 F, provided tests are performed to evaluate reductions in the concrete strengths and elastic modulus, and these reductions are applied to design allowables. *During the approval of Amendments related to reracking of SFPs, the staff reviews the structural, thermal and seismic loadings on the SFPs and the proposed storage racks to ensure their compliance with the regulatory provisions (relevant SRPs and Regulatory Guides).

.I..

. *~

10 Under normal operat;ng condit;ons (includjng that assoc;ated with reactor refueling activities), the regulatory provi~ions ensure that the sustained concrete surface temperatures are below 150 F.

However, during a rise in the SFP bulk temperature due to temporary loss of forced cooling, the low thermal diffusivity of concrete and the large thermal capacity of the SFP concrete cause the temperature distribution within the concrete structure to change slowly after a rise in the temperature. *Evaporative cooling of the pool limits the maximum temperature attainable at the concrete surface following a temporary loss of forced cooling. Thus, the concrete material properties will not be affected due to a temporary rise in SFP bulk temperature above 1so* F.

The inside surfaces of the concrete walls and floors of the SFP are provided with a leak tight and corrosion resistant (generally stainless steel) liner.

The liner is anchored to the concrete walls and floor by means of structural shapes and/or headed studs. The liner between the anchors could move away from the walls and the floor under differential temperature effects -on the walls, floor, and the Tin,r.

In most cases, the liner ductility and irichor strength would accommodate such differential temperature effects. However, some construction features of the lin~r and its arichorage could give rise to high *stress concentrations and liner weld failure under high temperature exposures.

Such failure, if they should occur would be localized, and would be detected during maintenance, and/or by the leakage detection system (see Section 3. 1. 5).

Therefore, it is reasonable to conclude that if thermal loads on pool structure are lim;ted and their effects monitored as discussed above, no significant structural degradation of.th~ SFP *structure is likely to occur.

3.2.2. Coolant Purification Temperature also has an indirect effect on fuel integrity and radiological*

co~ditions. *All SFPs"use an io~ exchange and filtration proc*sses to maintaih the purity of the coolant. The chemical contaminants in the coolant affect

. the corrosion resistance of components in the fuel pool and the activity of the coolant. However, the ion exchange resins may degrade at temperatures above 60°C {140°F], and the degradation can cause the release of previously absorbed* impurities in addition to reducing the effectiveness of the resin.

Some SFP purification subsystems operate using water from the outlet of the SFP heat exchanger~ which protects the ion ~xchange resin in these subsystems from high' pool temperature.

The purification subsy~tems for other Sf Ps must

~e isolated to protect the resin whe*n pool temperature is high.

Prolonged isolation of the purification subsystem creates the potential for increased operator exposure from radionuclide accumulation in the pool coolant and increased corrosion from impurities that accumulate in the coolant.

However, chemical and radiological monitoring of SFP water is routinely specified in each facility's safety analysis report and operating procedures.

Such monitoring ensures that the ~oolant is maintained sufficiently pure to avoid excessive accurriul at ion of radionucl ides or chemic.al impurities in the SFP coolant.

11

~'-~-~-3.2.3 Fuel Handl;ng

)

lastly, SFP temperature affects operator performance during fuel handling. A pool temp.erature abo_ve 37*c.[100.F) can lead, to frequent operator. rotation during fueJ movement to prevent _heat stress, and higher pool temperatures can result in fogging on the. operating floor that interferes with an operator's ability to observe fuel* assembly position.

To avoid these problems, most operating reactor licensees have i11Plemented administrative controls to maintain pool tempe_rature in a range* that does not hinder operator performance~

3.2.4 Enviro~ntal Effects.*of High Temp~rature in the SFP At very high temperatures in the SFP~,t.he evaporative cooling that occurs ~n the pool surface :can add a _significut amount of latent heat and.wat,r vapor to the atmosphere* of the building surrounding. the SFP.

Oepepding on* the ventilation system design and capability, the added heat and water vapor could increase building temperature and condensation on equipment.

The higher temperature and co~densation could impair the operation of.essential safety systems.

The staff has* extensively evaluated this issue at one operating reactor *s*ite, Susquehanna. : The deterministi~.analysi.~ of Susquehanna indicated that -s~stems used,to. cool the spe_n~ fu_el storage pool were adequate to pr~vent unacceptable challenges to the safety rehted systems nee~ed to protect public h.eal th and

• safety.during an~ following.design basis events. *The probabilistic review at

• Susquehanna indicated that event sequences' leading to a sustained loss of SFP cooling hav.e a low frequency of ocaarrence.

In particular, the staff found th~t loss of ope~ator access to Sf~cooling system components, which was a principal. contention.~f the report filed pursuant to 10 CFR eart 21 regarding loss of SFP cooling at.Susquehanna *. is not a significant.contributor to the frequency o( sustained loss of SFP cooling events because "the probabillty* of severe core damage that has the potential to deny operator access to the* *-

building housing the SFP is Nery low. - The staff recognized 'that ttie mechani sm,s by which the operators would "be unable to provide cooling to the SFP were _not 1 imj ted to the des ig~ bis is events and operator access considerations. Therefore. tbe staff modeled othe~ event sequences leading to SFP boiling. *The staff* concluded that. even with consideration *of the additional event s~qu~nces. loss of SFP cooling event~_presented a challenge of low safety significance to t~e-plant.

On -the.bash of deterministic. and probabilistic evaluations at Susquehanna, the staff-concluded that this concern can be adequately addressed through provi s io_n of a reliable SFP cooling system or through administrative controh that.extend ~he time ava-ilable to institute recov*ery a_ct_io_ns following a loss of cooling.

The.reliability of the SFP.cooling functfon at.each operating_.. --- *-------

reactor is dependent on the design of the SFP cooling system and each

~

• licensee's administrative controls on availability of systems capable of cooling the SFP.

The. time available for recovery action following a loss of SFP cooling is dependent on the initial temperature of the _SFP coolant, -the

• decay heat rate of the stored fuel, and the available passive heat sinks.

Because the decay heat rate within the SFP is at least an order of magnitude higher during refueling operations invo~ving a full-core discharge than during

12 reactor operation and because refueling i; a controlled evol.ution, administrative controls on refueling ope~tions affect the time available for recovery following a loss of SFP cooling~

Through the extensive evaluation of Susquehanna; the NRC staff ident"ified certain design characteristics that increase the probability that an elevated SFP temperature will interfere with the safe. operation of a reactor either at power or shutdown.

The first characteristic is an open path from the area around the SFP to areas housing safety systems. This path may.be through personnel or equipment access ports, ventilation system ducting, or condensate drain paths. Without an open path, the 1 arge surf ace area of the.enclosure *.

around a SFP would allow water vapor to condense and return to the SFP and allow heat to be rejected through the enclosure*to the environment without affecting reactor safety systems.

The second characteristic is a short time for the _SFP to reach elevated temperatures.

The Ume for the.*SFP to reach an elevated temperature is affected by initial temperature, coolant inventory, and the decay heai rate of irradiated fuel.

On the basis of*operating

~ractices and administrative* limits on SFP temperature, the NRC staff has determ*ined that short times to re~dl elevated temperatures* are credible only' when nearly the entire core fuel assembly invenfory has been transferred to the SFP and the reactor has been shut down for a short period after extended

• operation at power.

• These conditions establish the third des*ign characteristic, which is* a rea*ctor site with mult'i"ple 'operating units sharing structures.'a.nd systems related to.

the SFP~ At *a single-unit:*site, large coolant inventories in the SFP and in the reactor cavity_~ct.as a large'passive heat*sink for irradiated fuel dur;t1g fuel transfer." When the entire *cor.e fuel assemb*ly inventory has been transferred to the SFP at a single-unit site, safety systems *associated with the reactor are not essential,because no fuel remains.in the reactor vessel'. :..

Multi-unit sites with no shar~d *structures can:be treated as a ~ingle-unit: **

site. At a multi-unit site wfth shared structures~ a sh*ort time to reach an..

• elevated temperatu.re c~n exist'_in the SFP associated with a reactor* in * *,*

refueling whi.le safety systems in *Conun.unication with 'the area around that* SFP are supporting*ope~ation of another ~eactor*at ~~wer.

When these *three design characte~fstics coexist.at a single*site, one SFP could reach an elevated *temperature in *a short time (i.e., between. 4 and lo hours) after a sustained los~ of cooling,* the heat a.nd water vapor could propagate to systems necessary for shutdown of *an operating reactor, and these systems could subsequently fail while needed to support shutdown.

• The staff has determined through its survey of SFP design.fe'atures that these three design characteristics coexist at no more than seven operating reactor.

sites in addition to Susquehanna.

The staff determined through'its revi~w of design information and operational cori~rols that immediate regulatory action is not warranted on the basis of the capability of* available cooling systems, the passive heat capacity of the SFP, and the operational limits imposed by administrative controls at these seven sites.

In making this determination,.

the staff considered the findings from its review of this issue at Susq~ehanna. Nevertheless, *the staff ~ill conduct detailed reviews to*

13 ide

.. ntify enhancements to refueling procedures or cooling system reliability that are justified based on the reduced p~ential for SFP conditions to impact safety systems* supporting an operating reactor at these seven si_tes.

3.2.5 Cooling System Reliabil,ity and Capability The SFP cooling system reliability*and capability affect the ability of the licensee to maintain SFP temperature within an appropriate band.

Through its survey of operating reactors, the staff identified some convnonality with respect to control of the cooling system, but substantial variation in the design of fuel pool cooling systems with respect to reliability and capability.

The large, passive heat*sink provided by the SFP coolant reduces the signtncance of a short-term loss of cooling by providing ample time for operator diagnosis of'problems and implementation of corrective action.

Consequently, SFP cooling systems are typically aligned, operated, and

_ controlled by manual actions. Most plants have SFP cooling system pump controls only at local control st~tions near the pumps.

The staff identified a wide range of SFP cooling system conf1gurations.

The.

least reliable configuration consisted of a single-train system with no backup syste~ capable of providing SFP co~ling. This system w~s designed with two SO-percent flow-capacity pumps supplying a single heat exchanger..The electrical distribution system serving this reactor was not configured to supply -0nsite power to the SFP cooling pumps.

At the other end of the range, the SFP cooling system consisted of.two redundant, high-capaCity, safety-gr*ade trains.of cooling.

The primary SFP cooling system was supported by the safety-grade shutdown cooling system, which was capable of being aligned to coo 1 the SFP.. "' *

• The staff analyzed design information collected during the survey-to determine the susceptibility of SFP cooling systems to a sustained loss of SF~ cooling.

Specifically, the staff examined the minimum design capacity of the system

• with no failures,* the capacity of the system assuming long-term failure of a*

• single pump,' the capacity assuming a LOOP, the passive thermal capacity of the SFP, and the availability of a large-capacity backup syst~m. In order to have a consistent basis for comparison, the staff developed a *numerical rating for

• each reactor based on a ratio of heat removal capacity under limiting conditions relative to the rated thermal power of each*reactor.

On the basi' of design information collected through the staff's survey *jffort and* onsite assessment visits, the staff identified events that are'.mo$t li~elj to lead to* extended *reductions in SFP cooling capability. Because the SFP cooling.systems typically do not maintain train separation in control ca_binets

• • --- and power -cable raceways,- events such *as_Jire$ or internal floods may cause a complete loss of SFP-cooling. Also, the primary SFP coo.ling systems often are**

designed such that their cooling capacity would be eliminated during a LOOP.

However, operators are more likely to recover from minor electrical and control system faHures by reroutin-g power cables and bypassing control c~binets than they are to.recover from mechanical failures requiring a unique part for repair in the time available before the SFP reaches elevated temperatures.

O~ this basis, the staff concludes that the operating reactors

14

-identifled with relatively low cooling Ca..factty-ttrat-tack reaun*~ncyor- - --*--*-

mechanical components are more likely to experience elevated SFP temperatures than those reactors with greater SFP cooling capacity or mechanical component redundancy. Similarly, those reactors without an onsite source of power to a system capable of cooling the SFP are more likely to experience elevated SFP temperatures than reactors having a cooling system designed to be powered from an onsite power source. However, once again, the long period of time

• available for operator diagnosis of a problem and identification of appropriate corrective action reduces the level of risk from elevated SFP temperatures.

The staff noted that the SFPs for all but seven oper1ting reactors are capable of being cooled by ~ system powered from an onsite source without special re-configuration of the electr.,ical distribution system. However, nine of the operating reactors with onsite power available to a system* capable of co.oling the SFP rely on back.up SFP cooling using a mode of the reactor shutdown cooling.system. This mode of system operation often requfres significant

• realignment for fuel pool cooling.

The staff coricluded that all SFPs associated with U.S. operating reactors can withstand,."without bulk boiling'.in the SFP, a long-term loss of one SFP cooling system pump or cooling water system (i.e., service water or closed cooling water system) pump and maintain SO to 100 percent.of full decay heat removal capability using redundant or installed spare pumps. *However, with reduced cooling capabn ity, the rate of water vapor production from the SFP

• may be_ significant for operating reactors with lQwer heat removal cap~bility under certain conditions.

To addre~s concerns with the reliability and capability of SFP cooling systems, the staff will conduct evaluations and regulatory analyses at selected operating reactors.

The first category of operating reactors are those seven operating reactors lacking a design capability to supply onsite power to a system capable of cooling the SFP.

The staff will examine the capability to supply onsite power to the SFP cooling.. system relativ_e to the time available for recovery, actions based on procedural control~ to. determine*

the need for regulator:y analyses.

The second -category of operating reactors

• ar'e operat-ing reactors identified with low primary SFP cooling system cooling capacity relat.ive to potential spent fuel decay heat generation that have no backup cooling capabiHty. The staff will examine the administrative controls with respect to SFP temperature and available recovery time at four _operating reactors with low SFP cooling capacity to determine the need for regulatory analyses.

The final category of operating reactors are those reactors reliant on infrequently operated backup SFP cooling systems to address long-term LOOP events and mechanical failures.

The staff will examine administrative controls on the availability of the backup cooling systems during refueling and technical analyses demonstrating the capability of these backup. systems to cool the SFP at the ten operating reactors in this category to determine the need for further regulatory analyses.

3.2.6 Absence of Direct Instrumentation for Loss of the SFP Cooling Function*.

Inadequate SFP cooling can be indicated by a high SFP temperature aiarm, a SFP cooling system low flew alarm, a cooling system high temperat4re alarm, or a

/

15 SFP cooling system pump low discharge prejsure alarm.

The staff's survey

-*---~--~results indicate that ten operating reac~ors lack a direct-reading high SFP temperature alarm to identify a sustained loss of SFP cooling and, of those ten reactors, one lacks any associated alarms for a loss of cooling. Because the associated alarms provide annunciation of SFP cooling problem at nine of the operating reactors, because the SFP for the tenth operating reactor is located inside primary containment where equipment is qualified far harsh environments, and because routine operator monitoring also has the potential to detect a loss of the SFP coaling function, the staff deter.mined that invnediate regulatory action was not warranted.

However, the staff will examine these re*actor s 1 tes further ta determine if additional instrumentation or operational controls are warranted on a safety enhancement basis.

3.3 Fuel Reactivity All irradiated fuel storage racks are designed to maintain a substantial shutdown reactivity margin for normal and abnormal storage conditions:

The NRC staff acceptance criterion for all storage conditions, including abnormal or accident storage conditions (e.g., fuel handling accident, mispositioned fuel assembly, or storage.temperature outside of normal range), is a very high confidence that the effective neutron. multiplication factor is 0.95 or less.

Every licensee is required to maintain this shutdown reactivity margin as a design feature technical specification or as a commitment contained in ea~h licensee's safety analysis report. The NRC staff has accepted credit taken for the negative reactivity introduced by soluble boron in abnormal or accid*nt storage conditjons where dilution of the boron concentration would not be a possible outcome of the abnormal or accident.condition alone.

3.3.1 Solid Neutron Absorbers To maintain a subs~antial shutdown reactivity margin in a regulat array of fuel assemblies, the storage geometry, the neutron absorption characteristics of the storage array, and.the reactivity and position of fuel assemblie~.in.

the array are controlled. Reliance on geometry alone results in a low-density storage configuration.

No operating reactor currently uses only low-density storage in its associated SFP.

Intermediate storage density can be achieved by either special construction of the storage racks to form *flux traps" or by controlling the position and reactivity of fuel stored in the rack.

The

.reactivity of each fuel assembly is typically determined by its initial enrichment in the uranium-235 isotope, its integrated irradiation (burnup),

and its integral burnable neutron poison inventory.

The highest density fuel storage has been achieved through the use of solid neutron absorbers as integral parts of the storage racks.

. All solid neutron absorbers used at U.S. operating feactors utilize the high neutron abso-r-pfion cfoss-=se*ctio-n of the boron-10 isotope.-

Boron held.. in-a_ - ---****-*--

silicon-rubber matrix (Boraflex) is the most common solid neutron absorber, followed by an aluminum/bo~on carbide alloy (Baral).

Boron carbide clad in a metal sheathing is the next most *convnon neutron absorber. Borated stainless steel pins are in ~seat one SFP associated with an operating.reactor. The SFP storage racks associated with 14 of 109 U.S. operating reactots contain.no solid neutron absorbers.

The remaining SFPs use one or more of the solid.

neutron absorbers identified above to achieve higher storage density:

16 Because boron-10 is consumed by the intertction with neutrons, storage racks containing neutron absorbers are designecf assuming a finite neutron irradiation and, therefore, a finite operating life. Other mechanisms that deplete the boron-10 inventory in the storage racks can reduce the operating lHe of the storage racks under design storage conditions.

Alt~ough the SFP environment is relatively benign for most of the neutron absorbers in use, Boraflex has been observed to degrade by two mechanisms (1) ga111111 irradiation-induced shrinkage and (Z) boron washout following long-term gamna irradiation combined with exposure to the wet pool.environment.

In addition to issuing three information notices regarding Boraflex degradation, the NRC staff issued Generic Letter (GL) 96-04, *eoraflex Degradation in Spent Fuel Pool Storage Racks,* on June Z6, 1996. This GL requires licensees using Boraflex in their spent fuel stcrage racks to submit information to the NRC staff regarding their plans to address potential degradation of Boraflex material. This action.on Boraflex is outside the staff's action plan activities.

A review of neutron absorber performance as part of the action plan for spent fuel storage pool safety indicates that degradation in neutron absorption performance has not been observed in materials othe~ than Boraflex.

Some neutron.absorbing panels have been *observed to swell due to gas accumulation within the cladding material, but this effect has not degraded ~e~tron absorption performance.

3.3.2 Soluble Boron Soluble boron is used in pressurized water. reactors (PWRs) to control reactor coolant system reactivity. Because* the SFP interface*s*with the reactor coolant system during refueling, an adequate boron concentration must be maintained in th~ SFP to preclude i~advertent dilution of the re~ctor coolant system.

In addition, the boron concentration maintained in PWR SFPs*is also

.credited with mitigating reactivity transients caused by abnormal or accident

. fuel stor~ge conditions.

The NRC staff found that soluble boron concentration was adequately controlled by administrative controls.or technical specifications at PWRs.

4.0 PLANNED ACTIONS The staff has identified three courses of action to address the areas described in Section 3.0. These courses of action are (1) plant-specific evaluations or regulatory analyses for safety enhancement backfits, (2) rulemaking, and (3) revision of staff guidance for SFP evaluation. In addition, the staff will issue an information notice as a mechanism for distributing information in areas where regulatory analyses do not support rulemaking or plant-specific backfits.

4.1 Plant Specific Evaluations and Regulatory Analyses The staff has identified several areas for additional plant-specific evaluation. The bases for these additional reviews was *described in Section 3.0. The staff has identified specific operating reactors in each of the following categories for further evaluation:.

l.

z.

. 3.

4.

5.

6.

7.

9.

10.

17 Absence of Passhe Antisiphon Device; on Piping Extending Below Top of Stored Fuel Transfer Tube(s) Within SFP Rather Than Separate Transfer Canal Piping Entering Pool Below Top of Stored Fuel Limited Instrumentation for Loss of Coolant. Events Absence of Leak Detection Capability or Absence of Isolation Valves in.

• Leakage Detection System Piping Shared Systems and Structures at Multi-Unit Sites Absence of On-site Power Supply for Systems Capable of SFP Cooling Limited SFP Decay Heat Removal_ Capability Infrequently Used.Backup SFP Cooling Systems Limited Instrumentation for Loss of Cooling Events The specific operating reactors in each category are named. in the followi_ng summaries.

Each su1111ary also describes.existing design features at the named reactors and other capabilities that limit the risk from each identified concern.

Inventory Control Issues

l.

Absence of P~ssive Antisiphon*Devices on Piping Extending Below the.Top of Stored Fuel Plants:

Davis-Besse, Robinson, and Turkey Point 3 & 4

• Concern:

Misconfiguration of system has the potential to syphon coolant to such an extent that fuel could be exposed to air.

Current Protection:

Locked closed valve on line at level of pool liner penetration, liner penetration well above top of stored fuel, low level alarm, and operator action (stop syphon flow and add make-up water)

-*Action:._ ____ ____

Regulatory_ analy~is ~o assess potential enhancements 2;

Transfer Tube(s) Within SFP Rather Than Separate Transfer Canal Pl ants: **

Concern:

Crystal River, Maine Yankee, and Oconee 1, 2, & 3 Transfer tubes are normally open during refueling operations.

When these openings are below the top

18 of stored fuel any drain path from the refueling cavity has th~potential to reduce coolant inventory to an extent that stored fuel could be exposed to air.

Current Protection:

Low-level alarm, blank flange closure during reactor operation, and operator action (stop drainage and add makeup water)

Action:

Regulatory analysis to assess potential enhancements

3.

Piping Entering Pool Below Top of Stored Fuel Plants:

Concern:

Current Protection:

Action:

Oconee Units 1, 2, & 3 Pipe break_or misconfiguration of piping supporting the standbJ shutdown _fac'il i ty (SSF) at Oconee has potential to drain coolant to such an extent that fuel could be ~xposed to air.

[The SSF at Oconee uses SFP coolant as a supply of reactor coolant pump.

seal.water for certain low-probability events.

The supply pipe for the SSF is a 3 inch diameter, sehmically-qualified pipe that ties foto a transfer tube for each unit... The Oconee safety analysis report states that the transfer tube gate valve is normally open during reactor operation to support SSF initiation.]

Seismic qualification of piping,-normally closed.

valves on line, low level alarm, and operator action (stop drainage flow and add make-up water)

• Re*gulatory analysis to assess potential enhancements

4.

Limited Instrumentation for Loss of SFP Coolant Events Plants:

Concern:

Current Protection:

Action:

Big. Rock Point, Dresden 2 & 3, Peach Bottom 2 & 3, and Hatch I & 2 Insufficient.instrumentation to reliably alert operators to a loss of SFP coolant inventory or a sustained loss of SFP cooling.

Related alarms, operating procedures, and operator i den ti f; cation Regulatory analysis to assess potential enhancements

5.

Absence of Leak Detection Capability or Absence of Isolation Valves in Leakage Detection System Piping Plants:

D. C. Cook l & 2, Indian Point 2, and Salem 1 & 2

19 (possibly othe~- - -leak detection*systl!l'lrttn1n*- - ****-----

isolation inforfnation was not part of design survey

- staff will conduct further review of other sites]

Concern:

Coolant inventory loss is not easily isolated followfog ~vents that breach the SFP liner.

Current.Protection: Limited flow ar.ea through leak detection system tell-tale drains, low,lHk rate through concrete structure, controls on movement of loads over fuel pool, and,operator~action (plug leak detection system drains and add make-up)

Action:

Further Evaluation of Condition Decay.Heat Removaj Reliability Issues 6.*

Shared Systems _and Structures at Multi-Unit S.ites

7.

Plants:

Concern: :

'*', ~

. *l.

Current Protection:

\\..

Act i on: * - * *

• Calveri Cliffs 1 & 2, D. C. Cook 1 & 2, Dresden 2 &

3;* ~atch 1 (Hatch 2 lower levels are a separate secondary containment ione), LaSalle 1 & 2, Point Beach 1 & 2, and Quad Cities 1 & 2 With one unit in refueling, the decay heat rate in the SFP may be sufficiently high that the pool could*

reach boiling.in a short period of.time. foll9wing a loss of cooling. Communication between the fuel pool area and areas hou~ing safety equipment

.supporting the operating unit through shared ventilation systems or shared structures may cause f,a i 1 ure or degradation of those s~stenis.

Res~rictive a~ministrative.co~trols on ~efueling operations,.. reliable SfP cooling systems, and

. operator actions to restore forced cooling* and protect essential systems from the adverse environmental conditions that may develop during boiling SFP Regulatory analysis to assess potential enhancements Absence of On-site ~ewer Supply for Systems C1pab1e of SFP Cooling P*lants:------- ________ ANO 2, Prafrie Bland 1 & 2, Surry I & 2, and Z i o*n 1 & 2

• Concern:

A sustained loss of offsite power at plants without an on-site power supply for SFP cooling may lead to departure from subcooled decay heat removal in the fuel pool, intreased thermal stress in pool structures, loss of coolant inventory, increased levels of airborne radioactivity, and adverse

20 environmental effects in areas convnunicating with the SFP area.

Current Protection: Operator action (align a temporary power supply from an on-site source or establish alternate cooling such as feed and bleed using diesel powered pump),

high temperature alarm, filtered ventilation, and separation/isolation of areas containing equipment important.to safety from the SFP area Action:

Regulatory analysis to assess potential enhancements'

8.

Limited SFP Decay Heat Removal Capability Plants:

Concern:

Indian Point 2, 1,.ndian Point 3~ and Salem 1 & 2 Assuming a full core discharges at an equivalent.

time after reactor shutdown during a period of peak ultimate heat sink temperature, these plants will

-have higher SFP equilibrium temperatures and shorter recovery times than' oth'er similar plants.

Current Protectio~: *Administrative ~ontrols on refueling oper~tions

'Action:

E~aluation of admi~lst~ative controls

9.

Infrequently Used Backup SFP Cooling Systems*

Plants:

Concern:

Browns Ferry 2 & 3,, Davis~Besse, Dresden 2 & 3, Fermi~ Fitzpatdck'/ Hatch 1 & 2, and WNP-2.

These pl ants *are more re*li ant on i n'f re~uent 1 y operat~d backup*~o~ling systems than other similar.

plants because of the absence of *an onsite power supply for the primary SFP cooling system or low relative *capacity:of th~ primary cooling system~

Current Protection:'* Adminhtrative *controls on refueling operations and Action:

availability of backup SFP cooling capability Evaluation *of capability to effecthely use backup system JO.

Limite~ Instrumentation for Loss of Cooling Events Plants:

Concern:

ANO-I, Big Rock Point, Brunswick 1 & 2, Cooper, Hatch 1 & 2, LaSalle 1 & 2, and Millstone 1 Instrumentation to alert operators to a sustained loss of SFP cooling is *11mited in capability.

/

21

)

Current Protection: Related alarms at most of above reactors, operatfog procedures, and operator identification Action:

Regulatory analysis to assess potential enhancements 4.2 Imolementation of the Shutdown Ryle for Soe~t Fuel Pool Operations The primary benefit of including SEP operations in' the shutdown rule is the establishment of clear and consistent performance standards for forced cooling of the SEP.

Existing design features and operational controls provide assurance that a substantial shutdown reactivity margin will be maintained within the SEP.

Similarly, co1M1on SEP design features have resulted in a low,

probability of a significant loss of SEP coolant inventory. Those facilities that lack specific design features are best examined on a plant-specific basis to determine if any enhancements to operating procedures or modifications to structures or sys~ems are warranted.

A performance-based shutdown rule addressing SEP cooling would establish a consistent level of safety with specific performance goals. Those reactors with more.capable cooling systems and those licensees that more carefully plan refueling cycles would benefit from increa'sed maintenance flexibility during refueling outages. This approach is more, appropriate from a safety standpoint than is the current situation of applying stringent design basis limits to,

- reactors with *ore capable cooling systems.

4.3 Revision of Staff Guidance The staff will develop guidance supporting implementation of the Shutdown Rule for SEP shutdc~n operations. The staff will also develop revision~ to Regulatory Guide 1.13 and SRP Section 9.1.3. Regulatory Guide 1.13 will~be expanded to include guidance related.to design performance of SEP cooling systems, and SRP Section 9.1.3 will be revised to be consistent with that regulatory guide.

5.0 CONCLUSION

S The staff has found that existing structures, systems, and components related to the storage of irradiated fuel provide adequate protection for public health and safety. Protection has been provided by several layers of defenses.

that perform accident p~evention functions, accident mitigation functions, radhtion protection functions, and emergency preparedness functions. Design features addressing each of these *areas for spent fuel storage have been

• reviewed *and-appr*oved by*-the *staff. -In addition-, the 1 imited risk analyses available for spent fuel storage suggest that current design features and operational constraints cause issues related to SEP storage to be a small fraction of the overall risk associated with an operating light water reactor.

Notwithstanding this finding, the staff has reviewed each operating reactor's spent fuel pool design to identify strengths and weaknesses, and to* identify potential areas for safety enhancements.

~*..

~-

... ~

22

)

The staff plans to address issues relating to the functional performance of SFP decay heat removal, as well as the operational aspects r~lated to coolant inventory control and reacth;ty control, through expansion of the proposed, performance-based rule for Shutdown Operations at Nuclear Power Plants (10 CFR 50.67) to encompass fuel storage pool operations.

The staff also plans to,address certain design features that reduce the reliability of SFP decay heat removal, increase the potential for loss of spent fuel coolant inventory, or increase the potent_hl for consequential loss of essential safety functions at an operating reactor.

We intend to* pursue regulatory analyses for S'afety enhancement ~~ckfits on a plcant-specific bash pursuant to 10 CFR 50.109 at the operating reactor sites possessing one or more of these design features._

Concurrent with the regulatory.analyses for the potential safety enhancements, the staff will develop guidance for implementing the proposed rule for fuel storage pool operations at nuclear power plants. The staff will also develop

~lans to improve existing guidance documents related to SFP_ storage.

• ' "!.".