2CAN109308, Provides Written Documentation to follow-up 931022 Verbal Request for Enforcement Discretion Re Compliance W/Ts LCO Section 3.0.3 Re Failure to Meet Conditions of LCOs 3.5.2, ECCS Subsys & 3.6.2.1,containment Spray Sys

Provides Written Documentation to follow-up 931022 Verbal Request for Enforcement Discretion Re Compliance W/Ts LCO Section 3.0.3 Re Failure to Meet Conditions of LCOs 3.5.2, ECCS Subsys & 3.6.2.1,containment Spray Sys

ML20059B668
Person / Time
Site:	Arkansas Nuclear
Issue date:	10/23/1993
From:	Yelverton J ENTERGY OPERATIONS, INC.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
2CAN109308, NUDOCS 9310290049
Download: ML20059B668 (10)

Text

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==~ ENTERGY RxcMic, AR 72801 Tei 501E4-8883 Jerry W. Yelverton We Pmodent Owatin ANO October 23,1993 2CAN109308 U. S. Nuclear Regulatory Commission Document Control Desk Mail Station Pl-137 Washington, DC 20555

Subject:

Arkansas Nuclear One - Unit 2 Docket No. 50-368 License No. NPF 4 Request For Enforcement Discretion on ANO-2 Containment Sump Gentlemen:

This letter provides written documentation to follow-up the Arkansas Nuclear One, Unit Two (ANO-2) verbal request at 1930 (CDT) on October 22,1993, for Enforcement Discretion regarding compliance with Technical Specifications Limiting Condition for Operation (LCO)

Section 3.0.3. This LCO relates to the failure to meet the conditions of an LCO, specifically in this case 3.5.2 (E nergency Core Cooling System (ECCS) subsystems) and 3.6.2.1 (Containment Spray System). Technical Specification 3.5.2 requires two operable ECCS subsystems when average Reactor Coolant System temperature is above 300 degrees and 3.6.2.1 requires two independent Containment Spray Systems to be operable in Modes 1,2 and 3. Granting this Enforcement Discretion will allow sufficient time to repair identified deficiencies regarding the containment sump wi@ut subjecting the plant to an unnecessary transient.

At 1719 on October 22,1993, Technical Specification 3.0.3 was entered based on the potential inoperability of the containment sump and, therefore, the High Pressure Safety injection System (HPSI) and the Containment Spray System in their post Loss of Coolant Accident (LOCA) Recirculation mode of operation. Technical Specification 3.0.3 requires that the condition requiring entry into 3.0.3 be corrected within one hour or action initiated to place the plant in llot Standby within six hours and in Ilot Shutdown within the next six hours, and in Cold Shutdown within the following 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> unless corrective measures are completed that pennit operation under the permissible action statements.

A conference call was initiated with members of your staff and NRR representatives at 1930 to status the existing condition of the containment sump, explain the corrective action plan and to request Enforcement Discretion regarding Technical Specification 3.0.3. The Plant Kjb j t OOn in I

9310290049 931023 u

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PDR ADOCK 05000368 P

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.U. S. NRC October 23,1993 -

'2CAN109308 Page 2 Sirety Committee reviewed and approved the enclosed request. At 2013, the Staff gave verbal approval of a 36 hour4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> extension to the shutdown requirements of Technical Specification 3.0.3. If the containment sump cannot be returned to an operable status within :

the allotted time, the plant will be placed in Hot Standby by 0519 on October 24,1993 and in Hot Shutdown within the following six hours.

The attachment provides the information supporting the request for Enforcement Discretion.

Your cooperation regarding ANO's verbal request for Enforcement Discretion is greatly appreciated. If you have further questions regarding the attached information, please contact m e.

Very truly yours, J O 'L s t! A gz,c>/w

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/ JWY IUK/rhs Attachment i

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UJ S.NRC n

October 23,1993.-

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?2CAN109308 Page 3

- cc:

Mr. James L.'Milhoan 1

Regional Administrator U. S. Nuclear Regulatory. Commission Region IV.

611 Ryan Plaza Drive, Suite 400 Arlington,-TX 76011-8064 NRC Senior Resident Inspector Arkansas Nuclear One - ANO-1 & 2 i

Number 1, Nuc! car Plant Road Russellville, AR 72801 Mr. Roby B. Bevan, Jr.

NRR Project Manager Region IV/ANO-1 U. S. Nuclear Regulatory Commission NRR Mail Stop 13-11-3 One White Flint North 11555 Rockville Pike Rockville, MD 20852 Mr. Thomas W. Alexion NRR Project Manager, Region IV/ANO-2 U. S. Nuclear Regulatory Commission NRR Mail Stop 13-11-3 One White Flint North 11555 Rockville Pike -

Rockville, MD 20852 I

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i Attachment to 2CAN109308 i

Page1of7 ENFORCEMENT DISCRETION REQUEST FOR ANO-2 CONTAINMENT SUMPS Description of Condition / Requirements for Which Enforcement Discretion is Required On October 1,1993 a condition was identified at Arkansas Nuclear One, Unit One (ANO-

1) where the Reactor Building sump contained breeches. in integrity which could potentially allow intrusion of foreign materials into the sump. Based on initial reviews of the ANO-2 sump configuration, surrogate tour films and documentation regarding operationally required inspections of the sump, it was determined that the sump met its design requirements for preventing intmsion of foreign materials. However, to confirm the general integrity of the drains, sump screens and panels, it was decided that an entry into the ANO-2 Containment would be prudent. The scope of the couainment walkdown during the brief entry was to inspect the sump screens, sump panels for integrity and to perform a sample inspection of floor drains for proper configuration.

During the containment entry walkdowns performed on 10/22/93 at approximately 1600 hours0.0185 days <br />0.444 hours <br />0.00265 weeks <br />6.088e-4 months <br />., six 3 inch long by 1 inch high holes and one 1/2 inch high by 24 inch long hole were identified in the grout at the base of the containment sump screen. Therefore, this documents the Arkansas Nuclear One, Unit Two (ANO-2) verbal request at 1930 on October 22,1993, for Enforcement Discretion regarding compliance with Technical Specifications Limiting Condition for Operation (LCO) Section 3.0.3. This LCO relates to the failure to meet the conditions of an LCO, specifically in this case 3.5.2 (Emergency Core Cooling System (ECCS) subsystems) and 3.6.2.1 (Containment Spray System).

Technical Specification 3.5.2 requires two operable ECCS subsystems when average Reactor Coolant System temperature is above 300 degree = and 3.6.2.1 requires two independent Containment Spray Systems to be operabie in Modes 1,2 and 3. Granting this Enforcement Discretion will allow sufficient time to repair the identified deficiencies regarding the containment sump without subjecting the plant to an unnecessary transient.

At 1719 on October 22,1993, Technical Specification 3.0.3 was entered based on the potentialinoperability of the containment sump and, therefore, the High Pressure Safety injection System (IIPSI) and the Containment Spray System in their post Loss of Coolant Accident (LOCA) Recirculation mode of operation. Technical Specification 3.0.3 requires that the condition requiring entry be corrected within one hour or action be initiated to s

place the plant in Hot Standby within six hours and in Hot Shutdown within the next six hours, ar.d in Cold Shutdown within the follow'mg 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> unless corrective measures are completed that permit operation under the permissible action statements.

A conference call was initiated with members of your staff and NRR reresentatives at 1930 to status the existing condition of the containment sump, explain the corrective

Attachment to'

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2CAN109308 Page 2 of 7 action plan and to request Enforcement Discretion regarding Technical Specification 3.0.3. This request has been reviewed and approved by the Plant Safety Committee.- At 2013, the Staff gave verbal approval of a 36 hour4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> extension to the shutdown requirements ofTechnical Specification 3.0.3. If the containment sump cannot be returned to an

'l operable status in the allotted time, the plant will be placed in Hot Standby by 0519 on October 24,1993 and in Hot Shutdown within the following six hours.

1 Compensatorv Actions i

' The following measures are being taken as compensatory actions:

i A. Perform monitoring of the ANO-2 Containment on an increased frequency to detect -

any potential identified or unidentified leakage by:

1 Increasing the frequency of unidentified leakage calculations from once per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> Continuously monitoring plant parameters available for leak detection on the SPDS display Monitoring of containment temperature, humidity and pressure trends every hour B. Maintaining the following systems and equipment operable:

Both Service Water Loops Both Emergency Diesel Generators Both Containment Coolers All three HPSI pumps Both Containment Spray pumps C. Limit maintenance to ECCS systems during the effected period Evnluation of Safety Sienificance Design Requirements The ANO 2 containment sump is s eguired to be able to provide a water source for the ECCS following depletion of the Refueling Water Tank (RWT) during LOCAs, as required by 10CFR50.46 (i.e provide a sustainable mode oflong-term core cooling). The

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ANO-2 containment sump is designed to minimize the potential for debris introduction into ECCS equipment. This is accomplished by a grating ard screen design that i

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' Page 3 of 7 effectively filters out material from the injection water that could potentially degrade the post-accident performance ofECCS components.

Safety Assessment Unscreened flow paths into the ANO-2 containment sump introduce the potential to degrade the performance of ECCS in the recirculation mode of operation.. The significance of the impact on ECCS equipment is largely dependent on the location and size of potential unscreened flow paths into the ANO-2 containment sump, as well as the location and size of postulated RCS breaks (or relief paths). In addition, several.

mitigating factors exist that limit the potential to impact ECCS performance. Although l

these factors have been identified and discussed qualitatively below, they have conservatively not been incorporated into the quantitative safety significance assessment.

To conservatively assess the safety significance associated with the vulnerability of continued operation with the potential for degraded ECCS performance in the recirculation mode of operation, a simplistic risk assessment has been performed utilizing inputs and insights gained from the ANO-2 Individual Plant Examination (IPE). A review of the accident sequences presented in the ANO-2 Probabilistic Risk Assessment (PRA)

Summary Report indicates that potential LOCA initiating events, as well as transient ~

induced LOCA events must be assessed. In order to provide an initialindication regarding the risk significance associated with continued safe operation, ECCS performance in the recirculation mode has been conservatively assumed to be completely failed by potential unscreened flow paths into the ANO-2 containment sump.

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The identified sequences for potential evaluation (with the corresponding annual event frequency) from the ANO-2 PRA are:

Event / Sequence Break / Vent Size Annual Frequency AX (large LOCA)

> 4.3" 1E-04 MX (medium LOCA) 1.9" < X < 4.3" lE-03 SX (small LOCA) 0.3" < X < l.9" SE-03

]

TBX (TLOFW feed &

approx.3" approx. 2E-03 bhed cooling)

TQX (tr: nsus.t induced 1" to 3" approx. IE-03 stuck opea reliefvalve) 1 RX (SGTR long-term

< 1" not applicable isolation)

. Attachment to i

2CAN109308

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Page 4 of 7 Ih SGTR TLOFW feed

-<1" approx.1E-05 l

bleed cooling)

Total event / sequence 9.llE-03/rx-yr frequency These sequences were identified by recognizing that "X" sequences in the ANO-2 PRA represent long-term containment sump recirculation mode cooling. One exception to this is the RX sequence which represents a SGTR with subsequent long-term requirements to isolate RCS inventory leak paths from the afTected steam generator (which can challenge the ability to provide long-term core cooling, but are not impacted by the subject issue).

An upper bound for the potential risk associated with continued operation for 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> with the potential for degraded ECCS performance in the recirculation mode of operation -

can be readily quantified (conservatively assuming no ECCS capability during sump recirculation) by multiplying the event / sequence frequency by the 36 hour4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> condition duration, giving (9. I 1 E-03/yr) x (36 br) x (1 yr/8760 hr) = 3.74E-05 1

To provide a measure of comparison oy which to judge this upper bound risk value, the following references are provided:

this risk does not result in an ANO-2 core damage frequency greater than the NRC severe accident policy statement safety goal ofIE-04/rx-yr.

this risk is close to the " events oflow risk significance". screening guidance provided by the NRC Office for Analysis and Evaluation of Operational Data (AEOD)in NUREG/CR-4674. For post-event evaluation of the ACDF increase associated with faulted components, a conditional probability ofcore damage of less than 1E-06 is defined to be of" low risk significance" and excluded from further consideration.

the recently issued Regulatory Approach to Shutdown and. ow-Power Operations L

(SECY-93-190) conservatively evaluated the risk during shutdown and low-power operations. Although an estimated risk of approximately lE-04/rx-yr was identified for conditions with no new regulatory action and an estimated ACDF of approximately 8E-05/rx-yr was identified for proposed improvements, these risk i

values were characterized as providing adequate protection of the public health and safety, but potentially warranting improvement if shown to be cost beneficial.

Although not exhaustive, these comparison measures indicate that the upper bound risk value of 3.74E-05 can be characteriaed as a lower risk significant condition not warranting

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Attachment to lj 2CAN109308 Page 5 of 7 piant shutdown. It should be noted that this comparison focuses only on the core damage frequency impact and does not specifically address the potential that the subject a

recirculation mode performance issue could affect the post-accident containment response

'l capability (since the ANO-2 containment spray system is a part of the ECCS system and relies on the containment sump as a water source during the recirculation mode). To address the potential impact on containment performance associated with the upper bound.

risk assessment performed above, it must be recognized that the containment fan coolers are not dependent on the performance of the containment sump in any manner The.

ANO-2 PRA containment response analysis has shown that with the availability of the

.j containment fan coolers, containment performance (i.e. containment failure probability) is.

l not challenged significantly. Therefore, the subject recirculation mode performance issue does not pose a significant challenge to the containment response capability.

Mitigating Factors Several mitigating or risk reducing factors also exist which lower the quantitative risk -

calculated by this upper bound risk assessment. These mitigating factors are summarized below and serve to further substs-de the position that operation for 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> with the potential for degraded ECCS pr.

snce in the recirculation mode of operation (due to potentially unscreened flow pat;..,o the ANO-2 containment sump)is acceptable and does not pose an undue risk to the public health and sa ety.

r SDLOCAs & MDLOCAs are likely to be terminated successfully in the injection mode of ECCS ogration by cooldown to cold shutdown on the Shutdown Cooling system (without entering the containment sump recirculation mode). This fact is confirmed by the few events that have actually occurred in the industry.

For events that do progress to the containment sump recirculation mode, decay heat loads are such that significantly reduced ECCS flow (compared to that required for the injection mode) will still provide adequate core cooling. Therefore significant ECCS flow degradation margin exists before inadequate core cooling 1

occurs.

Multiple core cooling flow paths exist in the ECCS injection lines (i. c. cold leg and hot leg injection flow paths), providing redundancy for components potentially impacted by debris introduction during containment sump recirculation mode coeration.

Currently no RCP seals are operating under questionable conditions nor do any significant RCS leaks exist that could represent potentialincipient failures.

post-accident debris generation is low for the more likely small and medium break 1

scenarios.

Attachment to i

Page 6 of 7 2CAN109308 4

3 the post-accident debris transport mechanisms are such that only a small fraction of any debris generated by break flow impingement would likely pass through unscreened flow paths into the containment sump.

The most likely break scenarios (SLOCA, MBLOCA, transient induced LOCAs) are the least likely to generate debris that could be injested into ECCS equipment.

through unscreened flowpaths to the Containment sump. In these scenario the break (or relief) flow will likely be enclosed in piping to the quench tank.

As stated previously, these mitigating factors serve to reduce the magnitude of the upper bound risk estimate calculated in the safety assessment and provide further confidence that operation for 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> with the potential for degraded ECCS performance in the recirculation mode of operation (due to potentially unscreened flow paths into the ANO-2 containment sump)is acceptable and does not pose an undue risk to the public health and safety.

Ilasis for No Sienificant liarards Consideration The basis that no significant hazards are introduced by continued operation for 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> with the potential for degraded ECCS performance in the recirculation mode of operation is as follows.

Criterion 1:

The ANO-2 plant design is such that events which will require the plant to operate in the containment sump recirculation mode are minimal for the limited duration of proposed operation. Allowing continued operation of the plant for the requested time frame beyond the action statements contained in the Technical Specifications does not increase the probability of experiencing a LOCA requiring containment sump recirculation mode operation. In addition, based upon the safety assessment and event mitigating factors discussed above, it is recognized that the consequences of a design basis LOCA may be increased; however, based upon the low probability of such an event occurring during the limited time frame requested, coupled with the relatively unaffected containment response capability, the event significance (i.e. risk)is not appreciably increased.

_CntericQ Since there are no changes to the design function of the sump or new modes of operation associated with this request, the possibility of a new or different kind of accident from any accident previously evaluated is not created.

Qiterion 3:

The requested extension to allow time to address potential unscreened flow paths into the l

ANO-2 containment sump does potentially involve an increase in the exposure to LOCA i

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Attachment to 1

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'i$duced debris introduction into ECCS equipment. However, du;: to the event mitigating factors described earlier, coupled with the low probability of a LOCA event during the -

limited time frame ofinterest, the incremental decrease in margin to safety is not l

significant.

Ensis for No Environmental Consequences This request for Enforcement Discretion does not have a significant affect, impact, or change the quality of the human environment at ANO. This request, when implemented, does not impact the ANO Unit 2 Environmental Report -. Operating License (ER-OL).

Therefore, the request does not significantly increase irreversible environmental consequences.

i Conclusion The potential for unscreened flow paths into the ANO-2 containment sump to degrade the

. performance of ECCS in the recirculation mode of post-accident operation has been assessed and determined to be oflow risk. Therefore, continued operation for 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> with the potential for degraded ECCS performance in the recirculation mode of operation (due to potentially unscreened flow paths into the ANO-2 containment sump)is acceptable and does not pose an undue risk to the public health and safety.

References 1.

10CFR50.46, Acceptance Criteria for Emergency Core Cooling Systems for Light Water Nuclear Power R1qq1pn.

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2. Federal Register 50 FR 32138, Pqlicy Statement on Severe Reactor Accidents Brgardine Future Design. s and Existing Plan _13

3. NUREGICR-4674, Precursors to Potential Severe Core Damage Acciden.ls, dated August 1991.

4. SECY-93-190, Esgulatory Approach to Shutdown and Low-Power Operations. dated l

July 12,1993.

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