ML18346A293

CPC Letter of 7/6/1993, Responding to Inspection Report 93010 & Subsequent Conference Call of 7/22/1993, Letter Submit Supplemental Information to Inspection Report within 60 Days

ML18346A293
Person / Time
Site:	Palisades
Issue date:	09/22/1993
From:	Slade G Consumers Power Co
To:	Office of Nuclear Reactor Regulation
References
Download: ML18346A293 (6)

Text

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consumers Power G BSlade

<nrieral Manarrr PawERING~

.MICHlliAN"S PROliRESS

.Palisades Nuclear Plant: 27780 Blue Star Memoriai Highway, Cowrt. Mt. 49043

. September 22, 1993 Nuclear Regulatory Commission Document Control Desk Washington, DC 2055~

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DOCKET 50-255 - LICENSE DPR PALISADES PLANT - SUPPLEMENT TO THE JULY 6, 1993 RESPONSE TO INSPECTION REPORT No.*~3010:

• On July 6, 1993, Consumers Power.Company submitted a response to Inspection R~port 93010. That response.was discussed during.a cdnference telephone call p~tween with members of the NRC Region III and Palisades staffs on July 22, 19~3. During that* conference call, the* NRC membefs clarified several items where:they f~lt that the CPCo response did not ful.ly an~~e~ the ~nderlyi~9.

ccincerns: *It was agreed that a supplemental response to the I~sp~ction Report would be subm.itted within 60 days*; thjs *letter provides that s*upp.lement.

We understand .the NRC cpncerns associated with ~he subject inspection report, which w~re not fully. covere_d by our July.6, 1993*response, to be as follows:

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1.. : The.Emergency Operating Procedures (EOPs} m~st provjde cl*ar and timely instruction for entry fotoOnce-thr*ough Cooling.-(OTC}; ~hen*it :is required.

Operation with closed Power Operated .Reli*ef Valve (PORV.) block valves, which are not environmentally qualified. for th.e environment following*

the**~vent, combined with delay in initi~ting OTC ~ould eliminate the ability to cool the core.*

The Primary Coolant System (PCS} conditions caused-'bY the event may "uncouple" the Steam Generators (SGs} from the Reactor and *inhibit

• initiation of natural circulation.

2. Simulator modeling of containment response does not a*gree. with previous analyses. (Open Item 93010-05}

• Simulator model*ihg res~lts, which di.ffe~ fro~ ~afety a~alys~s results,

.may provide the operators with improper expectaticms. of plant responses to this and other events which release large amounts of energy to the containment.

• SEP 2 J kl93 I\

\_ . , A CMS ENERGY COMPANY

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• ~3-;- *

• Training on the event should be enhanced. (Open Item 93010-03)

No operator training has been provided on the specific event

. concerned, steam line break inside the containment with a concurrent failure of th~ Main Steam Isolation Valve (MSIV) on the opposite steam line (hereinafter, the "event"). . . * * .

No operator training has been provided on determining operability of instrumentation which may be adversely affected by its environment.

4. An additional concern, not specifically mentioned in the inspection report, is. that while the EOPs. provide information for correcting the narrow range SG level instruments for potential errors due to-adverse containment environment, no similar correcti~ns are provided for the wide rang~.

instruments. The wide range instruments are those *used to verify that adequate level is available for cooli~g the core with the steam generators.

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Several corrective actions were initiated as a result of the iubject inspection report. These actions were discussed in our July 6, 1993 response but, as evidenced by the NRC's continued concerns, not in sufficient detail.

Analysis and fvaluations The following analyses and evaluations have been completed in order to assure that EOP guidance and training inaterials.for the subject event are appropriate:

1. *The cbrrective.actions related *to appropriat~ EtiP guidance, event specifi~

operator training, and verification of simulator modeling all must be -based on a clear understanding of the expected plant response to the event.

Analyses have been* pe~formed, using a Consumer~ Power Company version of the MAAP code, CPMAAP, to provide a best engineering estimate .of PCS,. SG,

• ind *Cori ta i nme-nt response to t.he event.

• These analyses ~ere performed with several varied parameters to determine which parameters had significant *.

effects on the plant response and which did not~* Examples of these variations include: Immediate tripping, delayed tripping, and continuous running of the PCPs 1 variations in the amourit of containment ~ooling

• equipment available, and variations in the modeled break size. In addition*

cases were run, using the sami p~rameters, comparing .a larg* steam line break with and without the MSIV failure. These different analyses, all run

• with the same code changing only a single parameter, allow direct comparisons between cases. That comparison would not be valid if made between analyses done using different codes or ~ifferent basic assump~ions.

These analyse*s allow for verification that EOP strategy is*appropriate,-

_provide a basis for operator training,* and may be used as an alternate calculation.method for comparison with simulator modeling. Typical safety analyses are not always appropriate for these uses since their function is simply t6 demonstrate that the results of particular events ~ill Femain within design or regulatory limits. The simplifying and bounding assumptions made in typical safe~y analyses, while conservative with respect to the analytical goal, often make the results far different from expected plant response.

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The containment temperature and pressure results of these best engineering estimate analyse~ have been compared to the environmental qualification t~sting of the PORVs, the PORV block valves, and the wide range SG level transmitters.* The PORVs were successfully tested at conditions exceeding.

those in the calculated containment response; testing on the block valves and level transmitters, combined with thermal lag calculations imply that there is a high probability of this equipment re~aining operable. These items were chosen as the prime equipment, ~ithin the cont*inment, to assu~e core cooling with either the SGs or OTC.

3. The ability to cool the core using delayed once through cooling has.been analyzed. This ~nalysis concluded that OTC would be successf~l with one*

PORV flow path ~pen and either two charging pumps or one HPSI pump in .

series with one spray pump. The analysis assumed that OTC was initiated with the SG dry and the PCS above saturation temperature .for the set point .

of the secondary safety valves, about 545°F. With two PORV paths or two HPSI pumps available, the initial PCS temperature could be signifitantly hotter.

4. The ability to cool the core by usfng AFW, even after SG "dryout", has been analyz~d. The results show that a single AFW pump can provide enough makeup flow to maintain natural circulation in the primary coolant system.*

Again, the availability of additional pumps provides additional margin and more rapid cooling. *

5. . The ~otential er~brs in wide range indicated SG level *are included in the existing EOPs, although not through use of a ~orrection curve. - Instead, the specified instrument reading which corresponds to the minimum acceptable level for secondary cooling, -84%, has the maximum predicted error included. Engineering Analysis EA-GAW.:.89-EQ-Ol, Revision 1, concludes that .the maximum expected error for .the wide range SG level

• in~truments would b~ 36% ... When ~ 36% error is added to the minimum actual level of ~120%~ fhe specified minimum indicated level, -84%, is ~ttained.

EOP Strategy Review:

The strategy of the EOPs, with respect to initiation of OTC, has been rev.iewed. The existing strategy is, very briefly,_ to allow automatic initiation of feedwater, *ensured by manual action,_ with acceptable cool i.ng.

verified by SG level *and PCS conditions. If continued use of the SGs for decay heat removable is not possible, OTC.would be initiated.

This current strategy was compared to an alternate strategy of immediately initiating OTC upon observing the symptoms of a steam line break concurrent with the lack of full closed indication on an MSIV. The overriding consideration, bf course, is that the ch6seri strategy be capable of.

assuring adequate core cooling. Our conclu~ion is that either method would result i~ continued core cooling. Additional considerations, discussed

• below, result in our decision to retain the current strategy.

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• -* _. Immediate Initiation of Once Through Cool inq:

The considerations which tend~d to favor the alternate appr~ach 6f

. invnediate initiation of OTC were as follows:

a} Early analyses of use of OTC following a loss of all feedwater event, which assumed flow through an area equal to two smaller PORVs similar to those formerly installed at Palisades~*concluded that i nit i at ion of OTC must occur before SG dryout. Dryout was ,

predicted to occur about 20 ~inutes into the event. This ~esult, that OTC must be initiated within 20 minutes to be assured of succ~ss, was often considered to apply to other events requiring OTC. .

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this consideration is rio longer appropriate.for Palisades. lhe PORVs now installed at Palisades are significantly larger than those used in the earlier study.* As mentioned above, analyses of.

~he currently installed PORVs and.flow paths show more capability with a single flow path than the former analyses did with both.

The blowdown of both SGs could cause the containment e~vironment to exceed the environmental qualification envelope for electrical/

equipment preventing verification that AFW is functioning and

• preventing opening of the PORVs and block valves to achieve OTC._

• • This consid~ration is now less important than it w~uld have been prior to the installation of the new PORVs~ which are qualified

- for the containment :environmental conditions resulting from design events, .and the new SGs which incorporate flow r~strictors in their outlet nozzles. As discussed in the analy~is section

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above, the environmental testing envelope for the PORVs exceeds

. the predicted containment response for the."event"; the

• combination -0f environmental testing and thermal. lag cal~ulations

• indicate that the block valves and tha wide range SG le~el . *

• t~ansmitters should ~urvive the "event".* Therefore it is hi~hly probable that delaying the initiation of OTC while. the succes$ful initiation of AFW is being verified will not add significantly:to the risk ~f failing to maintain core cooling.

Initiation of Once Through Cooling onlv upon failure Coolirig using the Steam Generator: * *

• Those considerations which favor *the. current EOP strategy are as follows:

• a) The ~urrent strategy applies to any Ex~essive Steam Demand Ev~nt

~nd does not req~ire a special procedure, or special steps, for the subject event. The design concept of new EOPs is to avoid event ba~~d actions with special procedures for ea~h possible event.

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. ' 6 Class.room trainfog on the "event" is also currently scheduled to be completed prior to fhe end of 1993-. -Class room training will foclude discussion on the followi~g:

a) .How a blowdown of both SGs could occur

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b} ~n explan~tion of why there are differences between safety analyses and* simulator modeling of some events

• c} Discussions of symptoms, expected plant response, the*EOP paths invblved, and the potential for significant error ~r failure of i~strumentation located* in the containment.

d} Discussions* on verificati~n of instrument.reading validity and use of alternate instrumentatiOn* for* this a.nd other events which degrade the

• containment environment.**

• When the neces~~ry simulator modeling corrections are c.ompleted, the

• details of those EOPs ~ssociated with the "event" will be* validated.

Add~tional simulator training on* a full r~nge oi steam line break sizes,

~ith and*withput a co~iurrent failure of a MSJV,* will then* be included in the tr~ining curriculum. The "event,"~ l~rge break in one main st~ani line with a concurrent failure of the opposite MSIV, ,ca.nnot be exactly modeled *

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. on the simulator~ What ~ari be.modeled, closely simulating th~ "event," is a combination of the following: a.large *break in one main stea~ line, a somewhat smaller break (to eniulate'the piping fl-0w losses} in the other steam line, and a fail~re of closed.indication on one MSIV .

. *.'I( . * ' -

• • .**~~~.t,*

Plant General Manager CC: Regfon III Administratot .

Palisades -Resident Inspector

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- . b) The current strategy utilizes the defense in depth concept, by relying on the automatically initi~ted AFW system first. If cooling by_ AFW cannot be assured, then other cooling methods are

_employ~d; condensate pumps if available~ and then OTC.

The. initiation of OTC would inunediately reduce the PCS to saturation pressure, forming voids in the SG tubes and reactor vessel head, and reduce PCS inventory. *A subsequent failure of the PORVs or of the HPSI pumps would necessitate returning to .

cooling by natural circulation and SGs. Reduced-PCS inventory,*

additional PCS voids, and restarting or realignment of equipment used with the SGs add additional failur~ possibilities which are not.encountered with the ~urrent strategy.

A very simplistic fault tree an:alysis of the two choices_iinplied that there would be a reduction in risk of loss of core cooling.

• for th~ "event" of about an ordei of magnitude using the current*

strategy.* It is assumed that the early initiation of ~TC would adversely affect the failure pro_babil i ty of secondary coo 1i rig by a factor of 10, and that ~elayed initiation of OTC would adversely affect the failure probability of the block valves by

• the same amount (since the block valv_es typically fail as is,

• failures occurring after they are op~n are inconsequential).

Unaffected failure rates were set at 10*3 and degraded rates* at 1~ 2

• These ~aies were chosen'.simply to examine the effects of the two alternate choice~. The chosen rates have no analytical

~ ..-._ basis, but they.are not atypical, either. Since either cooling method transfers the decay heat to the containment, other failure rates, including that of the PORVs would b~ unaffected;

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• c) The current st~ategy avoid~ co~po~nding a steam line break event with a Loss of Cool*ant event. Such a ~ompound eveht is not within-the d~sign base of the plant~ **.

Jn sunvnary, the current EOP strategy of using OT( only if cooling using S.Gs cannot be verified is preferred to inunediate initiation of OTC. This choice reduces the risk of loosing the ability to cool the core, does not further compound an already co~plicated event, and conforms to the_appro~ed guidance for CE plant EOPs.

Actions Planned to. Address Training Issues of Ooen Items:

Several actions have been assigned to assure that appropriate op~rator training on the event is provided.

• A comparison is being* completed between simulator, CPMAAP, and Safety Analysis calculations for containment response to the event. Those corrections necessary for proper simulator modeling_are currently-scheduled to be completed prior to the end of 1993.