ML20118B238

Forwards Response to NRC 920817 Request for Addl Info Re GL 88-20, IPE for Severe Accident Vulnerabilities

ML20118B238
Person / Time
Site:	Beaver Valley
Issue date:	09/11/1992
From:	Sieber J DUQUESNE LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-88-20, TAC-M74379, NUDOCS 9210010222
Download: ML20118B238 (33)

Text

h Q Beaver va y Power Sist.on Shippngport, PA 1$077@D4 (412) 393 5255 R

JOHND WB[i N oea,o,oup vue er.aeni September 11, 1992 U. S. Nuclear Regulatory Commicsion Attn: Document Control Deck Washington, DC 20555

Subject:

lleaver Valley Power Station, Unit No. 2 Docket No. 50-412, License No. NPP-73 Ceneric Letter 8t!-20 (TAC No. M74379)

References:

1. NRC Letter to Duquesne Light Company (DLC),

Generic Letter 88-20 Individual Plant Examination (IPE) For Severe Accident Vulnerabilities - Request For Additional Information (TAC No. M74379), dated July 15, 1992

2. DLC Letter to the NRC, Generic Letter 88-20, dated August 17, 1992 Please find attached the first submittal of Duquesne Light Company's responses to the NRC's Request for Additional Information (RAI), Reference 1. Our plan to provide two submittals in response to the RAI is stated in Reference 2. However, not all of the responses scheduled for this submittal are included herein primarily because key personnel have been engaged longer than anticipated in completing the Beaver Valley Power Station Unit No. 1 IPE Summary Report. Therefore, those responses will be provided with the second cubmittal.

Should you have any questions regarding this submittal, please contact Ed Coholich at (412) 393-5224.

Sincerely, l l n l I[ &.bk,

/7. D. Sieber Attachment cc: Mr. L. W. Rosebach, Sr. Recident Inspector

$[/

l Mr. T. T. Martin, NRC Region I Administrator

! Mr. A. W. De Agazio, Project Manager l

Mr. R. R. Janati, Pennsylvania Department of Environmental Resources If Mr. M. L. Bowling (VEPCO)

• • -Q()(sn,~

9210010222 920911 2 PDR ADOCK OSOO P

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ADDITIONAL INFORMATION FOR BEAVER VALLEY UNIT 2 INDIVIDUAL PLANT EXAMINATION Question 1. a) Describe briefly the peer review performed on the Individual Plant Examination (IPE) to help assure the analytic techniques used in the back-end analysis were correctly applied. Identify specific areas reviewed, expertise of the reviewers, and characterize the peer review findings and any significant comments. ,

b) As an example of the internal review performed, provide a copy or summary of peer review comments and resolutions (as appropriate) for aspects of the Probabilistic Risk Assessment involving the " Emergency Switchgear Ventilation"

• from- system analysis through event tree quantification, plant improvements and conclusions.

Response 1. a) The analytical techniques used in the back-end analysis of the Beaver Valley Unit 2 IPE vere developed by PLG, Inc.,

and applied using results from previous NRC and industry analyse *. Particularly heavy emphasis was placed on the Surry analysis in NUREG-1150, since Beaver Valley and Surry are similar plants. The back-end analysis was reviewed within Duquesne Light by the Radiological Engineering group and Nuclear Engineering group' to assure that the parameters ,

used in the input appropriately described the Beaver Valley plant. The analysis was also reviewed with Sandia, the principle contributors to the back-end analysis for the NUREG-1150 analysia of Surry. Their comments were to include provisions within the model -to reduce the Reactor Coolant System pressure prior to versel break by vay of stuck open PORVs and Reactor Coolant Pump seal leaks. Ve had previously only modeled- induced steam generator tube ruptures and induced hot _ leg failures, as pressure reducing mechanisms.

b) The internal review focused mainly on system des 1 .; 6 and operation, and on Emergency Operating Procedures. There vere no specific comments on the Emergency Svitchgeat Ventilation System in the formal internal reviev, however, the system model, and the success criteria, vere-discussed with plant personnel during- the development of the system analysis. Proposed- plant improvements vere dAscussei vith the Unit 2 Operations Manager and General Manager.

4 Question 2. Describe hov containment loading vas assessed for each of the Containment Event Tree (CET) end-states. Discuss the development of plant-specific probability distribution functions of failure likelihood for the range of failure pressures.

Response 2. As discussed in Section 4.4, "The Beaver Valley Unit 2 containment is very similar in design to the Surry Unit I containment", which vas analyzed extensively in NUREG-1150. Both containments vere designed and constructed by the Stone & Vebster Engineering Corporation (SVEC), a member of the BV-2 back-end analysis team. Based on a detailed review of the BV-2 containment design and a comparison to the Surry Unit I design, it was concluded "vith a high degree of confidence that the _

failure distributions for Beaver Valley Unit 2 and Surry Unit I containments vould be similar, and that use of the Surry distribution vould be somewhat conservative for the Beaver Valley Unit 2 containment". Based on this conclusion, the NUREG/CR-4551 Surry Unit I distributions for containment failure pressute and conditional probability that the failure vould be large vere utilized without modification in the BV-2 study.

As shovn in Figure 4.5 '., the CET has 12,463 end starts, Therefore, it is assumed that this request is directed at ;he broad categories of end state discriminators as related to CET Top Events C1, AP, C2, CE vhich address early containment failures, and Top Events C3 and C4 which address late containment failures.

No pressure load considerations are addressed for Top Event C1 which addresses containment failure prier to vessel breach. In the BV-2 IPE, this top event addresses only whether the containment is isolated. It was assumed, as it was in NUREG/CR- _

4551, that containment threats (blovdown or hydrogen burns) prior to vessel breach could be ignored.

CET Top Event AP addresres containment failures due to in-vessel steam explosions. Containment loading was not evaluated for this top event. For the failure branch of this top event, it was assumed that the containment vould fail. Containment failures, resulting from in-vessel steam explosions, were assumed to be large.

CET Top Event C2 addresses the containment loading at vessel breach. Because of the similarity between the Surry plant analyzed in NUREG/CR-4551 and BV-2, the containment pressure rise distributions developed for the former vere adapted to BV-2, with minor adjustments to account for slight differences in the containment volume and power ratings. These loads distributions were compared to the failure of various CET paths.

- - - - - . - ~ . - - - . . . - - . - .- - .- - -

t

. 4 .

a

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No specific containment loads were calculated for Top Event CE which addresses containment failure within four (4) hours of i vessel breach, due to hydrogen burns within that time period, t including those that occurred at vessel breach in the absence of ,

HPHE. MAAP analysis performed for BV-2 indicated that the amount  !

of hydrogen generated in-vessel for most BV-2 sequences was typically of the order of 700 lbm (equivalent to the oxidation of ,

approximately 40% of the core Zircaloy). MAAP also indicated '

that the quantity of hydrogen generated ex-vessel in this time period was relatively small. Therefore, .the primary source of ."

hydrogen in this four (4) hour time frame is that which is Furthermore, concern regarding produced in-vessel. the significant hydrogen burns during -this tite period applies only to scenarios in which the steam concentrations in the containment atmosphere are lov (i.e., when containment sprays are in operation).

f For scenarios in which the contair.nent sprays are operating, it is likely that hydrogen burns vill occur at low concentrations if ,

hydrogen is " slowly" released into the -containment. Only when ,

the hydrogen is suddenly released into the containment (e.g., due to ah induced failure of the hot- leg or at vessel breach) vill the hydrogen concentrations achieve significant values. When .

vessel-breach is accompanied by HPME, the containment loads discussed for Top Event C2 ine'lude the contribution of hydrogen ,

burns. However, for " pour" type vessel breaches at high  !

pressure, there could be a sudden release of hydrogen into the reactor cavity and then into the containment. For those scenarios in which there-vas a sudden release of hydrogen into a I non-steam inerted containment atmosphere, it was assumed that if ,

the global concentration exceeded 12%, a burn vould occur which would, in turn, fail the containment. The intermediate logic ,

implicit in this assumption is as follovsr

1. A deflagration at a 12% hydrogen concentration, is not likely- to. fail the BV-2 . containment (based 1on- peak l containment pressures determined using the~. adiabatic hurn. j assumption).

2. Although MAAP simulations showed that the containment was well mixed when sprays were in operation, it was assumed

-that local- concentrations could be 20% higher than the global concentration.

3.. Although the BV-2 -containment configuration is not necesserily amenable to -a Deflagration to'. Detonation Transition (DDT), it was assumed that .a DDT vould occur if local concentrations exceeded a value of 15% (minimum value reported in Reference 4-8).

,, w .. - , a -, a ,-. . - - - . - . - ,.- - .. - - . - . . - . - - - - . . = -

1 l .

I 4 It was assumed that DDT vould result in a large containment failure.

Figure 4.2 (based on the in-vessel hydrogen generation distributions reported in Volume 2 of 11UREG/CR 4551) vas used to determine the probability that the amount of hydrogen generated in-vessel vould exceed a level necessary to produce a global concentration of 12%. This probabili y was estimated to be 0.38.

Top Event C3 addresses lat, hydrogen burns. If sprays are in opetation, the only late burns of significance are those resulting from sudden releases of hydrogen generated in-vessel into the containment. These releases were addressed in Top Event CE. At the time that the MAAP analysis vas performed for ~

BV-2, the HAAP program indicated that for scenarios in which there was uncooled debtis in the cavity, hydrogen vould recombine in the reactor cavity, or burn as it exited the teactor cavity as a hydrogen-laden jet.

In the absence of containment heat removal, the deposition of the energy associated with these burns, along vith decay heat and noncondensible gases generated from the decomposition of concrete, containment While the timing of overpressurization vould eventuntly occur.

such failure is certainly influenced by the rate of containment pressure and temperature rise, there is considerable uncertainty as to the failure pressure, especially when there are potentially multiple failure modes, some of which are sensitive to temperature. Industry practice is to assume that the time of conta!, ment failure corresponds to the median failure pressure.

In fact, however, there is a finite probability of containment failure at any pressure which exceeds the test pressure. Ilence, there is significant untertainty in the time of failure, even if the containment loading was known precisely.

~

Top Event C4 addresses slov, long-term overpressurization of the containment. In the absence of containment heat removal, the containment atmosphere is likely tc continuously pressurize until some mode of containment failure occurs. MAAP analysis performed for BV-2 provides containment pressure and temperature histories.

The same considerations regaiding the timing of containment failure that vere discussed above for Top Event C3, a,. ply to Top Event C4 as well.

Question 3. Describe hov phenomenological uncertainties were accounted for during the quantification of Contairment Event Trees.

Response 3. (LATER)

_4_

-^ - - - - - - - - - - - - . _ _ _ _ _

l l . .

Question 4. Sec t ion 4.1.4, "Eqt:ipment Survivability" (Page 4.1 6) of the IPE states that, " survivability of equipment for BV-2 is such that equipment failures under seve:e accident conditions vould not create instances of Unusually Poor Containment Performance (UPCP), given a severe accident."

a) State the defin!' ion of UPCP, and discuss the basic for this definition.

b) Vas the conditional and absolute probability of UPCP for internal events only estimated? If so, please provide the estimates.

Response 4. (LATER) t Question 5. a) Provide a ccncise discussion of how the IPE process treated equipment survivability during a severe accident scenario.

b) Vas any essential equipment identified which would fall as a result of severe environmental effects? How is it determined which equipment (qualified for Design Basis Accident jD.Aj B environments), vill be usable and assured to operate in severe accidents? Lov was credit'for such eauipment taken in the PRA?

c) Section 4.1.4.1 of the BV-2 IPE (Page 4.1-6) states that the containment response reported in Reference 4-7 for the Zion Plant can be taken as representative of that for BV-2. -

Discuss the applicability of the Zion analysis to BV-2. 4 d) Explain how the information in Table 4.1-3 was used in the BV-2 IPE process.

Response 5. (LATER) ,

-h

Question 6. Describe briefly the plant-specific insights obtained from the BV-2 back-end analysis, and discuss how the BV-2 back-end insights vere or vill be used to enhance plant safety.

Response 6. As noted in Section 1.7, the BV-2 containment configuration is not conducive to flooding of the reactor cavity, either before or after vessel breach (except for vessel injection following vessel breach). The OSS provides only limited flow to the cavity while it is operating, and the RSS spray coverage pattern is such that none of its flow reaches the cavity. The cavity does not communicate with the sump, and it cannot be flooded (without an external source of water) due to spillover from the remainder of the containment. The cost-benefit aspects of design changes to provide water to the cavity vill be examined during the accident _

management phase of the BV-2 IPE.

The BV-2 CDP contains a relatively high percentage (approximately 27%) of SB0 Events. Thus, a relatively high fraction of vessel breaches occur at RCS pressures, at which the effects of forced ejection of debris from the vessel must be considered. As noted in Section 1.5, "for sequences involving Station blackout and no steam generator cooling, current procedures (ECA 0.0) preclude RCS depressurization via the PORVs, as vould otherwise be directed for t.her sequences per FR-C.1." As also noted, consideration vill be given to extending existing procedural provisions for RCS depressurizat!on to cover Station blackout sequences where appropriate.

Core damage scenarios involving SGTKs, and a stuck open secondary side relief valve, have the potential for significant off-site releases. If low pressure injection is available, depressurization could extend the time to core damage, thereby providing a muc: larger time vindov for recovery actions, and -

significantly reduce the source term if core damage cannot be prevented. Existing procedures are being reviewed and updated to ,

more explicitly instruct the operators to perform the a depressurization for sequences in which all high head safety injection is also failed. Procedures and training are also being reviewed to ensure that a stuck-open main steam safety / relief valve vould be locally gagged, thereby isolating the faulted steam generator.

Question 7. Discuss the considerations given to in-vessel steam explosion as a contributor to early containment failure probability.

Response 7. In-vessel steam explosions were addressed in Containment Event Tree Top Event 12 - In-vessel Steam Explosion Falls Containment (AP). As noted in Section 4.6.3 of the IPE Summary Report, the failure frar'tions for this Top Event vere taken directly from

• Volume 3 oi NUREG/CR 4551 (0.008 for lov RCS pressure melts and s

0.0000 ^_or hib h pressure melts). All in-vessel steam explosion failures vere considered as large, early containment M caused failures. The contribution of in-vessel steam explosions to the g

_3 Irequency of large, early containment failures can be determined 0,r' by examining the importance of CET split fractions APL and APH in f- the split fraction importance table for Release Category Group I _

(see Table 7-1 attached to this response). The table is the

. . basis for Table 4.8 3 of the IPE submittal, which is an abbreviated version of the attached table. The sum (0.0465) of the importance of split fractions APL and APil represent the fractional contribution of in-vessel steam explosions to the frequency of Release Category Group I. This represents approximately 5% of the Release Category Group I frequency. In in-vessel steam explosions account termsofabso}ute frequency, for 3.7 x 10^ per reactor year, or approximately 0.2% of the total CDF of 1,9 x 10 " per reactor year.

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TABLE 7-1. Split Fraction Importanco for Largo, Eerly Containment Failures and Bypassss M3)EL hame: BV2LVL2 Split Fraction Irnpartance for Group LECFBY Sorted by Inportence Group Frequency = 8.0195E-06 .

16:30:10 26 AUG 1792 Page 1

...... St

.. Ipportance.. . Achievement. Redaction. Derivative . SF Value.. ... Frequency......

1. isF 1.0000E+00 1.0000E+00 0.0000t+00 0.0000E+00 1.0000E+00 8.0195E-06

2. CP1 1.0000E+00 1.0000E*00 0.0000E+00 0.0000E +00 1.0000E+00 8.0195E 06

3. IEF 9.3516E 01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 7.4995T-06

4. WRF 9.1330E 01 1.0000E+00 0.0000E+00 C.0000E+00 1.0000E+00 7.3282E-06

5. WMF 9.0300E-01 1.0000E+PJ 0.0000E+00 0.0000E+00 1.0000E+ 00 7.2415E-06 6, T8F 7.895BE-01 1.0000E +00 0.0000E+00 0.0000E+00 1.0000E+00 6.3320E 06

7. REF 7.3647E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 5.9061E-06

8. CCF 7.2410E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 5.8069E-06

9. HHF 6.7296E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 5.3968E-06

10. SP2 5.9243E-01 1.0000E+00 0.0000E+00 0.0000E +00 1.0000E+00 4.7510E "

11. ME3 5.6083E 01 1.04S7E+ 00 4.4027E 01 4.8790E-06 9.2000E-01 4.4976E- ~

12. WAF 5.2172E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 4.1839E-06

13. FAF 4.9575E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 3.9757E-06

14. LCF 4.9391E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 3.9609E-06

15. EAF 4.8792E 01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 3.91'BE-06

16. SEF 4.7874E-01 1.0000E +00 0.0000E+00 0.0000E+00 1.0000E+00 3.8392E 06

17. WBF 4.7689E-01 1.0000E+00 0.0000E+00 0.00n0E+00 1.0000E+00 3.8244E-06

18. LHF 4.5477E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 3.6470E-06

19. OsF 4.5419E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 3.6424E-06

20. SMF 4.538?E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 3.6400E-06

21. FBF 4.1475E -01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 3.3261E-06

22. R9F 4.0851E 01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 3.2760E 06

23. EBF 4.0696E-01 1.0000E+00 0.0000E+00 0.GJ00E+00 1.0000E+00 3.2636E-06

24. VLF 3.8451E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 3.0836E-06

25. C2S 3.5658E-01 2.5452E+00 6.4342E-01 1.5251E 05 1.8750E-01 2.6596E-06

26. L2S 3.5658E-01 1.24886+00 6.4342E-01 4.8550E-06 5.8900E-01 2.8596E-06

27. RCF 3.1569E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 2.5316E-06

28. ROF 3.1298E-01 1.0000D00 0.0000E+00 G.0000E+00 1.0000E+00 2.5100E-06

29. ME2 2.9400E 01 1.1087E+00 7.0600E-01 3.2298E-06 7.3000E 01 2.3577E-06

30. RPR 2.8011E 01 1.4057E

• 00 8.3430E-01 4.5822E 06 2.9000E 01 2.2464E 06 '

t

31. RSF 2.4861E-01 1.0000E400 0.0000E*00 0.0000E+00 1.0000E+00 1.9937E -06

32. 06F 2.2324E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 1.7903E-06

33. AOF 2.1992E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 1.7636E-06

34. C2J 2.0425E-01 1.8909E+00 7.9575E-01 8.7827E-06 1.8650E-01 1.6380E-06

35. L2J 2.0425E-01 1.1443E+00 7.9575E 01 2.7952E-06 5.8600E-01 1.6380E 06

36. SAF 1.9609E 01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 1.5726E 06

37. Sef 1.95?OE-01 1.0000E+00 0.0000E+09 0.0000E+00 1.0000E+00 1.5654E-06 -

38. NCF 1.9118E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 1.5332E-06

39. BPF 1.6441E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 1.4789E-06

40. AFF 1.7834E O' 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 1 !02E-06

41. C22 1.7787E-01 2.2227E+00 8.2213E-01 1.1232E-05 1.2700E 01 1. 264E 06

42. L?? 1.778?E -u1 1.1534E+00 8.2213E-01 2.6563E-06 5.3700E-01 1.4264E-06

43. IRF 1.7669E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 1.4170E-06 44 IWF 1.7597E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 1.4112E-06

45. CIF 1.7454E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 1.3997E 06

46. OFF 1.7436E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 1.3983E-06

47. G)F 1.6435E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 1.3180E-06

48. RPQ 1.6037E-01 1.6226E+00 8.7248E 01 6.0157E-06 1.7000E -01 1.2861E 06

49. OSF 1.5418E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 1.2365E-06

50. RPP 1.5195E-01 9.8012E 01 1.0229E+00 -3.4287E-07 5.3500E 01 1.2185E-06

51. WU4 1.4736E-01 2.7702E+00 8.5264E-01 1.537BE-05 7.6850E 02 1.1818E 06

52. WC2 1.4714E-01 1.4854E+02 6.5286E-01 1.1843E-03 9.9630E-04 1.1800E-06

53. RPT 1.4572E-01 1.0000E+00 1.0000E+00 0.0000E+00 5.0000E-01 1.1686E-06

54. vt1 1.4211E 01 1.3850E+02 8.5823E-01 1,1038E 03 1.0300E-03 1.1?96E 06

55. OCF 1.3956E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 1.1192E-06 ,

56. OPF 1.3784E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E*00 1.1054E-06

57. C12 1.3753E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 1.1029E-06

58. 00f 1.2541E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 1.0057E-06

59. IYF 1.1830E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 9.4869E-07

60. IBF 1.1820E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 9.47 Bot-07 l

1

.-________________________-__-___-_______________________________________________________________________-_______________________a

TABLE 7-1. Split Fraction importance for Large, Early Containment Failures and Bypasses MODEL Name: BV2 Lyt 2 Split Fraction Imortance for Group i LECFBI Sorted by I m ortance Group Frequency = 8.0195E-06 .

16:30:23 26 AUG 1992 Page 2

)

. . . . . . S F N ane . . . l @or t anc e. . . . Achievement . . Reduc tion. . . Der i va t i ve. . SF Value. . . . . . F requency. . . . . .

61. Bvf 1.179BE-01 1.0000E+00 0.0000E + 00 0.0000D 00 1.0000E+00 9.4611E-07

62. L2A 1.1613E-01 1.1081E+00 8.8387E-01 1.7979D 06 5.1800E 01 9.3130E 07

63. C2A 1.1613E-01 2.7185E+00 8.8387E -01 1.4712E 05 6.3300E-02 9.3130E-07

64. SE4 1.1151E-01 1.0000E+00 0.0000E+00 0.0000E+00 1.0000D 00 8.942BE-07

65. RESA 1.0747E 01 1.7691E+00 8.9253C 01 7.0299E-06 1.2260E 01 8.6186E-07

66. Bx2 9.4989E-02 6.7834E+00 9.0501E-01 4.7142E 05 1.6159E 02 7.6176E-07 67 BP5 9.4989E-02 1.5412E+00 9.0501E-01 5.1022E 06 1.4930E-01 7.6176D 07

68. LS2 9.3145E-02 1.0000E+00 0.0000E +00 0.0000E+00 1.0000E+ 00 7.4697E-07

69. IAF 8.2166D 02 1.0000E+00 0.00000 00 0.0000E*00 1.00000 00 6.5893E-07

70. MFF 8.1625E-02 1.0000E *00 0.0000E+00 0.0000C+00 1.0000E+00 6.5459E-07

71. LS3 7.8341E-02 9.3155E 01 1.0684E+00 - 1.097M -06 5.0000E 01 6.2826E 07 * ~

72. RP5 7.7523E-02 9.2248C-01 0.0000D 00 0.0000D00 1.0000E+00 6.2169E 07

73. A01 6.5877E 02 6.99512+01 9.3412E 01 5.534M -04 9.5450E-04 5.2830E-07 74 CS4 5.9120E 02 9.5379E-01 1.0059E+00 4.1824E-07 1.1391E 01 4.7411E-07

75. ISS 5.0757E 02 3.6731D00 9.5100E-01 2.1830E-05 1.8000E-02 4.0705E -07

76. 183 4.8377E-02 2.5341E+b0 9.5294E 01 1.2680D 05 2.9760E 02 3.8796E-07

77. AF4 4.5004E-02 1.6538D00 9.6582E-01 5.5169D 06 4.9679E 02 3.6091E-07

78. A02 4.4506E-02 1.36660 00 9.55'.?E 01 3.2971E 06 1.0825E 01 3.5692E-07

79. RPK 4.4122E 02 9.5588E-01 0.0000E+00 0.0000D 00 1.0000E+00 3.5384E-07

00. FB7 4.3226E-02 8.1779E +00 9.567. 5 01 5.7910E-05 5.9860E-03 3.4665E-0 7

81. BY2 4.2890E-02 1.0000E+00 0.00000 00 0.0000D 00 1.0000E*00 3.4396E 07 E2. LB2 4.2890D 02 1.0000D 00 0.0000E+00 0.0000E +00 1.0000E+00 3.4396E-07

83. APL 4.1645E-02 6.1390D 00 9.5839E-01 4.1706E-05 8.0000E-03 3.3397E-07

84. C0F 4.1086E-02 1.0000E+00 0.0000D 00 0.0000E+00 1.0000D 00 3.294BE-07

85. EB7 4.0771D02 2.8477E+00 9.5923E-01 1.5144E 05 2.1590D 02 3.2696E 07

86. RE1 4.0293E-02 8.9512E+00 9.5971E 01 6.4088E-05 5.0420b O3 3.2313E-07 87 PRF 4.0204E-02 1.0000D 00 0.00000 00 0.0000000 1.0000D 00 3.2241E-07

88. PR9 3.9416E 02 1.37030 00 9.6923E-01 3.2164E-06 7.6710E-02 3.1610E 07 89 BP7 3.4879E-02 4.1041E+01 9.6512E 01 3.2139E 04 8.7033E-04 2.7971E 07

90. RE2 3.351bE-02 1.2430E+00 9.6648E-01 2.2178E-06 1.2120E-01 '.6880E-07

91. OP1 3.0516E 02 3.6002E+02 9.6948E 01 2.8794D03 8.4990E 05 2.4472E-07

92. PL1 2.9792D02 1.0152D 00 9.7021E-01 3.6089E-07 6.6200E 01 2.3891E 07

93. RT1 2.9502E-02 3.0227E+02 9.7055E-01 2.4163E-03 9.7730E 05 2.3659E 07 94 HN1 2.6935E-02 4.6758E+01 9.7310E-01 3.6717E 04 5.8751E-04 2.1600D07

95. RPS 2.4401E-02 1.0000D 00 1.00000 00 0.0000D 00 5.0000E-01 1.9568E-07

96. BV2 2.3826E 02 4.5071E+02 9.7617E 01 3.6066E-03 5.2979E-05 1.9107E-07

97. 2.2985E-02 2.0933E 07 7.2680E-02 C07 9.7579E 01 1.0019E+00 1.8433E-07

98. OAF 2.2490E-02 1.0000E+ 00 0.0000E+00 0.9000E+00 1.0000E+00 1.8036E-07 90 RPW 2.2153E 02 9.7785E-01 0.0000E+00 0.0000E+00 1.0000E+00 1.7766E 07 100. COB 2.1797E -02 9.9737E 01 1.0005E+00 -2.4796E 08 1.4950E-01 1.7480E -07 101. CSF 2.0659E 02 1.0000E+00 0.0000D 00 0.0000E+00 1.0000E+00 1.6567E 07 102. RE3 1.9570E-02 1.2210E+00 9.8043E 01 1,9290E-06 8.1360E-02 1.5694E-07 103. BX1 1.9164E-02 O M 00E+00 9.8084E-01 0.0000E+00 5.685E-06 1.5368D07 104. BP3 1.9164E-02 4.21080 00 9.8084E-01 2.5903E 05 5.9330E 03 1.5368E 07 105. IPS 1.8508E-02 9.2967E 01 1.1808E+00 -2.0142E-06 7.2000E-01 1.4842D 0/

106. BP4 1.7778E -02 2.1523E+01 9.8222E-01 1.6472E 04 8.6550E-04 1.4257E-07

+ 107. 051 1.5939E-02 2.5027E+00 9.8408E-01 1.2179E-05 1.G?.80E -02 1.2782E-07 108. 011 1.3486E-02 1.0412E+01 9.8769D 01 7.5579D05 1.3060E-03 1.0815E 07 109. SA1 1.3425E-02 2.1994D 00 9.9081E-01 9.6920D 06 7.6010E-03 1.0766E 07 110. BF6 1.3314E 02 1.1206D 00 9.8669E-01 1.0742D 06 9.9390E-02 1.0677E-07 111. BK1 1.2398E 02 9.8773E-01 1.0012D 00 -1.0021E-07 9.0491E-02 9.9427F-08 112. RE7 1.2288E-02 1.50690 00 9.8771E-01 4.1633C-06 2.3670E-02 9.8546E-08 113. CD6 1.1994E-02 1.4725D 00 9.9057E-01 3.8649D 06 1.9560E 02 9.6182E 08 114 MUF 1.0674E-02 1.0000E+00 0.0000E+00 0.0000D 00 1.0000E+00 8.5600E-08 115. EB6 1.0569E-02 1.0031E+00 9.8943E-01 1.0999E-07 7.7060E 01 8.475Pi-08 116. EC2 1.0569E 02 1.1208E+00 .9.8943D 01 1.0534E-06 8.0458E 02 8.475F-08 117. FC2 1.0569E-02 4.0834E+00 9.8943D 01 2.4812E-05 3.4160E 03 8.4758D 08 118. FB6 1.0569E 02 1.0955E+00 9.8943C 01 8.5056D07 9.9650E-02 8.4758E-08 119. EB4 1.0563E-02 1.2650E+00 9.8944E-01 2.2101E 06 3.8330E-02 8.4712E-08 120. vt2 1.0143C 02 1.6501E+00 9.9124E-01 5.2838E 06 1.3300E-02 8.1339D 08 i

i

TABLE 7-1. Split Fraction importance for Largo, Ecrly Containment Failure.s cnd Bypasses DODEL Wome: BV2LVL2 Split f raction Imortance f or Oro@ t LECFBY Sorted by I mortance Group Frequency = 8.0195E 06 ,

16:30:36 26 AUG 1992 Page 3

... SF Nam. . Imortance. . . Achieveent. . Reduction. . Derivative.. $F Value. . . Freq;ency......

121. elf 9.7628E-03 1.0000E*00 0.0000E+00 0.0000E+00 1.0000E +00 7.8292E-08 122. OC1 9.7213E-03 8.614BE+00 9.902SE 01 6.1145E-05 1.2750E 03 7. 7959E-08 123. VL3 9.5258E-03 1.6959E+00 9.9083E-01 5.6543E 06 1.3000E-02 7.6392E-08 124. 0A1 8.6959E-03 3.3314E+00 9.9130E-01 1.8767E 05 3.7160E 03 6.9737E-08 125. R11 8.3581E-03 1.3815G+00 9.9164E-01 3.1263E-06 2.1440E 02 6.7027E-08 126. HC1 8.3197E -03 1.5088E +01 9.9168E 01 1.1305E-04 5.8990E-04 6.6720E-08 127. 582 8.2634E-03 1.3408E+00 9.9183E-01 2. 7987E-06 2.3400E 02 6.6268E 08 128. FB8 8.1626E-03 1. 2029E + 00 9.9184E 01 1.6923E-06 3.8680E 02 6.5460E-08 129. EC1 8.1405E 03 9.2960E+00 9.9186E-01 6.6595E 05 9.8029E 04 6.5282E 08 130. EB8 7.9913E-03 1.0728E+00 9.9201E-01 6.4766E-07 9.8950E-02 6.4086E-08 131. AF6 7.9353E-03 4.1938E+01 9.9208E 01 3.2837E-04 1.9343E-04 6.3637E 08 132. FA2 7.8870E~03 1.2222E+00 9.9211E 01 1.8448E-06 3.4285E-02 6.3249E-08 133. 164 7.8225E 03 1.1796E +00 v.9378E-01 1.4899E 06 3.3470E-02 6.2732E-08 134. EA2 7.6983E 03 1.0660E+00 9.9230E-01 5.9123E 07 1.0442E 01 6.1736E-08 135. FAI 7 5622E 03 6. 8149E + 00 9.9244E-01 4.6693E 05 1.298SE 05 6.0644E-08 136. BV4 7.4571E 03 5.6300E+01 9.9254E 01 4.4354E-04 1.3483E-04 5.9802E 08 137. EA1 7.3946E-03 1.2818E+00 9.9261E-01 2.3188E-06 2.5574E 02 5.9301E-08 138. Rwl 5.7550E-03 0.0000E+00 9.9424E 01 0.0000E+00 * . 7%C E -05 4.6152E 08 139. CEF 4.8911E 03 1.0000E +00 9.9511E 01 1.0322E-07 3.8000E 01 3.9224E-08 140. LEF 4.8911E 03 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 3.9224E-08 141. HEA 4.8911E 03 1.0002E +00 9.9562E 01 3.6413E 08 9.6500E-01 3.9224E 08 142. APH 4.8695E 03 6.2271E+0C 9.9581E-01 4.1952E-05 8.0000E-04 3.9051E 08 143. RC1 4.8665E b3 1.1921E+00 9.9513E-01 1.5794E-06 2.4709E-02 3.9027E -08 144. Ce1 4.3360E-0T 1.3040E+01 9.9566E 01 9.6590E 05 3.6000E-04 3.4772E-08 145. PR7 4.1252E-03 1.0633E+00 9.9671E-01 5.3404E-07 4.9460E-02 3.3082E 08 146. PRV 3.7277E-03 9.9652E-01 1.0015E+00 -3.9817E 08 2.9890E 01 2.9894E-08 147. 003 3.4900E 03 7.079BE+00 9.9651E 01 4.8785E 05 5. 7370E-04 2.7988E-08 148. t'o3 3.4519E-03 7.0760E+00 9.9655E-01 4.8754E-05 5.6780E-04 2.7682E 08 149. REA 3.2324E-03 1.020SE+00 9.9677E 01 1.9060E-07 1.3600E-01 2.5922E-08 150. AF3 3.0641E-03 1.0417E

• 00 9.9774E -01 3.5263E 07 5.1502F-02 2.4572E-08 s 151. 056 2.9872E -03 3.6572E +00 9.9714E 01 2.2936E 05 1.0000E-03 2.3956E -08 152. RD1 2.6511E-03 1.1044E +00 9.9735E-01 8.5819E-07 2.4774E-02 2.1261E-08 153. M2 2.5193E-03 3.V055E+00 9.9749E-01 2.3321E 05 8.6265E-04 2.0204E-08 154. BV1 2.4611E-01 0.0000L+00 9.9754E -01 0.0000E+00 1. 7241E -07 1.9737E -08 155. 581 2.3399E-03 8.294 H-0* 1.0012E+00 -1.3780E-06 7.2320E-03 1.8764E-08 156. BPA 2.2671E 03 1.4333E+01 9.9773E-01 1.0694E 04 1.7000E-04 1.8181E-08 M7. DO2 2.2559E-03 5.6244E+00 9.9774E-01 3.7103E-05 4.8760E-04 1.8092E-08 -

158. BV5 2.2309E 03 1.0711E+00 9.9777E 01 5.8789E-07 3.0431E 02 1.7890E-08 159. SA2 2.1838E-03 1.0089E+00 9.9990E-01 7.1919E-08 1.1470E-02 1. 7513E -08 160. HC3 2.0751E-03 1.1521E+00 9.9798E-01 1.2356E 06 1.3090E-02 1.6641E-08 161. R12 1.9922E-03 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E +00 1.5977E-08 162. H4 1.7802E-03 4. 0789E + 00 9.9822E 01 2.4705E 05 5.7782E-04 1.4276E-08

.63. OR3 1.7493E 03 1.1500E+00 9.9825E-01 1.2167E -06 1.1530E 02 1.4028E-08 164. CCB 1.7461E-03 1.2704E + 00 9.9836E-01 2.1814E-06 6. 0449E -03 1.4003E-08 165. OP2 1.7182E 03 4. 3786E + 00 9.9828E-01 2.7108E 05 5.0830E -04 1.3779E -08 166. 0A2 1.6386E-03 1.0478E + 00 9.9836F-01 3.9616E-07 3.3170E-02 1.3141E-08 167. UB1 1.6266E-03 1.3269E+00 9.9837E 01 2.6343E 06 4.9480E-03 1.3045E-08 168. HC2 1.5954E-03 1.1167E+00 9.98446-01 9.4825E-07 1.3230E-02 1.2794E-08 lb9 IW1 1.5892E-03 2.8063E+01 9.9841E-01 2.1704E 04 5.8720E -05 1.2745E-08 170. RE9 1.5818E 03 1.1363E+00 9.9842E 01 1.1059E-06 1.1470E-02 1.2685E-08 s 171. IR1 1.4877E 03 2.5757E +01 9.9851E 01 1.9853E-04 6.0090E-05 1.1931E-08 172. R02 1.4829E-03 1.0618E+00 9.9852E-01 5.0755E-07 2.3430E-02 1.1892E-08 1 73. SB6 1.4722E 03 1.0155E+00 9.9859E 01 1.3566E-07 8.3210E-02 1.1806E 08 1 T4. V!F 1.3668E-03 1.000%+00 0.0000E+00 0.0000E+00 1.0000E+00 1.0961E-08 175. SE2 1.3510E-03 1.2535E+00 9.9865E-01 2.0434E 06 5.3020E-03 1.0834E 08 176. FR1 1.3394E-03 3.6514E+00 9.9867E-01 2.1274E-05 5.0210E-04 1.0741E 08 1 77. BP8 1.3006E-03 1.0111E+00 9.9870E-01 9.9536E 08 1.0479E-01 1.0430E 08 178. OS2 1.2926E-03 1.0723E+00 9.9873E-01 5.9005E-07 1.7220E-02 1.0366E-08 179. IR2 1.1804E-03 4. 4797E + 00 9.98E2E 01 2.7915E 05 3. 3910E -04 9.4660E-09 180. 054 1.1696E-03 1.0000E+00 0.0000E+00 0.0000E+00 1.600 m 00 9.379BE-09

- 10

l TADLE 7-1. Split Fraction importance for Large, Early Containment Failures and Bypasses ML0EL hame: 6V2LVL2 split Fraction importance for Gro@ . LEEFBT

$orted by I mortance Gr :up Freqwncy = 8.0195E-06 .

16:31:05 26 AUG 1992 Pc9e 4

. . . . s f N are . . l yr>r t anc e . Achievement. R edx t i on. . . Der i va t i' LF Value.. . Freq;ency. .. .

181. RE4 1.1429E-03 1.0071DOU 9.9386D 01 6.6322' 1.3820E-01 9.1656E 09 102. $83 1.1228E-03 1.0863D00 9.9934E-01 6.974 % u7 7.6060E-03 9.0046E-09 183. AF2 9. 7147E - 04 2.9590D 00 9.9905E-01 1.5718E-05 4.8505E 04 7.7907E-09 184. RE6A 9.6348E-04 1.0049E+00 9.WO4E - 01 4.6714E 08 1.6540E 01 7. 7266E-09 155. R12 9.1242E 04 1.5134D00 9.WG7E-01 4.1242D 06 1.7740E-03 7.3171E-09 186. IW2 9.035 8E -04 3.6404E+00 9.9910E-01 2.1182E-05 3.4210E-04 7.2462E-09 187. RvF 9.025CE-04 1.00000 00 0.0000D 00 0.0000D 00 1.0000E+00 7.23B2E 09 188. M51 8.6553E-04 1.2825D00 9 9913E-01 2.2726E-06 3.053M 03 6.9395E-09 109. PS 6 8.4700E 04 9.6954E-01 1.0016D 00 -2.5906E-07 5.0960E-02 6.7925E-09 190. RI3 8.3793E 04 0.0000E+00 9.9916E-01 0.0000E+00 3.5780E 06 6. 7197E-09 191. Rif 8.3793E-04 1.0000E+00 0.00000 00 0.0000E+00 1.0000D 00 6.7197E-09 192. SE5 8.2849E 04 1.160$D00 9.9917E 01 1.2941E 04 5.1340E-03 6.6440E - 09 193. 082 8.2332E-04 1.13860 00 9.9923E-01 1.1180D 06 5.5180E-03 6.6026D 09 194 FRS 7.7929D 04 1.0182t*00 9.9953E-01 1.4972E 07 2.50700 02 6.2495E 09 195. AF1 7.5750E-04 0.0000D 00 9.99?5D 01 0.0000E+00 1.0720E -05 6.0748E-09 196. ss4 7.4990E 04 8.8755D01 1.0013D00 9.1202E 07 1.1210D 02 6.0138E-09 197. TB1 7.4687E-04 1.4517E+00 9.9935E-01 3.6274E 06 1. 460E 03 5.9895E-09 198. PA1 7.3445E 04 1.0448E+00 9.9927E-01 3.6515E 07 1.6130E 02 5.8899D 09 199. PR4 6.6156E 04 9.5462F 01 1.0004E+00 3.6729E-07 9.1130E-03 5.3053E-09 200. c16 6.5774E 04 1.0547E400 9.9934E-01 4.4400E 07 1.1880E-02 5.2747E 09 201. HR2 6.3435E 04 1.0957E +00 9.9937E 01 7.7286E-07 6.5820E-03 5.0870E-09 202. 001 6.0988D 04 8.3007E + 00 9.9939E-01 5.8553E-05 S.3530E-05 4.8909D 09 203. S89 5.4355E 04 9.9738D 01 1.0000E+00 2.1247D 08 1.1810E-02 4.3589E-09 204. SA4 5.2346E-04 9.9615E 01 1.0000E+00 3.1223E-08 1.1660E-02 4.2360E-09 205. LH2 4.%23E-04 1.0422D 00 9.9950E-01 1.4241E-07 1.1622E-02 3.9795E-09 206. PA2 4.8925E 04 1.0005E*00 9.9951D 01 8.030JE-09 4.8760E-01 3.9155D 09 207. CS2 4.8130E-04 8.9124E 01 1.0004E+00 -8.6748D07 3.8348E-03 3.8598E 09 208, HMF 4.1034 D 04 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 3.2907E-09 209. PRJ 3.6'.80E -04 9.9931E 01 1.0003E+00 -7.9407E 09 3.034GE-01 2.9255E-09 210. AF5 3.5564E-04 1.5125E+00 9.W65 D 01 4.11310 06 6.819BE-04 2.8520E 09 p 211. RDA 3.482SE-04 t 0041 D 00 9.9965E-01 3.5837E -03 7.7930E-02 2. 7928E -09 212. Rx1 3.4825D 04 1.180$f+00 9.9965E-01 1.4503E-06 1.9257E-03 2.7928D 09 213. FC1 3.4687E-04 0.0000D 00 9.V965E-01 0.0000E+00 2.4771E-05 2.7817E -09 214 FB4 3.4687E-04 1.0178E+00 9.9965E 01 1.4587E-07 1.9070E -02 2. 7817E -09 215. HH3 3.4665E 04 1.5740D 00 9.9966E-01 4.6056E 06 5.8975E 04 2. 7800E-09 216. LH1 3.3198D 04 1,4810E+00 9.99676 01 3.8604E-06 6.8966E-04 2.6623E 09 217. HH5 3.0278D 04 1.4054D00 9.9970E-01 3.2538E 06 7.3 718E -0* 2.4281E-09 -

216. MU2 3.0248E 04 1.0148E +00 9.9970E-01 1.2129E 07 2.0000E-02 2.4257D 09 219. BK2 2.8812E-04 7.2190E 01 1,0001E+00 -2.2313E G6 5.0316D 04 2.3106E-09 220. FBI 2.4799E-04 'i .1901D00 9.9975E-01 1.5263E-06 1.3030E-03 1.9887E 09 221. Cs3 2.4156E-04 8.9129D 01 1.0009D00 -8.7930E 4 7 8.5727E- J3 1.9372D 09 222. WA2 2.3946E-04 1.0182D 00 9.9976E-01 1.4806E-0) 1.2970E -02 1.9203D 09 223. 083 2.3171L-04 1.0144D00 9.9978D 01 1.to92E-07 1.5200E-02 1.8582E-09 224. Sv3 2.3102E-04 0.0000E+00 9.9977E-C1 0.0000E*00 1.2627E -06 1.8527E 09 225. OR2 2.2900E-04 1.1276E+00 9.99T7D01 1.0248D 06 1.7920E-03 1.8365E-09 226. HM1 2.2840E-04 1.3977D00 9.9977E -01 3.1916E 06 5.7410E 64 1.8323E 09 227. ASF 2.2653E 04 1.0000E+00 0.0000D 00 0.0000D 00 1.0000D 00 1.8166D 09 228. SM? 2.2525E-04 1.0040E+00 9.9977E 01 3.3764E 08 5.3500E-02 1.8064E-09 229 Qs2 2.2525E 04 1.0363E+00 9.9977D 01 2.9322E P 6.1605E-03 1.8064E-09 230. W93 2.0532E-04 1.0166D 00 9.99NE 01 1.3474E 07 1.2220E-02 1.6466E-09 231. 006 2. 0087E - 04 8.1042E 01 1.0003D 00 -1.5224E-06 1.356DE-03 1.6109D 09 232. MLF 1. N63E-04 1.0000E+00 0.0000E+00 0.0000D 00 1.0000E+00 1.4405E-09 233. PRA 1.7682E-04 9.0528D 01 1.0002E+00 ~7.6117E 07 2.0010E-03 1.4180D 09 234 MSF 1.7061D 04 1.0000E+00 0.0000'U00 0.0000D 00 1.0000D 00 1.3682E-09 235. RE8 1.6108E-04 1.0078E+00 9.9984E-01 0.3792t-08 ?.0250E-02 1.2918E 09 236. OR5 1.5710E-04 1.4181E+00 9.9984E 01 3.3542E-06 3. 7560E-04 1.2598E-09 -

237. AFA 1.5682E-04 1.0369D 00 9.9984E-01 2.9694E-07 4.1872D 03 1.2576E-09 238. Cl2 1. 4977E -04 1.0087E + 00 9.9985E-01 7.08 W 08 1.6960E-02 1.2010E-09 239 CA3 1. 4745 E - 04 1.034'2E+00 9.9985E401 2.T.'51E 07 4.2610E-03 1.1825E-09 240. PA1 1.4410E-04 1.0002E v00 9.9986E-01 2.83375-09 4.0780E - 01 1.1556E-09

TABLE 7-1. Split Fraction importance for Largo, Early Containment Failures and Bypasses MODEL Names Bv2LYL2 Split Fraction Inportance for Group r LECFBY sorted by importance Croup Frequency = 8.0195E-06 i 16:31:22 26 AUG 1992 Pa9e 5

...... SF hame... Inpor t ance. . . . . Ach ievement . R educ t i on. . Deri vat i ve. . $F Val ue. . . . . . . Frequency. . . . . .

241. C11 1.4177E- 04 1.0273E + 00 9.9986E 01 2.2004E 07 5.1670E 03 1.1369E 09 242. AW1 1.3909E-04 1.2989E+00 9.9986E-01 2.3981E-06 4.6512E 04 1.1154E-09 243. PRH 1.3640E 04 1.0004E+00 9.9989E-01 4.0486E-09 2.1240E-01 1.0938E 09 244. SA7 1.2098E-04 1.0077E +00 9.9991E-0* 6.2205E-08 1.1740E-02 9.7019E-10

?45. $8J 1.2098E-04 1.0033E+00 9.9988E-01 2.7791E-08 3.4910L-02 9.7019E 10 246. C2T 9.5981E-05 1.0959E+00 9.9990E 01 7.6972E-07 1.0000E-03 7.6972E 10 247. L27 9.5981E-05 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 7.6972E-10 746. ASI 7.9922E 05 1.0079E+00 9.9992E 01 6.4093E-08 1.0000E-02 6.4093E-10 249. OF1 6.9267E-05 9.9520E-01 1.0000E+00 -3.8578E-08 1.2100E-03 5.5549E 10 250. SA5 6.3032E 05 1.0008E+00 9.9999E-01 6.7637E 09 1.3910E-02 5.0548E-10 251. IA1 5.1323E 05 3.6870e 01 1.0002E+00 -5.0645E 06 3.4241E-04 4.1158E-10 '

252. SBE 4.9633E-05 1.00 %E+00 9.9995E 01 5.2345E 09 7.4390E-02 3.9803E 10 253. FB5- 3.8593E-05 1.0012E+00 9.9996E-01 9.6309E-09 3.2140E 02 3.0954E-10 254. EB3 3.5644E-05 1.0014E+00 9.9996E-01 1.1285E-08 2. 53."r - 02 2.8584E-10 255 182 2.5281E-05 1.0478E +00 9.9997E-01 3.8348E-07 5.28tuE 04 2.0274E-10 256. TT2 2.1019E-05 1.0000E+00 0.0000E+00 0.0000E+00 1.0000E+00 1.6856E-10 257. L3C 1.8478E-05 1.0000E*00 0.0000E+00 0.0000E+00 1.0000E+00 1.4818E 10 258. C3C 1.8478E-05 1.0000E^00 9.9998E-01 3.8996E-10 3.8000E-01 1,4818E-10 259. H3C 1.8478E-05 1.0000E+00 0.0000E+00 0.0000E+00 1.00003 00 1.4818E-10 260. HH6 1.8215E-05 0.0000E+00 9.9998E-01 0.0000E+00 6.7642E-07 1.4607E-10 261. 007 1.7420E-05 9.5973E 01 1.0001E+00 -3.2349E-07 1.6470E 03 1.3970E-10 262. SBA 1.7203E-05 9.9995E 01 1.0000E+00 -4.0083E-10 3.5820E F 1.3796E-10 263. sBC 1.5854E 05 9.9753E 01 1.0000E+00 -2.0053E-08 1.3550E- 1.2714E-10 264. CCG 1.5537E-05 1.0371E+00 9.9999E 01 2.9778E-07 2,8030E-04 1.2460E-10 265. RT4 1.5175E-05 0.0000E+00 9.9999E-01 0.0000E+00 4.3000E-06 1.2170E-10 266. SLI 0.0000E+00 9.9372E 01 1.0002E+00 5.1973E-08 3.0970E-02 0.0000E+00 267. CC1 0.0000E+00 0.0000E+00 1.0000E+00 0.0000E+00 2.8S63E-05 0.0000E+00 2M. AF7 0.0000E+00 9.9963E 01 1.0000E+00 -2.997BE-09 2.2947E-04 0.0000E+00 269. MS1 0.0000r 40 9.9381E 01 1.0000E+00 -4.9671E-08 7.1010E 04 0.0000E+00 270. AFC 0.0000c+00 9.9972E-01 1.0000E+00 -2.27400-09 4.86752-04 0.0000E+00 271. PRI 0.0000E+00 9.9987E-01 1.0000E+00 -1.1944E 09 1.0200E-01 0.0e00E+00 272. CC7 0.0000E+00 9.9994E-01 1.0000E+00 -4.9264E-10 2.5825E 04 0.0000E+00 273. CC4 0.0000E+00 0.0000E400 1.0000E+00 0.0000E+00 4.0554E-05 0.0000E+00 274 CC2 0.0000E+00 0.0000E+00 1.0000E+00 0.0000E+00 3.1228E-05 0.0000E+00 275. OF2 0.0000E+00 9.9983E-01 1.0000r.+00 -1.3919E-09 3.3130E-04 0.0000E+00 276. PRK 0.0000E+00 9.9979E-01 1 G000E+00 1.7016E-09 2.0170E-03 0.0000E+00 2 77. LSI 0.0000E+00 0.0000E+00 1.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00

< 278. TT3 0.0000E+00 9.9996E-01 1.0000E*00 -2.9063E 10 1.6640E-02 0.0000E+00 279. TTI 0.0000E+00 9.8300E-02 1.0000E+00 -7.2315E-06 5.0560E 05 0.0000E+00 280. BY1 0.0000E+00 0.0000E+00 1.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 281. 050 0.0000E+00 0.0000E+00 1.0000E*00 0.0000E+00 0.0000E+00 0.0000E+00 282. TTS 0.0000E+00 0.0000E+00 1.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 283. ME) 0.0000E+00 0.0000E+00 1.0000E+00 0.0000E+00 0.0000E+00 0.000CE+00 284. SP1 0.0000E+00 0.0000E+00 1.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 285. AF8 0.0000E+00 0.0000E+00 1.0000E+00 0.0000E+00 1.2482E-05 0.0000E+00 286. MSO 0.0000E+00 0.0000E+00 1.0000E+00 0.0G00E+00 0.0000E+00 0.0000E+00 287. C11 0.0000E+00 0.0000E+00 1.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 288. 008 0.0000E+00 9.7667E-01 1.0001E+00 -1,8755E-07 2.2960E 03 0.0000E+00 289. C21 0.0000E+00 9.9509E-01 1.0000E+00 -3.9380E-08 2.0000E-04 0.0000E+00 290. IA2 0.0000E+00 6.6336E 01 1.0001E+00 -1.0964E-06 5.8650E-04 0.0000E+00

.291. Co1 0.0000E+00 9.996CE-01 1.0000E+00 -3.2138E 09 1.1950E-03 0.0000E+00 2N. PIS 0.0000E+00 0.0000E+00 1.0000E+00 0.0000E+00 0.0000E*00 0.0000E+00 293. PRO 0.0000E+00 0.0000E+00 1.00000+00 0.0000E+00 0.0000E+00 0.0000E+00 294 PR2 0.0000E+00 9.9298E 01 1.0000E+00 -5.6298E-08 5.2240E-04 0.0000E+00 295. CS6 0.0000E+00 9.9987E-01 1.0000E+00 -1.0699E-09 3.5740E-02 0.0000E+00 296. P!2 0.0000E+00 8.4886E-01 1.0040a 00 -1.2438E-06 2.5470E-02 0.0000E+00 297. DC3 0.0000E+0C 9.9998E-01 1.0000E400 -1.5598E-10 5.0000E-02 0.0000E+00 298. CSS 0.0000E+00 9.9994E-01 1.0000E+00 -4.8821E 10 4. 7728E-04 0.0000E+00 299. PRS 0.0000E+00 9.9905E-01 1.0000E+00 -7.7924E-09 2.5930E-02 0.0000E+00 300. IC2 0.0000E+00 9.VD0& O1 1.0000E+00 -4.0889E-08 3.2777E-04 0.0000E+00

. . . . . ... ..- - . ... - . ~ . - - . .. - - .. ~ . . . - - . . .

TABLE 7-1. Split Fraction importance for Large, Early Containment Failures arid Bypasses MODEL Name! BV2LVL2 Split f raction Iqnrtance for Group 1 LECfBY Sorted by Igjortance Cro @ Freq xncy = 8.0195E 06 ,

16:31:49 26 AUG 1992 Page 6

....., SF hame... I mortance.. Achievement. Reduction.. Derivati m .. SF Value..... . freq;ency... .

301. 101 0.0000E+00 9.4026E 01 1.0000E+00 -4.7919E-07 1.8347E 04 0.0000E + 00 302. .PR3 0.0000E+00 9.9321E-01 1.00WE+00 5.4508E-08 5.1040E 04 0.0000E+00 303. NH7 0.0000E+00 9.7979E-01 1.0000E+00 1.6228E-07 1.3939E-03 0.0000E+00 304. IP1 0,0000E+00 0.0000E+00 1.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 305. sal 0.0000E+00 9.9748E 01 1.0000E+00 2.0446E-08 1.2250E-02 0.0000E+00 306. CD3 0.0000E+00 9.9857E 01 1.0000E+00 -1.1526E 08 6.4980E-03 0.0000E+00 307 CD1 0.0000E+00 9.95226 01 1.0000E+00 -3.8356E-08 9.127,0E-04 0.0000E+00 308. CDs 0.0000E*00 0.0000E+00 1.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 ,

309. L12 0.0000E+00 0.0000E+00 1.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 310. CCD 0.0000E+00 9.9794E-01 1.00f.0E+00 -4.9267E-10 2.7463E*D4 0.0000E+00

!!1. CCJ 0.0000E+00 9.9455E 01 1.0000E+00 4.3740E-08 3.4410E-04 0.0000E+00 312. 009 0.0000E+00 9.9N.4 E -01 1.0000E+00 -4.5324E--09 1.6030E-03 0.0000E+00 313. P11 0.0000E+00 7.45740-01 1.0000E+00 2.0394E 06 1.81?0t 04 0.0000E+00 314. 151 0.0000E+00 0.0000E+00 1.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 315. RTS 0.0000E+00 0.0000E+00 1.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 316. RT5 0.0000E+00 8.8190E-01 1.0001E+00 -9.4756E-07 5.1510E 04 0.0000E+00 317. 003 0.0000E+00 9.9786E 01 1.0000E+00 -1.7213E 08 1.2900E 03 0.0000E+00 318. Ors 0.0000E+00 0.0000E+00 1.0000E+00 0.0000E+00 0.0000E + 00 0.0000E+00 319. Cs1 0.0000E+00 9.5622E-01 1.0000E+00 -3.5115E-07 5.4721E-05 0.0000E+00 E

9 i

Ouestion 8. a) Provide a discussion of the ignition sources and limits used in the hydrogen combustion analyses.

Vere sensitivity i

' studies performed to evaluate the impact on the IPE results, due to the uncertainties of the ignition limits used?

b) Provide the information requested in tWREG-1335 (Section 2.2.2.1), i.e., accurate but simple tepresentations of the containment showing the instrument tunnel, reactor cavity compartment, loop compartment (s), annular compertment(s) and upper compartment, with specific identification of potential reactor release pointu and vent paths indicated. Estimates of compartment free volumes and vent path flov areas should also be ptovided. Please address specifically how this _

information is used in the assessment of hydrogen pocketing and detonation.

c) Discuss the plant-specific effects on containment integrity and equipment survivability due to local detonations. The discussion should cover likelihoods of local detonation and potentials for missile generation as a result of local detonations.

d) In Page 4.6-19 on Top Event 20 - Late Burn of Cembustible Gases, the IPE states that, "If the containment is not inerted..., hydrogen burns are assumed to be assured in this time period; however, these burns are not expected to challenge the containment." Please discuss briefly the reasons for not expecting the hydrogen burns to challenge the containment.

Response 8. (LATER) e Question 9. NUREG-1335 recognizes the importance of considering uncertaintles in the accident progression and CET quantification. EPRI recommends that sensitivity studies be performed by MAAP users, which could provide qualitative insight into understanding uncertainties. Please specafy what specific revision (s) of the MAAP-3.0B Code were used for the BV-2 PRA. Address the Gabor Kenton & Associates report prepared for EPRI (" Recommended Sensitivity Analyses for an Individual Plant Examination Using MAAP-3.0B'). In particular, with respect to Appendix A of the report, indicate for each of the 78 indicated parameters:

a ,

(

i 9

a) ~ If the. recommended value(s). vere used, b) If value(s) other than the recommended value(s) vere used, and the basis for_the choice; or If the 1 sensitivity study indicated was not -performed, i c) provide the reasons for-omitting the recommended analyses.

+

Response 9. Calculations were performed vith MAAP-3.0B, Revisions 14 and 16.

The analysis for Surry described in NUREG-1150 was_used as the basis for the PRA quantification and no sensitivity studies were q performed by DLC.

Ouestion 10. Discuss briefly the quantification -results for each containment

~ isolation failure mode (including common-mode failure).

Response 10.. (1.ATER)

Question 11. The Table oa Pages 2.4 1 and 2,_ identifying valk-throughs,:does not explicitly identify any specific system valkdowns by analysts to account for the impact of plant modifications-prior'to_valk-~

throughs, or modifications conducted during the. time frame.of-the-1PE. In -addition, in the list of information sources (Table' .

2.4-1), there-is no mention of Engineering documents used to-control plant modifications.

What is the " FREEZE" date- used for the plant configuration analyzed in the IPE?

Since there is usually a lag _ time between documents'that request plant modifications'and revision to documents thatLvere used 'to base-the models on, _ vere any modifications incorporated in.the plant that were being done_just -before trna freeze date that vere not incorporated-in the medel?

Response ll, (HATER)

T-4 l

4

= , - .--. -- , , ,. .+o - s . = . -

--6w .

_. , . -. --- - ~ -. ..- -- . . . -

~

4 - _ _

u i O

Question 12. Duquesne' Light Company (DLC) has stated that the'PRA for B5- *s originally performed _by Plckard, Love and Garrick, Inc._'(PLG; and-Stone & Vebster Engineering --Corporation. (3&V),- and .that DLC _

personnel- incorporated plant-specific Ldata _ and _ requantified the However, Table 5.3-1 shows minimal involvement.of the-DLC-model.

organization-in reviewing the quantification.

Since expertise'in.the methods is -important to ensure that the ~ '

techniquer are correctly. applied, please discuss DLC' personnel participation in the update of Jhe' BV-2 Model and the completion '

of tlie Beaver Valley Unit 1 (BV-1) PRA. ,

Ret.ponse 12. ( LATER) .

Questien 13. Section 5.4 resolution of comments indicates thTt the review comment / resolutions vsce documented in accordance with the PLG-0223, " Quality Assurance Program". Does conformance with this program comply with the- DLC in-house requirements' for documentation?

Vill-comment / resolution for'BV-1 use PLG's program or DLC's?

Resoonse 13. The PLG Ouality Assurance Program requirements for documentation.

meet or exceed. the .DLC' program requirements. BV-1 Comment resolution; vili be documented per.the DLC-program.

Questioa 14. Table 3.1.1-2 identifies Instrument- Air. as being captured'under Initiating Event "TLMFV"' . However, there is no discussion-in e - Section 3.1.1 '(Initiating Events) which -indicates- that - the_ -- ,

frequency of -this -event: vas added to the "TLMFV". t' lea se '

identify the frequency of Loss of Instrument Air-(LOIA),,and the-i.e.. whether the frequency was obtained fromLgeneric or~

source, plant-specific data.'

Res'p~onse 14. Loss'of Instrument Air- (LOIA)' was not explicitly added to_the Total Loss of Main Feedvater (TLMFU) Initiating Event frequency because the: frequency of fLOIA is -a small percentage of TLMFU,

- The frequency of' LOIA from gen reported in:Ill Reference 3.3.1-3 is 2.0 -x. -

10~gricpersources year. .This frequency corresponds _to total Losses of' Instrument- Air._ It l's seen to be s very small compared to the Total-Loss of Main Feedvater frequency ~

of 0.12 per year. Partial losses of air to individual components-(e.g.,-NFU valves) are alr_ j accounted for'in the frequencies '

assigned to such - initiating events, i.e., such events are ,

included in the derivation of initiating event frequencies for j partial and; total losses of. Main Feedvater.

. 16:-

3

-. ,1 w+ -

f ,s n g --- o- -

g. v -q ~ .w w - ~, ,w- a- ,_ -m--r.+m ' - ,-,w -aA

Question.15. . Discuss-the_ impact; of LOIA on front line and support' systems designed to altigate the effects of failures sustained-during or after a trip, and the rationale used in combinAng the event with TLMFV as opposed to treating it as a unique Initiating Event.

Response 15. The impact of LOIA on systems la described in IPE Section-3.2.2, dependency _ tables. Both the intersystem dependencies associated with instrument air and the containment instrument air systems are identifded. The first page of the Support-to-Frontline System Dependency Table, Table-3.2.3-2, was inadnertently omitted from the submittal. This first 'page of the table is. attached as Page 18 of this submittal.

The loss of containment instrument air vould cause the air-operated containment isolation valves inside containment to-lail to the " fail-ssfe" position. As indicated in Table 3.1.l-2, this i vould cause the CCP isolation -valves for the RCP thermal barrier cooling to fail closed, but RCP seal injection and RCP motor cooling would remain available. Therefore, loss of this system-

- vould not cause a plant trip.

The immediate' impact on the plant of a loss.of Instrument Air would be closure of the feedvater control valves, the condenser:

steam dump valvtu, the isolation of letdown, and_the loss of control for1ncrmal pressurizer rpray. The'MSIVs vill eventually close when their accumulators are exhausted; i.e., after' approximately thirty (30) minutes.

The most significant impact of a -lors of Instrument. Air cm systems designed to mitigate a plant' trip is _the, loss 'of Hain Feedvatet and the Main Condenser. The TLHFV Initiating Event.

includes the same impact on . main" feedvater and tlue condenser:as the LOIA. Treating LOIA as a unique. Initiating Event would add a' '

- minor contribution..to the total _. core damage trequency. .This conclusion is based on the fact that-the Auxiliary'Feedvaterfflov valves and the: pressurizer PORVs nre'not dependent on compressed air at_ Beaver-Valley Unit 2, as they are at some other_ plants, i

a H

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1, n - - - - _ - _ _ _ _ - - - _ _ _ _ . _ _ _ - - _ . - - . _ - - . - - _ _ _ ._

Question 16. Discuss the technical basis, or provide a reference for

" assuming" that "very small LOCAs" (less than 1/2 in. equivalent diameter) are within the makeup capacity of the notmal charging system and, therefore, these events could be " conservatively" included with "r. mall LOCA" laitiating Events (Page 3.1-7 in Section 3.1.1).

Response 16. The referenca ?.o conservatively include very small LOCAs within the small LOCA Initiating Event category refers te only those events which lead to an immediate plant trip. The accident s e g e_, e model for small LOCAs is conservative for such cases, because it assumes that recirculation from the containment sump vill eventually be required. By contrast, in the analysis for Surry in NUREC/CR-4550, for very small LOCAs, credit was taken _

for cooling down and going on closed loop RHR as an alternative success path to that of recirculation from the sump. The omission of this success path makes the current analysis conservative for very small LOCAs. The PRA Team at Duquesne Light Company is unaware of any small or very small LOCA events at a U.S. nucleat plant, which resulted in the need for recirculation froa the containment sump. Instead, all such LOCAs J

vhich have occurred to date, have been successfully mitigated by RCS depressurization and successful closed loop RHR cooling.

For very small LOCAs which do not lead to an immediate plant trip, the leak rate must be within the capacity of normal charging; otherwise, the net loss of inventory vould lead to a plant trip. Normal charging is designed for mitigation of RCS breaks up to 3/8" in diametet. For very small LOCAs, less than this size, the operatocs vould initirte a controlled, manual plant shutdown, which is nor considered a plant initiator.

Question 17. Discuss the impact of LOCAs or Steam Line Breaks on mitigating systems as Initiating Events.

Resporse 17. (LATER)

! Question 18. Unlike the information provided for component data, there is no I discussion or identification of plant-specific data used in the "opdating process" for Iniciating Events.

1

. ... . . +-. , - - -. ~. - _ , - . .- _- - n.. . . . . . . . - -

f p ,

a) Provide a ]isting of the .frequencyLfof Initiating Even's-(e.g.,- Turuine Trip,: Reactor: Trip, Loss of Offslte Po'ver/Hain - ' P.V. lins t rument - Air) that were obtained-from  !

plant operating experience, as Lopposed to .those nrrived at- ,

'through system analysis.

b) Include a' discussion. of the. Updating process for the ,

Initiating Events and a discussion of the frequency of: those-events whose total frequencyf is made up of multiple events.

(e.g., TLMFV).

' Section 1.1-states that in 1991 DLC developed'a plant-specific. .

database and used- it te- requantify the Unit 2- PRA model.

However, Section 3.3.2.1 indicates 'that.the plant-specificJdata presenttd and discussed 'in Section 3.3.2 was. coll'ected--between 1

-11/87 and 12/88.

c) Has the data presented been captured through 1988 or 19917 d) -Is the PRA medel quantified ' using plant-specific data different from what is presented in the IPE?

p e) If the PRA model has' been quantified-using' planti specifici -

L data through 1988, please provide a discussion of any' plans y

to update the database andl the PRA model, ar:1 any component failures or Initiating Events occurring since 1988,-which1-would impact the IPE results.

Response 18. (IATf2) .

3 l

i Question 19. Generle Letter 83-20 and- ~NUREG-1335, request that- the .IPE.

submittal provide:a list =of all generic plant-data.forfequipment- "

and Initiating Events, including origin and method of analysis. .

Since Section 3.3.1 Indicates that for a majori ty of -components

! the generic-component failure rates were taken fr6m'" Database;ior PR/s of Light'. Water Nuclear-~ Power' Plants",. PLG-0500,- 1989, and?

since this document is not in the,public domain, please provide..a e listing of the generic component f ailure rates used f or - the' llV -

L IPE'(or the PLG database used in the. analysis)'.- Thisilist/should:

include those generic values used.as a basis for upda'ted values-. .

Response 19. (LATER) r- -aki- w , , . . - - - - --4,w.--+u-w-,,,>s n -,--..-+ ty Me, .

ia - v e + =- &nw rrr-ea=+ r r

• ww w w o-=* *

• w+ e Mch'*'ve- i 1 ' vir m .p--+*~-4- *kyd 64e%*-"'*-

, , ,.~ .- - . . -. -- n- - . .- . . . . - - -. . - - . .

T

. l c

'?.

. Question 20. -In-verifying that'the submittal contained a Idsting of Initiating Event frequencies, it was noted d.

- That the systera Initiating Event frequencies in Table 3.1.1-3 vere different from the~ values provided in Table 3.3.5-2.

A constant vslue is displayed for all ' parameters of the distribution for Initiating Events. VAX, VBX, and VXE.

Explain these apparent discrepancies, and. provide a discussion

-regarding any possible impacts on the results presented'in the IPE,-due to these discrepancies.

- Perponse 20. . Table 3.3.5-2 used Deaver Valley Unit 2 plant-specific data for obtaining the Initiating Event frequencies derived from system models, while Table- 3.1.1-3 used PLG generic component failure a rates. The values from Table 3.3.5-2 are correct and vere the ones used-to quantify the Ev(nt Trees. Table 3.1.1-3 should have been: updated to reflect these, values. ,

f Vhen developing the Service Vater Sys tem _ models f or Riskman,' it vos necessary to break the system .up into sevecal different smaller Top E/ents in order to generatt the cutsetc. The~ values for the VAX, VBX, and VXB initiators were derived;from equations

' initiating uncertainty-that used- .mean valuer from_ the, distributions.for these smaller Top Events, and are, therefore, or.ly point values based on the means of the smaller Tops-g Initiating Event frequencies. This - however, has no effect on l the core ' damage frequency, since Riskman only uses the mean values of the Iritiating . Event distributions to quantify the o Event Trees.

Question 21. The Internal Flooding Analysis indicated 'tt at mitigating features l such:ss_ redundancy 'and separation vere considered. However, l

actual opetating experience has demonstrated that separate rooms L -do not necessarily provide . protection because of drain systems i/ that are plagged. or allov backflow, _ unsealed doers ', or ll maintenance actions or situations.- Discuss hov consideration-was-h given to these conditions in the flooding analysis,-and how they l impacted theLchoice or quantification of Initiating Events.-

l.

I' l

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impact Response 21. The choice. -quantification and' -of--internal- flood Initiating Events is based on . evaluation of: actual flood sources' at each location, .as well 'as potential- propagation into.the.-

location. . In :considering propagation, the. numberLand size of drains vas considered, whether there are seals on the door was considered, and:vhether the' door -opens. out of-the-room or-into the room was considered. In addition, backflow through drains was reviewed. These considerations' vere checked in the field during walk-throughs. In general, ifithere were several drains .

.in a room, it was assumed that most vere functional (unplugged) and a large flood nource- vas. required to impact' equipment.

Maintenance actions were' considered with. regard to flood-Initiating Events and are included- in the Initiating Event database.- Maintenance was not explicitly considered with regard to open doors or plugged drains. Most ' ars are fire doors which require frequent inspections or fire .tches when open. Door seals vere qualitatively considered with regard to .the_mostL However, door seals-likely propagation path for smaller. floods.

-alone vere not _ .the basis for screening out propagation to an-adjoining location.

As an example, the Cable Vault Flood. Initiating Event (CVFL) is based on a flood that occurs in Room CV-2 where there is only-one (1) floor drain. The flood collects in this room, failing.one train of MCCs, and eventually fails the' door that opens into Room +

CV-1. The flood is ar.4med to fail redundant MCCs in CV-1. A potential ~ flood event .

CV-1 is assumed to be enveloped by the.

initiator in CV-2 because there are several drains in CV-1, there

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is less flood potential in CV-1, the area is much larger in CV-1, and the more likely propagation path is'into stairvells and to the pipe tunnel. There are doors that open into CV-1 fromLthe Emergency switchgear Room, however, the drains and floor areas-in the Switchgear rooms were. judged to :be sufficient to handle leakage into the rooms.

. ' Question 22. Sections 1.4 (Summary of' ' Major Findings), -3.3.8 -(Interior Flooding Analysis), and 4.8 .(Back-End Results) do - not characterize the impact of internal. flooding events, either asi important or not significant.- However, Figure 4.8-1 shows that Control Building Flood (CBFL) events- contribute.approximately 6.6% of the "small early containment failures or bypasses", which- .

is the third-largest contributing initiator.

Provide a discussion of the~ flooding analysis addressing whether the process yields non-conservative, realistic or conservative:- 17 estimates, and DLC's. assessment 1 of the IPE conclusions in light-of this, especially vith regard to CBFL.

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Response 22. Section 1.4 is a brief . executive summary of tiue major findings which did not include a summary of internal flood contributions.

However,- Section "1.4 -does - describ. the -dominanti core damage _ >

sequences (Level 1) and early large release sequences (Level 2),

which. indicate that internal floods are-not dominant sequences.

Section 3.4: summarizes the Level 1 results, and as shown in this section, internal floods provide a minor- contribution to core damage frequency. .

Section 3.3.8 provides a qualitative summary of the internal flood analysis, the resulting initiators identified- from the- ,

study, and insights from the study.- The final-results from' including tha initiators in the overall. accident sequence model are included in Sections 3.4 and 4.8.

Section 4.8 indicater that internal floods contribute,Ibut do not dominate releases. CBFL's contribution to- small early containment failure as based on a service water flood:in the Fan Room next to the Hain Control Room, and a fire water flood in-the  :

Cc.ble Tunnel. Btth floods are assumed to propagate to Elevation 707 of the Control Bu!1 ding which houses process racks and'other-electrical equipment. This vill likely- cause a plant trip and could spuriously operate equipment. A detailed-analysis of!the impact was not performed. It vas assumed that_ solid state protection-vould fail after the plant trip and, if-thefoperators fail to initiate safety inj ec t ion , they would; also fail.to isolate containment (small early release _ in Level 2), resulting in core damage. There are potential-conservatisms.in that the service water flood vould most -likely propagate.throughfdouble doots in the Fan- Room to the outside. However, it vas.

cons.evatively assumed that the flood .vould push the stairvell door open to Elevation 707. Credit was ;given to operator detection and-isolation for the service water flood. This was not the- case for. the fire._ vater flood.

Another potential conservatism could be the human error rate used for respondir.g. to this flood. As mentioned above, a: detailed analysis m the impact.of the flood was not performed, and'a detailed analysis of the timing of operator. respor.se was not; performed. 1The

. conditional probability of operator'. failure to initiate safety-injection Event was and isolate'103he 1.04 x .

. containment This process -used for=this' Initiating-is_ considered -to be conservative since the quaranteed failure of operators to isolate containment ef ter- failure of SSPS results_in_a.large percentage of'its end-states to be assigned to the small containment bypass-release group. Therefore, CBFL shows minor contributionito core damage frequency, bit indicated some importance to the Release Category Group II frequency.

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- Ouestion 23. It is _noted -that in the discussion of Top Events.DO, DP, IE, ID, IV and IY, the time that. power is specif3ad to ba available is dependent on "!!ow Long The- Batteries Last", and 1s-identified-ns either 3.5 or 8_ hours. Ilovever, the system's description for DC El etric Power (Section 3.2.1.2.9) states the assunption that-following a loss of AC power- DC power is evaluated for a mission time of just 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. -The BV-2 FSAR Chapter 8 also indicates that the life of the batteries under design loads is 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.

Discuss the technical basis, o r' provide a reference for the:

assumption of battery life longer than 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />,- as relates -to_ the Top Events above. 'i Response 23. (l.ATER)

Question 24. In Section 31.3.1 (General Transient /Small LOCA Tree) under the description provided for Top Event CI (Containment Isolation),.a-discussion is provided which relates to .the Seal LOCA Model, llovever , the discussion and -Section 3.3.3 (liuman Failure Data),

which is referred to therein as containing the Seal LOCA Model, do not explicitly describe the Model used for the IPE submittal.

Provide a discussion of the Seal--LOCA Model', as used in the BV-2 submittal including the various leak rates, timing of seal-failure, and the probability-of their occurrence with and without-the seal return line isolated. _

In addition, discuss the _ impact on Core Damage Frequency.(CDP), ,

if the assumption is incorrect that the lov pressure seal leakoff pipe vill withstand high- pressure on failure of_the_ number one-seal.

Response 24. The General Transient /Small LOCA_ Event -Trees are described'in Section 3.1.3.1. Section 3.3.3 provides a summary of-the electric power recovery approach. The electric power recovery results are also summarized in Table 3.3.3-11.

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t The seal LOCA model is described in Refetence 3.3.3-5, Appendix B, Section B.2. The specific seal LOCA leak rates, used as a functiun of time after loss of seal cooling, are provided in Table B.2-1, copy attached. The model for the pump seal leak rates was based on the four-loop RCP seal LOCA study of Reference B.2-4 for Vestinghoase RCPs with the old style 0-rings that existed in the Beaver Valley RCPs at the time of the study, and scaled by the number of loops at Beaver Valley to reflect the leak rates per pump. The flow rates listed in GPM define the effective flow area, assuming an RCS pressure of 2250 psig. The time to core uncovery for a given leak rate, which varies with time, was camputed accounting for the decrease in RCS pressure as the accident progresses and includes the effects of the operator action to depressurize the Steam Generators. Reference B.2-4 is __

as follows:

NUREG-11560, Report Reactor Coolant Seal LOCA, "Results of Expert Gpinions Elicitation on Internal .Cvent Front-End Issues for NUREG-1150: Expert Panel", NUREG/CR-5116, Volume 1, Sandia 88-0642, April 1988.

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Table B.21. Seal LOCA Flow Rates (GPM) per Pump with and without Prl' ry Depressurization-Time after Station Blackout (hours)

Cumulative Probability 0 1.0 1.0-1.5 1.5-2.5 2.5-3.5 4. 5- 5.5 5.5+

Probability (OPm) (gpm) (gpm) (gpm) (gpm) (gpm) 0.2712 .2712 21 21 21 21- 21 21 0.0151 .2863 21 -2! 21 61 61 61 0.0161 .3024 21 21' 61 61 61 61 0.0181 .3205 21 61 61 61 61 61 0.0120 .3325 21 61 108 108 108 108 0.0059 .3384 21 61 108 108 120 175 0.1120 4504 21- 61 250 250 250 250

-0.0136 .4640 21 120 250 250 250 250 0.5302 .9942 21 250 250 250 250 250 0.0016 .9958 21 308 308 308 -308 308 0.0042 1.0000 21 480 480 480 480 480 l

NSWIN0043.042591 B.2-18 PLG

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Questio! 25. Section 3.4.3 of the submittal provides information on the importance of the_ five (5) systems that perform Decay Heat Removal (DHR) function , and 'i ndicates- that no particular-vulnerabilities havo N een found. However, the-values provided in Table 3.4.3-1 as the " percentage of CDF in which event is failed",.show a_non-negligible contribution for.some Top Events due to loss of support (e.g., HFF 9.7% and AFF 20.2%). A value for HHF (High Head Safety Injection. Pumps, Suppor t Unavailable) is not provided; however, Table 3.4.2-1 shows the percentage of CDP vith this split fraction as 62%.

Generic Letter 88-20 and Appendix 5 therein, indicate that support systems are important to the DHR Function and' suggests that they be considered in the search for DHR related vulnerabilities. Therefore, please discu'* the impact of support systems on these five (5) systems, d4P _centiating between the-contribution from Loss of Power (LOSP and BVX), and other '

supports such as Service Water, Primary Component Cooling Vater and Instrument / Containment Instrument.

Response 25. (LATER)

Ques tion 'h5. Table 3.4.3-1 shows the percentage of CDF in which the Event AFF is failed as 20.2% (3.84E-5) identifying it as due to Large Flood in _ Safeguards Area. However, Figure. 3.3.8.2 (comparative contributions to core damage from floods) shows that only 16.6%

of the CDF from all floods (7.32E-6 _x 0.166 = 1'22E-6) is due to .

1 safeguards floods. Provide .a discussion of this apparent discrepancy and other- values in -the . table which may likewise impact the results of the IPE ,

Response-26. (LATER) 1

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Question 27. As indicated in the paragraph on Feed and Bleed Cooling, the BV-2 Edesign " minimizes the frequency of sequences involving failure of AFV and Bleed and Feed Cooling, relative to other PVRs previously studied", because of credit -taken_ for realigning the electric motor-driven MFV: pumps. It vould appear that this capability is of-significant benefit to BV-2.

Discuss the benefit' derived from- this capability'in terms'of CDF vith and without this capability. In concert with this, please provide the. benefit-derived from-the capability to feed.and. bleed- 1 upon loss of all secondary cooling- (i.e., MF and AF) in terms of CDP vith and without this capability.

Response'27. (LATER)

Question 28. Provide a list of the types of Initiating Events identified as "other" in Figure 3.4.0-2, and .the breakdown of their-contributions to CDP.

Response 28. See attached-Table 28-1.for the breakdown on all of'the Beaver-Valley Unit 2 Initiating Event contributions to the total core damage frequency. .

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TABLE 28-1. Beaver Valley Unit 2 nitia2ing Event Contributions initiator Percentage of initiator Percentage of Initiator Core Melt Total Core initiator Core Melt Total Core Frequency Melt Frequency Frequency Melt Frequency LOSP 2.86E-05 14.84 SGFL2 3.81 E-07 0.20 BVX 2.35E-05 12.17 LCVA 3.*5E-07 0.18 SLOCl 2.15E-05 11.18 VSX 3.44E-07 0.18 SLOCN 2.06E-05 10.69 TLMFW 3.37E-07 0.17 AOX 1.48 E-05 7.67 SLBD 3.34E-07 0.17 EpPX 9.31 E-06 4.83 VPFL 2.90E-07 0.15 inX 7.24E-06 3.76 MSV 2.84E-07 0.15 IWX 7.23E-06 3.75 LCV 2.84E-07 0.15 SGTR 7.21 E-06 3.74 ELOCA 2.65E-07 0.14 IMSIV 4.81 E-06 2.50 AOXA 2.29E-07 0.12 TT 4.56E-06 2.37 LPRF 2.23E-07 0.12 LB2A 4.25E-06 2.21 LB2AA 1.90E-07 0.10 CBFL 4.05E-06 2.10 DPXA 1.85E-07 0.10 WBX 3.55E-06 1.84 DOXA 1.82E-07 0.09 DPX 2.88E-06 1.49 IBXA 1.70E-07 0.09 RT 2.52E-06 1.31 LOSPA 1.49E-07 0.08 MLOCA 2.12E-06 1.10 BPXA 1.37E-07 0.07 SGTRA 2.01 E-06 1.05 SLBC 1.35E-07 0.07 PLMFWA 1.90E-06 0.99 CX1 1.22E-07 0.06 PLMFW 1.56E-06 0.81 CPEXC 1.21 E-0 7 0.06

' ISI 1.53E-06 0.79 LPRFA 1.01 E-07 0.05 WXB 1.29E-06 0.67 lYXA 9.08E-08 0.05 AMSIV 1.26E-06 0.66 IRXA 8.15E-08 0.04 DOX 1.25E-06 0.65 IWXA 8.10E-08 0.04 WAX 1.20E-06 0.62 lYX 5.03E-08 0.03 ISFL 1.13E-06 0.58 IBX 4.97E-08 0.03 TTA 8.89E-07 0.46 TBFL 4.72E-08 0.02 -

LLOCA 8.52E-07 0.44 CVFL 4.32E-08 0.02 SGFL1 8.37E-07 0 43 WXBA 1.09E-08 0.01

_EXFWA 8.26E-07 0.43 WAXA 1.09E-08 0.01 EXFW 6.78E-07 0.35 CX1A 8.13E-09 0.00 ABFL1 5.36E 07 0.28 ABFL2 1.75E-09 0.00 SLB1 5,10E-07 0.26 WBXA 3.35E 10 0.00 TLMFWA 4.10E-07 0.21 3

j Question 29. The submittal identified core damage as having occurred when loss of core heat removal progressed beycnd the point of core uncovery, and core exit temperatures exceed 1200*F.

How many sequences were screened out because of this double c iteria? Discuss the impact on the resultant CDF obtained using this criteria.

Please address the following:

- The basis for the temperature chosen (1200 F).

- Do all sequences with the core uncovered go to core damage, or was there recovery prior to reaching 1200*F? ___

- Vould the CDF be significantly different without the 1200*F core exit temperature criterion?

Response 29. There vere no sequences screened out by application of the 1200*F criterion. The use of this criterion only marginally impacts the time available for recovery actions. If the 1200*F criterion was replaced by just core uncovery, some sequences vould increase in frequency by a slight amount to reflect the incremental effects of recovery between the time of core uncovery and the time of core exit temperatures reaching 1200*F. For typical sequences in which the 1200*F criterion was applied, there vould only be about fifteen (15) minutes after core uncovery until core exit thermocouple readings in the Control Room would reach 1200*F.

This estimate is based on MAAP analyses performed for Seabrook Station, as documented in the following reference:

Fleming, K.N., et al, " Risk Management Actions to Assure Containment Effectiveness at Seabrook Station", PLG-0550, -

prepared for New Hampshire Yankee Division of Public Service Company of New Hampshire, July 1987, Table 6-3.

While the use of the 1200 F criterion does not appreciably impact the core damage frequency in comparison with cote uncovery, this value was selected for consistency with the Functional Restoration Guidelines that form part of the Emergency Operating Procedures. At Beaver Valley, Functional Restoration Guideline FR-C.1, Inadequate Core Cooling, is entered when core exit thermocouple temperatures exceed 1200*F. See, for example, Fart 12 of Figure 3.1.1-2, the Event Sequence Diagram for Beaver Valley Unit 2. The actions in FR-C.1 vere not credited in reducing the frequency of core damage.

Because of the small incremental time between core uncovery and 1200*F core exit temperatures, the use of this criterion has no significant impact on the estimation of the CDF.

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Question 30. The EV-2 submittal has': identified loss _of EmergencycSvitchgear- .

Room I!VAC as a significant contributor- to CDF, 'due?.to the-relatively rapid rise in room temperatures that-vill exceed the qualification temperature of equipment in the- room. However, experiences of other. plants' have indicated.that temperature _ rise determined by testuon loss of HVAC isinot as rapid as determined by calculation. ,

The possible prediction by calculation -of- temperature rise significantly more' rapidly than might be experienced and could-c cause a distortion inl the -identification'of contributors to CDF and subsequent misapplication of resources. Is DLC giving consideration to verification of the rate of temperature rise.

determined for the Emergency Switchgear Room on loss-of HVAC,-to establish if the contribution from this event is appropriate?

Response 30. (LATER).

Question 31. Section 6.1 indicates that. the two (2) risk factors of merit that have been considered are CDF and early release frequency.; In

. addition, . Section 6.3.1 states that 'in order to determine-vulnerabilities the major. accident " CATEGORIES" vere evaluated -

along with top ranking sequences, a) . Provide the definition- of -vulnerability, -and describe-the process.used in conjunction with- the above to identify the vulparabilities as requested lby NUREG-_1335.-

'l b) Discuss the findings- related .to identifying _ potential vulnerabilities-vith respect' to- containment-failure or by-- .

pass, and assessing'any associated plant modifications.

c) Discuss the anticipated benefit (decrease' in-CDF or impact on release category), the ' rationale by which the listed option was chosen from the' potential options, anothe implementation for those "under respective timing, if i

review".

d)L -Discuss the considerationc given- to independent failure-of the Service Water Headers (VA and VB involved in 13.7% CDF,.

L p and in top- ranking : sequences. involving lsmall;LOCAs which I

contribute 21%'to CDP)~,- and the common check valve in the-l suction af the HHSI pumps 1 (VL-1,- involved in approxianately '

15% CDF, and also in top ranked sequences involving loss of l-vital bus and small LOCA)'as-vulnerabilities.

Response 31. _(LATER)

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-Question _32. Discuss.briefly the IPE results (including the contributions to-CDF) of any analysis related to a_ small break LOCA due to a stuck-open safety valve event if the PORVs are blocked off to stop any leakage. The discussion should address the percentage of time the PORVs are blocked off due to leakage and failures of operator actions to open the PORV block valve during accident conditions.

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Response 32. (LATER)

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