ML20237E225

Suppl & Revs to SE for Amend 173 for Pigrim Nuclear Power Station

ML20237E225
Person / Time
Site:	Pilgrim
Issue date:	08/26/1998
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20237E220	List: ML20237E217 ML20237E225
References
NUDOCS 9808310044
Download: ML20237E225 (10)

Text

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. Men q p k UNITED STATES j

t NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. - =1

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NRC EVALUATION RELATING TO CLARIFICATION AND CORRECTION TO NRC's SAFETY EVALUATION APPROVING AMENDMENT NO.173 PILGRIM NUCLEAR POWER STATION j 1

DOCKET NO. 50-293 After issuance of the staffs Safety Evaluation (SE) granting license Amendment No.173 on j July 3,1997, the licensee, by letter dated December 30,1997, identified a number of statements contained in the SE that they felt required clarification or correction. The licensee l identified the following SE statements with their associated c!arification or correction. 1 SE Statement. Pace 4. Paraaraoh 2. Item.11 j

" Initial relative humidity of 100 percent in the drywell, and 80 percent in the wetwell".

I Licensee's Clarification The statement should read, " Initial relative humidity of 80 percent in the drywell, and 100 percent in the wetwell".

S.tafDL6Ssessment The staff has confirmed that the humidity numbers were transposed and corrected the

' statement.

SE Statement. Pace 6. Paraaraoh 5. 2nd Sentence "With regard to Figure 14.5-10, the benchmark analysis indicates..18 psia, whereas the original analysis...18.8 psia".

Licensee's Clarification The comparison values made in the SE appears to compare pressures for different assumed containment leakage rates (0.5 percent versus 5 percent leakage).

Staffs Assessment

' The staff has confirmed that the SE compared the calculated maximum containment pressures for two different containment leakage values. The correct comparisons for the 0.5 percent containment leakage assumption are 17.8 psia for the original FSAR and 18.0 psia for the benchmark case. The SE has been revised to read:

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"With regard to Figure 14.5-10, the benchmark analysis indicates ...18 psia, whereas the

- original analysis .-. 17.8 psia". f '

SE Statement. Paae 13. Paraaraoh 1. Last Sentence "The licensee's review identified ... for which additional (test results) was required to complete document files."

Licensee's Clanfication The submittal referenced " analysis" as the basis, not " test results". '

Elaff's Assessment The staff has confirmed that the submittal referenced " analysis" and not " test results". The SE l has been revised to:

j "The licensee's review identified ... for which additional (analysis) was required to complete document files." f

'SE Statement Paae 15 Paraaraoh 1 1st Sentence

"...licensee indicated that the Arrhenius equation has been applied starting at time zero and includes the LOCA transient as part of the calculation for degradation."

Licensee's Clarification No equipment qualified at Pilgrim Station requires the use of Arrhenius methodology until after the blowdown stage is completed, even though some existing documentation reflects application  ;

at time zero. l l

Staff's Assessment in its SE, the staff concluded that electrical equipment meets the requirements of 10 CFR 50.49. )

This conclusion was based on the following (A) the electrical equipment in question, prior to j

- changes (i.e., the need for increased salt Service water (SWW) injection temperature and i identification of an analysis error), was considered qualified in accordance with'the requirements of 10 CFR 50.49 as documented in past SEs colated to equipment qualificalvon; (B) the licensee cordinued to maintain the basis (i.e., the undefined engineering judgement) that was utilized by  ;

the staff and/or the licensee to conclude compliance With 10 CFR 50.49; and (G) the licensee's j assessment that: (1) the new urywsn spray flowrate of 1250 ppm completely offsets the drywell i temperature increase that would have resulted from the new 75 'F SSW injection temperature; i (2) EQ test profiles, thus, continue to envelop the new accident and post accident profiles; and

(3) equipment is qualified.

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3 The staff's SE, thus, concluded that the licensee's assessment provided reasonable assurance that equipment will function as required during accident conditions; and that equipment meets the requirements of 10 CFR 50.49.

In addition to the above evaluation finding, in its SE, the staff indicated that a more focused review was also considered to be needed for equipment which utilizes the Arrhenius -

methodology for post-LOCA qualification. The use of Arrhenius methodology to support qualification of equipment for LOCA and/or longer term post-LOCA environments has not been specifically endorsed by NRC Regulatory Guide, has not been generally accepted, by itself, to demonstrate qualification of equipment in post-LOCA environments, and has not been validated by test. Therefore, the staff has maintained that the use of the Arrhenius methodology, by itself, without supporting justification or technical basis, is not considered an acceptable approach for i supporting qualification of electric equipment for post-LOCA environments.

Concems relating to the Arrhenius methodology were resolved in the SE based on: (1) the existence of sufficient margin to compensate for any uncertainties with the utilization of the Arrhenius methodology; and (2) the judgement that the licensee's application of the Arrhenius

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methodology did not appear to have a significant impact on qualification of equipment. In addition, the SE indicated that the NRC staff would continue to review the use of the Arrhenius methodology for post-LOCA qualification, as a separate initiative outside the scope of the Pilgrim

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evaluation, in order to assure that its use is appropriate and conservative.

l Even though some existing documentation reflects application of the Arrhenius methodology at time zero, the staff in its SE, described above, concluded (although not explicitly stated) that existing EQ documentation continues to demonstrate qualification of equipment in accordance with the requirements of 10 CFR 50.49. The licensee's statement that no equipment qualified at Pilgrim requires the use of Arrhenius until after the blowdown stage is completed does not change the staff's original conclusion that this equipment can be considered qualified in accordance with 10 CFR 50.49. Because the staff's SE agrees implicitly with the licensee's clarification (independent of when Arrhenius was applied the equipment is cualified), an SE revision is not considered necessary.

SE Statement. Paae 15. Paraaraoh 4.1st Sentence

"....that Rockbestos wire is qualified with a 17% margin and all other equipment is qualified with a margin two times greater than the 10% margin required by lEEE 323-1974...."

Licensee's Clanfication The Rockbestos wire is part of the Limitorque operator and as such is qualified to the Division of

. Operating Reactors (DOR) Guidelines. DOR Guidelines do not require the inclusion of margin.

We have covered this point with a " sound reasons to the contrary" position as required under 10 CFR 50.49.

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l Staffs Assessment in its SE described above, the staff concluded (although not explicitly stated) that existing EQ documentation continues to demonstrate qualification of equipment in accordance with the requirements of 10 CFR 50.49. Even though some existing documentation (such as that for Rockbestos wire) reflects application of no margin in accordance with DOR guidelines, the staff agrees with the licensee's clarification - equipment qualified to DOR guidelines can continue to

- be considered qualified in accordance with 10 CFR 50.49 requirements based on past NRC staff evaluations. Because the staffs SE agrees implicitly with the licensee's clarification, an SE revision is not considered necessary.

SE Statement. Paae 16. Parmaraoh 3. Entire Narrative

- "... penetrations have been environmentally qualified and tested at accident temperatures with an applied short circuit."

Licensee's Correction The third paragraph of this section of the SE states that "...the electrical penetrations have been environmentally qualified (i.e., tested at accident environments while being subject to fault current) to demonstrate their capability for maintaining safety function-containment integrity."

This statement is not correct for the specific model of penetrations installed at PNPS. The General Electric cenister type penetrations used at PNPS were only short circuit tested at room temperature.

The lic' nsee further indicated that PNPS penetrations were qualified based on tests for short circuits under accident conditions performed on a similar penetration, similarity analysis, and operation of protective devic.ss to limit the penetration's exposure to temperatures above DBA levels that could be caused by fault currents.

Staff's Assessment The staff agrees with the licensee's assessment. The staffs SE acceptance was incorrectly based on testing of penetrations at accident temperatures with an applied short circuit.

To clarify qualification of General Electric canister type penetrations used at PNPS, the licensee, by letter dated December 30,1997, indicated the following:

1. General Electric Series 100, F02 modular type penetrations, were tested for short circuits under accident conditions. The F02 penetration was subjected to 168'C accident temperature plus short-circuit currents such that the penetration conductors reached a maximum temperature of more than 325"C during the test.

2. . The F02 penetrations use the same conductor sealing techniques and the same sealing epoxy and conductor insulation as the PNPS canister penetrations.

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3. PNPS's installed short-circuit protection, limits the temperature of the penetration conductors to less than 250*C. The temperatures of PNPS's penetration conductors are limited to temperatures significantly lower than the conductor temperatures encountered during the F02 test program (i.e.,325'C); therefore, PNPS's penetrations will maintain their integrity during short circuits under accident conditions.

Based on this additional information (or clarification of the licensee's original submittal), the staff finds that the licensee has corrected the staffs misunderstanding as to how containment electric penetrations are qualifM at PNPS. In order to assure appropriate compliance (or enforcement -

action), the staffs SE is being reissued utilizing the substitution of the following paragraph:

The licensee has submitted an evaluation that concludes that failure of cable that passes through primary containment would not adverse ly affect the primary .

containment boundary because: (1) current limiting devices have been installed in the electrical circuit so that any potentially damaging fault currents will be interrupted prior to loss of the penetration's safety function (i.e., containment integrity); and (2) the electrical penetrations have been environmentally qualified

. (i.e., similar penetrations have been tested at accident environments while being subject to fault current and a similarity analysis has been performed) to demonstrate their capability for maintaining safety function-containment integrity.

Based on the above, the staff continues to conclude, as expressed in staffs SE, that the licensee's evaluation provides reasonable assurance that containment penetrations which

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contain electrical circuits will function as required during accident conditions. ]

Principal Contributor: A. Wang J. Knox Date: August 26, 1998 4 .

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4 This formulation assumes that the drywell steam space is in equilibrium with the suppression pool vapor pressure, such that these two terms cancel in the equation for the available NPSH.

The drywell airspace is assumed to pressurize as an ideal gas at the same temperature as the

. suppression pool. The same methodology was used in the original NPSH calculation as described in the UFSAR.

To calculate conservative NPSH available values, the initial conditions and modeling assumptions used in the SHEX calculation were chosen to maximize the peak suppression pool temperature, and the methodology and input assumptions used to calculate the containment pressure in Calculation M-662 were chosen to minimize the calculated containment pressure.

These assumptions include the following:

1) initial thermal power of 102 percent rated thermal power.

2) Initial suppress % pool temperature of 80 'F.

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3) Continued feedwater addition to the reactor following the LOCA. }

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4) TS minimum torus water level.

5)- Rated horsepower (converted to heat) from ECCS pumps is added to ECCS flow.

6)- Minimum RHR heat exchanger flow rates and maximum allowable fouling : and tube plugging.

7) 75 *F service water inlet temperature.

8) ANS 5.1-1979 decay heat, with and without a 2-sigma uncertainty added.

9) Initiation of lower-than-rated containment cooling at 600 seconds, switching to rated containment cooi;ng at 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> from beginning of LOCA.

10) Initial drywell pressure of 1.3 psig, and initial wetwell pressure of 0.0 psig. l

11) Initial relative humidity of 80 percent in the drywell, and 100 percent in the wetwell. j

12) Initial temperature of 150 *F in the drywell, and 80 'F in the wetwell.

13) The effects of containment leakage on the calculated pressure were considered. i

! The first seven of these assumptions tend to maximize the peak calculated suppression pool 4 temperature, while the last four tend to minimize the containment pressure.

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in a request for additional information (RAl) dated March 13,1997, the staff ,

asked the licensee why it believed the use of an ideal gas / equilibrium  !

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o 6-ANS 5.1-1979 decay heat input has not been accepted by the staff and that to assure a conservative decay heat input a 2-sigma uncertainty should be added. As a bounding analysis to support this amendment BECo has estimated the effects of adding 2-sigma uncertainty by changing the suppression pool temperature. BECo hae committed to perform the actual 2-sigma uncertainty added analysis within 180 days of issuance of this amendment. The staff considers this a condition for approval of the amendment.

The licensee also presented 2 curves of the calculated containment pressure versus time, again corresponding to the decay heat model used (i.e., estimated plus 2-sigma or nominal ANS_5.1). The calculated pressure increases when the estimated 2-sigma uncertainty is added to the decay heat. However, because of the corresponding increase in suppression pool

- temperature with the estimated 2-sigma uncertainty added, the margin between the calculated containment pressure and the pressure required for NPSH is approximately the same for the nominal and the plus 2-sigma cases (approximately 6 psi). In either case, the peak pressure calculated in the minimum pressure analysis is approximately 7.5 or 9.9 psig for the decay heat with no uncertainty and with an estimated plus 2-sigma uncertainty, respectively. Both of these pressure profiles bound, with adequate margin, the overpressure requested (1.9 and 2.5 psig)-

over the time periods for which it is requested.

3.1.3 Benchmark A'nalysis The licensee submitted a comparison of the calculated containment pressure and suppression pool temperature produced by the equilibrium methodology used in this license amendment request. The same methodology is used in the current licensing basis, but because a code other than SHEX was used in the current licensing basis, an evaluation to compare, or benchmark, the results produced with the SHEX code and the original code is necessary.

When a benchmark analysis is performed using the same initial conditions and assumptions as the original analysis, any differences in the results can be attributed to differences in the code and/or methodology used.

' The licensee presented a comparison of recently obtained results with those depicted on Figures 14.5-9 and 14.5-10 of the UFSAR. These figures show the total NPSH available vs.

suppression pool temperature, and the containment pressure vs. time, respectively. Figure 14.5-10 also shows suppression pool temperature vs. time. The benchmark case used initial conditions and assumptions that were the same as those used in the original FSAR analysis

- (i.e., initial pressures, temperatures, humidities, etc.).

With regard to Figure 14.5-9, the total NPSH available in the benchmark analysis is essentially identical to that shown on current Figure 14.5-9, with the benchmark case showing about 0.2 ft.

greater NPSH available than the original analysis. With regard to Figure 14.5-10, the i benchmark analysis indicates a peak minimized pressure of approximately 18 psia, whereas L the original analysis results in a peak minimized pressure of approximately 17.8 psia. The [

suppression pool temperature profile and peak values are virtually identical between the two analyses.

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etc.) to which equipment must be qualified are affected by the 65 'F to 75 'F increase in the I SSW injection temperature and were further affected by an error identified in a previous analysis. The licensee: (1) re-evaluated the affected conditions to establish a new environmental qualification accident profile; and (2) reviewed and updated all 10 CFR 50.49 document files to demonstrate qualification to the new accident profile. The licensee's review l identified five motor-operated valves located inside the drywell and the containment electrical 'l penetration assemblies for which additional information (analysis) was required to complete l document files.

In response to an NRC RAI, the licensee by letter dated May 14,1997, indicated: (1) that during refueling outage #11, the drywell spray flowrate was increased to a minimum design value of 1250 gpm from its previous design value of 720 gpm; (2) the 1250 gpm flowrate completely offsets the drywell temperature increase that would have otherwise resulted from a proposed revision to the containment analysis; (3) all equipment environmental qualification test profiles, thus, continue to envelop the new accident and post-accident profiles; (4) for post-LOCA qualification, Arrhenius methodology continues to be utilized; and (5) containment

- electric penetrations continue to be qualified to the higher SSW temperature but do not have to meet the additional qualification requirements of 10 CFR 50.49.

Based on the licensee's assessment that environmental qualification test profiles envelop the new accident profiles for 75 *F SSW injection temperature and are qualified, the staff concluded that there is reasonable assurance that electrical equipment will function as required during accident conditions and that electrical equipment meet the requirements of 10 CFR 50.49; however, a more focussed review was considered to be needed for: (1) equipment which utilizes the Arrhenius methodology for post-LOCA qualification; and (2) electrical containment penetrations. The staffs evaluation of these two areas is described in the following sections.

3.5.1 Equipment Which Utilizes the Arrhenius Methodology For Post-LOCA Qualification BECo utilizes the Arrhenius methodology to demonstrate that post-accident operating time is acceptable using test data of a shorter duration than the PNPS specific accident profiles, but having higher temperatures than the required accident conditions. The ese of Arrhenius methodology to support qualification of equipment for LOCA and/or ionger term post-LOCA environments has not been specifically endorsed by NRC Regulatory Guide, has not been generally accepted, by itself, to demonstrate qualification of equipment in post-LOCA ,

environments, and has not been validated by test. Therefore, the staff has maintained that the  !

use of Arrhenius methodology, by itself, without supporting justification or technical basis, is not i considered an acceptable approach for supporting qualification of electric equipment for LOCA  ;

environments.

Electric Power Research Institute's (EPRl's), Nuclear Power Plant Equipment Qualification Reference Manual indica'.es that the Arrhenius method has been employed to relate accident

[- test temperatures to postulated accident temperatures. If the Arrhenius model and activation energy value are

4 licensee indicated that the Arrhenius equation has been applied starting at time zero and includes the LOCA transient as part of the calculation for degradation. If an additional peak transient is utilized to assure performance margin during testing, the licensee indicated that this additional transient is not applied to calculate degradation.

As implied by the above described industry guidelines, and based on discussion with others familiar with the application of the Arrhenius methodology, the staff has concluded that the Arrhenius model and activation energy value are generally not considered to be an accurate methodology for establishing degradation of equipment during transient temperature conditions i.e., the initial stage of the LOCA which are not constant. Thus, the staff disagrees with PNPS application of the Arrhenius m'ethodology during transient temperature conditions and its utilization as part of their process for assuring qualification of electrical equipment in post-LOCA environments.

In response to the above described disagreement, the licensee indicated by June 20,1997, letter that they have reviewed all in-containment EQ equipment utilizing the Arrhenius methodology starting with its application at times greater than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> past the transient peak temperature. The review focused on determining whether allin-containment equipment would still be qualified with a test margin two times greater than the 10 percent margin required by IEEE 323-1974. The licensee concluded that all equipment, except Rockbestos wire associated with Limitorque limit switches, meets the two times the 10 percent margin criteria.

The Roci oestos wire was determined to have a 17 percent margin. ]

I Based on the licensee's assessment (described above) that Rockbestos wire is qualified with a 17 percent margin and all other equipment is qualified with a margin two times greater than the 10 percent margin required by IEEE 323-1974, it appears that equipment has sufficient additional margin above that which is required to compensate for any uncertainties associated with the application of the Arrhenius methodology in post-LOCA environments. In addition, the licensee's application of the Arrhenius methodology during transient temperature conditions does not appear to have a significant impact on qualification of equipment. Thus, the licensee's assessment provides reasonable assurance that equipment required to meet the requirements of 10 CFR 50.49 will function as required during accident conditions with the higher SSW inlet temperature of 75 *F and is considered qualified. However, as a separate initiative outside the scope of this evaluation, the NRC staff will continue to review this type of analytical methodology in order to assure that the approach used was appropriate and conservative.

Subsequently, by letter dated December 30,1997, the licensee indicated that their environmental qualification document files have been revised such that the application of the Arrhenius equation is no longer applied starting at time zero as previously indicated. For PNPS, the Arrhenius methodology is utilized for those cases where the test profile does not

' envelop the accident profile for the required duration. To determine degradation, the licensee has indicated that the Arrhenius equation has been applied starting after the LOCA transient ,

has been completed.

l 3.5.2 Electrical Containment Penetrations in response to an NRC RAI, the licensee by letter dated May 14,1997, indicated that o' containment penetrations (either electrical or piping) are considered extensions of containment. l They are considered mechanical devices and therefore not subject to the requirements of 10  ;

l CFR 50.49. Containment penetrations that contain cables that power equipment required to mitigate the consequences of an accident are required to be qualified to the criteria specified in 10 CFR 50.49 only to the extent that failure of the penetration I ,

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will not affect operability of safety-related cables. Qualification of the penetration to assure its safety function (i.e., containment integrity) is not subject to the requirements of 10 CFR 50.49.

Penetrations that contain non-safety-related cable are similarly not subject to the requirements of 10 CFR 50.49.

The staff disagrees. Containment penetrations which contain either safety or non-safety-related circuits perform a safety function to maintain containment integrity. Containment penetrations should be considered safety-related electrical equipment. If failure of the containment electric penetration can cause loss of safety function (i.e., containment integrity), paragraph (b)(1)(iii or C) of 10 CFR 50.49 requires that the containment electric penetration be covered by 10 CFR 50.49.

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The licensee has submitted an evaluation that concludes that failure of cable that passes 1 through primary containment would not adversely affect the primary containment boundary {

because: (1) current limiting devices have been installed in the electrical circuit so that any  !

potentially damaging fault currents will be interrupted prior to loss of the penetration's safety function (i.e., containment integrity); and (2) the electrical penetrations have been environmentally qualified (i.e., similar penetrations have been tested at accident environments while being subject to fault current and a similarity' analysis has been performed) to demonstrate their capability for maintaining safety function-containment integrity.

The staff, however, believes that containment electrical penetrations should be considered electric equipment and should therefore be covered by 10 CFR 50.49. The staff also believes that the existence of current limiting devices and qualification do not provide an appropriate argument for excluding electrical penetrations from being covered by 10 CFR 50.49.

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SUMMARY

The staff has concluded that sufficient containment pressure exists post LOCA to assure that the NPSH available is greater than the NPSH required. This analysis included several changes in initial conditions assumed for the containment analysis, the most significant ones being the change to the decay heat input and service water temperature. The staff has also reviewed the effects of these changes on EDG loadings, EO, and any safety-related equipment directly or indirectly cooled by the RBCCW system and found the equipment to be operable. The staff, therefore, authorizes BECo to change the UHS administrative limit from 68 *F to 75 'F, and change the Updated Final Safety Analysis Repod (UFSAR) to reflect the use of containment pressure to compensate for the deficiency in NPSH following a design basis accident and increase the accident analysis design UHS temperature from 65* F to 75' F. As pad of this amendment, Boston Edison Company (BECo/iicensee) has proposed to submit a Technical Specification amendment for the UHS temperature by the first quarter of 1998. In addition,

' within 180 days ofissuance of this I

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