1CAN048605, Provides Info to Document 860327 Telcon Re Seismic Design Issue Noted in Insp Rept 50-313/86-01 on 860106-31.Disagrees W/Nrc Conclusion That Seismic Class 2 Structures Not Considered in Plant Design

Provides Info to Document 860327 Telcon Re Seismic Design Issue Noted in Insp Rept 50-313/86-01 on 860106-31.Disagrees W/Nrc Conclusion That Seismic Class 2 Structures Not Considered in Plant Design

ML20203B340
Person / Time
Site:	Arkansas Nuclear
Issue date:	04/11/1986
From:	Enos J ARKANSAS POWER & LIGHT CO.
To:	Stolz J Office of Nuclear Reactor Regulation
References
1CAN048605, 1CAN48605, NUDOCS 8604180150
Download: ML20203B340 (6)

Text

ARKANSAS POWER & LIGHT COMPANY POST OFFICE BOX 551 LITTLE ROCK, ARKANSAS 72203 (501)371-4000 April 11, 1986 1CAN048605 Mr. John F. Stolz, Director PWR Project Directorate No. 6 Division of PWR Licensing - 8 U. S. Nuclear Regulatory Commission Washington, DC 20555 Sl'BJECT:

Arkansas Nuclear One - Unit 1 Docket No. 50-313 License No. OPR-51 ANO-1 Seismic Design

Dear Mr. Stolz:

The following information is provided to document our March 27, 1986 conference call on the subject issue and to provide you with additional follow-up information.

This conference call was initiated in an attempt to resolve a; finding by the NRC's Safety System Functional Inspection (SSFI) Team identified during their inspection January 6-31, 1986.

Subsequent to the conference call, the SSFI Inspection Report (50-313/86-01) was issued on March 31, 1986 (1CNA038603).

The specific item (s) of concern are discussed in Sections II.B.2 and III.2 of that report.

In summary, the SSFI Team concluded that AP&L had not considered the interaction of Seismic Class 2 structures, systems, and components on Class 1 structures, systems, and components that might occur during a seismic event, now commonly known as Seismic 2 over 1 design.

We disaaree with this finding.

Such interactions are, and always have been, considered in the design of AN0-1.

It is recognized that plants of later vintage than ANO-1 address seismic 2 over 1 interactions differently.

ANO-1 does address those interactions consistent with applicable design and licensing requirements.

To understand our position more fully the following discussion is presented.

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'ANO-1 Design Basi;

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AP&L applied for the ANO-l's construction permit in December 1968 and j

received its Operating License in May 1974.

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Our review of NRC's guidance and regulation pertaining to seismic design indicate that seismic design requirements were evolving during the time period in which ANO-1 was undergoing its Operating License (OL) review.

i This evolution culminated in the issuance of Regulatory Guide 1.29 in August i

1973 and 10CFR100 Appendix A in November 1973.

These documents changed the i

criteria by which seismic structures, systems, and components were j

classified; defined (for the first time) Safe Shutdown Earthquake (SSE), and i

Operating Basis Earthquake (OBE); and established (for the first time) NRC j

guidance on designing Seismic Category II structures,- systems and components i

to SSE loads where their failure could reduce the function of a Seismic l

Category I structure, system or component.

These documents are the basis by j

which current vintage plants comply with General Design Criteria 2 (GDC2).

At the time of issuance of these documents, ANO-l's construction was i

essentially complete and it was only months away from receiving an Operating.

License.

ANO-l's basis for categorization of seismic systems and design requirements for those systems were established several years before issuance of these NRC documents.

The ANO-1 FSAR specifically addresses these points.

i Seismic Class 1 and Class 2 structures, systems, and components l

were defined in Section 5.A.2 (now 5.1.2).

The definition is the

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old (not RG1.29) definition consistently used for nuclear plants at that time.

Note that even the designation " Class 1 and Class

-j 2" is different than current " Category 'I and Category II" designation.

The NRC concluded in its SER for ANO-1 that these definitions were correct.

I The basis for seismic analysis as described in FSAR Section 5.A.3 (now 5.1.3) state that the seismic design of Class 2. structures, systems and equipment is "in accordance with the Uniform Building Code" and that the Seismic Class 2 systems and equipment are

" designed to withstand normal design loads combined with a j

horizontal acceleration of 0.05g."

l This section was approved by the NRC in its SER for ANO-1.

i i

i NRC's revised GDCs were issued in 1971 and Amendment 25 to the ANO-1 FSAR l

l (March 1972) addressed the revised criterion. ~This revision was made more l

than 1h years before the issuance of 10CFR100 Appendix A.

NRC specifically approved the ANO-1 response stating that "we conducted our technical review against the present version of the GDC and we conclude that the plant design conforms to the intent'of the current criteria."

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. Apri1 11, 1986 From the above, it seems clear that the methodology by the industry and NRC to comply with GDC2 during ANO-l's Licensing, was different from that which was applied to later vintage plants.

Specifically the definition of Seismic Class 1 and 2 equipment was different and Seismic 2 over 1 was considered to be adequately addressed by application of the UBC to Seismic Class 2 structures, systems, and components as opposed to SSE loads currently used.

This change in methodology can be seen when comparing plant vintages.

It can be shown that there is a distinct point in time where plant licensed earlier used UBC and plants licensed later used SSE.

As a specific example, the ANO-2 PSAR was submitted in late 1970 and contained almost identical design criteria to that which was in the ANO-1 FSAR. However, the ANO-2 FSAR submitted in late 1973 was substantially rewritten to reference Regulatory Guide 1.29, 10CFR100 Appendix A and current Seismic 2 over 1 criteria.

This is clear evidence the AN0-1 wording was not and could not be interpreted to mean a cor.mitment to current day guidance.

Current Application of 2 Over 1 at ANO-1 Interaction of Seismic Class 1 and Seismic Class 2 structures, systems, and components is currently addressed as follows.

Seismic Class 2 equipment and piping systems whose failure or excessive movement could cause a failure of Class 1 structures are restrained in l

such a way as not to cause a failure of Class 1 structures.

(FSAR Section 5.A.4.2 currently 5.1.4.2.1)

Where Class 1 piping is directly connected to Class 2 piping, the entire system is analyzed to the first seismic anchor as an integral Class 1 piping system.

(FSAR Section 5.A.4.2 currently 5.1.4.2.1)

All other Class 2 seismic structures, systems and components are designed to the Uniform Building Code.

(FSAR Section 5.A.4 currently 5.1.4.3)

)

As a matter of good engineering practice, ANO-1 design procedures require the application of Regulatory Guide-1.29 type 2 over 1 considerations, where practicable, for plant modifications.

l NRC Findings l

The NRC's SSFI Team had 2 findings in this area.

1.

"The licensee had not routinely considered the effec +, of equipment i

that is not designed to meet maximum design basis e.'thquake requirements (seismic class 1) at ANO-Unit 1 when eparing the civil portions of design change packages,"'

ll April 11, 1986 I

The SSFI Team sited the following statements from the ANO-1 FSAR as a commitment to current day 2 over 1 practices (SSE loads).

"Where Class 1 seismic structures are directly connected to or in close proximity to Class 2 seismic equipment and piping systems the failure or excessive movement of the Class 2 seismic systems are restrained in such a way as not to cause a failure of Class 1 l

structures." (FSAR Section 5.A.4.2 currently 5.1.4.2.1)

)

This statement was added to the ANO-1 FSAR in Amendment 24 (August 1972) in response to NRC question 5.28 dated November 1971.

The specific question was:

5.28 Where Class 1 (seismic) structures are directly connected to Class II (seismic) elements, such as equipment and piping systems, indicate if and how the influence of seismic activity of the Class II (seismic) elements on the Class I (seismic) structures has teen considered in the Class 1 (seismic) designs, such that damage or excessive movement of Class II (seismic) systems will not adversely affect Class I (seismic) structures.

It should be noted that this question was issued by the NRC 2 years before 10CFR100 Appendix A.

We do not interpret this question nor its specifically worded response to be a cammitment to any more than specifically what the words say.

It seems inappropriate to conclude the response was a commitment to guidance and regulation that did not exist at the time the question and response were written.

2.

"The team observed no documentation of instances where Class 1/ Class 2 interactions were evaluated, with the exception of minor statements in response to DCP Design Evaluation Questions and redesign of the support system for the EFW pump room chiller (DCP l

80-10838)."

As discussed above, Seismic Class 1 and 2 interactions are inherently considered by the design requirements applicable to ANO-1.

In addition, design procedures instruct the engineers to apply the latest criteria for 2 over 1 wherever practicable.

In fact, the DCP being reviewed by the SSFI Team that initiated the 2 over 1 concern was an upgrade of a Seismic Class 2 chiller (to withstand SSE loads) located over some Class 1 equipment.

Adequacy of UBC The Uniform Building Code is the design basis for many nuclear plants and i

affords considerable seismic protection.

The body of knowledge relative to the adequacy of the UBC is substantial.

The following is a brief discussion.

> April 11, 1986 The UBC is the same code used today in the design of high rise office buildings, hospitals, schools and public buildings throughout the United States.. Therefore protection is provided to Class 1 structures, systems and components from the interaction of Class 2 structures system and components during seismic events.

The additional strength required of the Seismic Class 2 equipment and piping who's excessive movement could cause the failure of a Class 1 structure was provided primarily to protect the Auxiliary Building, where the majority of the Class 1 equipment and components are housed, from damage which might occur as a result of the collapse of the turbine building.

At the. time this was the only additional protection deemed necessary for the Class 1 system and components.

There is a large body of data that has been collected by the nuclear industry which demonstrate the ability of conventionally designed structures, systems and components to withstand the effects of large earthquakes.

As a general rule the damage to conventional power plants, due

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to earthquakes, has been minimal. An example of this includes the response of the EL Centro Steam Plant to the 1979 Imperial Valley earthquake as described in NUREG/CR-1665.

The significant conclusions of NUREG/CR-1665 are as follows:

" Noteworthy is that the two operating units safely shut down after p

having experienced a severe seismic environment which generally exceeds

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that used in the design of nuclear power plants..."

"Most importantly there were no known malfunctions of electrical control and instrumentation equipment."

"Except for buckling of a few members in the boiler support frame, significant structural damage was not observed."

Another example is the study of observed damages to electrical facilities from the Coalinga earthquake of May 1983.

The facilities investigated were a PG&E substations close to the earthquake epicenter.

Generally, damage was limited to spilling of oil from large transformers, broken ceramic bushings on transformers and damaged anchor bolts.

There was no apparent structural damage except for an unreinforced block structure.

The Seismic Qualification Utility Group (SQUG), which was formed to support-the resolution of Unresolved Safety Issue A-46, " Seismic Qualification of Equipment in Operating Plants," has compiled a great deal of data which demonstrates that electrical and mechanical equipment used in existing fossil power plants can survive earthquakes of Design Basis Event magnitude with only minor damage.

Since this equipment was designed and anchored similarly to that of equipment used in plants of the ANO-1 vintage, _it can -

be surmised that there is a high degree of confidence that the Seismic Class-2 equipment will not fail and render Class 1 equipment inoperable.

The SQUG-groups finding have been endorsed by both the NRC and ACRS in Mr. Harold R.

Denton's letter to Mr. Neil Smith dated August 23, 1985 and in Mr. David A.

Wards's letter to Chairman Palladino dated August 13, 1985.-

• ' Apri1 11, 1986 i

In addition to the safety margin afforded Class 1 structures, systems and 3

companent from Class 2 structures, systems and component interaction, due to our conformance to the UBC, modifications to Class 1 structures, system and components have generally been prepared considering the current day 2/1 design practice.

The application of this design practice is controlled by the Civil Engineering Section procedures.

These procedures require the consideration of Reg. Guide 1.29 2/1 for_ all ANO-2 design changes and allows for the discretionary application of the 2/1 criteria to ANO-1 design i

changes (as practicable).

Since ANO-1 was not originally designed to the current day 2/1 criteria some design changes can not fully apply that criteria due to economics or the fact that the upgrade is simply not, feasible. Where upgrade modifications have been determined to be practicable and feasible, only minor modifications have typically been necessary to upgrade the Class 2 structures, system and components.

This is due to the fact that the original UBC design provides substantial support for the Class 2 structures system and components.

Summary The design and licensing requirements for definition of Seismic Class 1 and 2 structures, systems and components and the treatment of Class 1 and 2 interactions are different (for ANO-1) than current day guidance.

However, they are consistent with state of the art and regulation at the time of.

construction, consistent with other nuclear plants constracted during the same time period, and were specifically approved by the NRC.

Interactions of Seismic Class 1 and 2 structures, systems, and components at i

ANO-1 are being addressed by application of the design criteria.

In fact, efforts are taken to exceed the design criteria where practicable.

The Uniform Building Code provides substantial' design criteria resulting in sound structures when properly applied.

Actual earthquake experience has shown the UBC to provide for system and structural integrity providing a high degree of assurance that its application at ANO-1 provides adequate seismic protection.

Very truly yours, i

. Ted Enos, Manager.

Nuclear Engineering and Licensing JTE/DEJ/sg J

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