33968 Federal Register / Vol. 63, No. 119 / Monday, June 22, 1998 / Notices

1The Petitioner sought to add this concern to his

Petition dated September 22, 1996, wherein he

requested the NRC to shut down the SONGS facility

‘‘as soon as possible’’ pending a complete review

of the seismic design of the SONGS units based on

information gathered from the Landers and

Northridge earthquakes. By letter dated June 26,

1997, the NRC advised the Petitioner that his e-mail

request dated April 25, 1997, concerning the ability

of the SONGS steam generators to withstand a

major seismic event, would be treated as a separate

10 CFR 2.206 Petition. The Director’s Decision (DD–

97–23) issued by the NRC on September 19, 1997,

denied the Petitioner’s September 22, 1996, request

to shut down the SONGS units, providing a detailed

discussion of the adequacy of the seismic licensing

basis for the SONGS facility.

the nature of the requestor’s right under

the Atomic Energy Act of 1954, as

amended, to be made a party to the

proceeding; the nature and extent of the

requestor’s property, financial, or other

(i.e., health, safety) interest in the

proceeding; and the possible effect of

any order that may be entered in the

proceeding upon the requestor’s

interest.

Dated at Rockville, Maryland, this 16th day

of June, 1998.

For the Nuclear Regulatory Commission.

Stevens L. Baggett,

Acting Chief, Materials Safety Branch,

Division of Industrial and Medical Nuclear

Safety, Office of Nuclear Material Safety and

Safeguards.

[FR Doc. 98–16537 Filed 6–19–98; 8:45 am]

BILLING CODE 7590–01–M

NUCLEAR REGULATORY

COMMISSION

[Docket Nos. 50–361 and 50–362]

Southern California Edison Company,

et al.; San Onofre Nuclear Generating

Station, Units 2 and 3; Issuance of

Director’s Decision Under 10 CFR

2.206

Notice is hereby given that the

Director, Office of Nuclear Reactor

Regulation, has acted on a Petition for

action under 10 CFR 2.206 received

from Mr. Stephen Dwyer dated April 25,

1997, for the San Onofre Nuclear

Generating Station (SONGS), Units 2

and 3.

The Petition requests that the

Commission shut down the San Onofre

Nuclear Generating Station pending a

retrofitting of the steam generators. As a

basis for the request, the Petitioner

asserts that the ability of the steam

generators to withstand a major seismic

event is seriously compromised by the

degraded eggcrate supports discovered

in the SONGS Unit 3 steam generators.

The Director of the Office of Nuclear

Reactor Regulation has determined that

the request should be denied for the

reasons stated in the ‘‘Director’s

Decision Under 10 CFR 2.206’’ (DD–98–

06), the complete text of which follows

this notice and which is available for

public inspection at the Commission’s

Public Document Room, The Gelman

Building, 2120 L Street, N.W.,

Washington, D.C. 20555–0001, and at

the Local Public Document Room

located at the Main Library, University

of California, P.O. Box 19557, Irvine,

California 92713.

Dated at Rockville, Maryland, this 11th day

of June 1998.

For the Nuclear Regulatory Commission.

Samuel J. Collins,

Director, Office of Nuclear Reactor

Regulation.

Director’s Decision Under 10 CFR 2.206

I. Introduction

By e-mail dated April 25, 1997,

Stephen Dwyer (Petitioner) requested

that the Nuclear Regulatory Commission

(NRC) take action with regard to San

Onofre Nuclear Generating Station

(SONGS) regarding his concerns about

the ability of the SONGS steam

generators to withstand a major seismic

event.1 Specifically, the Petitioner

stated that the ability of the SONGS

steam generators to withstand a major

seismic event is seriously compromised

by the degradation observed in the

SONGS Unit 3 steam generator internal

tube supports (eggcrate supports) during

its 1997 refueling outage. The Petitioner

requested an investigation to determine

if Unit 2 has experienced degradation

similar to that found in Unit 3 and also

stated that further seismic analysis

should be performed for the SONGS

steam generators and that a retrofitting

upgrade of the steam generator supports

could be accomplished at this time. On

June 26, 1997, the NRC staff

acknowledged receipt of the Petition as

a request pursuant to Section 2.206 of

Title 10 of the Code of Federal

Regulations (10 CFR 2.206) and

informed the Petitioner that there was

insufficient evidence to conclude that

immediate action was warranted. Notice

of the receipt of the Petition indicating

that a final decision with respect to the

requested action would be forthcoming

within a reasonable time was published

in the Federal Register on July 3, 1997

(62 FR 36085).

My Decision in this matter follows.

II. Discussion

A. Request for an Investigation to

Determine if SONGS Unit 2 Has

Experienced Eggcrate Degradation

Similar to Unit 3

1. Background

The SONGS units utilize Combustion

Engineering Model 3410 recirculating

steam generators. This model of steam

generator contains 9,350 Inconel 600

(ASME Material Specification SB–163)

U-tubes with a nominal diameter and

wall thickness of 0.75 and 0.048 inch,

respectively. Secondary side tube

support structures consist of seven

horizontal full eggcrate supports, three

horizontal partial eggcrate supports, and

upper bundle supports (i.e., two

batwing diagonal supports and seven

vertical supports). The materials used

for fabrication of the steam generator

vessels and internals (including tube

supports) are low-alloy and carbon

steels, respectively. Figure 1 is a

simplified cross-sectional diagram of the

SONGS steam generators that clearly

displays the 10 eggcrate support levels,

and Figure 2 is a three-dimensional

representation of the steam generators

that gives additional structural detail.

The eggcrate supports consist of 1-

and 2-inch carbon steel strips

interlocked perpendicular to each other

as shown in Figure 3. The eggcrate

supports limit lateral motion of the

tubes and, at the same time, allow free

flow of fluid around the tubes.

During the 1997 refueling outage for

SONGS Unit 3, the licensee discovered

that portions of the eggcrate supports

had experienced degradation, ranging

from minor wastage of the eggcrate

material to severe thinning in localized

areas. The significant degradation

observed during this refueling outage

was confined mainly to the periphery

locations of the eggcrate supports. The

secondary sides of the steam generators

in both units were inspected during

their 1997 refueling outages and during

their 1998 mid-cycle outages and, as

discussed below, significant degradation

was limited to the periphery locations of

the SONGS Unit 3 eggcrate supports.

The licensee has extensively

researched the cause of the eggcrate

degradation and has concluded that the

degradation was caused by a form of

flow accelerated corrosion (FAC), a

general term describing processes that

use assistance from fluid flow to remove

the protective oxide layer from base

material. Removal of the protective

oxide layer exposes the base material to

the fluid environment, allowing further

material removal through corrision and/

or erosion processes. The carbon steel
Federal Register / Vol. 63, No. 119 / Monday, June 22, 1998 / Notices 33969

eggcrate material utilized in the SONGS

steam generators can be susceptible to

FAC in the presence of sufficiently high

fluid velocities.

The licensee concluded that the FAC

occurred during recent operation of Unit

3 primarily as a result of steam

generator secondary side increased fluid

velocities caused by the buildup of

deposits on the steam generator tubes.

This buildup of deposits on the tubes

significantly reduced the available flow

area within the tube bundle causing

flow diversion to the periphery of the

tube bundle. The flow diversion to the

periphery was also affected by the

increased steam quality of the fluid

within the tube bundle. The buildup of

deposits on the tubes changed the heat

transfer characteristics of the tubes

causing the steam quality to increase in

the central region of the steam

generators. This resulted in an increase

of the flow resistance in the central

portions of the steam generator, forcing

more flow to the peripheral regions,

with resulting higher velocities. The

resulting large velocity gradients at the

periphery initiated vortices which

further elevated local velocities that

were capable of dislodging the

protective oxide layer of the eggcrate

material and initiating erosive FAC.

The chemical cleaning of the SONGS

Units 2 and 3 steam generators during

the 1997 refueling outages removed the

deposit buildup and restored fluid flow

to their original design values (i.e.,

nominal conditions). The licensee stated

in its October 17, 1997, letter that with

the flow area restored to nominal

conditions, the high fluid velocities that

lead to FAC would no longer exist, thus

stabilizing eggcrate support degradation.

The licensee has also made changes to

the chemistry control program for the

secondary system at SONGS Units 2 and

3 to reduce the feedwater iron transport.

This is expected to prevent the level of

deposit buildup observed in the steam

generators before chemical cleaning was

done in 1997. The staff concurs with the

licensee’s evaluation that FAC was

caused by deposit buildup on the steam

generator tubes and that removal of the

deposits should restore the steam

generator secondary fluid flow to within

nominal design values, thereby

eliminating continued significant

eggcrate degradation. To confirm that

FAC has been stopped by the chemical

cleaning of the steam generators, and to

assure that no significant degradation of

the eggcrate support structure goes

undetected, the licensee has committed

to conduct periodic inspections of the

secondary side of the steam generators

in both units during future outages. The

licensee will conduct periodic

inspections of the secondary side of the

steam generators to check the level of

deposit buildup on the tubes and to

verify that future degradation of the

eggcrate, if any, remains within the

assumptions used in the analysis to

demonstrate continued operability of

the steam generators (discussed later in

this Decision).

2. Description of the Eggcrate

Inspections

The SONGS licensee inspected the

steam generator secondary side support

structures, which include the eggcrate

supports, in both SONGS units during

their 1997 refueling outages and during

their 1998 mid-cycle outages. The

results of these inspections are

contained in the licensee’s letters dated

May 16, 1997, and June 5, 1997 (SONGS

Unit 2 and Unit 3 refueling outage

inspections results, respectively), and

letters dated March 10, 1998, and April

15, 1998 (SONGS Unit 2 and Unit 3

1998 mid-cycle outages, respectively). The objective of the inspections for

both units was to provide video

documentation of all areas in which

indications of support bar degradation

was suspected and to verify that other

areas did not exhibit these same

characteristics. The extent and results of

these video inspections are summarized

below.

The inspection of the secondary side

of each steam generator was divided

into six areas: (1) general inspection, (2)

inner tube bundle, (3) batwings and

vertical straps, (4) eggcrate periphery,

(5) eggcrate interior (blowdown

lane),and (6) stay cylinder. Each of these

areas was inspected to the extent

necessary to understand, with a high

degree of confidence, the amount of

degradation present. The majority of

these areas did not exhibit any

significant degradation and therefore the

design function of the support

structures was not adversely impacted. The general inspections were

performed in the steam generators from

the top of the moisture separator can

deck and included the general area, Ubend, and annulus regions. The areas

inspected included I-beams, I-beam to

shroud attachments, drains, vertical

supports, batwings and the batwing

hoop, and baffle anti-rotational keys.

These inspections identified no

significant degradation in either unit in

these areas.

The inner tube bundle consists of that

area between the outer or peripheral

tubes to the inner tubes of the stay

cylinder. The inner bundle inspections

were performed in both steam

generators from the can deck. A small

camera was dropped down in between

the tubes in a number of different

locations to assess the general material

condition of the eggcrates away from the

periphery area. For the steam generators

in both units, the inspections indicated

that the inner bundle did not exhibit the

degraded characteristics of the

periphery eggcrates found in the Unit 3

steam generators during the 1997

refueling outage.

No indications of thinning were

detected during the inspections of the

interior batwing and vertical strips on

either unit.

Comprehensive peripheral eggcrate

inspections were performed in both

steam generators in the two units from

the can deck. This included the lattice

bars and tube to lattice bar interfaces at

each eggcrate. The area near the

periphery of the eggcrate supports in the

Unit 3 steam generators experienced the

maximum thinning, as shown in Figure

3 and discussed above. As stated earlier,

minor isolated instances of thinning

were observed in the peripheral eggcrate

locations in the SONGS Unit 2 steam

generators, but overall the thinning was

considerably less than that observed on

SONGS Unit 3.

Inspections of the blowdown lane

eggcrates were performed in the steam

generators through the 6-inch handhole

at the secondary face of the tubesheet

from the handhole to the stay cylinder.

This included the lattice bars and the

eggcrate rings. The inspection scope was

to sample the eggcrate area nearest the

tubes on both the hot- and cold-leg sides

of the blowdown lane. Minor amounts

of eggcrate degradation were found in

the steam generators of both units, with

the Unit 3 steam generators exhibiting

the larger amount of degradation in this

area.

For the inspection of the overall

condition of the eggcrates and ring in

the stay cylinder, a support plate

inspection device was used. Little or no

degradation was found in this area in

either unit.

3. Summary of SONGS Unit 2 Eggcrate

Inspection

The licensee’s initial assessment of

the Unit 2 stream generator eggcrate

supports, conducted after the

degradation issue was identified in the

SONGS Unit 3 steam generators, was

reported in its letter dated May 16,

1997. The licensee concluded that the

Unit 2 eggcrate supports were in very

good to excellent overall condition,

based on the limited video examinations

of the eggcrates performed in support of

the chemical cleaning process. Although

the licensee considered operation for

the normal period of operation between

refueling intervals to be acceptable on

the basis of this limited examination,
33970 Federal Register / Vol. 63, No. 119 / Monday, June 22, 1998 / Notices

2The SSE is defined, in part, as ‘‘that earthquake

which is based upon an evaluation of the maximum

earthquake potential considering the regional and

local geology and seismology and specific

characteristics of local subsurface material. It is that

earthquake which produces the maximum vibratory

ground motion for which certain structures,

systems, and components are designed to remain

functional.’’ See 10 CFR Part 100, Appendix A,

Section III.(c),

3The Standard Review Plan (SRP) is published as

NUREG–0800, and is used as guidance for the

Office of Nuclear Reactor Regulation staff

responsible for the review of applications to

construct and operate nuclear power plants.

4NUREG–0712, ‘‘Safety Evaluation Report related

to the Operation of San Onofre Nuclear Generating

Station, Units 2 and 3,’’ Chapter 3, February 1981.

the licensee conservatively performed a

more extensive video examination of the

eggcrates during a mid-cycle outage that

began on January 24, 1998. As reported

in its March 10, 1998, letter, the licensee

observed minor isolated instances of

thinning in the periphery areas of the

eggcrate supports, but overall the

thinning was considerably less than that

observed on SONGS Unit 3.

The NRC reviewed the program

established by the licensee to conduct

the video examinations of the eggcrate

supports during the SONGS Unit 2 midcycle outage and reported its findings in

Inspection Report 50–361/98–10; 50–

362/98–01, dated May 29, 1998. This

program was similar to the licensee’s

program for inspecting the Unit 3

eggcrate supports during its mid-cycle

outage. The primary difference between

the inspection programs for the two

units was that a larger portion of the

Unit 3 eggcrate structures was

inspected. The staff concluded in its

inspection report that the scope of the

SONGS Unit 2 secondary side visual

inspections was satisfactory and the

results supportive of the licensee’s

conclusion that no steam generator

tubes needed to be removed from

service due to insufficient support from

any secondary side support structures,

which includes the eggcrate support

structures.

4. Actions Taken as a Result of

Observed Eggcrate Degradation

Following the secondary side

inspection activities conducted during

the SONGS Unit 3 1997 refueling outage

and 1998 mid-cycle outage, the licensee

plugged and stabilized (by insertion of

a steel cable inside the subject tube)

some Unit 3 steam generator tubes as a

precautionary measure due to the

degradation observed in certain eggcrate

supports. No tubes in the Unit 2 steam

generators were removed from service.

Once the tube is removed from service

in the above described manner, support

from the eggcrate structures is no longer

needed. The criterion established by the

licensee for removing tubes from service

is described in detail below.

B. Concern About the Seismic Adequacy

of the SONGS Steam Generators

The Petitioner asserts that the

degradation of the steam generators,

eggcrate supports could seriously

weaken the supports and make the

steam generators vulnerable to seismic

events.

In its letter of May 16, 1997, the

licensee committed to perform an

evaluation of the effect of the degraded

eggcrates on steam generator tube

integrity in the SONGS Unit 3 steam

generators before return to power from

the Unit 3 1997 refueling outage. This

initial evaluation was provided by the

licensee in its letter of June 5, 1997, and

included the effects of a postulated

design-basis earthquake. The licensee

submitted the final version of the

degraded eggcrate support evaluation

for SONGS Unit 3 on October 17, 1997.

As stated in the previous section, the

amount of eggcrate support degradation

observed in SONGS Unit 2 was

considerably less than that observed in

Unit 3. Therefore, the staff concludes

that demonstrating the ability of the

SONGS Unit 3 steam generators to

withstand a design basis seismic event

will demonstrate the adequacy of the

Unit 2 steam generators as well.

The staff’s review of the seismic

adequacy of the SONGS Unit 3

generators is detailed below.

1. Methodology and Acceptance Criteria

The Petitioner did not specifically

request the staff to evaluate the eggcrate

supports assuming other design loads

concurrent with earthquake loads.

However, to provide additional

conservatism, and to conform with

General Design Criterion (GDC) 2 of 10

CFR Part 50, Appendix A, the licensee,

in its October 17, 1997, letter, evaluated

the ability of the eggcrate supports to

perform their intended safety function

assuming the most limiting combination

of load conditions.

GDC 2 requires, in part, that the

design bases for structures, systems, and

components important to safety reflect

appropriate combinations of the effects

of normal and accident conditions with

the effects of natural phenomena such

as earthquakes. The earthquake for

which these plant features are designed

is defined as the safe-shutdown

earthquake (SSE).2 The Petitioner’s

concerns on the adequacy of the seismic

design of the SONGS units, based on

information gathered from the Landers

and Northridge earthquakes, were

addressed previously by the staff in DD–

97–23 (see footnote 1).

Appendix A of Standard Review

Plan,3 (SRP) Section 3.9.3, ‘‘[American

Society of Mechanical Engineers] ASME

Code Class 1, 2, and 3 Components,

Component Supports, and Core Support

Structures,’’ delineates acceptable

design limits and appropriate

combinations of loadings associated

with normal operation, postulated

accidents, and specified seismic events

for the design of Seismic Category I

fluid system components (i.e., waterand steam-containing components).

This appendix also provides that

necessary plant features important to

safety meet the appropriate design

limits specified in Section III of the

ASME Boiler and Pressure Vessel Code

(ASME Code) when the component is

subjected to concurrent loadings

associated with the normal plant

condition, the vibratory motion of the

SSE, and the dynamic system loadings

associated with the faulted plant

condition. Faulted plant conditions are

those operating conditions associated

with postulated events of extremely low

probability, such as loss-of-coolant

accidents (LOCAs) or main streamline

break (MSLB) accidents. The design

limits and loading combinations

utilized by the licensee in the October

17, 1997, evaluation of individual steam

generator tubes are the same design

limits and loading combinations that

were reviewed and approved by the staff

at the time of plant licensing. This

evaluation is contained in Chapter 3 of

NUREG–0712.4 Therefore, the staff finds

acceptable the licensee’s use of these

design limits and loading combinations

in evaluating the impact of the degraded

eggcrate supports on individual steam

generator tubes.

The evaluation of the potential for

lateral movement of the entire steam

generator tube bundle (whole bundle

evaluation) was not explicitly addressed

during the staff’s review performed at

the time of plant licensing. Also, the

ASME Code does not provide specific

design limits for the whole bundle

evaluation. The whole bundle

evaluation contained in the October 17,

1997, letter performed by the licensee to

verify that the structural integrity of the

eggcrate is maintained to ensure that it

does not shift in a way that could

damage the tubes. This is not an ASME

Code evaluation; however, ASME Code

techniques were used by the licensee to

generate and assess the results. The staff

has reviewed the specific ASME Code

techniques utilized by the licensee, and

concludes that they provide

conservative results, and are, therefore,

acceptable for the whole bundle

evaluation.
Federal Register / Vol. 63, No. 119 / Monday, June 22, 1998 / Notices 33971

5Since the amount of support degradation in

SONGS Unit 2 was observed to be considerably less

than that observed in Unit 3, the NRC staff

concludes that the licensee’s October 17, 1997,

evaluation of SONGS Unit 3 steam generator

structural integrity and the staff’s review of that

evaluation support the adequacy of SONGS Unit 2

steam generators to withstand a design basis event

and perform their intended safety function.

Furthermore, the loading

combinations used in the licensee’s

whole bundle evaluation are the same

loading combinations used in the

individual tube evaluations, and are the

same loading combinations that were

reviewed and approved at the time of

plant licensing.

2. Degraded Eggcrate Support

Assumptions

The staff reviewed the assumptions

used in the licensee’s October 17, 1997,

evaluation regarding the amount of

eggcrate support judged to be available,

and verified that these assumptions

were supported by the results of the

licensee’s inspections.

For the individual steam generator

tube analysis, the licensee calculated

the maximum loads that could occur

assuming that adequate support was not

available at two consecutive eggcrate

levels (see Figure 1). The staff finds this

assumption conservative and acceptable

because the licensee has removed from

service all tubes where two consecutive

eggcrate levels were found degraded to

the point where adequate support could

not be assured.

For the whole bundle analysis, the

licensee used the inspection results to

sort the eggcrates into categories based

on a conservative estimate of the

remaining thickness of the eggcrate

lattice bars. The staff reviewed the

sorting criteria used by the licensee, and

concludes that the material strength

assumptions established by the licensee

for the degraded eggcrate supports are

conservative, and appropriate for

evaluating the ability of the eggcrate

structures to perform their intended

function.

The visual inspections performed by

the licensee during the 1998 mid-cycle

outages for both units confirmed the

appropriateness of these assumptions

pertaining to the amount of eggcrate

support degradation used in the

licensee’s evaluation.

3. Evaluation Results

Using the above described

methodology and assumptions, the

licensee determines that the peak

calculated loads on the individual steam

generator tubes would remain below the

allowable design limits approved by

NUREG–0712 during and following a

postulated design basis earthquake.

The results of the licensee’s whole

bundle evaluation confirmed that the

eggcrate structure will provide sufficient

support to ensure that the tube bundle

will not impact the eggcrate support

ring during and following a postulated

design basis earthquake.

The staff finds these results

acceptable, and as detailed above, also

finds acceptable the methodology and

assumptions used by the licensee in the

generation of these results. The staff

concludes, therefore, that the amount of

degradation observed in the eggcrate

supports will not prevent the SONGS

Units 2 and 3 steam generators from

performing their intended safety

functions.5

4. Confirmatory Actions

The licensee’s 1998 mid-cycle

inspection of the SONGS Unit 3 steam

generators confirmed that the condition

of the Unit 3 eggcrate internal supports

remained within the analytical

assumptions used in the licensee’s

evaluation contained in its October 17,

1997, letter and also supported the

licensee’s contention that the

phenomenon (FAC) that led to the

degradation of the eggcrates had been

arrested by the chemical cleaning of the

steam generators.

Furthermore, the licensee has

committed in its letters to the NRC

(April 15, 1998, for Unit 2 and October

17, 1997, for Unit 3) to inspect the

eggcrate supports during future outages

to assure that their condition remains

within the analytical assumptions used

in the licensee’s evaluation. These

inspections will continue to be

conducted until it is established that

further inspections are not required.

In summary, on the basis of the video

inspection results for the steam

generators in both units, and the staff’s

review of the detailed evaluations

performed by the licensee, the staff

concludes that the SONGS steam

generators are fully capable of

performing their intended safety

function during and following a

postulated SSE, and no retrofitting

upgrade of the steam generators is

required.

III. Conclusion

As explained above, there is no

evidence of significant degradation of

the SONGS Unit 2 steam generator

eggcrate supports, and the extensive

analyses demonstrate the ability of the

steam generators in both SONGS units

to perform their intended safety

function. Accordingly, the Petitioner’s

requested action, pursuant to Section

2.206, is denied.

A copy of this Decision will be filed

with the Secretary of the Commission

for the Commission to review in

accordance with 10 CFR 2.206(c) of the

Commission’s regulations. As provided

by this regulation, the Decision will

constitute the final action of the

Commission 25 days after issuance,

unless the Commission, on its own

motion, institutes a review of the

Decision within that time.

Dated at Rockville, Maryland, this 11th day

of June 1998.

For the Nuclear Regulatory Commission.

Original signed by

Samuel J. Collins,

Director, Office of Nuclear Reactor

Regulation.

Attachments: Figures (3)

BILLING CODE 7590–01–M
33972 Federal Register / Vol. 63, No. 119 / Monday, June 22, 1998 / Notices
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33974 Federal Register / Vol. 63, No. 119 / Monday, June 22, 1998 / Notices

[FR Doc. 98–16539 Filed 6–19–98; 8:45 am]

BILLING CODE 7590–01–C