ML20137G806

Safety Evaluation Supporting Util Proposal for Elimination of Arbitrary Intermediate Pipe Breaks in High Energy Piping Sys from Design Considerations in SRP Section 3.6.2

ML20137G806
Person / Time
Site:	South Texas
Issue date:	07/31/1985
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20137G762	List: ML20137G756 ML20137G806
References
NUDOCS 8508270388
Download: ML20137G806 (12)

Text

~

_ . . . - , = . . .

. . . . . . . -. '/'

=: )

i T

J ENCLOSURE SOUTH TEXAS PROJECT UNITS 1 AND 2 l

SAFETY EVALUATION FOR THE ELIMINATION OF ARBITRARY 1 INTERffEDIATE PIPE BREAKS J,

Docket No. 50-498 AND 50-499 1!

JULY 1985

~

j U.S. Nuclear Regulatory Comission Office of Nuclear Reactor Regulation Division Of Engineering Mechanical Engineering Branch l

3 850827o388Bjg$o39s PDR ADOCK PDR A

_ . _ _ _ . = _ _

/i '

1 TABLE OF CONTENTS o

Page I. INTRODUCTION ................................................. I j II. BASES FOR THE ELIMINATION OF ARBITRARY INTERMEDIATE j PIPE BREAKS ................................................... 3 J

,s hi III. EVALUATION OF THE BASES FOR THE ELIMINATION O F ARB I TRA RY B R EA KS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 IV. REFERENCES .................................................... 10 e

i 5

e i

I 1

1 I

l .

1

?

{

i I

l l

- ~

)

i SOUTH TEXAS PROJECT UNITS 1 AND 2 SAFETY EVALUATION FOR THE ELIMINATION OF ARBITRARY INTERMEDIATE PIPE BREAKS i I. INTRODUCTION l

In the " Background" to Branch Technical Position (BTP) MEB 3-1 as presented in

Standard Review Plan (SRP) Section 3.6.2 (Ref.1), the staff position on pipe j break postulation acknowledged that pipe rupture is a rare event which may only occur under unanticipated conditions such as those which might be caused by possible design, construction, or operation errors, unanticipated loads or un-anticipated corrosive environments. The BTP MEB 3-1 pipe break criteria were intended to utilize a technically practical approach to ensure that an adequate

, level of protection had been provided to satisfy the requirements of 10 CFR

! Part 50 Appendix A, General Design Criterion (GDC) 4. Specific guidelines were developed in MEB 3-1 to define explicitly how the requirements of GDC 4 were to be implemented. The SRP guidelines in BTP MEB 3-1 were not intended to be absolute requirements but rather represent viable app ~ roaches considered to be acceptable by the staff.

The SRP provides a well-defined basis for performing safety reviews of light water reactors. The uniform implementation of design guidelines in MEB 3-1 assures that a consistent level of safety will be maintained during the licens-ing process. Alternative criteria and deviations from the SRP are acceptable provided an equivalent level of safety can be demonstrated. Acceptable reasons for deviations from SRP guidelines include changes in emphasis of specific guidelines as a result of new developments from operating experience or plant-unique design features not considered when the SRP guidelines were developed.

The SRP presents the most definitive basis available for specifying NRC's design criteria and design guidelines for an acceptable level of safety for light water reactor facility reviews. The SRP guidelines resulted from many years of experience gained by the staff in establishing and using regulatory requirements in the safety evaluation of nuclear facilities. The SRP is part of a continuing regulatory standards development activity that not only docu-ments current methods of review, but also provides a basis for an orderly modification of the review process when the need arises to clarify the content, I correct any errors, or modify the guidelines as a result of technical advance-l ments or an accumulation of operating experience. Proposals to modify the guidelines in the SRP are considered for their impact on matters of major l safety significance.

I l The staff has recently received a request from the applicant for South Texas Project (STP) Units 1 and 2 to consider an alternate approach to the existing l guidelines in SRP 3.6.2, MEB 3-1 regarding the postulation of intermediate l pipe breaks (Refs. 2 and 3). For high energy piping systems identified in

Reference 2, the applicant proposes to eliminate from design considerations those l

breaks generally referred to as " arbitrary intermediate breaks" (AIBs) which are

defined as those break locations which, based on piping stress analysis results, are below the stress and fatigue limits specified in BTP MEB 3-1, but are selected to provide a minimum of two postulated breaks between the terminal ends of a piping system. The applicant has documented the cost savings and reduced radiation exposure benefits resulting from the elimination of the structures associated with the protection against the effects of pipe rupture. The applicant has further stated that all dynamic effects associated with previously postulated arbitrary intermediate pipe breaks will be excluded from the plant design basis and that pipe whip l' restraints and jet shields associated with previously postulated arbitrary

' intermediate breaks will be eliminated. However, the applicant has stated that the elimination of AIBs will not affect the environmental qualification of

.j equipment. The break postulation for environmental effects is performed 1 independently of break postulation for pipe whip and jet impingement.

4 In the early 1970's when the pipe break criteria in MEB 3-1 were first drafted, the advantages of maintaining low stress and usage factor limits were clearly recognized, but it was also believed that equipment in close proximity to the

, piping throughout its run might not be adequately designed for the environmental consequences of a postulated pipe break if the break postulation proceeded on a purely mechanistic basis using only high stress and terminal end

breaks. As the pipe break criteria were implemented by the industry, the impact of the pipe break criteria became apparent on plant reliability and costs as well as on plant safety. Although the overall criteria in MEB 3-1 have resulted in a viable method which assures that adequate protection has been provided to satisfy the requirements of GDC 4, it has become apparent that the particular criterion requiring the postulation of arbitrary inter-mediate pipe breaks can be overly restrictive and may result in an excessive number of pipe rupture protection devices which do not provide a compensating level of safety.

At the time the MEB 3-1 criteria were first drafted, high energy leakage cracks were not being postulated. In Revision 1 to the SRP (July 1981), the concept of using high energy leakage cracks to mechanistically achieve the environment desired for equipment qualification was introduced to cover areas which are below the high stress / fatigue limit break criteria and which would otherwise not be enveloped by a postulated break in a high energy line. In the proposed elimination of arbitrary intermediate breaks, the staff believes that the essential design requirement of equipment qualification is not only being re-tained but is being improved since all safety-related equipment is to be quali-fied environmentally, and furthermore certain elements of construction which may lead to reduced reliability are being eliminated.

In addition, some requirements which have developed over the years as part of the licensing process have resulted in additional safety margins which overlap the safety margin provided in the pipe break criteria. For example, the cri-teria in MEB 3-1 include margins to account for the possibility of flaws which might remain undetected in construction and to account for unanticipated piping steady-state vibratory loadings not readily determined in the design process.

However, inservice inspection requirements for the life of the plant to detect flaws before they become critical, and staff positions on the vibration monitoring of safety-related and high energy piping systems during preoperational testing, further reduce the potential for pipe failures occurring from these causes.

Because of the recent interest expressed by the industry to eliminate the arbitrary intermediate break criteria and, particularly, in response to the detailed submittals provided by several utilities including HL&P, the staff has reviewed the MEB 3-1 pipe break criteria to determine where such changes may be made.

II BASES FOR THE ELIMINATION OF ARBITRARY INTERMEDIATE PIPE BREAKS j The applicant's submittals (Refs. 2, S and 4) suggest a general consensus in the nuclear industry that current knowledge and experience support the conclusion

, that designing for the arbitrary intermediate pipe breaks is not justified.

The bases for this conclusion are discussed in the following paragraphs.

4 1) Operating Experience Does Not Support Need for Criteria The combined operating history of commercial nuclear plants (extensive operating i experience in over 80 operating U.S. plants and a number of similar plants

.; overseas) has not shown the need to provide protection from the dynamic effects j.

of arbitrary intermediate breaks.

2) Piping Stresses Well Below ASME Code Allowables 1 Currently, AIBs are postulated to provide a minimum of two pipe breaks at the two highest stress locations between piping terminal ends. Consequently, i arbitrary intermediate breaks are postulated at locations in the piping system

where pipe stresses and/or cumulative usage factors are well below ASME Code 3 allowables. Such postulation necessitates the installation and maintenance of complicated mitigating devices to afford protection from dynamic effects such i as pipe whip and/or jet impingement. When these selected break locations have

' stress levels only slightly greater than the rest of the system, installation of mitigating devices not only lends little to enhance overall plant safety, but also provides the potential for inadvertent restraints of piping during thermal growth and seismic motion.

3) Arbitrary Intermediate Breaks Complicate the Design Process The design of piping systems is an iterative process and, therefore, the location of the highest stress points usually change several times during design.

Although SRP Section 3.6.2 (Ref.1) provides criteria intended to reduce the need to relocate the intennediate break locations when high stress points shift due to piping reanalysis, in practice, these criteria provide little relief from moving arbitrary break locations since the revised break locations must still be evaluated as to their effects on essential equipment and structures.

l

_4_

4) Substantial Cost Savings The cost benefits to be realized from the elimination of the arbitrary inter-mediate break locations center primarily on the elimination of the associated pipe whip restraints and jet shields. While a substantial reduction ($5 million) in capital and engineering costs for these restraints and structures can be realized in the design and construction stages of the plant, there are also significant operational benefits to be realized over the 40 year life of the plant, as reduced manhours for inservice inspection and maintenance will result.

! 5) Improved Inservice Inspection Pipe whip restraints are normally located adjacent to or surrounding the welds j at changes in pipe direction. Access during plant operation for inservice inspection activities can be improved due to the elimination of congestion created by these pipe rupture protection devices and the supporting structural

, framing associated with arbitrary pipe breaks.

6) Reduction in Radiation Exposure

, In the event of a radioactive release or spill inside the plant, decontamination operations could be more effective if the pipe whip restraints and jet shields associated with AIBs and the large structural frameworks supporting the restraints were eliminated. Recovery from unusual plant conditions would also be improved by reducing the congestion in the plant. A significant reduction in man-rem exposure can be realized through fewer man hours spent in radiation areas.

The applicant, as part of its justification for the elimination of arbitrary intermediate breaks, has estimated that the reduction in operational radiation exposure due to elimination of arbitrary intermediate pipe breaks and the resulting decrease in pipe whip restraints and jet deflectors over the 40 year life of the plant will be in excess of 100 person-rem for both units. (Ref. 2).

7) Improved Operational Efficiency The elimination of pipe whip restr6 nts associated with arbitrary breaks will preclude the requirement for cutback insulation or special insulating assemblies near the close fitting restraints. This will reduce the heat loss to the surrounding environment, especially inside containment.

III EVALUATION OF THE BASES FOR THE ELIMINATION OF ARBITRARY BREAKS The technical bases for the elimination of the arbitrary intermediate break criteria as discussed in the preceding section of this report provided many arguments supporting the applicant's conclusion that the current SRP guidelines on this subject should be changed. However, it is not apparent that a unila-teral position by the utility concluding an unconditional deletion of the ar-bitrary intermediate break criteria can be justified without a clear understanding of the safety implications that may result for the various classes of high energy piping systems involved. In this section, we will discuss the bases behind the current arbitrary intermediate break criteria from an ASME Code design standpoint and put into perspective the uncertainty factors on which the need to postulate arbitrary intermediate breaks should be

e evaluated. We further evaluate the acceptability of the applicant's proposed deviation from SRP Section 3.6.2 ASME Code Class 1 Pipino Systems In accordance with BTP MEB 3-1 (paragraph B.1.c.(1)) breaks in ASME Code Class I piping should be postulated at the following locations in each pia'ag and branch run:

(a) at terminal ends; (b) at intermediate locations where the maximum stress range as j calculated by Eq. (10) and either Eq. (12) or (13) of ASME Code

.NB-3650 exceeds 2.4 Sm;

-L l (c) at intermediate locations where the cumulative usage factor exceeds 0.1.

(d) If two intermediate locations cannot be determined by (b) and (c) above, two highest stress locations based on Eq. (10) should be selectod.

The arbitrary intermediate break criteria are stated in (d) above. It should be noted that the request for alternative criteria does not propose to deviate

~

from the criteria in (a), (b), and (c) above. Pipe breaks will continue to be postulated at terminal ends irrespective of the piping stresses. Pipe breaks are to be postulated at intermediate locations where the maximum stress range as calculated by Eq. (10) and either (12) or (13) exceeds 2.4 Sm. The stress evaluation in Eq. (10) represents a check of the primary plus secondary stress intensity range due to ranges of pressure, moments, thermal gradients and combinations thereof. . Equation (12) is intended to prevent fomation of plastic hinges thermal in the piping anchor systemEquation movements. caused (13 only)by moments represents due to for a limitation thermal expansion and primary plus secondary membrane plus bending stress intensity excluding thermal bending and thermal expansion stresses; this limitation is intended to assure that the K - factor (strain concentration factor) is conservative. The K - factor was dIveloped to compensate for absence of elastic shakedown when pri$ary plus secondary stresses exceed 3 Sm.

With respect to piping stresses, the pipe break criteria were not intended to imply that breaks will occur when the piping stress exceeded 2.4 Sm (80% of the primary plus secondary stress limit). It is the staff's belief, however, that if a pipe break were to occur (in one of those rare occasions), it is more likely to occur at a piping location where there is the least margin to the ultimate tensile strength.

l

Similarly, from a fatigue strength standpoint, the staff believes that a pipe break is more likely to occur where the piping is expected to experience large cyclic loadings. Although the staff concurs with the industry belief that a

, cumulative usage factor of 0.1 is a relatively low limit, the uncertaintibs involved in the design considerations with respect to the actual cyclic load-ings experienced by the piping tend to be greater than the uncertainties involved in the design considerations used for the evaluation of primary and secondary stresses in piping systems, The staff finds that the conservative fatigue considerations in the current SRP guidelines provide an appropriate margin of safety against uncertainties for those locations where fatigue failures are likely to occur (e.g. at local welded attachments).

In its presentation to the ACRS on June 9, 1983 and in an October 5, 1983 meet-

,i ing between a group of PWR near-term operating license utilities and the NRC staff, the staff indicated that the elimination of arbitrary intermediate breaks was not to apply to piping systems in which stress corrosion cracking, large unanticipated dynamic loads such as steam- or water-hammer, or thermal fatigue in fluid mixing situations could be expected to occur. In addition, the elimination of arbitrary intermediate breaks was to have no effect on the requirement to environmentally qualify safety-related equipment and in fact i this requirement was to be clarified to assure positive qualification i requirements.

For Class 1 piping, a considerable amount of quality assurance in design, analyses, fabrication, installation, examination, testing, and documentation is provided which ensures that the safety concerns associated with the uncertain-

ties discussed above are significantly reduced. Based on the staff evaluation of the design considerations given to Class 1 piping, the stress and fatigue limits provided in the MEB 3-1 break criteria, and the relatively small degree of uncertainty in unanticipated loadings, the staff finds that dispensing with arbitrary intermediate pipe breaks is justified for ASME Code Class 1 piping in which large unanticipated dynamic loads, stress corrosion cracking, and thermal

, fatigue such as in mixing situations are not expected to occur. This finding is based in part on two actions: 1) the piping designers have complied with the current SRP guidelines (Ref. 1) that provide an appropriate margin of safety against uncertainties for those locations where fatigue failures are likely to occur (e.g., at local welded attachments) and 2) all safety-related equipment in the vicinity of Class 1 piping systems have been environmentally qualified for the non-dynamic effects of a non-mechanistic pipe break with the greatest consequences on the equipment. In addition, systems may actually perform more reliably for the life of the plant if the SRP criterion to

!' postulate arbitrary intermediate breaks for ASME Code Class 1 piping is elimi-nated. The staff has concluded that the above described requirements are present for those ASME Code Class 1 piping systems identified in the applicant's submittal of August 20, 1984 (Reference 2). Since the applicant has committed to implement the above design considerations (Refs. 2, 3 and 4), the requested deviation from the SRP for Class 1 piping is acceptable.

9

-- . .--- , . - , . * - .,,.m.,_., we.__..-e,_,.,_.m _ ,__.__._s- - ,-,- ,

7 m

ASME Code Class 2 and 3 Piping Systems In accordance with MEB 3-1 [ paragraph B.1.c.(2)] breaks in ASME Code Class 2 and 3 piping should be postulated at the following locations:

(a) at terminal ends (b) at intermediate locations selected by one of the following criteria:

(i) at each pipe fitting, welded attachment, and valve

' S but (ii) at each location where the stresses exceed 0.8 (1.2 Sat not less than a

highest stress.

3 In its proposal the applicant has not proposed changing criterion (a) above.

Postulation of pipe breaks at terminal ends will not be eliminated in the pro-posed SRP deviation for Class 2 and 3 piping systems. Breaks are required to be postulated at terminal ends irrespective of piping stresses.

The " arbitrary intemediate break criteria" is stated in (b)(ii) above where l breaks are to be 0.8 (1.2 Su + S3 ) but postulated "at not less at intermediatethan two separated locations wherechosen locations the stresses on the exceed basis of hTghest stress." The stress limit provided -in the above pipe break i

criterion represents the stress associated with 80% of the combined primary and secondary stress limit. Thus, a break is required to be postulated where the

+

maximum stress range as calculated by the sum of Equation (9) and (10) of NC/

ND-3652 of the ASME Code,Section III, exceeds 80% of the combined primary and-secondary stress limit, when we consider those loads and conditions for which i level A and level B stress levels have been specified in the system's design o specification (i.e. sustained loads, occasional loads, and themal expansion) including an operating basis earthquake (OBE) event. However, the Class 2 and

, 3 pipe break criteria do not have a provision for the postulation of pipe breaks based on a fatigue limit since an explicit fatigue evaluation is not

( required in the ASME Code for these classes of construction because of

[i favorable service experience and lower levels of operating cyclic stresses.

. For those Class 2 and 3 piping systems which experience a large number of stress cycles (e.g., main steam and feedwater systems), the ASME Code has

! provisions which are intended to address these types of loads. The rules

, governing considerations for welded attachments in ASME Class 2 and 3 piping 4

which do preclude fatigue failure are partially given in paragraph NC/ND-3645 of the ASME Code. The Code states:

" External and internal attachments to piping shall be designed so as not to cause flattening of the pipe, excessive localized bending stresses, or harmful thermal gradients in the pipe wall. It is important that such attachments be designed to minimize stress concentrations in applications where the number of stress cycles, due either to pressure or thermal

, effect, is relatively large for the expected life of the equipment."

Code rules governing the fatigue effects associated with general bending i stresses caused by thermal expansion are addressed in NC/ND-3611.2(e) and are

- generally incorporated into the piping stress analyses in the form of an

allowable stress reduction factor.

j i

, ..-__-__..E_ ,_m,___, ,.,_,,_.,-___x . . _ . . , , - . . - . . _ . _ . _ . . ~. . , _ . , . - . , - _ - - - ~ . _ _ _ _ . _ ,

..a ..-

Thus, it can be concluded that when the piping designers have appropriately considered the fatigue effects for Class 2 and 3 piping systems in accordance with NC/ND-3645, the likelihood of a fatigue failure in Class 2 and 3 piping caused by unanticipated cyclic loadings can be significantly reduced. The applicant has stated in Attachment D to its August 20, 1984 submittal that for Class 2 and 3 piping systems fatigue is considered in the ASME Code allowable stress range check for thermal expansion stresses, and that these stresses are included in the total stress value used to determine postulated break locations. If the number of thermal cycles is expected to be greater than 7000, then the allowable stresses are further reduced by an amount dependent on the number of cycles (Ref. 2). The staff concludes that this representation is acceptable.

Because of the susceptibility of feedwater (FW) systems to water hamer, the applicant has incorporated several water hamer prevention /minimi-zation features into the design of the STP feedwater system (Ref. 3).

Westinghouse has conducted extensive investigations into potential sources of water hammer in preheat steam generators as used at STP. Initiation of main feedwater is controlled by procedure and system interlocks to minimize the potential for water hammer in the main FW system (Ref. 2). The FW piping employs feedwater injection in the feed preheater section of each of the 4 Westinghouse (W) Model E2 steam generators (SGs) instead of a feedring type design. The W criteria for piping layout to minimize or eliminate water hammer are complied with by the provision of loop seals and the shortest possible horizontal length of piping imediately upstream of the SGs.

Westinghouse studies have shown that pressure transients (water hamer) due to steam void collapse can occur in the SGs if FW below 250 is introduced to the SG main feedwater nozzle concurrent with low SG water level or low SG pressure.

The applicant has incorporated the Westinghouse " Main Feedwater Temperature Pegging System" (deaerator pegging) in the design and operation of the FW system to ensure that the (W temperature is always above 250 F. The details of this system are described in Reference 3. A review of the additional information regarding the anti-water hamer features described in the Attachment 1 to Reference 3 indicates that the potential for SG feedwater preheater and upstream piping water hamer is minimized.

The applicant has stated that, although Westinghouse plants with preheat SGs l

have never experienced a bubble collapse type water hamer event in the main FW system, the SGs and the FW piping are designed for these water hammer events (Ref. 2).

The Attachment 3 to Reference 3 gives the details of the auxiliary feedwater (AFW) system design features that reduce the potential for condensation-induced water hamer. A separate AFW line and nozzle has been provided to each SG to supply feedwater when the main feedwater is unavailable or is below a specified minimum temperature. The arrangement of the AFW discharge pipe inside the SG is such that AFW piping will not drain following a drop in SG water level and therefore the nozzle and the upstream piping will not fill with steam. Also the horizontal piping immediately upstream of the SG nozzle is short with a down turned elbcw located near the SG. Backleakage is prevented or minimized

. in the AFW system piping by means of properly located check valves. Based on a

-g-review of these provisions and comparing them with the causes and evaluation of water hamer occurrences discussed in NUREG-0927 Revision 1, as stated in Reference 3, the staff concurs with the applicant's conclusion that the design features and operating procedures described above will minimize the potential for water hammer occurrence in the FW piping systems.

Based on the staff evaluation of the design considerations given to Class 2 and 3 piping, the stress limits provided in the SRP break criterion, and the rela-tively small degree of uncertainty in unanticipated loadings, the staff finds that dispensing with arbitrary intermediate pipe breaks is justified for Class 2 and 3 piping in which stress corrosion cracking, large unanticipated dynamic loads, or thermal fatigue in fluid mixing situations are not expected to occur.

This finding is based on applicant's representation in references 2 and 3 that: 1) the piping designers have appropriately considered the effects of local welded attachments per NC/ND-3645, and 2) all safety-related equipment in the vicinity of Class 2 and 3 piping systems have been environmentally qualified for the non-dynamic effects of a non-mechanistic pipe break with the greatest consequences on the equipment. Therefore, the requested deviation from the SRP (Ref. 1) for Class 2 and 3 piping is acceptable.

Piping Systems Not Included in Proposal For those piping systems, or portions thereof, which are not included in the applicant's submittals (Reference 2), the staff requires that the existing guidelines in BTP MEB 3-1 of the SRP (NUREG-0800) Revision 1 be met. However, should other piping lines which are not specifically identified in the applicant's submittal (Reference 2) subsequently qualify for the conditions described above, the implementation of the proposed elimination of the arbitrary intermediate break criteria may be used provided those additional piping lines are appropriately identified to the staff.

Conclusion The applicant has proposed a deviation from the current guidelines of the SRP by requesting relief from postulating arbitrary intermediate pipe breaks in i high energy piping systems which are not susceptible to intergranular stress l

corrosion cracking, steam or water hammer effects and thermal fatigue in fluid mixing. The SRP guideline which requires that two intermediate breaks be postulated even when the piping stress is low resulted from the need to assure that equipment qualified for the environmental consequences of a postulated pipe break was provided over a greater portion of the high energy piping run.

This proposal is based, in part, on the condition that all equipment in the spaces traversed by the fluid system lines, for which arbitrary intermediate breaks are being eliminated, is qualified for the environmental (non-dynami 4 l conditions that would result from a non-mechanistic break with the greatest

, consequences on surrounding equipment. In addition, the applicant has committed to perform preoperational testing of all the systems identified in Reference 2 and also monitor those systems for vibration during preoperational j and startup testing, in its responses to MEB questions 210.41 and 210.42.

The staff has evaluated the technical bases for the proposed deviation with respect to satisfying the requirements of GDC 4. Furthermore, the staff has considered the potential problems identified in NUREG/CR-2136 (Ref. 5) which could impact overall plant reliability when excessive pipe whip restraints are installed. Based on its review, the staff finds that when those piping system conditions as stated above are met, there is a sufficient basis for concluding that an adequate level of safety exists to accept the proposed deviation.

, Thus, based on the piping systems having satisfied the above conditions, the staff concludes that the pipe rupture postulation and the associated effects are adequately considered in the design of the South Texas Project Units 1 and 2 and, therefore, the deviation from the Standard Review Plan is acceptable.

IV REFERENCES J

1) " Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants", NUREG-0800 (Revision 1) dated July 1981.

2) Letter from J. H. Goldberg, HL&P, to H. Denton, NRC, subject, " South Texas Project Units 1 and 2, Elimination of Arbitrary Intermediate Pipe Breaks," dated August 20, 1984.

3) Letter from M. R. Wisenburg, HL&P, to G. W. Knighton, NRC, subject, " South Texas Project Units 1 and 2, NRC Request for Additional Information,"

dated March 8, 1985.

4) Letter from M. R. Wisenburg, HL&P tp G. W. Knighton, NRC, dated June 11, 1985,

Subject:

Elimination of Arbitrary Intermediate Pipe Breaks.

5) "Effect of Postulated Event Devices on Nonnal Operation of Piping Systems in Nuclear Power Plants", NUREG/CR-2136 dated May 1981.

---._..w.. . -,---,.,--.,.s-..--m , -*+=% -