Text

Forwards Safety Evaluation of SEP Topic III-5.A Effects of Pipe Break on Structures,Sys & Components Inside Containment. Licensee Program Plan Adequate.Items to Be Addressed in Integrated Plant Safety Assessment Listed
	ML17194B309
Person / Time
Site:	Dresden
Issue date:	09/21/1982
From:	Oconnor P; Office of Nuclear Reactor Regulation
To:	Delgeorge L; COMMONWEALTH EDISON CO.
References
	TASK-03-05.A, TASK-RR LSO5-82-09-066, NUDOCS 8209230404
	Download: ML17194B309 (11)
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September 21, 1982 Docket No. 50-237 LS05-82-'09-066 Mr. L. DelGeorge Director of Nuclear Licensing Conunonwealth Edison Company Post Office Box 767 Chicago, Illinois 60690

Dear Mr. DelGeorge:

SUBJECT:

DRESDEN NUCLEAR POWER STATION, UNIT 2 - SEP TOPIC III-5.A, EFFECTS OF PIPE BREAK ON STRUCTURES, SYSTEMS AND COMPONENTS INSIDE CONTAINMENT Enclosed is our evaluati.on of SEP Topic III-5.A. This assessment compares your facility with the criteria currently used by the regulatory staff for licensing new facilities.

We conclude that the licensee's program plan, *methods of approach and the criteria used for the evaluation of the subject topic are, in general, adequate.

However, we will review the results when it is available.

The resolu-tion of the following i~ms w11 l b~,1addres~sed ~in the Integrated Plant

. *Safety Assessment:

A.

~Ihe schedules for submitting the* anal.ys.es.for which the Sta.ff has

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Evaluation of jet impingement *on target pipe;

c.

Evaluation of postulated broken pipe impacting target pipe; and

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Criteria for satisfying the detectability requirement for the U""

alternative safety assessment using fracture mechanics analysis.

The need to actually implement changes as a result of these items will be determined du.ring the integrated safety assessment. This safety evaluation may be revised in the future if your facility design is changed or if NRC criteria relating to this topic are modified before the integrated assessment is completed.

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NRC FORM 318 (10-80) NRCM 0240 OFFICIAL RECORD COPY USGPO: 1981-335-960

SEP EVALUATION OF EFFECTS OF PIPE BREAK ON STRUCTURES, SYSTEMS AND COMPONENTS INSIDE CONTAINMENT TOPIC II I-5. A FOR THE DRESDEN NUCLEAR POWER STATION, UNIT 2

TABLE OF CONTENTS I.

INTRODUCTION II.

REVIEW CRITERIA III.

RELATED SAFETY TOPICS AND INTERFACES IV.

REVIEW GUIDELINES

v.

EVALUATION A.

BACKGROUND B.

SUMMARY

OF FINDINGS VI.

CONCLUSIONS VII.

REFERENCES I

I.

INTRODUCTION The safety objective of Systematic Evaluation Program (SEP) Topic III-5.A, Effects of Pipe Break on Structures, Systems and Components Inside Containment," is to assure that pipe breaks would not cause the loss of required function of "safety-related" systems, structures and components and to assure that the plant can be safely shutdown in the event of such breaks.

The required functions of "safety-related" systems are those functions required to mitigate the effects of the pipe break and safely shutdown the plant.

II.

REVIEW CRITERIA General Design Criteria 4 (Appendix A to 10 CFR Part 50) requires in part that structures, systems and components important to safety be appropriately protected against dynamic effects, such as pipe whip and discharging fluids, that may result from equipment failures.

III.

Background

On July 20, 1978, the SEP Branch sent a letter (Reference 2) to KMC, Inc. requesting an analysis of the effects of postulated pipe breaks on structures, systems and components inside containment for SEP Plants.

In that letter, the staff included a position that stated three approaches were appropriate for postulating breaks in high energy piping systems either P?275 psig or T~200°F. The approaches are:

1.

Mechanistic

2.

Simplified Mechanistic

3.

Effects Oriented The staff further stated that combinations of the three approaches could be utilized if justified.

On December 7, 1978, the NRC staff sent another letter (Reference

3) to CECo. requesting the licensee to provide some technical informition and evaluation of the subject topic for staff to compare the plant design to current criteria and to evaluate the significance of potential differences.

Subsequently, several meetings were held between the staff and the representatives of the licensee (Commonwealth Edison) and its consultants (EDS Nuclear) to discuss the subject matter.

As part of redirection of the NRC Systematic Evaluation Program, the licensee provided the Interim Progress Report on the subject topic on June 4, 1982, (Reference 1).

The objective of Reference l is to present the program plan for resolution of SEP Topic III-5.A at Dresden 2 Nuclear Power Station as well as key elements of the technical approach being utilized.

As a result of the review of Reference 1, the NRC staff issued a draft safety evaluation of SEP Topic III-5.A dated June 29, 1982, (Reference 4)..

By 1 etter dated August 23, 1982, (Reference 5), the licensee.

submitted a report (dated July 27, 1982) addressing *the issues identified in Reference 4, B. *Summary of Findings

1.

The program plan developed by Commonwealth Edison for resolution of SEP Topic III-5.A at Dresden 2 Nuclear Power Station consists of the following six major tasks:

a.

finalize program plan

b.

define mechanistic break locations

c.

develop target evaluation criteria

d.

perform interaction evaluation

e.

perfprm cost/benfit analysis

f.

perform additional analysis (as required)

i.

fracture mechanics evaluation ii.

rigorous jet impingement and pipe whip analysis iii. rigorous containment and structure damage analysis iv.

piping stress analysis

v.

restraint feasibility study The licensee's analysis is near completion.

The results of analysis will be reviewed when it is 'available to the NRC staff.

2.

Current criteria require that through-wall leakage cracks be postulated in moderate energy line piping (<200°F and<275 psig}.

The licensee has proposed a set of criteria to be used for the evaluation.

Based on the information submitted in Reference 5 and the clarification to be docketed in the final report, we have concluded that the proposed criteria are acceptable.

3.

The licensee has defined high energy fluid systems as those that are maintained under conditions where either or both the maximum operating pressure exceed ~200°F and~ 275 psig respectively.* Those piping systems that operate above these limits for only a relatively short portion (less than approxi-mately two percent) of the period of time to perform their intended function, are excluded from evaluation.

This is consistent with current criteria.

4.

The licensee has utilized the Mechanistic Approach in its evaluation of high energy pipe break inside containment.

Based on the information submitted in Reference 1, we have concluded that the criteria used to define the break locations and the break types are in accordance with currently accepted standards~

5, We have reviewed the licensee's information pertaining to pipe whip load formulation, Based on the information currently available, we have determined that the licensee's approach is*,

in general, acceptable.

However, the detailed methodology and specific application of Reference 6 to the licensee's pi~e whip load calculation will be reviewed when the results of licensee evaluation become available.

6.

The licensee's calculations of jet impingement loads on various targets are based on the methodology presented in ANSI/ANS 58.2-1980.

Based on the information submitted in Reference 1, we have concluded that the licensee's methodology including its basic assumptions for calculating the jet impingement loads is acceptable.

7.

We have reviewed the information pertaining to the pipe whip and jet impingement interactions with the drywell liner, Reactor Pressure Vessel (RPV) pedestal and biological shield wall.

Based on the information submitted in Reference 1, we have determined that the licensee's approach is, in general, acceptable except as follows:

a.

Section 4.2 of Reference l references Chicago Bridge &

Iron Company (CB&I) Test Report (Reference 7).

The CB&I test indicates that when a spherical shell segment having a shell thickness.of 0.75 inches is loaded over a large enough area, i.e., equivalent to a 14 inch diameter or larger circle, deformation of the plate over 3 inches can occur without failure of the plate segment.. Based on this test result, the licensee concludes that for breaks occurring in piping greater than 14 inches in diameter, even if contact occurred with the drywell liner, the amount of liner deformation, as limited by the concrete shield wall, would not result in a liner failure.

Accord-ingly, no unacceptable interactions are considered to result with the drywell as a consequence of breaks postulated in piping greater than 14 inches in diameter.

However, it should be noted that the CB&I test was perfonned under essentially static conditions.

It is not clear that the test result is also valid for the dynamic loading which would be experienced as a result of pipe whip.

In addition, the particular test applies a concentrated load of 235 tons over an area. equivalent to a 14 inch diameter or larger circle.

This assumption may not always be valid because the impact area of a 14 inch diameter or larger pipe may be smaller than the assumed area.

Thus, our concern is that in the case of applying concentrated dynamic load over a small area the steel plate may be perforated before the deformation is terminated by the concrete shield wall. Therefore, the use of the CB&I test results by the licensee as the sole justification for the containment liner integrity is not sufficient.

In Reference 5, the licensee responded to the staff's questions concerning the methods of approach and the criteria used for further justification for the interac-tion of pipe whip and jet impingement with the containment liner.

We have concluded that the licensee's methods of

\\ approach and the criteria are, in general, acceptable.

However, the results will be reviewed when they become available.

8.

In considering the damage criteria {Section 4.5 of Reference 1), the licensee has used the assumption that a jet or whipping pipe is considered to inflict no damage.on other pipes of

9.

equal or greater size and equal or greater thickness.

It is the staff's position (Reference 9) that the effects of jet impingement should be considered and evaluated regardless of the ratio of impinged and postulated broken pipe sizes.

The licensee provided some justifications in Reference 5 and concluded that the same rule which i~ applicable to pipe whip should also be applicable to jet impingement considerations.

However, the staff felt that the energy absorption mechanism for a pipe-to-pipe impact is different from that for jet impingement on a pipe.

Therefore, it is the staff's position that the licensee should evaluate and address the effects of jet impingement regardless of the ratio of impinged and postulated broken pipe sizes.

in determining the acceptability of target pipe {Section 4.3.2 of Reference 1), the licensee has used a criteria that ~he limiting factor for an applied equivalent static load is that the resulting strain in the target pipe material does not exceed 45 percent of the minimum ultimate uniform strain of the material at the appropriate temperature.

This criteria is acceptable for avoiding cascading pipe breaks.

However, some piping systems are required to deliver certain rated flow and should be designed to retain dimensional stability when stressed to the allowable limits associated with the emergency and faulted conditions, i.e., the functional capability of the piping is required to be demonstrated.

The licensee was requested to provide justification to assure that the target piping will remain functional as a result of jet impingement and pipe whip interactions.

!n Reference 5, the licensee indicated that he performed a parametric study covering a range of geometric and load parameters.

The nonlinear finite element dynamic analysis results indicated that the coexistence of large localized strain levels and small global ~eformations~ Thus, the licensee concluded that it is possible to achieve strain levels approaching 45 percent of the minimum uniform ultimate strain of the material in a localized region without affecting the overall deformation or functionability of the target pipe.

f

In reviewing the example presented in Reference 5, the staff found that the 45 percent of the minimum uniform ultimate strain reached at the point of load application was a global strain since a beam model was used for analysis.

The licensee agreed to demonstrate that the localized defor-mation associated with a global strain of 45 percent of the minimum ultimate uniform strain of the material would not affect the functionability requirement of the target pipe.

10. The licensee's approach for the alternative safety assessment for selected high energy pipe break locations using fracture mechanics analysis is not completely consistent with the staff guidance on the subject as described jn'Appendix I to Attachment to Reference 4.

For example, the licensee did not address the detectability requirements.

The staff.recorrunends that the licensee consider the staff guidance as provided in Reference 4 for resolution of unresolved interactions.

The licensee, in his submittal of Reference 5, proposed an approach different from that of the staff's recommendation for satisfying the detectability requirement.

The staff has reviewed the licensee's approach and found it unacceptable.

Therefore, this issue will be determined in the Integrated Assessment.

VI.

CONCLUSIONS Based on the information submitted by the licensee, we have reviewed the criteria pertaining to the locations, types and effects of postulated pipe breaks in high energy piping systems inside containment.. We have concluded that the criteria used to define the break locations, the break types, the jet impingement loads, and the pipe whip analysis are, in general, in accordance with currently accepted standards.

We have also determined that it is acceptable under current SEP criteria to use the interaction study to evaluate the effects of postulated pipe breaks to determine the acceptability of plant response to pipe breaks.

However, the following items have not been addressed adequately in the licensee's evaluation.

The resolution of the following items will be discussed in the Integrated Plant Safety Assessmerit:

A.

The results of the licensee's implementation of the criteria acceptable to the NRC staff will be reviewed; B~ The licensee should evaluate and address the effects of jet impinge-ment regardless of the ratio of impinged and postulated broken pipe sizes;

. C.

The licensee should demonstrate his criteria assumption that the localized deformation associated with a global strain of 45 percent of the minimum ultimate uniform strain of the material would not affect the functionability requirement of the target pipe; and D.

Criteria for satisfying the detectability requirement for the alternative safety assessment using fracture mechanics analysis.

VII. REFERENCES

1.

Letter from T. J. Rausch (CECo) to D. M. Crutchfield (NRC), dated June 4, 1982, Attachment I - Report, "Dresden 2 Nuclear Power Station SEP Topic III-5.A, High Energy Pipe Break Inside Containment*

Interim Progress Report, 11 dated May 18, 1982.

2.

Letter from D. K. Davis {NRC) to KMC, "Assessment of Postulated Pipe Breaks Inside*containment for SEP Plants," dated June 20, 1978.

3.

Letter from D. L. Ziemann (NRC) to Cordell Reed (CECo), "Pipe Breaks Inside Containment for the Dresden l and 2 Facjlities, 11 dated December 7, 1978.

4.

Letter from D. M. Crutchfield (NRC) to L. DelGedrge (CECo),

"Draft Safety Evaluation of SEP Topic III-5.A, High Energy Pipe Breaks Inside Containment, Including Request for Additional In-formation for the Dresden Nuclear Power Station, Unit 2, 11 dated June 29, 1982.

5.

Letter from Thomas J. Rausch (CECo} to Paul O'Connor (NRC),

"Dresden 2 SEP Topic III-5.A, High Energy Pipe Break Inside Containment," dated August 23, 1982.

6.

Enis, R. 0., Bernal, D. B., and Burdette, E. *G., "A Design Guide for Evaluation of Barriers for Impact from Whipping Pipes."

Paper from Second ASCE Conference on Civil Engineering and Nuclear Power, dated September 1980,

7.

Thullen, Philip, "Loads on Spherical Shells," Oak Brook Engineering Department, Chicago Bridge & Iron Company, dated August 1964.

8.

"Report of the ASCE Committee on Impactive and Impulsive Loads, 11 Civil Engineering and Nuclear Power,_ Volume v*., dated September 1980.

9.

Letter from D. Ziemann (NRC). to D. L. Peoples, "Evaluation of Pipe Whip Impact and Jet Impingement Effects of Postulated Pipe Breaks for SEP Topic IIl-5.A and Ill-5. B, 11 dated January 4, 1980.

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Dear Mr. DelGeorge:

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Dear Mr. DelGeorge:

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