ML19210B229
| ML19210B229 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 06/01/1973 |
| From: | Deyoung R US ATOMIC ENERGY COMMISSION (AEC) |
| To: | John Miller METROPOLITAN EDISON CO. |
| References | |
| NUDOCS 7911040176 | |
| Download: ML19210B229 (4) | |
Text
4 pp h-lkW JUN 1 1973 Docket No. 50-289 Metropolitan Edison Company ATTN: Mr. John C. Miller Vice President P. O. Box 542 Reading, Pennsylvania Gentlemen:
We have reviewed the information on high energy line failures for Three Mile Island Unit 1 presented in Amendment No. 38 and have discussed the matter with your staff. You have concluded that no design modifications are necessary to cope with high energy line ruptures outside containment.
The highest energy lines in question are located within the Intermediate Building which also houses the emergency feedwater system. You have concluded that, if one of these lines suffers a major break, the external valls of the Intermediate Building would retain their structural integrity but the sequence or extent of failures within the building could not be predicted. Consequently, you have assumed the loss of the emergency feedwater system following such an event and have claimed that the reactor can be brought to cold shutdown safely by a feed-and-bleed procedura using the high pressure injection system to supply or feed cold
- ! ster to the system from the borated water storage tank and allowing hot reactor (bleed) coolant to be released through the pressurizer relief valves. You have not presented an analysis of such feed-and-bleed cooling to demonstrate its adequacy to bring the plant to cold shutdown safely.
In view of the grave consequences that could result from a break in a line carrying high energy fluid inside the Intermediate Building, modification of the design will be required. We er. courage you to analyze reactor coolant system feed-and-bleed as a backup method to cooldown using the emergency feeduster system. However, we cannot accept initial reliance on the feed-and-bleed method; design modifications are necessary to assure the integrity and availability of the emergency feedwater system. Such modifications might be to increase the vent area of the affected subcompartments, to encapsulate the high energy lines in the regions of high stress or some ccabination of suitable measures.
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John G. Miller JUN 1 1973 In considsring the encapsulation of' high energy lines at critical locations, the Regulatory staff has developed a list of tentative criteria that should be used for guidance in providing an acceptable encapsulation design. We are enclosing a copy of these tentative criteria to assist you in designing high energy line encapsulation sleeves for the Three Mile Island Unit 1 plant if you should choose to utilize this option. If it is determined that mechanical design changes are not practical for some locations, a significantly augmented inservice inspection program could provide acceptable assurance of the integrity of these lines. The augmented inspcetion program would have to include volumetric = = % tion of 100% of circumferential and longitudinal weld seams at each refueling outage or plant cold shutdown (but not more often than every six months). Such examination should be performed in acecrdance with the rules of inservice inspection contained in Section II of the ASME Code and inspection results would have to meet the acceptance standards of the Code to permit resumption of operations.
9 Because of the nature and timing of this problem, you are invited to
.diecuss the matter at a meeting with AEC staff at the earliest opportunity.
Sincerely, R. C. DeYoung, Assistant Director for Pressurized Water Reactors Directorate of Licensing
Enclosure:
Tentative Criteria DISTRIBUTION cc:
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' '* TENTATIVE CRITERIA FOR THE APPLICATION OF ENCAPSULATION SLEEVES ON HIGH ENERGY FLUID CARRYING LINES The following requirements shall be met for the application of encapsulation sleeves at design basis break locations as means of reducing compartment pressurization levels in the event of a pipe severance:
1.
The encapsulation sleeve shall be designed and supported in a manner which will not introduce significant strain concentrations on the encapsulated section of piping.
2.
The piping beyond the encapsulation sleeve shall be provided with pipe whip restraints (or anchors) which restrict its axial displacement ase motion within the sleeve following a postulated circumferential pipe break.
3.
The encapsulation sleeve shall be designed (a) to withstand the dynamic forces of internal pressurization resulting from the escape of high energy fluid at the postulated pipe break location assuming complete pipe severance and axial separation to the extent permitted by the pipe restratnts, and (b) to restrict the flow at the open ends of the sleeve to a level required to preclude compartment pressurization beyond the allowable structure design limits.
4.
The stresses imposed on the encapsulation sleeve during dynamic pressuriza-tion shall be limited to the design limits associated with " emergency condition" as permitted by the rules of ASME Section III-Nuclear Power Plant Components Code, for Class 2 components.
5.
The encapsulation sleeve shall be constructed in accordance with the rules of ASME Section III Code Class 2 or ANSI-B31.7 Class II components with the added requirement that each pass of the final assembly welds shall be nondestructively examined by surface examination techniques (i.e., liquid penetrant or magnetic particle).
6.
The encapsulation sleeve shall be provided with open vent and drain pipe nipples which extend beyond the pipe insulation as a means of monitoring the encapsulated pipe section for any leaks which might develop in service.
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7.
The design of the encapsulation sleeve shall permit either its removal by machinery or flame cutting techniques or the replacement of encapsulated pipe section in the event leaks develop which require repair or replacement of the pipe.
8.
Pipe weld jointo located within the encapsulation sleeve and not accessible for subsequent inservice inspection in accordance with the rules of ASME Section XI-Inservice Inspection Code shall be nondestructively examined and the results satisfy the acceptance standards of this Code, prior to the assembly of the encapsulation sleeve.
9.
The piping welds not encapsulated within the piping runs traversing safety-related areas, or within compartments adjoining safety related areas shall be subjected to periodic inservice examinations in accordance with ASME Section XI Code Class 2 component requirements except that 100 percent of such welds shall be examined during each inspection interval.
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