ML19225B284
| ML19225B284 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 06/05/1979 |
| From: | Kuzmycz G Office of Nuclear Reactor Regulation |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19225B285 | List: |
| References | |
| NUDOCS 7907240449 | |
| Download: ML19225B284 (7) | |
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UNITED STATES y
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. E W ASHINGTON, D. C. 20555 JUN 5
$79 Docket No. 50-267 Licensee:
Public Service Company of Colorado (PSCo)
Facility: Fort St. Vrain (FSV)
Subject:
Sumary of Meeting Held on May 2,1979 to Discuss In-service Inspection A meeting was held in Bethesda, Maryland on May 2,1979 ta discuss various items related to the FSV inservice inspection (ISI) progra:. as per the agenda presented in Enclosure 1.
The purpose of the meeting was to provide PSCo the opportunity of discussing their ISI program with members of the NRC and obtaining preliminary feedback as to the program.
A list of meeting attendees is presented in Enclosure 2.
Several slides were presented during the meeting and these are included in Enclosure 3.
I.
Summary and Introduction Public Service of Colorado is developing an inservice inspection and testing program for Fort St. Vrain that is based on the current surveillance program provided in the Technical Specifications.
The program will consider industry experience, past operating experience of Fort St. Vrain, provisions of Section XI of the ASME Code (Divisions 1 and 2), certain needs not originally provided for in the Technical Specifications, and differences in design and design philosophy between Fort St. Vrain and the designs for large HTGRs and LWRs. This last consideration was given as the reason for for not basing the revised program on substantive conformance to the ASME Code.
Public Service comitted to provide a progress report on the developing program by the end of July 1979 where items of schedule, secondary system valves, ASME Code compliance, and items remaining open from this meeting will be described.
F. Swart stated that existing portions of the ASME Code would be incorporated into the program when applicable.
Further, PSCo will follow the general philosaphy of the Division 2 code which requires the inspection and testing of all safety related equipment in addition to surveillance of the primary system pressure boundary.
We noted while the Division 2 ASME Code had not yet been approved by the NRC or the ASME, that the NRC personnel who had carticipated in the drafting of the code were encouraging its NRC aporoval, and that ASME approval had been deferred principally because the code had no trial use.
We reminded PSCo that we preferred that Fort St. Vrain nse the Division 2 Code as a foundation for the ISI program rathe_r than the existing Technical Specifications
,C 7907 M D E 7 4 59-36 7 /g
JUN 5 1979
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as this approach would be expected to require less NRC review effort than approval of a custom developed program.
We stated, however, that we believed the current customized approach also acceptable, but that we would review its continued viability af ter additional information is made available in July.
Public Service Company then presented a discussion on their plant safety functions and philosophy.
FSV was designed with the " defense-in-depth" philosophy in mind and contains numerous back-up system from reactivity control to water supply for the steam generators and circulator water pelton wheel drive.
The case of complete loss of forced :irculation also contains backup cooling water supply system. The cooling is provided by means of a PCRV liner cooling system whose water is normally supplied by the service water system but uses the firewater system as a backup.
In addition to a discussion of the approaches and philosophy of the developing ISI program the following priority items were discussed:
(1) PCRV pressure relief system, (2) primary loop isolation valve monitoring, (3) steam generators, (4) PCRV monitoring, (5) PCRV closures and coverplates, (6) seismic isolation valves, and (7) inspection of core support structures.
II.
Discussion and Details 1.
PCRV Pressure Relief System The PCRV pressure relief system was discussed in the context of our concern regarding re-seating of the pressure relief valves.
Causes that would necessitate lifting of one-of-the-two Target Rock relief valves were seen as very remote and would involve multiple failures of safety systems.
Block valves upstream from the relief valve could be manually operated if either relief valve failed to seat, but this is not a planned action.
In July PSCo will propose responses to our concerns regarding (1) habitability considerations that could prevent manual closing of the block valves, (2) inservice inspection and leak testing of the block valves, and (3) the seismic classification of the vant piping from the relief system to the building rocf.
In response to a question PSCo identified the other potential leakage paths through primary containment which included several gas sampling lines and the helium circulator bearing seals.
2.
Primary Loop Isolation Valve Monitoring In the exit duct of each helium circulator a dual vane flapper valve falls closed whenever signific&nt flow through the circulator ceases.
Closure of a loop isolation valve prevents back flow through the circulator, which is necessary to preclude in order that emergency core cooling requirements under single circulator cooling can be fulfilled.
Failure of the valve to close can be detected by pressure measurements 367 6 1%
s
.. across the circulator and by circulator self-turbining in the reverse direction.
In a letter of March 15, 1979, PSCO stated it will investigate incorporation of surveillance data on loop isolation valve perfomance into the Fort St. Vrain surveillance program.
We infomed PSCo that the response in the March letter was satisfactory at present, although we believed an observed failure of any loop valve to function prcperly should become a reportable event.
PSCo reported that only one instance of failure to close has occurred and this was under conditions of unusually low pressure differential.
PSCo stated it will propose a method for monitoring and reporting loop valve performance in July.
3.
Steam Generators At present there is no formal program for steam generator surveillance.
It is a characteristics of the HTGR concept that both the main sections and reheater sections are continuously monitored for leakage.
The main sections are monitored by moisture ingress into primary helium and the reheater sections by radiation levels in the secondary system.
In the March letter PSCo stated that it is developing an ISI program which will assess the desirability and feasibility of additional steam generator inspections beyond those which had already perfonned under DOE auspices (subheader tube removal, ring header valve disassembly, temperature and pressure drop data).
All previous inspections, including information gained during PSCo's plugging of a single subheater, have indicated corrosion rates.are well within design allowences.
Inspection of tubing by internal methods is difficult if not impossible due to the design of the steam generator.
4.
PCRV Monitoring PSCo stated it believes that its present surveillance specifications presently exceed the monitoring requirements for tendons given in Regulatory Guides 1.35 and 1.103.
We will evaluate this position.
All inspections have thus far shown no traces of rust on any tendo %.
A DOE program for liner tube corrosion inspectioq verified that corrosion rates were below allowances and that the water treatment was satisfactory.
5.
PCRV Closures and Coverplates PSCo will document justifications for certain desired exemptions from the ASME Division 2 code in July on closure bolting rings.
With respect to the (hold-down) coverplates on the refueling regions, PSCo stated a proposal for their surveillance will be made in July.
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- 6.
Seismic Isolation Valves Remaining open items on this topic are revisions of the P and I diagrams to show the correct status of normally closed valves. A change notice will document completion of the seismic qualification program and the seismic design of the Cardox tank.
Single failure criteria is achieved by providing valve operations for two loop firewater cooling when only loop cooling is actually needed for safety shutdown.
7.
Inspection of Core Support Structures PSCo has no immediate further plans for inspection of the core support structure.
The upper surface of core support blocks in regions 13 and 35 were inspected visually during the recent refueling shutdown and found satisfactory.
PSCo is aware that PNL is developing a technique to correlate graphite strength with sonic speed and will be open to suggestions for the use of this technique if it is applicable to grade PGX graphite.
PSCo is working with General Atomic to develop an improved model relating PGX oxidation to support block strength and lifetime.
Progress on this model will be reported in July. We noted that our recently issued Safety Evaluation supporting the insertion of the PGX test specimens in the reactor summarizes our current position with respect to the core support blocks.
In response to our recent phone request, PSCo presented the results of an exploratcry computation estimating the potential damage if the central fuel column should arbitrarily drop.
Based on a free fall drop of 41 inches and a weight of 42,000 lbs PSCo calculated that the allowable stresses of both the stsel and concrete in the floor would not be exceeded.
This calculation took into consideration the cushioning effect of the Kaowool insulation layer in the floor.
III.
Items to be Resolved Several items were mentioned that would be further discussed during a June or July meeting with PSCo.
1.
Manual closing of valves might be a problem due to habitability of surroundings.
2.
Can valves be closed to fully isolate the PCRV containment?
3.
Is the relief valve venting to the atmosphere a Class I system?
4.
Each valve malfunction should be reported.
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- 5.- JUN 5 1379 5.
PSCo will consider visually checking the top head hold down plots bolts.
6.
Modifications to buffer helium system will be discussed at next ISI meeting.
7.
Responses will be submitted to the I&E bulletins dealing with the TMI-2 incident.
George Kyzmycz, Project Manager Advanced Reactors Branch Division of Project Management 367
GENDA FOR NRC-PSC MEETING May 2, 1979 F.E. Swart A.
Introduction B.
Fort St. Vrain Inservice Inspection and Testing M.L. Padovan 1.
PSC ISI Review Program F.E. Lesko 2.
FSV ISI Plant (afety Discussion C.
Review of NRC Priority ISI Items 1.
Primary System Valves M.H. Holmes a.
PCRV relief valve re-seating testing J.W. Gahm b.
Loop isolaticn valve closure monitoring 2.
Steam Generators F.E. Swart a.
Efrects of termination of DOE programs F.E. Swart b.
PS: :. l ans 3.
PCRV Monitoring Application of Reg. Guides 1.35 and 1.103 J.R. Reesy a.
b.
Closures - inspection of welds and bolting per M.L. Padovan ASME code M.L. I':devan Report on linear cooling system monitoring c.
4.
Status Report on Study of Seismic Isolation Valves Valves required of safe shutdown reactor cooling J.R. Reesy a.
M.H. 'iolmes b.
Yalve single-failure criteria 5.
Inspection of Mechanisms and Features Designed to J.W. Gahm Preclude Control Rod Ejection 6.
Inspection of Core Support Structures J.R. Reesy a.
Consequences of PGX failure b.
Plans beyond PGX surveillance specimens and PGX F.E. Swart visual inspections D.
General Discussion 14 0
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