ML19256F851
| ML19256F851 | |
| Person / Time | |
|---|---|
| Site: | Crystal River, Bellefonte, Crane  |
| Issue date: | 10/25/1979 |
| From: | Harold Denton Office of Nuclear Reactor Regulation |
| To: | Parris H TENNESSEE VALLEY AUTHORITY |
| Shared Package | |
| ML19256F850 | List: |
| References | |
| NUDOCS 7912260315 | |
| Download: ML19256F851 (4) | |
Text
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- s UNITED STATES
.T,, ~ i.
NUCLEAR REGULATORY CC',',M SSION WASHINGTON. O. C. 20555
{.
_i Nr Oc:cber 25, 1979 Docket ho.:
50-438 and 50-439 Mr. H. G. Parris Manager of Power Tennessee Valley Authority-500 Ches nut Street, Tower II Chat anooga, Tennessee 37401
Dear Mr. Parris:
SUBJECT:
10 CFR 50.54 REQUEST REGARDING THE DESIGN ADEQUACY OF BABCOCK
& WILC0X NUCLEAR STEAM SUPPLY SYSTEMS UTILIZING ONCE THROUGH STEAM GENERATORS (EELLEFONTE NUCLEAR PLANT)
Several haroware and procedural changes have been made to operating B&W plants to reduce the Iikelihood of recurrence of a TMI-type accident. These changes have been in the area of auxiliary feecwater systems, inte ated control system, reactor protection system, small-break loss-of-cociant accicent analysis and operator training anc procedures.
However, at th'is time, we are beginning to icok more deeply into additional design features of BJW plants to consider if any further system modifications are necessary.
The use of once-through-steam-generators (OTSG) in B&W plants has an opera-tional aavantage in that it provides a small degree of steam superheat, as contrasted with the conventional saturatec U-tube steam generator.
In adci-ion, it provides for less water inventcry thus making a steam line break less severe. However, the relatively low water inventory with the presence of a liquid-vapor heat transfer interface in the active heat transfer zone closely couples the primary system to the steam generator conditions with a consecuently high sensitivity to feedwater-flow rate perturbations. to this letter addresses system problems and staff concerns in this area. At present, we are investigating whether S&h plants are overlysensitive to feedwater transients, due to the' OTSG concept, as couplea with the pressurizer si:ing, ICS cesign, and PCRV/ reactor tri: set pcints.
As E. cf tne cost TMI-2 eff crt, cetailec ar.alyses nave beer, mace of under-ccci ng transier.ts for B&W c' 3nts.
bwever, cue tc :ne ser.sitivi y ef the
. a ces'gr, a,. :lants have 1150 beer ex:e-iencing a rur:er cf ela-ively severe c.ercocling events.
1638 289
? Yk nkjW 791g200
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Mr.
M. G. P arri s-For your information, NRC is initiating a researen tas<.
- cuantitatively assess B&W system designs, including the integrated control system, aimed at identifying obvious accident sequences leading to core damage having a high frequency as compared to the Reactor Safety Study, see Enclosure 2.
( A complete determination of risk will not be attempted). The objective of this assessment is to identify high-risk accident sequences (including TMI implications) utilizing event tree and simplified fac!: tree analyses.
Included will be estimation of release categories, approximate quantiff-cation of expected frequency of selected event sequences and sensitivity studies for reliability of operator response.
The study will focus on the risk implications of the se'nsitivity of the B&W cesign and on the potential interac-ions arising.from the integratec con:rc: system. W e' estimate this study to be completed in abou six mon ns. We will use the Crystal River, Unit 3 plant as the referencec f aci;i y :o be analyzed.
We have been holding generic discussions with Babcock anc Wilcox Company concerning this matter.
However, system sensitivity to feedwater transients involves balance-of-plant equipment and systems as well as the nuclear steam supply system, and such plant-specific characteristics m.st be considered.
We are also considering whether it is necessary to hal: :or-ions of the construction of B&W plants, pending the outcome of :ne reliability assess-ment. As a preliminary consideration, we have identifiec these systems and components that may be impacted by possible design changes as result of this study. is a preliminary listing of sucn systems and components.
Under the authority of Section 132 of the Atomic Energy 'c of 1954, as amended, and Section 50.54(f) of 10 CFR Part 50, additior.al information is requested to allow us to determine whether it is necessary to halt all or portions of the construction of your plant pencing the results of our stucy.
We request you provide:
a)
Identify the most severe overcooling events (consicering both anti-cipated transients and accidents) which could occur at your facility.
These should be the events which causes the greatest inventory shrinkage. Under the guidelines that no cperator action occurs before 10 minutes, and only safety systems can be used to mitigate the event, each licensee should show that the core remains adequately cool ed.
- )
Identify wnether action of the ECCS or RPS (c-c:e a Or action) is necessary to oro:ect the core 'cIlowing Se
- s severe over-cooling ransien; icen-ifiec.
If :nese syste s a-e recuired, you snocid show that its de;'gn cr terion #c
. e u :e* cf i
actua-icn cycles is acecuate, consicering a~i <a' a:es #cr excessive c0 cling transients.
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Mr. H. G. Parris c) trovide a schedule of completion of installation of the identified tystems and comconents, d)
Identify the feasibility of halting installation of these systems and components as compared to the feasibility of completing installation and then effecting significant changes in these systems and components.
e) Comment on the OTSG sensitivity to feedwater transients.
f) Provide recomendations on hardware and procedural changes related to the need for and methods for damping primary system sensitivity to perturbations in the OTSG, Include details on any design adequacy studies you have done or'have in progress.
We are sendinc sirilar letters to all utilities 5ciding cor.struction permits for ;1 ants with S&W nuclear steam supply systems.
We recuest your reply by December 3.,1979. We believe that a meeting with you and the other utilities together with the staff and the Sabcock and Wilcox Company to discuss this matter woulc be beneficial to all parties.
At that time, we will provide further details en the Crystal River Study.
We are scheduling such a meeting for Novem3er 5,1979 at 10:00 a.m. in Room 3-422 at our offices in Bethesda, 7920 Norf olk Avenue, Bethesda, Maryland.
Please call Dr. Anthony Bournia at (301) 492-7200 if you have iy questions concerning this letter.
Sincerely, Mhk n
Harold R. Denten, Director Office of Nuclear Reactor Regulation
Enclosures:
As stated cc:
See next page 1638 291 Y$N$$k,
Mr. H. G. Pa rris cc:
Herbert S. Sanger, Jr., Esq.
General Counsel Tennessee Valley Authority 400 Commerce Avenue, E11B33 Knoxville, Tennessee 37902 Mr. E. G. Beasley Tennessee Valley Authority 400 Commerce Avenue, W10Cl31C Knoxville, Tennessee 37902 Mr. D. Terrill Licensing Engineer Tennessee Valley Aut.hority 400 Chestnut Street Tower - II Chattanooga, Tennessee 37401 Mr. Dennis Renner Babcock & Wilcox Company P. 0.' Box 1260 Lynchburg, Virginia 24505 Mr. Robert B. Borsum Babcock & Wilcox Company Suite 420 7735 Old Georgetown Road Bethesda, Maryland 20014 4