ML20127M826
| ML20127M826 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 03/01/1967 |
| From: | Morris P US ATOMIC ENERGY COMMISSION (AEC) |
| To: | Palladino N Advisory Committee on Reactor Safeguards |
| References | |
| NUDOCS 9211300483 | |
| Download: ML20127M826 (1) | |
Text
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UNITED STATES i
ATOMIC ENERGY COMMISSION W ASHINGTON. D.C. 20546 g
Herch 1' 1967 Doeket No. 50-263
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Mr. Nunzio Palladino Chairman, Advisory Committee f
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on Reactor Safeguards U. S. Atomic Energy Commission Washington, D. C.
Dear Mr. Palladino Transmitted for theinformation of the Committee are three copies of the following NORTMERif STATES POWER COMPANY HollTICELLO MUCLEAR CENERATING PIMT Letter dated February 27, 1967, with list of addittomal i
information which is necessary ; to couplete the applica-tion filed by Northern States Power Cogamy.
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t Sincerely yours, b
Peter A. Morris, Dire: tor Division of Fonctor Licensing i
Enclosures As. stated above Din t ributt on_:
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% hf February 27, 1967 fN Rt PLY MutM Toi Docket No. 50-263 Northern States Power Company 414 Nicollet Avenue Minneapolis, Minnesota 55401 Attention Mr. David F. McElroy Vice President, rngineering Gentlement To verify the understanding reached during our rebruary 2 and February 24, 1967 meetings, enclosed is the list of additional information which we stated was necessary to complete your application.
Your reply to these questione should be submitted as an amendment to your application, Sincerely yours, A
i Peter A. Morris, Director Division of Peactor Licensinit i
Enclosure:
List of Questions
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ADDITIONAL INTORMATION REOUIRED NORTHERN STATES POWER COMPANY MONTICELLO NUCLEAR CENERATINO PLANT DorKET NO. 50-263 1.0 Based on the review of Amendnent No. 2 to the FDSAR, Northern States Power Company Monticello Nuclear Cennrating Plant " Design, Fabrication and Erection of the Reactor Vessel," and in order to obtain further asourance of the integrity of the field fabricated reactor vessel, we request that the following information be pro-vided:
1.1 Typical vessel test plate metallurgical evaluations, including macroetch crosa sections showinR the full thickness of the base plate and the weld metal and a thorough exploration of the heat af fected zones by hardness surveys.
In addition, the results of typical metallographic examinations.of base metal, weld metal, and heat af fected zones should be provided for correlation with mechanical properties. As an alternative, you may wish to provide the results of the tests outlined above on the Monticello vessel material.
1.2 From each vessel test plate, including typical plates used for welding quali-fication, suf ficient specimens should be obtained so that the complete Charpy temperatare transition curve can be established for the base metal, heat af fected zone, and weld metal. The radius of the Charpy specimen notch should be checked using a magnifying radius comparator. The other sensitive dinen-sfans should also be umasured. The root of the notch should be located as close to the coarse grain region as pnsoible (as determined by etching) and should be wholly within the heat af fected zone, with the notch oriented parallel to the plate thickness. Please describe your plans concerning the forecoing.
1.3 A chemical analysis of each plate, forging, and vessel test plate weld should be perforned which includes the trace elements, such as soluble and total A1, _
Ti, Sb, Sn, Pb, Cu, V. Zr, etc.
Please describe your plcas concerninn this analysis.
1.4 The outer surface of the reactor vessel should be examined by macnetic particle and ultrasonic tests after all post veld heat treatment and the 125% over-pressure test have been completed. The purpose of the examination is to detect any cracks caused by the heat treateent or' the overpressure test. Please describe your plans concerning such a test.
2.0 We have observed that core floodian af ter an ?'CA nay cause a reactivity transient if control rods fail to scram in part or in toto. As a means of providine an understandinc of the macnitude of this occurrence, discuss the consequences of potential transients that might occur should all or various nunbers of control rods fail to scram after an MCA.
Discuss the basis upon which such an occurrence is considered to be not credible.
Assuming a number of control rods f ail to scran, discuss possible means of limiting such transients.
3.0 We note that the turbine bypass capability,15%, is less than the 25, 40, and 100%
provided on other BWR power plants. Your response in Amendrent 4 to question No. 4.4 provides the calculated response of the plant to typical transients expected during plant operation.
In order to obtain a clear understanding of the safety significance of this lower bypass capability, please provide calculations similar to those of Figures 4.4-1 through 4.4-5, assuming a step load rejection from rated power and assuming a 100%, 40%, 25%, and 15% turbine bypass capability, How would the number of reactor scrams be af fected by the bypass capability?
Discuss your reasons for selecting 15% rather than a higher bypass capability.
4.0 From the informatica subadtted to date, it is evident that proper functionine of the engineered safeguards is predicated on their starting almost imrediately af ter the MCA.
Since this can best be assured by providing the most reliable source of of f-site power possible, it would be desirable to demonstrate that the ef fects of a loss of the Monticello generator on the power network are in accordance with predicted performance characteristics, please provide your comments and outline any plans you may have formulated to perform such a test. The benefit and inde-pendence of the six transmission lines should also be explained.
5.0 The inerting provisions in the pressure suppression containment protect against the combustion of hydrogen which micht be generated in metal-water reactions af ter a loss-of-coolant accident. The radiolytte decomposition of water, however, could result in oxygen as well as hydroren evolution. Your consideration of this prob-lem in question 1.9 in Amendrent No. 4 assumed that the decomposition would_ be equivalent to that observed during normal reactor operation.
Our calculations, based on experimental data at one atmosphere, indicate that this may be a potential long-te rn problem. In our calculations, the yield of hydronen and oxygen was calcu-lated using the constant G = 0.45 nolecules of hydronen per 100 ev of ramma _enerry absorbed in the water.
(
Reference:
" Reaction "echanism Leadine to the tornation of Molecular Hydrogen in the Radiation Chemistry of Water" by E. Haydon and M. Moreau, 3, Phv, Chen. De c., 1965).
Please report on your further consideration of this potential problem including whether additives are available which would retard the reaction.
6.0 Your response to question No.1.7 in Amendrent 4 discussed the conservatism in post MCA recovery calculations. However, our interest is related to the consequences of spraying cold water on the core or flooding the reactor vessel af ter core tempera-tures have risen above 3000*F if for any reason the engineered safeguards f ail to respond in the precise canner and time assumed in the calculations we have reviewed to l ate.
Accordingly, please describe the consequences of core cooling delays beyond _those which assume the diesel starts automatically within a few seconds after MCA.
Is it correct to assume that full core spray and core flooding, renard-less of the delay, are desirable, or is there some renaon for alterinc post MCA recovery procedures if spray and flooding were delayed?
7,0 - As noted during recent telephone conversations with your staf f, our_ criterion _ con-cerning emercency power for encineered saferuards is that in the event of loss of all off-site power, sufficient sources of alternate power shall be provided to assure a capability for performing the functions required of the engineered safe-guards.
For Monticello, we interpret this to mean that in the absence of other sources of on-site power, at least two diesel renerators should be provided. Ea ch should have the capability outlined in your response to question 2.3 in Amendnent '4
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8.0 Ceoloric anc Seismic Design 8.1 please provide the locations of the principal structures, including turbine and reactor buildings, intake structure, stack and diesel building. Provide e
foundation elevations, foundation. soil strata, soil bearine capacities and the loads to be imposed by the respective buildings.
Indicate which st ructures will be separate due to seismic response considerations. The drawings should indicate the location of borings in the immediate vicinity of the structures, and these boring logs should be included.
8.2 Provide a description of the desien of the intake structure includine founda-tion and scismic considerations.
8.3 Provide the justification for not performinR dynamic tests on the foundation soil beneath the reactor buildine to determine whether dif ferential settlement could take place.
Discuss potential liquif action of the soil beneath the reactor building, 8.4 Are interaction loadings between the reactor building substructure and the surrounding soil considered in the design of the building substructure for i
both static and dynamic loading conditions ?
8.5 Please provide the reasonine for the selection of the Taf t, rather than the El Centro, earthquake spectrum. A comparison of both the computed spectra and the averaned spectra should be presented for the Taf t and El Centro earth-
- quakes, Discuss the agreement of the time-history record used in the com-puter analysis with the response spectrum throuchout the frequency rance.
8.6 Please verify that the stresses arising from the earthquake in both the verti-cal and horizontal direction, and which occur simultaneously at a particular location, will be added directly to the stresses arising from the other appli-
- cble loadings, including pressures and temperature stresses arisine from an
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8,7 A table of damping coef ficients is given on page I1-6-5 It is noted therein that for the " reactor-building (uassive construction with many cross walls and equipment and providing only secondary containment)" a damping value of 5 percent is specified, Further elaboration on this point is riven in answer to question 2.8 of Amendment 4 As a result of Dr. Newmark's recent considera-tions, he would be in agreement with this value for cases in which-working stresses are no more than about one-half the yield point and in whidi there nay be considerable cracking associated with the concrete structure, In tho event that the concrete is not stressed to that level where it is considerably cracked, he recommends a value -of 2 or 3 percent as beinn more reasonabic, Picase_ discuss this recommendation in view of your proposed desten.
t 8.8 We understand that 5 percent rather than 10 percent critical dampine for ground rocking modes of vibration will be used in this desien. Please confirm this understanding.
8.9 Verify that the damping factors cited in Table II-6-3 are to be employed for both. design and maximum earthquake loading conditions, 1
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Please show that the proposed value is conse rvativa.
6.11 Dr. Newmark has recommended a damping value of 2 or 3 percent be used in the design of the stack.
In view of this recommendation, please discuss the damping values proposed for this design.
8.12 Please provide details concerning strengthening of areas around penetrations of the containcent, particularly the dryvell, to insure that the required strength and ductility under earthquake and service loadine are attained, 8.13 Please clarify the comment relatinn to safe shutdown of the plant in tables on pages V-3-2 and V-3-3 of FDS AR, Vol. I.
It is not clear whether gpecial stress criteria vill be employed for Loadinn Condition 2 or 3 respectively (for safe shutdown) or whether these references apply to the stresses listed previously in the tables.
8.14 Table V-3-3 (FDSAR) refers in Loading Condition 3 to a f actor of "M.O.L. +
2 x S.L." - This f actor of "2 x S.L." should be chanced to-reflect the maximum earthquake that is selected, which may not necessarily be twice the desien earthquake nor twice the response values appitcable thereto.
.