ML19322B614

Forwards 751218 Revised Info Methods to Prevent Boron Precipitation in Long-Term Following Postulated LOCA, to Replace 751031 Info Submitted in Response to 751014 Request. Also Forwards Addl Info Re ECCS Requested in Question 3(h)

ML19322B614
Person / Time
Site:	Oconee
Issue date:	12/18/1975
From:	Parker W DUKE POWER CO.
To:	Rusche B Office of Nuclear Reactor Regulation
Shared Package
ML19322B615	List: ML19322B614 ML19322B616
References
NUDOCS 7912040640
Download: ML19322B614 (1)

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DlIKIc Powicu COMPANY I'owru lhi:UMNO 122 SouTu Gu uncu STur.nT, GnAHLOTTE, N. C. ana42 WILUAM O. PA H M E R, ,J R.

Vict PetSiDENY TELE *MONc:Anta 704 Sf tm as Pm'3DuC%0's 373-4083 December 18, 1975 -

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Mr. Benard C. Rusche g) 's i Director of Nuclear Reactor Regulation ig? g / ,

U. S. Nuclear Regulatory Commission -

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Attention: Mr. R. A. Purple, Chief Y Operating Reactors Branch #1 x

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Re: Oconee Nuclear Station Docket Nos. 50-269, -270, r-287 RL . -

Dear Sir:

In response to your letter dated October 14, 1975, our letter of October 31, 1975 was submitted which provided information concerning post-LOCA long-term cooling capability. The response described a method of boron dilution consisting of a gravity ilowpath for the reactor coolant from the hot leg nozzle to the Reactor Building sump through the decay heat drop line. The method will prevent unacceptable boron concentrations from developing following a postulated loss-of-coolant accident and will satisfy the requirements of the single failure criteria. Since our October 31, 1975 submittal, certain changes have been made to the proposed design.

Consequently, a revised complete description of the proposed method of assuring boron dilution following a loss-of-coolant accident is attached. i I

Necessary station modificatic is and changes to station operating procedures will be implemented on each ( .snee unit prior to restart following each unit's next refueling. This will assure compliance.with the Commission's j Order for Modification of License issued on December 27, 1974 and assure '

Oconee compliance with 10 CFR 50 553.46.

Additionally, information is provided in Attachment 2 which pertains to I the Oconee Unit 1 ECCS evaluation requested in question 3(h) of your letter l dated October 30, 1975 to Mr. K. E. Suhrke of Babcock and Wf.lcox Company.

Information relative to the partial-loop LOCA-analysis is also included in Attachment 2. /' \N. I ' ', ; '

,e Very truly yours, ['\~

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l ,,y h, h f William O. Parker, Jr.f I W/}//

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t LP-2 at elevation 795' 3" and then continues downward to elevation 772' 10" where it is imbedded in the Reactor Building base slab and exits the Reactor Building. The line continues in a downward path until it intersects the Reactor Building emergency sump line and LPl A pump suction at approximately 767'. The tap for valves LP-X and LP-Y will be above LP-1 and will be designed to assure a minimum flow of 40 gpm following a postulated LOCA.

(c) The electrical power supplies for valves LP-1, 2, X, Y, Z, 3, 19 have not been determined at present. They will be arranged such that LP-X and LP-Y have one source which is independent of the sources for valves 4

LP-1, LP-2, LP-3 (Units 2 and 3), LP-Z (Unit 1), LP-19 (Units 2 and 3) such that a single electrical failure cannot affect both dilution paths.

All valve operators will be above the post-LOCA water level and all motor operators will be qualified for the post-LOCA environment. The capacity of the emergency power source is more than adequate to carry these additional loads.

(d) The only operator action required for initiation of the boron dilution loop is to open the valves LP-1, LP-2, LP-X, LP-Y, LP-7 (Unit 1),

LP-3 (Units 2 and 3), LP-19 (Units 2 and 3) from the control room. For large breaks, these valves may be opened following initiation of recirculation and within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> following a LOCA. For small breaks, the valves are to be opened only after the Reactor Coolant System is depressorized and recirculation has been initiated. Valve LP-4 on Oconee Unit 2 will be changed to a normally open valve.

i (e) Remote readouts of dilutica flow is not required for this method of boron dilution since flow is assured due to the gravity feed nature of j the lineup, and no action is dependent upon the actual dilution flow.

(f) The size and the minimum driving head of these drain lines will be such that a minimum 40 gpm will exist in each of these flowpaths.

(g) Remote valve operability and flow through these lines will be verified

. at the time the necessary modifications are implemented.

(h) The design, engineering evaluation and procurement effort for materials and equipment needed for the necessary station nodifications is currently being initiated. The modifications and necessary changes to procedures will be implemented prior to restart following each unit's respective

refueling.

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ATTACILMENT 2 December 18, 1975

Additional Information in response to Question 3h Table 1 provides additional information on the parameters used in the Oconce I ECCS evaluation. Utilizing Table 5-3 of BAW-10103, it is demonstrated that the oxide thicknesses used in the Oconea I analysis is consistant with the time-in-lif e analyzed.

As demonstrated in the tLee-in-life study (Section 5.4 of BAW-10103), the worst pin pressure (which is directly related to time-in-life) is the lowest that causes rupture at approximately mid-blow-down. In the study in BAW-10103, a pin pressure of 1190 psia caused rupture during blowdown (Rupture occured at 23.76, and the end of blowdown was 24.4 seconds). However, when the pin pressure was changed to 1250 psi, rupture occured at approximately mid-blowdown (14.73 seconds) and a marked increase in peak cladding temperature occured. The reason for this increase was explained in Section 5.4 of BAW-10103. Therefore, when LOCA limit calculations are per-formed, the pin pressure used must be the lowest that causes rupture during mid-blowdown in order to ensure a conservative calculation.

Figure 5-6 of BAW-10103 shows a typical cladding temperature transient during blowdown. The worst pin pressure causes rupture at the peak in the cladding temperature during mid-blowdown. The magnitude of this peak temperature and the time it occurs is dependent on the peak linear heat rate and elevation within the core that is analyzed. Therefore, the worst pin pressure will be different for each LOCA limits case analyzed.

In order to ensure that the worst pin pressure has been analyzed, the following procedure is used for the Category 1 plants. A CRAFT run is made using some initial pin pressure. Typically, rupture does not occur during blowdown. From this run, the time and maginitude of n

the peak temperature that occurs at approximatley mid-blowdown can be determined. An initial pin pressure that will cause rupture at this time is estimated. The estimated pin pressure is, in general, low because the extent of plastic deformation has been underestimated in the original CRAFT calculation. As documented in B&W's Evaluation Model, BAW-10104, the clad is assumed to deform plastica 11y when its Plastic temperature is within 200F of the value re' quired for rupture.

deformation results in a larger fuel to clad gap, degraded gap conductance, a reduction in internal pin pressure, and slightly lower cladding temper-

.atures. In order to acccount for these phenomena, the estimated pin pressure is increased by approximately 100 psi since uore plastic def ormation will occur when the pin pressure is increased. The CRAFT This analysis is then repeated with the revised initial pin pressure. )

procedure is utilized until cladding rupture is calculated at mid- (

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blowdown. Although not exact, this iterative procedure results f I

in the use of initial pin pressure that are at most 100 psi higher than the most conservative value. An BAW-10103 a 150 psi increase i

j over the worst pin pressure lowers peak cladding temperatures only l

8F and 16F for the unruptured and ruptured nodes respectively. ,

J Thus, the procedure outlined above would result in little or no loss in conservatism. In actuality, an c$ 100 psi error is not likely i

I because of the plastic deformation effects.

i In order to demonstrate that this approach was used in the Oconee I j evaluation, the results of the preliminary CRAFT runs are presented.

I For the 2-foot case, two additional pin pressures were analyzed,1575 j i

From j and 1800 psia. Neither case caused rupture at mid-blowdown.

the 1801 psi case, it was found that a pin pressure in excess of 1825 psi was needed. A pin pressure of 1910 psi was used to develop the i

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2-foot limit and it caused rupture at 10.5 r.econds. For the 4-foot case, one additional pin pressure was analyzed,1475 psia. This did not cause rupture during blowdown. From this case it was found that a pin pressure in excess of 1600 psi v s needed to cause rupture during mid-blowdown. When 1725 psi was used, rupture occured at 12.4 seconds. This is the case that the 4-foot LOCA limit is based on.

As demonstrated, the LOCA limits calculated in the Oconee I l

l evaluation were performed at the worst time-in-life and thus represent conservative limits for all cycles of operation.

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TABLE 1 Elevation, ft 2 4 Peak Linear Heat Rate, kw/ft 16.0 17.5 Burnup, MWD /MrU 38,200 28,200 Initial Pin Pressure, psia 1910 1725 Inside Oxide Thickness, inches 3.78x10- 2.8x10-

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Outside oxide Thickness, inches 3.5x10- 2.2x10 Peak Unruptured Node Temperature /

Time, F/s 1930/43.5 1978/43.0 Peak Ruptured Node Temperature /

Time, F/s 1882/43.0 1975/43.0 Rupture Time, s 10.9 12.4 r

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. 3 ADDITI0ttAL INFORMATION Off PARTIAL-LOOP LOC The par;ial-10o'p L'0CA analysis was performed using an in pressure of 1600 psi in order to compare to the Spectrum anal ysis reported in Section 6 of BAW-10103.

Since rupture occurs after blowdown, the worst pin pressure is the beginning-of-life pin pressure (760 psi) as was demon-strated in the time-in-life study in Section 5.4 of BAW-10103 .

The three pumps case with the break in the cold leg with the active e loop pump in' th with the idle pump was reanalyzed using an initialpsi. pin pressure The peak cladding temperatures for the unruptured and rupt ured nodes were 1784F and 1688 F respectively.

and This is an increase of 18 F 14F for these nodes relative to the 1600 psi case.

The sensitivity is not as large as that demonstrated in Section 5.4 of BAW-10103 d ue to the relatively low cladding temperatures for the partial-loop analysis.

LOCA As 'shown, the peak cladding temperature for partial-loop analysis LOCA is 416 F lower than the 2200 F criteria at the n life. worst time i Therefore, an extremely large safety margin is demonstrated for - partial loo p operation.

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