LD-83-025, Submits Addl Info Re Natural Circulation Cooldown of C-E Sys 80 NSSS, Transmitted by Per SER Confirmatory Item 9.Analysis Shows Available condensate,300,000 Gallons, Provides More than Sufficient Cooling Water
| ML20072N387 | |
| Person / Time | |
|---|---|
| Site: | 05000470 |
| Issue date: | 03/28/1983 |
| From: | Scherer A ABB COMBUSTION ENGINEERING NUCLEAR FUEL (FORMERLY |
| To: | Eisenhut D Office of Nuclear Reactor Regulation |
| References | |
| LD-83-025, LD-83-25, NUDOCS 8304010518 | |
| Download: ML20072N387 (2) | |
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C-E P:w r Sy;t;ms Tel 203/688-1911 Combustion Engineering. loc.
Telex 99297 1000 Prospect Hill Road Windsor, Connecticut 06095 H POWER SYSTEMS Docket No.:
STN 50-470F March 28, 1983 LD-83-025 Mr. Darrell G, Eisenhut, Director Division of Licensing U.S. Nuclear Regulatory Commission Washington, D.C.
20555
Subject:
CESSAR-F Confirmatory Item 9, Shutdown Cooling Analysis
Reference:
Letter LD-82-078, A. E. Scherer to D. G. Eisenhut, dated September 8, 1982
Dear Mr. Eisenhut:
As requested by NRC staff reviewers, Combustion Engineering (C-E) is providing additional information concerning our report, " Natural Circulation Cooldown of C-E System 80' NSSS", which was submitted via the reference letter.
The report was prepared to respond to the CESSAR-F SER Confirmatory Item 9, " Shutdown Cooling Analysis"; it evaluates-a-natural circulation cooldown with controlled Reactor Vessel Upper Head (RVUH) voiding. C-E has stated that it would be highly unlikely that a natural circulation cooldown under loss of off-site power conditions would need to be conducted.
In most cases, the plant could remain hot and pressurized until power is restored.
The report addresses several possible methods of void control including use of pressurizer heaters, auxiliary spray, charging, letdown and the Reactor Coolant Gas Vent System.
In addition, a detailed simulation was presented using the pressurizer heaters to control void formation. Choice of the pressurizer heaters resulted in an easily modeled process as well as the most likely operational procedure. Model development using charging flow alone to collapse voids would be complex. Correlation of the flow model, developed from the St.
Lucie 1 natural circulation cooldown data, to the RVUH of the System 80 design is not intuitively obvious. But, it appears as though the relatively slow cooldown, documented in the analysis provided in the reference utilizing pressurizer heaters, is conservative when compared to the relatively rapid i
cooldown of St. Lucie 1, during which charging flow was used to collapse the RVUH void,.
C-E believes that more rapid depressurization could be demonstrated without pressurizer heaters. However, a slightly different fill and drain process might be used with charging flow.
Rather than several small fill and drain cycles, one or two larger cycles could be used. The resultant larger void would leave less hot liquid to mix with the incoming Reactor Coolant System (RCS) water.
In the limiting case, the void could be expanded down to the top of the hot leg where there would be no need to model charging flow into the RVUH. Contact with the subcooled RCS fluid would continue to depressurize the RVUH.
(O B304010518 830328 PDR ADOCK 05000470 E
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Mr. Darrell G. Eisenhut Page 2 We have shown in our report that sufficient instrumentation is available to the operators and the capability of the operators to perform an expeditious natural circulation cooldown will be demonstrated during natural circulation testing at the Palo Verde Nuclear Generating Station.
In addition, the total amount of condensate needed falls within the 300,000 gallons specified in CESSAR. The total amount of condensate needed is directly proportional to the amount of heat that must be removed from the RCS and is unrelated to the cooldown path (temperature and pressure vs. time) that is followed. The amount of RCS heat removal needed during a natural circulation cooldown is determined by the amount of latent heat in the RCS that must be removed to cool down from hot standby to cold shutdown temperatures, which is a constant, and the core decay heat, which is a function of time.
Therefore, no matter what path is chosen to take the primary system to shutdown cooling entry conditions, total heat removal required is only dependent on the overall cooldown time.
As stated earlier, the cooldown at St. Lucie 1 was a more rapid process than our current analysis using pressurizer heaters has shown. We believe that our analysis shows a conservatively slow process, appropriate for assessing the feedwater requirements. The analysis shows an overall cooldown time of ten (10) hours which includes a one-hour period at hot standby. An assumption of four hours at hot standby would stretch the overall cooldown time to thirteen (13) hours.
As shown in Figure 4-2 of the report, the total condensate needed for plant cooldown and decay heat removal is 260,000 gallons at twelve (12) hours. At that tine, the coolant usage rate is approximately 10,000 gallons / hour. At this usage rate, the required 300,000 gallons of condensate will allow for decay heat removal to a total time of sixteen (16) hours. Thus, our analysis shows that the available condensate, 300,000 gallons, provides more than sufficient cooling water.
If you have any further questions on our analysis, please contact me or Mr. G.
A. Davis of my staff at (203) 688-1911, extension 2803.
Very truly yours, COMBUSTION ENGINEERING, INC.
e7 i
A. E. Scherer l
Director Nuclear Licensing i
AES:las cc: Gary Meyer (Project Manager / USNRC)