ML20206M562
| ML20206M562 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 08/13/1986 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20206M560 | List: |
| References | |
| IEIN-84-90, TAC-59005, TAC-59006, NUDOCS 8608210258 | |
| Download: ML20206M562 (3) | |
Text
s, ENCLOSURE b
SAFETY EVALUATION REPORT REGARDING MAIN STEAM LINE BREAK WIIH RELEASE OF SUPERHEAltU 5ftAM OUT5IDE CONIAINMENT MLbUIHL NUCLEAR blAIION, UNII5 182 INTRODUCTION AND BACKGROUND The Westinghouse analysis of a main steam line break (MSLB) has for years pre-dicted that saturated steam would be expelled from the break. Recently Westing-house has determined that under a certain accident scenario, a break in a main steam line (MSL) combined with uncovery of the steam generator tubes, superheated steam would be expelled from the break and thus result in higher environmental conditions for the area of the plant containing the break.
The resulting temperature and pressure could exceed the temperature and pressure for which safety-related equipment in the area was qualified.
On December 7, 1984, the NRC issued "IE Information Notice 84-90: Main Steam Line Break Effect on Environmental Qualification of Equipment."
In this notice, the NRC stated that the " staff considers steam superheating during steam generator tube bundle uncovery as a result of postulated main steam line breaks and sub-sequent release to compartments, if omitted from plant analysis, to represent a potential deficiency in the equipment environmental qualification required by 10 CFR 50.49."
At the request of the NRC staff, a meeting was held with Duke Power Company (thelicensee)onJuly 20, 1984 to discuss the status of the main steam line break analysis for McGuire Units I and 2.
As a result of that meeting, Duke Power provided a summary analysis to the staff by letter dated August 8,1984 i
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't 9 that concluded that plant safety would not be adversely affected in the event of a design basis main steam line break in the Doghouse or inside containment.
By letter dated June 21, 1985 the licensee provided the results of additional analysis / evaluation for McGuire that showed that the higher temperatures gener-ated in the event of a MSLB in the Doghouse will not affect the capability to shutdown the reactor and to maintain it in a safe condition. This analysis /
evaluation also concluded that:
o All electrical equipment in the faulted Doghouse that is required to automatically actuate on a safety signal will perform its in-tended function for at least 30 minutes prior to reaching its qualification temperature, with at least a time margin of 433%
between the time actuation occurs and the time equipment internals exceed their qualification temperature.
o The Westinghouse core response analysis imonstrates that it is acceptable for the MSIV's, Steam Generatur PORV's and the Main Feedwater Isolation Valves located in the faulted Doghouse to fail during an MSLB in the Doghouse and still allow safe shut-down of the plant.
1
.S. i, EVALUATION The staff has completed its review of the sumary analysis, the additional analysis /
evaluation and some additional information provided to the staff by~the licensee's letter dated November 15, 1985. As a result of this review the staff concludes that:
o The modified LOFTRAN code used by the licensee to calculate the steam releases during blowdown has been reviewed and found acceptable and therefore the mass and energy releases during the event are properly obtained, o
The procedures for obtaining the core reactivity have been reviewed and found acceptable.
o The calculated doses resulting from steam releases meets the design basis for this event, therefore, they are acceptable.
Finally, as a result of the licensee's analysis and the staff's review, the staff concurs with the licensee's conclusions that the higher temperatures generated in the event of an MSLB in the Doghouse will not affect the capability to shut-down the reactor and to maintain it in a safe shutdown condition. Therefore, this issue has been adequately resolved.
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