ML19256B329
| ML19256B329 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 04/21/1979 |
| From: | Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | Eric Turner HOUSTON LIGHTING & POWER CO. |
| References | |
| NUDOCS 7906110002 | |
| Download: ML19256B329 (1) | |
Text
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paarcOg[o, UNITED STATES f
NUCLEAR HECULATORY COMMISSION REGION IV o
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,E 611 RYAN PLAZA DRIVE,SulTE 1000 2*
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April 21,1979 S
In Reply Refer To:
RIV Docket tio. 50-498/IE Bulletin 79-05B 50-499/IE Bulletin 79-05B Houston Lighting and Power Company ATTil: Mr. E. A. Turner, Vice President Power Plant Construction and Technical Services P. O. Box 1700 Houston, Texas 77001 Gentlemen:
The enclosed IE Bulletin 79-05B is forwarded to you for information.
tio written response is required.
We have also enclosed copies of recommendations of the ACRS to the Commission for your information.
If you desire additional infonnation regarding this matter, please contact this office.
Sincerely,
/IY4M sarl V. Seyfrit Director
Enclosures:
1.
IE Bulletin tio.79-05B with enclosures 2.
ACRS Recormiendations to the Commission dated April 18, 1979 and April 20, 1979 3.
List of IE Bulletins Issued in the Last Twelve Months 7 9 0 6110 00f2 9
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W.35 UNITED STATES c=P =
NUCLEAR REGULATORY COMMISSION m:r OFFICE OF INSPECTION AND ENFORCEMENT if = '-
WASHINGTON,-DC 20555
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APRIL 21, 1979
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.-. :7 EEk NUCLEAR INCIDEhi AT THREE MILE ISLAND - SUPPLEMENT ED:5_~
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Description of Circumstances:
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Continued NRC evaluation of the nuclear incident at Three Mile Island p':T=
gg Unit 2 has identified measures in addition to those discussed in IE Bulletin 79-05 and 79-05A which should be acted upon by licensees with h--'~~
reactors designed by B&W.
As discussed in Item 4.c. of Actions to be taken by Licensees in IEB 79-05A, the preferred mode of core cooling following a trancient or accident is to provide forced flow using reactor coolant pumps.
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{=qg It appears that natural circulation was not successfully achieved upon m:-
securing the reactor coolant pumps-during the first two hours of the P 4.E Three Mile Island (THI) No. 2 incident of March 28, 1979.
Initiation t_,.;.
of natural circulation was ~ inhibited by significant coolant voids, ig5:
possibly aggravated by release of noncondensible gases, in the primary
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coolant system. To avoid this potenti ' Mr interference with natural s-ea circulation, the operator should ensure tnat the primary system is subcooled, and remains subcooled, before any attempt is made to establish
- . r-natural circulation.
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Natural circulation in Babcock and Wilcox reactor systems is enhanced by G
mintaining a relatively high water level on the secondary side of the
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once through steam generators (OTSG).
It is also promoted by injection of auxiliary feedwater at the upper nozzles in the OTSGs.
The integrated
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Control System automatically sets the OTSG 1evel setpoint to 50% on the
===M operating range when all reactor coolant pumps (RCP) are secured.
- However, 31.0%
in unusual or abnomal situations, manual actions by the operator to F#
increase steam generator level will enhance natural circulation capability 3MJ in anticipation of a possible loss of operation of the reactor coolant pumps.
e-As stated previously, forced flow of primary coolant through the core is M1 preferred to natural circulation.
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isEf:T-Other means of reducing the possibility of void formation in the reactor gm_
coolant system are:
5 77 512 A.
Minimize the operation of the P 63 EG=
the pressurizer and thereby red reduction by a blowdown through DUPLICATE DOCUMENT gg#
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