ML19256B328
| ML19256B328 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 04/21/1979 |
| From: | Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | Humphreys L GULF STATES UTILITIES CO. |
| References | |
| NUDOCS 7906110001 | |
| Download: ML19256B328 (1) | |
Text
UNITE D STATES
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g>* '8 Cog,'o NUCLEAR REGULATORY COMMISSION g3
'g HEGION IV I
c 611 RYAN PLAZA DRIVE, SUITE 1000
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ARLINGTON, TEXAS 76011 April 21,1979 In Reply Refer To:
RIV Docket No. 50-458/IE Bulletin 79-05B 50-459/IE Bulletin 79-05B Gulf States Utilities ATTN: Mr. L. L. Humphreys, Senior Vice President, Energy Development P. O. Box 2951 Beaumont, Texas 77704 Gentlemen:
The enclosed IE Bulletin 79-05B is forwarded to you for information.
No written response is required.
We have also enclosed copies of recommendations of the ACRS to the Commission for your information.
If you desirt additional information regarding this matter, please contact this o?fice.
Sincerely, h$$dS~'
Karl V. Seyfrit Director
Enclosures:
1.
IE Bulletin No.79-05B with enclosures 2.
ACRS Recomendations to the Commission dated April 18, 1979 and April 20, 1979 3.
List of IE Bulletins Issued in the Last Twelve Months 790611000/,
i UNITED STATES i
NUCtEAR REGULATORY COMMISSION 0FFICE OF INSPECTION AND ENFORCEMENT L
WASHINGTON, DC 20555 APRIL 21, 1979 IE Bulletin 79-05B NUCLEAR INCIDENT AT THREE MILE ISLAND - SUPPLEMENT Description of Circumstances:
Continued NRC evaluation of the nuclear incident at Three Mile Island Unit 2 has identified measures in addition to those discussed in IE 1
Bulletin 79-05 and 79-05A which should be acted upon by licensees with j
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 I
following a trancient or accident is to provide f'orced flow using reactor coolant pumps.
It appears that natural circulation was not successfully achieved upon securing the reactor coolant pumps during the first two hours of the Three Mile Island (TMI) No. 2 incident of March 28, 1979 Initiation of natural circulation was inhibited by significant coolant voids, possibly aggravated by release of noncondensible gases, in the primary coolant system. To avoid this potential for interference with natural circulation, the operator should ensure that the primary system is subcooled, and remains subcooled, before any attempt is made to establish natural circulation.
Natural circulation in Babcock and Wilcox reactor systems is enhanced by maintaining a relatively high water level on the secondary side of the once through steam generators (OTSG).
It is also promoted by injection of auxiliary feedwater at the upper nozzles in the OTSGs. The integrated Control System automatically sets the OTSG level setpoint to 50% on the operating range when all reactor coolant pumps (RCP) are secured.
- However, in unusual or abnormal situations, manual actions by the operator to increase steam generator level will enhance natural circulation capability in anticipation of a possible loss of operation of the reactor coolant pumps.
As stated previously, forced flow of primary coolant through the core is preferred to natural circulation.
Other means of reducing the possibility of void formation in the reactor coolant system are:
A.
Minimize the operation et the pressurizer and there DUPLICATE DOCUMENT reduction by a blowdown t Entire document previously entered into system under:
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