ML19224C439
| ML19224C439 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 04/21/1979 |
| From: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | Nichols T SOUTH CAROLINA ELECTRIC & GAS CO. |
| References | |
| NUDOCS 7907020354 | |
| Download: ML19224C439 (1) | |
Text
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NUCLEAR REGULATORY COMMISSION T
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f ATLANTA, GEORGIA 30303 APR 211979 In Reply Refer To:
l RII:JP0 50-395 South Carolina Electric and Gas Company ATTN:
Mr. T. C. Nichols, Jr., Vice President and Group Executive Power Production and System Operations P. O. Box 764 Columbia, South Carolina 29218 Gentlemen:
The enclosed Bulletin 79-05B is forwarded to you for information. No written response is required. We have also enclosed copies of recomen-dations of the ACRS to the Comission for your information.
If you desire additional information regarding this matter, please contact this office.
Sincerely, James P. O'Reilly [
R W
N Director
Enclosures:
1.
IE Bulletin No.79-05B with Enclosures 2.
ACRS Recomendations to the Comission dated April 18, 1979 and April 20, 1979 271 230 790702030 g 7
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMEhT WASHINGTON, DC 20555 APRIL 21, 1979 I
IE Bulletin 79-05B NUCLEAR INCIDENT AT THREE MILE ISLAND - SUPPLEMEh7 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 Bulletin 79-05 and 79-05A which should be acted upon by licensees with 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 transient or accident is to provide forced 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 (THI) 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 circu'.ation, 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 1evel setpoint to 50% on the operating range when all reactor coolant pumps (RCP) are secured. However, in unusual or abnormal situations, sianual 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 formatico in the reactor coolant system are:
A.
Minimize the operation of the Power Operated Relief Va v on the pressurizer and thereby rg reduction by a blowdown through a DUPLICATE DOCUMENT _
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