ML19210A500
| ML19210A500 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 09/14/1977 |
| From: | Reid R Office of Nuclear Reactor Regulation |
| To: | Herbein J METROPOLITAN EDISON CO. |
| References | |
| NUDOCS 7910300538 | |
| Download: ML19210A500 (2) | |
Text
y e
s DISTRIBUTION September 14, 1977 Docket File /:
NRc POR Uocket No.:
50-283 Dg L PDR
[f
/;
ORB #4 Rdg 4/[9D[d RReid f
RIngram GZwetzig TCarter ittropolitan Edison Company ATTN: Mr. J. G. Hercein CNelson Vice President Attorney, OELD P. O. Box 542 Of&E (3)
Reading, Pennsylvania 19603 DEisenhut TBAbernathy Gentlescen:
JRBuchanan ACRS (16)
RE: THREE MILE ISLAND UNIT HG.1 Gray File Recently at an operating PWR facility, a limited boron dilution incident occurred due to the inadvertent injection of a portion of the contents of the Na0H tank into the reactor coolant system while the reactar was in the cold shutdown condition. While perfor:: ling surveillance testing (valve cycling) of the HaOH tank isolation valve, with the Decay Heat Renoval (DHR) system lined up for reactor coolant recirculation, a portion of the tank's contents drained into the DdR system. Upon resumption of coolant recirculation this NaOH was injected into the reactor coolant system.
In the above-mentioned case, only a limited niount of NaOH (approximately 600 gallons) was injected and the reactor remained subcritical by a large margin. However, this event highlighted the fact that a postulated single failure at this facility (i.e., misposition of the isolation valve for the NaOH tank when the DHR system is lined up for recirculation or operating in the recirculation mode) could result in a moderator dilution incident which had not been previously considered. Subsequent analysis by the licensee and his vendor revealed that, for certain conservative assumotions (e.g., reactor in the cold shutdown condition, vessel temperature less than 100 F, beginning of core life characteristics, vessel drained to a level approximately equal to the height of the outlet nozzle, lowest inital boron concentration allowed by Technical Specifications, the maxinum worth centrol rod stuck in the fully out position, and no credit assumed for operator action), the injection of the NaOH tank contents into the reactor coolant system cue to the misposition of a single isolation valve could result in reactor criticality with the control roos inserted.
/
3 1491 169 y-me..
7910300 h N P
e
~
P 21itan Edison Company f Based upon our review of this particular incident, we concluded that the assumption that operator action would not be taken in suf-ficient time to teminate the event orior to reactor criticality would be overly conservative. This detemination was influenced by the length of the dilution time necessary before return to criticality and by the number of indications and alarms available to the operator at this facility. Due to plant-specific system cesign ano instrunen-tation differences, we are not asle at this time to reach a similar con-clusion for all PWR's. Furthemore cost PWR boren dilution analyses have been limited to addressing a malfunction in the makeup and purification systen (chemical and volune control system). Tne incident discussea above is an example of a baron dilution accident not covered oy tnese analyses. Therefore we are requesting that each licensee of a PWR facility provide an analysis of the potential for and consequences of boron dilution accidents at his facility.
You are reauested to perfono and submit the results of such an analysis within 90 days of receipt of this letter. Your analysis should be based upon conservative assumptions consistent with the design of your facility and your Technical Specifications and should include the assue:ption of the most limiting single failure. The analysis should also incluce an assess-ment of the factors which affect the capability of the operator to take corrective action which would terminate the postulated events prior to achieving reactor criticality.
If, tased on the results of this analysis, you determine that corrective actions (design or procedural) are required to preclude the occurrence or mitigate the consequences of postulated boron dilution accidents, your response should include proposals for such actions.
Sincerely, Robert W. Reid, Chief Operating Reactors Branch f4 Division of Operating Reactors cc: See next page M
A\\ J}duc%uh lD
'(i%h9 9
a
_e ORBkk ORB #4: DOR C-D0R o,ne,
GZwetzig:_rm Cheh RReh
.vemm,
9ll!11.77_
9/fl77 9]N07-am +
NRC FORM SIS (%76) NRCM 0240 W u. e. oovannwant eninvine orrices s ove - ese4:4
.