ML19254D150

Discusses Limited Boron Dilution Incident at Operating PWR Facility.Requests Analysis of Potential for & Consequences of Boron Dilution Accident Based on Conservative Assumptions Consistent W/Facility Design & Tech Specs

ML19254D150
Person / Time
Site:	Arkansas Nuclear
Issue date:	10/05/1979
From:	Reid R Office of Nuclear Reactor Regulation
To:	Cavanaugh W ARKANSAS POWER & LIGHT CO.
References
NUDOCS 7910220443
Download: ML19254D150 (3)

Text

tVR c Po p-p' * * ;%',

d' UNITED STATES i*

S NUCLEAR REGULATORY COMMISSION i,b,. d' %i wasectes c. c. :osss

,e i.?M

%..'.'../ /

.7 Octeter e., i_,9 n

Cccket No. 50-358 g$gh (St#m Mr. William Cavanaugn, III Y

Vice President, Generation and Construction O

P. O. 50x 551 b

Little Rock, Arkansas 72203

>f 9%

Dear Mr. Cavanaugh:

RE: ARKAN5AS NUCLEAR CNE - UNIT 2 At an operating PWR facility, a limited bcron dilution incident occurred due to the inadvertent injection of a cortion of the centents of the NaCH tank into the reactor coolant system while the reactor was in the cr'd shutdcwn condition. While performing surveillance testing (valve cycling) of the NaCH tank isolation valve, with tne Cecay Heat Remcyal (DHR) system lined up for reacter coolant recirculation, a ;crtion of tne tank's contents drained into the CHR system. Upon resum tion of ccclant recirculation this NaCH was injected into the reactor coolant system.

In the a:cve-mentioned case, only a limited amcun: of NaOH (accroximately 600 gallons) was injected and the reactor remained subcritical by a large gargin. However, this event nignlighted the fact that a ;cstulated single rallure at this facility (i.e., mispositten of the isolation valve for the Na0H tank when the DHR system is lined up for recirculation or operating in the recirculation mode) could result in a mcderatcr dilution incident which had not been previcusly considered. Subse<;uent analysis by the licensee and his vendor revealed that, for certain censervative assuccticns (e.g., reactor 17 the cold shutdown condition, vessel temperature less than ICO*F, beginning of core life cnaracteristics, vessel drained to a level approximately equal to the height of the outlet no :le, icwest inital bcron cencentration allowed by Technical Specifications, the maximum wertn centrol red stuck in the fully cut positien, and no credit assumed for operator action), the injection of the Na0H tank centents into the reactor coolant system due to the misposition of a single isolation valve could result in reactor criticality with the control rods insertec.

7910220 $

2 164

a Mr. William Cavanaugh, III Octeter 5,1979 Sased u;on our review of this particular incident, we concluded tnat the assumption that operator action would not be taken in suf#icient time to terminate the event prior to reacter criticality w ulc be overly conservative. This determination was influenced ::y the length of the dilutien time necessary before return to criticality and by the number of indications and alarms available to the o; erat 0r at this facility. Due to plant-specific system design and instrurentation

' differences, we are not able at this time 1.o reach a similar conclusien for all FWR's.

Furthermore, most FWR bcron dilution analyses have been limited to addressing a malfunction in :ne makeup and ;urification system (chemical and volume centrol system). The incident discussed above is an example of a bcron dilution accident not covered by these analyses.

Therefore, we are requesting that each licensee of a F'aR facility provide an analysis of the :otential for and censequences of toren dilution accidents at his facility.

You are requested to perform and submit the results of sucn an analysis within 90 days of receipt of this letter.

Your analysis should be based u:en conservative assumptions consistent with the design cf y:ur facility and your Technical Specificaticns and should include the assum tien of the most limiting single failure. The analysis should also incluce an assess-ment of :ne factors which affect the capability cf ne c: erat:r to take corrective action which would terminate the postulated events prior to acnieving raactor criticality.

If, based on the results of this analysis, ycu determine that corrective actions (design or procedural) are recuired to creclude the occurrence or mitigate tne consecuences of postulated boron dilution acciden s, ycur respense snould incluce proposals for such actions.

Sincerely,

.3.

m

&!& D 1J Rcbert W. Reid, Chief 0;erating Reacters Branch !4 Divisien of Operating Reacters 4) cc: See next page w%

2 9

2 165

Arkansas Power & Light Cem;any cc:

Phillip K. Lycn, Esq.

Ecuse, Holms & Jeaeli 1550 Tower Building Little Rock, Arkansas 72201 Mr. Cavid C. Trimbie Manager, Licensing Arkansas Pc er & Light Company P. O. Ecx 551 Little Rock, Arkansas 72203 Mr. James P. O'Hanlon General Manager Arkansas Nuclear One P. O. Ecx 5CS Russellville, Arkansas 72501 Mr. William Jchnsen U. 5. Nuclear Regulatory C:missicn U

P. O. Ecx 2090 s-Russellville, Arkansas 72801

\\ "

Mr. Ecbert 3. 3:rsun Eab:cck & Wilccx k

Nuclea-Power Generation Civision g

Suite c20, 7735 Old Georget:en Rcad g*

5etnesda, Maryland 20014 g

9 Troy 3. Cor.ner, Jr., Esq.

Conner, Pccre & Corber 17c7 Pennsylvania Avenue, N.w.

Wasnington, D.C.

20006 Arkansas Folyte:hnic Ccilege Rut.sellville, Arkansas 72501 2

166 4

.