ML20038A098

PWR Moderator Dilution,Ct Yankee Atomic Power Co,Haddam Neck Plant

ML20038A098
Person / Time
Site:	Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png
Issue date:	10/21/1981
From:	Vosbury F FRANKLIN INSTITUTE
To:	Nelson C NRC
Shared Package
ML20038A099	List: ML20038A098 ML20038C380
References
CON-NRC-03-81-130, CON-NRC-3-81-130 TER-C5506-81, NUDOCS 8110270260
Download: ML20038A098 (10)

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W-TECHNICAL EVALUATION REPORT x&,

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FRC PROJECT C5506 NRC DOCKETNO. 50-213

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f NRC TAC NO. 08382 FRC ASSIGNM,ENT ' 3

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N i. NRC CONTRACT NO. NRC-03-81-130 FRC TASK 81.

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%em Preparedby e-ji

' Franklin Research Center Author:

F. W. Vosbury 3

The Parkway at Twentieth Street M

Philadelphia, PA 19103 FRC Group Leader:

T. J. DelGaizo sM Q

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h~l Prepared for Nuclear Regulatory Commission

_. Washington, D.C. 20555 Lead NRC Engineer:

C. C.' Nelson

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October 21, 1981

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7 This report was prepared as an account of work sponsored by an agency of

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the United States Government. Neither the United States Government nor any agency thereof, or any of their employees, makes any warranty, ex.

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. :' pressed or implied, or assumes any legal liability or responsibility for any -

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product or process disclosed in this report, or represents that its use by

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TER-C5506-81 4

CONTENTS Section Title Page 1

BACKGROUND 1

2 EVALUATION CRITERIA.

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TECHNICAL EVALUATION.

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3.1 Potential for Injection of NaOH Tank Contents 3

r 3.2 Analysis of Most Limiting Moderator

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Dilution Incident 3

4 CONCLUSIONS.

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REFERENCES.

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BACKGROUND A' limited moderator (boron) dilution incident occurred at an operating '

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pressurized water reactor (PWR) facility due to inadvertent injection of a portion of the NaOH tank contents into the reactor coolant system while the i

reactor was in a cold shutdown condition. Although only a small amount of the r

NaOH solution (approximately 600 gallons)' was injected and the reactor '

remained suberitical by a large =argin, the event highlighted the fact that' a single failure at this facility (misposition of an isolation valve) could result in a previously unconsidered moderator dilution incident. Subsequent analysis, using certain extre=ely conservative-assumptions, revealed that injection of the entire contents of the NaOH tank into the reactor coolant system could result in reactor criticality, with the control rods inserted.

i Consequently, on September 26, 1977 (1], the NRC requested that Connecticut Yankee Atomic Power Company (CYAPCO) provide an analysis of the i

potential for and consequences of boron dilution accidents at the Haddam Neck plant. The analysis was to be based upon the NRC's conservative assumptions consistent with the design and technical specifications of the Eaddam Neck l

Plant, including the assumptio^n of the most limiting single f ailure.

It,also was to assess the factors affecting the i::spability of the operator to termi-nate postulated-events prior to reactor criticality. Finally, CYAPCO was f

requested to use the results of the analysis as the basis for proposals for any 1

corrective action (design or procedurai) required to preclude the occurrence i

or mitigate the consequences of postulated boron dilution incidents.

1 CYAPCO responded to the NRC's request. in a letter dated January 13, 1978 (2].

In reply to certain correspondence f rom the NRC, CYAPCO submitted additional information on June 4, 1980 (3) and August 13, 1981 (4].

4 This report is a technical evaluation of the Licensee _'s responses to NRC's analysis request of Reference 1.

Its purpose is to ensure that the potential f

for boron dilution incidents has' been reduced and to ensure that the worst i

l possible dilution scenario has been an,alyzed.

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TER-C5506-81 2.

EVALUATION CRITERIA The NRC provided dual criteria for this review.

First, when the Licensee determines that a moderator dilution incident could occur due to misposition of the isolation valve for the NaOH tank, proposed corrective action should be evaluated to determine if it significantly reduces the potential for such an inc ident. Any proposed changes are to be reviewed to ensure that they will accomplish the intended purpose without adversely affecting plant enginee' red safety features.

Second, where the Licensee determines that another potential moderator dilution incident is more limiting than the one analyzed in the FSAR, the Licensee's analysis of the more limiting incident should be reviewed' for acceptability in accordance with Section II of Standard Review Plan 15.4.6.

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TECHNICAL EVALUATION d

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-- 3.1 POTENTIAL FOR INJECTION OF NaOH TANK CONTENTS In Reference 2, CYAPCO stated:

"In response -to NRC Staff requests ' in Reference (1), CYAPCO has -

reassessed the boron dilution incident considering the extremely i

conservative assumptions outlined.in Reference _ (1). As a result of this, it has been reconfirmed that all inputs of unborated water (including I

chemical)' f rom any system into the ' Reactor Coolant System (RCS),' ente'r the RCS via the Primary Water System. Since the Primary Water System has.

a capacity of 180 gpm, this would constitute.the maximum possible flow of I

unborated water into the RCS.

It has also been concluded that even using the more conservative assumptions, there is sufficient time available (within the criterion of at least 10 to 15 minutes) for operators to recognize and to terminate the dilution flow before.the reactor'would go critical."

FRC Evaluation In addition to CYAPCO's statement that all inputs of unborated water s

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(including chemical) from any system into the RCS enter via the primary water system,_FRC has reviewed the FSAR and system drawings of the Haddam Neck plant I

l and has determined that there is no NaCH tank which could be interconnected with the RCS.

1 FRC Conclusion a

l There is no potential for inadvertent moderator dilution from the NaOH tank because the Haddam Neck plant does not have a NaOH tank which could inject unborated water into the RCS.

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i 3.2 ANALYSIS OF MOST LIMITING MODERA':OR DILUTION INCIDENT In Reference 2, CYAPCO sta*ed:

"In response to NRC Staff requests in Reference (1), CYAPCO has reassessed the boron d~ilution ini::ldent corisifer'ing the extremely

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j conservative assumptions outlined in Reference (1). As a result of this, it has been reconfirmed.that all inputs of unborated water -(including chemical) from any system into the Reactor Coolant System (RCS), enter the RCS via the. Primary Water System. Since the Primary Water System has a capacity of 180 gpm, this would constitute the maximum possible flow of

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.unborated: water into the RCS.

It has also been concluded that even using the more conservative assumptions, there is sufficient time available (within the criterion of at least 10 to 15 minutes) for operators to recognize and to tecninate the dilution flow before the reactor would go critical."

In Reference 3, CYAPCO reconfirmed that all possible dilution paths had been considered and evaluated, and that in the worst case (i.e., the shortest time for operator response), the operator had 31.5 minutes to recognize and terminate the dilution flow before the reactor would achieve criticality...

In Reference 4, CYAPCO distinguished the time which the operator had to recognize the dilution event from the time to terminate flow as follows:

"For the worst case dilution event, the operator would have approximately 31.5 minutes before criticality. As the dilution event progresses, the source count rate will increase. After approximately 15 minutes, the oper.ator will receive an alarm from the source range instrument string upon doubling of the source range count rate.

The, operator would then, l

have approximately 16.5 minutes to term'inate the dilution flow before cri ticality. This assumes a new core with the most reactive control rod stuck in, the fully withdrawn position and reactor coolant system temperature less than 100*F.

"In summary, for the worst case boron dilution incident, the operator has approximately 16.5 minutes f rom the time he receives an alarm before the,

reactor goes critical.

Therefore, the 15 minute criterion is satisfied."

FRC Evaluation 72e Eaddam Neck plant does not have the potential for a moderator dilution incident from mispositioning of isolation valves of the NaOH tank.

Further, the Licensee's review of all possible dilution paths revealed that-

' the incident analyzed in the FSAR' remains the most limiting dilution scenario. Nevertheless, by substituting or adding the NRC's conservative assumptions of Reference 1 (i.e., reactor coolant temperature below 100*F, new core, most reactive rod fully withdrawn), the Licensee determined that 31.5

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minutes existed f rom the initiation of the event until the shutdown margin was lost, -16.5 minutes 'of which remains af ter receipt bf the alarm.

The 16.5-minute time satisfies the minimum requ,irement for the shutdown condition (15 minutes) to terminate a dilution incident af ter receipt of the alarm as set out in Standard Review Plan 15.4.6.

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4 TER-C5506-81 FdCConclusion There are no potential boron dilution incidents for which the time available.to the operator to terminate the incident is less than the minimum j

times of Standard Review Plan 15.4.6.

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CONCLUSIONS The following is a summary of conclusions regarding CYAPCO's review of potential moderator dilution incidents at the Haddam Neck plant:

There is no potential for an inadvertent moderator dilution incident o

from a NaOH tank since no tank exists which could inject water into the RCS.

There are no potential moderator dilution incidents for which the. time o

available to the operator to terminate the incident is less than the minimum times of Standard Review Plan 15.4.6.

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REFERENCES 1.

A. Schwencer (NRC)

Letter to D. C. Switzer (CYAPCO)

September 26, 1977 2.

D. C. Switzer (CYAPCO)

Letter to A. Schwencer (NRC)

January 13, 1978 3.

W. G. Counsil (CYAPCO)

Letter to D. M. Crutchfield (NRC)

June 4, 1980 4.

W. G. Counsil (CYAPCO)

Letter to D. M. Crutchfield (NRC)

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11. NRC generated documents for mailing to multiple addressees must be handlea in accordance with NRC Bulletin 0240-23 that requires a service or mailing list be used and that only the original signed copy or Concurrence copy of the document with an attached service / mailing list be sent to DCS.

12.

Before sending enclosure / attachments that are themselves identifiable, stand-alone documents to the DCS, the forwarding office must confirm that t

the document is not already on DCS. Such confirmation can be rade by determining if a DCS Accession Number already appears on the document or by consulting a DCS terminal. If the document is on DCS, the DCS Accession Number (ANO) must be written on the enclosure / attachment before it is sent to DCS. If the attachment / enclosure is not on DCS, an original copy should be sent. If the original is not available, the forwarding office must so certify in writing on the document.

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14.

Routine questions concerning placement of documents tr. DCS should be made to Michael Collins, Document Control Desk 016 Phillips; other questions may be made to Steve Scott, Chief, Document Management Branch. 058 Phillips.

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NOTE TO:

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Document Control Desk 016 Phillips The attached document was not sent to Document Management Branch in accordance with the " Procedures for placement of Docunents in the Document Control System" (See Below). A check mark indicates the procedure (s) this document does not comply with. To facilitate prompt entry into the DC5, Please return the corrected document at your earliest opportunity.

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