ML16341C696
| ML16341C696 | |
| Person / Time | |
|---|---|
| Site: | Salem  |
| Issue date: | 02/08/1982 |
| From: | Nelson C Office of Nuclear Reactor Regulation |
| To: | Delgaizo T FRANKLIN INSTITUTE |
| References | |
| CON-NRC-03-81-130, CON-NRC-3-81-130 NUDOCS 8203020624 | |
| Download: ML16341C696 (10) | |
Text
I FEB 8 1982 pgz R5-olb Mr. T. J. DelGaizo Franklin Research Center Benjamin Fran',glin Parkway Philadelphia, Pennsylvania 19103
Dear Mr. DelGaizo:
RE:
NRC CONTRACT NRC-03-81-130 FRC !'PROJECT'C5506 Enclosed please find the licensee's response to your August 7, 1981 request for information regarding Salem Unit 1 and the Pl<R Moderator Dilution issue.
Sincerely, oriyna( si.n;d by:
Chr isti'an C, Nelson, Prqjtect Manager Operating Reactors Branch 83 Division of Licensing Encl osure:
As,",stated DISTRIBUTION:
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+/<XW Company 80 Park Plaza, Newark, NJ 07101 /201 430-7000 MAILINGADDRESS / P.O. Box 570, Newark, NJ 07101 February 3,1982 Director of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission 7920 Norfolk Avenue
- Bethesda, MD 20014 Attention:
Mr. Steven A. Varga, Chief Operating Reactors Branch 1
Division of Licensing Gentlemen:
PWR MODERATOR DILUTION.
NO.
1 UNIT SALEM NUCLE g
TING STATION DOCKET NO. 50-727 +7~
As committed in our October 5, 1981 submittalr this letter transmits to you, in its enclosure,'he
.results of the anal-ysis undertaken to identify the potential for an inadvertent
.boron dilution in the Reactor Coolant System.
Credible causes of such an event were analyzed to determine the potential,:or occurrence and their overall implications.
Should you have any questions in this regard, do not hesi-tate to contact us.
Very truly yours, E'. A. Liden, Manager
~Nuclear Licensing and Regulation FAM:srd
. CC:*
Mr. Leif Norrholm Senior Resident. Inspector Mr. Gar C.
Me er Licensin Pro'ect Mana er
4 P
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.Page 1
of 3 Date 2/5/82 SAFETY EVALUATION OF THE POSSIBLE
.CAUSES AND EFFECTS OF.
AN INADVERTENT BORON DILUTION OF THE REACTOR COOLANT SYSTEM.
I DISCUSSION:
A thorough analysis was conducted on the Chemical and Volume Control System (CVCS) and all other interconnecting systems at all modes of reactor operation.
Attention was directed towards identi-fication of possible paths for an inadvertent boron dilution of the Reactor Coolant System (RCS) to occur.
Each path was analyzed as to the required modes of failure, if any, and the likelihood of occurence.
Tube failures of all heat exchangers located in the CVCS and other interconnecting (RHR, SI, etc.)
systems.
was one area.of evalua-tion. It was found that the Seal Rater Heat Exchanger has seal water return flowing at a lower pressure than that of the cooling
- water, component cooling.
A postulated mode of a failure for.this heat exchanger was a single tube failure.
Should this 'occur the total quantity of clean component cooling wate'r leaking into the RCS would not cause a sharp drop in boron concentration, thereby initiating a sudden increase in reactivity.
The low level alarm in the component cooling surge tank or high level of chromates in the RCS would notify the operators of the. problem.
A total tube rupture was considered to be extremely unlikely and was not evaluated.
Al'1 other heat exchangers are designed such that the primary sy'tem. pressure is'reater than the cooling water system pr'essure, thus precluding the above situation from occurring.
A second possible path was primary water entering the CVC system while flushing resins from the Ion Exchange Demineralizers.
'This process involves a'otal of 600-1,000 gallons of primary water to be flushed with spent resins to the spent resin storage tank.
The only possible path of entry of primary water into the CVCS would be due to a failure to close of the process outlet valve located in
'he'ischarge line of each demineralizer.
CVCS pressure at this
'point is slightly less than that of the primary system pressure.
The majority of primary water used to flush the spent resin would, therefore, flow through the demineralizers to the spent resin storage tank (this bein'g the 'path of least resistance).
The amount of primary water capable of entering the CVCS would be a small percentage of the total available volume of water.
In order to postulate the worst possible case it was assumed that all 1,000
'gallons enter the CVCS via the letdown. line flowing to the Volume.
Control Tank.(VCT)
~
The amount of primary water fXowing into the VCT depends upon the exi'sting level. in. the tank.
A three way valve diverts letdown flow to the CVCS hold-up tanks on high level signals in the VCT. 'he portion of water. flowing into the VCT
v~
Pr
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2/5/82 enters as. a spray mixing with approximately 1,000-2,000 gallons of borated water present
'in the tank.
One charging pump noimally takes suction from the VCT to provide water for charging and for RCP Seals.
Total charging flow into the RCS runs as high as 100 gpm. 'his enters via the Reactor Coolant Pump Seals (20 gpm for all four pumps)
'and through the charging line to the RCS (55-80 gpm).
Therefore, a situation could occur where there is 100 gpm of primary water entering the RCS.
In order for this to occur, all 1,000 gallons of primary 'water must flow into the VCT with a minimum amount of mixing with the borated water already present.
The. probability of this occurring is extremely low.
Nevertheless, if indeed the situation did arise in which 100 gpm of primary water was ent'ering the RCS for a period of around 10 minutes and mixing with an approximate volume of 94,000 gallons of" borated water the probability of an inadvertent boron dilution is minimal.
The reactor makeup portion of the CVCS was also reviewed.
This area is addressed in the FSAR under Uncontrolled Boron Dilution, Section 14.1.4.
This system is designed to limit the boron dilution rate such that under various postulated failures, indication.through instrumentation and alarms provide sufficient time for the operator to coirect the situation.
It should also be noted that the boron dilution procedure is one that is carried out under very strict administrative controls and also must adhere to the technical specification.
Review of tbis portion of the'VCS did not uncover any postulated paths for.
inadvertent boron dilution that could not be corrected by 'operator action in a safe and orderly manner.
A limited boron dilution incident occurred at another operating PWR facility due to the injection of NaOH while the reactor was in a cold'shutdown condition (reference 1).
While performing surveil-.
lance testing of the NaOH tank isolation valves, a portion of the tank's contents drained into the RHR system.
PSE&G provided
. conf'irmation that.the design of the RHR system at Salem precluded
.the above accident from occurring (reference 2).
PSE&G was notified by. Westinghouse of their concerns and recommended actions regarding the potential for an inadvertent bo'ron dilution event at cold or hot shutdown. conditions while on the'HR system (references 3
a 4).
These recommendations have been adopted.
A shutdown margin of at least 5% is maintained wpen less than or equal to 350'F while on RHR.
- Recently, Salem experienced an inadvertent dilution'of the RCS to less than the 2'000 ppm
.minimum boron concentration required by Technical Specification 3.9.1 (reference 5).
This occurred while the RCS was. drained to approximately one-half loop level and a hydrolazer was being used to decontaminate the steam generator channel heads.
Water was
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2/5/82 entering'he RCS due to the inability of'he hydrolazer suction connection'o remove 'all of the scattered spent spray water.'
routine Reactor Coolant Boron sample notified the operators of the problem and the RCS was borated to within specifications.
Procedures have since been revised such that additional safeguards are present to prevent the above situation from occurring.
Measures have been taken to sample on a much more frequent basis and to constantly keep the reactor operators aware;that hydrolazing is going on.
Westinghouse has provided a description of a new boron protection system developed in response to additional requirements imposed by the NRC.
This protection system uses a source range instrumenta-tion system to detect a reactivity increase due to a dilution while
.the reactor is subcritical.
In addition to this, an automated means of detecting and terminating an inadvertent boron dilution is provided.
PSEaG plans to review the system as soon as it becomes available from Westinghouse.
If.our review indicates that the system provides an added margin of safety against the occurrence of an inadvertent boron dilution, then it will be incorporated at Salem.
'I CONCLUSION Careful consideration has been exercised in examining possible.
scenarios for an inadv'ertent boron dilutibn of the RCS.
This safety, evaluation has assessed the likelihood of each scenario and has also examined past cases where an inadvertent boron dilution occurred.
It is concluded that the scenarios evaluated do not.
contain any adverse safety implications. with regard to an inadvertent boron diluti'on at Salem..
I'EFERENCES 1.
NRC Letter, G.:Lear,. to F.
P. Librizzi, PSEaG, dated September 19, 1977.
2.'SEaG Letter, F.'. Librizzi, to G. Lear, NRC, dated February 1, 1978.
3.
Westinghouse Letter No.
PSE-80-48, dated July 9; 1980.
4.
Westinghouse Letter No. PSE-80-49, dated July 15, 1980.';
'PSEaG Letter Reportable Occurance 80-53/03-1, R.
A. Uderitz to Boyce H. Grier, NRC dated March 17, 19'81.
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