ML20040A184
| ML20040A184 | |
| Person / Time | |
|---|---|
| Site: | Midland |
| Issue date: | 01/14/1982 |
| From: | Jackie Cook CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| 15450, NUDOCS 8201200485 | |
| Download: ML20040A184 (4) | |
Text
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James W Cook 0
Obf Vice President - Projectc, Engsneenng and Construction General Of fices-1945 West Parnall Road, Jackson, MI 49201 e (517) 788 0453
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January 14, 1982 f,
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Harold R Denton, Director W)7 M U/
Office of Nuclear Reactor Regulation N
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Division of Licensing US Nuclear Regulatory Commission Washington, DC 20555 MIDLAND PROJECT MIDLAND DOCKET NOS 50-329, 50-330 ADDITIONAL INFORMATION REGARDING INADVERTENT BORON DILUTION FILE: 0505.815 SERIAL:
15450 ENCLOSURE: RESPONSES TO NRC QUESTIONS 211.190, 211.191, 211.192 The additional information regarding inadvertent boron dilution protection requested by the R L Tedesco letter to J W Cook dated December 15, 1981 is enclosed.
The NRC questions and responses will be incorporated into the next scheduled revision of the Midland Plant FSAR.
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JWC/JRW/fms CC RJCook, Midland Resident Inspect r RHernan, US NRC DBMiller, Midland Construction (3)
RWHuston, Washington
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8201200485 820114 oc0182-0568a131 PDR ADOCK 05000329 A
Question 211.190 (15.4.6)
Justify that conservative assumptions have been utilized in mixing of the boron within the primary system. When calculating boron dilution rate to demonstrate a sufficient operator response time, realistic values for water volumes and flows may be used. However, because of the uncertainty on water mixing during cold shutdown and refueling modes, the fluid in the upper head of the reactor vessel and in the primary loop should be considered to be in poor communication with the fluid circulating in the lower part of the reactor vessel and in the DHR loop. This relatively stagnant fluid should not be credited when defining the reactor ccolant volume susceptible to dilution, unless experimental evidence is presented justifying the inclusion of this volume.
Response
l The boron dilution rates considered in Section 15.4.6 for the various oper-ating modes are based on a detailed examination of fluid system lineups l
possible for each operating mode.
The borated fluid in the volume susceptible l
to dilution is assumed to mix uniformly with the diluted fluid entering via l
the cold leg prior to reaching the core region.
I The refueling dilution event consists of emptying a full makeup tank of dilute water into a reactor vessel volume not inclusive of the vessel head, RCS piping, or DHR loop. The core reactivity is demonstrated to remain suberiti-cal.
Two possible dilution events can be considered during cold shutdown condi-tions; dilution of a full RCS system volume under forced flow conditions, and dilution of the lower vessel under DHR circulation.
In either event, a continuous dilution of the magnitude of 250 gpm requires violation of existing Technical Specifications and lack of response to multiple alarms. The first event, with RC pumps running, is presented in Section 15.4.6 and considers a 250 gpm flow of dilute makeup water mixing with the RCS volume resulting in a uniform dilution. Under these conditions, approximately 17 minutes of dilution is required to deplete the minimum 1% suberitical margin. The second event, a 250 gpm dilution of only the lowar reator vessel volume still requires approximately 6 minutes of dilutioa before the boron concentration is lowered sufficiently to deplete the 1% shutdown margin.
In light of the assumptions made in the analysis, the errors requ. ired and the ala rms present, it is improbable that any dilution event would cause recriti-cality in less than the time presented in Eaction 15.4.6 of the FSAR.
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Question 211.191 (15.4.6)
Justify the adequacy of alarms to the operator which would warn of a boron dilution event. The following criteria indicate the level of safety that would be acceptable to the staff:
(1) At least two separate and redundant means for detecting and alerting the operator to a boron dilution event should be available during all modes of operation.
(2) Technical Specifications for each operating mode where operator actions are the only protective measures should require that operable alarm channels cannot be taken out of service on purpose if this removal from service results in less than two separate and redundant alarm channels being available to alert the operator to boroa dilution events.
(3) If all alarms are lost while in one of these modes, the plant conditions shall be monitored using a method and frequency clearly specified in Technical Specifications.
Response
Midland has alarms for a potential boron dilution event that are indicated by l
makeup flow, valve position, or boron concentration. At least two of these alarms are normally functional during all modes of operation. A high makeup flow alarm is provided since the most rapid boron dilution event is predicated on high makeup flow. The potential sources of boron dilution have isolation valves which, when opened, will alarm after a time delay.
See the response to Question 211.183 for further details of these alarms.
In addition, an on-line boronometer provides high and low boron concentration alarms. The boronometer is shown in FSAR Figures 9.3-31, Sh I and 9.3-33, Sh 1, and is functional when letdown flow is present.
The existing Technical Specifications, along with these alarms, are considered adequate in response to the concern over boron dilution events.
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Question 211.192 (15.4.6)
Justify that protection at Midland is adequate for the events tabulated in the attached Licensee Event Reports (LER's). You are requested to specifically address incorrect loading of demineralizer resin and back-leakage of water from the secondary to the primary side of the steam generators. Steam genera-tors leakage rates corresponding to the Technical Specification allowable rates during power operation should be assumed.
Response
Based on existing Technical Specifications and the alarms described in the response to Question 211.191, the protection at Midland against recriticality due to boron dilution is considered adequate. The tabulated Licensee Event Reports demonstrate a variety of ways that the boron concentration can be decreased. However, the reports also reinforce the adequacy of existing Technical Specifications since in no case was an unsafe condition reached.
1 The dilution was always detected. Boron dilution due to incorrect loading of demineralizer resin is unlikely at Midland since procedures require that the boron concentration through the demineralizer remains constant. The boron concentrations are checked off-line before the flow stream can be redirected to the reactor coolant system.
Utilizing the conservative analysis in FSAR Section 15.4.6, approximately 4350 gallons of water are necessary to bring the reactor critical. At a secondary to primary leak rate of I gpm (TS 16.3.4.6.2), 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> is available to detect the condition. This is considered acceptable and within the surveillance T
requirements of TS 16.3.1.1.1 for Mode 5.
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