ML20052A373
| ML20052A373 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 04/26/1982 |
| From: | Caruso R Office of Nuclear Reactor Regulation |
| To: | Kay J YANKEE ATOMIC ELECTRIC CO. |
| References | |
| TASK-15-10, TASK-RR LSO5-82-04-073, LSO5-82-4-73, NUDOCS 8204280276 | |
| Download: ML20052A373 (9) | |
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April 26,1982 9
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o Docket No. 50-29 c
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_ N Mr. James A. Kay
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Senior Engineer - Licensing Yankee Atomic Electric Company s
1671 Worcester Road Framingham, Massachusetts 01701
Dear Mr. Kay:
SUBJECT:
YANKEE - SEP TOPIC XV-10. CHEMICAL AND VOLUME CONTROL SYSTEM MALFUNCTION THAT RESULTS IN A DECREASE IN BORON CONCENTRATION IN THE REACTOR COOLANT By letter dated June 30, 1981, you submitted a safety assessment report for the above topic.
Your letter of March 29, 1982, provided further information. The staff has reviewed this assessment and our conclusions are presented in the enclosed safety evaluation report, which completes the review of this topic for the Yankee Nuclear Power Station.
This evaluation will be a basic input to the integrated assessment for your facility. The evaluation may be revised in the future if your facility design is changed or if NRC criteria relating to this topic are l
modified before the integrated assessment is completed.'
Sincerely, d
Ralph Caruso. Project Manager g
Operating Reactors Branch No. 5 D5" Division of Licensing gg g, Beyk
Enclosure:
As stated cc w/ enclosure:
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r Yankee Mr. James A. Kay Docket No. 50-29 Revised 3/30/82 cc Mr. James E. Tribble, President Yankee Atomic Electric Company 25 Research Drive Westborough, Massachusetts 01581 Chairman
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- Board of Selectmen Town of Rowe Rowe, Massachusetts 01367 Energy Facilities Siting Council 14th Floor One Ashburton Place Boston, Massachusetts 02108 U. S. Environmental Protection Agency Region I Office ATTN:
Regional Radiation Representative JFK Federal Building Boston, Massachusetts 02203 Resident Inspector Yankee Rowe Nuclear Power Station c/o U.S. NRC Post Office Box 28 Monroe. Bridge,* Massachusetts 01350 Ronald C. Haynes, Regional Administrator Nuclear Regulatory Commission, Region I 631 Park Avenue l
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SYSTEMATIC EVALUATION PROGRAM TOPIC XV-10 YANKEE NUCLEAR POWER STATION TOPIC:
XV-10, Chemical and Volume Control System Malfunction that Results in a Decrease in Boron Concentration in the Reactor Coolant
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I.
INTRODUCTION A decrease in the boron concentration in the reactor coolant adds reactivity to the core. This produces a loss of shutdown margin or power anC temperature increases depending on the condition of the core at the time of the loss of boron.
The concentration of boron in the Yankee reactor coolant can be decreased by transferring the suction of a charg-ing pump in the Volume Control System from borated water in the Low Pressure Surge Tank.to unborated water in the Demineralized Water Supply.
It can also be decreased by circulating reactor water from the Bleed System through the Purification and Chemical Ion Exchangers. IToeprevent an inadvertent cfiticality (or power increase) the operator must stop an unplanned decrease in boron concentration before the shutdown margin is eliminated (or thermal limits are approached) by isolating the primary makeup water system, stopping the charging pumps, stopping *the' Low' Pres.
sure Surge Tank makeup pumps, or closing the charging isolation valves.
The Yankee Atomic Electric Company (YAEC) first analyzed the boron dilution event for the FSAR (Reference 1).
It was reanalyzed for the core XI refueling (Reference 2) and then again for the core XV refueling (Refer-ence 3).
For Reference 3 the complete spectrum of boron dilution events covering all plant operational modes (1 through 6) was analyzed.
II.
REVIEW CRITER,IA Section 50.34 of 10 CFR Part 50 requires that each applicant for a construction permit or operating license provide an analysis and
evaluation of the design and performance of structures, systems, and components of the facility with the objective of assessing the risk to public health and safety resulting from operation of the facil'ity, including determination of the margins of safety during normal operations and transient conditions anticipated during.the. life of the facility.
Section 50.36 of 10 CFR Part 50 requires the Technical Specifications te include safety limits which protect the integrity of the physical barriers which guard against the uncontrolled release of radioactivity.
The General Design Criteris (Appendix. A to 10 CFR Part 50) establi.ch minimum requirements for the principal design criteria for water-t.ooled reactors.
GDC 10 " Reactor Design" requires that the core and associated coolant, control and protection systems be designed with appropriate margin to ' assure that specified acceptable fuel design limits are not exceeded during normal
' operation, including the effects of anticipated operational occurrences.
m GDC 15 " Reactor Coolant System Design" requires that the reactor coolant and l
associated protection systems be designed with sufficient margin to assure that the design conditions of the reactor coolant pressure boundary are f
not exceeded during nonaal operation, including the effects of anticipated operational occurrences.
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GDC 26 " Reactivity Control System Redundancy and Capability" requires
'S that the reactivity control systems be capable of reliably controlling reactivity changes to assure that under conditions of normal operation, t
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including anticipated operational occurrences, and with appropriate margin for malfunctions such as stuck rods, specified acceptable fuel design limits are not exceeded.
III.
RELATED SAFETY TOPICS Various other SEP topics evaluate such items as the reactor protection system. The effects of single failures on safe shutdown capability are considered'under Topic VII-3.
IV.
REVIEW GUIDELINES The review is conducted in accordance with SRP 15.4.6.
The evaluation includes review of the analysis for the event and identification of the features in the plant that mitigate the. consequences of the event as well as the ability of these systems to function as required.
The extent to which operator action is required is also evaluated.
Deviations from the criteria specified in the Standard Review Plan are identified.
V.
j_ VALUATION As stated in the NRC's evaluation (Reference 4) of YAEC's analyses for Rr.ference 3, these analyses were performed using the most limiting combination of:
1.
Initial boron concentration 2.
Inverse Boron Worth 3.
Reactor Water Volume 4.
Reactor Water Temperature 5.
Boron Dilution Rat'e
_4 for each of the six operational modes.
The initial boron concentrations, which determine the shutdown margins, are those stated in the Yankee Technical Specifications.
For Modes 4, 5, and 6, YAEC assumed the reactor water volume to be that for a drained upper reactor vessel head with all four main coolant loops isolated, so that their volumes were not 3
included.
This reactor water volume is 1276 ft 0 It takes into accour.t the possibility of a partially drained hot leg while operating in Mode 5.
These analyses were use'd to determine the minimum period of time that an operator would have for acting after the receipt of an alarm for a boron dilution event before the shutdown margin would be lost.
The Yankee plant is designed to provide the following alarms for a boron dilution event:
Modes 1 & 2 1.
Low pressure surge tank high level 2.
High Reactor Coolant System average temperature 3.
Hig.h Core power 4.
Audible indication of rod motion from Vapor Container Intercom System (automatic control)
Modes 3, 4 & 5 1.
High neutron flux recorder 2.
High level in the pressurizer surge tank 3.
High pressure in the pressurizer surge tank 4.
High tenperature in the pressurizer surge tank Mode 6 1.
Two independent source range detector channels with audible alarms 2.
Two independent range detector channels with audible alarms.
3.
High neutron flux recorder
Thus, the Yankee system provides an audible alarm even assuming a single failure of the first alarm during all modes of plant operation. The available operator action times were determined to be:
Action Time Mode (Minutes) 1&2 0>45 for manual control 15 for automatic control 3
?>30 4
- >20 5
> 20 6
-,.21. 5 All of these times conforp to those allowed by SRP 15.4.6 except that for' Mode 6 for which 30 minutes is required.
In Reference 5, the licensee described some of the conservatisms in Mode 6 analysis and stated that if the excess conservatism were removed..the
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~ calcu1aie'd' time to loss' of shutdown margin would exdeed 30 minutes.~~
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On the basis of this result, the administrative and procedural controls and the multiple alarms to alert the operator, the staff considers that this event has been adequately addressed by the licensee.
If the reactor is initially critical at the' time a boron dilution begins.,
the automatic safety features of the reactor protection system are designed to ensure that the departure from nucleate boiling (DNB) ratio remains above the Technical Specification minimum value of 1.3.
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CONCLUSION As part of the SEP review for the Yankee Nuclear Power Station, the analyses for a chemical and volume control system malfunction that results in a decrease in boron concentration in the reactor coolant have been evaluated. We have concluded that all of the consequences of this event are in conformance with the criteria of SRP Section 15.4.6 except the available operator action time during Mode 6 opera-tion. As discussed above, we conclude that the calculated action time is an acceptable time interval for the Yankee Nuclear Power Station.
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_REFEREi4C'ES 1.
_ Yankee Nuclear Power Station Final ~ Safety Analysis Report; Yankee Atomic Electric Company, Westboro, Massachusetts; January 3,1974; Volume III, pages 15.2 15.2-7 2.
YAEC letter to NRC; Core XI Refueling; March 29,.1974; Section 402..
3.
Chapnan, J. R. et al; Yankee Nuclear Power Station Core XV Performance Analysis; March,1981; pages 69-80.
4.
U.S. NRC; Safety Evaluation by the Office of Nuclear Reactor R_equlation
_ Supporting Amendment No. 69 to Facility Operating License No. DPR-3, Yankee Nuclear Power Station (Yankee-Rowe); Washington, D.C.; July 22,1981; pages 6-7.
5.
YAEC letter to NRC, Boron Dilution Event in Mode 6, J. Kay to D; Crutchfield, March 29,1982.
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