ML20009C548
| ML20009C548 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 07/10/1981 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20009C546 | List: |
| References | |
| NUDOCS 8107210219 | |
| Download: ML20009C548 (6) | |
Text
{{#Wiki_filter:.. SAFETY EVALUATION REPORT Submittal: Letter from A. E. Lundvall, Jr., to R. A. Clark, dated March 23, 1981, and attachment
Subject:
Calvert Cliffs Nuclear Power Plant Units 1 and 2, Detection of Boron Dilution Accident Originating Organization: Baltimore Gas and Electric Cogany BC KGROUND As a part of the submittal for Calvert Cliffs Unit 1 Cycle 5 fuel load application, the licensee presented an analysis of an inadvertent boron dilution event.The a 5 calculated time from the initiation of the event until the loss of shutdown margin was 19.7 minutes in the cold shutdown mode and 38.6 minutes in the refueling mode. he licensee also stated that the operator has no positive means of being alerted to a boron dilution event. The acceptance criteria for a boron dilution event is provided in section SRP 15.4.6, and calls for a minimum time interval of 30 minutes from an alarm to the time a loss of shutdown margin occurs when the plant is in the refueling mode. If tha olent is in cold shutdown or any other mode, an interval of 15 minutes is accepted. In the evaluation of the submittal for the Cycle 5 fuel load application, the staff requested that a positive means be provided to alert the operator and allow him adequatItimetoterminate boron dilution event (Reference 1). he licensee agreed to develop a means for such notification during the current cycle for each unit. M7210219e1073o p ADOCK 05000317 PDR
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EVAL UATION - ___.._________.a_...__.._.y ?The licensee has. proposed an alarm system in which the Wide Range Log Channels (WRLC)}[ ( of the nuclear instrumentation 'are monitored by the plant computer. The total number of' channels'is fourland the minimum' number required to' be operable is two. Computer avcilability to'date is reported to be better than 98% for both units. With less than the required alarm functions operable, the operator. has to monitor-h?LC signals at a-frequency such.that the required time interval for corrective measures is assured. As a backup to WRLC signals, the licensee has identified tha. plant boronometer which provides the operator with a continuous indication of reactor coolant outlet boron concentration. The licensee has also proposed Technical Specification changes to increase the timeL from initiation of the dilution event uniti shutdown margin is -lost. These changes apply only to cold shutdown mode with low reactor coolant inventory. The staff's' conclusion of the proposed alarm system is that the main principles are acceptable and the licensee may continue his developing efforts. However, before final. conclusion can be reached, the hcensee has to provide the staff with - additional information and possibly to make some additional changes 1in Technical Specifications. In the following, are listed the remarks and questions the i-licensee has to address to make sure that SRP 15.4.6 acceptance criteria are met: i 1. The criteria in SRP 15.4.6 do not refer to the time of initiation of a l , dilution event, but to the time of alarm. In order to determine that the time interval available for corrective measures meets the intervals j stated in SRP 15.4.6, additional information on alarm setting and alarm i l time is needed. To support proposed alarm settings, calculational I results'which describe the correlation between the neutron d
flux and boron dilution nave to be presented. Instead of general require-ments as proposed in Technical Specifications, table 3.3-1, notation (g) and section 3.9.2, last sentence, more specific alarm settings should be defined. The requirements should be in a form readily understandable to the operator. 2. Calver: Cliffs Unit 1 FSAR, table 9-12, gives a range of measurement of 0-2000 ;,7m for the boronometer. If this is correct, we do not understand how the boronometer could be used during cold shutdown or refueling as stated in the background section of the submittal letter, since the boron concentra-tion wcald exceed the measurement range. It is the staff's position that the single #ailure criteria should be met 5 when evaluating the capability to protect against boron dilution events. To meet this criteria, two independent means should be available for de-tecting and alerting the operator to a boron dilution event during all modes of operation. Alerting means an audible signal. 3. In the proposed Technical Specification change, section 3.9.2, last sentence, an alarm system using the source range neutron flux monitors is mentioned. It is unclear to the staff if that system is the same as the system using WRLC. Please explain. 4. In the proposed Technical Specifications change you ha.ve split section 3.1.1.2 in two parts. The second of them, subsection 3.1.1.2.2, to be applied when partially draining the reactor coolant system in the cold shut-down mode, requires that the shutdown margin is increased to 4.3% and two charging pumps are taken out of service. An analysis of this partially drained cold shutdown mode has given a minimum time of 51.7 minutes from the initiation of the dilution event to criticality. However, we do not think it is the most limiting case because: i
4-(1) the active volume of coolant circulating in the reactor pressure vessel and the RHR loop during the cold shutdown mode with the primary circuit fil' led up is not significantly larger than the active volume in the drained mode, and 4 (2) the proposed subsection 3.1.1.2.1 of Technical Specifications 9ermits a shutdown carpin of only 3.01, and does not limit the number of operable charging pumps. You should either present an analysis of an event caused by inadvertent oper-ation of all three charging pumps during a normal cold shutdown mode, or con-sider upgraded limitations to the shutdown margin and to the number of available charging pumps in the normal cold shutdown mode. ,s 5. It is not apparent that the proposed requirements in the Technical Specifica-tions, table 3.3-1, action 5, would be clear to the operator. Neither do the requirements specify how often the operator must monitor the signals. Since the primary method of protection relies upon detection and automatic alarm, the Technical Specifications should restrict the ability of the alarms to be taken out of service during all modes of operation in which manual operator corrective action initiated by alarm is required. Technical Specifi-cations requiring monitoring frequency by the operator'should be implemented only where the alarms are taken out of service or otherwise not available. A fixed monitoring frequency based on the minimum calculated dilution time should be provided. 6. In your analyses, you do not take into account the possibility of having continuous flow of unborated water through the s tanding charging pumps. 1
-5 Such flow might be established by the operation of a nake-up purp controlling level in the CVCS tank. The capacity of that pump is not given in FSAR. Please discuss the possibility of flow higher than 44 gpm with two charging pumps out of service. COXCLUSI0il5 The staff has found the submittal deficient and is not able to conclude that the olant will be adequately protected against boron dilution events. Specifically, we find the plcnt does not meet the criteria in SRP 15.4.6. It is the staff's position that a system be provided to protect against boron d dilution events which meets the criteria ii. SRP 15.4.6. Specifically, this 3 system should: o meet the ngle failure criteria o meet tne time limits for operator action in SRP 15.4.6 for all modes of operation. This time limit is measured from the time of the first alarm to the time shutdown margin is lost. o provide clear, audible alarms to alert the operator o be restricted in the ability to take it out of service. We will consider this issue open until an acceptable response is received from the licensee. ~ l A
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REFERENCES:
1. foemorandum for T.N. fiovat 00L.- from Paul S. Check, DSI, on Calvert Cliffs, i Unit l-Cycle 5 Fuel Reload Review, December 2,1980. d i i I .J i 6
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