ML23027A243
| ML23027A243 | |
| Person / Time | |
|---|---|
| Site: | University of New Mexico |
| Issue date: | 01/18/2023 |
| From: | Robert Davis, Willis C Univ of New Mexico |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| EN56313 | |
| Download: ML23027A243 (1) | |
Text
Unintentional high power scram event, 11/23/2022, at the University of New Mexico AGN-201M reactor (License 50-252)
Event Number EN56313 Description, Analysis, and Proposed Corrective Actions Carl Willis (Chief Reactor Supervisor), Rowdy Davis (Reactor Supervisor) 1/18/2023
- 1. Event, and facility response An unscheduled high power scram occurred at the UNM AGN-201M reactor on 11/23/2022 when a sample of iodized table salt, under irradiation as part of a standard experiment, was withdrawn from the reactor Glory Hole, causing an increase in power to the safety channel high power trip point of 6 W.
Further details of this event were recorded in the reactor log at the time (Appendix A). The Senior Operator on duty called the Chief Reactor Supervisor immediately after the event and a memo was prepared by the Senior Operator on duty that was communicated to the Chief Reactor Supervisor on the same day (Appendix B). Times referenced in these documents are in Mountain Time.
The Chief Reactor Supervisor determined the event was a Reportable Event on 1/17/2023 and notified the NRC Project Manager and the NRC Operations Center on 1/18/2023 (notification time: 15:24 Eastern Time). The memo in Appendix B was transmitted to the NRC Operations Center (acknowledged received at 15:43 Eastern Time.
- 2. Analysis of event (per TS 6.9.2)
- a. Background The activity underway at the time of the event involved irradiation of one of a set of samples used annually for gamma spectrometric analysis by a laboratory class (NE-323L, Radiation Detection and Measurement). The operation was approved on a facility Request For Use and followed a standard experiment procedure. The facility was staffed appropriately for conduct of the experiment (one licensed RO, operating, assisted by one licensed SRO). The experiment is routine at the UNM AGN-201M facility, typically repeated a dozen or more times on an annual basis with various samples. Sections 2.b-2.d discuss the causes, consequences, corrective actions, and measures to prevent recurrence of the unscheduled scram as required by TS 6.9.2.
- b. Causes The proximate cause of the unscheduled high power scram was the removal of a sample with high negative reactivity from the reactor without adequate coordination between the Reactor Operator and the assisting Senior Operator. The Reactor Operator was unable to withdraw control rods rapidly enough to offset rising power when the sample was removed, and the 6 W setpoint was reached, causing the scram.
Facility staff did not report the unscheduled event promptly to the NRC due to confusion about the reportability of the high-power scram. Significant prior staff experience and the bulk of documentation in the Training and Operation Manual relate to high-power scrams that are not considered reportable.
- c. Probable consequences No significant consequences were observed or are anticipated. The reactor safety channels performed according to specification.
- d. Corrective actions and measures to prevent recurrence High-power safety channel scrams are avoidable if proper experimental technique is observed and the operator and assistant work in coordination. The operator is expected to anticipate the reactivity addition from removal of strongly absorbing samples by driving rods out toward the previously-logged empty critical position before the assistant withdraws the sample, or while the assistant slowly withdraws the sample. The assistant must communicate with the operator about the intent to withdraw the sample, and the operator is ultimately responsible for communicating permission to the assistant when readyi.e., when the reactor control rods have been positioned to counteract the anticipated reactivity of the sample movement.
The staff will drill appropriate technique (see below for example) and distribute this document to cultivate awareness about the circumstances of the unscheduled high-power scram.
Below is an example of good technique and coordination, where operator verbalizes the expected rod movement to compensate for the sample movement, and where operator gives permission to the assistant to move the sample after making rod movements to compensate:
Assistant takes position at the Glory Hole to withdraw sample carrier.
ASSISTANT: Permission to withdraw the sample?
OPERATOR: WAIT for my permission. FCR will be moved down 10 cm to compensate.
ASSISTANT: Standing by.
Operator drives rod out toward previously-logged empty critical position.
OPERATOR: GO to withdraw.
Assistant withdraws sample.
Emphasis will be placed on the operators responsibility to coordinate all actions that influence reactivity, by giving the orders to stand by or to withdraw the sample according to his/her readiness.
Licensed facility staff need to establish better delineation between unscheduled conditions that are Reportable Occurrences (TS 6.9.2.a.7) and the specific scenario discussed at some length in the Training and Operations Manual (D.5.b) in which a situationally-aware licensed operator allows a student authorized operator to let power rise to the safety channel high level limit, which is not considered reportable. Two conditions appear to be required to satisfy the non-reportable scenario identified in D.5.b of the Manual: (A) specific awareness of the licensed operator on duty of an impending high-level scram, and (B) a planned instructional purpose. These elements comprise a scheduling of the
condition in the sense applicable to TS 6.9.2.a.7. It is clear that the event under consideration here occurred without operator awareness and was part of a standard operation to support a laboratory course unrelated to reactor operations instruction. Clarifying language will be added to the Training and Operations Manual, at the beginning of Section D.5.b: Unscheduled high-power scrams are Reportable Occurrences and must be promptly reported to the NRC (TS 6.9.2.a.7). The only exception is discussed below. This document will be circulated to all facility administrative and operating staff.
- 3. Facility documentation references The Technical Specifications language (6.9.2.a.7) pertinent to the reportability of unscheduled safety channel scrams reads:
- 7. Unscheduled conditions arising from natural or manmade events that, as a direct result of the event, require reactor shutdown, operation of safety systems, or other protective measures required by Technical Specifications.
The Training and Operations Manual context for unintentional safety channel scrams reads (D.5.b):
Sometime, during the course of an experiment or training, a student will let the power drift up to the 6 Watt limit, whereupon a reactor scram occurs. The RSAC decided that such an observed (by the reactor supervisor, but not by the student) unintentional Safety Channel scram is not a reportable event. It was pointed out that in these cases, the reactor supervisor could have kept the scram from occurring but allowed it to happen as part of the educational process for the student(s). In this sense, the scram becomes part of the learning process. Clearly, no Technical Specification is violated under such circumstances as long as a Safety Channel scram does occur and the Reactor Supervisor is aware of the situation, yet permits the scram to occur as part of the educational process.
The student invariably gets the message loud and clear. The RSAC agreed (May 2006) that such events during student training should be treated as observed unintentional scrams, permitted for education/training; thus, not reportable events.
Appendix A. Reactor logbook entry.
Appendix Ill B THE UNIVERSITY OF NEW MEXICO AGN-201M REACTOR OPERATIONS LOG OPERATIONAL INFORMATION:
OPERATOR
[.,,\\:. 11 't A f Page 1/ ?,
Date 11 I 1 °"!>/ l ~- Z.-l---
AUTHORIZEDEXPERIMENTS fvt-1:,z.:~.. /WL (). t~,,.,,, -r,.. J,,/.,,,
_..-i.:1l u,,.,~t RFU# 6SI AUTHORIZED CHANGES (loading, instruments, etc.): A 1 vwl*J I" '
DATE LAST MONTHLY WATER TEMP.
I '1 0 REMARKS ;J' v1 e_..
SUP RR VJ SOR' S APPRov AL_;_v,j,_I_.-\\ _________________ _
(SIGNATURE REQUJRED FOR NEW EXPERIMENTS)
PRECRITICAL START-UP CHECK-OUT
- a. Nearhy perwnneJ in.formed (Rad Sajery informed if after normal hours)
- h. Radialion monitors operational
- c. Radiation Sun*ey OK
- d. Reactor Inspectio11:
Thermal column secured Manhole cover secured Shield doors in place Check/or water leaks Srair gate locked. access alarm works Cadmium in Glory Hofe
- e. TURN ON CONTROL PANEL POWER J
I V J DO NOT CONl'INUE UNLESS BELi" RING S!
- f. Data Display 011.
- g. Source drive operalional
- h. NIM bin & HVPS ( 1-2-3-Aux.) on
- i. Channel I instrument check:
_J_
-J CounJ.l* per minule
/Jeteclor high voltage Amplifier gain.*
1.,Sc voe
/Ji.1criminalor level Fine Coarse Automatic H Vremoval okay Compare to previous condi1io11s Revised January 2021 40
- j. Channel 2 instrument check:
Detector high voltage lOO Low level INTERLOCK OK High le~*el SCRAM OK Calibra,e check@ lxJ0-11 Amps Calibrate check@5x10-7 Amps
- k. Channel 3 instrument check:
Detector high voltage b O 0 High level SCRAM OK Calibrute check @ lxJ0-11 Amps Ca/ih1*ate check @ 5xl u-7 Amps I. Magnet current check:
t b Magnet current level
____ ma /
Low curre11r trip operational J
- m. Safety Interlocks cleared J
- n. Verification of Rod Interlocks
- o. Manual SCRAM operalional f
r-nata Oisplay operational Pr~criticul Starl-up check-out completed
- ~cw,'"""";'"' ~
Appendix III B Page2J_~--
'). -..o Time of startup _\\_v_-_u _____ _
Instrument Readings I
Elapsed time meter _'3,_,t_._S_1 ____ hours Channel All Rods OUT Safety Rods IN Reactor Asst removed Cd from Glory Hole 1
16]
Cl'M 711:4-CPM Console radiation levcl.~D~*-o_t ___ mR/hr 2
1,l*t0-1\\ Amps 7, 7 /(J-11 Amps Control Rod Lower Lim it Positions:
3 ii) _,-1,
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- IC Amps A*~,z..Amps Fine rod O O
- l'\\
cm Aux.
1,,S.* 10_,, Amps
{ ~ - li°f'IAmps Coarse rod 60
- l \\
cm Previous Meter Readings Noted C..
- d.
nttcal Rea mizs Time of day \\1.; I'.)
Channel,+'2,
'b, 5-lO - 7 Amps Reactor Top 100 mR/hr Elapsed time 3.5: 11..
Hours Channel 3 tS
- lO -li' Amps Reactor Console l,-3 mR/hr Power Level 4,(>~
Watts Aux. Channel ~ 0
- 1(; 1 Amps Check Pt. 3 z.,s mRihr OPERA. TIONAL DAT A*
Time Channel 3 Fine Rod Coarse Rod Comments Reading Position Position (loading changes, power level, changes, scrams )
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REACTOR SHUTDOWN:
Scram method..cl..\\-c.i.
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_ ~_,_]:---'---'1-'-*..;,.?-----------------
Time of day Elapsed time All rods down Startup source inserted Reactor Assistant Authorized Operator Revised January 2021
($ : ID J~'.\\~
\\I 41 Cadmium inserted in Glory Hole Data Display off Console power off Portable radiation monitors off
~
Reactor Supervisor I
Appendix III B Page ? / *5 OPERATIONAL DATA:
Date 11/n/,cu Time Channel 3 Fine Rod Coarse Rod Comments Reading Position Position (loading changes, power level, changes, scrams) lt*,1<;, {.5.10-&' 2,L 7tJ 1..:i. 5 0 C./, *I, <" (
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Revised March 2019 39
Appendix B. Event memorandum Unintentional High-Level Scram RO: E. Boldt Supervisor: R. Davis Date: 11/23/2022 Time: 13:20:00 Iodized Table salt was inserted to centerline at 12:22 to be irradiated at 4.0 W. At 12:27, the reactor was established as critical at 4.0 W. The iodized table salt was irradiated until 13:20. At 13:20, R. Davis communicated to E. Boldt that the salt would be removed. R. Davis pulled the Salt out with the power level at 4 W. The reactor then entered a positive period and jumped to 6.0 W, resulting in an unintentional high level scram. R. Davis called C. Willis and alerted him immediately of the event who then advised to create a report of the event. C. Willis then advised that in the future, better communication is necessary to account for the reactivity differences between an inserted sample and the inserted fuel rods. This event will be added to "Lessons Learned" for future trainees.
Prepared by: