ML19249E854
| ML19249E854 | |
| Person / Time | |
|---|---|
| Site: | Humboldt Bay |
| Issue date: | 07/30/1979 |
| From: | Crane P PACIFIC GAS & ELECTRIC CO. |
| To: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| References | |
| NUDOCS 7910020610 | |
| Download: ML19249E854 (4) | |
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F 77 B E A L E S T R E E T, 31 S T FLOOR. SAN F R A N Cl 5 ':0, C A LI FO R N I A 94106 (415) 781 4211 JOHN C. M ORRIG S Cy 9
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Mr.
R. H.
Engelken, Director 4"
Office of Inspection and Enforcement h
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Region V
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S. Nuclear Regulatory Commission
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Walnut Creek, California 34596 u
Re:
Docket No. 50-133 License No. DPR-7
Dear Mr. Engelken:
Enclosed as Attachment A is our response to your lot.ter dated May 31, 1979, which transmitted IE Bulletin No. 79-12 c cerning short period scrams at BWR facilities.
Very truly yours, j
Attachment CC w/ attachment:
Director Office of Inspection and Enforcement Division of Reactor Operations Inspection U.
S. Nuclear Regulatory Commission Washington, D.
C. 20555 79100208/O Oq n - -) '/ t 7f's&.
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PACIFIC GAS AND ELECTRIC CCt?P/M 1Rt<BOLDT BAY POWER PIANT UNIT NO. 3 DOCKET NO. 50-133
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LICENSE NO. DPR-7 S.!'l ATTACIU<ENT A RESPGiSE TO IE BULLETIU UO. 79-12 DATED MY 31, 1979 IE Bulletin 79-12, concerning short period scrams at BWR facilities, requested that we describe our actions taken, or to be taken in response to each of the following:
1.
" Review and revise, as necessary, f cur sperating procedures. to ensure that an estimate of the critical rod pattern be made prior to each approach to critical. The method of estimating critical rod patterns should take into account all it;ortant reactivity variables (e.g., core xenon, moderator temperature, etc. )."
The required review has been completed and indicates that our practices are satisfactory.
Dar procedures and check lists require that an estimate of the critical rod pattern be made prior to each approach to criticality. The procedure for estimating critical rod pattern takes into account all important reactivity variables. A memorandum was issued in 1971 which specifies the allowable error permitted in a critical prediction and the administrative controls applicable if this allowable prediction error is reached. Extensive training was conducted for all Senior Licensed personnel concerning these requirements.
The mcmorandum will be incorporated into our procedures and check lists and additional training will be conducted prior to the time the Unit returns to operation.
2.
"Where inaccuracies in critical rod pattern estimates are antici-pated due to unusual conditions, such as high xenon, procedures should require that not :h-step withdrawal be used well before the estimated critical position is reached and all SRM channel indicators are monitored so as to permit selection of the most significant data."
Our existing control rod withdrawal procedure requires that control rods being withdrawn after the first two and one half groups (eight of the thirty-two control rods) be n'+ch withdrawn.
Notch withdrauals are not required for the first two and one half groups since insufficient rod coupling exists to allow the reactor to go critical prior to this point.
Only the nuclear Engineer with concurrence from the Shift Foreman can authorize notch over-ride withdrawals.
Our procedures and training have stressed response of the nuclear instrumentation (both period and power level change) as the indicators of approach to critical. The nuclear instrumentation has been extremely sensicive to control rod movement throughout the core due to its relatively small size.
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" Review and evaluate your control rod withdrawal sequences to assure that they minimize the notch worth of individual control rods, especially those withdrawn immediately at the point of criticality.
Your review should ensure that the following related criteria are also satisfied:
Special rod sequences should be considered for peak xenon a.
c onditions.
b.
Provide cautions to the operators on situations which can result in high notch worth (e.g., first rod in a new group will usually exhibit high red worth)."
During thirteen years of reactor operation, the reactor has been brought critical tmder a wide variety of conditions using a vendor developed rod sequence including critical approaches during peak xenon, maximum xenon decay, high (but normal) rates of pressure decay, thus maximizing control rod worths.
The Nuclear Engineer is authorized to make minor deviations in the pattern to minimize control rod worth but special patterns or sequences have never been required.
Due to the relatively small size of the core and the small number of control rods, variations in rod sequence have not been shown to be practical since a change in one part of the sequence generally causes an undesirable effect at a later point in the sequence.
The procedures for reactor startup do not contain specific prc~
cautions regarding situations leading to high notch worths.
The procedures will be revised to include these precautions, which are presently included in detail in the operator training programs as discussed in the response to item 5 below.
L.
" Review and evaluate the operability of yoUr ' emergency rod in' switch to perform its function under prolohged severe use."
There is no " emergency rod in" switch on this Unit.
5
" Provide a description of how your reactor operator training program covers the considerations above (i.e., items 1 thru 3)."
The reactor operator training program (both initial license training and licensed operator requalification) includes study assignments, lec'ures and discussions about the factors and variables that can af'.ect reactivity during an approach to critical.
The procedure PJed by the nuclear Engineers to predict criticality is discussed in detail to familiarize the operators w:+h the conditions con-sidered and the variables involved. Exp(
.ed nuclear instrument responses and the general guidelines used caring an approach to critical are discussed. Special operating conditions that could lead to high control rod worths are discussed along with the expected operator response to those conditi ons.
In addition, all
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prospective license candidates are required to cbserve and partici-pate in actual reactor startups to become familiar with the actual plant r esponse and what factors affect this response.
Administrative controls applicable to critical approaches are discusscd. These include check lists for startup, the permissible error in critical prediction before an evaluatice is required and the requirements f or control rod withdrawal.
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