ML20010H845
| ML20010H845 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 09/23/1981 |
| From: | Vincent R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| TASK-15-08, TASK-15-8, TASK-RR NUDOCS 8109290348 | |
| Download: ML20010H845 (3) | |
Text
e i
O Consumers Power Company General offices: 212 West Machigan Avanue, Jackson, MI 49201 *(517) 738 0550 September 23, 1981 Director, Nuclear Reactor Regulation Att Mr Dennis M Crutchfield, Chief Operating Reactors Br h No 5
, edssion US Nuclear Regulator, Washington, DC 20555 DOCKET 50-155 - LICENSE DPR BIG ROCK POINT PLANT - SEP. TOPIC XV-8, CONTROL ROD MISOPERATION Attached is the Consumers Power Company evaluation of SEP Topic XV-6 for the Big Rock Point Plant. This evaluation has been prepared using the same general format as the sa=ple NRC evaluation of this teri-for Oyster Creek.
We trust that this infomation vill satisfy the starr's needs.
I
\\
I
/
\\ -
%T\\%
o}\\kL/is' '/'
p Robert A Vincent
.gx
- 9 h g
,O g s
Staff Licensing Engineer
'j h(
h CC Director, Region !h, USHRC URC Resident Inspector - Big Rock Point g
035
///
8109290348 810923 3 PDR ADOCK 05000155i P
PDR^
~.
i B'IG~ ROCK POINT FIJLTf EVALUATION OF CONTROL ROD MISOPERATION EVENTS SEP TOPIC XV-8 4
SYSTEM AND OPERATING PROCEDURES In the Big Rock Point reactor the control ods are moved one at a time. During startup and over the entire range of power operation, rod withdrawal and inser-tion is governed by a preselected-sequence. Because the Plant is not equipped with a recirculation f3cw control. feature there is a unique critical control red density for each power level for each point in core life, so that except for special tests, one continuous sequence usually suffices far.all modes of i
operation.
Conformance to the withdrawal sequence ensures that the worth of inserted rods are kept within technical specification limits, and that the desired power distributbr. is attained during operation.
A control rod misoperation event occurs when a control rod is moved out of sequence. Big Rock Point has no Rod Worth Minimizer or Rod Block Monitor, so that there is no c*matic system that prevents the operator from moving control rods in an incorrect sequence. There is, however, a procedural require-i ment during startups that a second licensed operator observe centrol rod move-I ments to assure conformance to the sequence.
There are two possible modes of operation of the Big Roc 2 tint control rods; normal, and " jog bypass." The norm 1 mc.ie of cperation moves a control rod in discrete three inch intervals (not-hes), pausing at each one. The jeg
~
bypass mode allows continuous movemer t sf a control rod at normal drive speed, which is limited by technical spen'fications to 0.25 ft/sec. irr.lementa-l tion of the jog bypass mode takes a denberate action by the operew, wherein
~
the spring loaded jog
- ss hand switch must be hd.d ir, position with one hand and the witheraw/ insert lever manipulated vith tne other. The Jog bypass mode is used for special tests such as the coupling integrity check, insert and withdrawal rate timing tests, friction tests, o.* for rod insertion during shut-down margin checks. During startup and power operation the operator moves the rods in jog mode one notch at a time, and jog byIass is allowed only for rod l
insertion or for the coupling check when a rod is fully withdrawn.
CONTROL ROD MISOPERATIONS An evaluation of control rod misoperations resulting from single failures in j
the control system was submitted as a response to SEP Topic IV-2 (CPCo letter of &y h, 1981). It was concluded in that evaluation that the worst single failure event is an inadvertent continuous withdrawal or drift-out of a j
control rod. The worst misoperation due to operator error would be a similar event. Referenced analyses of this event considered both low power and high 4
power initial conditions. Fcr the low power events it was concluded that j-fuel damage limits are not exceV.ed even when rod worths and rod withdrawal i
rates are greater than normally allowed.
In the event of a continuous rod withdrawal from high power, it was concluded that a few fuel pins in the neighborhood of the withdrawn rod could experience cladding damage, but that 4
radioactive releases would.be well within 10CFJ100 guidelines. This analysis assumed no RPS overpower trip due'to excore visibility and no operator action, allowing the reactor power to achieve a steady state value of 140f, of rated j
thermal power.
_. - -, _ _ _ -, -,. _, _,.. _, _ ~.- _ --.-
o A continuous rod withdrawal event of this severity caused by operator error is considered to be extremely improbable for the following reasons:
1.
To implement continuous withdrawal in jog bypass mode requires a control manipulation sequence significantly different from normal notch by notch withdrawal, as d.14 cussed previously.
2.
Operstors are instructed to observe the flux response following control rod withdravds to assure that the blade is coupled to the drive. He is therefore likely to recognize immediately after a misoperation that t?.e power is increasing beyond limits and take appropriate action.
3 The rod drift from high power analysis assumed that the rod T.oved out slowly enough so that there was no porer overshoot and no RPS trip on high flux. However, continuous withdrawal of a high worth control rod at normal drive speed is likely to cause a flux spike large enough to result in a RPS trip. Because of the finite amount of time required to transfer heat to the cladding and for clad burn-out to occur after DNB, the probability of fuel damage is reduced.
CONCLUSION The Big Rock Point reactor differs from current generation boiling vater reactors in that it does not have some of the control system features intended to prevent control rod misoperation events. Even so, serious control rod misoperations are considered to be enremely. low probability events. The most serious event, a continuous rod # thdrawal from full power, has a potential to cause a small amount cf fuel da;aage, but results in doses well within acceptance criteria for infrequent accidents.
It is therefore concluded that the consequences of control rod misoperation events at Big Rock Point are acceptable, and that no remedial action is warranted.
-