Control element assembly position system

Compliance with administrative limits on cumulative exposure of control rod groups in the reactor core, is monitored by computing the incremental effective exposure for each group commensurate with core power, for each time increment at which each group is within the position range where an administrative limit is imposed. The increments of effective exposures for each group are accumulated, and the accumulated effective exposure for each group is compared with the administrative limit to each group. This comparison is then displayed to the reactor operator, preferably using either a "rolling wheel" or "sliding bar" format.

BACKGROUND OF THE INVENTION 
The present invention relates to nuclear power plants, and in particular, 
to on-line monitoring of control rod positions relative to regulatory 
requirements for short term, long-term, and transient insertion limits. 
Commercial nuclear power plants are subject to comprehensive regulatory 
compliance covering virtually every phase of nuclear reactor operation. 
Many of these regulatory constraints are manifested in the form of 
so-called "Technical Specifications", which are an integral part of the 
operating license for the power plant. Each vendor of a nuclear steam 
supply system (NSSS), achieves compliance with the technical 
specifications, by formulating and justifying operating procedures for 
approval by the regulatory authorities. 
In pressurized water nuclear power plants (PWR plants), one type of 
Technical Specification concerns the accumulated time during which control 
rods are present in the reactor core. As is well known, control rods serve 
two important functions. The extent of insertion directly affects the 
gross power level in the reactor core. Another function is to control the 
local distribution of power in the core, thereby avoiding high localized 
power peaking, relative to the average power generated in the core. The 
prolonged insertion of particular control rods in the core, especially 
during periods of relatively high power, can have two detrimental effects 
long term. First, the pattern of fuel consumption can be distorted to the 
extent that upon removal of these rods, new, previously unpredicted local 
power peaking or power oscillations may arise. Furthermore, control rods 
can prematurely lose effectiveness over time. 
It is also well known that individual control rods can be ganged together 
as an assembly for insertion and removal by a single drive mechanism, and 
that a plurality of assemblies, such as four or eight, can be controlled 
as a group for substantially simultaneous movement into and out of the 
core. Four or five groups are typically programmed for staggered insertion 
and withdrawal from the core (unless, of course, all groups are to be 
dropped simultaneously to trip, or "scram", the reactor). For purposes of 
the present disclosure, a cluster of control rods which are moved by a 
single drive mechanism, are referred to as a "control element assembly" 
(CEA), whereas a plurality of CEA's which are controlled for substantially 
simultaneous movement into and out of the reactor, are referred to as a 
"CEA group". 
According to one approach for compliance with Technical Specifications, 
plant Limiting Conditions of Operation (LCO) are established to impose 
operational constraints with regard to CEA rod group insertions and 
thereby assure that the design bases which underlie the Technical 
Specifications are not violated. These limitations are typically 
characterized in terms of restrictions imposed on CEA rod group insertions 
between the Long Term Steady State Insertion Limit (LTSSIL) and the 
Transient Insertion Limit (TIL). These restrictions are typically 
expressed in terms of either clock hours, or effective full power days 
(EFPD) of exposure. An EFPD is the exposure equivalent of 24 hours at the 
licensed full power operation of the reactor. In addition, restrictions 
are imposed upon exceeding the Short Term Steady State Insertion Limit 
(STSSIL) under certain conditions. In a PWR, all CEA's are typically out 
of (above) the core at full steady state power, and are inserted 
downwardly into the core to reduce power level. Typical examples of 
limiting conditions of operation are set forth in the following Table 1. 
TABLE 1 
______________________________________ 
ROD GROUP OPERATIONAL LIMITATION 
APPLICABILITY 
(LCO) CRITERIA 
______________________________________ 
Regulating Insertion between STSSIL and 
Limit to 4 hours 
TIL per 24 hour 
interval 
Regulating Insertion between LTSSIL and 
Limit to 5 EFPD 
TIL per 30 EFPD 
interval 
Regulating Insertion between LTSSIL and 
Limit to 14 EFPD 
TIL per 365 EFPD 
interval 
Regulation Insertion beyond the STSSIL 
Take Prescribed 
with COLSS out ot service 
Action within 
1 hour 
Part Strength 
Insertion between LTSSIL and 
Limit to 7 EFPD 
TIL per 30 EFPD 
interval 
Part Strength 
Insertion between LTSSIL and 
Limit to 14 EFPD 
TIL per 365 EFPD 
interval 
______________________________________ 
These restrictions limit the duration (in terms of hours) that CEA rods can 
be positioned between the STSSIL and the TIL, and the amount of CEA 
exposure which can be accumulated (in terms of Effective Full Power Hours) 
for insertions between the LTSSIL and the TIL. The graph of FIG. 20 
depicts typical operational regions bounded by these insertion limits. 
The LTSSIL is a position limit in which there is no restriction for CEA rod 
insertions which are above this position. However, CEA rod insertions 
below this position and bounded by the TIL are constrained to the limits 
of CEA exposure as noted in Table 1. 
The STSSIL is a position limit below (i.e., greater than) the LTSSIL in 
which further restrictions on insertion (time duration--as opposed to CEA 
exposure accumulations) are imposed on CEA rod insertions which are below 
this position and bounded by the TIL. These limits are noted in Table 1. 
The TIL is a position limit below the STSSIL which CEA rod insertions must 
not exceed. This limit is designed to allow for plant maneuvering using 
CEA insertions (as long as the CEA's do not go below this limit and as 
long as they maintain the CEA exposure and time limit durations for 
insertion as previously noted). Should CEA's be inserted below the TIL, 
the plant annunciator system normally outputs an alarm message and the 
operator must then take corrective action (such as--restore the CEA rods 
to within the prescribed limits within a defined time period; or reduce 
plant thermal power). 
It is conventional to identify groups of CEA's beginning with number 1 and 
proceeding, e.g., to number 5 according to the order in which they are 
withdrawn from the core in a zero power condition at which all CEA groups 
are fully inserted. The corollary is that in the initial condition where 
the reactor core is at full power, with all rods out (the most desirable 
operating condition), Group 5 is the first to be inserted, followed by 4, 
3, etc. 
The Long-Term Steady State Insertion Limit is shown in FIG. 20 as a 
vertical line extending through range of 1.0-0.2 power fraction and (when 
projected) intersecting the Group 5 insertion representation bar at an 
insertion distance of 108 inch (274 cm), out of a total group rod length 
of 150 inches (381 cm). Because Group 4 and subsequent groups follow in 
staggered relationship, it is clear that whenever Group 5 is positioned in 
the core anywhere within the Steady State Insertion Limit, no other Groups 
are in the core. It is evident that Group 4 does not begin entering the 
core, until Group 5 is at the 60 inch (152 cm) withdrawal position (i.e., 
90 inches (229 cm) of insertion). 
The Short Term Steady State Insertion Limit for Group 5 is also shown in 
FIG. 20 as a vertical line which has an upper limit at a power fraction of 
0.75 and extends downward to 0.25, and intersects the Group 5 bar at the 
60 inch (152 cm) withdrawal position. Thus, it can be appreciated from 
FIG. 20, that the Group 5 Short Term Steady State Insertion Limit, would 
not be accompanied by a Short Term Steady State Insertion Limit for any 
other Group. 
On the other hand, the Transient Insertion Limit allows for a variety of 
CEA insertion configurations including the fifth and fourth Groups fully 
inserted and the third Group inserted at the 60 inch (152 cm) withdrawal 
position. Not all configurations are permitted at every power level, 
however, i.e., the greater extent of Group insertion, the lower the 
permitted power level even during a transient. 
Thus, it may be appreciated that the LCO's impose concurrent limitations on 
insertion. For example, even if the CEA groups have not reached the limit 
of 5 EFPD per 30 EFPD interval, for insertion between the LTSSIL and the 
TIL, desirable repositioning of the Groups may be foreclosed by the 
further requirement that insertion between the STSSIL and the TIL must not 
exceed 4 hours per 24 hour interval. 
The foregoing operational requirements are presently maintained by manual 
surveillance. The inventor has concluded that this approach has the 
following shortfalls which are remedied by the present invention: 
1. Manual monitoring is cumbersome and prone to human error. 
2 There is no automatic method to display and analyze the monitored data 
which, in turn, reduces the situational awareness for the operator of the 
existing accumulated CEA group exposures relative to the operational 
limits. 
3. There is no automatic early notification of approach to operational 
limits so that corrective action can be taken prior to exceeding an 
operational limit. 
4. There is no automatic alarm notification when the operational limits are 
exceeded so that corrective action may be immediately initiated. 
5. The resolution of the manually recorded data is coarse. 
6. Manual recording of accumulated EFPD and hours for CEA rod group 
exposures does not conveniently lend itself to monitoring a contiguous 
data interval or window. This may result in the selection of discrete 
monitoring intervals which are sequential. Such discrete monitoring 
intervals can lead to potential circumscribing of the intent of the 
operational limits. For example, the restriction of 5 EFPD per 30 EFPD 
will seemingly be satisfied by two sequential monitoring intervals in 
which 4.5 EFPD exposure occurs during the last 4.5 days of the first 
monitoring interval (of 30 EFPD) and in which 4.5 EFPD exposure occurs 
during the first 4.5 days of the following monitoring interval (of 30 
EFPD). Each monitoring interval seemingly satisfies the restriction of 5 
EFPD per 30 EFPD interval but, in fact, 9 contiguous EFPD of exposure have 
occurred. If the starting period of the first monitoring interval was 
advanced 5 EFPD, then the total EFPD exposure for the first monitoring 
interval would have been 9 EFPD (rather than 4.5 EFPD) which exceeds the 
operational limit. In this example, the operational limits were either 
complied with or violated depending upon the happenstance of when the 
start of a discrete monitoring interval was chosen. 
SUMMARY OF THE INVENTION 
According to the present invention, these deficiencies in conventional 
techniques are overcome by a method and apparatus, in which the 
incremental effective exposure for each CEA group is computed commensurate 
with core power, for each time increment at which each group is within the 
position range where an administrative limit is imposed. The increments of 
effective exposures for each group are accumulated, and the accumulated 
effective exposure for each group is compared with the administrative 
limit for each group. This comparison is then displayed to the reactor 
operator. 
The displaying of the comparison to the reactor operator, preferably 
provides for continuous monitoring, alarming, and reporting of accumulated 
group exposure, expressed in terms of hours and effective full power days 
relative to the established operational limits. Although the 
administrative limits are preferably LCO's, other administrative limits, 
whether or not based directly on the plant Technical Specifications, can 
provide the applicable limits. 
In a further preferred embodiment, the display provides graphical 
information utilizing a "rolling wheel" and "sliding bar" format. 
In a still further preferred embodiment, a display sectoring mode is 
included. 
In yet further embodiments, query and predictive modes of operation, 
pre-alarm notification upon approach to applicable limits, and alarm 
notification upon exceeding applicable limits, are also provided. 
In the predictive mode, the effect on the LCO's of a planned power maneuver 
is assessed. If insufficient EFPD margin is available, a projection is 
made as to when suitable margin will be regained to allow the maneuver to 
occur while maintaining compliance with the LCO's. 
In the pre-alarm feature, an early warning of an indication of approach to 
an LCO limit regarding accumulated EFPD is displayed, so that action can 
be taken to avoid an actual violation of the LCO. 
The invention is preferably implemented to receive as continuous inputs: 
the current plant power level; the CEA Group positions; and the 
operational status of the Core Operating Limit Supervisory System (COLSS). 
The COLSS determine automatically and on-line, the gross thermal power 
level of the core. One implementation of such as system is described in 
U.S. Pat. No. 3,752,735, issued Aug. 19, 1973, and U.S. Pat. No. 4,330,367 
issued May 18, 1982, the disclosures of which are hereby incorporated by 
reference. An internal clock maintains an accurate time base so that plant 
EFPD may be calculated as a function of the current plant power level, 
accumulated time, and licensed full power level. Accumulated time (in 
terms of hours), is also maintained employing the internal clock. 
Utilizing the positions of the Regulating and Part Strength rod groups, and 
the internally calculated EFPD and accumulated time, the system 
continuously determines the exposure for these groups whenever they are 
inserted between the Long Term Steady State Insertion Limit and the 
Transient Insertion Limit. The exposures are determined for contiguous 
monitoring intervals which are defined by the Limiting Conditions for 
Operations (see examples in Table 1). The computed exposures are then 
continuously compared with the operational criteria. 
In addition, the positions of the Regulating groups are continuously 
compared with the Short Term Steady State Insertion Limit whenever the 
applicable LCO's are exceeded (such as whenever the Core Operating Limit 
Supervisory System is out of service). For such occurrences, excursions 
beyond the Short Term Steady State Insertion Limit are annunciated and the 
time remaining to take corrective action, in accordance to the Technical 
Specifications for operations, is displayed. 
For cases in which the Limiting Conditions for Operation are not applicable 
(such as for a Reactor Power Cutback event) an inhibit signal prevents 
unwanted exposure accumulations or spurious alarm messaging. A reactor 
power cutback system of the type mentioned herein, is described in U.S. 
Pat. No. 4,075,059 issued Feb. 21, 1978, the disclosure of which is hereby 
incorporated by reference. It should be appreciated that the use of part 
strength CEA's is an option, and the implementation of the invention 
follows the same procedures for part strength CEA's as for regulating 
CEA's. As the term is used herein, regulating CEA's is meant to include 
all the Groups which are normally controlled for sequential insertion and 
removal, as depicted in FIG. 20, for the purpose of regulating power 
and/or power distribution during power generation in the reactor. The 
reactor may also have additional control rods which are not normally 
intended for regulating purposes, but which are available for rapid 
shutdown or extended zero power outages. 
These features of the invention provides significant advantages over 
conventional techniques. 
Automatic calculation and continuous display of accumulated time (hours) 
and accumulated Effective Full Power Days (EFPD) of CEA rod group exposure 
relative to the Limiting Conditions for Operation (LCO) for insertion 
between the Long Term Steady State Insertion Limit and the Transient 
Insertion Limit, is provided. Real-time monitoring of plant power and CEA 
rod group positions allows automatic and continuous calculation and 
updating of Effective Full Power Days and rod group exposures. This 
simplifies the operator workload and provides timely information relative 
to monitoring compliance with operational limitations on CEA rod group 
insertions and assists with the planning of future CEA rod group 
maneuvers. 
Continuous comparison of Regulating rod group positions with the Short Term 
Steady State Insertion Limit under applicable conditions as noted within 
the LCO's (such as whenever COLSS is out of service), provides automatic 
notification of exceeding the Limiting Condition for Operations for 
Regulating rod groups. 
Graphical representation of accumulated time (hours) and Effective Full 
Power Days (EFPD) relative to the LCO's, utilizing unique "Rolling Wheel" 
and "Sliding Bar" display formats, is intuitive. The display formats 
provide the user with an easily understood representation of the 
accumulated time and accumulated EFPD exposure for CEA rod groups relative 
to the operational limits as defined by the LCO's. The display formats are 
designed to accommodate a contiguous monitoring interval in which old 
exposure data is continuously discarded (rolls off for the "Rolling Wheel" 
format or slides off for the "Sliding Bar" format) while new data is 
continuously added (rolls on for the "Rolling Wheel" format or slides on 
for the "Sliding Bar" format) for the monitoring intervals as defined by 
the LCO's. These graphical displays provide a spatial representation of 
accumulated rod group exposure for a contiguous monitoring interval which 
is readily understandable to the end user. The displays improve the 
situational awareness and comprehension of the existing accumulated rod 
group exposures and readily indicates when exposure margin can be 
regained. 
The Sector mode which is associated with the graphical displays allows 
users to define "sectors" within the "Rolling Wheel" and "Sliding Bar" 
displays to be expanded and thus examined at higher resolutions. The 
ability to "sector" to finer resolutions allows finer detail to be 
observed, for the interval of interest, than can normally be displayed on 
a Video Display Unit. 
The Predictor Mode of operation allows the effect of a planned CEA Rod 
Group maneuver on the LCO's to be assessed in advance of performing the 
actual maneuver. This minimizes the likelihood of exceeding the 
operational limits for CEA rod group exposure. If insufficient time 
(hours) or EFPD margin is available, the Predictor Mode projects when 
suitable margin will be regained to allow the maneuver to occur while 
maintaining compliance with the LCO's. Various "what if" scenarios can be 
investigated using the Predictor Mode. 
The Query Mode allows the user to recall historic information and to 
determine when a certain level of accumulated exposure (in terms of hours 
and/or EFPD) will "roll off (slide off)" and be regained as usable margin. 
This allows the user to review previously recorded information and to 
determine when accumulated exposure margin (expressed in terms of hours 
and/or EFPD) will be regained which serves as an advanced planning tool. 
In the event of a system outage, the Update mode allows the system to be 
recalibrated to the current operational conditions. In event of a system 
outage the Update mode allows the user to enter the appropriate 
time--power--and rod group exposure history for the outage interval in 
order to recalibrate the system to the current operational conditions. 
Thus, the system can account for outages and be immediately reinserted 
into service when the system is restored to operation. 
The Summary Report allows the user to observe the accumulated exposure and 
remaining exposure margin for all Regulating and part Strength rod groups 
on a single display. Provides the user with an overall assessment of the 
current accumulated exposure and remaining exposure margin utilizing a 
single convenient display page. This alleviates the necessity of searching 
through multiple display pages to obtain an overall assessment of the 
current operational status. 
The pre-alarm notification alerts the user to an impending approach to an 
established Limiting Condition for Operation. Advanced notification of an 
impending limit excursion provides the user with time to take corrective 
action before the limit is actually exceeded. 
Alarm notification alters the user to any excursion beyond an established 
LCO boundary. Such alarming alerts the operator that an operational limit 
has been exceeded to that he may take appropriate action as called forth 
within the Technical Specifications for plant operations. 
Time remaining for completion of corrective action is displayed whenever an 
Alarm is annunciated (via exceeding an LCO boundary). Display of such 
information provides the operator with a convenient assessment of the 
progress of corrective action(s) relative to requisite "Completion Times" 
as stated within the Technical Specifications for plant operation. 
In cases for which the Limiting Conditions for Operation are not applicable 
(such as for a Reactor Power Cutback event) an inhibit signal prevents 
unwanted exposure accumulations or spurious alarm messaging. 
A contiguous monitoring interval is maintained for calculating rod group 
exposure relative to the LCO's for insertions between the Long Term Steady 
State Insertion Limit and the Transient Insertion Limit, rather than 
sequential discrete intervals. A contiguous monitoring interval avoids 
potential ambiguity in determining compliance with the LCO's.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 is a diagrammatic illustration of the CEA Rod Position System in 
accordance with the present invention, for a pressurized water nuclear 
reactor. The reactor is controlled by CEA's which are actuated by drive 
mechanisms 22 which, in turn, are controlled by a Control Element Drive 
Mechanism Control System (CEDMCS) 50 (or equivalent rod control system). 
During operation of a pressurized water reactor, the coolant is circulated 
through the reactor core, contained within the nuclear rector vessel 10, 
which extracts heat from the core and heats the coolant. This heated 
primary coolant is then passed through a steam generator 12 where it 
exchanges its heat with a secondary coolant that circulates through the 
secondary side of the steam generator 12. After transferring its heat to 
the secondary coolant, the primary coolant is then recirculated by reactor 
coolant pumps 19 back to the reactor 10. 
The secondary coolant, which is ordinary water, is heated from its normal 
liquid phase to vapor phase as a consequence of the heat transfer from the 
primary coolant which occurs in the steam generators 12. It is then passed 
to the plant turbine 14 which converts the heat energy of the vaporous 
phase into mechanical energy. The secondary coolant is then condensed and 
is recirculated to the steam generator 12 by means of steam generator 
feedwater pumps 16. 
A digital computer 54 receives certain plant input signals and then 
processes them to perform the requisite on-line monitoring of CEA 
Regulating and Part Strength rod groups relative to the Limiting 
Conditions for Operation (LCO) for insertion between the Long Term Steady 
State Insertion Limit and the Transient Insertion Limit. In order to 
properly perform this function, the digital computer 54 requires the CEA 
rod positions for the Regulating and Part Strength rods, indications if a 
reactor power cutback condition is present, and the values of certain 
plant parameters. 
The CEA rod positions are obtained from the Control Element Drive Mechanism 
Control System (CEDMCS) 50 (or equivalent rod control system). The CEDMCS 
determines rod positions for each Control Element Assembly by keeping an 
aggregate count of the number of "up" and "down" pulses which are 
generated by CEDMCS whenever a request is sent to move the rods up or down 
by one position (e.g. -0.75 inches or 1.9 cm of vertical displacement) to 
the control rod control mechanisms 22. These signals are generated within 
CEDMCS by an Automatic CEA Timing Module (ACTM) which outputs "up" and 
"down" pulses of 300 to 500 millisecond duration. The "up" and "down" 
pulses are accumulated within CEDMCS via pulse counters for each of the 
rods. The rod positions are determined within CEDMCS by taking the 
difference in aggregate pulse counts between the "up" and "down" pulses 
and multiplying this difference by the vertical displacement due to a 
single pulse command. 
EQU Rod Position=(S{up pulses}-S{down pulses}).times.0.75 inch 
Pulse counters are reset to zero whenever a rod is fully inserted into the 
core and encounters a "bottom contact" switch. The individual CEA rod 
positions, as determined via CEDMCS pulse counting, are transmitted from 
CEDMCS 50 to the digital computer 54 via a data link. These values are 
then stored in the plant computer data base 60 where they are accessible 
by the CEA Rod Position Program 56. 
Alternately, rod positions can be directly determined via a control rod 
position detector 24 which is common to pressurized water nuclear 
reactors. 
Indication of the initiation of an accelerated power reduction, known as 
Reactor Power Cutback (RPC), is determined by the RPC Monitor 52. The RPC 
Monitor notes whenever an event is present which requires an accelerated 
power reduction (such as the failure of a steam generator feedwater pump 
16) and sends a signal to the digital computer 54 indicating that a RPC 
event is present. The status of the RPC condition (RPC event present or 
not present) is stored in the plant computer data base 60 where it is 
accessible by the CEA Rod Position Program 56. 
Certain plant parameter values are required by the digital computer 54 in 
order for the COLSS program 58 to calculate the reactor power level. These 
values are obtained from the plant sensors as follows: primary coolant 
flow rate 32, primary coolant pressure 34, cold leg temperature (T cold) 
36, hot leg temperature (T hot) 38, feedwater temperature 40, feedwater 
flow 42, steam flow 44, and steam pressure 46. These values are then 
stored in the plant computer data base 60 where they are accessible by the 
COLSS program 58 (or equivalent). COLSS 58 utilizes this data to determine 
plant power by determining the net energy leaving a control volume taken 
out of the reactor (primary calorimetric method) and by performing an 
energy balance based on the plant secondary system (secondary calorimetric 
method). Alternately, plant power may be directly determined via the 
neutron flux detectors 30 which are common to pressurized water nuclear 
reactors. 
The COLSS program 58 computes plant power and stores this value along with 
the COLSS program status (operating mode, off-line mode, test mode) into 
the computer data base 60 where it can be accessed by the CEA Rod Position 
Program 56. 
The CEA Rod Position Program 56 determines if the restrictions imposed upon 
CEA rod group insertions between the Long Term Steady State Insertion 
Limit and the Transient Insertion Limit (expressed in terms of hours and 
EFPD exposure) are maintained. This program acquires individual rod 
positions (as determined via CEDMCS 50) from the data base 60, acquires 
the LCO limits for CEA insertion from the data base 60, acquires RPC 
status (as determined via the RPC monitor 52) from the data base 60, and 
acquires the value of plant power and COLSS status (as determined via 
COLSS 58) from the data base 60. A magnetic data storage disk 62 (or 
equivalent long term data storage device) is used to store CEA exposure 
files and CEA historic records which are utilized by the CEA Rod Position 
Program 56. A keyboard 64 accepts operator inputs and a CRT 66 displays 
output data and alarm annunciation messages. (Alternate data entry and 
display devices, such as touch screens and LCD flat panel displays, may 
also be utilized in place of the CRT and keyboard.) 
Positions for the Regulating Groups and Part Strength Groups, as used in 
the CEA Rod Position Program 56, are determined by the "Middle Group 
Average" method. This method eliminates the highest and lowest CEA's from 
the averaging calculation so that the group average position is based on 
the "middle" CEA positions, and is not skewed by an unusually high or low 
individual CEA element position. This method is illustrated below for the 
case of Regulating Group 1 which consists of "n" CEA elements whose 
positions are stored in array RG1(J). The calculation proceeds as follows: 
##EQU1## 
Where: "P1min" contains the value of the lowest CEA position for Reg Group 
1; 
"P1max" contains the value of the highest CEA position for Reg Group 1; 
"P1sum" contains the sum of all CEA rod positions for Reg Group 1; 
"n" contains the number of CEA elements in Reg Group 1; 
"RG1.sub.-- Position" is the average position of Regulating Group 1 as 
determined by the "Middle Group Average" method. 
These calculations may be performed within the data base using "composed 
data base points" (in which the aforementioned calculations are performed 
directly within the data base), or alternately, can be performed as a 
separate CEA group position module associated with the CEA Rod Position 
Program 56. 
FIG. 2 provides an overview of the software structure for the CEA Rod 
Position Program 56 for the key operating functions. Box 150 is the 
Program Executive which controls and schedules the execution of the other 
program modules which comprise the CEA Rod Position Program (The specific 
instructions contained therein are dependent upon the particular software 
operating system which is employed by the digital computer). Box 151 
performs a calculation of Effective Full Power periods and then 
sequentially calls the next four modules (boxes 152 to 155) in the chain. 
Box 152 performs an update of the CEA exposure accumulation history for 
all Regulating and Part Strength groups, box 153 performs a determination 
of the current value of CEA exposure for all Regulating and Part Strength 
groups, box 154 scales the exposure accumulation data so it conforms to 
the pixel display constraints of the display CRT, and finally box 155 
draws the graphical output in either "rolling wheel" or "sliding bar" 
display formats. Box 156 supports the recall of historic CEA exposure 
accumulation records. Box 157 contains the main Predictor Module which 
predicts when sufficient CEA exposure margin will be regained to allow a 
planned CEA rod maneuver without violating the LCO's. Boxes 158 to 161 
contain software modules which support additional calculations that are 
required for the Prediction Function. Box 158 performs margin prediction 
calculations, box 159 performs a mapping of CEA exposure history from 
array "P(J)" (which contains the current CEA exposure data) into array 
"PP(J)" (which is utilized for exposure history prediction calculations), 
box 160 updates the CEA exposure margin for the predictor array "PP(J)", 
and box 161 calculates CEA exposure margin using the predictor array 
"PP(J)". Box 162 contains the main update module which is used to update 
time dependent CEA exposure data in the event of a computer outage of the 
CEA Rod Position System. After execution of box 162, then box 163 is 
called. Box 163 performs additional calculations on the update intervals 
(by shifting elements of array "P(J)" up by 1 position) that are required 
to support the Update Function. The detailed functional operation of these 
software modules is subsequently described herein. 
Prior to describing the requisite logic associated with this system, an 
understanding of the data storage structure is a helpful prerequisite in 
order to follow the subsequent algorithmic functions which operate 
directly upon the stored data. The following descriptions are provided for 
the case utilizing data storage intervals based upon Effective Full Power 
(EFP) criteria (EFP hour intervals) rather than standard time intervals 
(hours) as these are the more complex data recording intervals to 
maintain. (For criteria based on standard time intervals (hours), the 
array elements correspond to "hours" instead of "EFP hours" and there is 
no correspond calculation required to determine "EFP hourly intervals".) 
FIG. 3 illustrates a generic data array structure for maintaining the CEA 
exposure records. There are multiple arrays to track each of the CEA 
exposure criteria (e.g. -5 EFPD per 30 EFPD interval for Regulating 
groups, 14 EFPD per 365 EFPD interval for Regulating groups, 7 EFPD per 30 
EFPD interval for Part Strength groups, etc.). Each of the Regulating and 
Part Strength groups has a corresponding set of such arrays to track the 
requisite CEA exposures. Each of these arrays consists of N elements. The 
number of elements (N) is dependent upon the CEA exposure which is being 
maintained (e.g. -5 EFPD per 30 EFPD interval for Regulating groups, 
etc.). Each element in an array corresponds to a fixed Effective Full 
Power (EFP) interval of exposure, with element 1 corresponding to the most 
recent EFP interval and element N corresponding to the oldest EFP 
interval. 
As an example, for the "5 EFPD per 30 EFPD interval" criteria for 
Regulating groups, and utilizing an EFP data recording interval of 1 
EFP-hour, a total of 1*24*30=720 array elements would be required to 
contain 30 days worth of EFP exposure, recorded at a resolution of 1 
EFP-hourly intervals. For this array, element N=720 would correspond to 
the oldest data (720 EFP-hours old) while element N=1 would correspond to 
the most recent data (1 EFP-hour old)). EFP-hourly intervals are computer 
based upon plant power operating level and time duration (for 
example--with a plant power level of 0.5 EFP, a two hour time interval 
would be required to obtain a 1 EFP-hour interval). The contents of each 
array element indicate what the CEA exposure accumulation was for the CEA 
group during the EFP-hourly interval that the array element corresponds 
to. If CEA exposure accumulation occurred during an EFP interval, then the 
total exposure accumulation which occurred during that interval is stored 
as the array element value; otherwise a "0" is stored (for example, if a 
Regulating group was inserted between the Long Term Steady State Insertion 
Limit and Transient Insertion Limit for 1/2 the time during the EFP hourly 
period that occurred 4 EFP hours ago, then the contents of array element 
N=4 would be "0.5 EFP hour", i.e., P(4)=0.5). 
FIG. 4 provides a flowchart representation of the EFP COMPUTATIONAL MODULE 
which is utilized to determine Effective Full Power (EFP) hourly intervals 
and to determine the EFP exposure which has occurred during these 
intervals. This module runs periodically, at 30 second intervals, under 
the direction of the PROGRAM EXECUTIVE (other time intervals may be 
utilized if increased resolution in computing the 1 EFP-hour interval is 
desired). 
With reference to FIG. 4, the EFP COMPUTATIONAL MODULE initially reads the 
current status of COLSS and Reactor Power Cutback via box 200. Then, via 
box 201, it determines if COLSS is out of service (determined via the 
COLSS module, box 58 of FIG. 1) or if a Reactor Power Cutback condition 
exists (determined via the RPC Monitor, box 52 of FIG. 1). If either of 
these conditions is present, the module bypasses the computation of an EFP 
interval and waits until the next 30 second scheduled execution interval. 
If COLSS is in service and there is no current Reactor Power Cutback 
condition, the present value of plant reactor power is read at box 202. 
Then, via box 203, this is divided (normalized) by the sampling interval 
for this variable (1/120 hour which corresponds to the 30 second scheduled 
program execution rate) and then summed with variable "Phr" which is used 
to accumulate the 30 second `normalized` values of plant reactor power 
("Phr" is set to zero as an initiation task upon program bootup and is 
reset to zero after each 1 EFP-hour period is calculated, by box 218). 
Boxes 204 to 206 next determine if the accumulated value of "Phr" is equal 
to or greater than a 1 EFP-hour interval and if true sets variable STOP to 
1, or if not true sets variable STOP to 0. Then boxes 207 to 211 determine 
if the positions of each of the Regulating Groups and Part Strength groups 
(a total of `Kreg` such positions which are contained in array 
"Pgroup(k)") lie between the Long Term Steady State Insertion Limit (L1) 
and the Transient Insertion Limit (L2). For such groups, box 212 then 
updates the corresponding EFP exposure by accumulating the current EFP 
normalized value for this interval in array "Pnew(k)" (Array "Pnew(k)" is 
set to zero as an initiation task upon program bootup and is reset to zero 
after each 1 EFP-hour period is calculated, by box 218). Box 213 next 
determines if a 1 EFP-hour interval has occurred (this occurs when 
STOP=1). If this is true, box 214 performs a call to the CEA EXPOSURE 
ACCUMULATION HISTORY MODULE to update the CEA exposure history, box 215 
performs a call to the CEA EXPOSURE CALCULATION MODULE to update the 
current value of CEA exposure, box 216 performs a call to the SCALING 
MODULE to scale the graphical outputs to fit within the pixel constraints 
of the CRT screen, box 217 performs a call to the DRAWING MODULE to draw 
the graphical display on the CRT, and then box 218 resets variable "Phr" 
and the elements of array "Pnew(k)" to zero for use during the next 1 
EFP-hour interval calculation. The program then terminates. If box 213 
determines that 1 a EFP-hour period has not yet occurred, then the 
calculation for this 30 second period terminates. In either case, after 
the program terminates the PROGRAM EXECUTIVE schedules this module for 
execution again during the next periodically scheduled 30 second interval 
(box 219). 
FIG. 5 depicts the functional logic for the CEA EXPOSURE ACCUMULATION 
HISTORY MODULE. This module is called by the EFP CALCULATION MODULE if 
condition STOP=1 is true. This modules updates the CEA exposure for the 
CEA Exposure Data Arrays. When called, this module shifts up by one 
position each element in the CEA Exposure Array (for each of the Program 
arrays). Thus, the latest CEA exposure which occurred during the previous 
1 EFP-hour interval is moved into the first array position, the CEA 
exposure from the first array position is moved into the second array 
position, etc. until all CEA exposure data has been shifted up 1 EFP-hour 
interval in the array. The value of CEA exposure from the last array 
element "N" (which represents the oldest CEA exposure data) is removed 
from the array since it is now beyond the LCO EFP duration criteria. This 
value is stored in the archival records file (where it can be accessed as 
historical data in conjunction with the HISTORICAL DATA PLAYBACK MODULE 
which is discussed further below). 
This process of shifting the contents of each array element up by one 
position is illustrated in FIG. 6. It is this process whereby a 
"contiguous monitoring interval" is maintained. For simplicity, the logic 
for the CEA EXPOSURE ACCUMULATION HISTORY MODULE is illustrated for the 
case of a single program array (Each of the program arrays, which 
correspond to the CEA Exposure criteria for each of the Regulating and 
Part Strength Groups, is similarly operated upon). 
Referring again to FIG. 5, box 250 first stores the oldest value of "Pn" 
(from array element N) to the CEA exposure archival file which is 
contained on disk. The value of "Pn" is saved along with a time stamp that 
notes the year, date and time that the point was recorded. Box 251 then 
obtains the CEA Exposure Accumulation History file from the digital 
computer disk (item 62 on FIG. 1). Boxes 252 to 255 then shift up the 
contents of the data array elements, beginning from the last array 
position (that is, first the contents of array element "N-1" is shifted 
into array position "N", then the contents of array element "N-2" is 
shifted into array position "N-1", etc.) until array element 1 (the last 
shift performed by boxes 252 to 255 is from array position 1 to array 
position 2). After the contents of array position 1 is shifted into 
position 2, box 256 inserts the value of "Pnew" (the most recent 
calculated value of CEA Exposure as determined via the EFP Calculation 
Module) into array position 1. A time stamp is also saved which notes the 
year, date and hour in which the value of Pnew was determined (this time 
stamp is utilized when recalling archived historical CEA exposure 
records). Box 257 then saves the updated CEA Exposure History file to disk 
storage (via the digital computer disk, item 62 on FIG. 1). The process is 
repeated until all program arrays are similarly operated upon. 
For increased computational efficiency, the actual computer implementation 
of the above process may utilize "circular data storage buffers" for the 
CEA Exposure Arrays. The shift of positions would then occur by 
overwriting the oldest CEA exposure value with the newest value and then 
incrementing software "pointers" which indicate the array starting 
position (array element=1) and the array ending position (array element=N) 
within the circular data storage buffer. Thus, the shifting up of the each 
array element by one position is accomplished with a minimum set of 
software steps which reduces the computational impact on computer 
processing resources. The actual logic which would be utilized with 
circular data storage buffers is dependent upon the chosen 
hardware/software and is therefore not depicted here. 
FIG. 7 depicts the functional logic for the CEA EXPOSURE CALCULATION 
MODULE. This module is called by the EFP CALCULATION MODULE if condition 
STOP=1 is true. This module updates the CEA exposure for each of the CEA 
Exposure Data Arrays. For simplicity, the logic for this module is 
illustrated for the case of a single program array--however, all such 
aforementioned data arrays are similarly processed. Boxes 300 to 304 
calculate the current value of CEA exposure by summing the contents of the 
CEA Exposure Data Array ("P(I)") in which each array element contains the 
value of CEA exposure for a given 1 EFP-hour interval. The total 
accumulated CEA exposure is then stored in variable "EXPOSURE" via box 
305. The module then determines the CEA exposure margin ("MARGIN") in box 
306 by calculating the difference between the Exposure Limit (such as 5 
EFP days) which is stored in variable "LIMIT" and the current value of CEA 
exposure which is stored in variable "EXPOSURE". Boxes 307 to 309 next 
determine if there is positive margin (MARGIN&gt;0) or negative margin 
(MARGIN&lt;0). If the CEA exposure margin is negative (MARGIN&lt;0) then the 
Alarm Flag is set to one (1) and an alarm is annunciated, alerting the 
operator that a CEA exposure technical specification has been violated. If 
the CEA exposure margin is positive (MARGIN&gt;0) then the "Alarm Flag" is 
set to zero and the CEA exposure margin is further tested by boxes 310 to 
312 to determine if the remaining CEA exposure margin ("MARGIN") is less 
than the pre violation warning limit ("Lwarn"). If the remaining CEA 
exposure margin ("MARGIN") is less than the pre violation limit 
(MARGIN&lt;Lwarn), then "Warning Margin Flag" is set to one (1) and a "pre 
violation CEA exposure" alarm is annunciated, alerting the operator that 
he is approaching the CEA exposure LCO. If the remaining CEA exposure 
margin ("MARGIN") is greater than the pre violation limit (MARGIN&gt;Lwarn), 
then "Warning Margin Flag" is set to zero (0) and no alarm annunciation 
occurs. 
The logic for the SCALING MODULE is provided in FIG. 8. For simplicity, the 
logic for this module is illustrated for the case of a single program 
array--however, all data arrays associated with the CEA Rod Position 
System are similarly processed. This module is called by the EFP 
CALCULATION MODULE if condition STOP=1 is true. The SCALING MODULE 
performs a scaling of the CEA Exposure Accumulation Array Elements so that 
they may be pictorially represented on the CRT (item 66 on FIG. 1) in 
"rolling wheel" or "sliding bar" formats. The scaling is necessary in 
order to accommodate the CEA exposure accumulation array information 
within the pixel constraints imposed by the CRT. The SCALING MODULE 
examines an interval of CEA exposure accumulation data (such as every 4 
consecutive EFP-hourly periods) as stored in the CEA Exposure Accumulation 
Array Elements (4 consecutive array elements) and determines if any of the 
array elements within that interval indicate that a CEA exposure 
accumulation has occurred. If there is any CEA exposure accumulation for 
the examined interval, the SCALING MODULE then updates a corresponding 
array (CEA Scaling Array) which is used to drive the output graphics on 
the CRT. The CEA Scaling Array consists of elements that correspond to 
each examined interval (such as 4 consecutive EFP-hourly periods) from the 
CEA Exposure Accumulation Array Elements (that is, 4 consecutive array 
elements from the CEA Exposure Accumulation Array are mapped into a single 
array element in the CEA Scaling Array). For cases in which there has been 
CEA exposure during the examined interval, the SCALING MODULE updates the 
corresponding array element in the CEA Scaling Array with a one (1), 
elsewise with a zero (0). The CEA Scaling Array is subsequently utilized 
by the drawing module to draw either a solid or blank picture segment 
(depending on the store value in the CEA Scaling Array element--either "1" 
or "0") for the "rolling wheel" or "sliding bar" output display formats. 
FIG. 9 illustrates the correspondence between the CEA Exposure Accumulation 
Array and the CEA Scaling Array. 
With reference to FIG. 8, boxes 325 and 326 initialize the computation 
elements for this module. Variable "Z" is set to "N/4" where "N" 
corresponds to the number of elements in the CEA Exposure Accumulation 
Array. In this particular case, the SCALING MODULE will scan intervals 
corresponding to 4 EFP-hours, which corresponds to four consecutive array 
elements in the CEA Exposure Accumulation Array. Boxes 327 and 328 are 
used to determine when all such 4 EFP-hour intervals in the CEA Exposure 
Accumulation Array have been examined (since there are "N" array elements 
in the CEA Exposure Accumulation Array, then there are Z=N/4 such 
intervals). Boxes 329 to 332 are used to examine four consecutive array 
elements in the CEA Exposure Accumulation Array (which corresponds to an 
interval of 4 EFP-hours). Box 332 determines if any of the four 
consecutive array elements in the CEA Exposure Accumulation Array contain 
any CEA exposure accumulation. It performs this determination by examining 
the contents of each array element for a non-zero value of CEA exposure 
accumulation (P(4*(J-1)+I)&gt;0). If any four consecutive array elements in 
the CEA Exposure Accumulation Array contain a non zero value, then the 
corresponding element S(J) of the CEA Scaling Array is updated with a one 
(1) via box 333, elsewise box 334 updates element S(J) with a zero (0). 
When box 328 determines that all of the elements of the CEA Exposure 
Accumulation Array have been examined it then resets variables "J" and "I" 
via boxes 336 and 337 and sets variable "Kend" to the value of variable 
"J" via box 335. Variable "Kend" is subsequently used by the DRAWING 
MODULE. This process of assigning values to array S(J) based on examining 
the contents of four consecutive elements of array P(N) is illustrated in 
FIG. 9. 
Since the CRT has limited pixel resolution relative to the data which is 
stored in the CEA Exposure Accumulation Array (in this case CEA exposure 
will be displayed with a granularity of 4 EFP hour intervals), the 
pictorial displays will have greater "granularity" than the numeric data 
which is output on the display pages. However, the resolution is still 
considered sufficient to indicate, pictorially, the relative periods in 
which CEA exposure accumulation occurred. The numeric data, as output via 
the normal displays, will always contain the exact values of CEA exposure 
and the PREDICTOR MODULE will always output when CEA exposure margin will 
be regained; with a time resolution to the nearest hour. 
The logic for the DRAWING MODULE is provided in FIG. 10. For simplicity, 
the logic for this module is illustrated for the case of a single program 
array--however, all data arrays associated with the CEA Rod Position 
System are similarly processed. This module is called by the EFP 
CALCULATION MODULE if condition STOP=1 is true. The DRAWING MODULE 
provides the graphical outputs for the "rolling wheel" and "sliding bar" 
display formats. The module functions are described in generalized 
functional terms as the actual draw commands are dependent upon the 
specific graphics drawing package which is utilized. Referring to FIG. 10, 
box 350 determines the requested display format (either "rolling wheel" or 
"sliding bar" dependent upon the last drawing format selection as made by 
the operator). Box 351 queue's the corresponding drawing templet (either 
"rolling wheel" or "sliding bar" display format). Boxes 352 to 354 then 
keeps track of the number of segments to draw from the CEA Scaling Array 
(S(J)). This array ranges from array element number 1 (S(1)) to array 
element number "Kend" (S(Kend)) where "Kend" is calculated via box 335 in 
FIG. 8. Box 355 determines the contents of each array element for the CEA 
Scaling Array (S(J)). If the value of a CEA Scaling Array element is equal 
to 1 (S(J)=1) then the corresponding segment in the drawing templet is set 
to 1 via box 357 (which specifies that a solid arc segment for a "rolling 
wheel" display format or a solid rectangular segment for a "sliding bar" 
display format is to be drawn). If the value of a CEA Scaling Array 
element is not equal to 1 (i.e. S(J)=0) then the corresponding segment in 
the drawing templet is set to 0 via box 356 (which specifies that a null 
arc segment for a "rolling wheel" display format or a null rectangular 
segment for a "sliding bar" display format is to be drawn). The selected 
drawing segment is then drawn on the CRT (item 66 on FIG. 1) via box 358. 
Box 359 reinitializes counting variable "J" to zero (0) after all "Kend" 
segments have been drawn as determined by box 354. 
The graphical displays provide the user with an easily understood 
representation of the accumulated time and accumulated EFPD exposure for 
CEA rod groups relative to the LCO's. The display formats are designed to 
present the data in terms of a contiguous monitoring interval using a 
spatial representation. 
FIG. 21 illustrates the format of the "Rolling Wheel" display. In this 
embodiment, two Part Strength CEA groups are assumed and a LCO limitation 
of no more than 5 EFPD exposure per 30 EFPD interval is specified (where 
exposure is defined as a Part Strength group being inserted between the 
Long Term Steady State Insertion Limit and the Transient Insertion Limit). 
The 30 EFPD interval is defined to be a contiguous 30 EFPD period. The 
contiguous 30 EFPD interval is depicted by rotating wheels; one for each 
Part Strength group. Each wheel rotates in a counterclockwise direction. A 
full rotation of a wheel (360 degrees) corresponds to the 30 EFPD 
contiguous monitoring interval. Shaded pie segments within a wheel 
represent the EFPD exposure for the Part Strength group whenever it was 
inserted between the Long Term Steady State Insertion Limit and the 
Transient Insertion Limit. As EFPD is accumulated, old exposure data is 
continuously discarded (rolls off the "Rolling Wheel"), while new data is 
continuously added (rolls on to the "Rolling Wheel"). Thus, the exposure 
of the Part Strength rod groups is maintained for a contiguous monitoring 
interval (window) using a spatial representation. 
FIG. 22 illustrates the format of the "Sliding Bar" display. As with FIG. 
21, two Part Strength CEA groups are assumed and a LCO limitation of no 
more than 5 EFPD exposure per 30 EFPD interval is specified (where 
exposure is defined as a Part Strength group being inserted between the 
Long Term Steady State Insertion Limit and the Transient Insertion Limit). 
The 30 EFPD interval is defined to be a contiguous 30 EFPD period. 
The contiguous 30 EFPD interval is depicted by a linear line. The length of 
the line represents the contiguous 30 EFPD interval. There are two such 
linear lines, one for each Part Strength group. "Bars", which are located 
above each line, represent the EFPD exposure for the Part Strength group 
whenever it was inserted between the Long Term Steady State Insertion 
Limit and the Transient Insertion Limit. The "Bars" slide along the line, 
moving from right to left. A full translation of the line by a "Bar" 
corresponds to a "Bar" fully transitioning the 30 EFPD contiguous 
monitoring interval. As EFPD is accumulated, old exposure data is 
continuously discarded ("Bars" or portions thereof slide off the line), 
while new data is continuously added ("Bars" or portions thereof slide on 
to the line). Thus, the exposure of the Part Strength rod groups is 
maintained for a contiguous monitoring interval (window) using a spatial 
representation. 
The Sector feature which is associated with the graphical displays (FIGS. 
21 and 22) allows users to define "sectors" within the "Rolling Wheel" and 
"Sliding Bar" displays to be expanded and thus examined at higher 
resolutions. After the user enters the desired sector region to be 
expanded, the scales on the "Rolling Wheels" or "Sliding Bars" are 
rescaled to the range as entered by the user and the accumulate exposure 
data is displayed with proportionally greater resolution. 
The Query Mode (selected per FIGS. 21 and 22) allows the user to: (1) 
recall historic information and (2) to determine when a certain level of 
accumulated exposure (in terms of hours and/or EFPD) will "roll off/slide 
off" and be regained as usable margin (by having the user enter the future 
planned "power-time" profile for the plant). 
The Summary Display Mode (FIG. 23) provides an overall assessment of the 
current accumulated exposure and remaining margin for all Regulating and 
Part Strength rod groups utilizing a single convenient display page. 
Alarming capability (where is this depicted?) is provided to alert the user 
of an approach to an alarm condition (LCO), so that action may be taken 
prior to actually exceeding the alarm setpoint. In the event that the 
alarm setpoint is exceeded, an alarm annunciation alerts the user and 
provides a display (countdown clock) of the remaining time to take the 
prescribed corrective action relative to the required Completion Time as 
specified within the Technical Specifications for operation. In cases for 
which several corrective actions with differing Completion Time lines are 
specified, a count down clock representation for each corrective action is 
displayed. 
FIG. 11 depicts the functional logic for the HISTORIC DATA PLAYBACK MODULE. 
This module is activated whenever an operator selects the "Historic Data 
Option" function key on the keyboard (item 64 on FIG. 1) that is 
associated with the digital computer (item 54 on FIG. 1). The HISTORIC 
DATA PLAYBACK MODULE recalls previously archived CEA exposure historical 
data for playback and allows the operator to review CEA exposures from 
previous time intervals. The playback is for one day periods (as 
determined by the time stamp which is associated with each saved CEA 
exposure value). Box 300 prompts the operator to enter the "Start Time" 
point for the historic data and places the requested year and day for the 
playback into variables "YEAR" and "DAY". Box 301 determines if the "Start 
Time" requested by the operator is valid and within range of the existing 
historic data records (Limit D2 is either 364 days or 365 days dependent 
if "YEAR" corresponds to a "leap year" or not, or it is the current day if 
"YEAR" is equal to the current year. Limit D1 is either 1 if "YEAR" is 
greater than the first year of recorded archived records or it is equal to 
the first day in which the archived record exits if "YEAR" is equal to the 
earliest year of recorded archived records. Limit Y1 corresponds to the 
earliest year of recorded archived records and limit Y2 corresponds to the 
current year.). If an invalid time request is entered, box 302 rejects the 
request and displays an error message to the operator on the CRT (item 66 
on FIG. 1). If the operator request is for a valid "Start Time", box 303 
then recalls the historic archived CEA exposure record file (via the 
digital computer disk, item 62 on FIG. 1) based on the "YEAR" and "DAY" 
values. The program will use the first array element it encounters that 
begins on the requested day. Array elements are time stamped with the 
hour, day and year that they were recorded. The selected historic data is 
then formatted in a tabular format via box 304 and is output on the CRT 
(item 66 on FIG. 1). 
The playback of historic data is terminated when the operator selects a 
"Return to Real Time Data" option. This option is only displayed on the 
CRT when a Historic Data Playback is active. The "Return to Real Time 
Data" option is activated via a function key on the computer keyboard 
(item 64 on FIG. 1). 
The Predictor Mode (selected per FIGS. 21 and 22) allows the effect of a 
planned CEA Rod Group maneuver (for accumulated hours and/or EFPD 
exposure) to be assessed in advance of performing the actual maneuver. The 
user enters the planned Rod Group maneuver ("position-time" profile for 
the rod groups) and the anticipated plant "power-time" profile. The system 
then determines if there is sufficient margin (hours or EFPD exposure) to 
perform the maneuver based on the current exposure data and the 
information as entered by the user. If insufficient time (hours) or EFPD 
margin is available, the Predictor Mode projects when suitable margin will 
be regained to allow the maneuver to occur while maintaining compliance 
with the LCO's. 
An overview of the logic for the PREDICTOR MODULE is provided in FIG. 12. 
This module is called by the PROGRAM EXECUTIVE whenever a request is made 
for the Predictor Mode of operation. Requests are made via a function key 
on the digital computer keyboard, item 64 on FIG. 1. The PREDICTOR MODULE 
predicts if sufficient CEA exposure margin currently exists to perform a 
planned CEA maneuver. If insufficient margin exits, the PREDICTOR MODULE 
predicts when sufficient CEA exposure margin will be regained to perform 
the planned CEA maneuver. Referring to FIG. 12, an estimate of the CEA 
exposure for the planned CEA maneuver is entered by the operator, a 
determination is then made if sufficient CEA exposure margin currently 
exists to perform the planned CEA maneuver. If sufficient CEA exposure 
margin currently exists, a message is output to the operator indicating 
that sufficient margin exists to perform the planned maneuver. If 
insufficient CEA exposure margin currently exists, then the program 
predicts when sufficient margin will be regained to perform the planned 
maneuver. 
FIG. 13 depicts the basic logic for the PREDICTOR MODULE. In box 400, the 
value of the estimated value of CEA exposure for the planned maneuver is 
entered by the operator and stored in variable "Delta.sub.-- Margin". Box 
401 next obtains the current value of CEA exposure ("EXPOSURE") as last 
computed by the CEA EXPOSURE CALCULATION MODULE (box 305 of FIG. 7) which 
is stored in the data base. Box 402 then determines the total required CEA 
exposure which would occur if the planned CEA maneuver is performed at the 
current point in time ("Required.sub.-- Margin"). This total required CEA 
exposure margin is the sum of the current CEA exposure ("EXPOSURE") and 
the estimated CEA exposure to perform the planned maneuver ("Delta.sub.-- 
Margin"). Next, box 403 determines if there is sufficient margin to 
perform the planned CEA maneuver by comparing variable "Required.sub.-- 
Margin" to the LCO ("LIMIT"). The LCO limit is stored in the data base of 
the digital computer (item 60 of FIG. 1). If there is presently sufficient 
total CEA exposure margin to perform the planned maneuver then box 405 
outputs a message to the operator on the CRT indicating that sufficient 
margin exists to perform the planned maneuver. If insufficient total CEA 
exposure margin currently exists, then box 404 predicts when sufficient 
margin will be regained to perform the planned maneuver by executing the 
MARGIN PREDICTION MODULE which is illustrated in FIG. 14. 
With reference to FIG. 14 (MARGIN PREDICTION MODULE), box 420 first maps 
the Accumulated CEA Exposure data, stored in the CEA Exposure Data Array 
(array "P(J)") into a second array (array "PP(J)") which is then further 
utilized in the MARGIN PREDICTION MODULE to predict when CEA exposure 
margin will be regained. For simplicity, the logic is illustrated for the 
case of a single program array--however, all requisite data arrays 
associated with the CEA Rod Position System are similarly processed. Array 
"PP(J)" is used to avoid altering data in array "P(J)" while performing 
the prediction computations. 
The logic for the Array Mapping is now explained. After this logic is 
described, an explanation of the MARGIN PREDICTION MODULE, FIG. 14, will 
resume. The Array Mapping is illustrated in FIG. 15 (ARRAY MAPPING 
MODULE). Box 450 initiates the logic by setting the counting variable "J" 
to zero. Boxes 451 and 452 determine when all the array elements from 
array "P(J)" have been mapped into array "PP(J)". The completion of the 
array mapping occurs when counting variable "J" is greater than the 
highest numbered array element in the CEA Exposure Data Array (array 
element number "N"). Box 453 performs the mapping by setting the value of 
array element "PP(J)" to the value of array element "P(J)". When all the 
array elements from array "P(J)" have been mapped into array "PP(J)" then 
box 454 resets counting variable "J" to zero. 
Returning to the MARGIN PREDICTION MODULE of FIG. 14, after the array 
mapping, then box 421 determines the maximum allowable accumulated CEA 
exposure which would still allow the planned CEA maneuver to occur by 
computing the difference between the LCO margin limit ("LIMIT") and the 
CEA exposure required to perform the planned CEA maneuver ("Delta.sub.-- 
Margin"). This value is stored in variable ("Max.sub.-- Exposure") and 
represents the amount of accumulated CEA exposure that can exist prior to 
beginning the planned CEA maneuver (values of CEA exposure which are 
larger than this amount will result in insufficient CEA exposure margin to 
perform the planned maneuver; i.e.--the sum of the CEA exposure required 
to perform the maneuver and the current value of CEA exposure is such that 
they collectively exceed the LCO as specified in variable "LIMIT"). Boxes 
422 to 426 then continually update array "PP(J)" until sufficient CEA 
exposure margin is lost (as determined via variable "New.sub.-- 
Exposure"). This is determined as follows: a value of zero is inserting 
into position "PP(1)" (which represents the most recent 1 EFP-hour 
interval); each element of array "PP(J)" is then upward shifted by one 
position; and finally the value of the last array element "PP(N)" is 
deleted. This process simulates plant operation with all CEA rods above 
the Steady State and Transient Insertion Limits (for this condition, no 
CEA exposure accumulation occurs). Box 422 initializes the counting 
variable to zero while box 423 accumulates the number of simulated 1 
EFP-hour intervals with zero CEA exposure accumulation (this is equivalent 
to the number of program passes for the "Margin Prediction Calculation"). 
For each program pass, box 424 (UPDATE CEA EXPOSURE FOR ARRAY PP MODULE) 
updates the CEA exposure for array "PP" (zero CEA exposure for the most 
recent simulated 1 EFP-hour interval) and box 425 (NEW.sub.-- MARGIN 
CALCULATION MODULE) calculates the corresponding new value of accumulated 
CEA exposure (which is stored in variable "New.sub.-- Exposure"). Program 
passes are continually made (each pass representing 1 EFP-hour interval 
with no CEA exposure accumulation) until sufficient old margin "rolls off" 
and the remaining accumulated CEA exposure ("New.sub.-- Exposure") is 
sufficiently reduced to allow the planned maneuver, as determined by box 
426. 
The logic for the UPDATE CEA EXPOSURE FOR ARRAY PP MODULE is now explained. 
After this logic is described, explanation of the MARGIN PREDICTION 
MODULE, FIG. 14, will resume. The UPDATE CEA EXPOSURE FOR ARRAY PP MODULE 
is illustrated in FIG. 16. When called, this module updates (shifts up by 
one position) each element of array "PP(J)" and inserts a value of zero 
into the first array position ("PP(1)"). Thus, the first position of the 
array "PP(1)" is updated with a value of zero, the second array position 
is updated with the value from the first array position, etc. until all 
CEA exposure data has been shifted up 1 EFP-hour interval in the array. 
The last array element "N" (which represents the oldest CEA exposure data) 
is discarded since it is now beyond the LCO EFP duration criteria. This 
shifting of elements of array "PP(J)" represents a 1 EFP-hour interval of 
operation with zero CEA exposure accumulation. 
Box 460 first initializes the counting variable. Boxes 461 to 463 shift up 
the data array elements, beginning from the last array position (that is, 
first array element "N-1" is shifted into array position "N", then array 
element "N-2" is shifted into array position "N-1", etc.) until array 
element 1 (the last shift performed by boxes 461 to 463 is from array 
position 1 to array position 2). After array position 1 is shifted into 
position 2, box 464 inserts a value of zero (0) into array position 
"PP(1)". This shifting which occurs during a single program pass 
represents 1 EFP-hour interval of operation with zero (0) CEA exposure 
accumulation. 
Returning now to the MARGIN PREDICTION MODULE of FIG. 14, after execution 
of the UPDATE CEA EXPOSURE FOR ARRAY PP MODULE is completed, then box 425 
determines the new value of CEA exposure for array "PP(J)" which is 
calculated by the NEW.sub.-- MARGIN CALCULATION MODULE. 
The logic for the NEW.sub.-- MARGIN CALCULATION MODULE is now explained. 
After this logic is described, explanation of the MARGIN PREDICTION 
MODULE, FIG. 14, will resume. The NEW.sub.-- MARGIN CALCULATION MODULE is 
illustrated in FIG. 17. This module determines the value of CEA exposure 
for array "PP(J)". This module is called by the MARGIN PREDICTION MODULE 
immediately after the elements of array "PP(J)" have been shifted up by 
one position (equivalent to a 1 EFP-hour interval with no CEA exposure 
accumulation). Referring to FIG. 17, boxes 480 to 485 calculate the 
current value of CEA exposure in array "PP(J)" by summing the contents of 
each array element. The contents of each array element contains the value 
of CEA exposure for a given 1 EFP-hour interval. The total accumulated CEA 
exposure is then stored in variable "SUM" via box 484 after all "N" array 
elements are added (as determined via box 483). The module then sets 
variable "New.sub.-- Exposure" to variable "SUM" in box 485. 
Returning to the MARGIN PREDICTION MODULE of FIG. 14, after the value of 
"New.sub.-- Exposure" is determined, box 426 then determines if the value 
of "New.sub.-- Exposure" is greater than the value of "Max.sub.-- 
Exposure". If true, then insufficient CEA exposure margin has yet to "roll 
off" (the present CEA exposure accumulation as stored in variable 
"New.sub.-- Exposure" is such that there is insufficient available margin 
to accommodate the "Delta.sub.-- Margin" and remain within the LCO as 
defined in variable "LIMIT") and the module then begins another program 
pass (equivalent to another 1 EFP-hour interval with zero CEA exposure) by 
returning to box 423. When sufficient CEA exposure margin has "rolled off" 
(false condition for box 426) then the total number of EFP intervals to 
achieve the reduction (as contained in counting variable "I") is then 
stored in variable "INTERVALS" via box 427. Variable "INTERVALS" therefore 
represents the number of hours in which sufficient CEA exposure margin 
will be regained to perform the planned maneuver, assuming the plant 
operates at a power rating of 100% EFP. Boxes 428 to 430 convert 
"INTERVALS" into equivalent time in terms of "days" and "hours" and box 
431 translates this time interval into calendar time. Box 432 displays the 
predicted time (at a power condition of 100% EFP) when sufficient CEA 
exposure margin will be regained to perform the planned CEA maneuver. An 
example of the displayed output would be as follows: "Sufficient Margin 
will exist after "DD" days and "HH" hours of operating at a power level of 
100% EFP which corresponds to "DAY, MONTH, YEAR and TIME". If operating at 
less than 100% EFP, then the time period will be proportional to the value 
of EFP relative to 100% EFP e.g., (100% EFP)/(actual EFP)". Finally, box 
433 resets the counting variable to zero. 
In the event of a system outage, the Update Mode allows the system to be 
recalibrated to the current operational conditions. After the system is 
brought on-line, the user enters the appropriate plant "time-power" 
profile and the rod group exposure profile for the outage interval. Based 
on this information and the rod exposure information stored up to the time 
of the outage, the system is recalibrated to the current operational 
conditions and restored to operational service. 
FIG. 18 depicts the basic logic for the UPDATE MODULE. This module is 
called by the PROGRAM EXECUTIVE whenever there is a computer restart or 
whenever requested by the operator via a function key on the keyboard 
(item 64 on FIG. 1) associated with the digital computer. Box 500 first 
requests that the operator confirm that an Update is to be performed. If 
the operator enters a "yes" to this prompt (using the keyboard) then, via 
box 501, the operator is prompted to enter the CEA exposure history for 
the outage period. The operator enters this information using the keyboard 
in conjunction with an update data templet which appears on the CRT screen 
(item 66 in FIG. 1). For each hourly EFP interval which occurred during 
the outage, the operator determines if there was any CEA exposure for that 
interval. For hourly EFP intervals in which there was no CEA exposure, the 
operator enters zero. For hourly EFP intervals in which there was CEA 
exposure, the operator enters the value of the CEA exposure which 
occurred. If the rods were inserted for the full time during a given 
hourly EFP interval then the CEA exposure corresponds to 1 EFP-hour; if 
they were inserted for only a portion of the hourly EFP interval, then the 
CEA exposure would correspond to a fraction of 1 EFP-hour. The operator 
enters this information for each affected CEA rod group. If a CEA rod 
group was not inserted during the outage interval, the operator enters a 
"not inserted" command and the computer sets the CEA exposure for all the 
hourly EFP intervals to zero for that CEA rod group. This allows a quick 
update for such cases so the operator need not manually insert a zero for 
each 1 EFP-hour interval. The operator estimates the EFP information based 
on written logs of plant power and rod positions for the outage period. 
Upon completion of the operator entry of the CEA exposure history for the 
outage period, variable "KNUMBER" stores the value of the total number of 
hourly EFP intervals which occurred during the outage period and array 
"E(J)" stores the value of CEA exposure (as entered by the operator) for 
each of the hourly EFP intervals which occurred during the outage. Boxes 
502 to 505 then shift the elements of array "P(J)" up by one position and 
inserts a value of "E(m)" for into the first array element, thus updating 
the CEA exposure history for a 1 EFP-hour interval. Box 504 determines 
when the shift has been completed (when condition "m&gt;KNUMBER" is true). 
The logic for box 505 is now explained. After this logic is described, 
explanation of the UPDATE MODULE, FIG. 18, will resume. The HOURLY EFP 
INTERVAL UPDATE MODULE is illustrated in FIG. 19. When called, this module 
updates (shifts up by one position) each element of array "P(J)" and 
inserts the CEA exposure value as entered into "E(m)" into the first array 
position ("P(1)"). Thus, the first position of the array "P(1)" is updated 
with the value of CEA exposure as was entered by the operator into "E(m)" 
for this EFP hourly interval, the second array position is updated with 
the value from the first array position, etc. until all CEA exposure data 
has been shifted up 1 EFP-hourly interval in the array. The last array 
element "N" (which represents the oldest CEA exposure data) is discarded. 
This shifting of elements of array "P(J)" up by one position represents a 
1 EFP hourly update interval. 
Referring again to FIG. 19, box 520 first initializes the counting 
variable. Boxes 521 to 523 shift up the data array elements, beginning 
from the last array position (that is, first array element "N-1" is 
shifted into array position "N", then array element "N-2" is shifted into 
array position "N-1", etc.) until array element 1 (the last shift 
performed by boxes 521 to 523 is from array position 1 to array position 
2). After array position 1 is shifted into position 2, box 524 inserts the 
value of CEA exposure as was entered by the operator into "E(m)" for this 
EFP hourly interval. Thus array "P(J)" is updated for a 1 EFP hourly 
period. 
With further reference to the UPDATE MODULE of FIG. 18; after the elements 
of array "P(J)" have been updated for 1 EFP hourly interval, then boxes 
503 and 504 determine when the array has been updated for all of the EFP 
hourly periods which occurred during the outage. This occurs when box 504 
determines that the condition "m&gt;KNUMBER" is true. Box 506 then resets the 
counting variable to zero. 
From the foregoing, it can be appreciated that the invention has been 
described in the context of a nuclear power plant having a nuclear reactor 
core and a multiplicity of control rods arranged for movement through the 
core for controlling the reactor power. This multiplicity of rods includes 
a plurality of groups of control rods, the groups being movable through 
the core in staggered sequence. Each group is subject to an administrative 
limit on the cumulative exposure in the core while each group is situated 
within a pre-established position range in the core. 
Independent of any symbology utilized in connection with FIGS. 1-20 and 
associated description hereinabove, one administrative limit can be 
expressed in the form of a limit index W:X defined by a maximum of W hours 
of accumulated effective exposure on the sum S of effective exposure 
occurrences w.sub.1,w.sub.2 . . . during any X hour reference period, with 
W&lt;X. Increments in the associated time base, are one hour each. Another 
form of the administrative limit can be expressed as a limit index Y:Z 
defined by a maximum of Y effective full power hours of exposure 
consisting of the sum of effective exposure occurrences y.sub.1,y.sub.2 . 
. . during any Z hour reference period of effective full power operation 
of the core, with Y&lt;Z. Increments in the associated time base, are one 
effective full power hour each. Yet another administrative limit can be 
the maximum permitted time interval T during which a group can be 
positioned between, e.g., the Short Term Steady State Insertion Limit and 
the maximum insertion position which is permitted during a normal 
operational transit. 
The invention also includes a novel form of displaying the comparison of 
the accumulated effective exposure for each group with the administrative 
limit for each group as shown in FIGS. 21-23. In terms of the symbology 
described immediately above, the display 600,600' of FIGS. 21 and 22 
includes at least one scale 601,601' of Z uniform intervals 602,602', 
marked by a plurality of numeric values 603,603' indicative of an initial 
zero value 604,604' and a final value Z 605,605'. An indicator 
configuration 606,606' for each group is displayed, each indicator 
configuration having a scale associated therewith, and consisting of an 
indicator 607,607' for each component y of the sum S. Each indicator 
initially appears at the zero representation of the scale and grows in 
size toward the scale value Z to span the number of scale intervals 
corresponding to the ratio of effective exposure of component y to the 
effective power interval Z. Independently of but simultaneously with the 
indicator growth, each indicator along the scale advances toward the scale 
value Z, at a uniform rate. The sum S of all components y during the 
immediately preceding interval is displayed 608,608' adjacent to the scale 
Z. Instantaneous margin M=Y-S, can also be displayed 609,609'. Thus at any 
given moment, the operator can visually recognize the number of and 
effective exposure for each component y during the immediately preceding 
core effective full power interval Z; the total exposure of S during the 
immediately preceding interval of Z; and the margin M. 
In one embodiment, as shown in FIG. 21, a respective scale 601 is displayed 
for each group. Each scale is displayed as a circle with coincident zero 
and Z values. Each indicator 607 of a component y is displayed as a sector 
of the circle, which grows by increasing the included angle of the sector 
and which advances by continually rotating about the center of the circle 
toward the value Z. Another display embodiment is shown in FIG. 22. One 
scale 601' is displayed as a linear segment with the zero value 604' at 
one end and the Z value 605' at the other end. The indicator configuration 
606',606" for each of at least two groups is associated with the one 
scale. Each indicator 607' of a component y is displayed as a horizontal 
bar, which grows by increasing in horizontal length, and which advances by 
continually moving horizontally toward the value Z. Similar displays can 
be presented for monitoring a limit expressed by W:X. FIG. 23 shows a 
summary report in a tabular form.