PWR Boron Dilution & Reactivity Insertion Calculator

Determine primary system boron concentration drop over time, reactivity insertion rate (pcm/min), and time to critical threshold.

RCS Volume & Chemical Shim Parameters

Initial Boron Concentration C_0 (ppm):

Critical Boron Concentration C_crit (ppm): Estimated Critical Position (ECP)

RCS Active Water Volume V_rcs (gal): Typically 70,000 to 90,000 gal in 4-loop PWR

Unborated Makeup Water Flow Q_in (gpm):

Differential Boron Worth DBW (pcm/ppm): Typically -7.0 to -10.0 pcm/ppm

Elapsed Dilution Time t (minutes):

Reactivity Insertion & Criticality Horizon

Current Boron Concentration:

—

Total Positive Reactivity Inserted:

—

Reactivity Insertion Rate:

—

Make-up Water Volume Added:

—

Time to Reach Criticality:

—

Criticality Margin Status:

—

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Chemical Shim Soluble Boron Dilution Mechanics

Pressurized water reactors utilize boric acid ($H_3BO_3$) dissolved in primary coolant as a chemical shim to control slow core reactivity variations such as fuel burnup and xenon poisoning. Because boron-10 ($^{10}B$) has an immense thermal neutron absorption cross-section ($sim 3840\text{ barns}$), injecting pure unborated demineralized water dilutes the boron concentration, introducing positive reactivity.

Inadvertent Dilution Event (10 CFR 50 / NUREG-0800)

An uncontrolled boron dilution event during shutdown or refueling could lead to premature criticality. Licensing bases evaluate the time available for control room operators to identify dilution alarms and isolate primary makeup water before the shutdown margin is completely eroded.

PWR Boron Dilution & Reactivity Insertion Calculator

RCS Volume & Chemical Shim Parameters

Reactivity Insertion & Criticality Horizon

Chemical Shim Soluble Boron Dilution Mechanics

Inadvertent Dilution Event (10 CFR 50 / NUREG-0800)

Frequently Asked Questions