How do you calculate spare part obsolescence risk?

Multiply the three scores together: criticality times supply availability risk times lead-time exposure. The example shown computes to a 6.55 risk score from inputs of 8, 6, and 5 on the configured scale.

What makes a spare part high obsolescence risk?

High criticality combined with a fragile single-source supply chain and long replacement lead times. Any one being high raises the score; all three high makes the part a top candidate for proactive action.

How is this different from an FMEA RPN?

It uses the same multiply-three-factors structure as an RPN but targets supply and obsolescence exposure rather than failure mode severity, occurrence, and detection.

What should I do with a high score?

Prioritize it for a last-time buy, alternate part qualification, commercial-grade dedication, or reverse-engineering before the original supplier exits, since lead time to qualify a replacement can be long.

What scoring scale should I use?

Any consistent scale works, commonly 1 to 10, as long as you apply the identical scale to every part. The ranking is only meaningful in relative terms across the catalog.

Can a low-criticality part still be high risk?

Its score will be capped by the low criticality factor, but a part that is cheap and uncritical yet impossible to source can still warrant attention if it gates a system. Always sanity-check the ranking against engineering judgment.

Nuclear & Critical Infrastructure Manufacturing calculator

Spare Part Obsolescence Risk Calculator

Spare part obsolescence risk is the priority score that tells a nuclear plant or critical-infrastructure operator which safety-related spares to qualify a replacement for before the original becomes unobtainable. This calculator multiplies three scores, how critical the component is, how exposed its supply chain is, and how punishing its lead time and stocking situation are, into a single ranking number, much like an RPN in FMEA. Obsolescence engineers, strategic sourcing leads, and reliability teams managing aging fleets use it to direct limited dedication and qualification budget at the parts most likely to leave them stranded. It matters because in nuclear, a single obsolete relay or valve with no qualified alternate can hold up an outage or force an unplanned shutdown.

What this calculator does

Score the obsolescence risk of spare parts for nuclear and critical infrastructure assets, so reliability and procurement teams can rank which parts need last-time buys, requalification, or stocking first.
Use it when ranking spare parts for obsolescence action and you need a defensible risk score that combines component criticality, supply availability, and lead-time exposure.
It multiplies component criticality, supply availability risk, and lead-time and stocking exposure into one obsolescence risk priority score for ranking spares.

Formula used

Obsolescence risk score = component criticality score × supply availability risk score × lead-time and stocking exposure score
Use the same scoring scale across all spare parts being ranked.

Inputs explained

Component criticality score:
Supply availability risk score:
Lead-time and stocking exposure score:

How to use the result

Use it when triaging a spares catalog to decide which parts get a proactive last-time-buy, alternate qualification, or commercial-grade dedication first.
It is a relative ranking tool, not an absolute probability; scores are only comparable when every part is rated on the same defined scale.

Common questions

How do you calculate spare part obsolescence risk? Multiply the three scores together: criticality times supply availability risk times lead-time exposure. The example shown computes to a 6.55 risk score from inputs of 8, 6, and 5 on the configured scale.
What makes a spare part high obsolescence risk? High criticality combined with a fragile single-source supply chain and long replacement lead times. Any one being high raises the score; all three high makes the part a top candidate for proactive action.
How is this different from an FMEA RPN? It uses the same multiply-three-factors structure as an RPN but targets supply and obsolescence exposure rather than failure mode severity, occurrence, and detection.
What should I do with a high score? Prioritize it for a last-time buy, alternate part qualification, commercial-grade dedication, or reverse-engineering before the original supplier exits, since lead time to qualify a replacement can be long.
What scoring scale should I use? Any consistent scale works, commonly 1 to 10, as long as you apply the identical scale to every part. The ranking is only meaningful in relative terms across the catalog.

Last reviewed 2026-05-12.